Reliability Evaluation Of Distribution System Including Distributed Generations

With the characteristics of flexible and environment-friendly, more and moredistributed energy resources will be embedded into the distribution power systems.The penetration of distributed generations (DGs) will bring a series of impacts on thestructure and operation of distribution system, and will also change its originalreliability evaluation method. Because customers could be supplied either bytraditional power resources or by DG, the failure mode and effect analysis (FMEA)process of distribution system will be changed fundamentally, in which the islandedoperation mode should be considered. What’s more, the random power fluctuationcharacteristic of renewable DGs such as wind turbine and photovoltaic and the impactof energy storage will make the problem more complicated.Based on the reliability evaluation method of traditional distribution powersystem and the analysis of the characteriscs of DGs, this paper proposed three MonteCarlo simulation methods for the reliability assessment of distribution systemincluding DGs, which can evaluate system reliability from different perspectives. Theworks in this dissertation are summarized as follows:1) A reliability evaluation method using the concept of segment and networkcoding technique for traditional distribution system is introduced. The combination ofsegment concept and network coding technique can simplify the FMEA procedure ofcomplex distribution system, and the FMEA list could be generated rapidly andautomatically. All the failures of system components including feeder, distributiontransformer, circuit breaker, fuse, isolation switch and bus could be considered, andthe method is applicable in both total loss of continuity principle (TLOC) and partialloss of continuity principle (PLOC).2) From the perspective of overall power balance, a Monte Carlo simulationmethod is proposed for the reliability evaluation of distributed generating systemincluding wind turbine, photovoltaic and lead-acid battery storage. The sequentialsimulation models of wind turbine output, photovoltaic output, battery bank’s state ofcharge (SOC) and system dispatch strategy are established. The adequacy-relatedreliability indices can be obtained using this method. The reliability impacts of utility grid capacity, renewable DG capacity, battery bank capacity as well as systemdispatch strategy are analyzed.3) A pseudo-sequential Monte Carlo simulation method for the reliabilityevaluation of distribution system including DGs with low penetration rate is proposed.The customer-related reliability indices can be obtained using this method withoutconsidering the utility grid capacity constraint. Using the concept of segment, theFMEA process of the DG-enhanced system is studied. The islands in the system areclassified taking into account the impacts of DG and the heuristic strategy isemployed for load shedding during the period of islanded operation. In the premise ofsufficient utility grid capacity, the states of the non-active elements are sampledsequentially and the active elements are sampled non-sequentially in this method,which can improve the simulation speed while still ensure a certain accuracy.4) With the combination and reformation of the above two methods, a systemstate transition sampling based reliability simulation method is proposed. Using thismethod, both the adequacy-related indices and the customer-related indices can becalculated. The state space of the system is divided into two categories of generationstate and distribution state. The system is treated as distribution system when somenon-active element is in its down state, and treated as generating system when all thenon-active elements are in up states. This method could take the utility grid capacityinto account and has a higher accuracy, which can be used for the reliabilityevaluation of the system with high DG penetration rate.