Current Ripple Prediction and DPWM-Based Variable Switching Frequency Control for Full ZVS Range Three-Phase Inverter

In this article, a variable switching frequency full zero-voltage switching (ZVS) range bidirectional three-phase voltage-source inverter is proposed. Discontinuous pulsewidth modulation is used so that at any time only two phase legs need to achieve ZVS. The boundary switching frequency can be calculated in a digital controller based on current ripple prediction instead of current zero-crossing detection. No additional high-frequency sensor or auxiliary circuit is needed. The frequency variation range is narrow in a line cycle at any load condition. An LCL filter is used to attenuate the inverter-side high ripple current and improve the grid current quality. Owing to the high switching frequency and the small filter parameters, the power density can be greatly increased. Both the device and the filter losses are reduced, and the efficiency is high. A 3.5 kW simulation and experimental prototype with silicon carbide (SiC) device interfacing 400 V dc with three-phase 110 V ac grid is developed to verify the effectiveness of the proposed control strategy.