A Comparative Study on Different Cooling Topologies for Axial Flux Permanent Magnet Machine

The thermal behaviour of electrical machines would affect the lifespan and the electric performance of electrical machines. Hence, the maximum continuous operating torque of electrical machines is generally defined by the critical temperature in electrical machines. In order to increase the power density and efficiency of electrical machines, an effective cooling method needs to be chosen. Here, comparison of different type of cooling methods for axial flux permanent magnet motor is presented, in which the forced air cooling, water jacket stator cooling and rotor shaft liquid cooling methods are investigated. Due to the stator copper loss is the major loss, the stator liquid cooling is the most effective method to extract heat from the machine. However, the use of rotor liquid cooling can still be considered for a certain situation, as the magnet can be more effectively cooled. Therefore, the hybrid cooling approach, which combines both forced air cooling and rotor shaft liquid cooling, is presented in this paper. The thermal analysis is based on Lumped Parameter Thermal Network (LPTN) model, where the thermal properties of the test motor were experimentally verified.