@article{zhu_xu_wu_chen_zhou_2024, title={Fault Estimation for a Class of Markov Jump Piecewise-Affine Systems: Current Feedback Based Iterative Learning Approach}, volume={11}, ISSN={["2329-9274"]}, DOI={10.1109/JAS.2023.123990}, abstractNote={In this paper, the issues of stochastic stability analysis and fault estimation are investigated for a class of continuous-time Markov jump piecewise-affne (PWA) systems against actuator and sensor faults. Firstly, a novel mode-dependent PWA iterative learning observer with current feedback is designed to estimate the system states and faults, simultaneously, which contains both the previous iteration information and the current feedback mechanism. The auxiliary feedback channel optimizes the response speed of the observer, therefore the estimation error would converge to zero rapidly. Then, sufficient conditions for stochastic stability with guaranteed <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$H$</tex> <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</inf> performance are demon-strated for the estimation error system, and the equivalence relations between the system information and the estimated information can be established via iterative accumulating representation. Finally, two illustrative examples containing a class of tunnel diode circuit systems are presented to fully demonstrate the effectiveness and superiority of the proposed iterative learning observer with current feedback.}, number={2}, journal={IEEE-CAA JOURNAL OF AUTOMATICA SINICA}, author={Zhu, Yanzheng and Xu, Nuo and Wu, Fen and Chen, Xinkai and Zhou, Donghua}, year={2024}, month={Feb}, pages={418–429} }
 @article{jin_wang_chen_xie_wu_wen_2024, title={Modeling and energy management strategy of hybrid energy storage in islanded DC micro-grid}, ISSN={["1432-0487"]}, DOI={10.1007/s00202-024-02376-x}, journal={ELECTRICAL ENGINEERING}, author={Jin, Jiashu and Wang, Zhewei and Chen, Yuepeng and Xie, Changjun and Wu, Fen and Wen, Yinghan}, year={2024}, month={Apr} }
 @article{xu_zhu_wu_ahn_2024, title={Sampled-Data Control for Buck-Boost Converter Using a Switched Affine Systems Approach}, ISSN={["1558-0806"]}, DOI={10.1109/TCSI.2024.3369037}, journal={IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS I-REGULAR PAPERS}, author={Xu, Xiaozeng and Zhu, Yanzheng and Wu, Fen and Ahn, Choon Ki}, year={2024}, month={Feb} }
 @article{jin_chen_xie_wu_2023, title={Remaining useful life prediction of PEMFC based on the multi-input cycle reservoir with jump network}, volume={48}, ISSN={["1879-3487"]}, DOI={10.1016/j.ijhydene.2022.12.170}, abstractNote={In recent years, fuel cells have attracted more and more attention in the energy field. However, accurate evaluation of durability is one of the key aspects of large-scale commercial application of fuel cells. The data-driven method has good fitting performance for predicting remaining useful life (RUL) at complex and nonlinear systems. In this paper, Cycle Reservoir with Jump with multi-inputs and multi-outputs (MIMO-CRJ) is proposed to further improve the fitting speed and reduce the complexity of the system which improved the structure of echo state network (ESN). Different from the previous method that only uses voltage to predict the voltage, this paper considers stack current, temperature and pressure, reactant flow rate in fuel cell operation as input variables, and extracts more degradation information to predict the voltage trend. Experimental results show that MIMO-CRJ has better performance than Cycle Reservoir with Jump with single -inputs and single-output (SISO-CRJ) and ESN networks under both static and quasi-dynamic current conditions.}, number={34}, journal={INTERNATIONAL JOURNAL OF HYDROGEN ENERGY}, author={Jin, Jiashu and Chen, Yuepeng and Xie, Changjun and Wu, Fen}, year={2023}, month={Apr}, pages={12844–12860} }
 @article{wang_li_wu_sun_2023, title={Switching Anti-Windup Synthesis for Linear Systems With Asymmetric Actuator Saturation}, ISSN={["2168-2275"]}, DOI={10.1109/TCYB.2023.3264913}, abstractNote={This article proposes a switching anti-windup strategy for linear, time-invariant (LTI) systems subject to asymmetric actuator saturation and L2 -disturbances, the core idea behind which is to make full use of the available range of control input space by switching among multiple anti-windup gains. The asymmetrically saturated LTI system is converted to a switched system with symmetrically saturated subsystems, and a dwell time switching rule is presented to govern the switching between different antiwindup gains. Based on multiple Lyapunov functions, we derive sufficient conditions for guaranteeing the regional stability and weighted L2 performance of the closed-loop system. The switching anti-windup synthesis that designs a separate anti-windup gain for each subsystem is cast as a convex optimization problem. In comparison with the design of a single anti-windup gain, our method can induce less conservative results since the asymmetric character of the saturation constraint is fully utilized in the switching anti-windup design. Two numerical examples, and an application to aeroengine control (the experiments are conducted on a semiphysical test bench), demonstrate the superiority and practicality of the proposed scheme.}, journal={IEEE TRANSACTIONS ON CYBERNETICS}, author={Wang, Ke and Li, Pengyuan and Wu, Fen and Sun, Xi-Ming}, year={2023}, month={Apr} }
 @article{wang_wu_sun_2023, title={Switching Anti-windup Control for Aircraft Engines}, volume={70}, ISSN={["1557-9948"]}, DOI={10.1109/TIE.2022.3163464}, abstractNote={In this paper, we propose a switching anti-windup scheme for the aircraft engine control. The linear engine model with asymmetric saturation is first transformed into a switched system, each subsystem of which is subject to symmetric saturation. A state-dependent switching logic is presented to orchestrate the switching among multiple anti-windup compensators. We then establish the sufficient condition to guarantee the regional stability and L2 performance of the resulting closed-loop system. This condition is less conservative since the non-symmetric nature of the saturation nonlinearity can be fully exploited in the control design. Optimization algorithms are further developed for the anti-windup gain design. The theoretical aspect of the proposed method is analyzed rigorously, and the effectiveness is validated through experiments performed on a semi-physical test bed.}, number={2}, journal={IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS}, author={Wang, Ke and Wu, Fen and Sun, Xi-Ming}, year={2023}, month={Feb}, pages={1830–1840} }
 @article{ban_zhang_wu_2022, title={Advanced controller synthesis for fuzzy parameter varying systems}, volume={359}, ISSN={["1879-2693"]}, DOI={10.1016/j.jfranklin.2020.12.038}, abstractNote={A novel nonlinear time-varying model termed as the fuzzy parameter varying (FPV) system is proposed in this research, which inherits both advantages of the conventional T-S fuzzy system in dealing with nonlinear plants and strengths of the linear parameter varying (LPV) system in handling time-varying features. It is, therefore, an attractive mathematical model to efficiently approximate a nonlinear time-varying plant or to serve as a type of time-varying controller. Using the full block S-procedure, sufficient stability conditions have been derived in the form of linear matrix inequalities (LMIs) to test quadratic stability of the open-loop FPV system. Moreover, sufficient conditions have been derived on synthesizing both state feedback and dynamical output feedback fuzzy gain-scheduling controllers that can stabilize the FPV system. An inverted pendulum with a variable length pole is utilized to demonstrate advantages of the FPV system compared to the conventional T-S fuzzy system in representing a practical time-varying nonlinear plant and to validate the controller synthesis conditions.}, number={2}, journal={JOURNAL OF THE FRANKLIN INSTITUTE-ENGINEERING AND APPLIED MATHEMATICS}, author={Ban, Xiaojun and Zhang, Hongyang and Wu, Fen}, year={2022}, month={Jan}, pages={762–785} }
 @article{chen_zhu_wu_zhao_2022, title={Fault Estimation Observer Design for Markovian Jump Systems With Nondifferentiable Actuator and Sensor Failures}, ISSN={["2168-2275"]}, DOI={10.1109/TCYB.2022.3169290}, abstractNote={This article addresses the simultaneous actuator and sensor fault estimation (FE) problem for a class of Markovian jump systems (MJSs) with nondifferentiable actuator failures. In order to overcome the difficulties brought by the nondifferentiable actuator failures, we construct an extended vector composed of states, sensor faults, and disturbances, where the derivatives of actuator failures are not required in this augmented system. Then, two novel observer-based approaches are developed for the augmented descriptor system to cope with the FE problem. The first one is a reduced-order FE observer, where the actuator failures can be estimated by the algebraic input reconstruction strategy. The second one refers to an iterative learning observer (ILO) design method, which can obtain the accurate FE result by integrating the estimations in the iterative processes. The two proposed FE observer design methods can avoid the sliding surface switching problem produced by sliding-mode observers in the area of MJSs. Finally, a practical example of the F-404 aircraft engine system is presented to show the validity of the proposed FE observer design techniques.}, journal={IEEE TRANSACTIONS ON CYBERNETICS}, author={Chen, Liheng and Zhu, Yanzheng and Wu, Fen and Zhao, Yuxin}, year={2022}, month={May} }
 @article{wang_tan_wu_wang_2021, title={Fault-Tolerant Attitude Control for Rigid Spacecraft Without Angular Velocity Measurements}, volume={51}, ISSN={["2168-2275"]}, DOI={10.1109/TCYB.2019.2905427}, abstractNote={In this paper, a fault-tolerant control scheme is proposed for the rigid spacecraft attitude control system subject to external disturbances, multiple system uncertainties, and actuator faults. The angular velocity measurement is unavailable, which increases the complexity of the problem. An observer is first designed based on the super-twisting sliding mode method, which can provide accurate estimates of the angular velocity in finite time. Then, an adaptive fault-tolerant controller is proposed based on neural networks using the information from the observer. It is shown that the attitude orientations converge to the desired values exponentially. Finally, a simulation example is utilized to verify the effectiveness of the proposed scheme.}, number={3}, journal={IEEE TRANSACTIONS ON CYBERNETICS}, author={Wang, Xianghua and Tan, Chee Pin and Wu, Fen and Wang, Jiandong}, year={2021}, month={Mar}, pages={1216–1229} }
 @article{cheng_wu_wu_lu_chen_cao_2021, title={Modeling and Control of Drill-String System With Stick-Slip Vibrations Using LPV Technique}, volume={29}, ISSN={["1558-0865"]}, DOI={10.1109/TCST.2020.2978892}, abstractNote={In this article, a systematic linear parameter-varying (LPV) model and a gain-scheduled control methodology for drill-string systems are proposed to analyze drill-string dynamics and suppress stick-slip vibrations, finally achieving efficient drilling. First, the changing length of drill string over the entire drilling process is emphasized and the corresponding LPV model is presented by combining the existing multi-degree-of-freedom (DOF) drill-string model, so as to capture length-varying effect. Then, we construct a generalized gain-scheduled control structure based on the $\mathcal {H}_\infty $ framework and gain-scheduling technique. Procedures for obtaining original and reduced gain-scheduled controllers are designed. Using the measured top drive speed and drill-string length in real time, the gains of the proposed controllers are automatically scheduled, enforcing satisfactory tracking and disturbance rejection performances. Finally, simulations and comparisons between our model and finite-element method-based model and our control method and existing active damping controller are carried out. The simulation results illustrate the effectiveness of the proposal.}, number={2}, journal={IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY}, author={Cheng, Jun and Wu, Min and Wu, Fen and Lu, Chengda and Chen, Xin and Cao, Weihua}, year={2021}, month={Mar}, pages={718–730} }
 @article{jin_chen_xie_zhu_wu_2021, title={Remaining useful life prediction of PEMFC based on cycle reservoir with jump model}, volume={46}, ISSN={["1879-3487"]}, DOI={10.1016/j.ijhydene.2021.09.233}, abstractNote={Accurate prognosis of limited durability is one of the key factors for the commercialization of proton exchange membrane fuel cell (PEMFC) on a large scale. Thanks to ignoring the structure of the PEMFC and simplifying the prognostic process, the data-driven prognostic approaches was the commonly used for predicting remaining useful life (RUL) at present. In this paper, the proposed cycle reservoir with jump (CRJ) model improves the ESN model, changes the connection mode of neurons in the reservoir and speeds up the linear fitting process. The experiment will verify the performance of CRJ model to predict stacks voltage under static current and quasi-dynamic current conditions. In addition, the reliability of the CRJ model is verified with different amount of data as the training and test sets. The experimental results demonstrate that the CRJ model can achieve better effect in the remaining useful life prognosis of fuel cells.}, number={80}, journal={INTERNATIONAL JOURNAL OF HYDROGEN ENERGY}, author={Jin, Jiashu and Chen, Yuepeng and Xie, Changjun and Zhu, Wenchao and Wu, Fen}, year={2021}, month={Nov}, pages={40001–40013} }
 @article{xue_wu_yuan_2021, title={Robust consensus for linear multi-agent systems with structured uncertainties}, volume={94}, ISSN={["1366-5820"]}, DOI={10.1080/00207179.2019.1612096}, abstractNote={ABSTRACT This paper addresses a robust consensus problem for linear multi-agent systems subject to structured uncertainty and external disturbances under the leaderless framework. A distributed dynamic output-feedback protocol is proposed, which utilises not only relative output information of neighbouring agents but also relative state information of neighbouring controllers. Through model transformations, the robust consensus control problem of multi-agents network is reduced to a set of independent stabilisation problems for single linear subsystems. For robust consensus, it is shown that the analysis and full state-feedback synthesis conditions for such subsystems can be formulated as linear matrix inequality (LMI) optimisation problems. On the other hand, the synthesis condition for dynamic output-feedback protocol is formulated as non-convex bilinear matrix inequality (BMI) optimisation problem. An iterative LMI algorithm is then presented to solve the resulting BMI optimisation problem. An example of multiple mass-spring-damper systems has been used to demonstrate theoretical results.}, number={3}, journal={INTERNATIONAL JOURNAL OF CONTROL}, author={Xue, Xiangming and Wu, Fen and Yuan, Chengzhi}, year={2021}, month={Mar}, pages={675–686} }
 @article{xie_han_wu_zhu_2020, title={H-infinity observer-controller synthesis approach in low frequency for T-S fuzzy systems}, volume={14}, ISSN={["1751-8652"]}, DOI={10.1049/iet-cta.2019.0242}, abstractNote={For the output feedback control problem of continuous-time T–S fuzzy systems with unknown premise variables, an H ∞ observer–controller design method in the low-frequency domain is proposed. First, an observer–controller structure is given, the unknown premise variables are limited by Lipschitz conditions. Then, the system stability conditions are obtained by the negativeness of eigenvalues' real parts. To achieve better control performance of the system in low frequency, the H ∞ index for attenuating the unknown low-frequency disturbance is guaranteed by generalised Kalman–Yakubovich–Popov lemma. Then, the stability and robustness conditions are converted into linear matrix inequality forms, which can be solved directly by a convex optimisation technique. Finally, several simulation examples carried out to show the effectiveness of the proposed method.}, number={5}, journal={IET CONTROL THEORY AND APPLICATIONS}, author={Xie, Wen-Bo and Han, Zhao-Kun and Wu, Fen and Zhu, Song}, year={2020}, month={Mar}, pages={738–749} }
 @article{xue_yuan_wu_2019, title={Convexified H-infinity output-feedback consensus synthesis for linear multi-agent systems}, volume={13}, ISSN={["1751-8652"]}, DOI={10.1049/iet-cta.2018.5337}, abstractNote={This study addresses the H
 ∞
 consensus problem for linear multi-agent systems subject to external disturbances under the leaderless framework. A novel distributed dynamic output feedback control protocol is proposed, which utilises not only relative output information of neighbouring agents but also relative state information of neighbouring controllers. Through model transformation, the H
 ∞
 consensus control problem of multi-agents network is reduced to a set of independent H
 ∞
 stabilisation subproblems for n
