Bar-Wound Machine Voltage Stress: a Method for 2D FE Modeling and Testing

Advancements in semiconductor technology present new challenges in electric machine construction, operation and control. Silicon carbide (SiC)-based power electronics are becoming the new standard for high-power consumer and commercial devices, and are implemented in technologies such as power inverters, converters and rectifiers. This paper focuses on the effects of inverter drives for traction motors in electric vehicles with high dV/dt rates on bar-wound machine windings, including the expected impacts on insulation materials under prolonged periods of high voltage stress. A simulation model was constructed using finite element analysis, the results of which were validated with experimental results using a commercially available SiC inverter and traction motor. The results presented in the analysis pertain mostly to a single phase of a three-phase IPMSM in order to reduce simulation and testing complexity and runtime, so that the accuracy of the simulation in relation to the physical model can be demonstrated before proceeding to three-phase analysis. Some three-phase testing and analysis is also included. Correlation has been established between the preliminary simulation results and experimental data. It is proven that as DC bus voltages increase with the capabilities of SiC devices, the voltage stresses inside the stator windings approach levels which could cause partial discharge and premature insulation degradation in existing stator designs.