This paper presents an observer-based nonlinear control method that was developed and implemented to provide accurate tracking control of a limited angle torque motor following a 50Hz reference waveform. The method is based on a robust nonlinear observer, which is used to estimate system states and perturbations and then employ input-output feedback linearization to compensate for the system nonlinearities and uncertainties. The estimation of system states and perturbations allows input-output linearization of the nonlinear system without an accurate mathematical model of nominal plant. The simulation results show that the observer-based nonlinear control method is superior in comparison with the conventional model-based state feedback linearizing controller.

Authors and Affiliations

1. Department of Electrical Engineering and Electronics, The University of Liverpool, Liverpool, L69 3GJ, UK

   J. Chen, E. Prempain & Q. H. Wu

Corresponding author

Correspondence toQ. H. Wu.

Jian-Chi Chen received his B.Sc. degree in Electrical and Electronic Engineering from Wuhan University, China, in 2001. He is currently an M.Phil. research student in Department of Electrical Engineering and Electronics, The University of Liverpool. His research interests include nonlinear control, robust control and their applications in electric power systems.

Emmanuel Prempain obtain a PhD from the University of Bordeaux in November 1995. After completing the PhD study, he worked in Bordeaux and worked for the Dynamics and Automatic Department of the French National Space Centre (CNES) of Toulouse, France on an Active Suspension System. In 1997, he joined the Control Group, the Department of Engineering at the University of Leicester, as a Postdoctoral Research Fellow working on Simultaneous Stabilisation and Static Output feedback Synthesis. In September 2002 he was appointed Lectureship in Control Engineering and joined the Intelligence Engineering and Automation Group, the Department of Electrical Engineering and Electronics, The University of Liverpool. His research interests include H-infinity and Robust Control Methods, Linear Matrix Inequalities (LMIs), Flight Control Systems (Helicopter Control, Missile Control) and Induction Machines Control.

Qing-Hua Wu obtained an M.Sc. (Eng) degree in Electrical Engineering from Huazhong University of Science and Technology (HUST), China, in 1981. From 1981 to 1984, he was appointed Lecturer in Electrical Engineering in the University. He obtained a Ph.D. degree from The Queen’s University of Belfast (QUB), U.K., in 1987. He worked as a Research Fellow and Senior Research Fellow in QUB from 1987 to 1991 and Lecturer and Senior Lecturer in the Department of Mathematical Sciences, Loughborough University, U.K. from 1991 to 1995. Since 1995 he has held the Chair of Electrical Engineering in the Department of Electrical Engineering and Electronics, The University of Liverpool, U.K., acting as the Head of Intelligence Engineering and Automation group. Professor Wu is a Chartered Engineer, Fellow of IEE and Senior Member of IEEE. His research interests include nonlinear adaptive control, mathematical morphology, neural networks, learning systems, pattern recognition, evolutionary computation and power system control and operation.

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