Multi-objective Operation Model Research Articles

Utilizing the Sobol’ Sensitivity Analysis Method to Address the Multi-Objective Operation Model of Reservoirs

The operation of reservoirs has significantly influenced the river ecological system. Upholding the ecological integrity of rivers during reservoir operations has been the focus of research over the years. When the Dahuofang reservoir project started, focus moved to ecological goals to address the Biliuhe reservoir’s environmental issues. The water strategy limits usage for various purposes and outlines the diversion route, complicating Biliuhe operations. In this study, to comprehend the effects of individual water level guidelines and their combined influence on these goals, the Sobol’ sensitivity analysis was introduced as an initial measure to tackle the optimization challenge. The results show that removing the insensitive water levels during specific periods of reservoir scheduling lines and beginning with sensitive water levels for local optimization to identify viable solutions, and then moving to wider optimization, significantly enhances the search efficiency, solution quality, and operational speed compared with an exhaustive search without any preceding steps. This sensitivity analysis technique is crucial for fine-tuning multi-objective reservoir operations.

Balancing economic and ecological benefits for hydro-junction operation based on the ecological flow from the four major Chinese carps: a case study from Xinjiang River, China

The construction and utilization of the hydro-junctions would change the water flow and affect the hydrologic process required for the survival and reproduction of the aquatic organism in the river basin. To investigate the influence of the construction of the Jiepai (JP) and Bazizui hydro-junction (BZZ) on the hydrologic process in the Xinjiang River and coordinate the benefits between power generation and downstream ecological protection of the four major Chinese carps (FMCC), a one-dimensional hydrodynamic model is established to simulate the river hydrological regime of the spawning site before and after the construction of BZZ. Meanwhile, eleven ecological hydrologic parameters are used to evaluate the degree of hydrological changes for the spawning site caused by JP and BZZ, and four hydrological methods are applied to calculate the minimal and optimal ecological flows to satisfy the demands of FMCC. The multi-objective operation model combined with the non-dominated sorting genetic algorithm II(NSGA-II) is established to evaluate the relationship among the objective functions and design the ecological operation scheme of BZZ. The results indicate that the hydrologic changes in the spawning site has been moderately changed since the construction of the JP and would change more after the construction of BZZ. An obvious antagonistic relationship between electricity generating and ecological changes are presented in the simulation results, and the multiobjective operation model could clearly increase the comprehensive benefits under three typical years (dry, average, and abundant) by 20%, 19%, and 34% with the corresponding electricity generating lost by 4.9%, 3.5%, and 4.1%, respectively. This study is expected to provide scientific guidance to coordinate the restrictions and conflicts between economic and ecological benefits of hydro-junction operation in the lower reaches of the Xinjiang River.

Research on comprehensive benefit of hydrogen storage in microgrid system

Although the installed capacity of renewable-energy power generation continues to increase in China, wind, light, and water resources are still being abandoned. In addition, the volatility of renewable-energy power generation decreases the reliability of power supply. In this study, a novel “wind–light–water–hydrogen” power system is developed by introducing hydrogen storage into a microgrid system. To optimize the reliability and economic and environmental benefits of the power system, a multi-objective operation model is established, and the twin delayed deep deterministic policy gradient algorithm (TD3) is used to optimize the model. Further, the power system with hydrogen storage is compared with a system without energy storage and a system with lithium batteries. Notably, the hydrogen energy storage system affords stable power supply and maximum renewable energy consumption and are thus more desirable than lithium batteries. Furthermore, the economic benefits can be increased through the sale of hydrogen and waste-heat recovery and the consumption of surplus hydrogen in transportation, which can also help reduce carbon emissions.

Scenario-based multi-objective optimization of reservoirs in silt-laden rivers: A case study in the Lower Yellow River

Severe sedimentation often takes place in the river channel of silt-laden rivers, which is often mitigated through water-sediment regulation of the reservoirs. However, watersediment regulation is often competitive with other objectives of reservoirs, like water supply and hydropower generation; on the other hand, the reduction of channel sedimentation is often achieved at the expense of reservoir sedimentation, which reduces the service life of reservoirs. The Yellow River used to be the river with largest sediment transport over the world, but has experienced significant declination of runoff and sediment in recent years. This study presents a scenario-based multi-objective optimization operation model for the Xiaolangdi reservoir considering hydropower generation, reservoir sedimentation and channel sedimentation, with a generalized linear model coupled to calculate channel sedimentation based on runoff and sediment time series. A stochastic model that can reproduce both spatial correlations and low frequency attributes of the data series is adopted to generate two different scenarios based on different periods of observation and the performance of the multi-objective operation model under different scenarios is tested. The results indicate that: (1) the proposed optimization model can generate different schemes of reservoir operation and enhance operation performance; (2) the generalized linear model can well fit the relationship between daily channel sedimentation and runoff-sediment factors, but tends to overestimate the erosion efficiency after 2005; (3) the reservoir sedimentation and channel sedimentation show linear competitive relation, i.e., an average increase of 1 ton in reservoir sedimentation would result in declination of channel sedimentation from 0.455 to 0.488 tons, while the competitive relationship between hydropower generation and reservoir sedimentation is non-linear and weak; (4) the increase in the proportion of non-flood sediment load to the total sediment load makes it more difficult to prevent the reservoir from silting up.

