Analysis of Operation and System Losses of an Inductive Power Transfer System for Wireless Charging of Electric Vehicles

Abstract

The promotion of resource-saving technologies by the public authority was being intensified during the last years in order to reduce energy consumption and CO2-emissions. If charged from renewable energy sources, electric vehicles can contribute significantly to these objectives. Additionally, they can be employed to store and balance the fluctuating energy production of renewable sources. Therefore, however, a high availability of electric vehicles in the grid has to be guaranteed. In order to achieve a widespread dissemination of electric vehicles, several barriers for the usage have to be dismantled. Available charging systems for electric vehicles use cables to connect the vehicle to the grid, although this involves certain disadvantages such as risk of vandalism, additional effort for the user and present safety issues due to the open contacts and hanging charging cables in public areas. Unplugged cables lead to uncharged batteries, which causes a minimization of mobility. A further reduction of the available range of electric vehicles is not acceptable. An alternative is wireless charging on the basis of resonant inductive energy transfer. This technology provides galvanic isolation, has no open contacts and hanging charging cables, which represent potential hazards in public places, and are susceptible to vandalism allowing an automatic, reliable and safe charging process. Therefore, automatic resonant inductive charging will improve the user acceptance of electric vehicles in general and will contribute to the integration of electric vehicles into the market and thus will support the full exploitation of benefits through electro-mobility. This thesis discusses a topology for charging electric vehicles, the basic principles of wireless resonant inductive energy transfer, different coil configurations, resonant converter topologies and presents experimental results of a 3.3kW inductive energy transfer system with bidirectional energy flow capability operating at 140kHz.