Research On Fault-tolerant Performance And Thermal Characteristics Of Modular In-wheel Motor

Distributed electric drive systems have become popular candidate for the electric drive system of the next generation electric vehicle due to its high transmission efficiency and high mobility.As the development of the electric vehicles with distributed drive,the requirement for in-wheel motor systems becomes higher and higher.They not only meet high torque density and high efficiency,but also have high reliability and high fault tolerance to adapt to fu ture complex and changeable operating conditions and driving faults.Existing fault-tolerant permanent magnet motors are difficult to get the high torque density while paying attention to the fault-tolerant performance of the motor.Therfore,this paper proposes a modular permanent magnet in-wheel motor with high fault-tolerant capability.The advantages of the modular scheme are fully developed under the premise of ensuring the high torque density.The design and optimization principles for this type of motor,electromagnetic characteristics,temperature field modeling,thermal characteristics of the motor under fault-tolerant operation of open-circuit faults and short-circuit faults are studied.The main work of this paper includes the following aspects:Firstly,in terms of the technical requirements for high power density and high fault-tolerant performance,the design principles of modular permanent magnet in-wheel motors are proposed.According to the working mechanism and main fault y types of the modular fault-tolerant motor,the corresponding fault-tolerant control strategies are given,and the pole-slot combination with high fault-tolerant performance for the modular motor is developed.The magnetic field characteristics of the modular fault-tolerant in-wheel motor are investigated.The relationship between the fault-tolerant performance and the inductance parameters is linked through the magnetic coupling coefficient.The design requirement for the inductance of this kind of motors is proposed.The torque performance of the modular in-wheel motor is studied,and the factors affecting torque performance during fault and fault-tolerant operation are revealed.The cooperation schemes of various unit module and module numbers are compared and studied,the electromagnetic scheme of 16P24 S four modules is proposed,and the prototype is developed.The electromagnetic characteristics of the modular motor under normal and fault-tolerant operation are verified by experiments.Secondly,in order to accurately obtain the temperature distribution of the motor under normal and fault-tolerant operations,a method for modeling the temperature field of the modular in-wheel motor windings based on equal-area multi-block method is proposed.The model fully considers the temperature effect of end windings on active windings of the same coil inside two slots,as well as the temperature effect between adjacent coils.The heat transfer coefficient(HTC)of the end winding surfaces is obtained by computational fluid dynamics(CFD).The influence of speed on HTC of end winding surfaces is analyzed,and compared with the empirical formulas.Based on the model,the temperature field models of open-circuit faults and short-circuit faults are established respectively,and the temperature distribution under normal operating conditions and open-circuit faults is verified through experiments.Thirdly,in order to solve the high temperature of local windings when the winding of the motor under open-circuit faults runs asymmetrically,the temperature distributions of the motor under unit module open-circuit faults are analyzed.The influence of the faulty module on the winding temperature of the healthy modules is revealed,and the relationship between the overload current multiple and the loss and temperature rise of the motor under various unit module open-circuit faults are given.In terms of one-phase open-circuit in an unit module,the temperature distribution of winding during fault-tolerant operation is studied,and a fault-tolerant strategy to avoid high temperature of local winding is proposed.The fault-tolerant strategy are compared with minimum copper loss strategy and same current strategy in winding temperature distribution.Thereafter,the application effect of the fault-tolerant strategy in multi-phase open-circuit conditions is analyzed and summarized.Finally,the analytical models of the modular fault-tolerant in-wheel motor under one-phase short-circuit fault and interturn short-circuit are established respectively,which are verified by finite element method(FEM)and experiments.The influence of short-circuit faults on the torque performance of the modular motor are analyzed;the main influence factors of short-circuit current are explored,and the amplitude and phase of fault-tolerant currents for active fault-tolerant method are given.The passive fault-tolerant methods and the active fault-tolerant method for the modular permanent-magnet motor are compared in terms of reducing short-circuit current,suppressing torque ripple,outputting average torque,and improving the thermal characteristics of the winding.The short-circuit fault-tolerant methods suitable for the modular motor are given.