High-efficiency three-phase bidirectional dc-ac converter for energy storage systems

This study presents a high-efficiency three-phase bidirectional dc-ac converter for use in energy storage systems (ESSs). The proposed converter comprises a modified three-level T-type converter (M3LT(2)C) and a three-level bidirectional dc-dc converter. The M3LT(2)C comprises two T-type cells to interface with a three-phase grid. By directly connecting the S-phase of the grid to a neutral point on the dc link, the active and passive components are required for only two grid phases, which reduces power losses, system volume, and production cost. A direct nominal voltage compensation control algorithm enables the converter to obtain high grid power quality. Also, the three-level bidirectional dc-dc converter enables low switching and conduction losses with reduced voltage stress across the switches. In addition, a simple dc-link voltage-balancing algorithm enables the balancing of two split dc-link capacitor voltages. To confirm the theoretical analysis of the proposed converter and assess its validity, a 10-kW prototype was implemented and tested.