Variable Switching Frequency Control for Three-Phase Four-Leg ZVS Inverter Under Arbitrary Resistive-Load Conditions

The three-phase four-leg inverter is a suitable topology to handle the three-phase unbalanced load operation. To improve the conversion efficiency while reducing the volume of passive elements, a variable switching frequency zero-voltage switching (ZVS) strategy is proposed for the three-phase four-leg inverter. Three-dimensional space vector discontinues pulse width modulation is adopted to simplify the switching frequency calculation. The frequency can be easily calculated by digital controllers. Based on the proposed control, the variation range of the switching frequency is narrow and the abrupt changes in the frequency is avoided. Additionally, the size of filter inductors is reduced due to current ripple requirement and high switching frequency. Thus, the power density is improved. Simulation and a 1.5kW experimental prototype are developed to verify the feasibility and effectiveness of the proposed control strategy.