Light Load Efficiency Improvement for Distributed Battery Energy Storage System

A light load efficiency improvement approach for distributed battery energy storage system (BESS) is analyzed in detail. The system is constructed by the non-isolated bidirectional DC-DC converters (BDC) integrated a buck-boost BDC with a dual-active half-bridge (DAHB) BDC. With the equivalent DAHB BDCs in parallel connection and the buck-boost BDCs high voltage side in parallel connection, the independent battery charging and discharging can be realized to obtain the state of charge (SOC) balance. Meanwhile, an additional low voltage DC bus is generated. Hence the high voltage side circuit in some DAHB BDCs can remain off at light load to decrease the total power losses while the battery input or output power can be transferred through this low voltage DC-bus to ensure the battery balance. While at heavier load, all the non-isolated BDCs are operated independently with no power transferred through the low voltage DC-bus. System architecture and the light load efficiency improvement method are analyzed. Experimental tests based on two 1kW prototypes verify the effectiveness of the approach.