Damping of power swings in large-scale AC power system by simultaneous control of HVDC links and series FACTS devices

The paper presents the algorithm of a simultaneous control of multiple HVDC links and series FACTS devices (such as phase angle regulator) to improve stability of an AC power system. The purpose of the study is to demonstrate that such stabilizing control, optimal from the perspective of the whole AC power system and insensitive to the loading condition and network configuration (robust control) may be clearly determined mathematically. The proposed method of control was derived using the direct Lyapunov method. The control system is a multi-loop control system using state variables as input signal, activated in the transient state and supplementary to the main steady-state control designed for regulating the power flow. Efficiency of the methods was confirmed with computer simulations. The algorithm perfectly damps the inter-area power swings, showing at this very high robustness to changes in network configuration, loading conditions. Moreover, the proposed control produces additive damping i.e. each controlled HVDC line and/or FACTS device contributes to positive damping in AC power system.