Reliable transformerless battery energy storage systems based on cascade dual-boost/buck converters

In this study, the cascade dual-boost/buck half-bridge and full-bridge bidirectional ac-dc converters are proposed for grid-tie transformerless battery energy storage systems (BESSs). The proposed converter contains the advantages of the traditional cascade H-bridge (CHB) converter. However, compared with CHB converter, there is no shoot-through issue in the proposed converter, which is more reliable for BESS. In addition, a unified control scheme is proposed for active-power control and individual state-of-charge-balancing control of BESS, which is very modular and easy to implement. At the end, a laboratory BESS is constructed and tested combining a cascade two-unit dual-boost/buck half-bridge converter with nine lead-acid series-connected battery units. Experimental results obtained from the laboratory system verified the feasibility and effectiveness of the proposed BESS and unified control scheme.