Application of discrete-time sliding mode control method to the servo systems

ABSTRACT PhD Thesis APPLICATION of DISCRETE-TIME SLIDING MODE CONTROL METHOD to THE SERVO SYSTEMS Mehmet İlyas BAYINDIR Firat University Graduate School of Natural and Applied Sciences Department of Electrical - Electronics Engineering 2003, Page: 101 In this thesis, a new position control method is developed for the electrical drive systems in order to provide a robust position control under inertial and frictional variations and external disturbances. The proposed control algorithm is based on the Reaching Law Control (RLC), which is an approach to the Sliding Mode Control (SMC) design, and the time-optimal (also known as 'minimum-time') control methods. SMC is a well known robust control method. On the other hand, it is also well known that the time-optimal control provides a theoretical perfect performance in position control systems. The analysis and design of the position control system is done in discrete-time since the practical implementation is realized using a microprocessor system. It is shown that the sampling effects should be taken in to account when the discrete-time implementation of the SMC is considered. It is also shown in the thesis that when the large position references are applied to the system and/or a high performance (high slope of the switching line) is desired, the discrete-time implementation of the SMC method results in undesirable overshoots especially under large inertial variations. Thus, a new control method having a time-varying sliding surface is proposed to avoid especially the undesired overshoots and to provide a robust control under large parameter variations and high position reference demands. The proposed method is applied to a vector controlled induction motor position control system. The experimental and simulation results showing the effectiveness of the developed control approach is presented in the thesis. Keywords: Sliding mode control, reaching law approach, position control, time-optimal control, minimum-time control. XV