A Transformerless Energy Storage System Based on a Cascade PWM Converter with Star-Configuration

This paper describes a 6.6-kV transformerless energy storage system based on a cascade PWM converter with star-configuration. The system is intended to make a power system reliable and efficient, and to improve power quality in power systems. The paper pays attention to active-power control and voltage-balancing control that are indispensable for proper operation of the energy storage system. A 200-V, 10-kW, 8.8-kJ down-scaled laboratory system is designed, constructed, and tested replacing EDLCs (electric double layer capacitors) with large-capacity electrolytic capacitors. Experimental results obtained from the laboratory system verify the viability and effectiveness of the 6.6-kV system.