Resistive behavior of thyristor-controlled series capacitors at subsynchronous frequencies

The thyristor-controlled series capacitor (TCSC) does not have resistive main components in ideal form. Yet, a resistive behavior has been reported at subsynchronous frequencies for this device. The paper investigates the source of this resistance and suggests a way to compute it when a periodic steady state can be found or approximated for the test circuit. The results are compared with two methods proposed by other research groups, one for frequency response and the other for dynamic modeling of TCSC, which are also examined as to their treatment of the resistive behavior. Finally, three open-loop firing schemes are compared with respect to the impedance they present to subsynchronous currents.