-dimensional linear systems. Sufficient analysis conditions are derived using the Lyapunov method. An important contribution of this work lies in that the leaderless H
 ∞
 output-feedback consensus synthesis conditions are convexified without introducing any conservatism and formulated as linear matrix inequalities, which can be solved efficiently via convex optimisation. This is achieved by using a novel dynamic output-feedback controller structure. A numerical example has been used to demonstrate the advantage of theoretical results.}, number={11}, journal={IET CONTROL THEORY AND APPLICATIONS}, author={Xue, Xiangming and Yuan, Chengzhi and Wu, Fen}, year={2019}, month={Jul}, pages={1619–1628} }
 @article{long_wu_2019, title={Iterative-Learning-Control-Based Tracking for Asteroid Close-Proximity Operations}, volume={42}, ISSN={["1533-3884"]}, DOI={10.2514/1.G003884}, abstractNote={No AccessEngineering NotesIterative-Learning-Control-Based Tracking for Asteroid Close-Proximity OperationsJiateng Long and Fen WuJiateng LongBeijing Institute of Technology, 100081 Beijing, People's Republic of China and Fen WuNorth Carolina State University, Raleigh, North Carolina 27695Published Online:2 Jan 2019https://doi.org/10.2514/1.G003884SectionsRead Now ToolsAdd to favoritesDownload citationTrack citations ShareShare onFacebookTwitterLinked InRedditEmail About References [1] Kawaguchi J. I., Fujiwara A. and Uesugi T., "Hayabusa–Its Technology and Science Accomplishment Summary and Hayabusa-2," Acta Astronautica, Vol. 62, Nos. 10–11, 2008, pp. 639–647. doi:https://doi.org/10.1016/j.actaastro.2008.01.028 AASTCF 0094-5765 CrossrefGoogle Scholar[2] Chesley S. 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T., "Hybrid Cartesian and Orbit Element Feedback Law for Formation Flying Spacecraft," Journal of Guidance, Control, and Dynamics, Vol. 25, No. 2, 2002, pp. 387–393. doi:https://doi.org/10.2514/2.4893 JGCODS 0731-5090 LinkGoogle Scholar[19] Kumar K., "Attitude Dynamics and Control of Satellites Orbiting Rotating Asteroids," Acta Mechanica, Vol. 198, Nos. 1–2, 2008, pp. 99–118. doi:https://doi.org/10.1007/s00707-007-0508-y AMHCAP 0001-5970 CrossrefGoogle Scholar Previous article FiguresReferencesRelatedDetailsCited byPassivity-Based Iterative Learning Control for Spacecraft Attitude Tracking on SO(3)Xiaoyu Lang and Anton de Ruiter11 February 2022 | Journal of Guidance, Control, and Dynamics, Vol. 45, No. 4Saturated Adaptive Relative Motion Coordination of Docking Ports in Space Close-Range RendezvousIEEE Transactions on Aerospace and Electronic Systems, Vol. 56, No. 6Neural Network Augmented Intelligent Iterative Learning Control for a Nonlinear SystemSimultaneous Learning Optimization of Hamiltonian Systems and Trajectory Tracking Around an AsteroidAsuto Taniguchi, Satoshi Satoh and Katsuhiko Yamada13 December 2019 | Journal of Guidance, Control, and Dynamics, Vol. 43, No. 2Quaternion-based adaptive attitude control of asteroid-orbiting spacecraft via immersion and invarianceActa Astronautica, Vol. 167 What's Popular Volume 42, Number 5May 2019 CrossmarkInformationCopyright © 2018 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. All requests for copying and permission to reprint should be submitted to CCC at www.copyright.com; employ the eISSN 1533-3884 to initiate your request. See also AIAA Rights and Permissions www.aiaa.org/randp. TopicsAsteroidsAstronomyCelestial Coordinate SystemCelestial MechanicsControl TheoryFeedback ControlGuidance, Navigation, and Control SystemsPlanetary Science and ExplorationPlanetsSolar PhysicsSpace Science and TechnologySpacecraft GuidanceSpacecraft Guidance and Control KeywordsIterative Learning ControlAsteroidsSpacecraft TrajectoriesFeedback ControlNumerical SimulationSolar RadiationConvergence AnalysisRight AscensionSolar SystemOrbital InclinationAcknowledgmentsJ. Long would like to thank the support of the Graduate Technological Innovation Project of Beijing Institute of Technology 2017CX10028 and the China Scholarship Council for sponsoring this research. The authors greatly appreciate the Associate Editor and anonymous reviewers for their patient and rigorous review with high standards, which are of significant benefit for the quality improvement of this paper.PDF Received12 June 2018Accepted18 November 2018Published online2 January 2019}, number={5}, journal={JOURNAL OF GUIDANCE CONTROL AND DYNAMICS}, author={Long, Jiateng and Wu, Fen}, year={2019}, month={May}, pages={1195–1203} }
 @article{hao_duan_chen_wu_2019, title={New Controllability Conditions for Networked, Identical LTI Systems}, volume={64}, ISSN={["1558-2523"]}, DOI={10.1109/TAC.2019.2893899}, abstractNote={A new necessary and sufficient condition for the controllability of networked linear time-invariant systems is derived, where the network topology is general and the nodes have identical higher dimensional dynamics. The condition is easier to verify, explicitly illustrating how the network topology, node-system dynamics, external control inputs, and inner interactions altogether affect the controllability of the whole networked system. Furthermore, the controllability of the specified Cartesian product networks is revisited, revealing that the necessity of the controllability criterion established in the work presented by Chapman et al., does not hold. In view of this, a modified, necessary, and sufficient condition is established. The effectiveness of the conditions is demonstrated using several examples.}, number={10}, journal={IEEE TRANSACTIONS ON AUTOMATIC CONTROL}, author={Hao, Yuqing and Duan, Zhisheng and Chen, Guanrong and Wu, Fen}, year={2019}, month={Oct}, pages={4223–4228} }
 @article{zhu_wu_karimi_lu_2019, title={Special issue on advanced analysis and control design of switching linear parameter-varying systems and its applications}, volume={233}, ISSN={["2041-3041"]}, DOI={10.1177/0959651818819594}, abstractNote={As the linear parameter-varying (LPV) system has a large range of parameter variations, it is very difficult to achieve satisfactory control performance for the whole range of parameter variation merely through a constant controller. An effective approach to ensure the desired control performance is to divide the whole parameter range into some sub-ranges, and each sub-range corresponds to a controller. The desired performance can be satisfied via the switching of controllers belonging to different sub-ranges. Accordingly, the LPV control issues involved with certain switching properties (e.g. nondeterministic or stochastic) have received increasing interests within recent decades, and a quite large number of useful results have been reported assuming the switching signals with nondeterministic (e.g. average dwell time (ADT), persistent dwell time) or Markov stochastic properties. However, about some applications in practice, various non-ideal situations might occur, for instance, the exact values of scheduling parameters may not be valid to adapt to controller parameters owing to sensor drift and noise; the system states are not measurable completely for the desired controllers/filters in that a full knowledge of the state vector is rarely available; the various complex dynamics such as model uncertainty, time delays, and faults often exist in the practical systems, all of which bring new challenges and opportunities for theoretical researchers and applied practitioners alike. In terms of the above discussion on motivations, eight papers are chosen in this special issue from a large number of submissions via a normative peer-review process. These collections contain both theoretical and application-oriented studies for showcasing emerging innovative ideas and technologies, to address various unresolved issues and challenges in the field of hybrid LPV control systems. The main contributions of these studies are briefly provided as follows. First, considering the switched LPV systems with nondeterministic switching properties in the continuous-time domain, Zhao et al. investigate the issue of HN fault-tolerant control for a class of continuous-time switched LPV systems with actuator failures by the multiple discretized parameterdependent Lyapunov functions approach. The proposed Lyapunov technique avoids the Zeno behavior produced by the parameter and state-dependent switching approach. A new switching strategy is established depending on the parameter, state, and dwelltime (DT), which eliminates the assumption on the finite number of switching for any finite time. An application to a turbofan engine is illustrated to verify the utility of the obtained results. Next, Ren et al. address the input–output finite-time stability and finite-time boundedness for a class of continuous-time switched LPV systems with ADT switching based on an eventtriggered communication scheme. An asynchronous switching strategy is considered when deriving the sufficient conditions of stability and boundedness in finite time, and the design of parameter-dependent asynchronous controllers is performed by resolving a group of linear matrix inequalities. The effectiveness of the proposed methods is demonstrated via a numerical example. Furthermore, Ren et al. discuss the finite-time non-fragile full-order controller design issue for a class of continuous-time switched LPV systems based on the multiple Lyapunov function approach. Finally, under the ADT switching, Wang et al. study the HN filter design problem for a class of continuous-time switched LPV systems with both time-varying state and parameter delays. An improved reciprocally convex inequality is used to deal with the terms of delays, and the multiple Lyapunov function method is employed to derive the stability condition with less conservatism, which ensures the existence of novel parameterdependent filters with a guaranteed HN performance. Turning to the field of switched LPV systems with Markov stochastic switching properties, Shen et al. deal with the passive gain-scheduling filtering problem for a class of discrete-time Markov jump LPV systems in the presence of random occurring fading channels. The description of mode information between the system and the presented filter is made via a hidden Markov model. The sufficient conditions are obtained to ensure the existence of an available passive gain-scheduling filter with the aid of the stochastic analysis theory. Besides, Wang et al. concern with the issue of stochastic finite-time HN filtering issue for a class of continuous-}, number={1}, journal={PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART I-JOURNAL OF SYSTEMS AND CONTROL ENGINEERING}, author={Zhu, Yanzheng and Wu, Fen and Karimi, Hamid Reza and Lu, Bei}, year={2019}, month={Jan}, pages={3–4} }
 @article{yuan_duan_wu_2018, title={Almost output regulation of LFT systems via gain-scheduling control}, volume={91}, ISSN={["1366-5820"]}, DOI={10.1080/00207179.2017.1309573}, abstractNote={ABSTRACT Output regulation of general uncertain systems is a meaningful yet challenging problem. In spite of the rich literature in the field, the problem has not yet been addressed adequately due to the lack of an effective design mechanism. In this paper, we propose a new design framework for almost output regulation of uncertain systems described in the general form of linear fractional transformation (LFT) with time-varying parametric uncertainties and unknown external perturbations. A novel semi-LFT gain-scheduling output regulator structure is proposed, such that the associated control synthesis conditions guaranteeing both output regulation and disturbance attenuation performance are formulated as a set of linear matrix inequalities (LMIs) plus parameter-dependent linear matrix equations, which can be solved separately. A numerical example has been used to demonstrate the effectiveness of the proposed approach.}, number={5}, journal={INTERNATIONAL JOURNAL OF CONTROL}, author={Yuan, Chengzhi and Duan, Chang and Wu, Fen}, year={2018}, pages={1161–1170} }
 @article{waghela_bryant_wu_2018, title={Control design in cyber-physical fluid-structure interaction experiments}, volume={82}, ISSN={["0889-9746"]}, DOI={10.1016/j.jfluidstructs.2018.06.018}, abstractNote={Cyber-physical fluid dynamics is a hybrid experimental–computational approach to study fluid–structure interaction (FSI). It enables on-the-fly changes to structure inertia, damping, stiffness, and even kinematic constraints by replacing traditional elastically-mounted structures with actuators and a controller. The control design plays a central role in matching the closed-loop dynamics of the cyber-physical structure (CPS) to those of the desired structure. Control designs based on traditional proportional–integral–derivative (PID) and post-modern H∞ control are presented. The controllers are synthesized to match the linearized desired structural dynamics (or the input–output response) but no assumption of linearity is levied on the fluid behavior. To quantify the matching of input–output response, a CPS deviation index is defined based on H∞ norms. To evaluate and compare the performance of the control designs, two well-known FSI instabilities are considered, galloping and aeroelastic flutter. These FSI instabilities represent convenient test cases because they can be analyzed with linear aerodynamic models. Comparing the critical instability flow velocity and oscillation frequency of the CPS with different control designs and the desired mechanical structure demonstrates that the internal structure of the controller is crucial to fully matching the response of the desired structure. H∞ model-matching control with admittance causality is found to be the most adept control design for the CPS.}, journal={JOURNAL OF FLUIDS AND STRUCTURES}, author={Waghela, R. and Bryant, M. and Wu, F.}, year={2018}, month={Oct}, pages={86–100} }
 @article{yuan_wu_2018, title={Cooperative output regulation of multi-agent systems with switched leader dynamics}, volume={49}, ISSN={["1464-5319"]}, DOI={10.1080/00207721.2018.1454537}, abstractNote={ABSTRACT In this paper, the cooperative output regulation problem for heterogeneous multi-agent systems is addressed by considering a switched leader dynamics. The switched leader dynamics consists of multiple linear models and a switching rule governing the switches among them. A switched leader is capable of generating various sophisticated reference signals for more complicated multi-agent coordination tasks. A novel distributed hybrid impulsive switching control scheme is proposed to achieve cooperative output regulation. Distributed switching stability is established using the average dwell-time technique with multiple Lyapunov functions. Moreover, the associated distributed control synthesis conditions are formulated in terms of linear matrix inequalities plus linear matrix equations. As a result, both switching rules for the leader and distributed switching protocols for the followers can be jointly synthesised via efficient semi-definite programming. An example has been used to demonstrate the effectiveness of the proposed approach.}, number={7}, journal={INTERNATIONAL JOURNAL OF SYSTEMS SCIENCE}, author={Yuan, Chengzhi and Wu, Fen}, year={2018}, pages={1463–1477} }
 @article{yuan_wu_2018, title={Cooperative state estimation of multi-agent systems subject to bounded external disturbances}, volume={49}, ISSN={0020-7721 1464-5319}, url={http://dx.doi.org/10.1080/00207721.2018.1482380}, DOI={10.1080/00207721.2018.1482380}, abstractNote={Abstract This paper deals with the problem of cooperative state estimation of general linear multi-agent systems subject to heterogeneous bounded external disturbances. This problem specifies the objective that each agent estimates its own state by using only relative information from its neighbours. Because of the existence of external disturbances, the problem is challenging especially when stringent exact estimation performance is desired. To this end, two cooperative estimation protocols are proposed, including the discontinuous nonlinear protocol for exact state estimation and the continuous nonlinear protocol for estimation with bounded errors. The overall network stability and convergence properties are analysed using the Lyapunov function method. A simulation example has also been used to demonstrate the effectiveness of the proposed results.}, number={9}, journal={International Journal of Systems Science}, publisher={Informa UK Limited}, author={Yuan, Chengzhi and Wu, Fen}, year={2018}, month={Jun}, pages={1985–1996} }
 @article{zhang_ban_wu_2018, title={Stability analysis and controller design for a novel nonlinear system: Fuzzy parameter varying system}, volume={34}, ISSN={["1875-8967"]}, DOI={10.3233/jifs-18190}, abstractNote={The novel fuzzy parameter varying system is proposed to deal with nonlinear time-varying models. It has the advantages of the T-S fuzzy system and the linear parameter varying system. It provides a new idea for solving nonlinear time-varying control problem. In this paper, some sufficient condition s are provided to guarantee the globally asymptotically stable of the equilibrium and to synthesize a T-S state feedback control law which can stabilize the closed loop fuzzy parameter varying system. Numerical simulations verify the effectiveness of our results.}, number={6}, journal={JOURNAL OF INTELLIGENT & FUZZY SYSTEMS}, author={Zhang, Hongyang and Ban, Xiaojun and Wu, Fen}, year={2018}, pages={4387–4395} }
