Research On Virtual Inertia Control Of DC Power Distribution System Integrated With Electric Vehicles

With the development of power electronic technology and power switching device technology,the rapid development of DC distribution technology,a large number of DC distribution lines have been put into use.Compared with AC distribution system,DC distribution system has the advantages of small interference to the outside world,low power loss,large power supply capacity,high power quality,strong power supply reliability and easy to accept distributed generation.DC distribution system has become a new development direction of urban distribution system in the future.DC distribution system is easier to access distributed generation,so it has become an electric vehicle access to the power grid It’s our first choice.However,due to the small inertia of DC distribution system,the charging and discharging behavior of electric vehicles also brings new problems and challenges to the stable operation of DC distribution system.In this paper,the virtual inertia control of DC distribution system was studied based on the characteristics of electric vehicle power battery and charge discharge(1)Combined with the charging and discharging characteristics of different charging and discharging modes of electric vehicles,the small disturbance dynamic admittance stability analysis model of flexible DC distribution system with electric vehicles was established.The stability analysis model of electric vehicle under different charging and discharging modes,voltage source converter stability analysis model,DC load and line stability analysis model,etc.through the Nyquist stability criterion theory,this paper analyzes the influence of electric vehicle access on system stability under different charging and discharging modes.A typical DC distribution system example based on DIg SILENT simulation software was built.The theoretical analysis and simulation results show that the voltage stability of DC distribution system in constant current discharge mode and constant power discharge mode decreases in turn;the voltage stability of DC distribution system in constant current charging mode,constant voltage charging mode and constant power charging mode decreases in turn.(2)In view of the negative damping effect caused by electric vehicle access,a virtual inertia control method based on electric vehicle was proposed by introducing the form of virtual inertia compensation function,and the stability of the system before and after introducing the compensation function was analyzed through the stability model.The results show that the proposed control method can effectively improve the system inertia,and realize plug and play of electric vehicle.The effectiveness of the proposed chopper control system was verified by the simulation of a typical DC distribution system.(3)In order to solve the problems of weak inertia,low damping and poor anti-interference of DC distribution system,reduce the instability of the system when the DC load and DC line parameters change.This paper presents a hierarchical virtual inertia control method based on electric vehicle and converter.On the basis of virtual inertia control of electric vehicle,the compensation function of virtual inertia control based on converter was introduced to enhance the inertia of DC system,which can not only effectively suppress the negative damping effect caused by electric vehicle access,but also suppress the system fluctuation caused by other load fluctuations,enhance the anti-interference ability of the system,and realize the orderly hierarchical stability control of DC distribution system.The above control method was built in DIg SILENT simulation software,and the effectiveness of the control method was verified by time-domain simulation.