A Hybrid DPWM Based Variable Switching Frequency Scheme for ZVS Three-Phase Three-Level Neutral-Point-Clamped Inverter

In this article, a hybrid discontinuous pulsewidth modulation (DPWM) based variable switching frequency scheme to achieve zero voltage switching (ZVS) is proposed for the three-phase three-level neutral-point-clamped (NPC) inverter. The switching frequency can be calculated based on current ripple prediction using fully digital control without zero-crossing detection circuits. The dc-link neutral point voltage can also achieve self-balancing utilizing the hybrid DPWM method. The proposed ZVS scheme can not only improve the efficiency but also effectively balance the power loss among the four switches in each phase to simplify the thermal design. Owing to the high switching frequency and small filter parameters, the power density can be greatly increased. Finally, a 6.6-kW three-phase three-level NPC inverter experimental prototype using silicon carbide (SiC) mosfet s is built to verify the effectiveness of the proposed method.