Research On Holomorphic Embedding Power Flow Calculation Method In Active Distribution Network

In recent years,with the rapid development of the economy,the demand for electricity has continued to grow,which has led to increasingly serious environmental pollution and fossil energy crisis.To address the above issues,countries around the world have successively introduced policies to support the development of renewable energy.Therefore,it is necessary to transform the energy utilization architecture,develop and utilize renewable energy,and achieve a high proportion of renewable energy integration into the grid.However,with a large number of distributed generation(DG)connected to the distribution network and the introduction of soft open point(SOP)into the distribution network,the power flow(PF)calculation of the distribution network needs to consider the impact of different types of DG grid-connection modes and different SOP control strategies on PF distribution,which makes PF calculation of the distribution network with multiple types of DG and SOP more complicated and is a challenge to accurately solve PF of distribution network.Therefore,studying PF calculation method for active distribution network with various DG and SOP is of great value.At present,PF solution methods of distribution network mainly include Newton Raphson(NR)method and Forward Backward Substitution(FBS)method.However,they may fail in convergence and computational efficiency for distribution networks with large R/X ratio of lines,high load level and radial or weak network structure.The holomorphic embedding method(HEM)as a novel PF method can effectively avoid the above problems,but the existing HEM does not fully consider the different types of DG,the diversity of the control modes of SOP,and the voltage and frequency characteristics of the loads,which is also difficult to solve PF of active distribution network under different operating modes.Under such research background,the following research work is completed in this paper:Firstly,according to the topology of the active distribution network and the operation characteristics of each part of the active distribution network,taking into account the static voltage characteristics and frequency characteristics of the load,the different grid-connection modes of different types of DG and the flexible control mode of SOP,the construction of the active distribution network PF calculation models are completed.At the same time,the embedding mechanism of holomorphic functions and the basic conditions for constructing holomorphic functions are introduced,and the calculation process of direct method to achieve Pade approximation is briefly analyzed.Then,to achieve the solution of PF distribution in active distribution networks with multiple types of DGs,according to the principle of holomorphic embedding,the construction and solution of the holomorphic embedding PF calculation models of active distribution network with multiple types of DG are completed,and a holomorphic embedding PF calculation method for active distribution network with multiple types of DG and operating in grid connection mode is proposed.This algorithm can effectively avoid the problems of poor PF convergence and low computational efficiency that occur in the NR and FBS methods for solving PF distribution of active distribution networks with multiple types of DGs,and the algorithm can achieve accurate and efficient solution of PF distribution in active distribution networks with multiple types of DGs.The validity and accuracy of the proposed method are analyzed and verified by the modified IEEE-33 distribution network test system under grid-connection operation mode.Finally,a unified HEM for active distribution network,which can solve PF of active distribution network including multiple types of DG,SOP and operating in grid-connected or islanded mode is proposed.This method fully considers the different grid-connection modes of different types of DGs,the flexible control mode of SOP,and the static voltage characteristics and frequency characteristics of loads under island operation and grid connection operation modes.The accuracy and effectiveness of the proposed PF calculation method of active distribution network method based on HEM are validated by the modified IEEE-33 and IEEE-123 distribution network test system under grid-connected/islanded operation mode.The results of numerical examples show that the proposed method can accurately solve PF distribution of active distribution networks with multiple types of DG and SOP and can operate in grid connection/island mode,and the proposed method has good versatility and better robustness in PF calculation.Meanwhile,compared to NRM,the proposed method does not rely on initial value selection,and has higher computational efficiency while ensuring the accuracy of PF solution.