Research On Distribution Network Protection Method Under V2G Operation Mode

As a new type of mobile energy storage tool,electric vehicles occupy an important role in the future development of the power grid due to its excellent interactivity.However,with the continuous improvement of the penetration rate of electric vehicles,its charging and discharging behavior will have obviously impact on the operation mode,topology structure,power flow direction and electrical quantity characteristics of the distribution network.At the same time,it also puts forward higher requirements for the setting and cooperation of distribution network protection.This thesis analyzes the working principle,mathematical model and control strategy of each module of electric vehicle two-way charger and discharge machine,establishing a distribution network simulation model within electric vehicles in PSCAD/EMTDC software to analyze the impact of electric vehicle access on the current level and direction of the distribution network.Considering the electric vehicle in discharging state has the same characteristics with Inverter-Interfaced Generator,the characteristics of the electric vehicle after the occurrence of fault are analyzed to explore the impact on the conventional power direction component.This thesis proposes a centralized protection scheme based on wide-area information for the distribution network under V2G(Vehicle-to-Grid)operation mode.Firstly,the phase information of the positive sequence fault component current is used to construct a new fault direction component,which uses the positive and negative derivatives of the positive sequence fault component current to form the reference phasor.The fault direction is judged according to the phase difference between the reference phasor and the positive sequence fault component current in the faults in the area and outside the area,the impacts of electric vehicle access on the directional components can be minimized.The method of judging the fault direction of the branch by using the fault component current phase information measured by other branches of the same busbar is proposed.In order to adapt to the flexible and variable topology of the distribution network under the V2G operation mode,the fault direction information is uploaded to the primary station after determined,The primary station performs fault location based on the collected fault direction information combined with the system real-time topology.This method has good adaptability in the case of distribution network topology changes and information loss.