Multi-Objective Optimal Operation of the Inter-Basin Water Transfer Project Considering the Unknown Shapes of Pareto Fronts

Studies have shown that the performance of multi-objective evolutionary algorithms depends to a large extent on the shape of the Pareto fronts of the problem. Although, most existing algorithms have poor applicability in dealing with this problem, especially in the multi-objective optimization operation of reservoirs with unknown Pareto fronts. Therefore, this paper introduces an evolutionary algorithm with strong versatility and robustness named the Multi-Objective Evolutionary Algorithm with Reference Point Adaptation (AR-MOEA). In this paper, we take two water conservancy hubs (Huangjinxia and Sanhekou) of the Hanjiang to Wei River Water Diversion Project as example, and build a multi-objective operation model including water supply, ecology, and power generation. We use the AR-MOEA, the Non-dominated Sorting Genetic Algorithm II (NSGA-II), the Multi-Objective Evolutionary Algorithm based on Decomposition (MOEA/D) and the Indicator-Based Evolutionary Algorithm (IBEA) to search the optimal solutions, respectively. We analyze the performance of four algorithms and the operation rules in continuous dry years. The results indicate that (1) the AR-MOEA can overcome the difficulty of the shape and distribution of the unknown Pareto fronts in the multi-objective model. (2) AR-MOEA can improve the convergence and uniformity of the Pareto solution. (3) If we make full use of the regulation ability of the Sanhekou reservoir in the dry season, the water supply for coping with possible continuous dry years can be guaranteed. The study results contribute to the identification of the relationship among objectives, and is valued for water resources management of the Hanjiang to Wei River Water Diversion Project.

Long-term water-sediment multi-objectives regulation of cascade reservoirs: A case study in the Upper Yellow River, China

Water-sediment regulation (WSR) is an effective non-engineering measure to alleviate the problem of suspended river and bring benefit to flood control security in sediment-laden river. However, WSR may decrease the socio-economic benefit of reservoirs, for example, reduction of hydropower production and water supply. In order to satisfy the practical requirement of WSR and other utilization objectives, this paper presents a multi-objective operation model for a cascade reservoirs simultaneously considering the maximization water volume for WSR and power generation and water supply, as well as various complex constraints. Then, the Non-dominated Sorting Genetic Algorithm (NSGA-II) is improved to solve the aforementioned model and key control indicators of WSR are analyzed. Meanwhile, a sediment transport model has been introduced to quantify the effect of WSR. The models are applied to the cascade reservoirs in the Upper Yellow River. The following conclusion can be drawn from results (1) Pareto fronts of the model solution demonstrate a strong competition between WSR and water supply, water supply and power generation, a low sensitivity between WSR and power generation; (2) the ability of WSR in Upper Yellow River is 6 times in 24 years, which means the frequency of WSR is four years averagely; (3) 233.77 million tons of sediments are transported by long-term WSR in the Ningxia-Inner Mongolia reaches, account for 19.10% of sediment deposition; (4) the risk-free conditions of LYX and LJX reservoirs’ water volume for WSR are 137.42 × 108 m3 and 41.08 × 108 m3, respectively, which could be used as a reference in actual operation. The research results have an important practical significance and application for sediment control and governance of suspended river, and the multi-objective operation model of WSR proposed in this study can be effectively and suitably used in sediment regulation with similar conditions.

Multi-Objective Optimal Operations Based on Improved NSGA-II for Hanjiang to Wei River Water Diversion Project, China

It is important to investigate the laws of reservoir multi-objective optimization operations, because it can obtain the best benefits from inter-basin water transfer projects to mitigate water shortage in intake areas. Given the multifaceted demands of the Hanjiang to Wei River Water Diversion Project, China (referred hereafter as “the Project”), an easy-to-operate multi-objective optimal model based on simulation is built and applied to search the multi-objective optimization operation rules between power generation and energy consumption. The Project includes two reservoirs connected by a water transfer tunnel. One is Huangjinxia, located in the mainstream of Hanjiang with abundant inflow but no regulation ability, and the other is Sanhekou, located in the tributary of Hanjiang with multi-year regulation ability but less water. The layout of the Project increases the difficulty of reservoir joint optimization operations. Therefore, an improved Non-dominated Sorting Genetic Algorithm-II (I-NSGA-II) with a feasible search space is proposed to solve the model based on long-term series data. The results show that: (1) The validated simulation model is helpful to obtain Pareto front curves to reveal the rules between power generation and energy consumption. (2) Choosing a reasonable search step size to build a feasible search space based on simulation results for the I-NSGA-II can help find more optimized solutions. Considering the influence of the initial populations of the algorithm and limited computing ability of computers, the qualified rate of Pareto points solved by I-NSGA-II are superior to NSGA-II. (3) According to the characteristics of the Project, water transfer ratio threshold value of two reservoirs are quantified for maximize economic benefits. Moreover, the flood season is a critical operation period for the Project, in which both reservoirs should supply more water to intake areas to ensure the energy balanced of the entire system. The findings provide an easy-to-operate multi-objective operation model with the I-NSGA-II that can easily be applied in optimal management of inter-basin water transfer projects by relevant authorities.

