Research On Methods Of Optimization And Comprehensive Judgement Of Transmission Network

Reasonable planning power network structure is important to ensure the safe and steady operation of power system. The transmission network planning process can be divided into two stages, that is, the forming stage of superiority planning scheme and the stage of comprehensive decision-making, according to the two-step planning approach which is widely used in actual engineering practice. However the two-step planning approach depends on theoretical knowledge and designing experience of the planners, so the planning result is strong with subjectivity and seriously influenced by preference of the planners. So intelligent optimization algorithm is adopted to form the superiority planning scheme set and scientific decision-making method is used, considering each factor having effect on planning scheme. In this way, the planning process turns out to be scientific and reasonable, and the subjective factors in the process of planning can also be decreased.In the forming stage of superiority planning scheme, object function is established only considering economic factors. Relying upon random walk of artificial fish when the inferior solution has to be accepted unconditionally, the artificial fish school algorithm (AFSA) applied to transmission network expansion planning gets rid of local extremum, however the defect of this approach lies in its evident blindness, and convergence speed of AFSA is different in optimization stages, in the initial optimization stage its convergence speed is fast and in the later optimization stage the convergence speed decelerates. To remedy above-mentioned defect, combining with simulated annealing algorithm (SA) , a hybrid artificial fish school algorithm (HAFSA) is proposed, in which the utilization of probabilistic kick search mechanism of SA makes the skip capability of local extremum controllable, thus the blindness of AFSA algorithm is alleviated and the efficiency of the algorithm is improved. Lead in the feedback mechanism of the piecewise adaptive adjustment strategy of visual field, both global search ability and local mining ability are considered; adding in the mutation operator of pseudo-genetic algorithm speeds up the convergence speed in later optimization stage. Simulation results of IEEE 6-bus system and Southern Brazilian 46-bus system show that the proposed HAFSA is correct and effective and can also exert its potential in solving planning problems of large-scale transmission network.In the stage of comprehensive decision-making, principal component analysis (PCA) is applied to determine the weight coefficients of factors having impact on the planning scheme, based on the evaluation of each factor. PCA depends entirely on the characteristics of objective data to determine the weight, which can reduce the subjective factors in the evaluation process and also avoid the difficulty for the expert to determine the weight. The simulation results prove that PCA applied in comprehension decision-making of transmission network planning scheme is reasonable and credible.