Research On Flux-weakening Control Strategy Of Permanent Magnet Synchronous Motor

Permanent magnet synchronous motors(PMSM)are widely used in electric vehicles,aerospace and CNC machine tools because of their outstanding advantages such as high efficiency,high torque density,high power density,wide speed range,large output torque,and small size.The thesis mainly studies the flux-weakening control system of the PMSM,deeply analyzes the mechanism and realization method of the flux-weakening control system,and proposes the improved method,which has certain theoretical and engineering practical value.The thesis first analyzes the principles and implementation methods of vector control technology,including the mathematical model of the built-in PMSM under abc three-phase stationary coordinate system and dq two-phase rotating coordinate system,the theoretical principle of coordinate transformation,and several different vector control technologies,analysis of their characteristics and their respective scope of application,and detailed analysis of the basic principles and digital implementation of space vector pulse width modulation(SVPWM),and finally how to determine the PI parameters for simulation.The selection of PI parameters directly determines the performance of the control system Therefore,in order to ensure that the system achieves the best control performance,it is very important to choose appropriate PI parameters.Then the basic principle of PMSM flux-weakening control is studied.In view of the shortcomings of traditional negative id current feedback flux-weakening control,an improved negative feedback current flux-weakening control strategy based on voltage feedback closed loop is used.The traditional flux-weakening control algorithm can only run in the linear region,and the voltage utilization rate has not reached the maximum.When the motor running speed is high,the torque output capacity is insufficient and the dynamic performance is poor.In order to further improve the utilization rate of the DC bus voltage,the over-modulation technology is studied.The over-modulation technology and the flux-weakening control are combined.After the over-modulation technology is added,the motor can be operated in the over-modulated area.The utilization rate reaches the maximum,and its operation is simple.It does not need to distinguish the over-modulation area,and can be handled uniformly,ensuring a smooth transition of the system from the linear area to the over-modulation area.In order to improve the dynamic response of the system in the overmodulation area,the paper studies a transient current control,which can significantly improve the dynamic response of the system.When the motor is running in the overmodulation area,especially the six-step operation,the dynamic response of the system is very poor.A method for improving the current dynamic response by modifying the reference voltage vector effectively improves the current transient response capability of the motor in the overmodulation region.Next,some shortcomings of traditional lead angle flux-weakening control are studied,and improvements are proposed to address the above deficiencies.When the motor speed is high,the traditional lead angle flux-weakening control has poor dynamic response performance,the current will oscillate,and the motor speed will also fluctuate.Due to the presence of the field weakening ring,the values of the d and q axis reference voltage vectors are limited.As a result,its dynamic response capability is poor,and the load capacity of the motor at high speed is not strong.In order to improve the dynamic performance of the motor in the high-speed region,this paper applies an improved lead angle flux-weakening control algorithm,that is,using the q-axis current error closedloop to perform field weakening control to improve the system’s load capacity and dynamic performance in the high-speed region.Finally,through the MATLAB / Simulink simulation software,the simulation model of the permanent magnet synchronous motor control system based on the fluxweakening control method and the traditional flux-weakening control method proposed in this paper is built,and the simulation results are compared and analyzed to verify the feasibility of the above method.