 @article{yuan_wu_2017, title={Almost output regulation of switched linear dynamics with switched exosignals}, volume={27}, ISSN={["1099-1239"]}, DOI={10.1002/rnc.3735}, abstractNote={Summary}, number={16}, journal={INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL}, author={Yuan, Chengzhi and Wu, Fen}, year={2017}, month={Nov}, pages={3197–3217} }
 @article{yuan_wu_2017, title={Consensus for multi-agent systems with time-varying input delays}, volume={48}, ISSN={["1464-5319"]}, DOI={10.1080/00207721.2017.1363927}, abstractNote={ABSTRACT This paper addresses the consensus control problem for linear multi-agent systems subject to uniform time-varying input delays and external disturbance. A novel state-feedback consensus protocol is proposed under the integral quadratic constraint (IQC) framework, which utilises not only the relative state information from neighbouring agents but also the real-time information of delays by means of the dynamic IQC system states for feedback control. Based on this new consensus protocol, the associated IQC-based control synthesis conditions are established and fully characterised as linear matrix inequalities (LMIs), such that the consensus control solution with optimal disturbance attenuation performance can be synthesised efficiently via convex optimisation. A numerical example is used to demonstrate the proposed approach.}, number={14}, journal={INTERNATIONAL JOURNAL OF SYSTEMS SCIENCE}, author={Yuan, Chengzhi and Wu, Fen}, year={2017}, pages={2956–2966} }
 @inproceedings{yuan_wu_duan_2017, title={Cooperative output regulation of multi-agent systems with switched leader dynamics via smooth switching}, DOI={10.1115/dscc2017-5055}, abstractNote={This paper deals with the leader-following cooperative output regulation problem for heterogeneous multi-agent systems by considering a switched leader dynamics. The switched leader dynamics is composed by multiple linear models and a switching rule governing the switches among them, which is capable of generating more diverse and sophisticated reference signals so as to enhance the multi-agent system’s capability in coping with more complicated coordination tasks. A novel distributed switching control scheme, namely, the smooth switching control strategy, is proposed to achieve cooperative output regulation performance. Distributed switching stability of the overall network is established using multiple Lyapunov functions from the switching control theory. Moreover, under the proposed design framework, the overall cooperative switching output regulation problem can be decomposed into several independent switching stabilization subproblems, and the associated switching control synthesis conditions for each subproblems are formulated as a set of linear matrix inequalities (LMIs) plus linear algebraic equations. As a result, stabilizing switching rules for the leader and distributed switching protocols for the follower agents can be jointly synthesized via semi-definite programming. A numerical example has been used to demonstrate the effectiveness of the proposed approach.}, booktitle={Proceedings of the ASME 10th Annual Dynamic Systems and Control Conference, 2017, vol 2}, author={Yuan, C. Z. and Wu, F. and Duan, C.}, year={2017} }
 @article{liu_wu_ban_2017, title={Dynamic Output Feedback Control for Continuous-Time T-S Fuzzy Systems Using Fuzzy Lyapunov Functions}, volume={25}, ISSN={["1941-0034"]}, DOI={10.1109/tfuzz.2016.2598852}, abstractNote={A novel relaxation approach is proposed for the analysis and dynamic output feedback control of continuous-time Takagi–Sugeno (T–S) fuzzy systems using fuzzy Lyapunov functions. Previous relaxation methods for T–S fuzzy systems have some drawbacks in relaxing quadratic functions depending on normalized fuzzy weighting functions. They often introduce conservatism or lead to computational difficulty in analysis and control synthesis. Different from previous works, the proposed approach employs linear fractional transformation mechanism and full-block <inline-formula><tex-math notation="LaTeX">$S$</tex-math></inline-formula>-procedure to reduce the conservatism in analysis. Furthermore, the relaxation technique proposed in this paper can be used in solving the controller synthesis problem effectively. As a result, a design procedure of a nonparallel distributed compensation output feedback controller, which ensures asymptotic stability and optimizes <inline-formula><tex-math notation="LaTeX">${\mathcal L}_2$</tex-math></inline-formula> gain performance of the closed-loop systems, is provided. Several examples have been used to illustrate the advantages and efficiency of the proposed method extensively.}, number={5}, journal={IEEE TRANSACTIONS ON FUZZY SYSTEMS}, author={Liu, Yang and Wu, Fen and Ban, Xiaojun}, year={2017}, month={Oct}, pages={1155–1167} }
 @article{yuan_wu_2017, title={Exact-memory and memoryless control of linear systems with time-varying input delay using dynamic IQCs}, volume={77}, ISSN={["1873-2836"]}, DOI={10.1016/j.automatica.2016.11.015}, abstractNote={Input delay is an important type of actuator nonlinearity in control systems. In this paper, we will address the output-feedback control synthesis problem for linear systems with time-varying input delay under the integral quadratic constraint (IQC) framework. A new exact-memory control scheme is first proposed, which consists of a standard linear output-feedback control law and an internal delay loop. The delay loop is embedded in the controller structure so as to reproduce the input delay behavior of the plant. By using quadratic Lyapunov functions incorporated with dynamic IQC multipliers, the resulting dynamic output-feedback delay control synthesis problem is fully characterized by a set of linear matrix inequalities (LMIs), which are convex on all design variables including the scaling factors associated with the IQC multipliers. Moreover, the corresponding result on memoryless control is also derived for the case when the plant input-delay information is not available for feedback control. An application to network systems has been used to illustrate the effectiveness and usefulness of the proposed approach.}, journal={AUTOMATICA}, author={Yuan, Chengzhi and Wu, Fen}, year={2017}, month={Mar}, pages={246–253} }
 @article{liu_ban_wu_lam_2017, title={Gain-scheduling control of T-S fuzzy systems with actuator saturation}, volume={32}, ISSN={["1875-8967"]}, DOI={10.3233/jifs-16546}, abstractNote={. This paper presents a gain-scheduling output feedback control design method for T-S fuzzy systems with actuator saturation. Different from existing control design methods for T-S fuzzy systems, the basic idea of the proposed approach is to transform the T-S fuzzy model with saturation nonlinearity into the form of linear fractional transformation (LFT). Instead of commonly used fuzzy controllers, a gain-scheduled output feedback controller in the LFT form is introduced to stabilize the saturated T-S fuzzy system with guaranteed H 1 performance. The problem of establishing regional stability and performance of the closed-loop nonlinear system are tackled by using robust control techniques. As a result, the conservatism introduced by dealing with the quadratic terms of normalized fuzzy weighting functions can be avoided. The proposed controller synthesis problem is cast as a convex optimization in terms of linear matrix inequalities (LMIs) and can be solved efficiently. An example of balancing the inverted pendulum with bounded actuation is provided to illustrate the effectiveness of the proposed design method.}, number={3}, journal={JOURNAL OF INTELLIGENT & FUZZY SYSTEMS}, author={Liu, Yang and Ban, Xiaojun and Wu, Fen and Lam, H. K.}, year={2017}, pages={2579–2589} }
 @article{rui_zhang_wang_wu_2017, title={New Developments in Multibody System Dynamics and Its Applications 2015}, volume={9}, ISSN={["1687-8140"]}, DOI={10.1177/1687814017695685}, abstractNote={Multibody system dynamics is nowadays a widely used toolbox in the development of modern engineering science and technology. It provides powerful dynamic design theories, computational and analytical methods, as well as test technologies for innovative engineering applications. In order to systematically show the important effects of multibody system dynamics on the development of modern science and technology, and to strengthen the academic exchanges in the research field of multibody system dynamics and its applications, we organised the annual Special Collection ‘New Developments in Multibody System Dynamics and Its Applications 2015’, which is the third one of this Special Collection first started from 2013, for the Journal Advances in Mechanical Engineering. The present Special Collection contains 12 papers selected from the contributions coming from several countries. The 12 papers selected for this Special Collection are devoted to the following topics: the modelling, simulation and analysis of a passive dynamic walking robot with flat feet; the test technique for eliminating the accelerometer’s mass effects from frequency response functions using sensitivity analysis; the formulation for automatic deduction of overall transfer equation for branch systems using the transfer matrix method for multibody systems; the modelling, simulation and analysis for an offshore wind turbine installed on a floating spar platform using a hybrid method of finite element multibody system; the application of the transfer matrix method for multibody systems to dynamics analysis of a reinforced concrete shear wall structure during earthquakes; the modelling and simulation of the lifting operation of an offshore supply vessel; the dynamics modelling and simulation of industrial robot subject to constraint using Udwadia–Kalaba equation; the modelling and simulation of the drilling system considering fluid–solid coupling using absolute nodal coordinate formulation; the experimental study and numerical simulation of multi-impact phenomena exhibited during the collision of a sphere onto a steel beam; the application of semi-analytical finite strip transfer matrix method to the buckling analysis of thin-walled members; and the dynamics modelling and simulation of a self-synchronisation vibrating pile driver system. Thus, the general fundamental theories and several key engineering applications are covered representing the state of the art of recent intensive and extensive research activities in the field of multibody system dynamics to a certain extent. The guest editors hope that this Special Collection will provide some valuable information and guidance for scientists and engineers working on multibody system dynamics and its applications in modern engineering science and technology.}, number={3}, journal={ADVANCES IN MECHANICAL ENGINEERING}, author={Rui, Xiaoting and Zhang, Chuanzeng and Wang, Shimin and Wu, Fen}, year={2017}, month={Mar} }
 @inproceedings{ban_liu_huang_wu_2017, title={Output feedback control for fuzzy systems subject to actuator saturation based on fuzzy Lyapunov functions}, DOI={10.1115/dscc2016-9879}, abstractNote={In this paper, a novel fuzzy gain-scheduling output feedback control method is presented for T-S fuzzy systems subject to actuator saturation. To deal with saturation nonlinearity, the dead-zone function of control input is treated as an additional controller input. With the help of set conclusion condition, the controller can be synthesised based on fuzzy Lyapunov functions to guarantee the exponential stability of the closed-loop system in a larger region and a better L2 gain performance. Moreover, the full block S-procedure, which is widely used in robust control theory, is introduced to relax the synthesis conditions for T-S fuzzy systems to reduce the conservatism caused by quadratic terms in the conditions. Finally, a numerical example is provided to illustrates the effectiveness of the proposed control method.}, booktitle={Proceedings of the ASME 9th Annual Dynamic Systems and Control Conference, 2016, Vol 1}, author={Ban, X. J. and Liu, Y. and Huang, X. L. and Wu, F.}, year={2017} }
 @article{oduola_li_duan_qian_wu_dougherty_2017, title={Time-Based Switching Control of Genetic Regulatory Networks: Toward Sequential Drug Intake for Cancer Therapy}, volume={16}, ISSN={["1176-9351"]}, DOI={10.1177/1176935117706888}, abstractNote={ As cancer growth and development typically involves multiple genes and pathways, combination therapy has been touted as the standard of care in the treatment of cancer. However, drug toxicity becomes a major concern whenever a patient takes 2 or more drugs simultaneously at the maximum tolerable dosage. A potential solution would be administering the drugs in a sequential or alternating manner rather than concurrently. This study therefore examines the feasibility of such an approach from a switched system control perspective. Particularly, we study how genetic regulatory systems respond to sequential (switched) drug inputs using the time-based switching mechanism. The design of the time-driven drug switching function guarantees the stability of the genetic regulatory system and the repression of the diseased genes. Simulation results using proof-of-concept models and the proliferation and survival pathways with sequential drug inputs show the effectiveness of the proposed approach. }, journal={CANCER INFORMATICS}, author={Oduola, Wasiu Opeyemi and Li, Xiangfang and Duan, Chang and Qian, Lijun and Wu, Fen and Dougherty, Edward R.}, year={2017}, month={May} }
 @article{yang_wu_zhang_2017, title={Tracking control of hybrid systems with state-triggered jumps and stochastic events and its application}, volume={11}, ISSN={["1751-8652"]}, DOI={10.1049/iet-cta.2016.1086}, abstractNote={This study addresses the tracking control problem for a class of hybrid systems with both state-triggered jumps and stochastic events. The outputs of the plant are required to follow exactly the time-varying reference trajectories which are generated by the corresponding hybrid system. Since the jump times of the plant do not coincide with those of the references, the tracking error in terms of Euclidean distance will exhibit ‘peaking phenomena’, and is not suitable for this kind of situation. By invoking a novel definition of the tracking error which is insensitive to state-triggered jumps and stochastic events, sufficient conditions for asymptotic stability are obtained. Exploiting the asymptotic stability criteria and the proposed non-Euclidean measure of the tracking error, the tracking control problem of a simplified flexible single-link robotic arm is successfully solved by the hybrid controller.}, number={7}, journal={IET CONTROL THEORY AND APPLICATIONS}, author={Yang, Ting and Wu, Fen and Zhang, Lixian}, year={2017}, month={Apr}, pages={1024–1033} }
 @article{liu_ban_wu_lam_2016, title={A Gain-Scheduling Control Approach for Takagi-Sugeno Fuzzy Systems Based on Linear Parameter-Varying Control Theory}, volume={138}, ISSN={["1528-9028"]}, DOI={10.1115/1.4031914}, abstractNote={Due to the universal approximation capability of Takagi–Sugeno (T–S) fuzzy models for nonlinear dynamics, many control issues have been investigated based on fuzzy control theory. In this paper, a transformation procedure is proposed to convert fuzzy models into linear fractional transformation (LFT) models. Then, T–S fuzzy systems can be regarded as a special case of linear parameter-varying (LPV) systems which proved useful for nonlinear control problems. The newly established connection between T–S fuzzy models and LPV models provides a new perspective of the control problems for T–S fuzzy systems and facilitates the fuzzy control designs. Specifically, an output feedback gain-scheduling control design approach for T–S fuzzy systems is presented to ensure globally asymptotical stability and optimize H∞ performance of the closed-loop systems. The control synthesis problem is cast as a convex optimization problem in terms of linear matrix inequalities (LMIs). Two examples have been used to illustrate the efficiency of the proposed method.}, number={1}, journal={JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME}, author={Liu, Yang and Ban, Xiaojun and Wu, Fen and Lam, H. K.}, year={2016}, month={Jan} }
