A Three-Phase Partial Power Processing Soft-Switched Inverter

This article presents a three-phase partial-power-processing inverter with provisions to soft-switch over the entire cycle of the grid. Each modular phase of the inverter is constructed from a reconfigured dual-active half bridge (DAHB) that has been folded across its galvanic isolation and its primary and secondary sides placed in series through stacking. The power processed through each stacked DAHB is less than its output power, with the ratio between processed and output powers defined by the voltage conversion ratio of the stacked DAHB. Analysis of the stacked DAHB is presented within the framework of the Manhattan topology, a multilevel converter topology defined by a set of series stacked capacitors where there exists a scheme to transfer power between capacitors. The capacitive power transfer mechanism in the proposed is a DAHB. This analysis shows that the stacked DAHB operates as a controlled current source. This feature is leveraged by configuring three stacked DAHBs as a three-phase grid-following inverter where the inverter is only responsible for injecting a current into the grid. Two control schemes are provided, one with a constant switching frequency that is susceptible to hard-switching and another that uses a variable switching frequency to maintain soft-switching over the cycle of the grid. A 3 kW prototype is constructed using GaN FETs and a switching frequency of up to 1 MHz. Experimental efficiency, current quality, transient, and power step results are provided for the two different control schemes.