Time filter

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Yang Y.,Shanghai University of Electric Power | Wei G.,Shanghai University of Electric Power | Zhou B.,Shanghai University of Electric Power | Zhang X.,Shanghai Electric Power Company
Diangong Jishu Xuebao/Transactions of China Electrotechnical Society

In traditional distribution network planning, uncertain planning parameters is difficult to deal with. To study further this problem, load forecast values is taken into account and the credibility theory and uncertain programming is introduced into it. Then a distribution network planning model is presented, which is based on fuzzy expected value model. The optimal solution is found using genetic algorithm. In this model, trapezoidal fuzzy variable is used to represent load predictive value. Moreover, the objective function and constraints of the model possess definite mathematical meaning, and the solution can be found by the strict mathematical approach. This model overcomes the defects of traditional distribution network planning model, such as, neglects the fuzziness of the load forecasting results or constructed fuzzy optimal planning model has no obvious mathematical meaning. An example illustrates that comparing to the traditional distribution network planning, the grid planning result obtained by this method is more adaptable to the uncertainty of the load in the future. Source

Liu L.,Shanghai JiaoTong University | Wang H.,Shanghai Electric Power Company | Cheng H.,Shanghai JiaoTong University | Liu J.,State Power Economic Research Institute
Dianli Xitong Zidonghua/Automation of Electric Power Systems

In order to overcome the neglect of medium-and long-term costs while underestimating short-term investment in current power systems in economic evaluation, a 3-dimensional life cycle cost (LCC) model for the power system as a whole is developed in the perspective of the component dimension, the cost dimension and the time dimension. The cost dimension is studied by structurally analyzing the device layer, the system layer and the cost of surroundings. A series of strategies for economic evaluation based on LCC is presented. The conversion methods are studied for devices with different life cycles. Multistage calculation is applied for devices with different runtimes. The traditional economic evaluation indicators are improved and the efficiency indicators based on LCC are proposed. Case studies are made on an actual 500 kV substation and 110 kV distribution network, respectively. It is shown that the economic evaluation results are much more accurate and valid, providing a reference for further deepening asset management of power systems. Source

Hu R.,Shanghai Electric Power Company
Dianli Zidonghua Shebei/Electric Power Automation Equipment

When the more prevailing LCL filter is adopted in mid/high-power grid-connection system, special control strategy should be applied to suppress the resonant peak caused by it. A low-cost dual-loop strategy of the inner filter capacitor current control loop and the outer grid-connecting current control loop is proposed for bi-directional power conversion system, which is thoroughly discussed in three aspects: main circuit parameter design, controller parameter design and controller performance analysis. A parameter design method of inner-first-outer-last is given and a prototype of 50 kW bi-directional power conversion system is built. Experimental results verify that, the proposed control strategy ensures the stable operation of LCL filter and reduces the harmonic of grid-connecting current. Source

Lei Z.,Shanghai University of Electric Power | Wei G.,Shanghai University of Electric Power | Cai Y.,Shanghai University of Electric Power | Zhang X.,Shanghai Electric Power Company
Dianli Xitong Zidonghua/Automation of Electric Power Systems

With a large scale of distributed generations (DGs) being installed and operated in distribution network, variety of power sources and complexity of their operation will greatly effects the reliability of distribution network. Different DGs'models and various operation situations have been studied, in which a network model called zone-nodes including DGs is introduced. The calculation model of reliability is build based on different failure types affected by zone-nodes, and the principle of island operations is definite. Then, on the above basis, a Monte Carlo simulation method is applied to solve this model. An example demonstrates the validity and practicability of the model and simulation method. The result of test example indicates that DGs can improve the reliability of distribution network, but also have some adverse impacts on it. The traditional reliability indices can not perfectly evaluate advantages or disadvantages of DGs'impact, it is recommended to standardize the evaluation system of the impacts of DGs on distributed system. © 2010 State Electric Power Research Institute Press. Source

Yin J.-L.,North China Electrical Power University | Zhu Y.-L.,North China Electrical Power University | Yu G.-Q.,Shanghai Electric Power Company
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control

The transformer fault diagnosis is naturally a multi-classification problem with few sample data and a lot of uncertainties. Among the existing transformer fault diagnosis methods, a large number of sample data and amount of computation are needed for Bayesian Network (BN), and the adjustment of the coefficient is difficult for support vector machine (SVM). So a new method of transformer fault diagnosis based on multi-class relevance vector machine (M-RVM) is proposed. The method takes ratios of feature gases as inputs and Fast Type-II ML and expectation maximization (EM) are adopted. Diagnostic outputs are probability for each fault category and fault type with the highest probability is taken as diagnosis result. Experimental results show that the diagnosis speed is sufficient for project needs and M-RVM shows higher diagnosis accuracy compared with BN and SVM. Source

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