Research On The Flux-Weakening Speed Regulation System Of Permanent Magnet Synchronous Motor For Electric Vehicle

In this paper,permanent magnet synchronous motor(PMSM)for electric vehicle is taken as the research object.The flux-weakening division and track planning,the improvement and optimization of the flux-weakening algorithm and the design and realization of the drive system for interior permanent magnet synchronous motor(IPMSM)are studied respectively.Aiming at the problem that the permanent magnets of IPMSM may be irreversibly demagnetized at high temperature and high speed,a novel control strategy for the optimal flux-weakening track of the stator current vector is proposed.And a voltage feedback flux-weakening control strategy with negative q-axis current compensation is proposed to solve the problems such as large current and torque oscillations,and the current regulator easy to saturate in the deep flux-weakening control system.(1)The mathematical model of IPMSM in three-phase ABC stationary coordinate system and two-phase d-q rotating coordinate system is established.The concept of vector control is introduced based on the mathematical model of d-q axis rotating coordinate system,and the basic principles and implementation of the Maximum Torque per Ampere(MTPA)control strategy are analyzed with d-q axis current vector diagram.Finally,the three-phase voltage source inverter control technology and space vector modulation technology are briefly described.(2)The flux-weakening trajectory of IPMSM is planned and the optimal current operation algorithm is designed.The i_d-i_q coordinate system is established to analyze the voltage and the current constraints of the motor during the flux-weakening operation.The flux-weakening current operation trajectory is divided according to the principle of optimal efficiency control,and the current characteristics of each area are introduced in detail.(3)The optimal flux-weakening trajectory control of the stator current vector for IPMSM considering the irreversible demagnetization of the permanent magnet at high temperature and high speed is studied.The demagnetization principle of the permanent magnet is introduced,and the maximum demagnetization current of the permanent magnet is calculated by the method of the equivalent magnetic circuit.Combined with the Maximum Torque per Voltage(MTPV)control method realized by gradient descent method in the flux-weakening region II,an optimal flux-weakening trajectory control strategy of the stator current vector to avoid irreversible demagnetization of the permanent magnet is proposed.The simulation results of MATLAB/Simulink indicate that the proposed method ensures the safe operation of the motor within the specified working conditions and current limits,and improves the safety performance of the vehicle.(4)The deep flux-weakening control strategy of IPMSM is studied.The traditional negative i_d compensation flux-weakening control strategy based on voltage feedback is introduced,and the oscillating phenomenon of the current and torque in the deep flux-weakening region is pointed out.Combined with the MTPV control method realized by the curve fitting method in the flux-weakening region II,a novel flux-weakening method with negative i_q current compensation is proposed.And the novel method can reduce the q-axis current loop gain to a certain extent is pointed out through the analysis of the small signal linearization.The simulation results of MATLAB/Simulink show that the deep flux-weakening control strategy based on negative i_q current compensation for IPMSM can effectively suppress the current and the torque oscillations in the deep flux-weakening region,and improve the stability of the system.(5)The hardware and software designs and the experimental verification of the PMSM drive system with the vector control and the flux-weakening control are carried out.The experimental results prove the feasibility of the proposed method.