Enhancing stability of a weakly connected AC power system by supplementary control of embedded HVDC lines

This paper deals with supplementary control of HVDC lines embedded to a weakly connected AC transmission system in order to enlarge power transfer ability and to enhance the transient stability. The proposed control is a WAMS-based control modulating the real and reactive power at the terminals of the HVDC lines. Relevant control formulas have been derived for a linear multi-machine system model with the application of the direct Lyapunov method. Validity and robustness of the proposed control has been verified by computer simulation for a nonlinear model of a multi-machine test system. The proposed control is robust and insensitive to changes in the network configuration and loading conditions in the AC power system. Moreover, the proposed control produces additive damping i.e. each controlled HVDC line contributes to positive damping in AC power system.