Analytic Model of the Voltage Oscillation in a Power Conversion System with DC-Link Capacitors

Capacitors are usually utilized at the DC-link of a power conversion system. Generally low parasitic inductance capacitors such as ceramic capacitors and film capacitors can reduce overshoot voltage during switching and DC bulk capacitors can address the low-frequency ripple. Due to the parasitic inductance, the energy swinging between the two types of caps via parasitic inductance leads to the oscillation which is typically at Mega-Hertz level and increases the voltage stress and power loss of the power devices. This phenomenon has been discovered repeatedly in the power converters with bus bar, integrated power module, and device characterization setup. To investigate and address this oscillation, the mechanism behind this oscillation is analyzed in details via a frequency-domain model in this paper. The impact of various electrical parameters are summarized. The proposed analytical model is validated via SPICE simulation and experimental study.