In-slot Direct Cooling Design and Optimization for Electric Machines

This work strives to apply the in-slot direct cooling technique in electric machines and optimize the cooling design to improve the machine performance in both cooling and electromagnetic (EM) aspects. The in-slot cooling directly removes the heat from the heating source, but requires extra spaces in the slots that possibly reduce the electromagnetic performance of the machine. It needs an overall evaluation considering both EM and thermal performances to achieve an optimal machine design for in-slot cooling systems. This work utilizes a thermal-network based numerical modeling approach combined with finite element (FE) EM simulations to evaluate the proposed in-slot cooling scheme and compares it with a drip-cooled machine product from multiple aspects, such as torque output, temperature, efficiency and pump power. The thermal network model was verified with thermal FE simulations and is capable of predicting the transient temperature of the machine system. The temperature distribution and corresponding power losses of the electric machines with in-slot cooling designs were calculated on various machine operating points. The final efficiency of the in-slot cooled machine was compared with the drip-cooled machine. Then, an in-slot cooling design was chosen based on the simulation results and comparison for prototyping. Finally, a 3D printed prototype of a partial machine with in-slot cooling channels was designed and constructed to check the manufacturability of the proposed cooling design.