• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.11
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• pp.96-103
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• 2013

In this paper, resonant wireless power transfer systems are designed with double loop resonant coils for the resonant frequency of 150kHz. The transfer efficiency characteristics is analyzed according to the coil size, and the distance and misalignment between the coils. Then the change in efficiency is investigated when a human model is located between the resonant coils using the homogeneous human phantom of IEC-62311 standard. Also, in order to assess the safety of the wireless power transfer system, the induced current density inside the human model is calculated when it is exposed to the magnetic field of a plane wave and resonant coil. Then, the results are compared with the exposure limits in the EMF (electromagnetic field) safety guidelines.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.6
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• pp.542-545
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• 2016

This work proposes a capacitive coupling-based wireless battery charging circuit that is built with vehicle glasses for electric vehicles. A capacitive coupling wireless power transfer offers many advantages, such as low metal impact and low energy transfer efficiency changes in accordance with changes in position. However, a large coupling capacitor is needed for high power transfer. Therefore, a new capacitive coupling-based wireless power transfer LLC resonant converter built with the glasses of an electric vehicle is proposed. The proposed converter is composed of coupling capacitors with glasses of an electric vehicle and two transformers for impedance transformation. The proposed LLC converter can transfer large power and obtain high efficiency with zero voltage switching. The validity and features of the proposed circuit is verified by experimental results with a 1.2 kW prototype.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.4
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• pp.279-285
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• 2019

This study proposes an enhanced switching pattern that can improve energy transfer efficiency in an active cell-balancing circuit using a multiwinding transformer. This balancing circuit performs cell balancing by transferring energy stored in a specific cell with high energy to another cell containing low energy through a multiwinding transformer. The circuit operates in flyback and buck-boost modes in accordance with the energy transfer path. In the conventional flyback mode, the leakage inductance of the transformer and the stray inductance component of winding can transfer energy to an undesired path during the balancing operation. This case results in cell imbalance during the cell-balancing process, which reduces the energy transfer efficiency. An enhanced switching pattern that can effectively perform cell balancing by minimizing the amount of energy transferred to the nontarget cells due to the leakage inductance components in the flyback mode is proposed. Energy transfer efficiency and balancing speed can be significantly improved using the proposed switching pattern compared with that using the conventional switching pattern. The performance improvements are verified by experiments using a 1 W prototype cell-balancing circuit.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.1
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• pp.79-84
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• 2020

Wireless power transfer is more convenient than wired power transfer, but has a shorter transfer distance and lower efficiency. In addition, it is difficult to charge multiple devices simultaneously. In this paper, we propose a method of magnetic beam forming by using multiple transmitters in order to increase transfer distance and improve efficiency of wireless power transfer. To do this, the relationship between the transmitter coil current and magnetic field at the center of receiver coil is modelled, and calculate the optimal transmitter coil current using the characteristics of the pseudoinverse. Finally, the validity of the proposed method is verified by simulation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.11
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• pp.1651-1657
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• 2015

In MHz operating wireless power transfer systems, skin- and proximity-effect losses in the transmitter and the receiver coils dominate the coil-to-coil efficiency of the system. A Litz-wire was regarded as a common solution for minimizing such Ohmic losses in high frequencies. In this paper, equivalent series resistances of 12 different cables including Litz-wire and copper tubing have been calculated and measured for a 6.78 MHz, 100W, 30 cm wireless power transfer system. It has been shown that the copper tubing has lower resistances compared to the Litz-wire in that frequency and a wireless power transfer system with the copper tubing was able to achieve much higher efficiency than a system using the Litz-wire. Calculations of the resistances and efficiencies were accomplished with analytical equations and those calculations were evaluated by experimental results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.4
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• pp.237-243
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• 2016

