Control scheme to improve DPFC performance during series converter failures

The Distributed Power Flow Controller (DPFC) is a new device within the FACTS family. It is emerged from the UPFC and has relatively low cost and a high reliability. The DPFC consists of two types of converters that are in shunt and series connected to grids. The common dc link between the shunt and the series converters is eliminated. The active power exchange between the shunt and series converters that is through the common dc link in the UPFC, is now though the transmission line at the 3rd harmonic frequency. The redundancy of the series converters provides the high reliability of the system. In this paper, the DPFC behavior during the failure of a single series converter unit is considered. A control scheme to improve the DPFC performance during the failure is proposed. The principle of the control is based on the facts that, the failure of single series converter will lead to unsymmetrical current at the fundamental frequency. By controlling the negative and zero sequence current to zero, the failure of the series converter is compensated. In this paper, the principle of the DPFC are firstly introduced, and followed by the behavior of the DPFC during the failure of a single series converter. The design of the control scheme and corresponding simulation are presented.