High-Power VSC-Based Simultaneous Positive- and Negative-Sequence Voltage Regulator

A voltage-source converter-based static synchronous compensator (STATCOM) is used in transmission and distribution systems for the purpose of voltage regulation and reactive power compensation. In the transmission level, angle-controlled STATCOMs are of primary interest due to their high efficiency and excellent waveform quality. There is a considerable number of angle-controlled STATCOMs installed in the different utilities in the U.S. Despite the high efficiency and good voltage quality, this type of STATCOM shows poor performance under ac system faults. They are usually tripped under severe unbalanced condition and system faults to protect the switches from huge negative-sequence current flow. This paper provides a solution to improve the transmission-level STATCOM performance under power system faults. The proposed solution is based on adding a single-phase inverter in series with the converter dc bus. One specific controller is designed which provides the capability of simultaneously controlling positive- and negative-sequence voltages. The results are supported by detailed simulation studies on the New York Power Authority STATCOM model using PSCAD/EMTDC.