Research On The Flux-Weaken Speed Control System Of Permanent Magnet Synchronous Motor For Electric Vehicle

Permanent Magnet Synchronous Motor(PMSM)has high reliability because it has no brush and exciting power.And the high power density and high efficiency are the main characteristics of PMSM.Accordingly,PMSM is more suitable for the powertrain of electric vehicle.PMSM needs flux-weaken control in order to maintain a high torque output at and above the base speed.In this thesis,the flux-weaken speed control system of PMSM for electric vehicle is studied.In order to improve the accuracy of torque control in full speed range,the influence of the change of permanent magnet flux on the control precision of output torque control precision is analyzed and the correction algorithm of the instruction current lookup table is studied.And a fuzzy PI controller for voltage loop is established for further improve the dynamic response capability of the system.The specific contents of this thesis are as follows:Firstly,the structure and working principle of PMSM are introduced,and the mathematical model of PMSM under different coordinate systems is presented.Based on the dq axis current figure of PMSM,the concept of vector control is introduced in the thesis and the principle of PMSM Maximum Torque per Ampere(MTPA)control is analyzed.Then the implementation method of vector control is introduced in detail,namely Space Vector Pulse Width Modulation(SVPWM).Secondly,on the basis of vector control,the thesis introduces the principle of PMSM flux-weaken control.The influence of saliency ratio and flux-weaken ratio on the flux-weakening operation of the motor is analyzed.The conclusion has a certain reference for the structure design of PMSM and the selection of motor drives.Then,according to the principle of PMSM flux-weaken control,several typical PMSM flux-weaken control systems are introduced and their characteristics are analyzed in detail in this thesis.Specific to the phenomenon of the variation of permanent magnetic flux with the operating conditions.The reason of the output torque error of the motor under the traditional PMSM flux-weaken control with instruction current lookup table is analyzed.And a PMSM flux-weaken torque control system based on the instruction current lookup table method is proposed.The system consists of five parts.The five parts are speed correction,instruction current lookup table,current correction direction calculation,dq axis feed forward decoupling and voltage loop fuzzy PI controller.The proposed instruction current correction algorithm can significantly suppress the output torque error under permanent magnet flux variation.Finally,by using the Matlab/Simulink,the necessity and effectiveness of the main modules of the proposed PMSM flux-weaken torque control system are verified with the simulations.By the comparing simulation to the traditional instruction current look-up table flux-weaken control,the overall effectiveness of proposed flux-weaken torque control system is verified.The output torque error is significantly reduced under the flux variation of the permanent magnet,and the dynamic response is rapidly with the proposed PMSM flux-weaken torque control system.