Operational Flexibility And Economic Analysis Of Hydropower-wind-photovoltaic Energy Complementary System

The integrated development of hydropower,wind power and photovoltaic is an important way to promote the transformation of energy structure and realize the goal of "dual carbon".However,the fluctuation and intermittency characteristics of wind power and photovoltaic power output are obvious,resulting in the problem of scenery absorption and the decline of the economic benefit of hydropower units caused by long-term operation of hydropower units in non-optimal conditions,which become the pain points and difficulties that hinder the development.Therefore,it is of great engineering significance and practical value to study the optimization of the hydro-wind-PV complementary system(HWPCS).This paper focuses on the collaborative optimization operation of the hydro-wind-PV complementary system,constructs the comprehensive evaluation model of the flexibility of t HWPCS based on the hierarchy-entropy method and the economic evaluation model of HWPCS considering the life loss cost of hydropower units,and comprehensively evaluates the operational flexibility and economy of HWPCS.The main work is as follows:(1)In order to build a coupling model of HWPCS that can capture the output characteristics of each subsystem,the factors influencing the output and the output characteristics of three types of power sources,including hydropower,wind power and photovoltaic power,are analyzed in detail.Based on the complex coupling relationship between subsystems,Starting from the constraints of system power balance,upper and lower limits of unit output,unit climbing speed,water balance,reservoir level,reservoir storage capacity,reservoir discharge and discharge.A coupling model of HWPCS with a long-time scale is established,which takes the minimum total cost(including unit start-stop cost,operation and maintenance cost,penalty cost,unit climbing cost and power transmission cost,etc.)within the system operating cycle as the objective function.(2)Aiming at the problems that the existing system flexibility evaluation focuses on qualitative analysis and the evaluation process is easily affected by subjective factors.A comprehensive evaluation index set of flexibility was proposed based on net load volatility,solar absorption rate,flexibility abundance rate,flexibility deficit rate and power complementarity index.A comprehensive evaluation model of flexibility of HWPCS based on hierarchical entropy method was constructed to comprehensively quantify the influence of different wind-PV installed ratio on the flexibility of HWPCS.It provides a reference for improving the operational flexibility of the system and the system’s renewable energy planning.The results show that the flexibility of HWPCS will change with the change of the wind-PV installed ratio,but there is an optimal ratio that makes the system flexible.In the study of HWPCS,the optimal wind-wind installed ratio is 1:2,and the comprehensive evaluation value of the system flexibility is the highest 84.31.Under this scheme,the flexible supply of the HWPCS can meet the demand of net load fluctuation when the wind-PV output is continuous and steady.However,in extreme working conditions,curtailment of wind and PV and loss of load still exist,so a certain energy storage capacity is needed to further improve the flexibility of the system.(3)Aiming at the problem that the frequent fluctuation of output on the life loss cost of hydropower unit is not considered in the economic evaluation of traditional HWPCS,the life loss cost of hydropower unit under the HWPCS operation mode is included into the system operating cost,and the economic evaluation model is established with the minimum system operating cost,maximum generation capacity and minimum power load deviation as the objective function.The operation modes of hydropower units are divided into two types: nonvibration avoidance operation and vibration avoidance operation.The NSGA-Ⅱ intelligent optimization algorithm is used to solve the model,and the system operation economy under typical wind-PV output scenarios is analyzed.It has certain guiding significance to the operation mode of hydropower units in HWPCS.The model solution results show that,although the non-vibration avoidance operation mode performs better than the vibration avoidance operation mode in terms of power and load deviation,the comprehensive economic performance of the non-vibration avoidance operation mode is worse than that of the vibration avoidance operation mode due to the significant increase of operation cost and more prominent unit safety problems caused by unit fatigue loss.In the study of the water-wind-solar complementary power generation system,compared with the hydropower unit without vibration avoidance operation,the water-wind-solar complementary system with vibration avoidance operation mode reduces the mean value of power generation and power and load deviation by 0.09% and 2.10%,respectively,but at the same time,the mean value of system operation cost decreases by 0.24%,and the operation time of the hydropower unit in the vibration zone is reduced by more than 90%.Its economic performance is better.