Analytic Model of the Voltage Oscillation in a High-Power Converter With Silicon Carbide Devices

Parasitic inductance in the power conversion system can introduce various problems such as voltage overshoot and ringing, thus increasing the EMI noise and the risk of switching failures. The application of wide bandgap devices can worsen these problems due to a higher switching slew rate. DC-link capacitors are usually utilized to maintain the DC voltage and filter out oscillations. Generally, capacitors with low equivalent series inductance (ESL), such as ceramic capacitors, can be utilized in the DC-link to suppress the voltage overshoot and large capacitors can mitigate the voltage ripples. The DC-link capacitors, circuit ESL, and junction capacitance of the power device can form a high-order network and introduce energy swinging into the system during the switching event. In this article, the fundamental mechanism of the voltage oscillation caused by hard turn-off of the power device is comprehensively analyzed via a mathematic model. How different parameters affect the oscillation is quantified and summarized. It can be utilized for future design optimization of the power conversion system. Several solutions for DC-link oscillation and spikes are introduced. The proposed analytical model and proposed solutions are validated via simulation and experimental study with silicon carbide devices.

I. Introduction

A high-power conversion system which is typically comprised of a bus bar, power module, and control system [1], [2] is a critical part of heavy equipment such as traction inverter, air conditioner compressor, and electrified propulsion [3]. As the energy conversion hub, the design of bus bars determines the performance of the converter since the parasitic parameters in the power loop may affect the overshoot voltage, oscillation, and electromagnetic interference (EMI) noise [4]. The aforementioned problems may be worsened due to the increasing switching slew rate brought by the wide application of wide bandgap (WBG) devices particularly the silicon carbide (SiC) devices. However, the increasing penetration of WBG devices is an evitable trend since they enable the converter to realize higher power density [5], [6].