Ji H. Kim

Dipole-Coil-Based Wide-Range Inductive Power Transfer Systems for Wireless Sensors

A dipole-coil-based extremely loosely coupled inductive power transfer system (IPTS) for wireless sensors over a wide range is proposed. The overall superiority of dipole coils for a long-distance power delivery over loop coils with an identical configuration of a square core is verified by comparing the magnetizing inductance between primary and secondary coils. Series-parallel resonant circuits were used to achieve a higher load voltage than that of the series-series scheme. Contrary to conventional IPTSs or coupled magnetic resonance systems, the quality factor Q was set as low as 100, guaranteeing a frequency tolerance of 1%, where a prototype of narrow dipole coils with a length of 2 m was used to deliver 10.3 W of power up to 7 m away at a low frequency of 20 kHz. The powering capabilities of the proposed IPTS were experimentally compared inside and outside of a metal container 8 m × 4 m × 2.5 m in size at different frequencies ranging from 20 to 150 kHz, where the proposed IPTS is highly likely to be surrounded by arbitrary distributed conductors in most wireless sensor usage environments. The coupling coefficient κ between the primary and secondary coils was measured over a long distance from 2 to 12 m for different secondary coil positions, where κ is mostly much less than 0.01. A comparative analysis of the maximum amounts of load power among different core materials, i.e., two ferrite cores and an amorphous core, was conducted in relation to the design of a secondary coil. The results were verified by experiments at a given switching frequency of 20 kHz.

7m-off-long-distance extremely loosely coupled inductive power transfer systems using dipole coils

An extremely loosely coupled inductive power transfer system (IPTS) for 7m-off-long-distance wireless power transfer using dipole coils is proposed. The superiority of dipole coils for a-long-distance power delivery over loop coils with same configuration of square core, in general, is verified by comparing magnetizing inductance between primary and secondary coils. Series-parallel resonant circuits are used to achieve higher load voltage than the series-series scheme. Contrary to conventional IPTSs or coupled magnetic resonance systems, quality factor Q is set as low as 100, which is, moreover, fixed for guaranteeing frequency tolerance. An optimum number of turns of the secondary coil is derived theoretically and verified by experiments, where a prototype of narrow dipole coils with 2m-length were used to deliver 11.1 W power up to 7m-distance at a very low frequency of 20 kHz.

A Novel Source-Side Monitored Capacitive Power Transfer System for Contactless Mobile Charger Using Class-E Converter

A new source-side monitored capacitive power transfer system (CPTS) for contactless mobile charger using Class-E converter is proposed. Contrary to conventional contactless mobile charger, an exact battery voltage monitoring is achieved without additional cumbersome communication circuits. The proposed CPTS operates in two iterative modes; a main-charging-mode and a sub-battery-monitoring-mode. Not only the battery voltage sensing but also an agile battery charging current control is accomplished with a microprocessor at a transmitting side. The circuit parameters of class-E converter and primary circuit, which consists of the compensating inductors and the capacitive coupled metal plates, are determined for guaranteeing load tolerance. A detail analysis for the battery monitoring operation and design procedures of the proposed CPTS are fully established, and experimentally verified for 4 W prototype of Samsung GALAXY S3 Li-ion battery at the switching frequency of 1.237 MHz.

Coreless power supply rails compatible with both stationary and dynamic charging of electric vehicles

A universal wireless power transfer (U-WPT) system which can be used for not only roadway-powered electric vehicles (RPEVs) but also stationary charging of electric vehicles (EVs) is newly proposed in this paper. Contrary to previous WPT systems for RPEVs, the proposed U-WPT can also be used for pick-ups fabricated by the SAE J2954 standard for stationary charging. The proposed U-WPT adopts a new coreless power supply rail to increase its operating frequency from the conventional level of 20 kHz to 85 kHz, as specified in the SAE J2954 standard. With the adaptation of U-WPT, EVs in the future will simply be called wireless electric vehicles (WEVs) regardless of whether they use stationary or dynamic charging systems. A detailed comparison between coreless and with-core power supply rails is thoroughly made, with the results verified in simulations and experiments. This comparison shows that, with the same power rating, the proposed coreless power supply rail is superior to the conventional with-core power supply rail due to its low cost, less insulation voltage stress, lack of core loss, and only slight sensitivity to lateral misalignment, mitigating the condition of less induced voltage.

Synthesized Magnetic Field Focusing Using a Current-Controlled Coil Array

A novel synthesized magnetic field focusing (SMF) technology is proposed and nonradiative but focused magnetic field is experimentally demonstrated as a one-dimensional example. Contrary to common belief, a magnetic field can be focused arbitrarily by increasing the number of current-controlled transmitting coils in a manner similar to that of conventional beam-forming. Moreover, the proposed SMF is independent of frequency from dc to rf. Chronic problems associated with conventional wireless power transfer and magnetic induction tomography technologies, i.e., poor resolution and electromagnetic interference due to the extent of the magnetic field, can be resolved with the proposed SMF technology. The spatial resolution of the magnetic field of an experimental kit composed of 10 coils spaced 5 cm apart with a 90 cm long ferrite core was 12.5 cm at a distance of 10 cm, which is 4 times that of a nonfocusing coil and which may be improved if more coils are used.

