Permanent Magnet Synchronous Motor Accurate Control Method And Key Issues In Research

Due to the fact that PMSM has nonlinear feature and is characterized by strong coupling,the conventional control strategy adopted by traditional PMSM fails to reach transient or steady state as required.In addition,under some circumstances,the economic indicators of general types of PMSM are unreasonable,which limit the effective potential of the motor.To improve the performance of PMSM's control system,ensure the reliability and stability of the system,this paper dwells on some key techniques,including the inverter dead-time effect,current loop dynamic performance,current predictive control,and sliding mode control of PMSM.Moreover,the dissertation also analyzes the feasibility of some plans for improving PMSM's performance and puts forward some new methods of PMSM control.The dissertation's main research and innovative work are as follows:(1)The voltage compensation strategy for dead-time effect is adopted to solve the low speed torque ripple caused by nonlinear inverter.The focus is put on analyzing the effect of inverter's nonlinear characteristics on current distortion,adopting the method of current distortion suppression.Such method is introduced because the motor's electromagnetic response is greater than its mechanical response.Such method simplifies the motor's dynamic mathematical method and generates a new type of observer for dead-time voltage compensation which can realize the effect of real-time monitoring and compensation.Because of such observer,the motor can output ideal phase current waveform and effectively restrain current distortion phenomenon.(2)To improve the response speed of current loop in PMSM's servo system,the current loop's dynamic capability is enhanced by optimizing PWM duty cycle and current sampling.In addition,the method for optimal control parameters of current regulator is designed in this dissertation.The research is based on two control methods of servo system's current loop.Firstly,the relation between current control cycle and system bandwidth is certified by reasonable equivalent reduction which confirms the idea that current control cycle is the main factor that influences the dynamic responsecapability of current loop.Secondly,the dissertation explores the effect of feedback current's sampling and PWM duty cycle on current control's time delay,providing theoretical basis for optimizing the current loop control strategy.(3)Under the condition of the motor parameter mismatch and load disturbances,the traditional current control strategy for PMSM fails to juggle speed and robustness.To solve such problem,the dissertation introduces feedback compensation to improve PMSM's deadbeat current predictive control mode.Due to the consequent improvement,the degree to which the system stability relies on the motor parameter mismatch is greatly reduced.The global stability of such mode in the closed loop system has been confirmed by Lyapunov stability theory.Under such mode,the current tracking error of motor control system can be confined to a smaller span.Compared with traditional current controller,the improved current predictive controller enjoys ideal dynamic capability and super robustness.(4)For the speed-sensorless director torque control system of PMSM,the observation accuracy of stator flux is determined by the rotor position.The dissertation designs a new type of stator flux observer in light of sliding mode control.The new observer excludes the variable of rotor angle so it can accurately obtain the stator flux estimation.It has been proved by Lyapunov stability theorythat the observer can be quickly confined to a smaller span and the consequent robustness towards system parameters and disturbance is stronger.At the same time,in order to keep the good dynamic characteristic of linear PI controller and enhance the controller's robustness,a compound control method is put forward in the paper,namely linear sliding mode controller.Such controller enables the system to reach transient or steady state as required by adjusting control gains to enhance the balance between PI control and sliding mode control.(5)There is a margin of error in identifying the initial absolute position of stator flux in PMSM's servo system.To eliminate such error,the dissertation puts forward a simple and effective method for estimating the rotor's position and an error correction strategy.Such method does not require complex calculation and is easy to be realized.As for the phenomenon that the dynamic response and robustness of speed loop controller based on sliding mode control cannot coexist,a compound reaching law function based on the advantages of various reaching laws is put forward in the dissertation.Such function enables the motor speed loop to reach transient or steady state as required by switching conditions.