Study On Flux-weakening Control Technology Of Permanent Magnet Synchronous Motor Used In Electric Vehicles

Permanent magnet synchronous motor(PMSM)is widely used in the field of electric vehicle power drive because of its speed regulation ability in a wide speed range.But in fact,due to the dual constraints of the voltage and current capacity of the motor system,it is often necessary to use a certain flux-weakening method to achieve the drive in a wide speed range.Therefore,according to the requirement of wide speed range of electric vehicle,the flux-weakening control technology which can effectively widen the speed range of permanent magnet synchronous motor is studied.Firstly,on the current plane,the voltage and current constraints during the operation of the motor are analyzed,and the dynamic regulation region of the current is determined.The variation of the current point corresponding to the maximum torque output capacity of the motor with the speed in different regions is analyzed.And according to the principle of optimum efficiency of minimizing the amplitude of current vector needed to output the same torque,the current working point planning in the flux-weakening region is analyzed.According to the characteristics of the target motor system as a finite speed drive system,A closed-loop flux-weakening algorithm for current vector angle regulation based on voltage instruction feedback is designed.The whole algorithm consists of a voltage closed-loop controller and an angle calculator.For the distortion between the actual output voltage and the input voltage instruction of inverter caused by the nonlinearity of power switching devices,an algorithm of disturbance voltage compensation is designed.In theory,the proposed algorithm can achieve smooth transition between the MTPA stage and the flux-weakening stage,and the current operating point can be planned at the current point of theoretical analysis in the fluxweakening stage.Based on the software platform of Matlab/Simulink,the simulation model of permanent magnet synchronous motor control system is built,and the performance of the proposed flux-weakening algorithm is simulated and verified.A 1.5k W hardware platform of PMSM control system based on dual-motor pairtowing is built,and the C code software development of PMSM control system is completed based on the Myway motor control development prototype with TI DSP TMS320F28335 as the MCU.Based on the hardware of platform and the software of algorithm,the proposed algorithm is verified by experiments.Firstly,the output voltage distortion of the inverter is compensated by the relationship between the disturbance voltage and the phase current obtained from the calibration.The compensation results show that the inverter can output the instruction voltage well after compensation.Finally,the experimental verification of the flux-weakening regulator based on closed-loop voltage command is carried out.The results show that the flux-weakening algorithm can achieve smooth transition from the MTPA control stage to the flux-weakening control stage,widen the speed range of the motor.The system has good running robustness in high-speed flux-weakening region,under dynamic conditions,it can adjust the angle of current vector rapidly,and maintain the voltage instruction at the voltage limit,that is,the current working point is planned at the intersection of the voltage limit circle and the corresponding equivalent torque line,and the optimal efficiency of the motor is verified at the steady flux-weakening current point planned by the algorithm.