Design And Study Of Disturbance Observer In AC Servo System

The disturbance and model uncertainties are inevitable in almost all the control systems. Disturbance is the main factor which influences the performance of the AC speed servo system. The target of this paper is that on the base of usual disturbance rejection measure of hardware and optimum design of control system, use disturbance observer together with digital low-pass filter in the vector-controlled AC speed servo system to reject the disturbances such as load variations, the model uncertainties, the friction and the measuring noise for the improvement of the disturbance suppression and robustness performance.Considering the low and the high frequency disturbance comprehensively, this paper proposed a disturbance-rejection method, which uses the disturbance observer to suppress the low frequency disturbance and the digital low-pass filter to suppress the high frequency disturbance. The paper discussed the method of speed detection in AC speed servo system, analyzed the measuring noise of speed detection and proposed the design principles and methods of the low-pass filter in speed loop. The paper also analyzed the dynamic model and the model simplification has made, especially got a further simplified model corresponding to the low frequency disturbance. The design principles and methods of the disturbance observer were discussed. The simulation and design of the whole system have been carried out by MATLAB/Simulink, and the control methods mentioned above have been applied to the DSP based 3-phase asynchronous motor direct-vector-controlled system.The simulation and the experiment have got a similar result: The system achieved good dynamic performance and control effect; the time to reject step disturbance is less than 100ms and the speed filter has improved the system performance. The disturbance rejection methods proposed in this paper can reject disturbance effectively and be easily applied to high-speed/high-accuracy systems, and better than the traditional PID controller for the periodic alterative disturbance.