A new approach combing connection number and fuzzy simulation to calculating power flow of distribution network considering uncertainty

The power flow calculation considering uncertainty is the most basic way for solving the security issue of the system under uncertain conditions. As the renewable energy characterized by randomness and uncertainty, such as wind and solar power, has been applied to the distribution network, it is especially essential to study on power flow of distribution network considering uncertainty. The traditional models of uncertainty have the problem of singleness in expressing uncertainties while the uncertainty objectively shares two or more than two kinds of characteristics. A new model for describing the uncertainties, which combines connection number and fuzzy number and describes the interval quality and fuzziness of uncertain information comprehensively, is presented. Through improving the calculation of sample value and possibility measure, the traditional fuzzy simulation is modified and then applied to the power flow calculation in consideration of wind and solar power output uncertainty and load uncertainty. Two definitions, which are satisfaction index and degree of uncertainty, are introduced to measure the results accuracy with sample number changing and to represent the variation range of uncertain parameters respectively. The proposed model and modified algorithm are verified by case studies based on IEEE 33-bus system. The results are compared with those obtained from Monte Carlo simulation and proved to be correct. In addition, several other numerical examples are presented and discussed in order to achieve the influences of sample number, degree of uncertainty and membership function change on results. Through analysis of the power flow results considering uncertainty, we may find out the weak links of network, which can provide references for making electrical accident premeditation and then adjusting operation scheme.