Research On Unbalanced Power Flow Calculation Method In The Active Power Distribution System

With the development of human society,the needs of modern producing and living can be not easily satisified by the traditional energy network with one simple energy carriers.So the various energy forms has been the energy development trend,which creates various distributed generations integrated in the distribution system.This phenomenon makes traditional radial structure of distribution system change,so the intelligent distri'bution network needs a new topology structure,leading to the inadequacy of the traditional power flow.Based on the topological characteristics of intelligent distribution network,this paper presents the power flow model included initial guess estimation,remodels the distributed generations contained power electronic interface and analyzes the power flow algorithm of three-phase unbalanced systems.Detailed research contents are eas follows:1.Study on the intelligent distribution network and the reason of choosing the Newton method for power flow calculation.And the initial guess sensitivity issues of Newton method are discussed through the actual power system and standard bus system.According to the result of discussing,the next study goal can be determined.2.Referring to the initial guess sensitivity issues of Newton method,this paper proposes a convergence theorem of Newton power flow which contributes to develop a novel selection method of the initial guess and applies in the actual power system.Meanwhile,the proposed maximum iterations estimation theorem can ensure the rate of convergence.Proposed two theorems can be used to determine the convergence before calculation and directly select optimal initial guess from the feasible region.Many distributed generations are added into the power system simultaneously so that meet the needs of modern intelligent distruibution network.3.Based on the topological model of power system with distributed genenrations,and the power flow model of the electrical device in the intelligent distribution network can be built.DGs are modeled as PV or PQ depend on their operational modes and control characteristics.Based on physical network topology of DGs with AC-DC-AC interface,this thesis focus on its new mathematical model in the power flow and determines the wide range of applications.It is solve the problem that DGs are added into the power system.4.With.the increasing integration of distributed generations,there are some hindrance to keeping balance for conventional power grid.Based on the proposed convergence theorem and the mathematical model of DGs,we adopt the sequence of Newton metheod to solve the unbalanced problem.Meanwhile,the zero sequence and the negative sequence convergence theorems are proposed to ensure the convergence of power flow.