•An overview understanding of local flexibility markets (LFMs) is provided.•A comprehensive survey on formulations and clearing methods of LFMs are conducted.•Studies for solving operational issues ...of distribution systems are reviewed.•Deepen the understanding of LFMs in helping the operations of distribution systems.
With high penetration of renewable generation and distributed energy resources, distribution systems are facing new operational challenges due to their intermittency and uncertainty. To cope with these challenges, distribution system operators are seeking for market tools to enable more active system management and control using flexibility. Local flexibility markets provide opportunities to trade flexibility among distribution system operators and other participants (e.g., aggregators) in an economically efficient way. Studies have been carried out to define the concepts, design the mechanisms and formulate the market clearing methods of local flexibility markets in the literature. Therefore, there is a need to classify and organize the literature on potential designs and market clearing methods of local flexibility markets. This paper reviews local flexibility markets, which are currently being discussed and designed to provide trading platforms for local participants, including distribution system operators and aggregators. Starting with a survey on the concepts and definitions of local flexibility markets, we summarize the key elements, technologies and participants of local flexibility markets. Afterwards the formulations of local flexibility markets and the solution methods for market clearing are reviewed, based on which future research directions and challenges are suggested in the last section of this paper.
In recent years, the rapid development of Internet, Internet of Things, and Cloud Computing have led to the explosive growth of data in almost every industry and business area. Big data has rapidly ...developed into a hot topic that attracts extensive attention from academia, industry, and governments around the world. In this position paper, we first briefly introduce the concept of big data, including its definition, features, and value. We then identify from different perspectives the significance and opportunities that big data brings to us. Next, we present representative big data initiatives all over the world. We describe the grand challenges (namely, data complexity, computational complexity, and system complexity), as well as possible solutions to address these challenges. Finally, we conclude the paper by presenting several suggestions on carrying out big data projects.
•A hierarchical microgrid energy management method in an office building is proposed.•An office building is modelled as a virtual energy storage system (VESS).•A V2B control strategy is developed to ...dispatch the EVs as a flexible resource.•The VESS and the EVs are coordinated and dispatched in two different time scales.
A two-stage hierarchical Microgrid energy management method in an office building is proposed, which considers uncertainties from renewable generation, electric load demand, outdoor temperature and solar radiation. In stage 1, a day-ahead optimal economic dispatch method is proposed to minimize the daily Microgrid operating cost, with the virtual energy storage system being dispatched as a flexible resource. In stage 2, a two-layer intra-hour adjustment methodology is proposed to smooth the power exchanges at the point of common coupling by coordinating the virtual energy storage system and the electric vehicles at two different time scales. A Vehicle-to-Building control strategy was developed to dispatch the electric vehicles as a flexible resource. Numerical studies demonstrated that the proposed method is able to reduce the daily operating cost at the day-ahead dispatch stage and smooth the fluctuations of the electric power exchanges at the intra-hour adjustment stage.
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•We propose a delineation framework of ecological redline areas at river basin scale.•Social needs have strong effects on ecosystem services and ecological redline areas ...delineation.•The identified ecological redline areas exhibit improved connectivity and integrity.•Countermeasures to improve the implementation of protection policies are suggested.
China’s river basin ecosystems are facing serious environmental and structural fragmentation problems. However, there are no complete ecological redlines specifically for watershed ecological conservation. This study considers the Xiangjiang River Basin (XJRB) to propose a framework delineating the ecological redline area (ERA) on a watershed scale and highlights policy recommendations. It combines several evaluating indicators for coupling the response mechanism between human demand and ecological protection. Overall, the water supply in the XJRB meets the social demand. However, water supply in some places, such as the core area of Changsha Zhuzhou Xiangtan Urban Agglomeration and the Hengyang urban area, is still insufficient. This study considers ecosystem service functions, ecological sensitivities, and social needs and estimates the ERA of the XJRB to be 36,057 km2, accounting for 38% of the total watershed. The key ecological functional areas account for 60% of the total redline area and are concentrated in the upper reaches. Compared with the current method conducted at the national and administrative level, the redline area defined in this study by the sub-basin scale exhibits better connectivity and integrity. Moreover, the study can help ensure an accurate placement of the ecological redline while also providing an important reference for redline delineation of other river basins.
Abstract
To address the balancing challenge of real‐time power demand and supply in power systems caused by unpredictable output fluctuations of renewable energies, collaborative and effective ...scheduling of integrated energy systems is proposed with consideration for carbon restrictions. The model incorporates various energy resources, including cold, heat, electricity, and gas, and overcomes the barriers among different levels of heterogeneous energy grid systems. This makes it possible to coordinate the vertical complementarity of source‐grid‐load‐storage and the horizontal complementarity of multi‐energy while taking into account investment costs and carbon trading to achieve the economic operation of the system. This analysis shows that the proposed model can dissipate the excess of new energy generation from the grid. and achieve a balance between supply and demand, while effectively reducing the economic operation cost of the whole system.
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•We mapped Chinese land system from the perspective of nature, humanity and ecology.•A set of 24 indicators representing the multi-attributes of land were complied.•The ...Self-Organizing Map algorithm was adopted to derive land system types for China.•Our results facilitate a better understanding of human environment interactions.
