Reliability Evaluation Of Distribution Network With High-permeability Distributed Generation

With the increasing depletion of fossil energy and the increasing problems of environmental governance,countries around the world are increasingly focusing on the development of clean energy and the promotion and application of flexible loads such as electric vehicles,using clean energy to replace traditional energy sources to supply power to the power grid.At the same time,gradually replacing fuel-gas vehicles with electric vehicles has become the most effective measure to solve the energy crisis and environmental pollution.However,when distributed clean power sources and electric vehicles are increasingly access to the distribution systems,it will change the traditional method of reliability evaluation.At the same time,the output of the distributed power supply is fluctuating,intermittent and uncertain.This output characteristic will be superimposed on the charging load of the electric vehicle and the original load of the distribution network,which will further increase the peak-valley difference of the distribution network.This has brought new problems and challenges to the overall capacity and operation scheduling of the distribution network.Electric vehicles have the dual characteristics of energy storage and load.Through an orderly scheduling strategy,the charging and discharging behavior of electric vehicles can be adjusted to optimize the overall load curve of electric vehicles.At the same time,the implementation of demand-side response policies can change the user 's usage from the load side.Electrical behavior,in conjunction with electric vehicles,can cut the peak and fill the valley of the entire distribution network and improve the reliability of the distribution network.At this time,when multiple loads such as high-permeability distributed power sources and electric vehicles and demand-side response loads are connected to the distribution network,the distribution network reliability assessment method also needs to be further changed to adapt.This paper first introduces the index system and evaluation method of traditional distribution network reliability assessment,outlines the distributed power generation timing modeling methods of photovoltaic,wind turbine,energy storage,etc.and the real-time volatility model of load.And from the perspective of satisfying the load demand to the maximum,three coordinated operation strategies of wind-solar storage combined power generation system are proposed.Secondly,according to the operating characteristics of distributed power access to the distribution network,the regional division strategy of the island operation of the distribution network is proposed.Finally,the reliability evaluation process based on the sequential Monte Carlo method is outlined,and three coordinated operation strategies are proposed Establish three kinds of calculation scenarios,compare and analyze the impact of different coordinated operation strategies on the power supply of each load point and the overall reliability of the distribution network.It is concluded that different coordinated operations should be considered at different planning stages of the distribution network Strategies to improve the reliability and economy of distribution networks.After the high-permeability distributed power source is connected to the distribution network,the load types are also diversified.In this paper,electric vehicles and demand-side response loads are selected as two typical loads in the background of high-permeability distributed power access for reliability modeling and analysis.In terms of electric vehicle charging and discharging load model,this paper first obtained a mathematical model of its travel behavior based on the travel characteristics of private fuel vehicles.Based on the travel chain structure,the electric vehicle charging and discharging model was established by Monte Carlo sampling method Under the constraints of charge and discharge,an orderly charge and discharge model under the access of large-scale electric vehicles was established based on particle swarm optimization.In terms of demand-side response,the transferable load and load-reducible load are modeled and analyzed,and combined with the characteristics of the reliability evaluation method,a two-stage load optimization model based on demand-side response during the failure period is established.Finally,this chapter uses the sequential Monte Carlo method and a simplified reliability evaluation model of power generation-demand to analyze the reliability of distributed power generation systems,electric vehicles,and distributed power generation systems connected to demand side response loads.The orderly charge and discharge of the electric vehicle and the demand-side response during the fault period can improve the operational reliability of the distribution network to varying degrees and reduce the peak-valley difference of the distribution network.Moreover,different demand-side response ratios can also affect the distribution network reliability index to varying degrees.When high-permeability distributed power and multiple loads are connected to a specific distribution network structure,distribution network reliability assessment will face new problems,not only need to consider the timing status of components in the system,but also need to consider the matching state of distributed power and loads.In this paper,the Monte Carlo simulation method of system state transition sampling is used,combined with the component state transition process obtained by random simulation,to quantitatively evaluate the reliability of the distribution network divided into different scenarios.Analysis of numerical examples shows that the Monte Carlo method based on systematic sampling transfer is superior to the traditional Monte Carlo method in both convergence speed and calculation speed.Finally,the economics of the introduction of electric vehicles and demand-side response systems and energy storage systems were compared and analyzed.The introduction of demand-side responses can not only improve the reliability of power supply,but also reduce the upper limit of energy storage equipment capacity and energy storage batteries Quantity configuration.Therefore,the demand-side response can reduce the maintenance cost of the energy storage system and improve the economy of the system.