Automatic Current Control by Self-Inductance Variation for Dynamic Wireless EV Charging

In this paper, an auto-tuning control system (ACS), which utilizes variation of self-inductance of a transmitter (Tx) coil caused by 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 pass 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 reduction of the conduction losses from uncoupled Tx modules, but control also becomes simpler because sensors are not required for detecting EVs and constant output voltage characteristics can be obtained. Through simulations and experiments, it was found that the proposed ACS is suitable for applications in which a transportation runs along a track with a small air gap, such as a train or tram. 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 ohm of load resistance) at the laboratory scale. The measured maximum efficiency was 96.7% for 100 ohm of load resistance.