| With the global warming and increasing environmental problems, more and more attention are focused on the use of renewable energy. As huge reserves of clean energy, wind power is currently being widely concerned. Since wind energy mainly concentrated in remote areas and large numbers of power load are concentrated in the eastern coastal areas, which makes cross-regional long-distance transmission become an inevitable trend. In order to reduce the energy loss in the transmission process, series compensation capacitor is often installed in the transmission lines to improving transmission capacity and reduce losses. Transmission line installed with series compensators would raise the problem of subsynchronous resonance(SSR), which may endanger the safe and stable operation of system.Currently DFIG is the main model in wind power generation, the phenomenon of SSR has been found in DFIG wind farms which caused by the series compensation. Taking the evolution model of the first IEEE standard model as an example, the detailed model of series compensation doubly-fed wind power transmission systems is constructed. According to lyapunov small signal stability analysis method, the research model is built in the Matlab/Simulink simulation platform, and the eigenvalues of the characteristic matrix are calculated to analyze the relationship between series compensation and the system stability. Meanwhile, verification analysis is operated on PSACD/EMTDC transient simulation software. Studies show that the higher degree of series compensation, the higher possibility to evoke SSR. The reason for high degree of series compensation trigger SSR is the induction generator effect occurred.Most studies use an equivalent generator to replace a certain number of generators in DFIG wind farms. And most regard the wind speed as the same, which have great error with the actual scene. According to the principle of wind turbine, a concept of equivalent wind speed is put forward in this paper, and a new way based on this method to build equivalent wind farm model is created. A specific wind farm model is studied for steady state analysis and dynamic analysis under the same and different operation conditions, and the equivalent model is compared with the detail model to verify model adaptability. Study found that the aggregated model based on the method of equivalent wind speed is reasonable for static analysis and part of dynamic behavior, but the model need further modification when apply to SSR study. The generations should be divided according to different wind speeds to construct the detail model.Gate Controlled Series Capacitor(GCSC) is an important member of the family of FACTS. At this paper, the structure of GCSC, regular operation mode and structure of controller have been introduced, and the harmonic situation of GCSC has also been analyzed in detail. The open and closed loop control mode of GCSC have been studied comparatively to find the result in suppressing SSR. Using a desired impedance as the control target was found can not reduce the risk of subsynchronous resonance at maximum extent. Then an additional damping control strategy was proposed in this paper, taking the generator speed or the line current as the input control signal. After the electrical damping analysis, the line current was found to have a better inhibition result when take it as the input control signal. In order to verify the correctness of this analysis, then the two different input control signal are simulation analyzed respectively in this paper. The simulation result are consistent with theoretical analysis. |
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