A coordination scheme of FACTS-based WADC to improve small signal stability with transient stability constraints in multi-machine system

With the advent of smart-grid technology, the wide application of FACTS (Flexible AC Transmission Systems)- based damping controllers exerts influences on both small signal stability and transient stability. Traditional Modal Analysis (MA) method can hardly meet the requirements of online applications. According to the inter-area oscillation mode to be studied, the multi-machine system can be equivalent to a two-machine system, and the Wide-Area Measurement System (WAMS) supports real-time dynamic equivalents. This paper explores the electric torque analysis (ETA) method in the two-machine system and the criteria of stability. An online coordination scheme of SVC-based Wide-Area Damping Controller (WADC) to maximize the damping ratio of the inter-area mode with the transient stability constraints is presented in this paper. The scheme is treated as an optimization issue and a plant growth simulation algorithm (PGSA) is employed to search for the optimal controller parameters. A 4-machine-2-area benchmark is used to verify the effectiveness and advantages of the proposed scheme for online applications.