Numerical simulation of breakdown threshold voltage in charging coils of wireless power transfer systems

Wireless Power Transfer (WPT) systems have wide applicability in the electric transportation industry. However, the dielectric breakdown is a persistent threat affecting the reliability of insulated electrical components, including the charging coils of WPT systems. This paper presents simulation results of the breakdown threshold voltage the coil-ferrite gap in the ground assembly (GA) of a heavy-duty electric vehicle (HDEV) WPT system as a case study. To begin with, the standardized GA subsystem is modeled in COMSOL, and simulated under a 85kHz sinusoidal voltage in atmospheric air. The system configuration alongside the field model and breakdown theory are introduced. Based on this, the electric field distribution in the model is calculated and the influence of the coils’ coating materials on the breakdown related parameters is demonstrated. In addition to the critical field lines (CFL), the breakdown field strength and voltages across the gap lengths are also analyzed. The accuracy of the numerical approach in estimating the breakdown characteristics is established by the findings which reveals the significant impact of the coating material on gap voltage and field strength magnitude values. Also, the PDIV is seen to be highly influenced by the geometry of the coils’ coating as compared to the applied voltage magnitude and frequency. Furthermore, the magnitude of the breakdown electric field strength demonstrates a high potential for partial discharge (PD) activity in the gap, which can be prevented by utilizing the estimated values in selecting and designing the coils’ insulation system.