Study On Power Flow Calculation Of Weakly Meshed Distribution Network With Distributed Generation

In recent years,the world energy crisis has become increasingly acute and environmental pollution has become more and more serious.Various countries are stepping up research on the development and utilization of new energy sources.Gradually,wind power generation and solar photovoltaic power generation are becoming the symbol of green energy.The introduction of Distributed Generation(DG)has not only increased the complexity of network structure,but also caused a surge in the number of cable lines,resulting in the increase of line R-to-X ratio.At the same time,there are new node types.In addition,there are a small number of ring networks in the system,so that the forward back generation algorithm is no longer available.It may be difficult for Newton-Raphson algorithm to converge again.Therefore,the study of power flow calculation method with DG has certain theoretical significance and practical value.DG as a new power technology,has a broad development prospect.It not only provides users with more reliable and high quality electric energy,but also strengthens environmental protection.In this thesis,a power flow algorithm which can deal with DG and weak loop network is proposed,and simulated in the system,the influence of DG on voltage and network loss is obtained.The main research contents are as follows:(1)The working principle and operation mode of DG are analyzed,and mathematical models are established according to their characteristics.(2)In the analysis of node types when DG is connected to the grid,the equivalent simulation of different models DG is used.The method of dealing with PV nodes is the principle of reactive power allocation,which determining the initial value of reactive power and the compensator is used to complete the correction of power,making the initial value of reactive power closer to the actual value.The ring network is solved by establishing an analytical model,and calculating the injection current at the end of the ring.setting up the static model of the load voltage of the quadratic polynomial model and the power function model when dealing with the load.(3)Using the improved forward back generation algorithm to carry out the calculation of the power flow.The simulation results of IEEE33 node distribution system and actual distribution system of HuangHua in Qinghai Province show that the algorithm proposed in this thesis can deal with the power flow of distribution network containing various kinds of DG,and the simulation results show that the algorithm proposed in this thesis can deal with the power flow of the distribution network with various DGs.It has better convergence and adaptability,and reduced the number of iterations and convergence time compared with the traditional algorithm based on superposition principle,making convergence stronger.(4)Different types of DG are connected in the distribution system of IEEE33 node and the distribution network of HuangHuain Qinghai province.The influence of DG on system voltage and network loss is analyzed from three aspects of access type,access location and access capacity of DG.Among them,the PV type DG is most obvious to the system voltage improvement.The farther the access location is from the root node,the better the effect of voltage enhancement.The access capacity is related to the access position,and the DG is connected to the node far away from the root node.The large capacity will increase the voltage increase,but the output capacity of the DG can not exceed the total load of two times,otherwise the system network loss will be increased.