Design And Performance Analysis Of Magnetic-geared Permanent Magnet Motor For Electric Vehicles

At present,the environmental and energy problems caused by the high popularity of fuel vehicles are becoming more and more serious.Due to their high efficiency,energy saving,and environmental protection,Electric vehicles are considered to be one of the methods to alleviate environmental pollution and energy depletion.In order to obtain low speed and high torque,electric vehicles have to be equipped with a huge gear transmission system,which makes the structure of the entire electric vehicle complicated.In addition,the traditional gear system also has the problems of high noise,high loss,and low reliability.Therefore,direct drive system without the gear transmission has a very broad application prospect.As a kind of direct drive motor with high torque density,magnetic-geared permanent magnet(MGPM)motor has great potential in low-speed high-torque application scenarios such as electric vehicles.However,in order to obtain higher torque density,magnetic-geared motor requires a large amount of rare earth permanent magnet.These rare earth materials not only increase the production cost,but also produce high eddy current loss during operation,which has a certain impact on the safety of the motor.Based on the MGPM with uncoupled magnetic circuit,an inner rotor consequentpole magnetic-geared PM(IRCP-MGPM)motor is proposed,which improves the utilization rate of the permanent magnets and reduces the eddy current loss and core loss of the motor.Further,in this thesis,Halbach arrays are applied to both sides of the inner rotor of the motor,and a Halbach consequent-pole magnetic-geared PM motor is proposed.This structure can effectively increase the output torque of the motor and reduce the magnetic saturation of the inner rotor yoke.The research work of this thesis is carried out from the following aspects:Firstly,the advantages of the magnetic-geared PM motor applied to the direct drive system of electric vehicles are analyzed,and the main parameters are matched and calculated.Based on the analytical method,the basic principle of magnetic fieldmodulating of the magnetic gear is derived and analyzed,and then,a magnetic gear are modeled by using finite-element analysis(FEA)method.The FEA results prove the analytical method's demonstration of the magnetic field-modulating effect.Secondly,the structure parameters of magnetic-geared PM motor and its internal motor are optimized.These parameters include the winding structure,the pole arc coefficient,the magnetic circuit,air gap length and magnetic ring.Finally,the model and specific parameters of the magnetic-gear PM motor are given.Thirdly,in order to improve the utilization rate of permanent magnets,three kinds of magnetic-geared PM motor with consequent-pole structure are put forward.Their electromagnetic performance and loss characteristics are analyzed by FEA.It is found that the inner rotor consequent-pole magnetic-geared PM(IRCP-MGPM)motor has higher permanent magnet utilization rate and lower loss characteristics.Finally,in order to improve the output torque of the IRCP-MGPM motor,Halbach magnetization is performed on the inner rotor of the motor.Compared with the radial magnetization structure,it is found that the IRCP-MGPM motor with Halbach array has higher output capability.