Study On Power Flow Calculation Of Weak Loop Distribution Network With Distribution Generation

With the improvement of production and living standards,human beings pay more and more attention to the improvement of their living environment.The momentum generated by this awareness is driving a dramatic shift in the modern energy mix.In recent years,Inverter Based Distributed Generation(IBDG)has been applied to traditional power distribution networks.Power flow calculation is the base of distribution network operation analysis and control,as the IBDG permeability is higher and higher,a great change of the distribution network topology structure and the trend of the distribution will,it puts forward a new challenge for the operation of the power distribution network management,especially in overloading or distribution network fault processing weak ring would appear,tide distribution will appear some new characteristics.Therefore,this paper studies the power flow calculation method of weak loop distribution network with IBDG.The main contents of this paper are as follows.(1)Establish the equivalent model of IBDG.By analyzing the output characteristics of IBDG under PQ control strategy,the equivalent model of IBDG and the calculation method of parameters are studied.In the process of power flow calculation,according to whether IBDG enters the current limiting state,the model before IBDG current limiting is equivalent to PQ bus,and the model after IBDG current limiting is equivalent to Iθ bus.(2)In this paper,an improved forward and back substitution algorithm for ring network is used to calculate and analyze the weak ring distribution network.Then,according to the superposition theorem,the loop network is decomposed into pure radiation network and pure ring network.The pure radiation power flow is solved by the road matrix method,and the pure ring power flow is solved by the loop current method.Finally,the power flow of the weak loop distribution network can be obtained by superimposing the power flow calculation results of the two networks.(3)A power flow calculation method for weak loop distribution network considering IBDG current limiting state is proposed.In the process of power flow calculation,the difference of equivalent models before and after IBDG current limiting is considered,and the judgment link of IBDG current limiting state is increased.Before current limiting,IBDG is equivalent to PQ bus,and the power flow of weak loop distribution network is calculated by road matrix and loop current method.After current limiting,IBDG is equivalent to Iθ bus,and the nonlinear equation is solved by bovine method.In this process,it is necessary to modify the diagonal elements related to Iθ bus in the Jacobian matrix (?)ΔP/(?)ΔU and(?)ΔQ/(?)ΔU.Finally,on the basis of the theoretical analysis,the relevant algorithm program is written to verify the analysis conclusion of the power flow calculation method of the weak loop distribution network.The simulation results are consistent with the theoretical results,which prove the correctness and effectiveness of the proposed method.