 @article{wu_song_ren_2016, title={A Nonlinear Gain-Scheduling Compensation Approach Using Parameter-Dependent Lyapunov Functions}, volume={138}, ISSN={["1528-9028"]}, DOI={10.1115/1.4031845}, abstractNote={This paper addresses the gain-scheduling control design for nonlinear systems to achieve output regulation. For gain-scheduling control, the linear parameter-varying (LPV) model is obtained by linearizing the plant about zero-error trajectories upon which an LPV controller is based. A key in this process is to find a nonlinear output feedback compensator such that its linearization matches with the designed LPV controller. Then, the stability and performance properties of LPV control about the zero-error trajectories can be inherited when the nonlinear compensator is implemented. By incorporating the exosystem, nominal input, and measured output information into the LPV model, the LPV control synthesis problem is formulated as linear matrix inequalities (LMIs) using parameter-dependent Lyapunov functions (PDLFs). Moreover, explicit formulae for the construction of the nonlinear gain-scheduled compensator have been derived to meet the linearization requirement. Finally, the validity of the proposed nonlinear gain-scheduling control approach is demonstrated through a ball and beam example.}, number={1}, journal={JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME}, author={Wu, Fen and Song, Xun and Ren, Zhang}, year={2016}, month={Jan} }
 @inproceedings{yuan_wu_2016, title={A new hybrid LFT control method for missile autopilot design}, DOI={10.1109/chicc.2016.7554273}, abstractNote={This paper presents a new hybrid gain-scheduling control method for missile autopilot design. The nonlinear missile dynamics is first converted to a switched linear fractional transformation (LFT) model for controller design and synthesis purpose. Then, by using multiple Lyapunov functions and average dwell time (ADT) techniques, a new hybrid gain-scheduling autopilot is designed, which consists of a switching dynamic output-feedback LFT controller and a controller state jump dynamics. The associated control synthesis conditions guaranteeing weighted ℒ 2 stability are formulated in terms of a finite number of linear matrix inequalities (LMIs), which can be solved effectively via convex optimization without parameter-space gridding. Nonlinear simulation studies show the effectiveness of the proposed approach.}, booktitle={Proceedings of the 35th chinese control conference 2016}, author={Yuan, C. Z. and Wu, F.}, year={2016}, pages={5852–5857} }
 @inproceedings{boker_yuan_wu_chakrabortty_2016, title={Aggregate control of clustered networks with inter-cluster time delays}, DOI={10.1109/acc.2016.7526506}, abstractNote={We address a control problem for networks that have multiple dense clusters with sparse interconnection structure. By making use of the time-scale separation properties of such networks, we design state-feedback controllers at the cluster level to guarantee stability in the presence of time varying delays in the inter-cluster feedback channels. Applying results from singular perturbation theory, we show that when these individual controllers are implemented on the actual network model, the closed-loop response is close to that obtained from the approximate models, provided that the clustering is strong and the time delay is below the maximum limit. The design procedure is demonstrated by a simulation example.}, booktitle={2016 american control conference (acc)}, author={Boker, A. M. and Yuan, C. Z. and Wu, F. and Chakrabortty, Aranya}, year={2016}, pages={5340–5345} }
 @inproceedings{oduola_li_duan_qian_wu_dougherty_2016, title={Analysis and control of genetic regulatory systems with switched drug inputs}, DOI={10.1109/bhi.2016.7455952}, abstractNote={Because cancer usually involves multiple genes and pathways, combination therapy is considered as a promising approach for cancer treatment. However, when multiple drugs are taken by a patient simultaneously, toxicity becomes a concern. A potential solution is to give the drugs sequentially rather than simultaneously. In this study, we try to explore the feasibility of such an approach. Specifically, this study investigates the response of genetic regulatory networks to sequential (switched) drug inputs. The switching mechanism is based on the combination of a state-dependent and time-driven switching function. The design of the switching strategy ensures that the genetic regulatory network will be stabilized and satisfies a decay rate performance index. Simulation results using a mTOR pathway model show the effectiveness of the proposed method.}, booktitle={2016 3rd IEEE EMBS International Conference on Biomedical and Health Informatics}, author={Oduola, W. and Li, X. F. and Duan, C. and Qian, L. J. and Wu, F. and Dougherty, E. R.}, year={2016}, pages={533–536} }
 @article{yuan_wu_2016, title={Dynamic IQC-Based Control of Uncertain LFT Systems With Time-Varying State Delay}, volume={46}, ISSN={["2168-2275"]}, DOI={10.1109/tcyb.2015.2503741}, abstractNote={This paper presents a new exact-memory delay control scheme for a class of uncertain systems with time-varying state delay under the integral quadratic constraint (IQC) framework. The uncertain system is described as a linear fractional transformation model including a state-delayed linear time-invariant (LTI) system and time-varying structured uncertainties. The proposed exact-memory delay controller consists of a linear state-feedback control law and an additional term that captures the delay behavior of the plant. We first explore the delay stability and the L2-gain performance using dynamic IQCs incorporated with quadratic Lyapunov functions. Then, the design of exact-memory controllers that guarantee desired L2-gain performance is examined. The resulting delay control synthesis conditions are formulated in terms of linear matrix inequalities, which are convex on all design variables including the scaling matrices associated with the IQC multipliers. The IQC-based exact-memory control scheme provides a novel approach for delay control designs via convex optimization, and advances existing control methods in two important ways: 1) better controlled performance and 2) simplified design procedure with less computational cost. The effectiveness and advantages of the proposed approach have been demonstrated through numerical studies.}, number={12}, journal={IEEE TRANSACTIONS ON CYBERNETICS}, author={Yuan, Chengzhi and Wu, Fen}, year={2016}, month={Dec}, pages={3320–3329} }
 @inproceedings{yuan_wu_2016, title={Dynamic IQC-based analysis and synthesis of networked control systems}, DOI={10.1109/acc.2016.7526507}, abstractNote={This paper presents a new control design approach for networked control systems under the integral quadratic constraint (IQC) framework. In order to apply the IQC and dissipation theory, the networked control system with network-induced time-varying delays is first transformed to an equivalent linear fractional transformation (LFT) model. As such, dynamic IQCs can be used to capture the input-output behavior of the delay nonlinearities. Then, a novel full-information feedback control law is proposed, which utilizes both plant states and the IQC dynamic states, as well as the network-induced delay amounts, as feedback information. Robust ℓ2 stability analysis of the resulting closed loop is performed via dynamic IQCs. Based on the analysis results, the synthesis conditions for the proposed full-information feedback controller are established in a linear matrix inequality (LMI) form, which can be solved effectively using existing convex optimization algorithms. Finally, a servo motor control system is used to demonstrate the effectiveness of the proposed IQC-based control design scheme.}, booktitle={2016 american control conference (acc)}, author={Yuan, C. Z. and Wu, F.}, year={2016}, pages={5346–5351} }
 @inproceedings{yuan_wu_2016, title={H-infinity state-feedback control of linear systems with time-varying input delays}, DOI={10.1109/cdc.2016.7798332}, abstractNote={In this paper, we will address the state-feedback control synthesis problem for linear systems with time-varying input delays under the integral quadratic constraint (IQC) framework. A new exact-memory control scheme is first proposed, which consists of a standard linear state-feedback control law and an internal delay loop. The delay loop is embedded in the controller structure so as to reproduce the input delay behavior of the plant. With this controller structure, the resulting delay control synthesis problem is fully characterized by a set of linear matrix inequalities (LMIs), which are convex on all design variables including the scaling factors associated with the IQC multipliers. The corresponding results on memoryless state-feedback control are also derived for cases when input-delay information is not available for feedback control. A numerical example has been used to illustrate the effectiveness of the proposed approach.}, booktitle={2016 ieee 55th conference on decision and control (cdc)}, author={Yuan, C. Z. and Wu, F.}, year={2016}, pages={586–591} }
 @article{yuan_liu_wu_duan_2016, title={Hybrid Switched Gain-Scheduling Control for Missile Autopilot Design}, volume={39}, ISSN={["1533-3884"]}, DOI={10.2514/1.g001791}, abstractNote={This paper presents a new hybrid switched gain-scheduling control method for missile autopilot design via dynamic output feedback. For controller design purpose, the nonlinear missile plant model is first converted to a switched linear fractional transformation system. Then, the new hybrid switched gain-scheduling autopilot is designed, which consists of a switching dynamic output–feedback linear fractional transformation controller and a supervisor enforcing a controller state reset at each switching time instant. The proposed hybrid control scheme is shown to provide a systematic yet simple framework for missile autopilot design. Specifically, the control synthesis conditions that guarantee weighted L2 stability performance are formulated in terms of a finite number of linear matrix inequalities, which can be solved effectively via convex optimization without parameter-space gridding. Furthermore, stringent controlled performance and strong robustness against parameter perturbations are achieved using t...}, number={10}, journal={JOURNAL OF GUIDANCE CONTROL AND DYNAMICS}, author={Yuan, Chengzhi and Liu, Yang and Wu, Fen and Duan, Chang}, year={2016}, month={Oct}, pages={2352–2363} }
 @article{yuan_wu_2016, title={Hybrid almost output regulation of linear impulsive systems with average dwell-time}, volume={20}, ISSN={["1878-7460"]}, DOI={10.1016/j.nahs.2015.11.001}, abstractNote={This paper deals with the hybrid almost output regulation problem for a class of linear systems with average dwell-time impulses. The proposed hybrid output regulator is constructed as a linear impulsive system that undergoes synchronous impulses with the controlled plant. Lyapunov-based sufficient conditions of the output regulability and weighted L2 performance for the linear impulsive systems are first derived. Based on the analysis results, the hybrid synthesis problem is formulated in terms of linear matrix equations plus a set of linear matrix inequalities (LMIs). With this hybrid synthesis scheme, both flow and jump dynamics of the hybrid regulator can be jointly designed by solving a convex optimization problem in minimizing the weighted L2 gain from the perturbation signal to the error output. A numerical example is used to demonstrate the proposed approach.}, journal={NONLINEAR ANALYSIS-HYBRID SYSTEMS}, author={Yuan, Chengzhi and Wu, Fen}, year={2016}, month={May}, pages={82–94} }
 @article{duan_wu_2016, title={New results on switched linear systems with actuator saturation}, volume={47}, ISSN={["1464-5319"]}, DOI={10.1080/00207721.2014.911386}, abstractNote={This paper further studies the analysis and control problems of continuous-time switched linear systems subject to actuator saturation. Using the norm-bounded differential inclusion description of the saturated systems and the minimal switching rule, a set of switched output feedback controllers is designed to minimise the disturbance attenuation level defined by the regional gain over a class of energy-bounded disturbances. The synthesis conditions are expressed as bilinear matrix inequalities, and can be solved by numerical search coupled with linear matrix inequality optimisation. Compared to the previous method based on polytopic differential inclusion, the proposed approach has good scalability and potentially renders better performance. Numerical examples are provided to verify the effectiveness of the proposed approach.}, number={5}, journal={INTERNATIONAL JOURNAL OF SYSTEMS SCIENCE}, author={Duan, Chang and Wu, Fen}, year={2016}, month={Apr}, pages={1008–1020} }
 @article{ban_wu_2016, title={Output feedback control of linear fractional transformation systems subject to actuator saturation}, volume={47}, ISSN={["1464-5319"]}, DOI={10.1080/00207721.2015.1110213}, abstractNote={ABSTRACT In this paper, the control problem for a class of linear parameter varying (LPV) plant subject to actuator saturation is investigated. For the saturated LPV plant depending on the scheduling parameters in linear fractional transformation (LFT) fashion, a gain-scheduled output feedback controller in the LFT form is designed to guarantee the stability of the closed-loop LPV system and provide optimised disturbance/error attenuation performance. By using the congruent transformation, the synthesis condition is formulated as a convex optimisation problem in terms of a finite number of LMIs for which efficient optimisation techniques are available. The nonlinear inverted pendulum problem is employed to demonstrate the effectiveness of the proposed approach. Moreover, the comparison between our LPV saturated approach with an existing linear saturated method reveals the advantage of the LPV controller when handling nonlinear plants.}, number={15}, journal={INTERNATIONAL JOURNAL OF SYSTEMS SCIENCE}, author={Ban, Xiaojun and Wu, Fen}, year={2016}, pages={3646–3655} }
 @article{yuan_wu_2016, title={Robust H-2 and H-infinity switched feedforward control of uncertain LFT systems}, volume={26}, ISSN={["1099-1239"]}, DOI={10.1002/rnc.3380}, abstractNote={This paper presents a new robust switched feedforward control scheme for a class of uncertain systems described in a standard linear fractional transformation form. First, the analysis conditions for switching stability are derived by using a piecewise Lyapunov function incorporated with the min‐switching control technique. Based on the analysis results, the synthesis conditions are then formulated as a special type of bilinear matrix inequalities, which can be solved by means of linear matrix inequalities and line search. Both robust ℋ2 and ℋ∞ feedforward control problems are considered. The proposed robust switched control scheme outperforms existing robust feedforward control approaches for uncertain systems based on single quadratic Lyapunov function, and leads to less conservative control design. Numerical examples will be used to illustrate the effectiveness and advantages of the proposed results. Copyright © 2015 John Wiley & Sons, Ltd.}, number={9}, journal={INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL}, author={Yuan, Chengzhi and Wu, Fen}, year={2016}, month={Jun}, pages={1841–1856} }
 @article{yuan_wu_2016, title={Robust switching output-feedback control of time-varying polytopic uncertain systems}, volume={89}, ISSN={["1366-5820"]}, DOI={10.1080/00207179.2016.1154607}, abstractNote={ABSTRACT The problem of designing a globally optimal robust output feedback controller for time-varying polytopic uncertain systems is a well-known non-convex optimisation problem. In this paper, new sufficient conditions for both robust and switching output-feedback control syntheses are proposed in terms of bilinear matrix inequalities (BMIs) under the multiple Lyapunov function framework. This set of synthesis conditions is further reduced to a special type of BMIs, which can be solved effectively using linear matrix inequality optimisation plus a line search. The associated robust output-feedback controller is constructed as a switching-type full-order dynamic output-feedback controller, consisting of a family of linear time-invariant subcontrollers and a min-switching logic. The proposed approach features the important property of computational efficiency with stringent performance. Its effectiveness and advantages have been demonstrated through extensive numerical studies.}, number={11}, journal={INTERNATIONAL JOURNAL OF CONTROL}, author={Yuan, Chengzhi and Wu, Fen}, year={2016}, pages={2262–2276} }
 @inproceedings{yuan_wu_duan_2016, title={robust gain-scheduling output feedback control of state-delayed lft systems using dynamic IQCS}, DOI={10.1115/dscc2015-9686}, abstractNote={This paper is concerned with the robust gain-scheduling output feedback control problem for a class of linear parameter-varying systems with time-varying state delay. The controlled plant under consideration is described as a linear fractional transformation (LFT) model of scheduling parameters. Dynamic integral quadratics (IQCs) are employed to characterize the input-output behavior of the state-delay nonlinearity. The robust stability and the L2-gain performance are first analyzed using quadratic Lyapunov function. Then, the design of dynamic output-feedback controllers robust against the plant state-delay nonlinearity and gain-scheduled by parameters is examined. The synthesis conditions of such robust gain-scheduling controllers are formulated in terms of linear matrix inequalities (LMIs) plus a line search, which can be solved effectively using existing algorithms. A numerical example has been used to demonstrate the effectiveness and advantages of the proposed approach.}, booktitle={Proceedings of the ASME 8th Annual Dynamic Systems and Control Conference, 2015, vol 3}, author={Yuan, C. Z. and Wu, F. and Duan, C.}, year={2016} }
