Research On Power Factor Characterstics And Optimization Design Of Flux-focusing Flux-modulated Permanent Magnet Motor

With the rapid development of facility agriculture and the increasingly prominent problems of food safety,agricultural electric tractors have the characteristics of zero emission,no pollution and low noise,etc.,which has been widely concerned by governments,agricultural machinery manufacturers and related scholars.In order to achieve the flexible control and high transmission efficiency of Electric tractors,in-wheel motors have attracted wide attention in the field of electric tractor driving system research.The flux-modulated permanent magnet motor has the characteristics of low speed and large torque,thus it becomes the potential application object of electric tractor hub motor.However,the flux-modulated permanent magnet motor has relatively low power factor,which limits the wide application of flux-modulated permanent magnet motor.Hence,in the research field of electric tractor hub drive system,how to improve the power factor of the flux-modulated motor has become an urgent problem to be solved.Therefore,this paper proposes an optimization method to improve the power factor of flux-modulated permanent magnet motor from the perspective of air gap harmonics.In addition,a flux-focusing flux-modulated permanent magnet motor is selected as the research object,and its power factor is analyzed theoretically,optimized and verified experimentally in this paper,.And the main research contents are as follows:Firstly,the operation principle of flux-focusing flux-modulated permanent magnet motor is revealed,and the distribution analysis model of the permanent magnetic field and the armature magnetic field of the motor is established.At the same time,the power factor characteristics and air gap harmonics of flux-focusing flux-modulated permanent magnet motor are studied.Secondly,an optimization method to improve the power factor of flux-modulated permanent magnet motor is proposed,which takes the air gap harmonics as the key bridge.In order to verify the feasibility of the proposed power factor optimization method,a flux-focusing flux-modulated permanent magnet motor is selected as the research object.In the proposed method,the theoretical relationship model between the structural parameters and the power factor of the motor is established with the air gap harmonics as the bridge.The power factor is measured by comprehensively evaluating the variation of the air gap harmonics.The key parameters affecting the power factor are analyzed and verified by sensitivity analysis method.Then,the optimized design variables are selected and the comprehensive power factor is defined.The motor parameters under different operating conditions are optimized and the optimal design parameters of the motor were determined comprehensively.Consequently,the related performance of the motor before and after optimization is analyzed and evaluated comprehensively,including no-load back electromotive force,cogging torque,magnetic field distribution,flux linkage,output torque,efficiency,inductance characteristics and overload capacity.The results verify the effectiveness of the optimization method,which provides an effective research path for improving the power factor of the flux-modulated motor.Finally,based on the optimization results,a prototype of the flux-modulated motor is manufactured,and the corresponding experimental test platform is built.And the no-load back electromotive force waveform,the power factor characteristics under different operating conditions,the dynamic response characteristics and steady state characterstics of the flux-focusing flux-modulated permanent magnet motor are tested.The experimental results verified the feasibility and effectiveness of the proposed power factor optimization design,which lays the foundation for the application of the flux-focusing flux-modulated motor in the in-wheel drive system of electric tractors.