Design And Research Of A New Type Of Magnetic Flux Leakage Variable Permanent Magnet Synchronous Motor

In recent years,the contradictory between the shortage of oil and environmental pollution is becoming severer because of the rapid development of the global traditional fuel vehicle industry.The electric vehicles(EVs)have aroused increasing attention in the field of new energy vehicles owing to the superiority of high effectivity and zero emission.In addition,due to the complex driving environments and variable driving modes of EVs,new challenges has been raised to EV's motor and its drive system.Currently,the permanent magnet synchronous motors(PMSMs)have been widely applied in drive systems of EVs because of their inherent advantages of high power density,high efficiency and high control accuracy.However,the constant excitation generated by permanent magnets(PMs)often leads to the nonadjustable magnetic flux,thus the PM motors may have difficulty in obtaining high-speed constant power operation and maintaining high efficiency over wide speed range.Therefore,how to widen the speed range and improve the efficiency of the medium-speed to high-speed zone has become a hot issue in the field of motor research.In this paper,on the basis of careful study of leakage flux phenomenon,a novel PMSM based on the concept of the variable leakage flux is proposed to widen the speed range and improve the overall operating efficiency within the wide speed range,so as to provide a certain theoretical basis and technical reference for the new generation of EVs driven.The main research contents of this paper include the following aspects:1.By adding an intentional leakage flux bridge between magnet poles in traditional PMSMs,a variable leakage flux interior permanent magnet motor(VLF-PMSM)is proposed.According to the magnetic circuit model,the mechanism of variable flux leakage is explored by systematically analyzing the reasonable matching of d and q axis currents.And then,the conditions of realizing controllable magnetic flux leakage are obtained.2.Based on the analysis of the relationship between salient ratio and flux linkage in PM/Reluctance motor.The condition of realizing reluctance torque greater than permanent magnet torque is discussed,and the rotor design method for realizing low salient ratio characteristic is studied.According to the analysis of the MTPA trajectories of four types of motors with different salient ratio in the flux linkage Map,the optimal rotor salient ratio suitable for the variable leakage flux property are finally determined.3.A step-by-step hybrid optimization strategy is proposed for the VLF-PMSMs motor in this paper.In the first stage,the method of regression design is used to optimize the key parameters of the intentional leakage flux bridge.And in the second stage,"sensitivity analysis","response surface analysis","continuous nonlinear programming" and other design optimization technologies are adopted to realize the performances of high torque,low torque ripple and wide speed range,and the final design results are determined by the tradeoff of multiple goals.4.The current trajectories of a salient pole permanent magnet synchronous motor from the flux-weakening base speed to the maximum flux-weakening speed are analyzed theoretically.According to the variable characteristics of d-axis airgap flux,a methodology for constructing the relationship between d-axis airgap flux and load current is proposed.Based on it,the variable speed ability and the distribution law of high efficiency area are systematically investigated.5.Based on the analysis of the electromagnetic vibration mechanism of the motor,the spatial distribution and harmonic characteristics of electromagnetic radial force waves under different working conditions are simulated.Then,different stator modal simulation models are established to investigate the influences of motor components on structural modal frequency.Based on the electromagnetic-structural coupling analysis,the motor vibration characteristics under different load conditions are explored.6.Based on the optimization of the motors and the finite element simulation evaluations of motor performances,a V-shape VLF-PMSM and a traditional PMSMs are prototyped.In order to verify the reasonability of the motor design and confirm the variable leakage flux characteristic of the motor,an experimental test platform is set up.And a series of performances such as torque characteristics,MTPA trajectory,driving characteristics under different load conditions and vibration characteristics are tested.