Joint Optimal Operation Of Large-Scale Reservoirs For Comprehensive Utilization In The Upper Reaches Of Yangtze River

The mianstream and tributaries of the upper Yangtze River including Jinsha River, Yalong River, Dadu River, Jialing River and Wu River, which have abundant water resources and hydropower, are very important water sources and hydropower bases of our country. In order to make full use of the water resources, a lot of major reservoirs have been built or planned, ensuring the flood control safety of downstream zones, as well as satisfying the demands of power generation, water supply, navigation and ecology. As these large-scale reservoirs are built and put into operation, the joint optimal operation of them will be the best choice. However, the joint optimization of reservoirs in the upper reaches of Yangtze River has the characteristcs of large scale system, multiple objectives, complex contraints and different regulating ability, it will be a high-dimensional, non-linear, strong coupled and multi-objective optimization problem which is hardly solved by the traditional reservoir scheduling theories and methods. Aiming at the key scientific problems in the joint optimal operation of large-scale reservoirs for comprehensive utilization in the upper reaches of Yangtze River, this paper carries out researches on the modeling, solving and applying of the joint optimal operation problem for make full use of water resources and hydropower, combined with the theories and methods of reservoir scheduling, water resources allocation, system analysis and optimizing decision. The obained achievements are applied to the dispaching center of Jinsha River and Central China Power Grid. The main contents and innovations of this paper are as follows:(1) The Three Gorges Cascade undertakes the tasks such as flood control, power generation and navigation in flood season. For maximizing the comprehensive benefits, this paper takes the exsiting small and medium-sized flood utilization achievements of the Three Gorges Cascade into account, presenting a flood control operation rule based on water level-inflow-water discharge boundary, deriving the relationship between water discharge and navigation guaranteed rate. Then, a model of comprehensive utilization in flood season based on multi-objective optimization is presented,6 different schemes of comprehensive utilization in flood season are drafted. Considering the design scheme and 2009 optimal scheme of the Three Gorges Cascade, we simulate and verify all kinds of dispatching schemes of the cascade reservoirs in flood season with historical runoff, typical flood and design flood. Compared to the exsting dispatching schemes, the comprehensive utilization scheme which has the objectives ordered by downstream flood control, navigation and power generation can increase the navigation guaranteed rate and total power generation of the cascade reservoirs while not increasing flood risk.(2) Focusing on the power generation scheduling of large-scale reservoirs, an economic optimization model of large-scale mixed reservoirs is developed when considering kinds of constraints as well as the complex hydraulic and electricty connection. In order to solve the problem, an improved LSSDC-DDDP hybrid optimal method is proposed based on large scale system decomposition coordination and discrete differential dynamic programming. In the proposed method, a randomly strategy is used to generate initial solution. Meanwhile, a relative coefficient is proposed to determine the coordination factor among subsystems. Moreover, an adaptive corridor and a bias corridor are adopted to enhance convergence speed. Finally, the proposed method is applied to the long-term optimal dispatching of large-scale reservoirs in the upper reaches of Yangtze River. The results indicate that the improved hybrid optimal method has competitive performances in convegence speed and optimization effect. The joint optimal scheduling of large-scale reservoirs can increase the total power generation by the compensation of reservoir's capacity and hydrologic characteristics.(3) For realizing the water resources optimal allocation in the upper reaches of Yangtze River, the built and planned reservoirs are taken to regulate runoff and water supply by their utilizable capacity. Considering kinds of water demands and reservoir comprehensive utilization demands, a novel water resources allocation combined with reservoir operation model is proposed to minimize water supply shortfall and maxminze power generation. According to the water demand variation and reservoir construction in the basin,2015 and 2025 are selected as current year and planning year, then many different water resources allocation scheme are simulated. The results show that the joint scheduling of large-scale reservoirs can reduce the total water supply shortfall while increasing power generation and ecology. Moreover, there are serious contradiction between water supply and demand in Jialing River and Mintuo River. So water conservation and water conservancy project are very necessary for Jialing River and Mintuo River.(4) In order to explore the compensation benefits and rules of power generation for the reservoirs in the upper reaches of Yangtze River, we take the main reservoirs in Yalong Rvier, Jinsha River, Dadu River, Wu River and the Three Gorges Cascade as case study. Considering the substream and owner of reservoirs, optimal scheduling schemes of single reservoir, cascade reservoirs and large-scale reservoirs are made. With the simulation of different schemes under historical runoff, the compensation relationships among different reservoirs and different cascades are revealed. Considering the contribution of reservoir and cascade during joint scheduling, an improved contributing coefficient method and a Shapley value method based on the equality of compensate party and benefited party are presented. Finally, the compensation benefits are divided among reservoirs and cascades reasonably, which can encourage reservoir and owner to take part in joint scheduling.