Modeling and Verification of Electrical Stress in Inverter-Driven Electric Machine Windings

This paper develops detailed models for predicting the voltage and current distributions in individual conductors of electric machine windings driven by pulse width modulation (PWM) inverter drives. This is the first step to better understand how PWM excitation voltage stresses the winding insulation of inverter-driven electric machines. A high-fidelity finite element (FE) model of electric machine windings was developed to account for frequency-dependent winding parasitic parameters. The model is capable of investigating the impacts that wire positions have on the winding parasitic parameters, hence the voltage and current distributions of individual conductors. A stator core with manually-wound windings was built to verify the fidelity of the FE model. Tests using both a form-wound winding and a random-wound winding with reduced number of conductors in slots were conducted to obtain the actual voltage and current distributions in individual conductors. Finally, the FE approach was applied to simulate a complicated winding structure with multiple serial turns and parallel branches to investigate the voltage and current distributions in individual conductors and the effects of wire positions.