Analysis of Subsynchronous Oscillation (SSO) Damping Characteristic of the AC/HVDC Parallel Transmission System Using TCSC

The complex torque coefficient approach realized by time domain simulation (the test signal method) is adopted in this paper to study the SSO problem for an AC/HVDC parallel transmission system. In order to analyze the effects of the damping characteristic of the system oscillations with TCSC in this new grid structure, three cases have been adopted: the normal AC system with HVDC lines, the system with FSC and HVDC lines, the system with FSC+TCSC and HVDC lines. The results showed that TCSC not only can inhibit the SSO, but also can improve the damping characteristic performance of the transmission system with HVDC. The results also demonstrated that the impedance characteristic of TCSC is related with the value of conduction angle, which will affect the damping characteristic performance of system.