Research On Joint Optimization Operation In Multi-reservoir Water Transfer-supply System

In recent years, water resources distribution is uneven temporally and spatially, and out of proportion with overall planning of social and economic development in our country, potential water shortage is an increasingly serious problem that poses a huge threat to the sustainable development of the social economy. There is no way to completely solve the problem of water shortage only by the potential local river-basin water resources. So inter-basin water transfer is a feasible artificial solution to reallocate water resources and relieve the water-supply pressure in receiving regions. At present, multi-reservoir joint optimization operation model and solution method in inter-basin water transfer have been achieved with a series of research results. However, the topologies of multi-reservoir systems, with the rapid development of the inter-basin water transfer in China, are becoming more and more complicated. Therefore, the adaptability of the patterns of operating rule and solution method, poses a few of new problems. For instance, how to resolve the "dimension disaster" problem in the optimizaton operations of large-scale complicated multi-reservoir systems; how to determine the water releases for joint water demand by each member reservoir; and how to distribute the total transferred water from donor reservoir into each recipient reservoir. Recently, there are less studies on water-transfer rules, which are developed mainly based on the topologies of multi-reservoir systems and also needed to be perfected so as to improve the efficient of water transfer. Moreover, due to the complexity of the operation problem with the rapid development of the inter-basin water transfer, computation efficiency and solution quality are paid more and more attention to in optimization operation. With the rapid development of computer technology and the increasing diversification of multi-core parallel compution platform, multi-core parallel compution has become an impotant method to improve computation efficiency and solution quality of the multi-reservoir optimization operation. As a consequence, this paper focuses on two aspects:operation model and solution method, and the main research results are as follows.(1) Firstly, we introduce the general situation and social-economic development layout of the study area. Based on the above analysis, the existing problems in the development and utilization of water resources can be recognized so that it is necessary to carry out the inter-basin water transfer. Then, the characteristic of the East-to-West North-line Inter-basin Water Transfer Project (IBWTS) in Liaoning Province, China, is summarized, and its structure is generalized reasonably. Besides, we specify the reservoir operation objectives and the characteristic materials needed in planning and management of multi-reservoirs. Finally, according to the history flow series over a long horizon, we make an analysis of the law of water demand and water inflow. All of the above materals and analyses, serving as the background of project and basic data, will be prepared for the data-input of the optimization operation model and the rational analysis of the operating rule.(2) Taking the North-line IBWTS Project in Liaoning Province, China as a study case, operating rules are developed according to the topology of multi-reservoir system.①Patterns of water transfer and hedging rule curves are predefined, which can divides the active storage space into different water-supply operation zones. In practice, the corresponding policies for water supply will be made in terms of the operation zones in which the water storage stays. It is worth noting that water transfer to importing reservoir is a combined decision-making process relying on the decisions made by both exporting and importing reservoirs.②For joint water demand, a main-control-reservoir with the larger regulating ability serves as to make water-supply decisions, and a water-supply allocation model is established to determine the water supply in the charge of each member reservoir.③the water-transfer allocation model is developed to determine the planned water transfers for each recipient reservoir from the donor reservoir. The results show that the proposed rules are rationable and effective.(3) To increase the benefits of water transfer-supply, this paper adopted two objective functions of maximizing water supply and minimizing water transfer, with corresponding system constraints. Simulation-optimization method is developed to deriving for mutil-reservior operating rule. In the simulation-optimization method, simulation model is incorporated in optimization model to dreving the optimal operation parameters (such as operating rule curves). The simulation model is used to obtain such indices as water supply, water spillage, reliabilities, fitness value, etc. And an improving PSO algorithm is used as the basic optimizing method in the optimization model to readjust optimization variables, according to the fitness fed back from simulation model. The results demonstrate the rationality of the model and the practicability of the simulation-optimization method.(4) An improving PSO algorithm (MPSO) is proposed for solving the joint optimal operation in multi-reservoir system under the condition of inter-basin water transfer with high-dimension, nonlinearity and dynamic. Several strategies such as crossover and mutation of chromosome, simulated annealing and reflective boundary are introduced in the basic PSO algorithm. These strategies can keep the diversity of population, improve the convergence speed and enhance the capability of global search, so that it can avoid the prematurity and slow convergence in later evolution. Numerical tests manifest the effectiveness of the proposed algorithm for solving high dimensional complex problems. A case study indicates that the efficiency of the proposed algorithm has been improved considerably, as well as the benefit of water supply and water diversion. The proposed algorithm can be an effective method for aiding the optimization operation of such complex multi-reservoir system.(5) In order to improve the computation efficiency and solution accuracy of the optimization operation in large-scale multi-reservoirs under the condition of inter-basin water transfer, a multi-core parallel PSO algorithm (PPSO) is proposed to solve the joint operation optimization model. This method with the merits of rapid searching and easy-to-parallel in basic PSO algorithm, also adopts a multi-swarm strategy to guarantee the swarm diversity and enhance the global searching ability. In addition, a Fork/Join framework based on the divide-and-conquer strategy is employed to assign each sub-swarm to different CPU cores for evolving separately. At the same time, the synchronization and communication mechanisms of Java are used to implement the information communication between sub-swarms to avoid trapping in local optimum. The results show that the proposed method can take full advantage of multi-core resources so as to effectively improve the convergence speed as well as the solution quality. Therefore, it can be a high-efficiency method for solving the optimal operation of large-scale multi-reservoir system.(6) From previous studies, it is necessary to improve the efficiency of water transfer. The purpose of this study is to develop a new water-transfer rule to improve the efficient of water transfer, and to figure out in detail the determination method of water transfer for each recipient reservoir. In the proposed rale, upper-and-lower water-transfer rule curves for each recipient reservoir with one water-transfer rule curve for the donor reservoir are developed to make water-transfer decisions. When the water storage of reservoir stays between the upper-and-lower rule curves, the quantity of water transfer equals to the quantity interpolated linearly within that in full water-transfer state. To deriving the operating rule, a model iteration method based on a parallel PSO algorithm is adopted to solve the operation model. The operation results show that the proposed rule can significantly reduce water transfer and water spills however with less influence on the water supply, especially in wet and normal years.