Research On Field-Weakening Control Strategy For PMSM Applied On Vehicles

Because of the characteristics of high-power factor,high efficiency and high reliability,permanent magnet synchronous motor has a wide range of applications in the field of electric vehicles.Since permanent magnet synchronous motor on vehicles requires a wide range of speed,it is necessary to use a field-weakening control strategy to achieve multiple speed expansion of the motor above the base speed.When the permanent magnet synchronous motor is running,it can be divided into two working sections.The section below the base speed is defined the constant zone,and the section above base speed id defined constant power zone.In the constant power zone,it is difficult to increase the motor speed due to the back electromotive force generated by the rotor and the limitation of the power supply voltage.In order to obtain a wider motor speed range,it is necessary to change the stator current vector to achieve smooth motor operation.Since in the deep field weakening region for permanent magnet synchronous motor,the stator current vector is influenced by temperature and current easily,which causes than the feedback current cannot track the given current.That quickly leads to saturation of the current regulator,resulting in losing control under field-weakening.Since the phenomenon,an offline parameter identification strategy based on motor mathematical model is proposed.The parameter variation trend of different sections of the motor is obtained according to the change of external influence factors.The full range of motor parameter values are fitted by two-dimensional interpolation method.The fieldweakening strategy is adjusted to optimize the stator current running trajectory,and the losing control under field-weakening operation in the deep field-weakening section is also solved.Based on the research of high-efficiency field-weakening control of permanent magnet synchronous motor in constant power region,an improved field-weakening control strategy is proposed to solve the problems of saturation of current controller and fluctuation of torque in constant power region.And this paper verifies the rationality and reliability of field-weakening algorithm by analyzing simulation model and experiment,the main contents are summarized as follows:The first chapter explains the research background and significance of the thesis.And it explains the research status of permanent magnet synchronous motor and its field-weakening control method in recent years,and analyzes the usage scenarios and advantages of the existing field-weakening control algorithm.The second chapter introduces the mathematical model of permanent magnet synchronous motor in different coordinate systems.The existing vector control method and its principle provide theoretical support for the proposed field-weakening control algorithm.The third chapter describes the current trajectory of the permanent magnet synchronous motor during operation,and analyzes the losing control under fieldweakening caused by the unreasonable distribution of current vector in deep section of field-weakening.And it proposes field-weakening control algorithm based on parameter identification for the interior permanent magnet synchronous motor.The fourth chapter and the fifth chapter introduce the hardware and software design of the field-weakening control system of permanent magnet synchronous motor,and prove the feasibility of the proposed algorithm in the third chapter from simulation and experimental results.