Study On Reliability Evaluation Model And Algorithm For Distribution System With Microgrids

As people require the higher power supply and reliability, the reliability ofdistribution network have been increasingly concerned and emphasized. Micro-grid hasbecome a hot research spot that drew worldwide scientists’ attention for the reason thatit can use the distributed power generation technology to improve power supplyreliability and to alleviate growing energy crisis and environmental pollution pressure.However, Micro-grid converts conventional radial distribution network with singlepower supply to a new one with all kind of distributed generators. Meanwhile, theoutputs of these distributed generators are not deterministic because of the intermittencyof renewable power, such as wind and solar energy. So it brings a lot problem since weevaluate the reliability of distribution network with micro-grid. This pepper focus on thereliability assessment of distribution network with micro-grid, the main work and resultsare listed below.①According to the features of closed-loop design and open loop operation ofdistribution network．A fast reliability evaluation algorithm for large scale distributionsystems based on backward/forward sweep method is proposed．The backward/forwardsweep formulae to calculate the reliability indices of nodes in different branches aregiven．Outage of node caused by the failure of downstream components has beencalculated during forward sweeping；then，it has been corrected during backwardsweeping considering the influence of the failure of upstream components．By reason ofcarrying out once of topological analysis and back/forward sweep calculation，time-consuming for reliability assessment is greatly reduced．The algorithm can be usedto evaluate reliability of distribution network with multiple backup powers which makesit has a better engineering practicability．The feasibility and validity of the proposedalgorithm is verified by simulation results of the example system．The results show thatthe proposed algorithm is faster than the existing algorithms．②Equivalent models of micro source for each load point have been builtconsidering uncertainty of distributed generators which is caused by intermittentrenewable power. Firstly, a multi-state Markova model is built for distributed generatorwith renewable energy; then two-state equivalent models of micro source for each loadpoint are gained according to the power supply and the cumulative load demand wheneach load can be supplied. At last, to evaluate the reliability of distribution system with micro-grid based on the backward/forward sweep algorithm, taking into accountintermittence of DG, DG availability ratio，the importance of the load and load level.This pepper also proposes some new indices to evaluate the capacity of micro sourcecontinual supply.③To evaluate the reliability of distribution system with micro-grid consideringthe node load correlation. Firstly, to calculate the probability density of each load pointusing non-parametric kernel estimation and divide each load into several categoriesaccording to the load size; then use the copula correlation theory to study the mode ofcorrelation of load point; at last, to enumerate load level for each load point inmicro-grid and calculate the probability of each composition scenario. And on this basisevacuate the reliably of distribution network with micro-grid.