A Non-Isolated Bidirectional Three-Phase Unfolder for Energy Storage Systems

This paper proposes a bi-directional DC-AC converter for grid-integration of Energy Storage Systems (ESS). The converter has the advantages of line frequency switching for the inverter stage leading to lower switching losses, reduced requirement of DC-link capacitance as well as reduced grid-side filter size. The non-isolated topology ensures improved power density over isolated versions available in literature. The control strategy as well as simulation results for bidirectional power flow in a 5 kW rated system has been discussed in the paper. A 2.5 kW rated laboratory prototype has been made to validate the converter operation and control. Preliminary open loop hardware results with resistive load have been presented.