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

Permanent magnet synchronous motor is widely used in high-power electric drive system because of its small size,high power density and high efficiency.In such applications,permanent magnet synchronous motor is normally required to have high torque overload and extending speed range with constant output power,but stator voltage will be limited by the DC bus maximum voltage when the motor speed arrived base speed,flux weakening control for permanent magnet synchronous motor could realize the operation of motor over base speed.Therefore,this article focuses on the modulation algorithm which could improve the utilization of DC bus and flux weakening control strategy for further raising motor speed.The main research work are as follows:Firstly,the theoretical analysis of flux weakening control strategy is established for PMSM based on its mathematical model,the optimal current vector trajectories and the theoretical maximum motor speed in the field-weakening operation process is deduced for different motor parameters.The performance of SVPWM and six-step operation are compared from the aspects of DC bus utilization,switching losses and application,hybrid modulation algorithm based on SVPWM and six-step modulation is proposed.Secondly,flux weakening control strategy based on SVPWM and six-step modulation are studied respectively,the performance of those strategies are verified by simulation and compared from aspects of torque ripple,dynamic performance and the principle of algorithm.On this basis,the performance of those flux weakening strategies are studied which used in hybrid modulation.Meanwhile,the problem of troque ripple when modulation algorithm changed are theory anslyzed,the flux weakening control strategy which apply to hybrid modulation is given.Thirdly,over modulation algorithm is proposed for a smooth transition from SVPWM to six-step modulation to solve the problem of troque ripple when modulation algorithm switched directly.Magnitude range of the output voltage by over modulation algorithm is deduced based on analyses of Fast Fourier Transform.Over modulation algorithms are anslyzed from aspects of the complexity of algorithm and the linearity of output voltage,the appropriate over modulation algorithm is given.Meanwhile,the optimal opint of switching of modulation algorithm is given based on analyse of the harmonic component of current under the condition of six-step modulation and SVPWM in different carrier ratios.Those control strategies are verified by simulation.Finally,PMSM flux weakening control system experimental platform is constructed,the experimental research on the output characteristic of different flux weakening control strategies based on SVPWM,hybrid modulation based on strategy of switching directly and hybrid modulation based on strategy of transition region designed with over modulation algorithm.Flux weakening control strategy of the article are evaluated and verified experimentally.