Dynamic modeling of a TCSC with application to SSR analysis

Conventional subsynchronous resonance (SSR) study methods such as eigenanalysis require a linear dynamic model of each device. FACTS devices such as thyristor-controlled series capacitors (TCSC) are difficult to model due to their nonlinear switching behaviour. Linearizing the TCSC steady-state average model is inadequate as this does not model the passive damping associated with the open-loop operation of a TCSC. The proposed approach exploits the fact that the thyristor controlled reactor associated with the TCSC is switched in a regular pattern. A linear model is obtained by linearizing the half-period map associated with sampling the TCSC capacitor voltage twice every cycle. Such an approach models the passive damping which varies with the steady-state conduction angle of the TCSC. It is shown that passive damping has a significant effect on the modal damping of the torsional modes associated with subsynchronous resonance phenomena.