Light Load Efficiency Improvement for CRM-Based Soft-Switching Three-Phase Inverter

This paper proposes a phase shedding control to improve light load efficiency for a two-channel paralleled three-phase inverter on the basis of a critical conduction mode (CRM)-based soft-switching technique. With the soft-switching method, switching frequency of the inverter increases significantly under light load condition leading to high switching loss. To reduce the loss, phase shedding for the second channel is conducted, which makes the first channel handle more power and lowers the switching frequency. The phase shedding is only applied to two phases in the second channel operating at high frequency to get rid of undesired circulating current between the two channels caused by the shared zero sequence voltage in the paralleled inverter structure. The proposed control method substantially curtails the switching loss and improves efficiency at light load. In this paper, the operation principle of the paralleled three-phase inverter with the proposed control and the analysis of the circulating current are discussed. Experimental results with a 25-kW SiC-based laboratory prototype shows that efficiency is improved by 0.5 to 2.4 % under different light load conditions.