Performance Evaluation of Rotor PM and Stator PM Machines under Different Cooling Strategies

This paper investigates the effect of various cooling strategies, including forced air, water jacket, and shaft cooling, as well as their combinations, on the electromagnetic performance of rotor PM and stator PM machines. These cooling strategies are analyzed by computational fluid dynamics, and the corresponding convection heat transfer coefficients are evaluated, which are further used in the 3D thermal finite element models to determine the maximum reachable output torque and power capabilities of the stator and rotor PM machines, considering thermal limits of PM and winding insulation. Amongst different cooling strategies, it is shown that the hybrid water jacket and shaft cooling can significantly extend the operational region of surface-mounted PM machines, while only water jacket cooling is required in switched-flux PM machines to produce a competitive torque. Both machines are fabricated for experimental validation under different cooling strategies and load conditions, where a good agreement between experimental and numerical results is achieved.