SSR mitigation with TCSC in power systems

Thyristor-Controlled Series Capacitor (TCSC) is considered as solutions to the fast increasing demand in modern power systems. The TCSC project located at Hutton substation in the Great Britain (GB) power system is used to reinforce the existing transmission line to meet the 2020 target by introducing more renewable energy into the network. It is also able to provide system stability improvement and Sub-Synchronous Resonance (SSR) mitigation with its flexbile operational princinples. SSR problems in power systems are caused by the interaction between the mechanical turbine shaft system and the electrical system resonance. The capability of TCSC in SSR mitigation in High Voltage Alternative Current (HVAC) systems is investigated. The study is conducted in two aspects, the inherent capability of TCSC to mitigate SSR and the active control scheme of TCSC for SSR damping. The operational principle of TCSC and the dynamic performance of TCSC under SSR impacts are analysed. It is found that the regulation of thyristors allows TCSC to transform sub-synchronous components into fundamental components. This ability of TCSC contributes to an improvement in SSR damping. A Sub-Synchronous Damping Controller (SSDC) for TCSC is to secure the mitigation of SSR. But conventional SSDC has its limitations and challenges in implementation. These limitations include communication delays due to remote information transmitting at the generator side and the poor performance of bandpass filters due to its variable frequency response. A new SSDC scheme is proposed to solve the limitations and to improve the performance of SSR damping. A physical TCSC device is designed and implemented at the laboratory scale. By interconnecting with Real-Time Digital Simulation (RTDS) and Power Amplifier (PA), III a TCSC platform is set up to perform experimental tests. The effectiveness of the proposed SSDC scheme is validated with both simulation software on PSCAD/EMTDC and the TCSC platform. The simulation results agree with the experimental test results. The developed TCSC platform can be utilised for testing other control schemes for SSR mitigations.