Optimization And Thermal Analysis Of A New Self-Decelerating PM In-Wheel Motor

With the increasing problems of energy shortage and environmental pollution, Electric Vehicles(EVs) have been paid much more attention. In-wheel motor drive is an advanced drive system, and it’s essential to develop new in-wheel motors with high torque density and high efficiency. In this thesis, a new self-decelerating PM in-wheel motor is proposed and optimized. It combines the magnetic gear and traditional high-speed inner-rotor PM synchronous motor. Thus, it takes both of the advantages, such as free maintenance of magnetic gear, small volume and light weight of the high-speed inner-rotor PM synchronous motor. Therefore, the torque density is improved.Firstly, a brief introduction is devoted to motor operating principle and topology. Then, the magnetic field distribution is analyzed. The finite element method(FEM) is used to analyze motor characteristics, including the back electromotive force(EMF) at no-load, cogging torque, inductances, steady electromagnetic torque, power loss and end effect, etc. The motor operating principle is verified, and the results lay a certain foundation for the following thermal analysis.Based on the motor design, five key motor structure parameters are analyzed with the parametric analysis tools, including PM width, PM thickness, stator tooth width, stator tooth length and stator yoke thickness, etc. The influences in motor characteristics are compared, including motor output torque, torque density, cost and efficiency, etc. The results set foundations for the following motor optimization.Then, the differential evolution(DE) algorithm for motor optimization is proposed, aimed at solving the issues of traditional motor design method. The mathematical model for motor optimization is constructed. The optimization process is introduced, and the optimized result of DE is compared with that based on traditional method. The optimized result of DE proves to meet the requirements of in-wheel motor, namely high torque density, high efficiency and low costs. Therefore, it’s reliable to apply DE to motor design.Due to high integration of in-wheel motor, it’s essential to conduct thermal analysis. Thus the motor performances can be checked, and the reliability of motor operation can be ensured. In this thesis, the thermal field and electromagnetic field are coupled. The temperature distributions of both motors at rated conditions are calculated iteratively. The results verify the motor reliability, so as to prove the rationality of the motor design.Based on the above theoretical analysis, a 2 kW prototype motor is experimented. The motor inductances, back EMF at no-load, losses and temperature distributions are tested. The tested results are compared with the simulation ones. The theoretical analysis and calculations are proved to be correct.At last, conclusions and future work of this thesis are summarized.