A Novel Balancing Method for DC Voltage of Cascaded Multilevel STATCOM

The stability of DC voltage is crucial to cascaded multilevel converter-based STATCOM. This paper introduces a hierarchical control scheme for DC voltage of cascaded STATCOM. The first layer of the control scheme maintains the phase voltage and the second layer balance the capacitor voltage within each phase. Specially, for the second layer we propose a novel method incorporating an extra balancing capacitor to redistribute energy among inverter modules. We develop two control strategies for the balancing process. Two-module five-level STATCOM was simulated as an example and results indicate that the proposed control scheme effectively stabilized the DC voltage. Finally, the two balancing strategies are theoretically compared.