Research On Reliability Evaluation In Distribution System With Distributed Generation

In this day and age,due to the continuous consumption of traditional energy sources and the increasing concern on environmental issues,countries around the world encourage the research on renewable energy and their policies support the development and utilization of distributed energy sources.Along with the development of society and the new round of power grid upgrading,more and more distributed generation units are interconnected into grid.This trend brings much uncertainty to grid and offers a new way for distribution network to improve power reliability.In this background,the undesired impact due to islanding detection failure and positive effect due to intentional islanding on distribution reliability are studied in this paper when different distributed generation units connect into distribution system under various levels of automation.The main research work and the results achieved are as follows:(1)Propose a simplified distribution network topology description method.In view of the complexity of the distribution network coding methods used in the existing literature,a simplified distribution network topology description method is presented in this paper,using array to store the information of the network nodes connected and their interconnected component type.Then the simplified partition,failure mode effects analysis and Monte Carlo simulation process are introduced based on the topology information array.(2)Propose a reliability evaluation method for distribution networks considering passive islanding detection failure.In an underdeveloped distribution automation system,if a failure occurs,distributed generation need to disconnect with the grid at once to make sure automatic reclosing can operate correctly.Their passive islanding non-detection zones vary because they utilize inverters using different control methods.Therefore,considering the probability of islanding detection failure,a reliability evaluation method for distribution networks considering passive islanding detection failure is presented and several test systems are built in this paper.The results show the reliability indices of local users dropped obviously after considering the impact of passive islanding failure.With the rated power of distributed generation changes,the reliability indices float up and down.When the rated capacity is larger than the sum of peak load,the system reliability indices gradually pick up.(3)Propose a distribution network reliability evaluation method with distributed generation based on short-term wind forecasting.Based on short-term load and wind power output forecasting data in distribution network,the effects on failure rates,component repair time and wind power output caused by wind speed variations are considered.According to the intentional islanding operation time,the islanding operation area needs to be divided to make sure distributed generation output is larger than load demand all the time.In the end,a distribution network reliability analysis method based on short-term wind forecasting is proposed and several test systems are built to prove the effectiveness of the proposed approach.The results show the distribution network reliability in windy weather is much lower than that in normal weather after considering the impact of wind speed on distribution network operation.Besides,due to the high wind speed in windy weather,wind power generation increases and the intentional islanding area is likely to expand,thus enhancing distribution network reliability.