Design And Optimization Of Direct-Drive In-wheel Motors For Electric Vehicles

Electrical energy is renewable clean energy,and electric vehicles can solve the contradiction between deteriorating environment,exhausted non-renewable energy and automobile market demand.Among various electric dive structures,in-wheel motors integrate driving,gearing and braking devices into hub,eliminating clutch,transmission shaft,transmission and differential parts,which simplifies the vehicle structure.External rotor direct-drive in-wheel motors have the advantages of simple structure,fast dynamic response and small axial size.In conclusion,the development of high-performance and highly reliable external rotor in-wheel motors is of great importance,and motor optimization can obviously enhance the motor performance.In this paper,the design procedure for Surface Permanent Magnet Synchronous Motor(SPMSM)based on magnetic circuit calculation was summarized.The requirement of motor performance was obtained by that of the vehicle.After the analysis of certain slot and pole combinations,four in-wheel motors with different slot and pole combinations were preliminarily designed based on the same standard.Based on simple genetic algorithm,an improved genetic algorithm which retains the best individual and combines pattern search method was proposed.The paper also established the mathematical model for motor optimization with penalty terms and analytical model for electromagnetic performance calculation.Then the maximum torques of the previous four designs were optimized respectively through the improved genetic algorithm.At last,the paper compared two end winding inductance analytical calculation methods of concentrated winding motors,and analyzed the electromagnetic performance,temperature rise,etc.The results verifies the validity of the improved genetic algorithm used in motor optimization.Besides,the optimized in-wheel motor with 30 slots and 28 poles can output the maximum torque and meet the design requirement.