Thermal Analysis of a Modular Permanent Magnet Machine under Open-Circuit Fault with Asymmetric Temperature Distribution

Abstract

A modular permanent magnet machine is composed of several stator modules, and the three-phase winding of each module can be controlled independently. The novel modular permanent magnet machine has good abilities in terms of fault tolerance when the machine is exposed to fault conditions. The current of each phase is different and will result in uneven loss distribution in each phase. Heat transfer occurs in the circumferential direction and temperature distribution will be asymmetric in the circumferential direction. This paper proposes a 3D finite element thermal model to accurately calculate the rise in temperature under open-circuit conditions for modular permanent magnet machines. When two modules are in operation, the machine can output rated torque. When one module is in operation and the temperature is 150 °C, the output torque is 0.76 times the rated torque. The temperature of the machine under the one-phase open-circuit condition with a zero-temperature-difference control strategy will be 0.8 °C lower than that with a minimum copper loss control strategy. Finally, a prototype with three stator modules is manufactured and the calculation results are validated by experimental test. It holds great significance for the accurate calculation of a machine with asymmetric temperature distribution in the circumferential direction.