Dynamic wavelet decomposition based multi-objective operation model for HESS enabling wind power output smoothing

The uncertainty of wind generation brings risk to power grid due to the variability and intermittency of wind. One promising technique to address challenge is deploying hybrid energy storage system (HESS) in wind energy conversion system to shape the wind power output by coordinating the operation of multi-type storage devices. In this paper, a multi-objective operation model of HESS based on dynamic wavelet decomposition (DWD) is presented. The model is characterized by two novelties: i) Life-cycle cost of storage devices and smoothness performance of wind output are simultaneously considered in the objective; ii) Parameters of wavelet analytics need to be optimally determined in a predictive control scheme. An improved NSGA-II is designed to provide efficient solution by analyzing Pareto frontier. A realistic case is studied to validate the presented method.

Multiobjective Operation Optimization of a Cascaded Hydropower System

AbstractIn order to satisfy the practical requirement of the power grid in China, this paper presents a multiobjective operation model for a cascaded hydropower system simultaneously considering th...

Multi-objective reservoir operation during flood season considering spillway optimization

Flood control and hydropower generation are two main functions of Three Gorges Reservoir (TGR) in China. In this study, a multi-objective operation model for TGR considering these two functions was developed. Since the optimal results of reservoir operation are mostly in the form of gross outflow which is hardly used to directly guide reservoir operation, the optimization of spillways operation was taken into account. For observed historical flood hydrographs and design flood hydrographs, the progressive optimality algorithm (POA) was employed to determine the optimal operation of spillways. For the real-time reservoir operation, a smooth support vector machine (SSVM) model was applied to abstract the optimal operation rules which consider the order and the number of spillways put into use. Results demonstrate that the use of different spillways has a significant impact on reservoir operation. Therefore, it is necessary to consider the order and number of spillways that should be used. Instead of optimizing outflow, direct optimization of the order and number of spillways can yield most reasonable results. The SSVM model simulates the relationship among inflow, water level and outflow satisfactorily and can be used for real-time or short term reservoir operation. Application of the SSVM model can also reduce flood risk and increase hydropower generation during the flood season.

基于年径流分类的水库优化调度函数研究

传统水库调度函数一般以最大化长系列多年平均发电、保证率等指标为目标函数，其内涵是水库多年运行的平均期望效益最大化，并未考虑年径流丰枯的区别。显然水库的优化调度函数与入库径流的丰枯情况有关，丰水年的优化调度函数与枯水年相比势必差异较大。为研究年径流分类对水库优化调度函数的影响，本文建立了考虑发电量及保证率的多目标优化调度模型，采用NSGA-II算法优化安康水库调度函数。结果表明：考虑径流分类，采用丰、平、枯水年的单独优化比长系列优化取得更好的效益。发电量最大非劣解提升发电量0.71%、保证率4.56%，保证率最高非劣解提升发电量1.37%、保证率2.57%。 The traditional reservoir operation function is generally to maximize the long-term average power gen-eration, the guarantee rate and other indicators as the objective function. The connotation is that the av-erage expected benefit of the reservoir is maximized for long time series, but does not consider the vari-ation of annual runoff. It is obvious that the optimal operation function of the reservoir is related to the abundance of runoff that is quite different between the wet and dry years. In order to study the effect of annual runoff classification on reservoir operation function, a multi-objective operation model considering power generation and guarantee rate was established. The NSGA-II algorithm was used to optimize the operation function of Ankang reservoir. The results show that the runoff classification method is better than the long series optimization method. The largest non-inferior power generation solution can increase 0.71% power generation and 4.56% guarantee rate. The largest non-inferior guarantee rate solution can increase 1.37% power generation and 2.57% guarantee rate.

Multi-Objective Operating Rules for Danjiangkou Reservoir Under Climate Change

The natural variations of climatic system, as well as the potential influence of human activity on global warming, have changed the hydrologic cycle and threatened current water resources management. And the conflicts between different objectives in reservoir operation may become more and more challenging because of the impact of climate change. This study aims at deriving multi-objective operating rules to adapt to climate change and alleviate the conflicts. By combining the reservoir operation function and operating rule curves, an adaptive multi-objective operation model was proposed and developed. The optimal operating rules derived both by dynamic programming and NSGA-II method were compared and discussed. The projection pursuit method was used to select the best operating rules. The results demonstrate that the reservoir operating rules obtained by NSGA-II can increase the power generation and water supply yield and reliability, and the rules focusing on water supply can significantly increase the reservoir annual water supply yield (by 18.7 %). It is shown that the proposed model would be effective in reservoir operation under climate change.

Multi-objective Operation Model for Supply Chain with Uncertain Prices Based on Fuzzy Sets and Robust Optimization

Multi-objective Operation Model for Supply Chain with Uncertain Prices Based on Fuzzy Sets and Robust Optimization