Crossed dipole coils for an omnidirectional wireless power zone with DQ rotating magnetic field

Crossed dipole coils for the wide-range 3-D omnidirectional inductive power transfer (IPT) are proposed. Free positioning of a plane receiving (Rx) coil is obtained for an arbitrary direction within 1m from a plane transmission (Tx) coil. Both the Tx and Rx coils consist of crossed dipole coils with an orthogonal phase difference; hence, a rotating magnetic field is generated from the Tx, which enables the Rx to receive power vertically or horizontally. Chronic installation problems associated with conventional coils for achieving omnidirectional characteristics, i.e. volumetric coil structure and high system complexity, can be resolved by the proposed plate type crossed-dipole coils. Simulation-based design of the proposed crossed dipole coils for a uniform magnetic field distribution is provided, and the 3-D omnidirectional IPT is experimentally verified by prototype Rx coils for a wireless power zone of 1 m3 with a prototype Tx coil of 1 m2 at an operating frequency of 280 kHz, meeting the Power Matters Alliance (PMA). The maximum overall efficiency was 33.6% when the input power was 100 W.

DCM Analysis of Single-Switch-Based ZVZCS Converters With a Tapped Inductor

The analysis of a novel single-active-switch-based zero voltage and zero current switching (ZVZCS) tapped boost converter in the discontinuous conduction mode (DCM) is proposed in this paper. The ZVZCS converter includes a lossless snubber composed of three diodes and two capacitors and exhibits novel ZVZCS operation for wide operating ranges of duty cycles, load currents, and input voltages. The voltage stress of the active switch is always less than the load voltage, and soft switching turn-on and turn-off are achieved without cumbersome current or voltage sensing, which could not have been obtained from quasi-resonant converters that also have an active switch. Detailed analyses of the DCM and the component stresses of the proposed converter are presented. Experiments for a 450-W prototype exhibited 99.0% of the maximum efficiency with a SiC JFET at the switching frequency of 50 kHz, and the ZVZCS operation is guaranteed, even for the DCM under the experimental conditions. Moreover, the proposed ZVZCS principle has been applied to a tapped buck-boost converter case, which was also experimentally verified.

High-Resolution Synthesized Magnetic Field Focusing for RF Barcode Applications

A prototype of a high-resolution synthesized magnetic field focusing (SMF) system for a possible application to radio frequency (RF) barcodes is proposed in this paper. It was recently found that coordinated control of array coil currents makes it possible to focus magnetic field, which is requisite for medical imaging, wireless power, and RF identification. Different from conventional phased array RF antennas, SMF is independent of frequency, which is quite promising for various applications. In this paper, an array of rectangular air coils is proposed, and various implementation issues, such as accurate control of coil currents and compact RF barcode design, are newly suggested. A prototype of an SMF system composed of a transmitter (Tx), an RF barcode, and a receiver (Rx) was implemented at below 1 MHz operating frequency. The Tx includes modularized control drivers, full-bridge switching converters, and 16 arrayed air coils, where the RF barcodes proposed in this paper include a self-resonating circuit at 20 mm × 20 mm and a tunable resonating circuit at 15 mm × 15 mm. In this way, a 5 mm resolution at a distance of 20 mm was achieved for the Tx arrayed air coils with spacing of 5 mm, which is about four times sharper magnetic field focusing compared to a nonfocusing conventional coil. Furthermore, the proposed SMF system allows the designed 5-bit RF barcode array to be fully distinguishable at a 15 mm distance.

Free space wireless charging in cars with fishbone DQ IPT coils

A new free space wireless charging system for inner vehicle use with a ferrite-core fishbone architecture is proposed in this paper. This system achieves wireless charging independent of the position and direction of its receiving side by means of two transmitting coils installed in one ferrite core structure. These direct (D) and quadrature (Q) coils generate a uniform rotating magnetic field inside the vehicle. In the proposed system, a double-sided LCC circuit topology is applied to each of the D and Q coils to provide load-independent current sources. The parameters of the LCC compensation circuits are determined to guarantee zero voltage switching for the switches of the high-frequency inverter and to limit the inverter output current simultaneously. A detail analysis of the operation and design of the proposed system was carried out, and its feasibility was verified with experiments for 1 W level of power receiving within 30 cm distance between transmitting and receiving coils at 280 kHz.

DCM analysis of a single SiC switch based ZVZCS tapped boost converter

The analysis of discontinuous conduction mode (DCM) for a novel single active switch based zero voltage and zero current switching (ZVZCS) tapped boost converter is proposed in this paper. The ZVZCS converter includes a lossless snubber composed of three diodes and two capacitors, and exhibits novel ZVZCS operation for wide operating ranges of duty cycle, load current, and input voltage. The voltage stress of the active switch is always less than load voltage, and soft switching turn-on and off is achieved without cumbersome current or voltage sensing, which could not have been obtained from quasi-resonant converters that also have an active switch. A detailed analysis for the DCM and the design procedures of the proposed converter are presented. Experiments for a 450 W prototype show 99.0% of maximum efficiency with a SiC JFET at the switching frequency of 50 kHz, and the ZVZCS operation is guaranteed even for the DCM under the experiment conditions.