The Research Of Discrete Time System Variable Structure Control Method Based On Improved Reaching Law

The development of sliding mode variable structure control (SMVSC) for discrete -time system always focuses on how to weaken the chattering phenomenon or eliminate it. As a switch theory of SMVSC, the reaching law has been researched intensively in recent years for its advantage that the controller is easy to design. Control system designed by reaching law also has chattering. After GAO's exponential law, many other improved schemes have been proposed. All these schemes can achieve the purpose of weakening or eliminating chattering. However, researches indicate that most of them can't preserve the characteristic of invariable to disturbances and parameter variations while restrain the chattering. It's very meaningful to research a new strategy giving attention to the two problems.This work researches the reaching laws for discrete-time system, based on study of SMVSC for discrete-time system, the paper accomplish following work:①Analyses most of the existing reaching law schemes, points out that most of these schemes don't match the six characteristics of SMVSC of discrete-time system. Concludes the improvement points and gives an improved scheme based on GAO's reaching law. The new scheme adopts GAO's law in the reaching phase, and designs the sliding manifold attenuating negatively after entering the quasi-sliding mode band and makes the quasi-sliding mode band to be a sector to restrain chattering, Proves the improved reaching law is stable and robust. Meanwhile, the designed scheme solves the problem in GAO's law that the value ofεcan't meet faster reaching speed and less chattering amplitude in the same time.②Designs a brushless DC motor (BLDCM) speed control system with Matlab/Simulink.The control system includes two close-loops. As main controller, the speed regulator is designed according to the improved reaching law, and the vice controller is current regulator which uses PI controller. Detailed design is given in the paper. The designed system is compared with another one which main controller uses PID controller.③Designs a brushless DC motor (BLDCM) speed control system based on DSP (digital signals processor), including hardware and software design. The hardware system contains three subsystems: DSP minimum system, motor driver inverter and phase current detecting circuit. The software system is designed to measure rotating angle and speed and to generate control signals, the realization is given with flowcharts. The theoretic analysis and simulation experiment indicate that comparing with the traditional PID control system the control system designed by the proposed reaching law has better performance. Finally, this paper concludes the whole work and points out the problems to solve in future.