Research On Direct-drive Permanent Magnet Machine For Electric Vehicle Based On Magnetic Gear Principle

In the conventional electric vehicle power system,a high-performance permanent magnet synchronous machine is usually used in conjunction with a corresponding mechanical reduction device to achieve low-speed and high-torque characteristic.In recent years,in order to overcome the shortcoming of the large mass of system and high energy consumption in the speed reducer,direct drive machines with low-speed and high-torque characteristic have attracted more and more attention.Direct-drive permanent magnet synchronous machines can achieve high-torque due to the design of high magnetic pole pairs number.However,the mass of the machine is larger than conventional permanent magnet synchronous machine.Due to the unique pole-slot combination,the permanent magnet vernier machine based on the magnetic gear principle not only has low-speed and high-torque performance without reduction device,the volume can also reach a similar level with conventional permanent magnet synchronous machine.Therefore,the transient output performance of a novel permanent magnet vernier machine is analyzed in detail in this thesis.This thesis proposes a novel triple-stator axial flux spoke-type permanent magnet vernier machine(TS-AFSTPMVM).The topology and design of TS-AFSTPMVM are presented and the flux modulation principle is introduced by analyzing the operation principle of TS-AFSTPMVM.Based on genetic algorithm(GA),the final optimal result of th e DR-AFAPMVM torque and power factor can be obtained,which is finally verified by 2D-FEA results.The three-dimensional finite element analysis model,equivalent two-dimensional finite element analysis model and mathematical analysis model can replace the three-dimensional finite element analysis model to obtain the result using short time in the machine design process.The influence of the airgap length on the no-load leakage flux is analyzed theoretically and verified by simulation.In this paper,the voltage equations and torque equation of TS-AFSTPMVM are established under the three-phase stator coordinate and the rotor rotating coordinate.At the same time,the machine model is built in MATLAB\Simulink.By applying stator current vector control(i_d=0 and maximum torque per ampere).The characteristics of TS-AFSTPMVM controlled by voltage are obtained and maximum torque per ampere control can reduce copper loss and improve machine efficiency.Maximum torque per ampere control algorithm,flux weakening co ntrol algorithm and 2D-FEA are used to obtain the efficiency map of TS-AFSTPMVM.The relationship between electric vehicle parameters and machine power is introduced.Finally,TS-AFSTPMVM is applied to the electric vehicle and the operation status of the TS-AFSTPMVM are analyzed.