 @inproceedings{yuan_duan_wu_2015, title={Almost output regulation of discrete-time switched linear systems}, DOI={10.1109/acc.2015.7171961}, abstractNote={In this paper, we propose a new hybrid control approach for almost output regulation of a class of discrete-time switched linear systems with average dwell time (ADT). Both controlled plant and exosystem are described by switched linear systems. The proposed hybrid controller is constructed as a switching impulsive system, where the controller states will undergo impulsive jumps at each switching instant. By using the ADT technique incorporated with multiple quadratic Lyapunov functions, the hybrid synthesis conditions for almost output regulation with asymptotic stability and weighted ℋ∞ performance are formulated as a set of linear matrix equations and linear matrix inequalities (LMIs), which can be solved effectively. The proposed hybrid control method has been demonstrated through a numerical example.}, booktitle={2015 american control conference (acc)}, author={Yuan, C. Z. and Duan, C. and Wu, F.}, year={2015}, pages={4042–4047} }
 @inproceedings{yang_wu_liu_huang_2015, title={An Optimization-Based Approach for Prosthesis Dynamic Modeling and Parameter Identification}, volume={1}, ISBN={9780791857243}, url={http://dx.doi.org/10.1115/dscc2015-9637}, DOI={10.1115/dscc2015-9637}, abstractNote={In this paper, we propose an effective approach to model the prosthetic leg dynamics for amputees wearing active-transfemoral prosthesis (ATP) which is self-powered. To accommodate unexpected effects of thigh on knee joints, the dynamic prosthesis model has been derived using both the thigh-knee-shank and the knee-shank configurations. Correlated with the amputee’s walking data, a nonlinear optimization problem is then formulated to identify the model parameters and the gains of the PD controller which is used to control the input torque for the ATP, while reducing measurement errors of the data. Moreover, the identified models are validated by comparing the predicted dynamics with experimental measurements. The advantages of proposed method in terms of simplicity, flexibility, and accuracy are demonstrated by the high correlation coefficients and the low root-mean-square errors.}, booktitle={Volume 1: Adaptive and Intelligent Systems Control; Advances in Control Design Methods; Advances in Non-Linear and Optimal Control; Advances in Robotics; Advances in Wind Energy Systems; Aerospace Applications; Aerospace Power Optimization; Assistive Robotics; Automotive 2: Hybrid Electric Vehicles; Automotive 3: Internal Combustion Engines; Automotive Engine Control; Battery Management; Bio Engineering Applications; Biomed and Neural Systems; Connected Vehicles; Control of Robotic Systems}, publisher={American Society of Mechanical Engineers}, author={Yang, Ting and Wu, Fen and Liu, Ming and Huang, He (Helen)}, year={2015}, month={Oct} }
 @article{yuan_wu_2015, title={Asynchronous switching output feedback control of discrete-time switched linear systems}, volume={88}, ISSN={["1366-5820"]}, DOI={10.1080/00207179.2015.1016454}, abstractNote={In this paper, the problem of dynamic output-feedback control synthesis is addressed for discrete-time switched linear systems under asynchronous switching. The proposed hybrid controller consists of a standard dynamic output-feedback switching control law and an impulsive reset law induced by controller state jumps. Using the average dwell time technique incorporating with multiple quadratic Lyapunov functions, the switching control synthesis conditions for asymptotic stability with guaranteed weighted ℓ2-gain performance are derived as a set of linear matrix inequalities (LMIs). The proposed hybrid synthesis scheme advances existing design methods for output-feedback asynchronous switching control of switched linear systems in two important aspects: LMI formulation of the synthesis problem; and arbitrary order of the controller state. A numerical example is used to illustrate the effectiveness and advantages of the proposed design technique.}, number={9}, journal={INTERNATIONAL JOURNAL OF CONTROL}, author={Yuan, Chengzhi and Wu, Fen}, year={2015}, month={Sep}, pages={1766–1774} }
 @article{ban_wu_2015, title={Gain scheduling output feedback control of linear plants with actuator saturation}, volume={352}, ISSN={["1879-2693"]}, DOI={10.1016/j.jfranklin.2015.06.005}, abstractNote={From a gain-scheduling perspective, we will study the output feedback control problem for linear systems with some of control channels subject to actuator saturation. This includes the scenario of all actuator saturation as a special case. A feedback controller, expressed in the form of linear fractional transformation, is proposed to guarantee regional stability of the closed-loop system and provide disturbance/error attenuation measured in L2 gain. The resulting synthesis condition is formulated as linear matrix inequalities (LMIs) and can be solved efficiently. Moreover, explicit formulas are derived to calculate controller gains, which reduces the computational cost compared to the method of directly solving the LMI-based condition. Numerical examples are provided to demonstrate the proposed saturation control approach.}, number={10}, journal={JOURNAL OF THE FRANKLIN INSTITUTE-ENGINEERING AND APPLIED MATHEMATICS}, author={Ban, Xiaojun and Wu, Fen}, year={2015}, month={Oct}, pages={4163–4187} }
 @article{yuan_wu_2015, title={Hybrid Control for Switched Linear Systems With Average Dwell Time}, volume={60}, ISSN={["1558-2523"]}, DOI={10.1109/tac.2014.2322941}, abstractNote={This technical note presents a hybrid control scheme for the output-feedback control of switched linear systems with average dwell time. The proposed hybrid controller consists of a standard switching output-feedback control law and a supervisor enforcing a reset rule for the switching controller states at each switching instant. This hybrid control scheme provides an efficient and systematic way for designing average dwell time switched linear control systems in the sense that the boundary condition can be incorporated into the synthesis problem in a convex formulation. Specifically, both full-order and reduced-order controllers with guaranteed stability and optimal weighted H∞ performance will be solved by linear matrix inequality (LMI) optimizations. Simulation studies are included to illustrate the effectiveness of the proposed approach.}, number={1}, journal={IEEE TRANSACTIONS ON AUTOMATIC CONTROL}, author={Yuan, Chengzhi and Wu, Fen}, year={2015}, month={Jan}, pages={240–245} }
 @article{rui_pfeiffer_zhang_wang_wu_2015, title={Preface}, volume={7}, ISSN={["1687-8140"]}, DOI={10.1177/1687814015604802}, number={9}, journal={ADVANCES IN MECHANICAL ENGINEERING}, author={Rui, Xiaoting and Pfeiffer, Friedrich G. and Zhang, Chuanzeng and Wang, Shimin and Wu, Fen}, year={2015}, month={Sep} }
 @inproceedings{liu_wu_ban_2015, title={Robust fault detection filter design for linear uncertain systems with unknown inputs}, DOI={10.1109/acc.2015.7170846}, abstractNote={In this paper, a robust fault detection filter design method for uncertain systems in linear fractional transformation (LFT) formulation with unknown inputs is proposed. The basic idea is to convert the complicated ℋ_/ℋ∞ problem to an easier ℋ∞ model following problem. Moreover, two major improvements have been made in this research. First, the uncertain systems in LFT formulation are studied. This class of uncertain models is capable of approximating complex nonlinear dynamics. Second, a more general form of filter is employed to achieve a better fault detection and disturbance rejection performance. It involves the widely used observer-based filter as a special case. With structured uncertainties, it has been shown the robust fault detection filter design can be solved by a convex optimization condition in terms of linear matrix inequalities (LMIs). An illustrative design example is used to demonstrate the effectiveness and better performance of the proposed approach.}, booktitle={2015 american control conference (acc)}, author={Liu, Y. and Wu, F. and Ban, X. J.}, year={2015}, pages={886–891} }
 @inproceedings{yuan_wu_duan_2015, title={Robust switching output feedback control of discrete-time linear polytopic uncertain systems}, DOI={10.1109/chicc.2015.7260096}, abstractNote={This paper presents a new switching control approach for robust output feedback control of a class of discrete-time linear systems subject to polytopic time-varying uncertainties. The proposed robust switching controller, which stabilizes the closed-loop system with a pre-specified H∞ performance level, consists of a family of dynamic output feedback controllers (of an arbitrary state order) and a switching law (the relaxed min-switching strategy). Both stability analysis and control synthesis conditions are derived using a piecewise quadratic Lyapunov function. The switching law combined with the controller gain matrices are jointly synthesized by solving a convex linear matrix inequality (LMI) based optimization problem. An academic example has been used to demonstrate the effectiveness and advantages of the proposed approach.}, booktitle={2015 34th Chinese Control Conference (CCC)}, author={Yuan, C. Z. and Wu, F. and Duan, C.}, year={2015}, pages={2973–2978} }
 @article{yuan_wu_2015, title={Switching control of linear systems subject to asymmetric actuator saturation}, volume={88}, ISSN={["1366-5820"]}, DOI={10.1080/00207179.2014.942884}, abstractNote={In this paper, we study the saturation control problem for linear time-invariant (LTI) systems subject to asymmetric actuator saturation under a switching control framework. The LTI plant with asymmetric saturation is first transformed to an equivalent switched linear model with each subsystem subject to symmetric actuator saturation, based on which a dwell-time switching controller augmented with a controller state reset is then developed by using multiple Lyapunov functions. The controller synthesis conditions are formulated as linear matrix inequalities (LMIs), which can be solved efficiently. Simulation results are also included to illustrate the effectiveness and advantages of the proposed approach.}, number={1}, journal={INTERNATIONAL JOURNAL OF CONTROL}, author={Yuan, Chengzhi and Wu, Fen}, year={2015}, month={Jan}, pages={204–215} }
 @article{duan_wu_2014, title={Analysis and control of switched linear systems via dwell-time min-switching}, volume={70}, ISSN={["1872-7956"]}, DOI={10.1016/j.sysconle.2014.05.004}, abstractNote={This paper addresses analysis and switching control problems of switched linear systems. To this end, a mixed time-driven and state-dependent switching strategy is proposed. It guarantees an average dwell time even when all subsystems are unstable. The switching rule and its associated switching output feedback controllers are designed to stabilize the switched system and satisfy a weighted L2 gain performance. The proposed analysis and switching control approach could refrain frequent switches commonly observed in min-switching based designs. The effectiveness of the proposed approach has been illustrated through a spherical inverted pendulum example.}, journal={SYSTEMS & CONTROL LETTERS}, author={Duan, Chang and Wu, Fen}, year={2014}, month={Aug}, pages={8–16} }
 @article{duan_wu_2014, title={Analysis and control of switched linear systems via modified Lyapunov-Metzler inequalities}, volume={24}, ISSN={["1099-1239"]}, DOI={10.1002/rnc.2886}, abstractNote={SUMMARY}, number={2}, journal={INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL}, author={Duan, Chang and Wu, Fen}, year={2014}, month={Jan}, pages={276–294} }
 @article{yuan_wu_2014, title={Analysis and synthesis of linear hybrid systems with state-triggered jumps}, volume={14}, ISSN={["1878-7460"]}, DOI={10.1016/j.nahs.2014.05.002}, abstractNote={This paper investigates first the stability and L2-gain problems for a class of linear hybrid control systems with state-triggered jumps by using an extended Lyapunov-like function (ELF) technique. The obtained results are then applied to facilitate the joint design of a hybrid controller (linear controller plus reset law) for a continuous-time linear time-invariant (LTI) plant. The hybrid H∞ synthesis conditions are expressed in linear matrix inequalities (LMIs) with two line search parameters. An inverted pendulum example is used to illustrate the effectiveness of the proposed approach.}, journal={NONLINEAR ANALYSIS-HYBRID SYSTEMS}, author={Yuan, Chengzhi and Wu, Fen}, year={2014}, month={Nov}, pages={47–60} }
 @article{yang_wu_2014, title={Control of Polynomial Nonlinear Systems Using Higher Degree Lyapunov Functions}, volume={136}, ISSN={["1528-9028"]}, DOI={10.1115/1.4026172}, abstractNote={In this paper, we propose a new control design approach for polynomial nonlinear systems based on higher degree Lyapunov functions. To derive higher degree Lyapunov functions and polynomial nonlinear controllers effectively, the original nonlinear systems are augmented under the rule of power transformation. The augmented systems have more state variables and the additional variables represent higher order combinations of the original ones. As a result, the stabilization and L2 gain control problems with higher degree Lyapunov functions can be recast to the search of quadratic Lyapunov functions for augmented nonlinear systems. The sum-of-squares (SOS) programming is then used to solve the quadratic Lyapunov function of augmented state variables (higher degree in terms of original states) and its associated nonlinear controllers through convex optimization problems. The proposed control approach has also been extended to polynomial nonlinear systems subject to actuator saturations for better performance including domain of attraction (DOA) expansion and regional L2 gain minimization. Several examples are used to illustrate the advantages and benefits of the proposed approach for unsaturated and saturated polynomial nonlinear systems.}, number={3}, journal={JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME}, author={Yang, Shuowei and Wu, Fen}, year={2014}, month={May} }
 @inproceedings{duan_wu_2014, title={Dwell-time min-switching for discrete-time switched linear systems}, DOI={10.1109/ecc.2014.6862224}, abstractNote={This paper addresses analysis and switching control problems of discrete-time switched linear systems. A mixed time-driven and state-dependent switching strategy is proposed to guarantee an average dwell time even when all subsystems are unstable. The switching rule and its associated switching output feedback controllers are designed to stabilize the switched system and achieve a disturbance attenuation performance. The proposed analysis and switching control approach could refrain frequent switches commonly observed in min-switching based designs. The effectiveness of the proposed approach is illustrated through a numerical example.}, booktitle={2014 European Control Conference (ECC)}, author={Duan, C. and Wu, F.}, year={2014}, pages={2540–2545} }
 @inproceedings{liu_ban_wu_lam_2014, title={Dynamic output feedback controller design for T-S fuzzy plants with actuator saturation using linear fractional transformation}, DOI={10.1109/fuzz-ieee.2014.6891617}, abstractNote={In this paper, a systematic synthesis method for Takagi-Sugeno fuzzy dynamic output feedback controller is proposed for T-S fuzzy plants with actuator saturation. By using the deadzone function, both the T-S fuzzy plant with actuator saturation and the T-S fuzzy dynamic output feedback controller are transformed into the form of linear fractional transformation (LFT). Within the framework of LFT, the issue of stability as well as H performance is cast as a convex optimization problem which can be approached by solving a set of linear matrix inequalities. A numerical example is presented to illustrate the effectiveness of the proposed method.}, booktitle={2014 ieee international conference on fuzzy systems (fuzz-ieee)}, author={Liu, Y. and Ban, X. J. and Wu, F. and Lam, H. K.}, year={2014}, pages={2125–2132} }
 @inproceedings{yuan_wu_2014, title={Output feedback reset control of general MIMO LTI systems}, DOI={10.1109/ecc.2014.6862225}, abstractNote={This paper presents a systematic Lyapunov-based approach for output-feedback reset control of linear time-invariant (LTI) systems with a general multiple-input multiple-output (MIMO) configuration. The reset controller consists of a base linear controller and a reset law that enforces resets to the controller states. Based on the extended Lyapunov-like function (ELF) technique, the reset controller with guaranteed exponential stability and weighted L2-gain performance is synthesized by solving a set of linear matrix inequalities (LMIs) with linear search over two scalar variables. A numerical example is used to illustrate the effectiveness of the proposed approach.}, booktitle={2014 European Control Conference (ECC)}, author={Yuan, C. Z. and Wu, F.}, year={2014}, pages={2334–2339} }
