A novel space vector modulation scheme for common-mode voltage reduction in the hybrid active neutral-point-clamped three-level inverter with balanced and unbalanced DC-links

The hybrid active neutral-point-clamped (HANPC) three-level inverter (TLI) requires much less SiC MOSFETs than a full-SiC ANPC TLI while providing comparable power density. Therefore, the HANPC TLI is an ideal solution for balancing performance and cost. However, excessive common-mode voltage (CMV) amplitudes are observed in conventional modulation methods, especially under unbalanced dc-links. This paper presents a CMV reduction method for the HANPC TLI with balanced and unbalanced dc-links. The scheme employs real-time sampling of photovoltaic array voltages on the dc side, followed by dynamic updates to the space vector diagram (SVD). Due to its inherent advantage of low CMV, zero vector and medium vectors are selected for reference vector synthesis. According to the position of the medium vectors in the updated SVD, the duty cycles are recalculated to ensure the output current quality. Furthermore, switching sequences are optimized through five-segment symmetrical patterning, ensuring minimal switching actions in power devices. Theoretical analysis demonstrates that this modulation method effectively reduces both the magnitude and root-mean-square (RMS) value of CMV while ensuring that SiC MOSFETs and Si IGBTs operate at high and low frequencies, respectively. The hardware-in-loop (HIL) tests validate the efficacy of the proposed modulation strategy.