Damping of subsynchronous oscillations using STATCOM - a FACTS controller

Analysis and damping of torsional oscillations in series compensated transmission systems is presented in this paper. Series compensation of transmission lines connected to turbogenerators can result in subsynchronous resonance (SSR) leading to adverse torsional oscillations. The use of flexible AC transmission system (FACTS) controllers like static synchronous compensator (STATCOM) are increasing in the network for enhancing power transfer capability, dynamic voltage support and also damping of power oscillations. Many countermeasures to SSR problem have been reported in the literature, which makes use of signals available at the generator station. In this paper, the damping of subsynchronous oscillations using STATCOM, which is provided at the middle of the transmission line, is presented. The effectiveness of an auxiliary signal designated as computed internal angle (CIA), which modulates the voltage reference of STATCOM, is investigated. The auxiliary signal CIA is synthesized by local measurements of voltage and line current at the STATCOM bus. The IEEE second benchmark model is considered for the analysis. The analysis of SSR is carried out using eigenvalue analysis and results obtained are validated by transient simulation using MATLAB-SIMULINK.