Research On Position Sensorless Control System Of PMSM Based On Improved High Frequency Square Wave Injection Method

Permanent magnet synchronous motors(PMSM)are widely used in industrial fields due to their high efficiency,high power density and small size.In a closed-loop system,the use of encoder leads to the decrease of system reliability and the increase of cost,so canceling the encoder become necessary.Recently the sensorless control strategy has become a research hotspot.High-frequency injection is an effective method to obtain position information at low speed.However,in the traditional high-frequency injection method,the use of the filter in the position sensorless part and the current feedback link limits the system bandwidth,which affects the dynamic performance and cannot adapt to some high-performance occasions.Therefore,some new high-frequency signal injection methods have been proposed in recent years.In this paper,the research on the vector control system of permanent magnet synchronous motor with high frequency square wave voltage injection method is studied.The two aspects of vector control system and high frequency injection method are studied respectively,and the existing problems are analyzed.The corresponding improvement measures are proposed.Turning to the high-frequency square wave injection method which increases the injection frequency to the switching frequency,the bandwidth frequency can be increased.However,the existing highfrequency square wave injection method still retains the filter in the position sensorless portion and the current feedback portion.Aiming at the existence of speed-dependent cross-coupling of current loop in the vector control system of PMSM,traditional PI controller can’t follow the speed to achieve decoupling,which leads to system performance degradation.Using complex vector analysis,a complex vector PI controller is designed.The system can be completely decoupled in the current loop to improve system performance.The research analyzes the traditional high-frequency sinusoidal signal injection method including the position information identification principle and the position observer design.Then the bandwidth on the pulse high-frequency injection method is analysed.The use of filters in the position sensorless section and the current feedback section greatly reduces the bandwidth frequency of the system and reduces the dynamic performance of the system.Corresponding improvements are proposed here,including improved fundamental current and high-frequency response current extraction,improved position and velocity observers,and initial position detection of high-frequency square wave injection.For the high-frequency injection method and improvement measures and initial position detection described above,a simulation model is built in the PLECS software for simulation analysis.In this paper,the surface-mount permanent magnet synchronous motor(SPMSM)is taken as the research object,and the experimental platform for the vector control system of PMSM with improved high-frequency square wave injection method is built.The results show that the improved high-frequency square wave voltage injection method can estimate the rotor position and speed in the low speed/zero speed range,and has good dynamic performance.The system bandwidth is obviously superior to the traditional high-frequency sinusoidal voltage injection method.