For commercialization of wireless stationary EV chargers, metal object detection (MOD) on a power supply coil and detection of position (DoP) of electric vehicles (EVs) are needed. In this paper, dual-purpose non-overlapping coil sets for both MOD and DoP, which detect a variation of magnetic flux on the power supply coil, are newly proposed, where the proposed MOD and DoP methods make no contribution to any power losses. The existence of metal objects on the power supply coil is determined by an induced voltage difference of the non-overlapping coil sets, whereas the position of the EV is determined by an induced voltage of the non-overlapping coil sets. A sensing circuit, which has a variable resistor that is different from the conventional overlapping coil for MOD, can make the induced voltage difference zero even when the magnetic flux distribution is distorted by moving the pick-up coil. The proposed non-overlapping coil sets with the sensing circuit have been demonstrated by simulations and experiments. When metallic coins and aluminum sheets are located on the power supply coil, the induced voltage difference of the coil sets, which is ideally zero without metal objects, significantly increases to 62.8 mV and 450mV, respectively, which is more than 10 times the value without metal objects throughout experiments. In addition, when the pick-up coil approaches the power supply coil, induced voltage of each coil set increased roughly 1.6 times at 10 cm air-gap.

In this paper, a metal object detection (MOD) system, a kind of foreign object detection (FOD), which is based on mistuned resonant circuits and utilizes variation of self-inductance of a sensing pattern, is newly proposed for wireless electric vehicle (EV) chargers. The sensing pattern that consists of multiple loop coil sets is mounted on the transmitting (Tx) pad of an EV charger, where a loop coil set has two coils connected in series with opposite polarity to cancel out the induced voltage generated by the Tx coil. Variation of self-inductance of the loop coil set is detected by a parallel-resonant circuit, driven by a current source and operating at near 1MHz. To increase the detection sensitivity of the proposed MOD system, a mistuned operating frequency near the -3dB point is utilized for the parallel-resonant circuit. In this way, the proposed MOD system can detect very small metal objects regardless of their position and orientation on the Tx coil without any blind zone. A prototype MOD system showed that output voltage change of the proposed MOD system becomes 22.7 % for a piece of aluminum foil of 3 x 3 cm2 and 40.9 % for 100 Korean Won coin, respectively.

In this paper, a simple and cost-effective symmetric sensing coil set to be used for metal object detection (MOD) in a stationary wireless electric vehicle charger is newly proposed. Compared to the conventional non-overlapping sensing coil using the magnetic field change detection method, the proposed symmetric sensing coil set design offers the considerable advantage of eliminating all blind zones, i.e., regions where metal is undetectable in the conventional method. Moreover, by reducing the number of layers to one, the fabrication of the proposed sensing coil is easier and more cost-effective. The design of the proposed sensing coil is optimized for highly sensitive metal object detection based on a sensitivity equation and on finite element method simulations. An experiment conducted with a metal object $40 \times 40 \text{mm}^2$ in size and a 20A transmitting (Tx) coil current verifies the reliability and blind-zone elimination feature of the proposed sensing coil.

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. 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 at the laboratory scale.

In this paper, a novel structure of a receiving (Rx) coil with only two coils, which enables omnidirectional wireless power transfer (WPT) for any type of transmitting (Tx) system, is proposed for the first time. The coil adopts each coils into plane cross-shaped ferrite core, with each leg of the ferrite core intersecting both coils. The intersecting direction of the ferrite core for one coil is identical to that of the other one when it is rotated 90 degrees. It is verified that voltage will be induced on at least one coil with any direction of magnetic flux. With an analysis of circuit diagram, it is shown that a high quality factor of each coil can guarantee an omnidirectional power transfer even when the coupling coefficient between two coils has a non-zero value. A simulation model and an experimental prototype is built to verify the omnidirectional WPT of the proposed Rx coil structure, with loop-type Tx coil as an example among various Tx types. Omnidirectional power transfer capability of the proposed coil was verified with a LED load. The superiority of the proposed coil was verified by comparison with other Rx coil structures also.

A new conductive-plate-integrated inductive power transfer (IPT) system for automated guided vehicles (AGVs) with little output power variation according to air-gap changes between the transmitter (Tx) and receiver (Rx) is proposed. The inductance change of the ferrite core due to variations in the air-gap is nullified by a corresponding change in an aluminum plate. Compared to conventional ferrite IPT systems, self-inductance of the proposed Tx coil is little changed against air-gap variations, which results in robust resonant frequency and output voltage. The self-inductance was experimentally verified to remain within 0.45% even when the air-gap changes by fivefold from 10 mm to 50 mm. The output power variation became a twelfth of that of the conventional ferrite IPT for air-gap variations of 30 ~ 50 mm, where the efficiency was found to be 96.0% when the output power was 1 kW.