Research On Flux Weakening For Permanent Magnet Synchronous Motor Based On Hybrid Overmodulation Algorithm

In the controller system of electric vehicle,PMSM is widely used in the transmission system of electric vehicle because of its small size,high efficiency and low cost.The core of permanent magnet synchronous motor control system is the motor and its drive system,which requires the motor has large torque at low speed,has good speed regulation at high speed regulation characteristics;it can output constant power in the wide speed domain.This paper mainly studies the algorithm switching strategy of PMSM under weak magnetic control,and analyzes how to improve volitage utilization,pulse processing and harmonic elimination.The specific research work are as follows:(1)Firstly,based on the mathematical model of PMSM,the characteristics and control principle of the motor under the condition of weak magnetic control are analyzed,and the optimal running trajectory of the current vector when the PMSM is working in the weak magnetic region is also studied.Finally,some traditional modulation algorithms are summarized,the principle of SVPWM linear modulation algorithm and six-step voltage modulation algorithm is analyzed emphatically,and the hybrid modulation strategy combining SVPWM algorithm and six-step voltage method is finally determined.(2)Secondly,the mixed modulation weak magnetic control strategy based on voltage feedback method and single current regulator is analyzed,and it is concluded that the mixed modulation strategy based on single current regulator can effectively reduce the torque fluctuation and speed oscillation of motor in low speed region.As the PMSM is switched from the SVPWM algorithm to the six-step voltage method,the single current regulation control strategy can make the motor work stably in square wave mode,which effectively improves the stability of the weak magnetic control of PMSM.thus,the weak magnetic control strategy using single current regulation is determined.(3)Furthermore,the over-modulation algorithm is used to realize the switching between the SVPWM and the six-step voltage method.In order to realize the smooth transition between the two algorithms,the dual mode overmodulation strategy and the single mode overmodulation strategy are proposed respectively.Fourier principle is used to derive the output voltage vector of the proposed over-modulation algorithm.the linearity of the output voltage vector and the complexity of the algorithm are analyzed and the single mode overmodulated strategy is determined.(4)Finally,the experimental platform of permanent magnet synchronous motor(PMSM)is set up to study the theory.the output characteristics of the motor under different weak magnetic control algorithms are studied respectively.the comparison experiments of mixed modulation based on direct switching strategy and mixed modulation based on overmodulation are carried out,and the output characteristics of the motor are analyzed.the rationality of the proposed weak magnetic control strategy based on mixed overmodulation algorithm is further verified.