Service composition has been introduced to exploit heterogeneous resources of distributed nodes for purpose of supplying ubiquitous services in ubiquitous stub environments, especially in MANETs. However, due to the c...
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Service composition has been introduced to exploit heterogeneous resources of distributed nodes for purpose of supplying ubiquitous services in ubiquitous stub environments, especially in MANETs. However, due to the characteristics of infrastructure-less, the limited resources of the nodes and dynamic topology caused by the mobility of nodes, service composition faces great risk of failure. Therefore, service recovery handling failure is crucial to guarantee composite service's successful execution. In this paper, we propose a novel recovery selection function which incorporates device effective rate, individual capability and cooperative capability. Then we elaborate an original heuristic thought-based backup recovery algorithm: Dynamic Local Backup Recovery Algorithm (DLBRA). Finally, simulation results demonstrate that the proposed strategy ensures high performance, effectively guarantees the sustainability and significantly reduces the response time of the composite service.
This paper is divided into two cases to study the communication transmission equipment reliability in the state of the ice storm, according to the huge losses of power system communication caused by the ice storm. For...
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This paper is divided into two cases to study the communication transmission equipment reliability in the state of the ice storm, according to the huge losses of power system communication caused by the ice storm. For the nodes or links which are not affected by the ice storm, we use the calculation with “the mean time between failures (MTBF)” and “the mean time to repair” (MTTR) to put forward the calculation methods;for the OPGW cable which influenced greater in ice storm, we use the fiber excess length and the elongation of fiber optic cable. It obtains all the paths of the network through improved adjacency matrix method, and then it uses binary decision diagram to obtain the overall reliability of the network. By testing the network nodes and links using “N-1” inspection, the key nodes and key links can be obtained. Finally, considering the importance degree of network transmission business, the reliability evaluation method of power system communication network based on the risk theory in the case of the ice storm has been put forward, and the example to verify that the method can provide the basis for the reliability assessment of the power system communication in the case of the ice storm has been given.
Aiming at the disadvantage of Monte Carlo simulation method in slow convergence and using a great number of computation resources, this paper, based on analytical approach, builds a quick power system operational reli...
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Aiming at the disadvantage of Monte Carlo simulation method in slow convergence and using a great number of computation resources, this paper, based on analytical approach, builds a quick power system operational reliability analyzing model. From the viewpoint of operation, this model which is based on Markov chain, assumes that equipment failure rate follows exponential distribution. Its core content includes three aspects. Firstly, a convenient criterion, used to divide power system operation into three states, and the corresponding state-space transition expression are proposed for engineering application. Secondly, Markov state transition probability matrix is obtained based on power system operation historical data (or simulation data sample). Thirdly, based on state transition probability matrix and current operating state of power system, state transition probability, steady state probability and the mean time to first failure can be acquired very quickly. Example analysis using RBTS-BUS6 system, testified the Markov property of power system state transition and the efficiency of this study.
In this paper we model the growth of living plants in two aspects. First, modeling growth and branching process by utilizing the inherent topological structure of P system, which can naturally produce branching struct...
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Traditional voltage injection methods for DVR are in-phase strategy which injects voltage in phase with the sag voltage and missing voltage technique which compensates for the difference between the sag and pre-sag vo...
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Traditional voltage injection methods for DVR are in-phase strategy which injects voltage in phase with the sag voltage and missing voltage technique which compensates for the difference between the sag and pre-sag voltages. Since a certain component of injected voltage is in-phase with the load current, DVR has to provide some amount of energy to the grid. This paper use DQ analyzing method based on instantaneous reactive power theories to detect and obtain the parameters of source side voltage for balanced faults of three-phase three-wire system. Through circumgyrating the phasor and injecting voltage with an appropriate advance phase relative to source side voltage, the minimum energy injection can be achieved. For unbalanced faults, fictitious three-phase voltages which come from a single- phase source can be constructed mathematically, so unbalanced faults can be dealt with easily in a balanced way. Simulation results are presented to demonstrate the validity of the proposed method.
Nowadays worldwide, distributed generation plays a more and more important role in world's energy supply system. But distributed resources' innate weaknesses cause some problems such as wavy output power and i...
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Nowadays worldwide, distributed generation plays a more and more important role in world's energy supply system. But distributed resources' innate weaknesses cause some problems such as wavy output power and instability of power generation. These innate weaknesses are hard to overcome only through improving one single distributed generation plant or adding energy storage equipment etc. In this article, a new concept of connecting several AC distributed generation plants (such as wind farm) via VSC-converter, and DC distributed generation plants (such as solar cell) via DC/DC converter and forming a low voltage DC network is given. This low DC network will be integrated into AC grid in some proper way. Namely equalize these small distributed generation plants to a big power generation farm to improve stability of electricity generation. Some simulations based on PSCAD/EMTDC are also given.
Voltage fluctuation and flicker are mainly caused by surge load with large capacity, which may lead to the unstable operation of the motor, the poor characteristics of electrical equipments and the mis-operation of th...
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Voltage fluctuation and flicker are mainly caused by surge load with large capacity, which may lead to the unstable operation of the motor, the poor characteristics of electrical equipments and the mis-operation of the electronic device even damage etc. Traditional SVC can adjust the reactive power ideally to maintain the system voltage of the connection point and play an excellent role in suppressing the voltage fluctuation and flicker. The minor defect is that it can not be directly applied to the ultrahigh or extra-high voltage system. This paper puts forward a topology of SVC based on the controllable reactor. It can be made into voltage at any level to connect to the ultra-high or extra-high voltage network directly, and can dynamically adjust the saturation degree of the controllable reactor according to the fluctuation of the reactive power of the system, smoothly change the reactive power it sends out, effectively suppress the voltage fluctuation and flicker. Meanwhile, H alpha control is taker as the main control strategy. The validity of proposed approach is verified by calculation and simulation.
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