Autotuning Control System by Variation of Self-Inductance for Dynamic Wireless EV Charging With Small Air Gap

In this paper, an autotuning control system (ACS), which utilizes the variation of self-inductance of a transmitter (Tx) coil caused by a ferrite core of a receiver (Rx), is newly proposed for the dynamic wireless electric vehicle (EV) charging. A Tx module consists of only passive elements that include a Tx coil, a partially compensated capacitor in series with the Tx coil, and a parallel compensation capacitor. All Tx modules share an ac bus line that passes the output filter of an inverter in parallel without any active switches. The current of the coupled Tx coil increases automatically without any manipulations such as controlling the power switches, sensing, or communication when the Rx module is approaching. Not only the system efficiency is increased by the reduction of the conduction losses from the uncoupled Tx modules, but control also becomes simpler because sensors are not required for detecting EVs, and the constant output voltage characteristics can be obtained. Through experiments, it was found that the proposed ACS is suitable for applications such as a tram that runs along an orbit with a small air gap, such as a train. The results showed that the current of a coupled Tx coil increased 11.6 times larger than that of an uncoupled Tx coil, at which time the dc-dc efficiency achieved was 88.4% for an output power of 766 W (10 Ω of load resistance) at the laboratory scale.