Light Load Efficiency Improvement for Two-Channel Paralleled Soft-Switching Three-Phase Inverter Using Phase Shedding Control

This article explores how to improve the light load efficiency of a critical conduction mode (CRM)-based two-channel paralleled soft-switching three-phase inverter. Although the CRM-based soft-switching scheme achieves high efficiency at heavy load, the efficiency drops rapidly as the output power decreases. Its CRM-based operation makes the switching frequency soar because of the small inductor currents at light load giving rise to the high switching-related loss. To enlarge the inductor current handled by the first channel of the inverter, a phase shedding control is proposed to not excite gate signals for the second channel, thus bringing the first channel's frequency down. The phase shedding is put into effect to only two phases in the second channel running at high frequency to circumvent the undesired circulating current in the two-channel paralleled inverter structure. In addition, for very light load conditions (below 10%), frequency limiting methods are introduced in conjunction with the phase shedding to further improve the efficiency. Experimental results with a 25-kW SiC-based inverter prototype verify that the phase shedding control improves the light load efficiency by 0.5 to 3.9%. It is further improved by 0.3 to 1.3% with the frequency limiting under very light load conditions.