Design and evaluation of a wireless power transfer system with road embedded transmitter coils for dynamic charging of electric vehicles

The cruising range of an electric vehicle (EV) can be greatly extended by a dynamic wireless charging system because the battery can be charged while the vehicle is moving. However, the investment in infrastructure can be enormous and has to be reduced to implement the system. This paper presents the design of a wireless power transfer system with road embedded transmitter coils to facilitate dynamic charging of EVs. A 30 cm by 1.6 m transmitter coil, which is relatively long compared with the 40-cm-diameter circular receiver coil, has been designed to reduce the cost of the transmitter circuit. A prototype transmitter coil has been embedded into a road for evaluation of its characteristics. The measured coupling coefficient of the transmitter and receiver coils is as small as 0.09 because of the asymmetry between the coils. Compensation circuits for the transmitter and receiver coils have been designed and optimized for such a small coupling coefficient condition. The designed dynamic charging system can transfer more than 1 kW of electric power with more than 90% efficiency. Five transmitter circuits have been embedded into a road surface for testing. Cement asphalt mortar was used to construct the road surface in this study to avoid damaging the transmitter coils by high temperature and high pressure during the construction work. The designed receiver circuit has been installed on a compact 2-seater EV. A demonstration was conducted to show that the retrofitted EV can successfully receive electric power transferred from the road.