 @inproceedings{yang_wu_2013, title={Feedback design for saturated polynomial nonlinear systems via higher order Lyapunov functions}, DOI={10.1115/dscc2012-movic2012-8644}, abstractNote={In this work, we develop a new control design approach to deal with saturated polynomial nonlinear systems by using higher order Lyapunov functions. By combining power transformation with Sum-of-Squares (SOS) techniques, we can augment the systems with more state variables representing higher order combinations of the original ones. Then, the search of higher order Lyapunov functions for original systems can be recast to the design of quadratic Lyapunov functions for augmented systems. By computing for higher order Lyapunov functions using norm-bounded differential inclusion (NDI) LMI conditions, the flexible representations of augmented systems can help us to achieve better performance than quadratic based method. Two examples illustrate the improvements to enlarge the region of attraction and to improve the ℋ∞ performance for nonlinear systems subjected to saturation nonlinearity, respectively.© 2012 ASME}, booktitle={Proceedings of the ASME 5th Annual Dynamic Systems and Control Division Conference and JSME 11th Motion and Vibration Conference, DSCC 2012, vol 2}, author={Yang, S. W. and Wu, F.}, year={2013}, pages={645–652} }
 @inproceedings{song_ren_wu_2013, title={Gain-scheduling compensator synthesis for output regulation of nonlinear systems}, DOI={10.1109/acc.2013.6580791}, abstractNote={This paper addresses the gain-scheduling output regulation synthesis problem for nonlinear systems. For gain-scheduling control, the linear parameter-varying (LPV) model is obtained from nonlinear plant by plant linearization about zero-error trajectories upon which an LPV controller is synthesized. In practical engineering application, a key issue is to find a nonlinear output feedback compensator related to the designed LPV controller which can guarantee that the closed-loop system of nonlinear plant and compensator linearizes to the interconnection of LPV model and LPV controller. So the stability and performance about the zero-error trajectories can be inherited when the nonlinear compensator is implemented. By incorporating equilibrium input and measured output into the auxiliary LPV model, the compensator synthesis problem is reformulated as linear matrix inequalities (LMIs) which can be solved efficiently using the interior-point method. Consequently the proposed output feedback compensator can satisfy the linearization requirement. Finally, the validity of the proposed approach is demonstrated through a ball and beam design example.}, booktitle={2013 american control conference (acc)}, author={Song, X. and Ren, Z. and Wu, F.}, year={2013}, pages={6078–6083} }
 @article{duan_wu_2013, title={NEW RESULTS ON CONTINUOUS-TIME SWITCHED LINEAR SYSTEMS WITH ACTUATOR SATURATION}, DOI={10.1115/dscc2013-3789}, abstractNote={This paper further studies the analysis and control problems of continuous-time switched linear systems subject to actuator saturation. Using the norm-bounded differential inclusion (NDI) description of the saturated systems and the minimal switching rule, a set of switched output feedback controllers is designed to minimize the disturbance attenuation level defined by the regional ℒ2 gain over a class of energy-bounded disturbances. The synthesis conditions are expressed as bilinear matrix inequalities (BMIs) and can be solved by numerical search coupled with linear matrix inequality (LMI) optimization. Compared to the previous method based on polytopic differential inclusion (PDI), the proposed approach has good scalability and potentially renders better performance. Numerical examples are provided to verify effectiveness of the proposed approach.}, journal={ASME 2013 DYNAMIC SYSTEMS AND CONTROL CONFERENCE, VOL 2}, author={Duan, Chang and Wu, Fen}, year={2013} }
 @article{wu_hays_2013, title={Nonlinear gain-scheduling output-feedback control for polynomial nonlinear systems subject to actuator saturation}, volume={86}, ISSN={["1366-5820"]}, DOI={10.1080/00207179.2013.792001}, abstractNote={This paper investigates nonlinear gain-scheduling control approaches for a class of polynomial nonlinear systems, containing an output-dependent vector field with input saturation. Using the polytopic differential inclusion and norm-bounded differential inclusion (NDI) of saturation and dead-zone functions, the nonlinear plants are transformed into systems with measurable parameters. For the polytopic differential inclusion description, a quasi-linear parameter varying (quasi-LPV) output-feedback controller will be sought for saturation control. On the other hand, the NDI model leads to a nonlinear fractional transformation (NFT) output-feedback controller for saturated nonlinear systems. The quasi-LPV and NFT output-feedback control synthesis conditions are derived in the forms of output-dependent matrix inequalities. They can be reformulated as sum-of-squares (SOS) optimisations and solved efficiently using SOS programming. The proposed nonlinear gain-scheduling saturation control approaches will be demonstrated using the Van der Pol equation.}, number={9}, journal={INTERNATIONAL JOURNAL OF CONTROL}, author={Wu, Fen and Hays, Scott}, year={2013}, month={Sep}, pages={1607–1619} }
 @article{duan_wu_2013, title={Robust Switched Filtering for Time-Varying Polytopic Uncertain Systems}, volume={135}, ISSN={["1528-9028"]}, DOI={10.1115/1.4025027}, abstractNote={This paper studies the problem of designing robust switched filters for time-varying polytopic uncertain systems. The synthesis conditions for a set of filters under a min-switching rule are derived to guarantee globally asymptotical stability with optimized robust H∞ performance. Specifically, the conditions are expressed as bilinear matrix inequalities (BMIs) and can be solved by linear matrix inequality (LMI) optimization techniques. The proposed approach utilizes a piecewise quadratic Lyapunov function to reduce the conservativeness of robust filtering methods based on single Lyapunov function, thus better H∞ performance can be achieved. Both continuous and discrete-time robust filter designs are considered. To simplify filter implementation, a method to remove redundancy in min-switching filter members is also introduced. The advantages of the proposed robust switching filters are illustrated by several examples.}, number={6}, journal={JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME}, author={Duan, Chang and Wu, Fen}, year={2013}, month={Nov} }
 @inproceedings{yuan_wu_2013, title={Robust control of switched linear systems via min of quadratics}, DOI={10.1115/dscc2013-3715}, abstractNote={In this paper, we will investigate the robust switching control problem for switched linear systems by using a class of composite quadratic functions, the min (of quadratics) function, to improve performance and enhance control design flexibility. The robustness is reflected in two prospectives including the ℋ ∞ performance and arbitrary switching of subsystems. A hysteresis min-switching strategy is employed to orchestrate the switching among a collection of controllers. The synthesis conditions for both state feedback and output feedback control problems are derived in terms of a set of linear matrix inequalities (LMIs) with linear search over scalar variables. The proposed min function based approach unifies the existing single Lyapunov function based method and multiple Lyapunov function based method in a general framework, and the derived LMI conditions cover the existing LMI conditions as special cases. Numerical studies are included to demonstrate the advantages of the proposed control design approach.}, booktitle={Proceedings of the ASME 2013 Dynamic Systems and Control Conference (DSCC2013), vol. 1}, author={Yuan, C. Z. and Wu, F.}, year={2013} }
 @article{wu_cai_2013, title={Switching fault-tolerant control of a flexible air-breathing hypersonic vehicle}, volume={227}, ISSN={["2041-3041"]}, DOI={10.1177/0959651812453914}, abstractNote={ In this paper, we will apply a switching fault-tolerant control approach to an air-breathing hypersonic vehicle subject to time-varying actuator and sensor faults. The faults under consideration include loss of effectiveness of the actuators and sensors. Possible fault scenarios are categorized into different fault cases based on the fault type and its location. For each case, a parameter-dependent (or constant gain) fault-tolerant control controller is designed to stabilize the faulty system with an optimal controlled performance. The synthesis condition of each local fault-tolerant control law is formulated in terms of linear matrix inequalities. To achieve both local optimal performance and switching stability, Youla parameterization of each individual local fault-tolerant control controller is performed and the result is applied to the closed-loop system. The quadratic stability of a fast switching closed-loop system is guaranteed by a common Lyapunov function. Simulation results based on the non-linear flexible hypersonic vehicle model and fault-tolerant linear-parameter-varying controllers are presented and the reults of these studies demonstrate the effectiveness of the proposed switching fault-tolerant control approach for application to a hypersonic vehicle. }, number={I1}, journal={PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART I-JOURNAL OF SYSTEMS AND CONTROL ENGINEERING}, author={Wu, Fen and Cai, Xuejing}, year={2013}, month={Jan}, pages={24–38} }
 @inproceedings{hays_wu_2012, title={Nonlinear robust H-infinity control with state-dependent scaling}, DOI={10.1115/dscc2011-5994}, abstractNote={This paper addresses the design of nonlinear robust H∞ controllers for nonlinear uncertain systems with polynomial vector field and norm bounded uncertainties. We derive state-dependent matrix inequalities, using Lyapunov’s direct method, that stabilize the nonlinear systems and guarantee robust performance using nonlinear state-feedback control. The state-dependent synthesis conditions incorporate state-dependent scaling to minimize the ℒ2 gain of the disturbance/output. Sum-of-squares (SOS) optimization is applied to solve the resulting synthesis condition with optimized ℒ2 gain for the nonlinear system, without requiring an iterative approach. Finally, a design example of nonlinear Van der Pol equation is presented.}, booktitle={Proceedings of the ASME Dynamic Systems and Control Conference and Bath/ASME Symposium on Fluid Power and Motion Control (DSCC 2011), vol 1}, author={Hays, S. and Wu, F.}, year={2012}, pages={581–588} }
 @inproceedings{duan_wu_2012, title={Output feedback control for continuous-time switched linear systems subject to actuator saturation}, DOI={10.1115/dscc2011-5925}, abstractNote={This paper is devoted to output feedback ℋ∞ control problem for continuous-time switched linear systems subject to actuator saturation. Using minimal switching rule, nonlinear output feedbacks, expressed in the form of quasi-linear parameter varying system are designed to satisfy a pre-specified disturbance attenuation level defined by the regional ℒ2 gains over a class of energy-bounded disturbances. The synthesis condition is further simplified and can be solved through efficient LMI optimizations. The proposed switched control approach is also illustrated by a simple example.}, booktitle={Proceedings of the ASME Dynamic Systems and Control Conference and Bath/ASME Symposium on Fluid Power and Motion Control (DSCC 2011), vol 1}, author={Duan, C. and Wu, F.}, year={2012}, pages={449–456} }
 @article{duan_wu_2012, title={Output-feedback control for switched linear systems subject to actuator saturation}, volume={85}, ISSN={["1366-5820"]}, DOI={10.1080/00207179.2012.691611}, abstractNote={This article is devoted to the output-feedback ℋ∞ control problem for switched linear systems subject to actuator saturation. We consider both continuous- and discrete-time switched systems. Using the minimal switching rule, nonlinear output feedbacks expressed in the form of quasi-linear parameter varying system are designed to satisfy a pre-specified disturbance attenuation level defined by the regional ℒ2 (ℓ2)-gains over a class of energy-bounded disturbances. The conditions are expressed in bilinear matrix inequalities and can be solved by line search coupled with linear matrix inequalities optimisation. A spherical inverted pendulum example is used to illustrate the effectiveness of the proposed approach.}, number={10}, journal={INTERNATIONAL JOURNAL OF CONTROL}, author={Duan, Chang and Wu, Fen}, year={2012}, pages={1532–1545} }
 @article{zheng_wu_2011, title={Adaptive control design for uncertain polynomial nonlinear systems with parametric uncertainties}, volume={25}, ISSN={["0890-6327"]}, DOI={10.1002/acs.1215}, abstractNote={In this paper, we will develop an adaptive ℋ︁∞ control approach for a class of polynomial nonlinear systems with parametric uncertainties. Motivated by the dissipation theory and the vector projection technique, we propose a nonlinear adaptive ℋ︁∞ controller and its associated parameter adaptation law. The proposed adaptive control strategy is capable of identifying unknown parameter values quickly and minimizing the effect of estimation error. To further improve adaptive controlled performance, the Lyapunov function will be relaxed from quadratic to higher‐order forms and the controller gains are generalized from constant to parameter‐dependent. All of the synthesis conditions are formulated in the framework of polynomial/constant linear matrix inequalities and solvable using available software packages. Copyright © 2010 John Wiley & Sons, Ltd.}, number={6}, journal={INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING}, author={Zheng, Qian and Wu, Fen}, year={2011}, month={Jun}, pages={502–518} }
 @article{zheng_wu_2011, title={Generalized nonlinear H-infinity synthesis condition with its numerically efficient solution}, volume={21}, ISSN={["1099-1239"]}, DOI={10.1002/rnc.1682}, abstractNote={Abstract}, number={18}, journal={INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL}, author={Zheng, Qian and Wu, Fen}, year={2011}, month={Dec}, pages={2079–2100} }
 @article{cai_wu_2011, title={Multiobjective fault detection and isolation for flexible air-breathing hypersonic vehicle}, volume={22}, ISSN={["1004-4132"]}, DOI={10.3969/j.issn.1004-4132.2011.01.006}, abstractNote={An application of the multiobjective fault detection and isolation (FDI) approach to an air-breathing hypersonic vehicle (HSV) longitudinal dynamics subject to disturbances is presented. Maintaining sustainable and safe flight of HSV is a challenging task due to its strong coupling effects, variable operating condi- tions and possible failures of system components. A common type of system faults for aircraft including HSV is the loss of effective- ness of its actuators and sensors. To detect and isolate multiple actuator/sensor failures, a faulty linear parameter-varying (LPV) model of HSV is derived by converting actuator/system compo- nent faults into equivalent sensor faults. Then a bank of LPV FDI observers is designed to track individual fault with minimum error and suppress the effects of disturbances and other fault signals. The simulation results based on the nonlinear flexible HSV model and a nominal LPV controller demonstrate the effectiveness of the fault estimation technique for HSV.}, number={1}, journal={JOURNAL OF SYSTEMS ENGINEERING AND ELECTRONICS}, author={Cai, Xuejing and Wu, Fen}, year={2011}, month={Feb}, pages={52–62} }
 @article{cai_wu_2010, title={Robust fault detection and isolation for parameter-dependent LFT systems}, volume={20}, ISSN={["1099-1239"]}, DOI={10.1002/rnc.1468}, abstractNote={Abstract}, number={7}, journal={INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL}, author={Cai, Xuejing and Wu, Fen}, year={2010}, month={May}, pages={764–776} }
 @article{cai_wu_2010, title={Robust parameter-dependent fault-tolerant control for actuator and sensor faults}, volume={83}, ISSN={["1366-5820"]}, DOI={10.1080/00207179.2010.481024}, abstractNote={In this article, we study a robust fault-tolerant control (FTC) problem for linear systems subject to time-varying actuator and sensor faults. The faults under consideration are loss of effectiveness in actuators and sensors. Based on the estimated faults from a fault detection and isolation scheme, robust parameter-dependent FTC will be designed to stabilise the faulty system under all possible fault scenarios. The synthesis condition of such an FTC control law will be formulated in terms of linear matrix inequalities (LMIs) and can be solved efficiently by semi-definite programming. The proposed FTC approach will be demonstrated on a simple faulty system with different fault levels and fault estimation error bounds.}, number={7}, journal={INTERNATIONAL JOURNAL OF CONTROL}, author={Cai, Xuejing and Wu, Fen}, year={2010}, pages={1475–1484} }
