Research On The Distribution Network Optimization With DG Based On Improved Harmonic Search Algorithm

As an effective supplement to the traditional centralized power supply mode,distributed generations(DGs)are widely used in distribution networks.Reasonable DG grid connection can effectively reduce the network loss and the node voltage deviation in distribution network.But DG is not properly connected,it may increase network loss and voltage fluctuation.Therefore,the optimization research of distribution network with DG has important practical significance.Firstly,the power flow calculation models of different node types DG are established.Then the formulas of branch voltage drop and branch active power loss after DG grid connection are deduced,and the influence of DG grid connection on them is analyzed.According to the characteristics of "closed-loop design and open-loop operation" of the distribution network,combined with the topological analysis theory,a hierarchical node forward-backward power flow calculation method is introduced,and the convergence and accuracy of the method in power flow calculation of distribution network with DG are verified by an example.For the integer programming problem of distribution network represented by DG locating and sizing,this thesis analyzes several common optimization algorithms and compares their optimization results.The harmony search algorithm is selected and improved in four aspects:1)The harmonic acceptance rate is dynamically adjusted with the deviation of objective function value;2)The harmonic fine tuning rate is adjusted to the actual optimization situation;3)The harmonic fine tuning bandwidth is optimized with the change of harmonic vector mean;4)A new learning mechanism is put forward.In the process of DG locating and sizing,in order to simplify the constraints,the penalty function is adopted to deal with the over-limit value.The improved harmony search algorithm is combined with the fast non-dominated sorting strategy to solve the multi-objective optimization problem of DG locating and sizing,the simulation results show that the proposed method has good convergence.In order to solve the problem that a large number of infeasible solutions are produced in the process of distribution network reconstruction optimization using the optimization algorithm,this thesis adopts the ring network decimal coding strategy,which greatly reduces the harmony vector dimension and search space and effectively reduces the probability of generating infeasible solutions.The switch-loop matrix and the upper node matrix are used to eliminate the infeasible solutions to make sure the generated harmonic vectors are feasible solutions.Finally,the coding strategy and generating solution judgment program are introduced into the improved harmonic search algorithm,and the feasibility and convergence of the improved method are verified by the simulation of distribution network reconstruction optimization.