Investigation Of Variable Structure Control Of Sliding Mode For Discrete Time Systems

Variable structure control (VSC) is well known for its robustness to system parameter variations and external disturbances.VSC has been widely used in many applications.In recent years,with the development of microcomputer technology and the needs of industrial automation,we use computer to realize the control algor- ithm.But during the time of realizing the VSC,because of the limits of sampling, the ideal sliding mode does not exist,and the switching control is not smooth any more,it is only a quasi-sliding mode.It is significant to study discrete-time VSC (DVSC) to reduce chattering of sliding mode.Firstly,in this dissertation,a detailed analysis of the history and current situation of study on variable structure and a discussion about the discrete-time systems VSC are stressed.Secondly,the related definitions of DVSC are proposed. After analyzing the arrival condition,the existence condition and stabilization of sliding mode in DVSC.It is discussed that the design of variable structure control for discrete time system using discrete reaching law.Based on the he attenuating variable rate and the attenuating power reaching law,two improved discrete reaching law are developed. Using global sliding mode variable structure control theory,a global sliding mode variable structure controller based on the attenuating power reaching law is developed.It used the advantage for robustness of the sliding mode. The simulation results show that the approach is effective.Finally,A discrete-time variable structure controller with a decoupled disturbance compensator its application to a CNC servomechanism is designed.And another kind of controller is designed by applying delay characteristic to estimate the uncertainty on-line.Both theory analysis and simulation can prove the validity of these methods.