 @inproceedings{cai_wu_2009, title={A Robust fault tolerant control approach for LTI systems with actuator and sensor faults}, DOI={10.1109/ccdc.2009.5191903}, abstractNote={In this paper, we study a robust fault-tolerant control (FTC) problem for linear systems with time varying actuator and sensor faults and propose an parameter-dependent solution by using L2 gain optimization techniques. Using estimated faults from a fault detection and isolation (FDI) scheme, parameter-dependent robust FTC gain will be scheduled by fault magnitude to stabilize and optimize the faulty system under all possible fault scenarios. The synthesis condition of such a FTC control law will be formulated as linear matrix inequalities (LMIs) and can be solved efficiently by semi-definite programming techniques. A numerical example is used to demonstrate the proposed fault-tolerant control approach for a simple faulty systems with different fault levels and fault estimation error bounds.}, booktitle={CCDC 2009: 21st Chinese Control and Decision Conference, vols 1-6, Proceedings}, author={Cai, X. J. and Wu, F.}, year={2009}, pages={890–895} }
 @article{wu_zheng_lin_2009, title={Disturbance attenuation by output feedback for linear systems subject to actuator saturation}, volume={19}, ISSN={["1099-1239"]}, DOI={10.1002/rnc.1306}, abstractNote={Abstract}, number={2}, journal={INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL}, author={Wu, Fen and Zheng, Qian and Lin, Zongli}, year={2009}, month={Jan}, pages={168–184} }
 @article{zheng_wu_2009, title={Lyapunov Redesign of Adaptive Controllers for Polynomial Nonlinear Systems}, ISBN={["978-1-4244-4523-3"]}, ISSN={["2378-5861"]}, DOI={10.1109/acc.2009.5160128}, abstractNote={In this paper, we study adaptive control redesign problem of polynomial nonlinear systems with matching parametric uncertainties. By transforming the system into its corresponding error dynamics, we will develop an adaptive control scheme in attenuating the effect of the unknown parameters on the controlled output, which is composed of tracking errors and control efforts. To achieve better controlled performance, the Lyapunov functions will be relaxed from quadratic to higher order and the resulting controller gain is generalized from constant to parameter dependent. The synthesis conditions of adaptive control will be formulated as polynomial matrix inequalities and are solvable by recast the resulting conditions into a Sum of Squares (SOS) optimization problem, from which the adaptive control law as well as the parameter adaptation law are derived with zero tracking and parameter estimation errors. An example is provided to demonstrate effectiveness of the proposed adaptive control redesign approach.}, journal={2009 AMERICAN CONTROL CONFERENCE, VOLS 1-9}, author={Zheng, Qian and Wu, Fen}, year={2009}, pages={5144–5149} }
 @article{zheng_wu_2009, title={Nonlinear H-infinity Control Designs with Axisymmetric Spacecraft Control}, volume={32}, ISSN={["1533-3884"]}, DOI={10.2514/1.40060}, abstractNote={In this paper, we study nonlinear control of a spacecraft symmetric about its principal axis with two control torques. Using a computationally efficient H ∞ control design procedure, attitude stabilization and command tracking problems of the axisymmetric spacecraft are solved locally. The proposed nonlinear H ∞ control approach uses higher order Lyapunov functions and reformulates the difficult Hamilton―Jacobian―Isaacs inequalities as semidefinite optimization conditions. Sum-of-squares programming techniques are then applied to obtain computationally tractable solutions, from which nonlinear control laws will be constructed. The nonlinear H ∞ control designs for spacecraft are capable of exploiting the most suitable forms of Lyapunov functions for performance improvement.}, number={3}, journal={JOURNAL OF GUIDANCE CONTROL AND DYNAMICS}, author={Zheng, Qian and Wu, Fen}, year={2009}, pages={850–859} }
 @article{dong_wu_2009, title={Online Switching Control of LFT Parameter-Dependent Systems}, volume={131}, ISSN={["1528-9028"]}, DOI={10.1115/1.3023140}, abstractNote={To improve controlled performance and expand gain-scheduling control capability, we propose a switching control approach of linear fractional transformation parameter-dependent systems using multiple Lyapunov functions combined with online control techniques. At each switching instant, a gain-scheduled controller working for the next switching interval will be designed online. The switching control synthesis condition is formulated as linear matrix inequalities and can be solved efficiently, upon which the controller will be constructed. The online switching control scheme is demonstrated using an uninhabited combat aerospace vehicle problem.}, number={2}, journal={JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME}, author={Dong, Ke and Wu, Fen}, year={2009}, month={Mar} }
 @article{zheng_wu_2009, title={Regional stabilisation of polynomial non-linear systems using rational Lyapunov functions}, volume={82}, ISSN={["1366-5820"]}, DOI={10.1080/00207170802627267}, abstractNote={In this article, we propose a new non-linear stabilisation approach based on the popular linear parameter-varying control techniques. The regional state-feedback control problem of polynomial non-linear systems will be studied using rational Lyapunov functions of states. By bounding the variation rates of each state, the domain of attraction will be embedded in the region specified by the non-linear vector field. As a result, the state-feedback stabilisation conditions will be formulated as a set of polynomial matrix inequalities and can be solved efficiently by sum-of-squares programming. The resulting Lyapunov matrix and state-feedback gains are typically state-dependent rational matrix functions. This approach is also extended to a class of output-dependent non-linear systems where the stabilising output-feedback controller can be synthesised using rational Lyapunov functions of outputs. Finally, several examples will be used to demonstrate the proposed stabilisation approach and clarify the effect of various choices of Lyapunov function forms and state constraints.}, number={9}, journal={INTERNATIONAL JOURNAL OF CONTROL}, author={Zheng, Qian and Wu, Fen}, year={2009}, pages={1605–1615} }
 @article{dong_wu_2008, title={Almost output regulation for parameter-dependent linear fractional transformation systems}, volume={2}, ISSN={["1751-8652"]}, DOI={10.1049/iet-cta:20070087}, abstractNote={An important problem of output regulation for linear fractional transformation (LFT) systems is considered. This problem is mainly concerned about tracking and/or rejection of persistent signals produced by some external generator. Necessary and sufficient solvability condition for LFT systems as two linear matrix equations, which is an extension of the existing output regulation results for the linear time invariant and nonlinear systems will be presented. On the basis of the analysis condition, the LFT almost output regulation problem of approximately tracking/rejecting persistent signals will be studied by minimising the ℒ2 gain from perturbation of the signal to error output. Its synthesis condition will be formulated as two matrix equations plus a set of linear matrix inequalities. An example will be used to demonstrate the proposed approach.}, number={3}, journal={IET CONTROL THEORY AND APPLICATIONS}, author={Dong, K. and Wu, F.}, year={2008}, month={Mar}, pages={200–209} }
 @article{zheng_wu_2008, title={Output feedback control of saturated discrete-time linear systems using parameter-dependent Lyapunov functions}, volume={57}, ISSN={["1872-7956"]}, DOI={10.1016/j.sysconle.2007.12.011}, abstractNote={In this paper, we present a new output feedback control approach for discrete-time linear systems subject to actuator saturations using parameter-dependent Lyapunov functions. The saturation level indicator serves as a scheduling parameter. The resulting nonlinear controller is expressed in a quasi-LPV (linear parameter-varying) form, and the stabilization and disturbance attenuation problems are formulated and solved as finite-dimensional linear matrix inequality (LMI) optimization problems. Our approach is less conservative than a single quadratic Lyapunov function method. Specifically, the proposed output feedback control law asymptotically stabilizes the open loop system with a larger domain of attraction and achieves better disturbance attenuation under energy and magnitude bounded disturbances.}, number={11}, journal={SYSTEMS & CONTROL LETTERS}, author={Zheng, Qian and Wu, Fen}, year={2008}, month={Nov}, pages={896–903} }
 @article{wu_lin_zheng_2007, title={Output feedback stabilization of linear systems with actuator saturation}, volume={52}, ISSN={["1558-2523"]}, DOI={10.1109/TAC.2006.886498}, abstractNote={The note presents a method for designing an output feedback law that stabilizes a linear system subject to actuator saturation with a large domain of attraction. This method applies to general linear systems including strictly unstable ones. A nonlinear output feedback controller is first expressed in the form of a quasi-LPV system. Conditions under which the closed-loop system is locally asymptotically stable are then established in terms of the coefficient matrices of the controller. The design of the controller (coefficient matrices) that maximizes an estimate of the domain of attraction is then formulated and solved as an optimization problem with LMI constraints}, number={1}, journal={IEEE TRANSACTIONS ON AUTOMATIC CONTROL}, author={Wu, Fen and Lin, Zongli and Zheng, Qian}, year={2007}, month={Jan}, pages={122–128} }
 @article{dong_wu_2007, title={Robust and gain-scheduling control of LFT systems through duality and conjugate Lyapunov functions}, volume={80}, ISSN={["1366-5820"]}, DOI={10.1080/00207170601080213}, abstractNote={In this paper, we study stability and performance properties of linear fractional transformation (LFT) parameter-dependent systems using duality theory and tools from convex analysis. A pair of conjugate functions, the convex hull and the maximum of a family of quadratic functions, are used for analysis and synthesis of LFT systems. Sufficient synthesis conditions for both robust state feedback and gain-scheduling output feedback control problems are formulated as a set of linear matrix inequalities (LMIs) with linear search over scalar variables. Finally, a numerical example is used to demonstrate the advantages of the proposed approaches.}, number={4}, journal={INTERNATIONAL JOURNAL OF CONTROL}, author={Dong, K. and Wu, F.}, year={2007}, month={Apr}, pages={555–568} }
 @article{wu_chen_2007, title={Robust receding horizon control for constrained linear fractional transformation parameter-dependent systems}, volume={1}, DOI={10.1049/ict-cta:20060305}, number={5}, journal={IET Control Theory and Applications}, author={Wu, F. and Chen, Y.}, year={2007}, pages={1423–1430} }
 @article{wu_chen_2007, title={Robust receding horizon control for constrained linear fractional transformation parameter-dependent systems}, volume={1}, ISSN={1751-8644 1751-8652}, url={http://dx.doi.org/10.1049/iet-cta:20060305}, DOI={10.1049/iet-cta:20060305}, abstractNote={A robust receding horizon control (RHC) scheme is proposed for parameter-dependent linear systems with linear fractional parameter dependency and input–output constraints. The cost function is defined over a moving finite horizon as the quadratic performance for future parameter trajectories. The robust stability of the proposed RHC scheme is guaranteed using a parameter-dependent control Lyapunov function as the terminal penalty term, which is available through off-line synthesis procedure. Moreover, it is shown that the domain of attraction will be enlarged and the controlled performance of the RHC scheme will be gradually improved as the upper bound of performance is monotonically decreasing on-line. Both off-line robust control synthesis and on-line RHC computation are formulated and solved using linear matrix inequality optimisation techniques.}, number={5}, journal={IET Control Theory & Applications}, publisher={Institution of Engineering and Technology (IET)}, author={Wu, F. and Chen, Y.}, year={2007}, month={Sep}, pages={1423–1430} }
 @article{wu_dong_2006, title={Gain-scheduling control of LFT systems using parameter-dependent Lyapunov functions}, volume={42}, ISSN={["1873-2836"]}, DOI={10.1016/j.automatica.2005.08.020}, abstractNote={In this paper, we propose a new control design approach for linear fractional transformation (LFT) systems using parameter-dependent Lyapunov functions. Instead of assuming parameter dependency in LFT fashion, we consider general parameter-dependent controllers to achieve better closed-loop performance. Using full-block multipliers, new LPV synthesis conditions have been derived in terms of finite number of linear matrix inequalities (LMIs). Both continuous- and discrete-time cases are discussed. A ship steering example has been used to demonstrate advantages and benefits of the proposed approach.}, number={1}, journal={AUTOMATICA}, author={Wu, F and Dong, K}, year={2006}, month={Jan}, pages={39–50} }
 @article{lu_wu_2006, title={Probabilistic robust linear parameter-varying control of an F-16 aircraft}, volume={29}, ISSN={["1533-3884"]}, DOI={10.2514/1.22495}, abstractNote={O PERATIONAL capability at high angles of attack, especially near and at post stall regimes, is critical for next generation fighter aircrafts and uninhabited aerial vehicles [1]. However, significantly large levels of modeling uncertainty are inevitably encountered inflight control design for those regimes. The sources of uncertainty include variations in mass, inertia, and center of gravity positions, uncertainty in the aerodynamic data, etc. [2]. The maneuverability at high angles of attack poses a challenging control problem that requires guaranteeing both robust stability and robust performance in the presence of large parameter variations. Traditional robust control techniques, like H1 and -synthesis, have been proven to be capable of producing robust uncertaintytolerant controllers for next generation aircrafts [2,3]. However, those techniques focus on deterministic worst-case robust analysis and synthesis, which often lead to overly conservative stability bound estimate and high control effort. Moreover, a large number of conventional deterministic problems in robustness analysis and synthesis are shown to be NP-hard. To reduce conservatism and computational complexity, one approach is to shift the meaning of robustness from its usual deterministic sense to a probabilistic one [4]. In contrast to traditional robust control techniques, only a probabilistic solution is given, and a certain risk-level should be accepted. However, such a system may be viewed as being practically robust from an engineering point of view. Algorithms derived in the probabilistic context are based on uncertainty randomization and usually called randomized algorithms, which may be divided into two families: methods based on statistical learning theory [5], and sequential methods based on subgradient iterations [6–8] or ellipsoid iterations [9,10]. The former can deal with nonconvex synthesis problems; however, it resorts to randomized search over the controller parameters to find a candidate solution. On the other hand, the sequential methods are formulated based on convex problems, thus avoiding the controller randomization issue [4]. The probabilistic robust control approach is still in the stage of algorithm development and improvement, and has not been explored in depth for flight control. The number of implementation of probabilistic techniques is therefore rather restricted. In the late 90s, Marrison and Stengel designed a linear quadratic regulator to control the nonlinear longitudinal dynamics of a hypersonic aircraft [11]. Recently, Wang and Stengel designed a robust flight control system for the high-incidence research model problem by combining stochastic robustness with nonlinear dynamic inversion [12]. Their work was based on statistical learning theory, and controllers were searched by using generic algorithms to minimize stochastic robustness cost functions. In our earlier paper, we applied an ellipsoid algorithm to design anH1 controller for a linearized F-16 longitudinal model [13]. Good stability and performance robustness have been achieved at the chosen flight condition. The motivation for this research is twofold. First, the probabilistic control design method for linear time-invariant plants in [13] is generalized to linear parameter-varying (LPV) systems. This generalization is very important because of the relevance of LPV systems to nonlinear systems. TheLPVcontrol synthesis condition is known to be formulated as a convex problemwith a set of parameterdependent linear matrix inequalities (LMIs) [14–16]. Second, the current state of the art does not allow accurate aerodynamicmodeling in the high angle of attack region. Because of its random nature, uncertainty in the aerodynamic data can be characterized using a statistical model, which can be handled effectively by the promising probabilistic robust control approach. Note that the study in this note focuses on the robustness issue with respect to the aerodynamic uncertainty at high angles of attack, and the results would be easily generalized to other parametric uncertainties, such as variations in mass and inertial properties. Because of the convex formulation of LPV control synthesis, the sequential method is more suitable for dealing with uncertainties and designing probabilistic robust LPV controllers. An ellipsoid algorithm with a stopping rule proposed by Oishi [10] is used to determine feasible solutions to LMI synthesis conditions. The paper is organized as follows. In Sec. II, the ellipsoid algorithm is presented, which either gives a probabilistic solution with high confidence or detects that there is no deterministic solution in an approximated sense. Section III first provides a brief overview of robust control problem of an uncertain LPV system, and then discusses the computational issues when the algorithm is applied to the robust LPV control problem. In Sec. IV, a robust LPV controller is designed for an F-16 aircraft with large aerodynamic uncertainty, and the robust performance is tested through nonlinear simulations. Finally, the paper concludes with a summary in Sec. V.}, number={6}, journal={JOURNAL OF GUIDANCE CONTROL AND DYNAMICS}, author={Lu, Bei and Wu, Fen}, year={2006}, pages={1454–1460} }
