Numerical Analysis for Negative Discharge Under High-Frequency Pulsed Voltage

Abstract

The increase in renewable energy and the development of silicon carbide (SiC) and gallium nitride (GaN) power switches have led to higher voltage magnitudes, slew rates, and switching frequencies, imposing greater electric stress on insulating materials. However, it is hard to recognize the partial discharge (PD) signal from background noise due to electromagnetic interference when diagnosing electrical equipment with high switching frequency. Therefore, we numerically analyzed negative corona discharge under a superposition of direct current (dc) and pulsewidth modulation (PWM) voltage, with a switching frequency of 80 kHz in a needle-plane geometry varying rising times of 100, 200, and 500 ns. The analysis model was coupled with Poisson’s equation and the drift-diffusion model. We considered three types of charge carriers—electrons, positive ions, and negative ions—and the generation and loss of each charge carrier. The discharge current was calculated from Poynting’s theorem. The discharge current pulses were regularly sustained, like the Trichel pulses in the previous research. However, the periods between pulses and the magnitude of the pulses changed depending on the applied voltage and rising time. With the increase in rising time, both the current pulse peak value and the pulse period decreased, affecting the charge distribution, especially for the ionization region and negative ions.