Land is an integrated and complex system consisting of multiple natural and anthropogenic elements. The long-term exploitation and utilization of land resources by humans have transformed the terrestrial surface of the Earth and profoundly impacted the spatial patterns of regional land use and land cover. Land use/cover (LULC) data have been extensively used to monitor regional land changes and contribute to land use policy making. However, these products objectively reflect only the current coverage and biophysical attributes of the terrestrial surface but fail to characterize the multiple functions and attributes of the human-environment system (HES). In this study, we present an integrated land system classification for representing the regional HES based on multisource datasets that characterize the attributes of land use and management, biodiversity conservation and cultural landscapes. Then, 40 land system types (LSTs) in China were identified using the self-organizing map (SOM) algorithm. According to the land system map, we found significant east–west differentiation in land use intensity, with high-intensive LSTs occurring mostly in eastern provinces and natural and seminatural LSTs dominating in central and western regions. The multifunctional LSTs that host food production, biodiversity conservation and cultural heritage were estimated to cover 32% of the terrestrial area in China. In summary, our results can provide a basis for regional land assessment and help identify the pressures on and threats to the eco-environment. Mapping regional land systems facilitates an in-depth understanding of human-environment interactions at the landscape level and serves as a useful tool in terms of forging sustainable land use strategies.
This paper proposes a stochastic and distributed optimal energy management approach for active distribution networks (ADNs) within office buildings. The proposed approach aims at scheduling office ...buildings fitted with heating ventilation and air conditioning (HVAC) systems, and electric vehicle (EV) charging piles, to participate in the ADN optimization. First, an energy management approach for the ADN with aggregated office buildings is proposed. And the ADN optimization model is formulated considering the detailed building thermal dynamics and the mobile behaviors of workers. Then, to consider uncertainties of photovoltaic (PV) power, scenario-based stochastic programming is integrated into the ADN optimization model. To further realize the stochastic energy management of the ADN within office buildings in a distributed manner, the alternating direction method of multipliers (ADMM) is used to solve the ADN optimization model. The original ADN optimization problem is divided into the network-side and the building-side sub-problems to effectively protect the privacy of the ADN and the office buildings. Finally, the ADN optimization model incorporating office buildings is validated in the winter by numerical studies. In addition, the impacts of comfort temperature range and expected state of charge (SOC) at departure are analyzed.
Traffic self-similarity has been discovered to be a ubiquitous phenomenon in communication networks and multimedia systems. Due to its fractal-like nature, performance modelling of self-similar ...traffic poses greater challenges and exhibits more complexity than that of traditional non-bursty traffic. As a result, most existing studies on analytical modelling of priority queueing systems with self-similar inputs have been restricted to a simplified scenario where only two traffic flows are taken into account. This study contributes to performance modelling of priority queueing systems by proposing a novel queue-decomposition approach, which offers several potential advantages and unique innovations. Specifically, we extend the well-known empty buffer approximation (EBA) method to model priority queueing systems with multiple traffic flows and decompose the original priority queueing system into a group of single-server single-queue systems, which can make the challenging performance modelling problem tractable. We further develop an analytical model to investigate the queue length distributions of individual traffic flows. The validity and accuracy of the model demonstrated through extensive simulation experiments make it a practical and cost-effective evaluation tool for quantitatively evaluating the performance behavior of priority queueing systems with multi-class self-similar traffic under various working conditions.
Event extraction is useful for many practical applications, such as news summarization and information retrieval. However, the popular automatic context extraction (ACE) event extraction program only ...defines very limited and coarse event schemas, which may not be suitable for practical applications. FrameNet is a linguistic corpus that defines complete semantic frames and frame-to-frame relations. As frames in FrameNet share highly similar structures with event schemas in ACE and many frames actually express events, we propose to redefine the event schemas based on FrameNet. Specifically, we extract frames expressing event information from FrameNet and leverage the frame-to-frame relations to build a hierarchy of event schemas that are more fine-grained and have much wider coverage than ACE. Based on the new event schemas, we propose a joint event extraction approach that leverages the hierarchical structure of event schemas and frame-to-frame relations in FrameNet. The extensive experiments have verified the advantages of our hierarchical event schemas and the effectiveness of our event extraction model. We further apply the results of our event extraction model on news summarization. The results show that the summarization approach based on our event extraction model achieves significant better performance than several state-of-the-art summarization approaches, which also demonstrates that the hierarchical event schemas and event extraction model are promising to be used in the practical applications.
Abstract
This paper aims at exploring the distinctive ways of baking time affecting the hardening degree of the cold-rolled steel. Therefore, with different time span, the annealed sample was baked ...to test its baking hardening properties. The sample was analyzed micro-structurally after being annealed, pre-deformed and baked. The internal friction was simultaneously measured in terms of different processing conditions during experiments. The following findings are the significant conclusion of the experiments: The important experiment result indicated that when the degree of pre-deformation setting at 5% and the baking temperature at 170°C, the BH value increased but remained unchanged afterwards. Furthermore, when the baking time span was set at 1000 minutes, the BH value reached the maximum but would remain unchanged afterwards. When the degree of pre-deformation was set at 5%, and the baking temperature was set at 17°C with baking time 20 minutes, the SKK peak reached the maximum. When the baking time was 1000 minutes and constantly extended, the height of SKK peak rarely changed. The above experiments are designed to better illustrate and understand the significance of the hardening steel properties for future application in the automobile industry.
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