Optimal Operation Of Cascade Energy Storage Systems Based On Hydro-wind-solar Hybrid Energy System

Under the driving force of the dual carbon goals of "carbon peaking" and "carbon neutrality."the scale of new energy installations will inevitably expand rapidly.However,due to the intermittency,randomness,and fluctuation of new energy output,it is challenging to adjust new energy,leading to a mismatch between power grid generation and load,and consequently,the phenomenon of new energy curtailment.This paper addressed the deep integration issue of new energy and proposed a new cascade energy storage scheduling method based on the complementarity of hydro,wind,and solar power.Taking the Longyangxia-Laxiwa cascade energy storage station in the upper Yellow River basin as the research object,the paper constructed medium and long-term and short-term optimization scheduling models for cascade energy storage and analyzed the long-term operation efficiency of cascade energy storage stations and the impact of cascade energy storage scheduling on the short-term operation factors of hydropower stations.The feasibility and economy of cascade energy storage scheduling were also discussed.The main work and conclusions were as follows:(1)The definition of a cascade energy storage station was given,which is a collection of hydraulic engineering projects that install large-scale pumping stations between cascade hydropower stations to serve large-scale new energy absorption.A simplified operation mode for cascade energy storage scheduling was proposed:when new energy generates surplus electricity,large-scale pumping stations are used to pump water from lower reservoirs to upper reservoirs,storing surplus electricity as potential energy of water,i.e.,charging;when the power grid demand cannot be met,existing hydropower station units generate electricity,i.e.,discharging.To address the issue of curtailment during specific time periods,the annual net load process of a certain power grid was calculated,combined with the actual curtailment rules of the power grid(curtailment is more likely to occur during low load periods and high new energy output periods),and it was comprehensively determined that the most likely curtailment periods are between 3-5 AM and 2-4 PM.(2)To address the long-term operational efficiency issue of cascade energy storage stations,a medium-and long-term optimization scheduling model based on daily scale was established,with the maximum multi-year average generation of cascade hydropower stations,the maximum power generation duration guarantee rate,the minimum water shortage index,and the minimum residual curtailment of the power grid as objective functions.To improve the accuracy of modeling,evaporation loss of water volume was considered in the modeling process,and a variable comprehensive output coefficient was adopted in the calculation of water energy.The Pareto solution set was obtained by solving the model using the multi-objective cuckoo search algorithm,and the equilibrium solution was selected using multi-attribute decision-making.By comparing the traditional medium-and long-term optimization scheduling schemes for cascade hydropower stations,the results showed that the long-term operational efficiency coefficient of cascade energy storage stations is about 0.43-0.82,meaning that 43-82%of new energy curtailment can be converted into incremental hydropower.Under the cascade energy storage scheduling mode,the power generation of the upper hydropower station increases,while that of the lower hydropower station remains almost unchanged.The main reason for the increase in power generation of the upper hydropower station is the increase in power generation flow.(3)To address the issue of how cascade energy storage scheduling affects the short-term operation factors of cascade hydropower stations,a short-term optimization scheduling model for hydro,wind,and solar complementary cascade energy storage was established,with the minimum standard deviation of residual load of the power grid,the highest benefit of hydrowind-solar-storage system,and the lowest comprehensive risk rate of generation plan as objective functions.A double-layer nested solving framework was adopted:the outer layer used the multiobjective cuckoo search algorithm to optimize the total output process of the system,while ensuring the stability of the system’s total output through a two-dimensional coding strategy;the inner layer used the K-value discrimination method to determine the load allocation strategy between cascade hydropower stations.By comparing the traditional short-term optimization scheduling schemes of cascade hydropower stations,the results showed that the hydro-windsolar-storage complementary scheduling can reduce the fluctuation of residual load in the power grid and the comprehensive risk rate.Although the power generation operation factors of cascade hydropower stations(power generation flow,power generation head)do not change significantly,the energy storage of the upper hydropower station increases,while that of the lower hydropower station decreases.