Research On The Model And Approach Of Stand-alone Microgrid Security Evaluation

Island economy has become China’s new economic growth point. The rationaldevelopment and utilization of island resources is inseparable from safe and reliableelectricity supply. Building a stand-alone microgrid with renewable energy is an effectivesolution to solve the problem of local electricity. However, the output of renewable energydistributed generation (DG) and load in island have strong uncertainty, which has a negativeimpact on the safe and reliable operation of microgrid. Thus, widespread application ofmicrogrid must be founded on the security evaluation. In addition, microgrid securityevaluation also plays a fundamental role in microgrid design, DG and storage capacityconfiguration, control strategies formulating, as well as technical and economic evaluation.So microgrid security research is of theoretical and practical significance.For these reasons, based on the microgrid security research, this paper carries out thefollowing research works.First of all, according to the characteristics of stand-alone microgrid, the main anduncertain factors of affecting stand-alone microgrid security are analyzed. Combined withthe principles of establishing indexes, the specific indexes of stand-alone microgrid securityare established in terms of the microgrid itself, micropower, and load.Second, owning to influence coming from many factors in stand-alone microgrid,uncertainty of certain factors and fuzzy information coming from experts, a method offuzzy comprehensive evaluation based on analytic hierarchy process (AHP) and entropyweight is proposed to assess stand-alone microgrid security. On account of stand-alonemicrogrid security indexes hierarchy, the integrated weight of each index is determined bycombining AHP brought in triangular fuzzy numbers as subjective weight with entropyweight as objective weight; then fuzzy comprehensive evaluation is conducted. The actualmicrogrid examples verify the feasibility of evaluation method.Third, in order to further ensure the objectivity and accuracy of the evaluation results,another stand-alone microgrid security evaluation method is proposed, namely fuzzycomprehensive evaluation based on back propagation (BP) neural network. After theestablishment of BP fuzzy neural network containing input layer, hidden layer, output layerneurons, learning samples are used to train the network, which makes the connectionweights between neurons of each layer get the correct internal representation throughadaptive learning. The trained neural network is applied to fuzzy comprehensive evaluation. The method overcomes the randomness of the evaluation process as well as the subjectiveuncertainty and vagueness of people’s perception. Case study shows the feasibility of theevaluation method.Finally, considering the microgrid security, this paper proposes the optimization designof stand-alone microgrid based on gravitation search algorithm (GSA). Taking total netlife-cycle costs, carbon emissions and renewable energy utilization as objective functionand taking load power shortage rate as constraint, a multi-objective optimization designmodel is established. The optimization model makes the lowest microgrid building andrunning costs, and effectively guarantees microgrid security. The optimization design of anisland stand-alone microgrid shows the rationality and feasibility of the optimizationmethod.Revolving around the study on stand-alone microgrid security evaluation, this paperputs forward two comprehensive evaluation methods and an optimization design model ofmicrogrid. The works can provide a reference for follow-up development studies onmicrogrid.