Comparison of Thermal Performance between Direct Coil Cooling and Water Jacket Cooling for Electric Traction Motor based on Lumped Parameter Thermal Network and Experimentation

Kurzfassung

This paper focuses on analyzing a novel direct coil cooling approach for electric traction motor. Its thermal performance is compared with conventional water jacket cooling concept by using analytical and experimental methods. Results show, the direct coil cooling approach has significant advantage regarding thermal performance, which allows the electric traction motor more suitable for high load applications. This study is performed on an ODIN switched reluctance prototype machine. For a convincing comparison result, the ODIN prototype is equipped with dedicated cooling circuits for each cooling approach. Based on the design parameters of the prototype, a lumped parameter thermal network (LPTN) model is established for analytical studies. For an accurate representation of heat transfer in the direct coil cooled motor through fluid flow, the key convective boundary is modeled based on the results of computational fluid dynamics (CFD). Studies with the developed LPTN model and experiments for validation are conducted. The results of the model analysis and the experiments both indicate that, through cooling coils directly in the stator slots with oil flows, direct coil cooled motor can effectively dissipate heat in the thermal critical winding areas. Current density in the ODIN prototype can be significantly increased. Thermal resistance from hotspots to coolant can be reduced by up to 80%. Direct coil cooling can increase the continuous torque output of ODIN machine to approx. 300%.