Study On Mitigation Of Subsynchronous Oscillation Based On SVC And TCSC

Series capacitors compensation is widely used in transmission lines to cut down losses, enhance the transmission capability and thus promote economic benefits. However, disturbance in power systems with series capacitors compensated in transmission lines would raise the danger of subsynchronous resonance (SSR). Development in power electronics advances flexible AC transmission systems (FACTS) greatly, which contributes the widely use of FACTS device in all fields of power systems research, and damping of subsynchronous oscillation (SSO) is no exception.A brief introduction is made to the main content of SSO research in this paper firstly, along with detailed analysis of the modeling of a turbogenerator shaft system. After a summarily presentation of principles of FACTS for SSO mitigation, a procedure of designing Supplementary Subsynchronous Damping Controller(SSDC) applied in this thesis is given. Then it comes to the main part of the paper:research on damping of SSO using Thyristor Controlled Series Capacitor (TCSC) and Static Var compensator (SVC).Given the fact that it’s almost impossible to suppress SSO for TCSC with conventional control methodologies, a SSDC is designed, adopting sub-modal control method and modified modal control method separately. The effectiveness of the controller is validated using modified IEEE SSR first benchmark model by means of electrical damping analysis and time domain simulation, taken the location of TCSC into consideration. Knowing that TCSC is always used together with fixed capacitor, so according to different ratio of TCSC/fixed capacitor, different controller parameters are given, and then the electrical damping is evaluated for benchmark model with TCSC and its SSDC. Finally time domain simulation in PSCAD/EMTDC is employed to verify the results of electrical damping analysis, that is the SSDC can mitigate SSO successfully.Static Var compensator (SVC) is widely used in power systems for its strong ability of voltage control and reactive power support but comparatively low cost, however neither SVC open-loop control nor closed-loop with automatic voltage regulator (AVR) is proved to be effective to mitigate SSO. Based on the idea of sub-modal control, a SSDC is designed to solve the SSO problem. The electrical damping of SVC with the designed SSDC is obtained, using the test signal method, the electrical damping when the location of SVC and rated capacity changes is also acquired. At last, the effectiveness of the SSDC is verified by time domain simulation carried out in PSCAD/EMTDC.