Effects of Square Pulse Rise Time on Partial Discharge Characteristics of Power Module Packaging Insulation

Abstract

Power modules with wide-bandgap (WBG) semiconductors tend to be applied in high voltage and high-temperature situations due to their superb properties. Partial discharge (PD) in the packaging insulation under square pulse with a high slew rate (SR or <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{d}V/\mathrm{d}t$</tex> ) is one of the main issues resulting in power module failure. Different rise times of the square pulse usually lead to different PD characteristics, such as partial discharge inception voltage (PDIV) and PD magnitude. This paper focuses on the effect of the square pulse rise time on PD characteristics of power module packaging insulation and a down-mixing PD detection method is proposed and applied to extract PD signals under square pulse with ultra-short rise time. A PD specimen based on the structure of power module packaging is designed and fabricated. PD experiments under square pulse with three different rise times of 120, 500, and 1000 ns are performed. The experimental results show that the partial discharge inception voltage (PDIV) gradually decreases as the rise time increases. The statistics of PD magnitude indicate that a shorter rise time could result in a larger average PD magnitude. According to the experimental phenomena, the mechanism of the rise time effects on PDIV and PD magnitude are analyzed based on the electron appearance stochastic delay theory. A shorter rise time of square pulse may result in a higher PDIV of the packaging insulation, but more PDs with a large magnitude will occur, which can lead to serious degradation of encapsulation and further influence insulation reliability.