Elimination of Overshoot and Oscillation in the Auxiliary Branch of a SiC Auxiliary Resonant Commutated Pole Inverter (ARCPI)

This paper investigates the mechanism of the overshoot and oscillation in the auxiliary branch and its elimination in a silicon carbide (SiC) auxiliary resonant commutated pole inverter (ARCPI). A mathematical model of the auxiliary branch including the parasitic capacitance of SiC MOSFETs has been derived, which reveals the oscillation mechanism in the auxiliary branch. The model shows that this oscillation is an inherent characteristic of the SiC ARCPI. To eliminate the overshoot and oscillation, a SiC ARCPI with two clamping diodes inserted between the DC bus and the auxiliary branch has been presented. The proposed auxiliary branch oscillation model and the performance of the clamped ARCPI are validated on a 3-kW, 3-phase SiC ARCPI prototype. Even though the overshoot and oscillation in the auxiliary branch has an insignificant impact on the output voltage, experimental results show that without clamping, the overshoot is more than 150% and the oscillation frequency is higher than 4 MHz. This significantly increases the required voltage ratings of the devices in the auxiliary branch. Furthermore, the overshoot and oscillation frequency in the auxiliary branch increases with the DC bus voltage because the output capacitance of the SiC MOSFETs reduces with the voltage. This degrade the electromagnetic interference (EMI) performance of the SiC ARCPI. In comparison, the clamped SiC ARCPI can mitigate the overshoot and oscillation and improve the EMI performance of the auxiliary branch. Specifically, around 6 MHz the spectral amplitude can be reduced by about 17% by the clamped ARCPI.