A Variable Switching Frequency Control for ZVS Three-Phase Three-Level T-Type Inverter Using Hybrid Discontinuous PWM

In this article, a variable switching frequency zero voltage switching (ZVS) control strategy is proposed for three-phase three-level neutral-point-clamped (3L-NPC) T-type inverter. A hybrid discontinuous pulsewidth modulation method is adopted. Full-range ZVS can be achieved at any load or modulation index without any additional sensors, auxiliary circuits, or current zero-crossing detection (ZCD) circuits. Meanwhile, neutral-point voltage self-balancing can be achieved naturally. The boundary switching frequency can be easily calculated in a digital controller based on inductor current ripple prediction instead of ZCD. The switching loss can be significantly reduced even operating at hundreds of kilohertz using silicon carbide MOSFETs. Owing to the high switching frequency and extremely low inductance, the power density and the dynamic response can also be improved. The size and the cost of the 3L-NPC inverter are greatly reduced. A 6-kW experimental prototype interfacing an 800 V dc with three-phase 380 V ac is developed to verify the proposed method.