| Due to the advantages of low carbon,environmental protection and sustainability,renewable energy such as wind power and hydropower will gradually become the main power supply in the future power grid.However,owing to significant volatility,high uncertainty and weak frequen-cy regulation,large scale wind power integration will pose challenges to power system frequen-cy control.In addition,as a result of the reverse adjustment brought by water hammer effect,it is likely to occur ultra-low frequency oscillation(ULFO)in the power system with high penetra-tion of hydropower generation.In view of the problems above,this work aims to improve fre-quency stability of power system with large scale renewable energy based on energy storage system(ESS)from two aspects.One is to improve the ramp of wind power integration using ESS on power supply side to reduce its impact on power system frequency stability,which en-hances the friendliness of renewable energy integration to power grid frequency control.The other one is to improve the ability of power system frequency control using ESS on power grid side to raise the level of fast frequency control and ULFO suppression,which enhances the adaptability of power grid frequency control to renewable energy integration.For improving the ramp of wind power integration with ESS:firstly,considering the power system ramp ability and the wind farm operation,a dynamic optimization method for wind pow-er ramp requirement is proposed to determine requirements for different wind farms.It is de-signed to realize the flexible management of wind power ramps,which is beneficial to the active power balance of power system with large scale wind energy,thus improving the power system frequency stability.Moreover,compared with the fixed ramp requirement,the utilization rate of wind energy can be also effectively improved;Then,wind power ramp control using ESS based on refined ramp event characterization is proposed.Considering the wind power ramp event prediction and the charge/discharge state of ESS,a simplified classification method is developed to characterize wind power ramp scenarios.According to characteristics of different ramp sce-narios,an adaptive adjustment strategy of state of charge(SOC)of ESS is presented to achieve an appropriate energy storage reserve,which enables ESS to provide continuous wind power ramp control support in the following periods.As a result,it helps to increase the satisfaction rate of ramp requirement and reduce the wind curtailment of wind farm;Finally,the effective?ness of the proposed wind power ramp requirement dynamic optimization and wind power ramp control with ESS is verified based on the actual wind power data.For improving the ability of power system frequency control with ESS:firstly,a model-free fast frequency control support with ESS is proposed.An online estimator is designed to ap-proximate the frequency characteristic of power system dynamically.Besides,an online optimi-zation controller is designed to adjust power output of ESS dynamically based on the approxi-mate model.Thus,through the coordination of the proposed estimator and controller,the func-tions of plug and play and adaptive determination are realized for fast frequency control with ESS.As a result,it not only enhances power system frequency stability under a large disturb-ance,but also improves the flexibility of fast frequency control with ESS;Then,a method on suppressing ULFO with ESS is proposed.Based on Prony algorithm,an oscillation evaluation index is established to characterize the oscillation trend of power system frequency and used for ULFO analysis and suppression.Next,a control scheme of suppressing ULFO with ESS and an optimization of the corresponding ESS control parameters are developed to provide effective positive damping when ULFO occurs,which improves power system frequency stability;Final-ly,the effectiveness of the proposed fast frequency control and ULFO suppression with ESS is verified based on the actual power grid data. |
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