With the increase of global environmental problems, the electric vehicle has become development trend of car and one of the hotspots, but the charging mode become the focus in the development process of electric vehicle. 

The air pollution in the big cities already can't be ignored, car emissions is one of the main pollution sources, 16 cities in China had been already listed as the most serious global air pollution in 20 cities.  oil resources isn't enough, hundreds of millions of tons of oil had been imported each year, with the development of economy, oil import will become a big problem.  So electric vehicle (EV) now had become development trend and one of the hotspots because of its good environmental protection, energy-saving characteristics.