Tae-Dong Yeo

Design of Maximum Efficiency Tracking Control Scheme for Closed-Loop Wireless Power Charging System Employing Series Resonant Tank

This paper presents a maximum efficiency tracking control scheme for a closed-loop wireless power charging (WPC) system for wireless charging of mobile devices. Generally, wireless charging systems need a precise output voltage and current with the highest possible efficiency. In an open-loop system, output voltage and efficiency depend strongly on the coupling coefficient and load condition. Alternatively, a closed-loop WPC system has a constant output voltage against coupling and load variations. Many studies have been carried out regarding closed-loop systems. However, those previous studies have the drawback of efficiency degradation. In this paper, we propose a maximum efficiency tracking control scheme to achieve the highest possible efficiency. Therefore, the proposed WPC system satisfies both the requirements of a constant output voltage and high efficiency. The proposed control scheme determines the current of the transmitter based on the data received by the receiver via Bluetooth. For validation, the proposed WPC system was implemented at 6.78 MHz using loosely coupled series-series resonant coils, and we verified that the proposed system can track the maximum efficiency while maintaining a constant output voltage.

Dual Resonance Frequency Selective Loop of Near-Field Wireless Charging and Communications Systems for Portable Device

In this letter, a frequency selective loop isolator using dual resonance for a mobile wireless charging system is presented. Resonance of the proposed frequency selective loop isolates a transmitting loop from a receiving loop at one frequency whereas it transfers wireless power between them at the second harmonic frequency. Simple arrangement of lumped elements changes operation of the proposed frequency selective loop to a series resonator at 6.78 MHz and a parallel resonator at 13.56 MHz. Experimental results show the difference in the transmission coefficient between with/without the frequency selective loop is approximately 21 dB at 6.78 MHz whereas it is about 2 dB at 13.56 MHz, without degradation of efficiency. Moreover, this approach suggests how to transfer wireless power based on frequency selection.

Dual-Band Half-Elliptic Hoof Antenna With Mathieu Function for a Femto-Cell Network

The design of a half-elliptic hoof antenna for a femto-cell network in a multi-input multioutput system is proposed. The proposed half-elliptic hoof antenna incorporates half-elliptic surfaces, and has multiresonance frequencies in its TM modes. The half-elliptic design of the proposed antenna resonates with two main current paths, and the resonant frequency of each mode can be calculated using the Mathieu function. Moreover, an additional resonator is inserted between the half-elliptic patch and a ground to obtain additional resonance frequency and a wider bandwidth on the high band. The proposed antenna covers the frequency bands from 880 to 960 MHz and from 1710 to 2170 MHz for Global System for Mobile Communications (GSM)/Digital Cellular System (DCS)/Personal Communications Service (PCS)/International Mobile Telecommunications (IMT) with a peak gain of 6.8 dBi. To validate the design of the proposed antenna, the analysis of the antenna using the simulated and measured results is presented and discussed.

Performance Improvement Using Real-Time Detection of Time-Variant Load Impedance of the Receiver in Wireless Power Transfer System

In this paper, an analysis of the effect of time-variant reflected impedance and its detection method on wireless power transfer(WPT) systems are presented. The reflected resistance at WPT systems is very important parameter as it indicates how well matched antenna is and will exhibit high efficiency. Proposed detection method is based on transmitter current variation analysis with respect to frequency sweep. Using the proposed design method, a wireless power transfer system operating at the frequency of 125 kHz, is design and detect reflected impedance variation. The proposed design method provides good agreements between measured and simulated results. Therefore, The proposed detecting method provides a nonintrusive method to detect harmful object in WPT system.

Adaptive load impedance matching using 5-port reflectometer with computationally simple measurement

Five-port architectures are investigated as a reflectometer for adaptive load impedance matching. The proposed reflectometer requires computationally simple control loop. Moreover, the adaptive load impedance matching system in RFID UHF band are proposed. Using simulation and measurement studies, it is shown that the five-port architecture can be used as a low-cost, simple and high-performance reflectometer in adaptive load matching systems.