Research On Control Method Of Permanent Magnet Motor Under Low Switching Frequency

Permanent Magnet Synchronous Motor (PMSM) has the advantages of simple structure, high efficiency and has great potential application in rail transit. In this paper flux weakening control of negative direct axis current compensation method are analyzed.That high power traction driving system requires low switch frequency, exacerbates current coupling problem of vector control and long switch cycle makes digital control inherent delay problem become more prominent, affect the control performance of the motor.In this paper, the current coupling and digital delay problems are analyzed theoretically. According to the complex vector and the system transfer function, the decoupling control methods of feed-forward decoupling, feedback decoupling, modified double PI decoupling, and the time delay compensation methods of optimal control based on the q axis current error and so on are proposed. Through the zero pole distribution figure and the bode plot drawn by the system transfer function of closed loop the above optimization methods are comparative analyzed. Compared to feed-forward decoupling and feedback decoupling, the modified double PI decoupling has better robustness to motor parameters, and the decoupling effect is better; Compared with direct angle compensation, time delay compensation method based on the q axis current error has more excellent dynamic performance and responses faster. A PMSM control optimization method combined decoupling control with delay compensation under lower switching frequency is put forward.Setting up a simulation model of PMSM drive system in MATLAB/Simulink and one7.5kW traction PMSM drive system experimental platform based on DSP28335, the accuracy and feasibility of optimization control method was verified by carrying on the analysis of flux-weakening control, decoupling control method and time delay compensation method.