Space Charge Measurement of Power Module Packaging Insulation Under Square Wave Voltage at Sub-Megahertz Repetition Frequency

With the development of wide-bandgap high-voltage power devices with high power density, such as SiC MOSFET, packaging insulation has attracted increasing attention for securing reliability. Packaging insulation of power modules withstands constant unipolar square wave voltages due to the anti-parallel diode of IGBT or body diode of MOSFET, which makes it vulnerable to space charge accumulation. However, it is hard to observe the space charge dynamic behavior under the unipolar square wave voltage since the rising or falling time of the square wave is relatively short, hence the ultra-fast space charge measurement is required. In this paper, a sub-megahertz space charge measuring method based on a high repetition rate pulsed electro-acoustic method is proposed. The pulse generator uses the Blumlein line and SiC MOSFET to form nanosecond pulse voltage with repetitive frequency up to 3 MHz. Then, the transient space charge waveform of silicone elastomer for packaging insulation under square wave voltage with high dV/dt is obtained. It is found the fast rising and falling edge of the high square wave voltage can generate electromagnetic interference to the acoustic-electric signal, which should be carefully handled. The proposed sub-megahertz space charge measurement method can provide references for the research of transient charge transport behavior and failure mechanism of high-voltage power module packaging insulation.