Research On Risk Analysis And Control Method Of Spillage For Cascade Reservoirs In Wujiang River Basin

Spillage is a key problem for reservoirs in flood season in hydropower-enriched areas.The study on risk analysis and control method of spillage are very important for reservoir dispatching,which directly affect the social and economic benefits of hydropower dispatching.The dicription of risk factors,the improvement of quantification index of spillage risk analysis and the joint spillage control operation of cascade reservoirs are the key issues in spillage research.This paper takes cascade hydropower plants in Wujiang River Basin as the study case,combines the method of nonlinear global optimization and Monte Carlo simulation,and studies the risk analysis and control method of spillage for cascade reservoirs,in order to provide decision support for reservoir dispatching in flood season.The main contents of the paper are as follows:(1)Based on the analysis for monthly data in history,the present situation of spillage of cascade reservoirs in Wujiang River is obtained.It is pointed out that the focus of risk analysis is the period from June to August in the main flood season.According to the characteristics of cascade hydropower plants,the risk of spillage in Dongfeng-Suofengying,Dahuashui-Geliqiao and Goupitan-Silin-Shatuo should be analyzed especially.The capacity of oneself and upstream reservoir should be used fully in risk anaylsis to minimize unnecessary spillage water.Reservoirs with good regulation performance can control risk of spillage of cascade reservoirs by using their own good ability of regulation when cascade encounter floods,and they can reduce risk of spillage of downstream reservoir by reduce discharge when downstream reservoir encounter floods.(2)A risk analysis method for spillage of hydropower station dispatching is proposed in the paper.On the one hand,based on the assumption of runoff forecasting error,Monte Carlo method is used to simulate a large number of runoff scenarios,which realizes the description of the main risk factors(runoff uncertainty).On the other hand,three risk indicators such as maximum probability spillage water quantity,expected spillage water quantity and up limit spillage water quantity are introduced to quantify the risk of spillage faced by generation plan.Firstly,aiming at maximizing the generation capacity,the output process obtained from the optimization calculation is taken as the generation plan.Then,calculating the several runoff scenarios which simulated by Monte Carlo method based on the generation plan,and the set of spillage water samples and the distribution of spillage water are obtained.Finally,the three risk indicators are calculated through the distribution of spillage water to quantify the risk of spillage water faced by the generation plan.The application example shows that the method enriches the system of quantification index of spillage risk and objectively reflects the real performance of spillage risk.(3)A spillage control method based on the optimization strategy of the upper limit of initial water level is proposed,since that the problem of how to determine the initial water level of large reservoirs in the joint operation of cascade reservoirs.Firstly,with the goal of minimizing spillage for cascade reservoirs,an optimal model is established,and solved by nonlinear global optimization method.Then,for an assumed flood combination scenario,the set of cascade spillage control scheduling schemes is obtained by inputting different initial water level strate-gies into the previous optimization model,and the optimal upper limit initial water level is achieved by comparing the amount of spillage between different schemes.Finally the upper limit initial water level control strategy table corresponding to different frequency flood scenarios is generated through the above idea.The application example shows that the spillage water of cascade and each reservoir can be controlled at a lower level by this method,when the cascade encounters the flood combination scenarios which most likely to occur in history or the flood combination scenarios whose magnitude is very large is extremely unfavorable to reservoir dispatching.Finally,this paper summarizes the whole research results,and prospects the next work content.