A Multilevel Approach for Optimal Participating of Wind Farms at Reactive Power Balancing in Transmission Power System

According to the different grid codes, wind farms which are connected to transmission network have to supply not only the active power, but also the reactive power to the grid. The aim of the proposed work is to present an optimal multilevel control system which allows the doubly fed synchronous generator based wind farms to participate at reactive power balancing in transmission network. In this method, we use a multilevel control system, consisting of two levels to regularly calculate the references of all wind turbines. First, the algorithm calculates the optimal reference values of reactive power for each wind farm at its point of common coupling with the grid. Second, it calculates the references of the wind turbines in each wind farm to consider the optimal reactive power references obtained at the first level. The proposed multilevel control system re-calculates the available reserve of the reactive power to determine the optimal references. A probabilistic method based on auto regressive integrated moving average is used to predict the available reactive power reserve which is strongly related to uncertain nature of wind speed. This control system is developed particularly to control the wind farm reactive power injected into the grid. It is well adapted to fluctuating nature of the wind speed. It is also faster than other methods with a global single level optimal control system.