A novel control strategy for Dc voltage stability and balancing in cascade STATCOM based on droop characteristic

Cascade STATCOM is constructed by cascading several identical H-bridge (single-phase full bridge) inverters, each with their own isolated DC bus. Since DC capacitors of cascade STATCOM are separate, their voltage may not be exactly balanced during operation periods. This paper presents a droop characteristic of DC voltage of H-bridge inverters, and a novel control strategy for DC voltage stability and balancing in cascade STATCOM based on this characteristic has realized. The validity and feasibility of this control strategy is verified by simulation results, and has been used on a practical engineering of plusmn4.33 Mvar STATCOM. Based on this, a basic insurance and good platform is provided for the study and development of cascade STATCOM, and has very important reference value for other cascade power conversion devices.