Impact Of DG’s Behavior On Voltage Sag In Distribution Network

In modern times,energy resources like coal,natural gas and petroleum are suffering the crisis of being exhausted when the pace of human society and technology runsat a high speed.Therefore it is necessary for us to explore and make use of new resources and to render them as the material that can generate electricity.Distributed generations or DGs now appearin various forms.And the most widely used DGs can be summarized as the wind power generation and solar power generation.On the back of centralized power generation and integral grid style,the modern power system is gradually transforming into the very system that contains certain sorts of DG.However,as a result of theirexcessive penetration,the voltage quality of the power system has been inevitably disturbed and becomes unfavorable for both the customer and the grid.In the first partthis paper describes the characteristics of DG’s behavior in power system and figures out how DG affects the voltage quality.Then the models of DG’s interconnection to the distribution network andtwomost widely used DGs are built in this paper.Theinterconnectionforms are synchronous motor,asynchronous motor and inverter.The wind power generation model consists of two main blocks,one is the wind speed function model and another is the wind turbine model.The solar power generation model is made up of the dynamic mathematic interconnection model and the control strategies of inverter.After the analysis for DG’s interconnection,this paper proposes the voltage quality problems and explains the voltage-power properties of distribution network with DG.When comes into the stochastic evaluation of voltage sag,the paper introduces three frequently used methods and choses to employ Monte Carlo method.This methodcontains the stochastic model that can come about the fault information.And this information can beregarded as the true casesin distribution network that are supposed to happen.Finally this paper employs a simulation tool,namely PSCAD/EMTDC,to conduct the research of voltage sag problem and DG’s influences.According to Monte Carlo method,a test system with 27 nodes is modeled in PSCAD.Then the simulation process will allow for DG’s different configurations such as types,sizes,positions and control strategies as well as the stochastic model of faults.The data that is collected from the process will be calculated into SARFI,an index that can evaluate the voltage sag.In the end,results show that the frequency of voltage sag can be alleviated obviously by adjusting the four configurations of DG mentioned above in right ways.This provides the theoretical references for optimizing the DG configuration and mitigating the voltage sag in distribution network.