@article{nabavi_chakrabortty_2017, title={Structured Identification of Reduced-Order Models of Power Systems in a Differential-Algebraic Form}, volume={32}, ISSN={0885-8950 1558-0679}, url={http://dx.doi.org/10.1109/tpwrs.2016.2554154}, DOI={10.1109/tpwrs.2016.2554154}, abstractNote={In a recent paper, we proposed a system identification method for constructing reduced-order models for the electro-mechanical dynamics of large power systems, divided into multiple coherent clusters, using Synchrophasors. Every cluster in the actual model was represented as an aggregate generator in the reduced-order model. An aggregate network graph connected one aggregate generator to another. In this paper, we extend this identification approach to differential-algebraic (DAE) models. First, every cluster is associated with a unique terminal bus, referred to as the pilot bus, that couples its internal network to the rest of the system. The proposed algorithm uses Synchrophasor measurements from the pilot buses to identify the dynamic model of the aggregate generator for each cluster using nonlinear least squares while retaining the identity of all the pilot buses. The resulting reduced-order model is in the form of a nonlinear electric circuit described by aggregate differential and algebraic equations. We illustrate our results using two case studies, one for the IEEE 9-bus power system and another for the IEEE 39-bus power system. We also discuss how these reduced-order DAE models may be useful for designing shunt controllers at the pilot buses by using Synchrophasor feedback.}, number={1}, journal={IEEE Transactions on Power Systems}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Nabavi, Seyedbehzad and Chakrabortty, Aranya}, year={2017}, month={Jan}, pages={198–207} }
 @article{jenkins_chapman_bryant_2016, title={Bio-inspired online variable recruitment control of fluidic artificial muscles}, volume={25}, ISSN={["1361-665X"]}, DOI={10.1088/0964-1726/25/12/125016}, abstractNote={This paper details the creation of a hybrid variable recruitment control scheme for fluidic artificial muscle (FAM) actuators with an emphasis on maximizing system efficiency and switching control performance. Variable recruitment is the process of altering a system’s active number of actuators, allowing operation in distinct force regimes. Previously, FAM variable recruitment was only quantified with offline, manual valve switching; this study addresses the creation and characterization of novel, on-line FAM switching control algorithms. The bio-inspired algorithms are implemented in conjunction with a PID and model-based controller, and applied to a simulated plant model. Variable recruitment transition effects and chatter rejection are explored via a sensitivity analysis, allowing a system designer to weigh tradeoffs in actuator modeling, algorithm choice, and necessary hardware. Variable recruitment is further developed through simulation of a robotic arm tracking a variety of spline position inputs, requiring several levels of actuator recruitment. Switching controller performance is quantified and compared with baseline systems lacking variable recruitment. The work extends current variable recruitment knowledge by creating novel online variable recruitment control schemes, and exploring how online actuator recruitment affects system efficiency and control performance. Key topics associated with implementing a variable recruitment scheme, including the effects of modeling inaccuracies, hardware considerations, and switching transition concerns are also addressed.}, number={12}, journal={SMART MATERIALS AND STRUCTURES}, author={Jenkins, Tyler E. and Chapman, Edward M. and Bryant, Matthew}, year={2016}, month={Dec} }
 @article{jenkins_chapman_bryant_2016, title={Control approach development for variable recruitment artificial muscles}, volume={9799}, ISSN={["1996-756X"]}, DOI={10.1117/12.2222201}, abstractNote={This study characterizes hybrid control approaches for the variable recruitment of fluidic artificial muscles with double acting (antagonistic) actuation. Fluidic artificial muscle actuators have been explored by researchers due to their natural compliance, high force-to-weight ratio, and low cost of fabrication. Previous studies have attempted to improve system efficiency of the actuators through variable recruitment, i.e. using discrete changes in the number of active actuators. While current variable recruitment research utilizes manual valve switching, this paper details the current development of an online variable recruitment control scheme. By continuously controlling applied pressure and discretely controlling the number of active actuators, operation in the lowest possible recruitment state is ensured and working fluid consumption is minimized. Results provide insight into switching control scheme effects on working fluids, fabrication material choices, actuator modeling, and controller development decisions.}, journal={ACTIVE AND PASSIVE SMART STRUCTURES AND INTEGRATED SYSTEMS 2016}, author={Jenkins, Tyler E. and Chapman, Edward M. and Bryant, Matthew}, year={2016} }
 @inproceedings{chapman_macleod_bryant_2016, title={Electrohydraulic modeling of a fluidic artificial muscle actuation system for robot locomotion}, DOI={10.1115/smasis2015-8834}, abstractNote={Fluidic artificial muscles have the potential for a wide range of uses; from injury rehabilitation to high-powered hydraulic systems. Their modeling to date has largely been quasi-static and relied on the operator to adjust pressure so as to control force output and utilization while little work has been done to date to analyze the kinematics of the driving-systems involved in their operation. This paper establishes a combined electro-hydraulic model of a fluidic artificial muscle actuated climbing robot to establish a method for studying the relationships between muscle size, robot size and function, and system design. The study indicates a strong relationship between appropriate system component selection and not only system efficiency but individual component effectiveness. The results of the study show that robot mass, operating pressure, muscle size, and motor-pump selection have noteworthy impacts on the efficiency and thereby longevity of the robot for performing its task.}, booktitle={ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, 2015, vol 1}, author={Chapman, E. and Macleod, M. and Bryant, M.}, year={2016} }
 @inproceedings{chapman_jenkins_bryant_2016, title={Parametric study of a fluidic artificial muscle actuated electrohydraulic system}, DOI={10.1115/smasis2016-9044}, abstractNote={Fluidic artificial muscles have the potential for a wide range of uses; from injury rehabilitation to high-powered hydraulic systems. Their modeling to date has largely been quasi-static and relied on the operator to adjust pressure so as to control force output and utilization while little work has been done to analyze the kinematics of the driving-systems involved in their operation. This paper utilizes an established electro-hydraulic model to perform a study of the components of a fluidic artificial muscle actuated climbing robot. Its purpose is to determine the effect of the robotic subsystems on function and efficiency for a small-scale system in order to extrapolate more general design and analysis schemes for future use. Its results indicate that important aspects to consider in design of the hydraulic system are system payload, operating pressure, pump selection, and FAM construction.}, booktitle={Proceedings of the asme conference on smart materials adaptive}, author={Chapman, E. and Jenkins, T. and Bryant, M.}, year={2016} }