Research On Field-weakening Control Of Permanent Magnet Synchronous Motor For Electric Vehicle

In the electric vehicle industry,as one of the key parts of the power transmission of the electric vehicle,the motor and its control system influence the main performance index of the electric vehicle.Because of the advantages of high torque,high power density and high efficiency,the interior permanent magnet synchronous motor(PMSM)has been attracted widely in the electric vehicle industry.Since the motor of new energy vehicle is limited by the capacity of inverter,it is very important to study the field-weakening control of permanent magnet synchronous motor for the requirement of speed regulation range and performance index.Therefore,it has great practical value to study the field-weakening control of permanent magnet synchronous motor for vehicles in depth.In this paper,aiming at the demand of electric vehicle in the actual operation,the field-weakening speed regulation process is optimized from two aspects:the design of control strategy and parameter identification.Firstly,the structure and classification of permanent magnet synchronous motor(PMSM)and its mathematical models and transformation methods in different coordinate systems are briefly introduced in this paper.The limiting conditions in its operation and the basic principles of field-weakening control are analyzed in detail,which lays a foundation for further research on field-weakening.Secondly,according to the demand of torque and output power during the operation of electric vehicle,the strategy of optimal control of stator current is selected,that is to say,by the control of stator current.The requirements of torque at low speed and power at high speed are satisfied respectively.At the same time,with the increase of motor speed,the direct-axis inductance and quadrature-axis inductance of the motor will change with the saturation degree of the magnetic circuit,and the effectiveness of the field-weakening control will be reduced.Considering the influence of stator current on magnetic circuit saturation and cross saturation,based on the model reference adaptive theory,the neural network algorithm is proposed for on-line identification of the direct-axis inductance and quadrature-axis inductance.The identification results are applied to the field-weakening control,and the robustness of parameter identification is improved obviously.Finally,the simulink simulation platform is applied to verify the validities of the stator current optimal control algorithm and inductance parameter identification.The simulation results verify the validity of the stator current optimal control algorithm and inductance parameter identification without affect of the normal operation of the motor.The wide range speed regulation of motor and fast identification of inductance parameters is realized,and the expected effect is achieved.