Overshoot and Duty Cycle Effects of Wide-Bandgap Drives on Hairpin Winding in EVs

This study investigates the turn-to-turn insulation of hairpin windings in EVs under electrical stress from wide-bandgap power converters. A custom-built SiC-MOSFET pulse generator is used to induce continuous partial discharge (PD) by applying 2.5 kV unipolar pulses with a 40 ns rise time and 5 kHz frequency to corona-resistant magnet wire samples for 24 hours. The effects of 10% and 20% overshoot; and 20% and 50% duty cycles on insulation degradation are analyzed. Diagnostic techniques, including PDIV measurement, dissipation factor analysis, and surface imaging, are used in assessing the aging effects. Results indicate that voltage overshoot significantly accelerated PDIV reduction and increased the dissipation factor, underscoring its critical role in insulation aging.