Decoupled Control System for Cascaded H-Bridge Multilevel Converter Based STATCOM

In conventional control systems for a static synchronous compensator (STATCOM) based on a cascaded H-bridgemultilevel converter, the action of individual voltage controllers that balance capacitor voltages can alter the output of a cluster voltage controller and a current controller due to a coupling effect. In this paper, first, the conditions that eliminate this coupling effect are derived, and then, a control system that enforces the derived decoupling conditions is proposed. It is also shown that an additional advantage of the proposed decoupled control system is that it enables the linearization of a cluster voltage control loop. Experimental studies on a single-phase seven-level STATCOM demonstrate the effectiveness of the proposed decoupled control system in improving the transient performance of the STATCOM.