Operation scheme for MMC-based STATCOM using modified instantaneous symmetrical components

Abstract

Modular multilevel converters (MMCs) are characterized by modularization and multielectric equality, andthe application of this structure to a high-voltage large-capacity static synchronous compensator (STATCOM) showsgood potential. In this paper, a modified instantaneous symmetrical component method is proposed for positive- andnegative-sequence decomposition, i.e. the critical part of the control device, which can accurately detect the instantaneousvalue of each sequence component in three-phase asymmetrical phasors in real time. Then, based on this method, thepaper proposes a control method for MMC-based STATCOMs that solves the problems of multi-DC (direct current)voltage balance, grid-connected current control, and circulation suppression. Finally, the proposed detection and controlmethods are verified by performing simulations and experiments. The results show that the proposed method can quicklyand accurately detect the positive- and negative-sequence reactive component that should be compensated by the device,thus realizing real-time reactive compensation for MMC-based STATCOMs.