Analysis And Mitigation Of Subsynchronous Oscillation Caused By Grid-Integration Of DFIG-Based Wind Farm Via Series Compensation

Wind energy is a renewable clean energy. Wind power has become the most mature, largest and the best commercial development way to power generation. Because the most wind farms are in remote areas and far away from the load centers, in order to transmit the large-scale wind power to the load centers, it need to take the series compensation technology. However, the series compensation technology can induce subsynchronous oscillation, and affect the stable operation of wind turbines. In this paper, subsynchronous oscillation caused by grid-integration of DFIG-based wind farm via series compensation is analyzed. The main contents include:First of all, the mathematical models of wind turbine, doubly-fed induction generator, dual PWM converter and its control systems are studied comprehensively. The system model for eigenvalue analysis of subsynchronous oscillation is built, which is based on IEEE first bench mark. The state equations are derived and state equations of the whole system is formed. The constraint equations of all algebraic variables are given in this process, which is more accurate. Program in MATLAB/Simulink software to calculate eigenvalues.Secondly, the impacts of series compensation level and wind speed on the grid mode and torsional mode are analyzed. For the subsynchronous control interaction(SSCI), The impacts of the proportion gain of current inner control and power outer control on SSCI are also analyzed and compared. The network mode is sensitive to the changes of current inner loop control parameters. Therefore, the current inner loop control parameters has great influence on subsynchronous control interaction(SSCI). In practical engineering, it is particularly important to set suitable current inner loop control parameters.Thirdly, a complete double-fed induction generator model is built in DigSILENT/Power Factory. Time domain simulations are made for subsynchronous oscillation caused by Grid-Integration of DFIG-Based Wind Farm via Series Compensation. Simulation results verify the correctness of the eigenvalue analysis results,Finally, static var compensator(SVC) is added to suppress subsynchronous oscillation in the basis of models for analyzing subsynchronous oscillation. Supplementary subsynchronous oscillation damping controller is designed. And the SVC model is built in DigSILENT/Power Factory. The simulation results show that, Supplementary subsynchronous oscillation damping controller can effectively suppress the subsynchronous oscillation. In addition, the capacity of the SVC also has some influence on its inhibitory effect. Increasing SVC capacity In a certain range can enhance the inhibition ability of subsynchronous oscillation effectively.