Research On STATCOM For Reactive Compensation In Wind Farm

Due to the pressure of energy crisis and environmental pollution, clean and renewable resource get rapid development in recent years. Among these new resources, the development of wind power technology is most mature, and the proportion of its installed capacity in the power system is growing year by year. The impact of wind farms on grid stability get more and more attention.The wind farm has many impacts on power grid, such as:random changes of wind speed can lead to a fluctuation of the active power output of the wind farm. The voltage of connection point will also fluctuate when the reactive power compensation capacity of wind farm is insufficient. This may bring an adverse impact on voltage and operational stability of the power grid. In addition, when the power grid voltage drops in a certain range, the wind power system must maintain connection to the grid, and provide reactive power support to help system restore from the fault. These two aspects request wind farm has enough and flexible reactive power compensation. Switchable capacitor banks is commonly used in wind farms for reactive power compensation, but its compensation speed is slow, and it can’t compensate continuously. So capacitor banks is not able to meet the dynamic reactive power needs of the wind farm. This paper proposes applying STATCOM in wind farms, and make it coordinate with the original reactive power compensation capacity of the wind farm. This can improve the stability of the grid-connected wind farms, and at the same time, can reduce the investment of the continuous compensation devices.First, the mathematical models of wind farms, wind turbines, and STATCOM are derived, and the overall models and control strategies of wind farms, wind turbines, and STATCOM for power system simulation are given.Then, STATCOM is applied to fixed speed induction generator (FSIG) based wind farms, and coordinates with original swithable capacitor banks to consititute a hybrid reactive power compensation system. Control strategy and block diagram of the proposed hybrid reactive power system are given. A simulation model of normal induction generator based wind farm is established in PSCAD. The steady-state and transient simulation demonstrate the accuracy and effectiveness of the proposed hybrid compensation method.Finally, STATCOM is applied to doubly fed induction generator (DFIG) based wind farms, and coordinates with the reactive power compensation capacity of DFIG to improve the fault ride through capability of the wind turbines. The control strategy and block diagram of coordination of STATCOM with DFIG are given. A simulation model of doubly-fed induction generator based wind farm is established in PSCAD. Simulation and analysis under different voltage dip verify the accuracy and effectiveness of the proposed compensation strategy.