Research On Grouped Reactive Power Optimization Control For Active Power Maximization Of Large-scale Doubly Fed Induction Generator Based Wind Farm

With the increase of the capacity and number of Wind Farms(WF)connected to the grid,the randomness and fluctuation of wind energy bring a great impact on the power quality and the stability and economic operation of the system.The large-scale Doubly Fed Induction Generator(DFIG)based WF is discussed,and then a grouped reactive power optimization control strategy is proposed in the light of the situation of low generating capacity and short lifetime of a WF in this paper.By reasonably distributing the reactive power flow in WF,the proposed control strategy improves the generating capacity,increases the lifetime of WFs,and ensures the reliability and economy of grid connection of WFs.Firstly,from the perspective of reactive power distribution among DFIGs in the WF,to ensure that large-scale DFIG based WFs can deliver more power to the system on the premise of meeting the reactive power dispatching requirements of power grid,a grouped reactive power optimization control strategy of large-scale DFIG based WF is proposed to maximize the single-cycle output active power in this paper.The proposed control strategy is based on the reactive power of DFIG in WF as the control variable,the maximum output active power in a single-cycle of the WF as the control objective,and the demand of grid reactive power disp atching,the power balance and the reactive power capacity limit of the DFIG as the constraints.Meanwhile,in this control strategy,the mathematical model of reactive power optimization of the WF is established,and the grouped reactive power optimization method is proposed to solve the proposed optimization model.The proposed control strategy’s effectiveness at different wind speeds and reactive power references is verified in a simulation experiment.Secondly,considering the problems of slow optimization speed,long period and mismatch with wind power fluctuation of large-scale DFIG based WF,this paper studies the problem of solving reactive power control optimization model quickly and proposes a grouped reactive power optimization method.In the proposed optimization method,the DFIGs in a WF are divided into groups to reduce the optimization variables.The reactive power distribution among groups is optimized by particle swarm optimization algorithm,and the proportional control strategy is used to distribute the reactive power requirements in each group.Meanwhile,the proposed control strategy optimizes the reactive power distribution between the stator and grid side converter in each DFIG.By solving the reactive power optimization model of WF quickly,the proposed grouped reactive power optimization method can improve the control speed of large-scale DFIG based WF,shorten the control period,and reduce the adverse impact of wind power fluctuation on the reactive power control.Finally,given the phenomenon that large-scale DFIG based WFs need to provide additional reactive power to the grid,which will greatly shorten their lifetime,the lifetime optimization of WFs is introduced into WFs’ reactive power optimization control,and a grouped reactive power optimization control strategy for large-scale DFIG based WFs is proposed to maximize the whole lifetime-cycle output active power.This control strategy takes the Levelized Production Cost(LPC)of the WF as the index to evaluate a wind farm’s output active power level in the whole lifetime-cycle.Firstly,based on the lifetime model and reactive power optimization control model of WF,the mathematical model of LPC minimization of a WF is established.Then the optimal solution of the mathematical model is obtained by the proposed group ed reactive power optimization method.Simulation results show that the proposed control strategy can effectively reduce the LPC of WFs,and improve the whole lifetime-cycle output active power of wind farm.