Fast Space Charge Measurement of Power Module Packaging Insulation Under Square Wave Voltage Based on High Repetition Frequency Pulsed Electroacoustic Method

High voltage power module packaging insulation such as silicone encapsulating elastomer endures unipolar square wave voltage with short transient time (~100 ns, high dV/dt) due to the recent booming of wide bandgap (WBG) semiconductor, which results in space charge accumulation and easier packaging failure compared with the traditional power equipment operating under 50/60 Hz sinusoidal stress. However, the charge dynamic behavior under the high-frequency square wave voltage with short transient time (rising/falling edge) is seldom reported due to the lack of fast space charge measurement. This paper proposes a fast space charge measuring system based on a high repetition frequency pulsed electro-acoustic (PEA) method. The measuring system mainly includes a nanosecond stimulating pulse generator with repetitive frequency up to 3 MHz based on Blumlein line, a high voltage square wave source capable of generating the same electric stress as that in WBG power module packaging, and an electrode system with properly set resistor and capacitor. Then, space charge accumulation with time in silicone elastomer under square wave voltage is observed and analyzed by the proposed sub-megahertz repetition PEA measurement. In addition, the effect of the transient time of square wave voltage on charge transport is explored, showing that more charges reside in the tested silicone elastomer for the 100 ns transient time than the 10 μs transient time. The charge decay near the cathode, anode, and bulk part also presents different patterns which may be related to the energies of trapped charges, electrode-insulation contact, and internal electric field distribution.