• Journal of Electrical Engineering and Technology
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• v.6 no.6
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• pp.776-785
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• 2011

Since the Internet-based real-time Global Positioning System(GPS) synchronized widearea power system frequency monitoring network (FNET) was proposed in 2001, it has been monitoring the power system frequency in interconnected United States power systems and numerous interesting behaviors have been observed, including frequency excursion propagation. We address the consistency of a frequency excursion detection order of frequency disturbance recorders in FNET in relation to the same generation trip, as well as the ability to recreate by power systems dynamic simulation. We also propose a new method, as an application of FNET measurement, to locate a tripped generator using power systems dynamic simulation and wide-area frequency measurement. The simulation database of all the possible trips of generators in the interconnected power systems is created using the off-line power systems dynamic simulation. When FNET detects a sudden drop in the monitoring frequency, which is most likely due to a generation trip in power systems, the proposed algorithm locates a tripped generator by finding the best matching case of the measured frequency excursion in the simulation database in terms of the frequency drop detection order and the time of monitoring points.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.387-390
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• 2006

This paper presents a novel soft-switching PWM utility frequency AC to high frequency AC power conversion circuit Incorporating boost-half-bridge inverter topology, which is more suitable and acceptable for cost effective consumer induction heating applications. The operating principle and the operation modes are presented using the switching mode and the operating voltage and current waveforms. The performances of this high-frequency inverter using the latest IGBTs are illustrated, which includes high frequency power regulation and actual efficiency characteristics based on zero voltage soft switching (ZVS) operation ranges and the power dissipation as compared with those of the previously developed high-frequency inverter. In addition, a dual mode control scheme of this high frequency inverter based on asymmetrical pulse width modulation (PWM) and pulse density modulation (PDM) control scheme is discussed in this paper in order to extend the soft switching operation ranges and to improve the power conversion efficiency at the low power settings. The power converter practical effectiveness is substantially proved based on experimental results from practical design example.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.3
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• pp.256-264
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• 2022

The frequency power control method (FCM) which has a wide operating frequency range is adopted for induction heating (IH) cooktops. When FCM is applied to the full-bridge series resonant converter (FB-SRC) based IH system, high-frequency switching of the inverter is required compared to the half-bridge SRC (HB-SRC)-based IH system. Therefore, the switching loss of the inverter increases, and applying FCM under the condition that the inverter operating frequency range is limited is difficult. Therefore, this paper proposes a control strategy with the phase shift power control method considering that limited frequency conditions are presented. Loss analysis following the control method is performed through simulation and mathematical analysis. In addition, the validity of the proposed control strategy is verified by analyzing the heating performance following the control method through the test results of the 3,200[W] prototype.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.603-605
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• 1997

A new algorithm using 1-dimensional wavelet transform for autofocusing of optical instrument has been developed. Previous studies based on the conventional frequency analysis have shown that as the lens-object distance approaches the optimum value, the high frequency energy in the corresponding image shows a consistent increase. However, as conventional frequency analysis techniques hide spatial distribution of each band energy, shape information in the original signal cannot be easily utilized. In this paper, a newly devised wavelet based focus measuring scheme is presented. Unlike other frequency domain analysis techniques that simply produce "frequency-only" spectra, wavelet analysis provides a "time-frequency" localized view of a given signal. As a result, both frequency band filtering and spatial distribution filtering can easily be realized. Depending on the proposed focus quality measuring algorithm, a fast and reliable automatic focus adjustment of optical devices could be implemented.

• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.64-66
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• 1998

This paper presents a new efficient method for transient analysis in magnetodynamic systems of linear eddy current problems. This mehtod employs the Fourier transform and the high-order frequency sensitivity of harmonic finite element method. By taking into account the time-constant of magnetodynamic system, the Fourier integral of continuous frequency is converted into the Fourier series of discrete frequency. And with the results of Fourier series expansion of converted input wave form, the responses of each sinusoids is superposed to give the total response of the magnetodynamic systems. But, if the frequency band of input wave form is broad, it takes long computational time since all responses for each sinusoids must be calculated. Therefore, the high-order frequency sensitivity method is employed to estimate the response variation to frequency. The proposed algorithm is applied to an induction heating system to validate its numerical efficiency.

