Using a cascaded H-bridge STATCOM for rebalancing unbalanced voltages

This paper considers specific issues related to using the cascade (also known as the H-bridge) multilevel STATCOM with unbalanced voltages and currents at the STATCOM-AC line connection terminals. Under this condition the average power into the individual phase legs of the converter, in general, is not zero, although the total three phase power is zero. The resultant phase cluster power unbalance can result in increasing or decreasing capacitor voltages within a phase leg. This paper will present a technique for zeroing the phase cluster average power under unbalanced line conditions when the control strategy is to rebalance unbalanced voltages.