1,008 research outputs found

    Control and Limit Enforcements for VSC Multi-Terminal HVDC in Newton Power Flow

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    This paper proposes a novel method to automatically enforce controls and limits for Voltage Source Converter (VSC) based multi-terminal HVDC in the Newton power flow iteration process. A general VSC MT-HVDC model with primary PQ or PV control and secondary voltage control is formulated. Both the dependent and independent variables are included in the propose formulation so that the algebraic variables of the VSC MT-HVDC are adjusted simultaneously. The proposed method also maintains the number of equations and the dimension of the Jacobian matrix unchanged so that, when a limit is reached and a control is released, the Jacobian needs no re-factorization. Simulations on the IEEE 14-bus and Polish 9241-bus systems are performed to demonstrate the effectiveness of the method.Comment: IEEE PES General Meeting 201

    Removing the CWB as a single desk grain marketer: Assessing the initial effects on the Canada-US feed barley market

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    This thesis examines some of the economic effects associated with the elimination of single desk marketing on Canadian feed barley exports. It focuses on the interactions between Canadian and US spot feed barley markets in transition after this policy change in Canada. A brief introduction about world and regional barley markets is provided. The role of the CWB single desk and its role in Canadian barley marketing are discussed to motivate analysis about the effects of its absence. This study postulates there should be no significant change in Canada–US regional feed barley markets, based on conclusions from previous studies. This postulate is broken down into three testable hypotheses under the framework of spatial price analysis. With respect to the Canada–US regional feed barley market as single desk marketing was eliminated in Canada; (1) There should not be a significant structural break in the feed barley prices; (2) There should not be a significant change in market integration; (3) There should not be a significant change in the direction of price transmission. To test these hypotheses, the study employs econometric tests on Canadian and US prices spot prices for substitutable feed barley. The hypotheses are tested using a structural break test, a cointegration test, a Granger causality test, and associated impulse response functions. Since structural break tests do not find significant breakpoints in the data, the first hypothesis cannot be rejected. Next, the sample is split into two subsamples at the date when single desk was eliminated. An Engle-Granger procedure and the Johansen procedure are used to test cointegrating relationships between the variables. The results do not allow us to reject the second hypothesis of no significant change in market integration. In contrast, the third hypothesis is rejected, as a significant change is uncovered using the Granger causality test. Simulated impulse responses are also consistent with this finding


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    Proceedings of the XXV ISUF International Conference “Urban Form and Social Context: from Traditions to Newest Demands” (Krasnoyarsk, July 5–9, 2018)In recent years, low carbon production and ecology have gradually become one of the most important topics in the field of architecture and urban design. Under the background of new urbanization in China, the status of eco-city theory and landscape design practice are gradually increasing in urban design. Therefore, as a new type of urban design, the landscape-oriented urban design has a strong practical significance. This method requires landscape going first in urban design and the layout of the buildings around the landscape design comes afterward. Fengxian District, part of Shanghai, is located in the southeast of the Yangtze River Delta. Since 1980s, the industry in Fengxian District has been developing rapidly with the main industry types of food, cardboard boxes, candy, printing, beauty and so on. This article takes the urban design of QiXian industrial zone as an example, introducing the application of the landscape-oriented urban design method. In this project, the venue is about 1.2 km long from east to west and 350 m wide from north to south. The original land function is for industrial use and it is to be transformed into a new industrial park where leading health and beauty as the leading industry. The design concept revolves around the “U-shaped” landscape corridors and creates a continuous corridor suitable for walking. A multi-story layout of “architecture-landscape-architecture” is adopted to construct the layout of the buildings around the landscape design and takes the form of courtyard. The paper explores landscape-oriented urban morphology design and provides new possibilities for landscape eco-city design. This paper is subsidized by NSFC project which is named as , NO.51678412

    Unsupervised Learning for Combinatorial Optimization Needs Meta-Learning

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    A general framework of unsupervised learning for combinatorial optimization (CO) is to train a neural network (NN) whose output gives a problem solution by directly optimizing the CO objective. Albeit with some advantages over traditional solvers, the current framework optimizes an averaged performance over the distribution of historical problem instances, which misaligns with the actual goal of CO that looks for a good solution to every future encountered instance. With this observation, we propose a new objective of unsupervised learning for CO where the goal of learning is to search for good initialization for future problem instances rather than give direct solutions. We propose a meta-learning-based training pipeline for this new objective. Our method achieves good empirical performance. We observe that even just the initial solution given by our model before fine-tuning can significantly outperform the baselines under various evaluation settings including evaluation across multiple datasets, and the case with big shifts in the problem scale. The reason we conjecture is that meta-learning-based training lets the model be loosely tied to each local optima for a training instance while being more adaptive to the changes of optimization landscapes across instances.Comment: Our code is available at: https://github.com/Graph-COM/Meta_C