Research On High-precision Rotor Speed Detection Method Of Motor Digital Control System

Permanent magnet synchronous motor(PMSM)is widely used in aerospace flight,electric vehicle,navigation system,ship electric propulsion and other fields because of its characteristics of low rotational inertia,high energy density,fast response speed and simple overall structure.The key step to achieve high-performance closed-loop vector control of permanent magnet synchronous motors is high-precision rotor speed detection.Fast(less phase shift),quasi(less attenuation),stable(less interference)are the targets of speed sampling.In general,the differential method of the output position signal of the photoelectric encoder is used to detect the speed of the motor,and the speed measurement accuracy will be limited by the quantization error of the grating disk;and the measured value is the average value of the speed in a sampling period rather than the instantaneous value at a certain time,so as to produce a lag link,so that the accuracy of the speed sampling is not very ideal.This paper focuses on improving the above two kinds of errors,and designs a high-precision speed detection method.Firstly,starting from the vector control model of permanent magnet synchronous motor,this paper expounds the related concepts,working process and three basic speed measurement methods of photoelectric encoder signal,namely frequency measurement method,period measurement method,applicable speed range of M/T method,error discussion,etc.Secondly,based on the analysis of common speed detection methods,aiming at the problem that the rising edge of the pulse signal generated by the photoelectric encoder in the control system cannot be strictly synchronized with the beginning or the end of the detection cycle,a speed observer with an unfixed detection cycle is designed to realize the synchronization of the detection cycle and the square wave pulse signal of the encoder,so as to reduce the quantization error.Then,in view of the inherent defect of the detection delay in the mean speed of PMSM running at low speed by means of the encoder pulse counting,a speed observer is designed based on the principle of Kalman filter in the environment of wide speed range and high noise,which can eliminate the detection delay and obtain high speed feedback accuracy.Finally,in order to solve the problem of large calculation and difficult parameter debugging of the full order Kalman filter speed observer,a reduced order speed observer based on the load torque observation is proposed to ensure the sampling effect of the instantaneous speed and reduce the running time of the system.In order to verify the accuracy and tracking performance of several speed detection algorithms,the above algorithms are applied to the Simulink simulation model of PMSM vector control system with incremental code disk,and the simulation results show the implementability and effectiveness of the high-performance speed detection method designed in this paper.