It is necessary to investigate the input power as well as the mass transfer characteristics of the aeration process in order to improve the energy efficiency of an aerobic water treatment. The objective of this study is to experimentally investigate the effect of orifice nozzle design and input power on the flow and mass transfer characteristics of a vertical two-phase flow. The mass ratio, input power, volumetric mass transfer coefficient, and mass transfer efficiency were calculated using the measured data. It was found that as the input power increases the volumetric mass transfer coefficient increases, while the mass ratio and mass transfer efficiency decrease. The mass ratio, volumetric mass transfer coefficient, and mass transfer efficiency were higher for the orifice configuration with a smaller orifice nozzle area ratio. An empirical correlation was proposed to estimate the effect of mass ratio, input power, and Froude number on the volumetric mass transfer coefficient.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.2
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• pp.202-211
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• 2014

The bulk current injection (BCI) and direct power injection (DPI) method have been established as the standards for the electromagnetic susceptibility (EMS) test. Because the BCI test uses a probe to inject magnetically coupled electromagnetic (EM) noise, there is a significant difference between the power supplied by the radio frequency (RF) generator and that transferred to the integrated circuit (IC). Thus, the immunity estimated by the forward power cannot show the susceptibility of the IC itself. This paper derives the real injected power at the failure point of the IC using the power transfer efficiency of the BCI method. We propose and mathematically derive the power transfer efficiency based on equivalent circuit models representing the BCI test setup. The BCI test is performed on I/O buffers with and without decoupling capacitors, and their immunities are evaluated based on the traditional forward power and the real injected power proposed in this work. The real injected power shows the actual noise power level that the IC can tolerate. Using the real injected power as an indicator for the EMS test, we show that the on-chip decoupling capacitor enhances the EM noise immunity.

• Journal of Power Electronics
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• v.16 no.1
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• pp.102-110
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• 2016

Contactless power transfer technology is gaining increasing attention in city transportation applications because of its high mobility and flexibility in charging and its commensurate power level with conductive power transfer method. In this study, an inductively coupled contactless charging system for a 48 V light electric vehicle is proposed. Although this study does not focus on system efficiency, the generic problems in an inductively coupled contactless power transfer system without ferromagnetic structure are discussed. An active load matching method is also proposed to control the power transfer on the receiving side through a load matching converter. Small signal modeling and linear control technology are applied to the load matching converter for port voltage regulation, which effectively controls the power flow into the load. A prototype is built, and experiments are conducted to reveal the intrinsic characteristics of a series-series resonant inductive power charger in terms of frequency, air gap length, power flow control, coil misalignment, and efficiency issues.

• Journal of Magnetics
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• v.21 no.4
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• pp.652-659
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• 2016

In this study, the efficiencies for both the angular aligned and unaligned positions of the receiver and transmitter coils of wireless power transfer (WPT) systems are examined. Some parameters of the equivalent circuit were calculated with Maxwell 3D software. The analytical solution of the circuit was calculated in MATLAB program through the composition of the system's mathematical modeling. The numerical solution of the system, however, was calculated using PSIM, which is circuit simulation software. In addition, with the use of the finite element method (FEM) in Maxwell 3D software, transient analysis of the three-dimensional system was performed. The efficiency of the system was estimated through the calculation of input and output power. The results demonstrated that power was efficiently transmitted to a certain extent in aligned and unaligned positions. The results also revealed that, for aligned positions, high efficiency with air gaps of 15-20 cm can be obtained and that the efficiency quickly dropped with air gaps of more than 20 cm. For spatially unaligned positions, it was observed that wireless power transfer could be realized with high efficiency with air gaps of up to 10 cm and that efficiency quickly dropped with air gaps of more than 10 cm.

• Journal of Electrical Engineering and Technology
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• v.9 no.2
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• pp.569-575
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• 2014

A highly efficient class E power amplifier is demonstrated for application to wireless power transfer system. The amplifier is designed with an L-type matching at the output for harmonic rejection and output matching. The power loss and the effect of each component in the amplifier with the matching circuit are analyzed with the current ratio transmitted to the output load. Inductors with a quality factor of more than 120 are used in a dc feed and the matching circuit to improve transmission efficiency. The single-ended amplifier with 20 V supply voltage shows 7.7 W output power and 90.8% power added efficiency at 6.78 MHz. The wireless power transfer (WPT) system with the amplifier shows 5.4 W transmitted power and 82.3% overall efficiency. The analysis and measurements show that high-Q inductors are required for the amplifier design to realize highly efficient WPT system.