• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.1262-1264
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• 2003

The author Present a modified multiloop algorithm including feedforward for controlling a 45kW step down chopper in the power supply of Maglev. The control law for the duty cycle consists of three terms. The first is the feedforward term which compensates for variations in the input voltage. The second term consists of the difference between the slowly moving inductor current and output current. The third term consists of proportional and integral terms involving the perturbation in the output voltage. This perturvation is derived by subtracting the desired output voltage from the actual output voltage. The proportional and integral action stabilizes the system and minimizes output voltage error. To verify the validity of the proposed multiloop controller, simulation study was tried using Matlab/sirnulink.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.36-39
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• 2000

A small electrical potential difference which appears on any solid body when subjected to illumination by a modulated light beam generated by laser is called photocharge voltage(PCV)[1,2]. This voltage is proportional to the induced change in the surface electrical charge and is capacitatively measured on various materials such as conductors, semiconductors, ceramics, dielectrics and biological objects. The amplitude of the detected signal depends on the type of material under investigation, and on the surface properties of the sample. In photocharge voltage spectroscopy measurements[3], the sample is illuminated by both a steady state monochromatic bias light and the pulsed laser. The monochromatic light is used to created a variation in the steady state population of trap levels in the surface and space charge region of semiconductor samples which does result in a change in the measured voltage. Using this technique the spatial variation of PCV can be utilized to evaluate the surface conditions of the sample and the variation of the PCV due to the monochromatic bias light are utilized to characterize the surface states. A qualitative analysis of the proposed measurement is present along with experimental results performed on amorphous silicon samples. The deposition temperature was varied in order to obtain samples with different structural, optical and electronic properties and measurements are related to the defect density in amorphous thin film.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.4
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• pp.332-341
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• 2014

A cascaded H-bridge multi-level STATCOM(STATic synchronous COMpensator), which is composed of many cell inverters with independent dc-sources, generates inevitably dc-side voltage unbalance among phases when it compensates unbalanced load. It comes from the difference of flowing active power in each phase when this compensator makes negative-sequence current to eliminate the unbalance of source-side current. However, this unbalance can be controlled by injecting zero-sequence current which is decoupled with grid currents, so the compensator can work well during this balancing process. Both a feedback control algorithm, which produces zero-sequence current proportional to dc-side voltage unbalance within each phase, and a feedforward control algorithm, which makes zero-sequence current directly from the compensator's negative-sequence current, were proposed. The dc-side voltage of each phase can be controlled stably by these proposed algorithms in both steady-state and transient, so the compensator can have fast response to satisfy control performance under rapid changing load. These balancing controllers were implemented and verified via simulation and experiment.

• Journal of the Korean Society of Industry Convergence
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• v.22 no.2
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• pp.219-226
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• 2019

This paper describes the development of a 500W DC/DC converter for use with a thermoelectric module(TEM). A thermoelectric device is a structure in which a P-type semiconductor and an N-type semiconductor are electrically connected in series and thermally connected in parallel. There is a feature that an electromotive force is generated by making a temperature difference between both surfaces of a thermoelectric element. This feature can be used as a renewable power source without the need for fossil energy. The proposed converter boosts the low generation voltage of the thermoelectric element to secure the voltage for the grid connection. This converter is a combination of a resonant converter for boosting and a boost-converter for output voltage control. This structure has an advantage that a voltage can be stepped up at a high efficiency and precise output voltage control is possible. We carry out simulations and experiments to verify the validity.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.2
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• pp.71-77
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• 2019

This study proposes a circulating current reduction method that uses high-frequency voltage compensation when carrier phase difference occurs between two inverters in MSIS. In MSIS, inverters are configured in parallel to increase power capacity and to increase efficiency by using inverters only as needed. However, in the parallel inverter structure, circulating current is inevitably generated. Circulating current increases the stress on the switch, adversely affects the current control performance, and renders load sharing difficult. The proposed method compensates for the output voltage reference of the slave module by using the high-frequency voltage so that the switching pattern of each module is matched even in asynchronous carriers. The validity of the proposed method is verified by simulations and experiments with 600 W IPMSM.

