Static Voltage Stability Analysis Of Distribution System Containing DG Based On Dynamic Equivalent Circuit

In recent years,energy crisis and environmental pollution are becoming increasingly serious,distributed generation technology has been developing rapidly for its flexible,environmental and efficient characteristics.The combination of distributed generation and power grid is an important direction of modern power system development.However,the distribution network changes from original single-power radial structure to multi-power structure after the combination of distributed generation,which will inevitably lead to the change of the size and direction of power flow and affect the static voltage stability of distribution network.Based on the analysis of advantages and disadvantages of Thevenin equivalence,this paper expounds the comprehensive dynamic equivalent analysis method of power system and impedance modulus margin index based on dynamic equivalent circuit,the index can effectively evaluate the static voltage stability of power system and determine the weak nodes of voltage stability.And it is applied to analyze the static voltage stability of distribution network containing distributed generation.In order to analyze the static voltage stability of distribution network containing distributed generation,the steady state models of doubly-fed wind turbine and photovoltaic power generation system are established,for the steady state model of doubly-fed wind turbine,the method of calculating the reactive power limit is given based on the law of rotation speed control.The distributed generations are divided into four node types according to the operation characteristics and network interfaces,the processing methods of various node types in power flow calculation are also given.Then,the equivalence circuit parameter model of doubly-fed wind turbine is established,it is equivalent to the model of the internal virtual PV node which is connected to distribution network through the equivalent impedance,and the equivalent process is expounded.The static voltage stability of distribution network containing distributed generation is analyzed by simulation.Firstly,the steady state models of doubly-fed wind turbine and photovoltaic power generation system are respectively connected to IEEE 33-node distribution system,using impedance modulus margin index to analyze their influence on static voltage stability from the following aspects:the access capacity,location,power factor and types of DG.And summarize the law from the above analysis.Then,the steady state model and the equivalent circuit parameter model of doubly-fed wind turbine are respectively connected to the above-mentioned power distribution system,the influences of the two models on the static voltage stability of distribution system are compared by simulation based on impedance modulus margin index.