Study On Optimal Switching Model And Algorithm For Electrical Distribution Networks

This dissertation is sponsored by the project ("Study on Optimal Switching Modeland Algorithm for Electrical Distribution Networks Using Immune-Algorithm",No.50307015) of the national natural science fund of China. In this paper, reliabilityevaluation, placement of optimal switching devices (POSD) and reconfiguration ofcomplex electrical distribution networks (EDNs) are studied. EDNs are connected directly with customers. It was researched that 80% of the totalcustomer interruptions resulted from EDNs. So, at present, the electric power utilities arefocusing on satisfying the demands of the customers and transmitting the electricitywithhigh quality and reliability to the customers. This dissertation proposes thesection-algorithm for evaluating reliability, the model of POSD taking into account thereliability and economy using the method of cost-benefit analysis, and the reconfigurationalgorithm for minimizing the system loss of EDNs. Because the models of POSD andreconfiguration are non-linear, combinatorial optimization problems, dynamicprogramming (DP) is introduced to solve these two problems. The main contents are asfollows. ① This dissertation presents a novel method of reliability evaluation for EDNs, i.e.,section-algorithm. Based on the structure characteristics, the proposed method forms allsections of the EDNsusing Width-First-Search technique. It applies the fault-spreading-method to determine the areas controlled by breaker and switching devices, and regards asection not a component as a unit during the computing process of reliability evaluation.This method can save sharply time consumed in searching repeatedly theswitching-devices. Assessment results of some RBTS systems and an actual EDN showthat the proposed algorithm has an obvious advantage in saving time and the engineeringpracticability. This algorithm is the basis of the POSD of EDNs in the next section. ② This dissertation presents a model based on DP for POSD in EDNs. The modelof POSD is formulated as a combinatorial constrained optimization problem with anon-linear, non-differentiable objective function. The DP based solving algorithm forPOSD is proposed. It regards the switching device and its location as the state, and thenumber of switching devices as the stage of DP. During the calculating process, acriterionhas been used to reduce the computing complexity: if the optimal value of somestate at the (k+1)th stage is not less than the optimal value at the kth, then the state will not III重庆大学硕士学位论文 英文摘要be considered at the later stages. This criterion of POSD improves the efficiency of theproposed algorithm. The test of RBTS-BUS6 and some practical ENDs show that theproposed algorithm is accurate and suitable for POSD. ③ Reconfiguration of EDNs(REDN) is formulated as a complex, large-scalecombinatorial optimization problem. The algorithm of REDN based on DP is presented inthis dissertation. The restrictions such as voltage, capacity, load balance and etc. are takeninto account and the relevant mathematical model of REDN is proposed. The conceptsabout DP such as state, decision-making, strategy, stage, index function and etc. areintroduced and deduced. The technique of effective combination and benefit are used toreduce the combination dimensions and sharply improve the efficiency. The proposedalgorithm is applied to IEEE-33 and IEEE-69 systems and a practical engineering EDN,and the results of voltage and system loss are compared with those obtained from someother methods, which show the accuracy and feasibilityof the proposed method. ④ Applying all the programs to the practical engineering EDNs, the excellentresults have been acquired. A practical EDN with 511 nodes is evaluated bysection-algorithm within 1.6 second, which is only the 5.33% of the traditional method.At the same tim...