Research On 54kW Permanent-magnet Synchronous In-wheel Motor System For Electric Vehicles

In the application background of electric vehicles,the torque and speed range of direct-drive in-wheel motors should satisfy the requirements and high reliability and fault tolerance should be required.Faults can be diagnosed and handled immediately to guarantee the safety of vehicles and people.Compared with the traditional three-phase motors,modular permanent-magnet in-wheel motors have the characteristics of strong fault tolerance and high degree of control freedom.The electromagnetic design of modular permanent-magnet in-wheel motors,the fault-tolerant control of open-circuit fault and turn-to-turn short-circuit fault,the fault diagnosis of turn-to-turn short-circuit fault,and temperature field analysis are studied in this paper.The main contents are as follows:Firstly,the electromagnetic design and optimization of modular permanentmagnet in-wheel motors are studied.The modular structure of stator is adopted in this paper,and the selection principle of slot/pole combination of the sub-modules in modular permanent-magnet in-wheel motors is studied.The influence of circumferential and radial magnets segmentation on permanent-magnet loss is studied.The influence of traditional magnetization methods and Hallbach magnetization method on the electromagnetic performance of motors is compared.The influence of slot width on short-circuit current is studied.The torque performance and efficiency distribution before and after the optimization are compared and analyzed.Secondly,the fault-tolerant control strategy of modular permanent-magnet inwheel motors is studied.The control principle of multi-module motors is derived.The fault-tolerant control methods of one-phase open-circuit fault and turn-to-turn shortcircuit fault of modular permanent-magnet in-wheel motors are studied.The normal performance and performance in faults of the motor are analyzed.The current compensation strategies under open-circuit fault and turn-to-turn short-circuit fault are derived by applying the principle of keeping the stator total magnetomotive force unchanged.Aiming at the problem that the current of neutral point is not equal to zero,two fault-tolerant topological structures of three-phase four-bridge arms and neutral point interconnection between modules are proposed.The fault-tolerant performance of different fault-tolerant topological structures are compared and analyzed.Thirdly,the online fault diagnosis method of turn-to-turn short-circuit fault is studied.Based on the equivalent circuit model of turn-to-turn short-circuit fault,the lumped parameter mathematical model of the motor in the a-b-c coordinate system is derived,and the simulation model of turn-to-turn short-circuit fault is established.The results show that the signals of currents,torque,impact currents can be served as the signals of short-circuit fault.The three-phase currents are selected as the fault signal,and the negative sequence current signal is taken as the fault characteristic signal.The influence of asymmetric windings on the negative sequence current is studied.The negative sequence current of 1% turn-to-turn short-circuit fault under different velocity is selected as the threshold to diagnose the turn-to-turn short-circuit fault online.Finally,the temperature distribution of modular permanent-magnet in-wheel motors under normal operation and fault-tolerant operation is studied.The threedimensional temperature field simulation model of modular permanent-magnet inwheel motors is established.The equivalent calculation methods of key areas are analyzed.The heat dissipation coefficient of circumferential spiral waterway is analyzed by simulations.The temperature distribution of the motor under normal operation and fault-tolerant operation is analyzed by simulations.The results show that the motor can operate continuously under one-phase open-circuit fault and turn-to-turn short-circuit fault by decreasing the ratings.