Analysis of supplementary controls in damping subsynchronous oscillations

Analysis and damping of torsional oscillations through thyristor controlled reactors (TCR) is presented in this paper. The reactive power control is achieved through TCR at the machine terminals. Generator speed signal is used as the auxiliary signal and the terminal voltage feedback signal as the main control signal for the TCR. The following control strategies for auxiliary control of TCRs have been analysed: (1) analysis of basic system without damping controls; (2) proportional control; (3) proportional control with filter; (4) proportional derivative control filter; and (5) proportional plus integral plus derivative control with filter. The main objective of this paper is to discuss the performance of different control strategies for damping torsional oscillations when a generator is connected to an infinite bus via a double circuit 400 kV transmission line, in which one circuit is series compensated. This configuration is similar to IEEE benchmark two model.