| With the iteration of the traditional distribution network and the penetration of high-proportion Distributed Generation(DG),the active distribution network is gradually becoming mature,and the energy pressure can be effectively alleviated.However,the active distribution network needs appropriate improvements and optimizations to adapt to the current new environment of the power industry,for there are still many problems presented by the large-scale grid connection of DGs in it,including the change from unidirectional power flow to bidirectional power flow in a certain area,voltage stability problems caused by changes in reactive power distribution and harmonics increasing.Solid State Transformer(SST)has the functions of maintaining system voltage stability,improving harmonics,and having high and low voltage DC output.Therefore,the active distribution network with SST can effectively solve the faster-growing power demand and power than the traditional distribution network.The contradiction between production,but it adds a certain degree of difficulty to the reactive power control of the active distribution network with SST,including finding new objective functions,SST constraint sets,control variables,etc.,and also increases the difficulty of solving complex models.With the development of new energy power generation,the distribution network faces a variety of situations.The establishment of an SST-containing active distribution network optimization model is a topic worthy of in-depth study,and the correct solution of the model is particularly critical.Firstly,the thesis gives a detailed overview of traditional distribution networks,active distribution networks with SST,and several common algorithms for solving distribution network optimization models,and analyzes the principles of reactive power optimization and voltage adjustment of typical AC/DC and AC/DC/AC SSTs,including SST working structure,mathematical models and control methods.Secondly,the power flow calculation is the most basic and most important when analyzing the reactive power optimization of the distribution network.Considering that the traditional power flow calculation of the distribution network is not applicable to the active distribution network with SST,so this thesis presents an improved forward backward power flow calculation method suitable for active distribution network with SST,and makes the case analysis and verification.Thirdly,aiming at the algorithms commonly used in reactive power optimization of distribution networks to find the Pareto optimal solution,this thesis detailly compares and analyzes the advantages and disadvantages of the current relatively new BAS algorithm and the classic NSGA-Ⅱ algorithm,then proposes a hybrid multiobjective algorithm of NSGA-Ⅱ algorithm and BAS algorithm to solve it.The hybrid algorithm combines the advantages of simple programming of the BAS algorithm and the stability of the NSGA-Ⅱ algorithm,making the hybrid algorithm stronger in optimizing and faster in converging.In addition,feasibility and effectiveness of it is verified through using test functions and comprehensive metrics.Finally,this thesis establishes the objective function and constraint conditions of the active distribution network with SST,apply the BAS and NSGA-Ⅱ hybrid algorithm to the reactive power optimization solution of the active distribution network with SST,and simulates the modified IEEE-33 node system under both normal load and heavy load.Meanwhile,the simulation also compares and analyses the system network loss and voltage quality under different optimization measures,and then verifies that the hybrid algorithm is superior to the single algorithm in the optimization calculation of active distribution network with SST.It is shown that the reactive power optimization of active distribution network with SST is better in terms of loss reduction and voltage quality,so that the distribution network can bring the maximum utilization efficiency into full play. |
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