Study On Credit Variables And The Maximum Hosting Capacity For Distributed Generations In Distribution Networks

The distributed generation is an important energy for social development,and can be employed as an effective substitute for a distribution network to a certain extent.On the other hand,the large-scale access of distributed generations results in the change from traditional passive networks into active ones,bringing new challenges to the planning and operation of distribution networks.Therefore,the following two aspects of study have been conducted in this paper.One is to evaluate the credit effect of distributed generations on distribution networks based on a simplified probability planning method,and the other is to calculate the maximum hosting capacity of distributed generations in a distribution network.Under the assumption of uniform load distribution,the substation probability planning problem with distributed generations is approximately simplified into two subproblems in this paper.First,the numbers of substations and feeder lines are found,then the substation capacities are determined.The former is to minimize the total cost including the fixed investment cost of substations and the cost of medium voltage feeders,while the latter is to minimize the total cost including the variable investment cost of substations and the outage loss cost of main transformers.In the model the effects of load change,distributed generation randomness and load transfer rate on power outage time and outage costs are comprehensively taken into account,and a line length estimation model is proposed for medium-voltage main and branch lines.Four types of credit variables are defined and the corresponding calculation formualre are given,which are used to evaluate the substitute effects for the substation number,substation capacity,feeder number and distribution network construction funds corresponding to distributed generations.The examples’ calculation results show that the probability planning can generally reduce the substation number,substation capacity and feeder number as compared with a traditional method,and the access of distributed generations has a certain substitution effect on a distribution network.For the electrically relatively independent feeder groups or subareas,an optimization model is established for the hosting capacity evaluation of multiple distributed generations with different types and locations under multiple constraints,and a corresponding fast solution method is proposed.In the model,the objective is to maximize the total access capacity of distributed generations,and the constraints involve technical standards of voltage deviation,voltage fluctuation,short-circuit current and relay protection.A single-constraint and a multi-constraint coordinated piecewise calculation method are presented based on a dynamic sensitivity of constraint indexes to distributed generations,which involves two calculation processes of backward and forward calculation.Among them,the multi-constraint coordination method can coordinate and consider the interaction between multiple types of constraints,which is suitable for a system with different types of distributed generations.The examples’ calculation results show that the proposed method is intuitive,stable and efficient,and can provide technical guidance for the siting and sizing of distributed power sources in distribution networks.