| Discrete-time Variable Structure Control (DVSCs) systems with time-delay are studied in this dissertation. Since 1950s, VSC was increasingly applied into many industrial domains, such as motors and power systems, spacecrafts, robots, chemical engineering and so forth. In the present digital era, with the advance of microcomputer technology, the discrete-time variable structure control research on the sampled systems become a hot-spot. In the DVSCs the switching control is not ideal continuous and smooth any more, it is only a quasi-sliding mode. This is because of the chattering phenomena which caused by the limited sample frequency and time-delay. Delays make the performance of control systems worse, so it must be considered while the DVSCs are studied and the research on DVSCs with time-delay becomes meaningful and worthful.The well-known advantage of VSCs are good robustness and adaptivity in its sliding mode. On the sliding plane the system response are insensitive to parameter variations and external disturbances. But there exists oscillation near the sliding plane, this phenomenon of chattering is a major drawback of VSC, which restrict its further application. So it is always explored that how to eliminate or weaken the chattering.The main contents in this dissertation include:The present status, both the DVSC and VSC with time-delay are analyzed all round. The basic definitions and properties are proposed. After analyzing the causes of chattering, three improved strategies are developed, they are boundary layer decay strategy, switching function reduction strategy and intelligent control strategy. Using the proposed three strategies, the simulations are performed respectively. The results indicate they are feasible and effective. After the simulations, based on DSP a experiment platform is set up, on which a servo motor control system using variable structure control is realized.In the end, a conclusion is made and the future research are prospected.
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