DC-side series active power filter for STATCOM performance under system faults

Voltage-Sourced Converter (VSC) 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. This type of the STATCOM is fired at line frequency to lower the switching losses. There are considerable numbers of angle-controlled STATCOMs installed in the different utilities in the United States. Despite the high efficiency and good voltage quality, this type of the STATCOM is showing 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. Proposed solution is based on adding a single phase inverter in series with converter DC-bus. This single phase inverter generates controllable oscillations with twice the line frequency on the DC-link voltage which will be reflected as negative sequence voltage at VSC output terminals. Generated negative sequence voltage limits the fault negative sequence current flow on the STATCOM tie line. Based on the proposed Solution one specific controller is designed which provides the capability of simultaneous controlling of the both positive and negative sequence voltages. The results are supported by detailed simulation studies on the New York Power Authority (NYPA) STATCOM model using the PSCAD/EMTDC.