 @article{wu_yildizoglu_2005, title={Distributed parameter-dependent modeling and control of flexible structures}, volume={127}, ISSN={["1528-9028"]}, DOI={10.1115/1.1898240}, abstractNote={In this paper, distributed parameter-dependent modeling and control approaches are proposed for flexible structures. The distributed model is motivated from distributed control design, which is advantageous in reducing control implementation cost and increasing control system reliability. This modeling approach mainly relies on a central finite difference scheme to capture the distributed nature of the flexible system. Based on the proposed distributed model, a sufficient synthesis condition for the design of a distributed output-feedback controller is presented using induced L2 norm as the performance criterion. The controller synthesis condition is formulated as linear matrix inequalities, which are convex optimization problems and can be solved efficiently using interior-point algorithms. The distributed controller inherits the same structure as the plant, which results in a localized control architecture and a simple implementation scheme. These modeling and control approaches are demonstrated on a non-uniform cantilever beam problem through simulation studies.}, number={2}, journal={JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME}, author={Wu, F and Yildizoglu, SE}, year={2005}, month={Jun}, pages={230–239} }
 @article{lu_wu_kim_2005, title={Linear parameter-varying antiwindup compensation for enhanced flight control performance}, volume={28}, ISSN={["1533-3884"]}, DOI={10.2514/1.4952}, abstractNote={Actuator saturation is one of the major issues of flight control in the high angle-of-attack region. This paper presents a saturation control scheme for linear parameter varyjing (LPV) systems from an antiwindup control perspective. The proposed control approach is advantageous from the implementation standpoint because it can be thought of as an augmented control algorithm to the existing control system. Moreover, the synthesis condition for an antiwindup compensator is formulated as a linear matrix inequality (LMI) optimization problem and can be solved efficiently. We have applied te LPV antiwindup controller to an F-16 longitudinal autopilot control system design and compared it with the thrust vectoring control scheme. The nonlinear simulations show that an LPV antiwindup controller improves flight quality and offers advantages over thrust vectoring in a high angle-of-attack region.}, number={3}, journal={JOURNAL OF GUIDANCE CONTROL AND DYNAMICS}, author={Lu, B and Wu, F and Kim, SW}, year={2005}, pages={494–505} }
 @article{wu_prajna_2005, title={SOS-based solution approach to polynomial LPV system analysis and synthesis problems}, volume={78}, DOI={10.1080/002071270500114865}, number={8}, journal={International Journal of Control}, author={Wu, F. and Prajna, S.}, year={2005}, pages={600–611} }
 @article{wu_prajna_2005, title={SOS-based solution approach to polynomial LPV system analysis and synthesis problems}, volume={78}, ISSN={["1366-5820"]}, DOI={10.1080/00207170500114865}, abstractNote={Based on sum-of-squares (SOS) decomposition, we propose a new solution approach for polynomial linear parameter-varying (LPV) system analysis and control synthesis problems. Instead of solving matrix variables over positive cone, the SOS approach tries to find a suitable decomposition to verify the positiveness of given polynomials. The complexity of the SOS-based numerical method is polynomial of the problem size, and is computationally attractive. This approach also leads to more accurate solutions to LPV systems than most existing relaxation methods. Several examples have been used to demonstrate benefits of the SOS-based solution approach.}, number={8}, journal={INTERNATIONAL JOURNAL OF CONTROL}, author={Wu, F and Prajna, S}, year={2005}, month={May}, pages={600–611} }
 @article{wu_lu_2004, title={Anti-windup control design for exponentially unstable LTI systems with actuator saturation}, volume={52}, ISSN={["1872-7956"]}, DOI={10.1016/j.sysconle.2004.02.007}, abstractNote={In this paper, a new saturation control technique in the framework of anti-windup compensation is developed for exponentially unstable linear time-invariant systems subject to input nonlinearities. The proposed control algorithm guarantees regional stability in the existence of input saturation, and provides less conservative performance than most existing anti-windup schemes. Moreover, an explicit form of anti-windup controller with its order no more than the order of the plant is derived. An inverted pendulum example is used to demonstrate the advantages of the newly proposed anti-windup control technique.}, number={3-4}, journal={SYSTEMS & CONTROL LETTERS}, author={Wu, F and Lu, B}, year={2004}, month={Jul}, pages={305–322} }
 @article{wu_soto_2004, title={Extended anti-windup control schemes for LTI and LFT systems with actuator saturations}, volume={14}, ISSN={1049-8923 1099-1239}, url={http://dx.doi.org/10.1002/rnc.943}, DOI={10.1002/rnc.943}, abstractNote={Abstract}, number={15}, journal={International Journal of Robust and Nonlinear Control}, publisher={Wiley}, author={Wu, Fen and Soto, Marco}, year={2004}, month={Oct}, pages={1255–1281} }
 @article{wu_bei_2004, title={On convexified robust control synthesis}, volume={40}, ISSN={["1873-2836"]}, DOI={10.1016/j.automatica.2004.01.010}, abstractNote={In this paper, we study a convexified robust control problem and its relation to gain-scheduling control. It reveals that the robust control synthesis condition becomes convex under a special plant structure. Moreover, for this class of robust control problems, the gain-scheduling control approach from scaled small-gain theorem will not provide any performance improvement over convexified robust controllers. Based on this observation, a convexified robust control synthesis framework with stringent performance and computational efficacy is proposed.}, number={6}, journal={AUTOMATICA}, author={Wu, F and Bei, L}, year={2004}, month={Jun}, pages={1003–1010} }
 @article{lu_wu_2004, title={Switching LPV control designs using multiple parameter-dependent Lyapunov functions}, volume={40}, ISSN={0005-1098}, url={http://dx.doi.org/10.1016/j.automatica.2004.06.011}, DOI={10.1016/j.automatica.2004.06.011}, abstractNote={In this paper we study the switching control of linear parameter-varying (LPV) systems using multiple parameter-dependent Lyapunov functions to improve performance and enhance control design flexibility. A family of LPV controllers is designed, each suitable for a specific parameter subregion. They are switched so that the closed-loop system remains stable and its performance is optimized. Two switching logics, hysteresis switching and switching with average dwell time, are examined. The control synthesis conditions for both switching logics are formulated as matrix optimization problems, which are generally non-convex but can be convexified under some simplifying assumptions. The hysteresis switching LPV control scheme is then applied to an active magnetic bearing problem.}, number={11}, journal={Automatica}, publisher={Elsevier BV}, author={Lu, Bei and Wu, Fen}, year={2004}, month={Nov}, pages={1973–1980} }
 @article{wu_jaramillo_2003, title={Computationally efficient algorithm for frequency-weighted optimal H-infinity model reduction}, volume={5}, DOI={10.1111/j.1934-6093.2003.tb00126.x}, abstractNote={ABSTRACT}, number={3}, journal={Asian Journal of Control}, author={Wu, F. and Jaramillo, J. J.}, year={2003}, pages={341–349} }
 @article{wu_2003, title={Distributed control for interconnected linear parameter dependent systems}, volume={150}, ISSN={["1350-2379"]}, DOI={10.1049/ip-cta:20030706}, abstractNote={Stability analysis and performance control problems for a class of interconnected parameter-dependent systems with linear fractional parameter dependency are considered. The time and spatially varying parameters are assumed measurable in real-time for controller use. The distributed controller inherits the spatial structure of the plant, which is implementable through parallel computation. The stability of the interconnected parameter-dependent systems is established using a distributed Lyapunov function. Moreover, the synthesis condition of distributed parameter-dependent control gain is formulated as a convex optimisation in the form of a linear matrix inequality. An explicit distributed controller formula is also provided by exploiting the connection between the continuous and the discrete interconnected system descriptions.}, number={5}, journal={IEE PROCEEDINGS-CONTROL THEORY AND APPLICATIONS}, author={Wu, F}, year={2003}, month={Sep}, pages={518–527} }
 @article{tan_grigoriadis_wu_2003, title={H(infinity) and L(2)-to-L(infinity) gain control of linear parameter-varying systems with parameter-varying delays}, volume={150}, ISSN={["1350-2379"]}, DOI={10.1049/ip-cta:20030708}, abstractNote={The analysis and state-feedback synthesis problems for linear parameter-varying systems with parameter-varying time delays are addressed. It is assumed that the state-space data and the time delays are dependent on parameters that are measurable in real-time and vary in a compact set with bounded variation rates. We explore the stability, L2 gain performance and L2 - to- L∞ gain performance for these systems using parameter-dependent Lyapunov functionals. In addition, the design of parameter-dependent state-feedback controllers that guarantee stability and desired induced norm performance are examined. Both analysis and synthesis conditions are formulated in terms of linear matrix inequalities that can be solved via efficient interior-point algorithms.}, number={5}, journal={IEE PROCEEDINGS-CONTROL THEORY AND APPLICATIONS}, author={Tan, K and Grigoriadis, KM and Wu, F}, year={2003}, month={Sep}, pages={509–517} }
 @article{wu_2003, title={Robust quadratic performance for time-delayed uncertain linear systems}, volume={13}, ISSN={["1099-1239"]}, DOI={10.1002/rnc.720}, abstractNote={Abstract}, number={2}, journal={INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL}, author={Wu, F}, year={2003}, month={Feb}, pages={153–172} }
 @article{tan_grigoriadis_wu_2002, title={Output-feedback control of LPV sampled-data systems}, volume={75}, ISSN={["0020-7179"]}, DOI={10.1080/00207170110101775}, abstractNote={In this paper, we address the analysis and the output-feedback synthesis problems for linear parameter-varying (LPV) sampled-data control systems with potentially variable sampling rates. We assume that the state-space matrices of the plant and the sampling interval depend on parameters that are measurable in real-time and vary in a compact set with bounded variation rates. We explore criteria such as the stability, the energy-to-energy gain (induced L 2 norm) and the energy-to-peak gain (induced L 2 -to- L X norm) of such sampled-data LPV systems using parameter-dependent Lyapunov functions. Based on these analysis results, the corresponding sampled-data output-feedback control synthesis problems are examined. Both analysis and synthesis conditions are formulated in terms of linear matrix inequalities (LMIs) that can be solved via efficient interior-point algorithms.}, number={4}, journal={INTERNATIONAL JOURNAL OF CONTROL}, author={Tan, K and Grigoriadis, KM and Wu, F}, year={2002}, month={Mar}, pages={252–264} }
 @article{wu_2001, title={A generalized LPV system analysis and control synthesis framework}, volume={74}, ISSN={["1366-5820"]}, DOI={10.1080/00207170010031495}, abstractNote={In this paper, a new approach for linear parameter-varying (LPV) system analysis and control synthesis is proposed. This unified framework combines two seemingly diversified methods in systematic gain-scheduling, LPV control theory, and extends the applicability of full block S -procedure to a general class of LPV systems. An example is used to demonstrate the proposed general LPV design approach, and to show its relative merits compared to other systematic gain-scheduling control techniques.}, number={7}, journal={INTERNATIONAL JOURNAL OF CONTROL}, author={Wu, F}, year={2001}, month={May}, pages={745–759} }
 @article{wu_2001, title={LMI-based robust model predictive control and its application to an industrial CSTR problem}, volume={11}, ISSN={["0959-1524"]}, DOI={10.1016/S0959-1524(00)00052-4}, abstractNote={In this paper, robust model predictive control (MPC) is studied for a class of uncertain linear systems with structured time-varying uncertainties. This general class of uncertain systems is useful for nonlinear plant modeling in many circumstances. The controller design is characterizing as an optimization problem of the “worst-case” objective function over infinite moving horizon, subject to input and output constraints. A sufficient state-feedback synthesis condition is provided in the form of linear matrix inequality (LMI) optimizations, and will be solved on-line. The stability of such a control scheme is determined by the feasibility of the optimization problem. To demonstrate its usefulness, this robust MPC technique is applied to an industrial continuous stirred tank reactor (CSTR) problem with explicit input and output constraints. Its relative merits to conventional MPC approaches are also discussed.}, number={6}, journal={JOURNAL OF PROCESS CONTROL}, author={Wu, F}, year={2001}, month={Dec}, pages={649–659} }
 @article{wu_grigoriadis_2001, title={LPV Systems with parameter-varying time delays: analysis and control}, volume={37}, ISSN={["1873-2836"]}, DOI={10.1016/S0005-1098(00)00156-4}, abstractNote={In this paper, we address the analysis and state-feedback synthesis problems for linear parameter-varying (LPV) systems with parameter-varying time delays. It is assumed that the state-space data and the time delays are dependent on parameters that are measurable in real-time and vary in a compact set with bounded variation rates. We explore the stability and the induced L2 norm performance of these systems using parameter-dependent Lyapunov functionals. In addition, the design of parameter-dependent state-feedback controllers that guarantee desired L2 gain performance is examined. Both analysis and synthesis conditions are formulated in terms of linear matrix inequalities (LMIs) that can be solved via efficient interior-point algorithms.}, number={2}, journal={AUTOMATICA}, author={Wu, F and Grigoriadis, KM}, year={2001}, month={Feb}, pages={221–229} }
 @article{wu_grigoriadis_packard_2000, title={Anti-windup controller design using linear parameter-varying control methods}, volume={73}, ISSN={["1366-5820"]}, DOI={10.1080/002071700414211}, abstractNote={In this paper, we seek to provide a systematic anti-windup control synthesis approach for systems with actuator saturation within a linear parameter-varying (LPV) design framework. The closed-loop induced L2 gain control problem is considered. Different from conventional two-step anti-windup design approaches, the proposed scheme directly utilizes saturation indicator parameters to schedule accordingly the parameter-varying controller. Hence, the synthesis conditions are formulated in terms of linear matrix inequalities (LMIs) that can be solved very efficiently. The resulting gain-scheduled controller is non-linear in general and would lead to graceful performance degradation in the presence of actuator saturation non-linearities and linear performance recovery. An aircraft longitudinal dynamics control problem with two input saturation non-linearities is used to demonstrate the effectiveness of the proposed LPV anti-windup scheme.}, number={12}, journal={INTERNATIONAL JOURNAL OF CONTROL}, author={Wu, F and Grigoriadis, KM and Packard, A}, year={2000}, month={Aug}, pages={1104–1114} }