A New Method Of Damping Subsynchronous Resonance Based On STATCOM

With the increasing construction of thermal plants and the project of West-East power transmission, large-scale and long distance electricity transmission will be the trend of grid in China, and high voltage AC transmission lines with series compensator is a practical solution. However, synchronous generators being connected with AC fixed series compensated transmission lines may cause subsynchronous resonance(SSR). This paper introduces basic concepts and analysis methods of SSR, and then studies a control method based on STATCOM to damping SSR. And the SSR risk of Shen Hua thermal plants based on planning grid structure is evaluated. Time domain simulations are done to validate the effectiveness of the mentioned SSR damping control strategy.In this paper, firstly, the basic concepts of SSR and common damping method are introduced, and practical SSR damping projects in China are listed. Secondly, small signal mathematical models of rotor shaft, synchronous machine and AC transmission lines with fixed compensator are built, common analysis methods of SSR with their range of application are introduced, an evaluation method on mode electrical damping of a simplified power system are given based on complex torque methods. Some suggestions are also given about evaluating the SSR risk of large power system. Then a control method based on STATCOM injecting active and reactive mode currents into synchronous machine to damping SSR is introduced. Factors that influence the damping provided by STATCOM such as parameters of components in the grid and operating condition of SG are analyzed. An optimal control method to provide the biggest damping of STATCOM is also introduced. Time domain simulations are done in PSCAD/EMTDC to validate the theory and control method above. At last, using analysis methods introduced above, the SSR risk of Shen Hua thermal plants based on planning grid structure is analyzed, and the SSR damping strategy is applied on shenhua synchronous machines to validate its effectiveness.