Active Common Mode Voltage Cancellation in SiC-based NPL.H Inverter with Imbalanced Load

Multilevel inverters (MLIs) combined with wide bandgap (WBG) power devices are increasingly gaining popularity in high-power density motor drives. However, the enhanced switching capabilities of WBG devices can exacerbate electromagnetic interference (EMI). The neutral-point-less H-type (NPL.H) inverter topology offers active common mode voltage (CMV) cancellation, thereby achieving EMI noise reduction. However, the EMI noise reduction performance is highly dependent on the symmetricity of two equal and opposite CMV waveforms, which can be distorted under unbalanced load conditions. Given that motor loads can exhibit imbalances over $10 \%$, the impact of such unbalance on CMV cancellation in the NPL.H inverter has not been thoroughly investigated. This paper provides a concise overview of the benefits and design considerations of the NPL.H inverter. The influence of load imbalance on inverter operation and CMV cancellation is analyzed using incrementally increased imbalance in the load. Simulation results reveal that, while CMV cancellation is not perfect, the NPL.H inverter is still able to achieve a major reduction in CMV as compared to a conventional MLI without active cancellation. A prototype inverter was constructed and tested with an RL load to validate its performance under practical imbalance conditions, demonstrating up to ${5 0 \%}$ reduction in individual peak CMV and an ${8 0 \%}$ reduction in sustained CMV voltage levels through active cancellation compared to conventional MLIs without active CMV cancellation.