Research On Speed Identification Of PMSM

With the improvement of power electronics technology, the performance of servo control system of Permanent Magnet Synchronous Motor(PMSM) is improving greatly, and PMSM is widely used in many industrial fields. The conventional speed identification for PMSM is through rotary optical encoder, but this speed-identification method has large error at low speed, which will seriously affect the performance of the servo control system. People demand accuracy of speed feedback increasingly. The velocity identified through position difference directly or through the low-pass filter by optical encoder cannot satisfy the requirements of accuracy of speed.In view of this, many international scholars has put forward speed observer to observe speed. Speed observer with high accuracy, high reliability, timeliness and other advantages can satisfy the requirements of speed-tracking basically. But because the algorithm is complex, which limits its application in engineering. In recent years, the rapid development of computer technology and fast growing of mathematical signal processor for processing data capacity have provided possibility of application of speed observer. Currently, speed observer has been applied well in many fields. The development of speed observer theory will greatly improve the overall performance of AC servo system.This article introduces speed identification methods in recent years, and analyze their strengths and weaknesses. And then the structure,the mathematical model,the controlling principle and sensor technology of PMSM are all studied. The weakness of speed identification directly through optical encoder feedback data directly is analyzed. For this shortcoming, the Luenberger speed observer and Kalman filter are put forward, then analysis and study of the two speed observers are done.`And then model-constructed and simulation analysis of above two speed observers through Matlab are done. It is found that Luenberger speed observer and Kalman filter can track the real condition well, have good dynamic performance and improve the controlling accuracy of the system.Finally, based on the simulations, some experiments are done at high and low speed on the hardware platform of PMSM servo drive system about comparison of the velocityidentified through position difference after the low-pass filter, Luenberger speed observer and Kalman filter. According to experiments, When the motor is running at high speed, it is can be found that Luenberger speed observer has short rising time,small overshoot and improve disturbance response and signal response performance of control system; when the motor is running at low speed, Luenberger speed observer still can track the speed with smaller error rate. Under the same conditions, the Kalman filter has higher precision, and can track well at lower speed.