Self-Adaptive Field-Grading Coating for Partial Discharge Mitigation of High Voltage Power Module Under High dv/dt Square Wave Voltage

Partial discharge (PD) in the packaging insulation of high-voltage power modules poses a significant risk to their reliability. Electric field (E-field) concentration is one of the main direct causes of PD occurrence and its mitigation method arouses much research interest. However, most of the reported studies primarily rely on simulations due to difficult manufacturing processes. Additionally, few experimental methods have validated the effectiveness of PD mitigation under square wave conditions. This letter proposes a self-adaptive field-grading coating method for PD mitigation in power modules. The so-called self-adaptive method refers to employing E-field to generate electrophoresis forming gradient distribution of coating materials at the triple points. The coating material is a silicone elastomer composite doping with ZnO micro-varistors with nonlinear electrical properties. The ZnO micro-varistors are self-adaptively distributed with the E-field profile, thereby alleviating the local E-field concentration. The proposed method is verified by PD experiments under high dv/dt square wave voltages for the first time. The PD experiment results show the proposed coating method increases the PD inception voltage (PDIV) of the tested direct-bonded copper (DBC) packaging sample with various trace spacings. The research presents an effective approach for reducing the risk of PD for high-voltage power module packaging and has great potential for industrial applications.