Principle And Simulation Analysis For STATCOM To Suppress Subsynchronous Oscillation

Due to the inverse distribution of coal endowment and economic development in China, high-voltage large-capacity and far-distance power transmittion becomes one of the dominant forms. To increase system stability and transmittion capacity, fixed series compansation is an economic and effective resolution. However, Subsynchronous Oscillation(SSO) problem caused by capacitor compansation shall not be neglected,which will threaten the safety of power grids.Static Synchronous Compensator(STATCOM) is a kind of Flexible AC Transmission Systems(FACTS),which consists of fully controlled power devices and is connected to the power system in parallel and. It can compensate the reactive power in both capacitive and inductive range and have high response speed. More obvious damping effect could be realised through using STATCOM as SSO suppressing device. Main research content of this thesis paper includes:(1) Based on IEEE first benchmark model which is a single generator infinite bus system, complex torque coefficient approach is used to mathematically deduce the principle of STATCOM suppressing SSO. The result indicates that if the phase difference between system voltage of access point and subsynchronous component of Sinusoidal Pulse Width Modulation(SPWM) signal is equal to180degree, STATCOM can provide positive damping for power system. Then based on damping coefficient produced by STATCOM, the factors which affects the positive damping are analysed.(2) This paper analyses and compares two kinds of additional damping control strategies, which are commonly used in the simulation of STATCOM for damping SSO. A kind of control strategy for exclusively mitigating SSO using STATCOM is proposed and frequncy scanning method based on complex torque coefficient method is used to simulating the damping of system with STATCOM in operation. Time domain simulation method is used to confirm the suppression effect of STATCOM. Simulation results indicate that this kind of STATCOM exclusively for SSO mitigation has better effect.(3)A real power system with SSO problem has been constructed based on Real Time Digital Simulator(RTDS). Using STATCOM model provided by RTDS, real time digital closed loop simulation is done with the control strategy exclusively for SSO mitigation, which provides further evidence that STATCOM with this kind of control strategy has better effect. And the work establishes the foundation for the research and development of the physical machine.