@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{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{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} }