In this article, a machine learning algorithm is applied for the first time in inductive power transfer (IPT) to find a ferrite core structure with high magnetic coupling between transmitting (Tx) and receiving (Rx) coils for an electric vehicle (EV) wireless charging system. Since formula-based theoretical design is not available due to the nonlinear magnetic field distortion stemming from the presence of the ferrite core in an IPT system, the proposed core structure design has been achieved through finite-element analysis simulation-based data learning. The proposed design methods are so general that they can be applied to any conventional IPT coil design. Furthermore, it can optimize the core structures for high coupling coefficient, mutual inductance, desired magnetic flux density in the specific area, etc. By training only 0.011% data out of the total possible cases, it is verified by simulation and experiment that the ferrite core structure obtained by the proposed method has a mutual inductance that is 0.6% higher than that of the conventional design level in the case of 15 cm distance between the Tx and Rx coils, even though the volume of the ferrite cores are reduced to 90%. Also, a prototype 3.0 kW stationary EV wireless charging system was implemented and showed fairly better performance than a conventional case.

A wide-range ubiquitous wireless power environment, called a ubiquitous Wi-power zone, where any electric devices can be charged by three-dimensional (3-D)-omnidirectional wireless charging, is newly proposed in this paper. By virtue of the proposed direct-quadrature (DQ) transmitting (Tx) coils composed of multiple Tx modules with same size, a ubiquitous Wi-power zone having the transmitting (Tx) coils can be provided over wide-range 3-D space. In this area, a number of electric devices can be simultaneously charged during operation. Therefore, the proposed IPT is expected to be the next generation of wireless power transfer (WPT), as the internet of things (IoT), mobile devices, and sensor technologies evolve. For magnetic shielding behind the Tx coils and high power efficient operation of the proposed DQ Tx coils, providing an evenly distributed magnetic field, a conductive plate is adopted, and the effects of the conductive plate for the dipole coil structure were thoroughly evaluated by a 3-D FEM simulation. To create the proposed ubiquitous Wi-power zone, simulation-based optimum design procedures are established based on four design considerations and the optimized number of modularizations for the DQ Tx coils can be found by an optimum point of figure of merit (FoM). The DQ Tx module composed of the DQ Tx coils and series resonant capacitors was adopted as a standard unit of the proposed IPTso that different sizes and shapes of 3-D space can be utilized for universal use of the proposed ubiquitous IPT; hence, a general solution to create the proposed ubiquitous IPT is provided in this paper. A prototype 5 × 5 modularized IPT composed of 25 DQ Tx modules having the same size of 10 × 10 cm × 2 cm was fabricated and experimentally verified for a 1 m × 1 m × 0.7 m ubiquitous Wipower zone. Experimental results showed that 95.5%, 92.1%, and 98.8% of high magnetic field uniformity for z ₁ = 25 cm, 50 cm, and 75 cm, respectively, and 3-D omnidirectional wireless power delivery have been achieved; thus, meeting essential requirements for the proposed ubiquitous Wi-power zone. Nine Rx coils can be simultaneously charged with 14.2 W of total received load power and 8.2% power efficiency at z ₁ = 70 cm.

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.

New coreless transmitting (Tx) coils with a conductive material plate for wide-range ubiquitous inductive power transfer (IPT) zones, i.e., a U-IPT zones, where electric devices can be wirelessly charged during operation, are proposed in this paper. Because commercialized IPT systems are only available for short distances of several centimeters and one-to-one charging, the demand is increasing for U-IPT zones in which long-distance wireless charging with 3-D free-positioning and simultaneous charging of multiple receiving (Rx) coils can be achieved. To satisfy this demand, U-IPT zones should be constructed to have a uniform magnetic field distribution in a wide space, which also poses no risk to the human body. In addition, to generate a uniform magnetic field in a wide 3-D space, such as a single room, the system requires the installation of many Tx coils above the ceilings and behind the walls of the room, and these coils should be capable of high electrical performance to support the efficiency of the entire IPT system and should be of excellent mechanical quality. Therefore, a U-IPT zone should meet the following four criteria: human safety, free-positioning of Rx coils, magnetic field uniformity, and economization. By virtue of a conductive material plate that cancels out the undesired direction of magnetic flux generated from the return wires, the proposed coreless Tx coil does not need any heavy ferromagnetic cores, which can cause non-uniformity of the magnetic field distribution and difficult construction. A prototype coreless Tx coil with the dimensions of 1 m × 1 m × 10 cm was fabricated and experimentally verified for a 1 m × 1 m U-IPT zone. The experimental results showed that 74%, 83%, and 76% high magnetic field uniformity could be achieved for $z1$ = 25 cm, 50 cm, and 75 cm, respectively, and 3-D omnidirectional wireless power delivery was achieved, while the guideline of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) for human safety was satisfied throughout the entire U-IPT zone. Moreover, the weight of the entire system was only 9 kg, enabling easy installation. In the multiple wireless charging experiments, 47 W of power was consumed in total by load resistors, each of them connected to nine Rx coils, respectively, with 32 % power efficiency at $z1$ = 20 cm.

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.

In this paper, a reinforcement learning algorithm is applied for the first time to find a ferromagnetic core structure with optimal coupling coefficient between transmitting (Tx) and receiving (Rx) coils of a wireless power transfer (WPT) system. Since formula-based theoretical design is not available due to the non-linear magnetic field distortion stems from the presence of the ferromagnetic core in a WPT system, the proposed design has been achieved through finite element analysis (FEA) simulation-based data learning. The proposed design methods are so general that they can be applied to any conventional WPT coil types. We applied the proposed algorithm to the ferromagnetic core structure design of a simple dipole coil first. By training only 2.3 % data out of total possible cases, it is experimentally verified that the core structure obtained by the proposed method has a coupling coefficient 7 % higher than that of the example design level in the case of 98 cm distance between Tx and Rx coils.