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.Index Terms-Active-power control, cascade converter, EDLC (electric double layer capacitor), energy storage system, voltagebalancing control.
SUMMARYThis paper deals with a 6.6-kV transformerless STATCOM cascading multiple single-phase H-bridge PWM converters in each phase. The AC voltage of the STATCOM is almost sinusoidal, so that it requires no harmonic filter. Each converter is equipped with a capacitor and a voltage sensor on the DC side, which are electrically isolated from each other. The STATCOM has the capability of self-starting and voltage-balancing without any external power supply or equipment. Experiments using a threephase 200-V, 10-kVA laboratory system, along with computer simulations, are carried out to confirm the viability and effectiveness of the STATCOM.
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