Multi-Stage Planning For High Percentage Renewable Energy Distribution Networks Based On System Flexibility Assessment

Under the background of "double carbon",wind power,photovoltaic and other renewable energy sources have become the core means to solve the energy supply problem in the world.The rapid development of different types of renewable energy and the year-on-year increase in penetration rate have greatly improved the economics of power system generation and reduced the capacity and carbon emission pressure of traditional thermal power generation units.However,the renewable energy output is closely related to the regional meteorological conditions,geographical distribution and system operation status,with typical randomness and uncertainty.Given the substantial penetration of renewable energy in the distribution network,the system experiences an ongoing rise in net load regulation demand due to the uncertain nature of renewable energy output and the random behavior of electricity consumption by users.This leads to an elevated level of variability in the system’s net load.In order to assess the ability of high percentage of renewable energy distribution grid to maintain the power balance between source and load,the flexibility regulation resources and demand of the system need to be modeled and analyzed to solve the difficult problem of power system flexibility which is difficult to quantify.Through the flexibility calculation results,a multidimensional system flexibility deficiency can be obtained,and based on the target constraint of flexibility optimality,the flexibility resources of the high percentage renewable energy distribution grid can be reasonably planned to meet the challenges of uncertainty brought by the high percentage renewable energy access to the distribution grid,so as to achieve the objectives of reducing the distribution grid planning cost,improving the utilization rate of renewable energy generation and ensuring the flexible and stable operation of the system To achieve the objectives of reducing distribution network planning cost,improving the utilization rate of renewable energy generation and ensuring flexible and stable system operation.To this end,this paper constructs a comprehensive assessment model for the flexibility of high percentage renewable energy distribution network from the perspective of uncertainty of renewable energy output,and proposes a multi-stage planning model for the flexibility resources and grid of high percentage renewable energy distribution network based on the established flexibility index system.The completed work and main research results of the thesis include:(1) Based on uncertainty analysis theory,wind power,PV and load are modeled and clustered,and the impact mechanism of renewable energy output uncertainty on high proportional renewable energy distribution networks is investigated.Firstly,various uncertainty analysis methods applicable to high proportional renewable energy distribution networks are introduced,and the uncertainty of wind power PV output is characterized based on the error probability density distribution function,and the uncertainty set of wind power,PV and load considering robust theory is constructed;secondly,the clustering analysis study based on the traditional renewable energy output scenarios,the Davies-Bouldin classification is introduced The reliability index is optimized for the number of clustering scenarios,and an improved cohesive Hierarchical clustering method with reliability is proposed to realize the clustering of wind power and PV typical generation scenarios;finally,the influence mechanism of the net load regulation demand of high percentage renewable energy distribution network is discussed under different renewable energy generation trends and penetration rates.(2) Based on the power system flexibility analysis theory,a quantitative assessment model of the flexibility of a typical scenario of high proportional renewable energy distribution network is constructed to take into account the uncertainty of wind power and photovoltaic.Firstly,on the basis of the power system flexibility analysis theory,the impact of system flexibility deficiency and its guiding role in source-load dispatching are studied,and the flexibility characteristics of high proportional renewable energy distribution network are summarized;secondly,the flexibility resources and demands of high proportional renewable energy distribution network are modeled,and then the quantitative flexibility assessment indexes are proposed from three aspects.Finally,we set up an example for the historical output data of a high proportion of renewable energy distribution network,and based on the improved Hierarchical cluster analysis method proposed in this paper,we make an optimal classification of the output of scenery units for reliability,and construct a set of typical renewable energy output scenarios.Finally,based on the improved Hierarchical clustering analysis method proposed in this paper,a typical scenario set of renewable energy output with scenery uncertainty is constructed,and the impact of different scenery penetration rates and energy storage units on system flexibility is analyzed by substituting into the flexibility evaluation model to verify the effectiveness of the proposed flexibility evaluation method.(3) Based on the flexibility optimal target constraint of high proportional renewable energy distribution network,a multi-stage planning model of high proportional renewable energy distribution network flexibility resources and grid is constructed.First,based on the flexibility evaluation indexes proposed in this paper,the AHP empowerment and scenario method are used to construct the planning penalty function of high proportional renewable energy distribution network;second,micro gas turbine and energy storage are used as the system flexibility resources to construct the multi-stage planning model of high proportional renewable energy distribution network flexibility resources and grid;finally,the planning analysis is carried out by 24-node test system,and the planning The results show that the planning scheme containing energy storage with optimal memory and flexibility can effectively improve the flexibility and economy of distribution grid construction and operation,which verifies the effectiveness of the planning model proposed in this paper.