Study On The Short-term Optimal Operation Of Three Gorges Cascade With Impacts Of Dynamic Storage Capacity And Backwater Jacking

Thus far,the short-term optimal operation problems of the Three Gorges cascaded hydropower reservoirs have been intensively studied by many scholars at home and abroad.The previous works,however,usually did not take into account the impacts of dynamic storage capacity and backwater jacking from the downstream reservoir.Both the Three Gorges and Gezhouba,however,are typically river-type reservoirs with a great portion of dynamic storage capacity,which has impacts that cannot be ignored on the optimal operation of the cascade.Also,the backwater of active storage in the Gezhouba reservoir,when being operated,can reach far to the Three Gorges and push up its tail-water level more or less,causing inundation loss of energy due to the loss of water head for power generation even at the same conditions.Therefore,it is necessary to study on the impacts of dynamic storage capacity and backwater jacking from the Gezhouba reservoir on the short-term optimal operation of the Three Gorges Casecade.This paper analyzes the impacts of dynamic storage capacity and backwater jacking on the optimal operation of the Three Gorges Cascade,with the main works summarized as follows.(1)The research focus of this dissertation is established after a review on the international research progress of short-term reservoir optimal operation,as well as an analysis on difficulties and outstanding problems in short-term cascade optimal operation of hydropower systems.(2)The characteristics of dynamic storage capacity for the Three Gorges and Gezhouba,as well as the backwater jacking effects of Gezhouba on the Three Gorges,are analyzed.The storage functions with dynamic storage capacity for both the Three Gorges and Gezhouba,as well as the tail-water level function with backwater jacking effects for the Three Gorges,are fitted to the collected and treated data by using a multivariate nonlinear regression model.(3)Taking into account the influences of dynamic storage capacity and backwater jacking,a short-term optimal operation model for the Three Gorges Cascade is formulated to maximize the energy production of the cascade,and a case study is presented and dealt with by using the dynamic programming(DP).For the optimal operation of the Three Gorges Cascade,this work also analyzes the impacts on the model and results of different fitting functions determined with different data samples,as well as different inflows in magnitude to the Three Gorges due to the dynamic storage capacity and backwater jacking.When the dynamic storage capacity and the backwater jacking effect are included,the results of this work suggest that the total energy produced by the Three Gorges Cascade will increase,by 0.225% for the case study presented in this dissertation.The Gezhouba tends to lower its water level as a whole,operating at lower water levels.Also,taking into account the dynamic storage capacity and the backwater jacking effect gives processes of outflow and power generation more stable for both the Three Gorges and Gezhouba,with less probability of spillages occurred.The study also tells that with inflows to the Three Gorges Reservoir different in magnitude,the impacts of dynamic storage capacity and backwater jacking on the short-term optimal operation of the Three Gorges Cascade are also different in degree.When inflows to the Three Gorges Reservoir are big enough,the total energy produced by the Three Gorges Cascade increases by a percentage that shows an increasing trend with the inflow increasing in magnitude.