Dual solutions analysis of TCSC in quasi-steady-state operation

Thyristor controlled series capacitor (TCSC) is expected to control line power flow, improve system stability, and enhance power transfer capability. The bottom control is the basis for TCSC applications, in which the relationship between frequency impedance and firing angle is the key factor. In this paper, the expression between firing angle and conduction angle is ascertained considering the resistance effects of reactor and thyristor valves firstly. Then the dual solutions phenomena is discovered and analyzed. This paper also points out that TCSC can just move along one branch of frequency impedance curve and do not step to the other one if only the firing angle is changed. Finally, the digital simulation and the data of dynamic simulation experiment all support the existence of dual solution phenomenon. Many conclusions and experiment results can provide reference for TCSC design.