Decentralized Synchronization of AC-Stacked Voltage Source Converters

A decentralized control method is proposed for a system of multiple voltage source converters (VSC) stacked in series on the AC side. Using the proposed method, a group of low-voltage rated VSC modules can be utilized to implement converters for medium/high voltage grid-tied applications. Each converter module can maintain synchronization using only its local measurements without any communication or any form of centralized synchronization signal. A mathematical model of such a system consisting of N number of VSC modules employing the proposed control scheme is presented and a linearized model is developed for small signal stability assessment. The proposed method is robust against grid frequency variation and can naturally correct power sharing errors among modules caused by sensor inaccuracies or reference mismatches. Real time simulation results are presented to validate the proposed controller.