Research On Islanding Detection Technology For Electric Vehicle Charger Connected To The Grid In V2G Application

With the popularization of electric vehicles and the rapid development of smart grid,V2 G technology attract more attention and research.V2 G realizes the power interaction between vehicles and grid.A large number of power batteries of EV are stable energy sources with considerable capacity.Participating in the dispatch of the power grid with the help of communication technology can improve the efficiency and stability of the power grid.However,the islanding effect is one of the key problems in the field of gridconnected power generation.Because the islanding effect will cause serious safety problems,it's stipulated that grid-connected inverters must have anti-islanding capabilities in the international standard.Therefore,for the two-way charger of electric vehicles with V2 G function,islanding-detection technology is essential to ensure the safety when the V2 G charger works as a grid-connected inverter.Compared with other distributed power generation systems,the flow of electrical energy between vehicles and networks is more flexible,so the working conditions are more complicated when the current flows from charger to grid.And the islanding effect is more harmful to cars,charging stations and urban power grids.Therefore,the islanding detection technology used for V2 G needs faster detection speed and more reliable detection accuracy.Based on the above background,this paper studies the islanding detection technology applicable to V2 G.The main contents are as follows.(1)Explain the research background and research significance of the subject.First,the important value and development status of V2 G technology is introduced.Then the mechanism of island effect and introduce the development status of island detection technology are briefly discussed,and the relevant regulations and standards of island detection are given.The unique significance and requirements of island detection in V2 G scenarios are summarized.(2)Establish the model of V2 G charger in inverter mode.The research goal is the gridconnected discharge protection of the V2 G charger.According to the electrical structure of the existing vehicle chargers,the three-phase full-bridge inverter circuit is used as the main circuit model of V2 G charger DC / AC part,and its control strategy working as a grid-connected inverter is discussed.The control strategy is realized by a digital processor because of the characteristics that vector modulation is discrete,which become the basis of the digital island detection scheme proposed in this paper.(3)A digital island detection method is proposed for the anti-islanding protection of the V2 G charger.The working principle and implementation process in the digital system are elaborated in detail.Then the analysis of the non-detection zone and elimination strategy of non-detection zone are given.(4)According to the control strategy and islanding detection scheme of the V2 G charger connected to the grid,the hardware scheme and software scheme of the experimental system are designed based on the digital processor.(5)Based on the Matlab / simulink software platform,the modeling and simulation are carried out,and the experiment is carried out according to the simulation model.The results of simulation and experiment are respectively given and analyzed.The experiment proves that the islanding detection method described in this article can quickly and accurately detect the abnormal working state of the V2 G charger when the grid doesn't work and turn it off quickly.The protection reaction time meets the relevant regulations.The elimination strategy of non-detection zone can not only effectively realize the island protection in the discharge state of electric vehicles under complex load characteristics,but also indirectly improve the efficiency and stability in the charging mode.