Current Injection Methods for Ripple-Current Suppression in Delta-Configured Split-Battery Energy Storage

Cascaded H-bridge (CHB) converters are receiving growing attention in battery energy storage systems (BESS) due to their modularity and flexibility. However, direct generation of ac output in CHB-BESSs incurs large second-order current ripple in the batteries, which causes additional loss and might accelerate battery aging. Existing methods for ripple-current suppression usually require bulky passive components due to the high energy content of the ripple components. This paper presents a class of current injection methods for delta-configured CHB-BESSs. The injected currents flow through the CHB arms and transfer the original second-order oscillating power to the fourth or the sixth order, or even to an arbitrarily high-order frequency. As such, the battery current ripple appears at much higher frequencies with lower oscillating energy and can be easily filtered by small passive components. In the laboratory setup, the proposed methods reduced the battery root-mean-square current ripple to less than 10% of the dc component with negligible distortion in the loads. The proposed methods and the filter implementations show good tolerance to load frequencies and to the control error of the injected currents.