A novel active damping control of TCSC for SSR suppression in a radial corridor

One of the favorite features of thyristor controlled series capacitors (TCSCs) is to provide inherent passive damping in suppressing torsional interaction (TI), which can cause the fatigue of turbine shaft or even damage. The power system can be highly exposed to such risks in the scenario where a thermal power plant is connected to a remote load center through a series compensated radial transfer corridor. This paper will use a real example to illustrate the TCSC capability under two different modulation strategies, constant firing angle control and synchronous voltage reversal (SVR). Then based on SVR strategy, a novel control strategy using pure local measurement is proposed to inject additive damping guaranteeing the system to be SSR free, regardless the trivial contribution of mechanical torque. The paper is organized as follows. Firstly, the operation mechanism of TCSC and two different firing strategies are briefly introduced. Furthermore, a test signal technique based on complex torque is used to scan electrical damping under subsynchronous frequency range through detailed electromagnetic transient simulation. Frequency scanning results show that SVR strategies can contribute with a much better performance than constant firing angle control, and damp the risk modes even under low boost level. Thus a novel active damping control scheme can be easily implemented to pull the remaining slight undamping into a secure range. Simulation results with detailed shaft spring-mass model validate its control effect.