A novel control algorithm for a static series synchronous compensator using a Cascaded H-bridge converter

This paper presents a novel control scheme for a Cascaded H-bridge (CHB) converter-based Static Series Synchronous Compensator (SSSC). The SSSC is a Flexible AC Transmission Systems (FACTS) device which is a Voltage Source Converter (VSC) connected in series with the transmission line and is primarily used for real power flow control over that transmission line. SSSCs can find applications in integration of renewable energy resources within modern power systems since they can allow transmission lines to transfer power beyond their stability limits. Further, SSSCs can be used as power oscillation damping (POD) controllers within an area. CHB-based SSSCs are advantageous as compared to conventional SSSCs since they eliminate the series transformer which usually interconnects the VSC with the transmission line. This paper proposes a DC capacitor charge-balancing algorithm for the CHB VSC specific to the SSSC operation. An eleven-level CHB-based SSSC was implemented in PSCAD along with the proposed voltage-balancing algorithms and its performance was evaluated in controlling real power flow along the transmission line.