• Journal of the Korean Vacuum Society
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• v.15 no.2
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• pp.180-185
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• 2006

Microwatt power level at relatively high voltage(order of volt) was produced by $Bi_{0.5}Sb_{1.5}Te_{3}/Bi_{2}Te_{2.4}Se_{0.6}$ thin film thermoelectric generators, and maximum output power varied with temperature difference in the square-law relation. Output voltage and current were possible to control by changing the way of electrical connection as well as the number of stacking plate-modules. Variation of open circuit voltage and short circuit current with temperature difference showed a linear relationship. There were, however, some differences in variations; open circuit voltage were dependent on the number of plate-module when connected in series, but it was not for parallel connection. On the other hand, short circuit current showed the opposite behavior to the case of open circuit current.

• Journal of the Korean Society of Radiology
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• v.12 no.2
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• pp.185-191
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• 2018

The purpose of this study was to evaluate the usefulness of BMI application to Urography CT by applying different tube voltages in accordance with body mass index. Group A (n = 38) with body mass index of lower than 25 was examined with tube voltage of 100 kVp while Group B (n = 45) with a BMI of 25 and higher was examined with tube voltage of 120 kVp. C group (n = 37) with body mass index (BMI) of lower than 25 was examined with tube voltage of 120kVp. Although the difference in average dose between group A (100 kVp) and group C (120 kVp) with low body mass index (BMI) of lower than 25 was $214.8mGy{\cdot}cm$, there was no significant difference in qualitative evaluation and, compared with patient group with body mass index of 25 and higher, results obtained were rather good. Therefore, this study verified that the tube voltage of lower than 100 kVp does not have adverse effect on the quality of image for patients with body mass index (BMI) of lower than 25.

• Journal of the Institute of Convergence Signal Processing
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• v.13 no.4
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• pp.201-206
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• 2012

The indirect-contact ECG measurement is a newly developed method for unconstrained and nonconscious measurement in daily life. This study introduced a new method of electrode circuit design developed for reducing the 60Hz power line noise observed at the indirect-contact ECG measurement. By the introduced common-mode-driven shielding, the voltage of the electrical shield surrounding the capacitive coupling electrode is maintained at the same as the common mode voltage. Though the method cannot reduce the level of common mode voltage itself, that reduces effectively the differential mode noise converted from the common mode voltage by the difference of cloth impedance between the two capacitive coupling electrode. The experiment results using the actual indirect-contact ECG showed that the 60Hz power line noise was reduced remarkably though the reduction ratio was smaller than the expected by the theory. Especially, the reduction ratio became large for the large difference of cloth. It is expected that the introduced method is useful for reducing the power line noise under condition of poor electrical grounding.

• Journal of Sensor Science and Technology
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• v.11 no.3
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• pp.145-154
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• 2002

NiCr-heaters with three different thicknesses ranging from 400 nm to 800 nm were fabricated and their characteristics were compared for the purpose of developing a chromel-alumel multijunction thermal converter for low input voltage with low frequency. The thermoelectric effect-induced AC-DC voltage transfer difference of the thermal converter with a built-in NiCr-heater of 400 nm-thickness was ${\pm}0.51{\sim}1.69\;ppm$ in the DC reversing frequency of $40\;Hz{\sim}10\;kHz$ with appling $0.5\;V_{rms}$ and the difference was increased to ${\pm}40{\sim}{\pm}115\;ppm$ in the frequency of $40\;Hz{\sim}1\;MHz$, when both thermoelectric effects and frequency effects were considered, showing the thermal converter would be suitable for the low input voltage application with low frequency.

• Proceedings of the KIEE Conference
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• 2002.06a
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• pp.187-190
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• 2002

In contrast to conventional electromagnetic motor, USM(Ultrasonic Motor), as piezoelectric ceramic applying ultrasonic mechanical vibration and as frictional-movement type motor, get rotational torque by elastic friction between stator and rotator, The USM, which is small motor without iron cores and coil as a simple structure, has little load weight, has character of high torque at low speed, and can apply a direct drive type without deceleration gear as low speed type. A response of USM from control input is satisfactory, and also generates much torque in low speed driving, and holding torque is much without supplying power. In this study, I designed and made Ultrasonic motor-digital multi controller(USM- DMC) using FPGA chip, A54SX72A made in Actel Corporation. By the minute, USM-DMC can control frequency, duty ratio, and phase difference of USM by llbit digital input from Pc. Therefore, when we use this controller, we can apply to typical parameter, frequency, phase difference, and voltage parameter, to control as well as we can do mixing control like phase-frequency, phase-voltage, frequency-voltage, frequency-phase-voltage, What is more, the strongest point is that it can trace frequency based on optimized frequency because we can input optimized resonant frequency while in motoring.