Research On The Interaction Stability And Ancillary Service Of Scaled Electric Vehicles Access To Urban Power Grid

Electric vehicles(EVs)are now widely regarded as an important means of changing the energy structure of the transportation sector,saving energy and reducing emissions,and promoting a low-carbon society.With the popularity and quantity increasing of electric vehicles,it is an inevitable trend that a large number of electric vehicles are connected to urban power grids through power electronic equipment.Scaled electric vehicles connected to urban power grids through V2 G technology will have an impact on their stable operation.At the same time,a large number of suspended electric vehicles have great potential to participate in the city grid voltage and frequency regulation,power supply reliability improving and other ancillary services.At present,the problem of the interaction stability of scaled electric vehicles access to urban power grid and the provision of ancillary services for urban power grids are receiving much attention.Therefore,this paper focuses on the dynamic stability modeling and analysis of electric vehicle access to urban power grid and electric vehicle participate in urban power grid ancillary services.The main work of the thesis is:(1)For the residential level single-phase charging pile,a model for electric vehicles and urban power grid interaction stability analysis is build,impedance ratio-based stability criterion is applied for influence factors of interaction stability analysis.When the electric vehicle is running on state of charge,the grid side is regard as the power source subsystem,which is composed of an ideal voltage source and an output impedance.The load subsystem is composed of the electric vehicle and the charging pile.When the electric vehicle is running on state of discharge,the electric vehicle and the charging pile are regarded as source subsystem together.The electric vehicles inject current into the power grid under the control of the controller.The equivalent output impedance of the electric vehicle side is derived through the closed control loop of the electric vehicle charging pile,and the grid side equivalent impedance is determined by the grid side line and transformer.On this basis,the stability criterion based on impedance ratio is used to analyze the influence of the number of electric vehicles,access location,charging strategy,filtering parameters,control parameters and operation mode on the interaction stability.(2)For the three-phase charging pile of the urban fast charging station,a model for electric vehicles and urban power grid interaction stability analysis is build,an improved forbidden region stability criterion for multi-input and multi-output system is proposed.According to the three-phase structure of the fast charging pile,the multi-input and multioutput dynamic model of the fast charging pile and the power grid are established from the current control loop in the rotating coordinate system.The input admittance matrix of the fast charging station and the output impedance matrix of the power grid obtained respectively.Based on the existing stability criteria of forbidden region,an improved forbidden region stability criterion for symmetric multiple-input and multiple-output systems is proposed.The influence factors of the dynamic interaction stability between the electric vehicle fast charging station and the urban power grid are analyzed based on this criterion.(3)In solving the problem of electric vehicle participate in the voltage and frequency regulation of urban power grid,this paper proposes a unified scheduling strategy for electric vehicles to participate in voltage and frequency regulation.In view of the active powerfrequency and reactive power-voltage relationship adopted in the traditional voltage frequency regulation,combined with the characteristics that the ratio of resistance and reactance of the urban power grid is large,the active power is applied for both types regulation.Firstly,according to the travel demand and SOC status of electric vehicle owners,the electric vehicle charging power demand is obtained,and then the power and capacity model of electric vehicle participating in voltage and frequency regulation is established,and finally distributed the V2 G power according to the regulation demand of the grid side voltage and frequency.Simulation shows that the proposed strategy can scheduling the electric vehicle to participate in the regulation of the urban power grid voltage and frequency without affecting the travel demand of the EV owner.(4)In coordinating electric vehicle V2 G to provide electric power to improve the reliability of urban power supply,a reliability evaluation method that considering the power supply path and power supply range is proposed.This algorithm considered the reliable action probability of the breaking device,the probability of the load being successfully transferred to the standby power after the fault,and considers the occurrence of multiple faults,introduces the expected value of the reliability index,and passes the reliability index between the main network and the branch network.The influence of the electric vehicle V2 G on the reliability index of each node is determined by the power supply path and power supply range of the electric vehicle.The proposed algorithm indicates that the electric vehicle V2 G has significant effect for improving the reliability of urban power supply.In summary,the theoretical research system for the interaction stability of scaled electric vehicles connected to urban power grid and participation in ancillary service is formed in this paper.This theoretical research system includes the analysis of the interaction stability of electric vehicles connected to urban power grid,the unified control strategy for electric vehicles participate in voltage and frequency regulation and the evaluation method of urban grid power supply reliability considering the electric vehicle power supply path and power supply range.It can provide theoretical support and solutions for the research on key issues of scaled electric vehicles access to urban power grid and participate in grid ancillary services.