Research On Sliding Mode Theory And Its Application In DTC Systems

Variable structure control with sliding mode is a kind of nonlinear control method, which is used quite widely now as its sliding mode is of global robustness against parameter variations and external disturbance, but this characteristic can't obtained when the system is out of the sliding mode. So in the reaching mode step, it is lack of robustness for the system is controlled only by feedback control, as a result, the robustness of sliding mode control is influenced strongly.A new fuzzy time-varying sliding mode control method for a class of nonlinear systems with uncertainties is presented. It combines the advantages of fuzzy control and sliding mode control, as a result, the system is of global robustness against parameter variations and external disturbance as the state lies on the sliding surface from any arbitrary initial states, and the performance is much better improved. Computer simulation results show it is correct and efficient.Direct torque control (DTC) system for induction motor has got wide attention with the advantages such as its new thoughts, simple control scheme and excellent performance. In this thesis the author made a study of asynchronous motor model, designed a hybrid simulation system of DTC and analyzed the characteristics of the DTC system and the existing problems detailedly.The DTC system is a high-performance AC driving system. But conventional speed controller in DTC system is PI adjuster, which can't make the system have enough quick response, the ability to restrict the noise and strong robustness to the parameters of the system. So the author designed a speed regulator based on sliding-mode control theory, which make the system has strong robustness to the parameters, excellent dynamic and steady-state performance. Simulation results show the method is effective.