A fast filtering scheme for capacitor voltages of a cascaded H-bridge multilevel converter based STATCOM

In this paper a capacitor voltage filtering scheme for a cascaded H-bridge (CHB) multilevel converter based STATCOM is proposed. The scheme is based on an analytic formula derived from the system model in order to cancel out the low frequency ripple of the capacitors voltages. The scheme remains effective even under high magnitude voltage ripple which would be present when lower capacitance film capacitors are used. Hence, the scheme would enable the use of reliable film capacitors instead of conventional electrolytic capacitors in the CHB multilevel converter based STATCOM system. Another advantage of the proposed scheme is that imposes only a negligible delay to the control system. Simulations on a 1100 W, single-phase, 7-level CHB converter based STATCOM confirm viability of the proposed filtering scheme.