Research On Direct Torque Control Strategies Of Permanent Magnet Synchronous Motor For Electric Vehicle

In recent years,the rapid development of China's automobile industry has brought enormous pressure to the problems of energy consumption and environmental pollution.Therefore,new energy vehicles,especially battery electric vehicles,have become a new direction for the future development of the automotive industry.Permanent magnet synchronous motor(PMSM),as a kind of motor with high efficiency and high power density,has great potential and broad prospect for the development of China's automobile industry.Therefore,in this paper,the permanent magnet synchronous motor driving system based on direct torque control(DTC)is studied in depth according to the actual operation requirements of electric vehicles.This paper first introduces the structure and classification of PMSM,and expounds the mathematical model of permanent magnet synchronous motor in different coordinate systems,and then analysis the control principle and realization method of PMSM-DTC speed control system.The permanent magnet synchronous motor direct torque control system model is simulated in MATLAB/Simulink environment,the performance of the speed control system is discussed,and provides theoretical basis for motor operation efficiency optimization system and flux weakening system.To solve the problem of short driving distance of electric vehicle,this paper proposes to optimize the motor operation efficiency and improve its endurance.First,the maximum torque per ampere(MTPA)control method for efficient operation of the motor under DTC is studied,and points out the disadvantage which the parameters change will make the motor run out of the optimal efficiency,and result in reduced control accuracy.Aiming at this problem,the method of determining the relative position between the actual operating point and the optimal efficiency point is analyzed,and combined with the requirements which adjusting the speed must be fast under actual operation condition,the fuzzy control method is selected to search the optimal efficiency point by variable step size adaptive optimization,so that the motor always maintains the highest efficiency operation.During the process of simulation,it is found that torque ripple increases in the fuzzy optimized system.Then the reasons for increasing torque ripple are discussed and analyzed in depth,and on the basis of this analysis,the factors that cause pulse increase will be screened and excluded,the fuzzy adaptive MTPA control system is finally formed.The simulation results show that the optimized system efficiency is improved and the speed and torque characteristics of the original system are maintained well.Then the principle of flux weakening of PMSM is studied for the high-speed running ability of permanent magnet synchronous motor,and its realization method in DTC are introduced.The function of zero vector insertion in DTC of PMSM is analyzed in depth,it is concluded that the zero vector maintains torque at low speed and weakens torque at high speed,according to this characteristic,the zero vector is applied to the operation of flux weakening field,and the zero vector is used as the control method of limiting torque angle.Finally,the hardware structure of PMSM direct torque control system is designed,and the hardware selection is analyzed and introduced.At the same time,the software algorithm of the whole system is designed.