Research On Cogging Torque Of Hybrid Excited Switching Flux Permanent Magnet Machines

Hybrid excited switching flux permanent magnet(HESFPM)machine inherits the advantages of simple structure and high efficiency of permanent magnet machine,and has the ability to adjust the air-gap flux density.It can be applied in the fields of aerospace,new energy generation and drive.However,due to the double salient pole structure in the HESFPM machine,high cogging torque and consequently high noise and vibration can be observed.In this paper,the cogging torque of HESFPM machine was studied.This paper takes the 12/10 HESFPM machine as an example to introduce the basic structure of the machine.The operation principle and magnetic regulation principle of the machine are analyzed,and the corresponding mathematical model was derived.The variation of air-gap flux density,open circuit flux linkage,back EMF and torque under different excited currents was analyzed by finite element analysis.The reason for the cogging torque of the 12/10 HESFPM machine is introduced.Based on the Fourier decomposition method and magnetic circuit model,the two analytical expressions of cogging torque are derived.The influence of machine parameters,such as the number of stators and rotors,the air-gap and the permanent magnets on the cogging torque were studied.By skewing the rotor and increasing the rotor tip,the cogging torque was investigated.Due to the simple rotor structure of the HESFPM machine,four methods such as using the auxiliary slot,step tooth,rotor tips and eccentric tooth,are employed in HESFPM machine.The finite element analysis was used to optimize the structural dimensions.The effectiveness of different methods for reducing the cogging torque analyzed.A prototype machine was test to verify the finite element.It shown that all the methods can reduce cogging torque.Under different field current densities,the other conclusions in this thesis are:(1)From the effectiveness aspect,the auxiliary slot method has the best.(2)In terms of machine performance,the V-slot method has less influence on flux linkage,back EMF and output torque of machine.In the flux weakening condition,the V-slot rotor exhibits the highest torque.