Research On Operational Flexibility Evaluation And Optimal Dispatching Of Power System

In recent years,driven by environmental pollution and shortage of fossil fuels,the green and low-carbon transformation of energy consumption has reached broad consensus and the basic framework for promoting green and low-carbon transformation of global energy is taking shape.In this context,wind power,solar energy and other variable renewable energy sources(VRES)generation technology has been rapidly developed.However,the VRES output presents volatility due to its resource endowment characteristics,which poses a huge challenge to the power system that is strictly required for safe,stable and efficient operation.The newly-created concept of'"power system flexibility"which focus on flexible regulation ability of the system provides new ideas for solving the above problem.The characteristic analysis of power system flexibility is the basic link of flexibility research.Clarifing the basic concepts,analyzing the basic mechanism and summarizing the basic features of flexibility systematically,provide theoretical support to solve the volatility of power.This paper defines the key problem,research connotation and research approach of flexibility by closely following the core characteristics of volatility and comparing the power system reliability concept.On this basis,the basic mechanism of flexibility,namely flexibility balance equation,is derived from the traditional power balance equation.Then the basic features of flexibility are analyzed and summarized.Power system flexibility evaluation of is the core link of flexibility research.Establishing a set of reasonable and practical flexibility evaluation metrics is the basis for subsequent optimization operation and configuration of flexibility resources.Therefore,this paper conducts in-depth research on evaluation metrics and evaluation method of power system flexibility with VRES from the point of view of dispatching operation.The volatility models which aggregating VRES and load are established considering spatiality,timeliness and directionality of volatility firstly.On this basis,10 flexibility evaluation metrics of node are proposed from the perspective of dispatching operation:total upward/downward regulation capability,existing upward/downward regulation capability,available upward/downward regulation capability,insufficient upward/downward regulation capability,insufficient upward/downward regulation energy.Then,the metrics solution models are determined by considering the constraints,including load balance,line power flow,flexibility resource adjustment capability.The modified IEEE39 system test results show that the proposed metrics take the spatiality.timeliness and directionality of flexibility into account,as well as the regulation ability of flexible resources,and the flexibility distribution of the system at all times is described in detail.Optimal operation of flexibility resources is the fundamental goal of flexibility research.In order to improve the ability to withstand volatility risk of system,a flexibility optimal dispatching model considering the net load fluctuation interval is established.Among them,the volatility of the system is characterized by the net load forecasting value and its fluctuation interval.The conventional thermal units and energy storage equipment are taken as flexibility resources,and their flexibility adjustment models are established using affine policy.The model takes the operating cost of thermal units and energy storage equipment as the optimization goal.The operational constraints include the startup and shutdown,climbing,technical output of unit,charging and discharging power,capacity of energy storage equipment,load balance and line power flow are considered.The flexibility regulation constraints of units and energy storage equipment are also take into account.The model is transformed into a mixed integer linear programming problem by piecewise linear approximation,constraint relaxation and equivalent transformation method.Finally,the example analysis is conducted based on the improved IEEE39,and it shows that the proposed optimal dispatching approach has certain practical application value in promoting the power system operation flexibility.