Circulating current derivation and comprehensive compensation of cascaded STATCOM under asymmetrical voltage conditions

Abstract

Cascaded static synchronous compensator (STATCOM) with delta‐connected configuration is an effective solution to compensate reactive and negative‐sequence currents. This study focuses on the circulating current and compensation method of delta‐connected STATCOM under asymmetrical voltage conditions. According to the phasor analysis, constrains of voltage phasors and current phasors under reactive current compensation mode, negative‐sequence current compensation mode and comprehensive compensation mode are deduced. On the basis of this, the analytical expressions of circulating current under the three modes are derived. Furthermore, a comprehensive compensation method for delta‐connected STATCOM is proposed. In the proposed method, phase current references are calculated directly with the instantaneous voltage and current signals, which could enhance the dynamic behaviour and cluster‐balancing control performance especially under asymmetrical voltage conditions. Finally, simulation and experiment results have been given to verify the effectiveness and feasibility of the proposed control method.