• Journal of Korean Physical Therapy Science
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• v.11 no.1
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• pp.28-35
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• 2004

The purpose of the present study was to investigate the effectiveness of silver spike point (SSP) low frequency electrical stimulation on glomerular filtration rate (GFR), specifically, such as diuretic action in 24 hour urine and in plasma analysis from normal volunteer. The current of 1 Hz continue type (CT) of SSP low frequency electrical stimulation significantly decreased in plasma creatine from normal volunteer. However, the urine creatinine clearance (Ccr) was significantly increased by SSP low frequency electrical stimulation in normal volunteer. These results suggest that the SSP low frequency electrical stimulation, especially current of 1 Hz continue type, significantly regulates urine creatinine clearance and glomerular filtration rate from normal volunteer. Therefore, the SSP low frequency electrical stimulation is a good regulator through a diuretic action of hypertension.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.1
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• pp.61-65
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• 2017

In this paper a prototype of high frequency heating power supply system based on the high frequency heating principle is designed to take the place of acupuncture, moxibustion, warm dressing treatment and some other traditional physical therapy methods. Which possess the advantages of low cost, convenient, easy operation and good effect. The high frequency heating power supply can generate a pulse voltage of more than 1KV with 300KHz switching frequency to heat the patient's skin. The skin temperature can reach to $41{\sim}42^{\circ}C$. The peak current control method is used to maintain the skin temperature in the designed range. The design of the main circuit is based on the flyback converter topology. An easier and practical design method is proposed in this paper. The power supply system prototype is verified to be stable and reliable by both the simulation and experimental results.

• Journal of Electrical Engineering and Technology
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• v.7 no.3
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• pp.389-395
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• 2012

In this paper, we analyzed the frequency spectrum of the electromagnetic waves radiated by an electric discharge as a basic study to develop an on-line diagnostic technique for power equipment installed inside closed-switchboards. In order to simulate local and series arc discharges caused by an electric field concentration and poor connections, three types of electrode systems were fabricated, consisting of needle and plane electrodes and an arc generator meeting the specifications of UL 1699. The experiment was carried out in an electromagnetic anechoic chamber, and the measurement system consisted of a PD free transformer, a loop antenna with a frequency bandwidth of 150 kHz-30 MHz, an ultra log periodic antenna with a frequency bandwidth of 30 MHz-2 GHz, and an EMI test receiver with a frequency bandwidth of 3 Hz-3 GHz. According to the experimental results, the frequency spectra of the electrical discharges were widely distributed across a range of 150 kHz-400 MHz, depending on the defects, while commonly found between 150 kHz and 10 MHz. Therefore, considering the ambient noise and antenna characteristics, the best frequency bandwidth for a measurement system to monitor abnormal conditions by detecting electromagnetic waves in closedswitchboards is 150 kHz-10 MHz.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.5
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• pp.372-376
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• 2012

This study focused on the performance characteristics of solar cell using the impedance technique. We measured an impedance according to frequency from 1 Hz until 1 MHz. It could know that the impedance was decreased according to the frequency increases in solar cell. The impedance of single crystal solar cell was 0.61 ${\Omega}$ at 1 Hz, and kept almost settled value to $1{\times}10^2$ Hz. However, the impedance of polycrystal solar cell was $7{\times}10^3{\Omega}$ at 1 Hz.

• Journal of The Korean Society of Agricultural Engineers
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• v.50 no.5
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• pp.63-72
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• 2008

This study was conducted to define a characteristics of Electrical Resistivity of weathered soil against volumetric water content and frequency. It is essential to analyze and understand a characteristics of the Electrical Resistivity for evaluation of soil as subsurface contaminant detection. Before the test, an effect of pore water and ion were checked using four liquids(distilled water, tap water, potassium chloride 1.8mM, and 3.7mM). As a result, the correlation between the volumetric water content and the Electrical Resistivity was estimated. The Electrical Resistivity decreases with increasing frequency and water content. Also, Electrical Resistivity could be described by an exponential function of volumetric water content with the constants.