| Large scale wind power integration into the power grid has brought many challenges to the stable operation of the power system.With the improvement of wind power penetration,the equivalent inertia of the power grid will be reduced,and the defects of wind power will be amplified,which will bring severe challenges to frequency stability.In order to avoid largescale wind power integration aggravating the pressure of power grid frequency regulation,wind turbines need to participate in power grid frequency regulation.Wind turbine adopts Stepwise Inertia Control(SIC)participating in power grid frequency regulation can significantly improve the lowest point of frequency drop.However,even if the optimal parameters are selected,there will still be a large power drop in the speed recovery stage,which will cause the secondary drop of system frequency and is not conducive to the recovery of power grid frequency.Aiming at this problem,this paper optimizes and analyzes the power curve of SIC strategy.Based on the optimal power curve,an improved SIC strategy is designed to effectively reduce or even avoid the frequency secondary drop caused by the sudden power drop of the conventional SIC strategy.Firstly,this paper analyzes the reasons for the sudden power drop of SIC strategy,and puts forward the optimal duration of temporary over-production stage and the idea of adding power transition stage in temporary over-production stage and speed recovery stage.On this basis,this paper constructs the power curve optimization model of the improved SIC strategy,obtains the optimal power curve,and summarizes the characteristics of the curve.Secondly,aiming at the problems of poor applicability and single application scenario of the optimal power curve obtained by the optimization model,an improved SIC strategy based on the optimal power curve is proposed to improve the applicability.The improved SIC strategy is divided into three parts: temporary over-production stage,power transition stage and recovery stage.For the temporary over-production stage,this paper analyzes the value of overproduction power,and designs the over-production power optimization model to optimize the value of over-production power under different operating conditions;For the power transition stage,this paper constructs the power transition stage strategy considering the power grid frequency state and wind turbine speed by designing the fuzzy controller and setting the power transition range;The recovery stage is the maximum power point tracking stage,which is MPPT control.At last,this paper constructs a simulation model in Matlab / Simulink,and verifies that the frequency regulation effect of the improved SIC strategy is close to the optimal power curve,and the applicability is better than the optimal power curve.On this basis,the proposed strategy is simulated and compared with different strategies to analyze the effectiveness and superiority of the strategy under different conditions.The simulation results show that,compared with the conventional SIC strategy,the wind turbine participating in power grid frequency regulation by using the strategy proposed in this paper can significantly improve the lowest point of frequency drop,and can effectively reduce or even avoid the secondary frequency drop. |
