Research On Distribution Network Reactive Power Optimization With DG Accessed Based On Solid State Transformer

With the development of smart grid,there are more and more Distribution Generation(DG)appeared in the distribution network.Although distributed generation has its unique advantages,the increase of its proportion has brought new problems to the network.It included that the traditional AC distribution network into a certain range of AC/DC hybrid distribution network,the distribution network voltage stability problems caused by the changed of reactive power distribution,and harmonic increased,etc.The traditional distribution network optimization model is no longer suitable for the new environment,how to deal with these problems has very important practical significance.SST(Solid State Transformer)compared with the traditional power transformer has the advantages of reducing harmonic,keeping voltage stably,controlling reactive power and having high and low DC voltage output characteristics.With the flexible substation project started,how to establish a distribution network reactive power optimization model with DG and use algorithm for optimal utilization based on SST is very critical,when we are using SST for distribution network reactive power control.First,this thesis has introduced the principle of solid state transformer and common topology;Established the simulation model of AC/DC/AC SST and given the control strategy.According to the typical simplified structure and control strategy of SST,the simplified simulation model of SST has built in the Matlab/Simulink environment.Based on simulation model of SST,this thesis has done kinds of simulation under various conditions,which verified the function and explained the control rationale of SST.Secondly,this thesis analyzed the interface in the system power flow model of the characteristics of various types of DG,and the reactive power control method and power flow calculation model of SST,and given the way that how SST access to distribution network;This thesis also analyzed the commonly way of power flow calculation,and given the calculation method and calculation the process according to the characteristics of hybrid AC/DC power distribution system with DG.Thirdly,this thesis analyzed the objective function and constraints,and the reactive power optimization algorithm’s main steps and flow which was prepared for distribution network with SST and DG.Through examples,the results show that the optimization results based on SST was better than the optimization results based on OLTC transformer in reactive power optimization of distribution network with DG,no matter how in power loss or voltage deviation.The results also shown the advantages of solid state transformer.At last,in order to achieve a greater degree of optimization in the distribution network operation,the thesis chose to combine reconstruction of distribution network with reactive power optimization.Therefore,a new algorithm of distribution network reconfiguration is proposed,and a model is built for the case of after reconstruction.The optimization results based on SST was better than that based on OLTC Power Transformer.Otherwise,the result of integrated optimization scheme was better than basic scheme.Therefore,it’s practical to take the integrated optimization scheme.