Study On Suppression Of Subsynchronous Oscillation In Power System Applied TCSC

The water resources are mainly distributed in the Midwest and most of the electricity load was distributed in the eastern coastal region, therefore a long-distance transmission was needed to send the Large-capacity electrical energy in our country. Series capacitor compensation technology has the ability to improve the transmission capacity of the AC transmission lines, control power distribution between the parallel lines and enhance the transient stability of power system. However, the system of series compensated transmission lines are easily lead to instability of the Sub-synchronous oscillation(SSO), which consists of the coupled generator and the network and excited each other; caused the generator shaft torsional vibration, accelerated fatigue accumulation, Cut expected work life and thus threaten the security and stability operation of the Power system. Flexible AC Transmission Systems (FACTS) have the flexible and rapid adjust ability, which based on power semiconductor devices, have been widely used.This paper selects thyristor controlled series capacitor (TCSC) to suppression the SSO of system as the research object, the mechanism of sub-synchronous oscillation and related research methods are described briefly, the test signal method was used to analysis the system electrical damping which based on IEEE first benchmark case for sub-synchronous resonance studies. The time domain simulation model of TCSC was established, the fundamental frequency, sub-frequency and harmonic frequency haracteristics was studied detailed, the unit capacity cost function of Fixed Series Capacitor(FSC) was explored as well as the optimal capacity ratio between TCSC and FSC in suppression of subsynchronous oscillation was researched. The optimal control parameters of TCSC based on IEEE first benchmark sysystem was researched. Because of the fact that TCSC can’t provide adequate electrical damping for system, a SSDC is designed, adopting sub-modal control method. The electrical damping of system was analyzed when TCSC operated on open loop control, close loop control and switching on SSDC separately. And considering the superiority that prony algorithm doesn’t depend on the specific model, the effectiveness of test signal method was validated.Take a typical two-machine system as an example, The application of TCSC to suppress SSO in multi-machine system is researched as well as the equivalence classification and the particular double resonance peak phenomenon; Take into account the different working condition that same type machines in a power plant, different type machines in a power plant and Two machines in different power plants, The effectiveness and necessity is studied separately when applied TCSC to suppress SSO. Prony algorithm is used to validate the stability of system; the reasons why two machines in different power plants do not easy to inspire each others shaft torsional vibration are explained. Finally, the effectiveness of TCSC and SSDC in suppression of subsynchronous oscillation is verified by time-domain simulation in PSCAD/EMTDC.