Algorithm Applied Research For Permanent Magnet Synchronous Motor Used In Electric Vehicle

Facing the increasingly serious energy and environmental problems, developing electric cars is the inevitable choice to replace fuel cars. Motor drive technology is one of the three key technologies of electric vehicles, which has always been a hotspot in research of electric vehicle technology. Permanent magnet synchronous motor (PMSM) could have limitless applications in the field of electric vehicle drive due to the desirable features such as small volume, high efficiency, high power density, larger torque to inertia ratio and wide speed range. This proposed research is directed to the control strategies for PMSM drive system used in electric vehicle.First of all, the structure and classification of permanent magnet synchronous motor are discussed and studied in this paper. According to the application requirements of the electric vehicles, interior permanent magnet synchronous motor (IPMSM) is selected as the research object. According to the relations among the three kinds of coordinate transformation, the mathematical model for IPMSM is setted up in the d-q rotating coordinate. On this basis, the PMSM vector control scheme and the realization of the space vector modulation (SVPWM) technology are studied. The double closed loop system of PMSM was analyzed, and the current loop and speed loop are designed respectively.Secondly, since the electric vehicle require high torque at low speed, the maximum torque per amper (MTPA) control scheme is adopted in constant torque area below the base speed. For the implementation in engineering, a MTPA control scheme based on polynomial fitting is presented. The reference value of the d/q axis current component are calculated through online calculation. The proposed method is simple with high precision and-less calculating quantity. Its feasibility is verified by the simulation in Matlab, which meet the requirement of high torque at low speed.Thirdly, since the electric vehicle require a wide speed range, the field-weakening control scheme is adopted in constant power area above the base speed. The basic principle of field-weakening control for permanent magnet synchronous motor is analyzed. And a kind of field-weakening method based on SVPWM technology is proposed, which improved the utilization rate of DC bus voltage. To avoid the adjust lag of the q axis components, the lead angle control is applied during the field-weakening progress.Finally, in order to improve the robustness to external disturbance for the speed loop system, fractional order controller is introduced to the speed regulation of PMSM. The fractional order PIλDμ controller with robustness to gain change are studied and designed. Simulation result shows that the proposed controller not only can improve the control quality of speed loop system, but also has stronger robustness to the change of system gain.