• Journal of the Korean Institute of Telematics and Electronics
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• v.25 no.5
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• pp.536-541
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• 1988

The push-pull current-fed DC-to-DC converter has only one energy storage reactor in series with the input for any number of outputs. It is considered that this property of the converter has considerable advantages over other multiple-output circuits. The steady state characteristics of the converter with two outputs is analyzed. It is known that the voltage difference between the two outputs appears by existing the 2nd winding resistance of transformer and there is a region of the duty ratio in which the voltage difference of the converter is smaller than that of the forward converter.

• Journal of Power Electronics
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• v.12 no.1
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• pp.83-87
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• 2012

Input-series-output-parallel (ISOP) modular converters consisting of multiple modular DC/DC converters can enable low voltage rating switches for use in high voltage input applications. In this paper, an input voltage sharing control strategy for input-series-output-parallel (ISOP) full-bridge (FB) DC/DC converters is proposed. By sensing the difference in the input current of two modules, the system can achieve input voltage sharing for DC-DC modules. The effectiveness of the proposed control strategy is verified by simulation and experimental results obtained with a 200w-50kHz prototype.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.177-180
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• 1999

In this paper, we studied Surface Discharge Type Flat Fluorescent Lamp(FFL) with High Luminance for LCD Backlighting. This lamp is Surface Discharge Type structure with a pair of Sodalime glass, insulator layer, phosphor layer, and Xe gas gap. There are two influences of Electric field on different dielectric thickness. The Electric field difference at the dielectric layer itself enhances minimum value of firing voltage and luminance uniformity. So, we measured the Electric filed at 0.5mm, 1mm gap length and discharge voltage for difference dielectric layer thickness. In experiment result, the thicker dielectric layer has higher firing voltage and lower current.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.3
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• pp.343-348
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• 2008

We investigated the quench characteristics accordance with increase of turns and applied voltage of matrix-type superconducting fault current limiter (SFCL) with $1{\times}3$ matrixes. The matrix-type SFCL consists of the trigger part to apply magnetic field and the current-limiting part to limit fault current. The fault current limiting characteristics according to the increase of magnetic field and applied voltage were nearly same. This is because the application of magnetic field has not an affect on total impedance of SFCL. When number of turns of reactor increased, the voltage difference between two superconducting units in the current-limiting part according was decreased. The resistance difference generated in two superconducting units also was decreased. Therefore, we confirmed that the differences of critical behaviors between superconducting units by application of magnetic field were decreased. By this results, we could be decided the optimum number of turns of reactor to apply magnetic field.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.8 s.185
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• pp.64-71
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• 2006

In this paper, a uniform speed controller for an ultrasonic rotary motor is developed using the phase-difference method. The phase difference method uses traveling waves to drive the ultrasonic motor. The traveling waves are obtained by adding two standing waves that have a different phase to each other. A compact phase-difference driver system is designed and integrated by combining VCO(Voltage Controlled Oscillator) and phase shifter. Theoretically the relationship between the phase difference in time and the rotational speed of the ultrasonic motor is sine function, which is verified by experiments. Then a series of experiments under various loading conditions are conducted to characterize the motor's performance that is the relationship between the speed and torque. Proportional-integral control is adopted for the uniform speed control. The proportional control unit calculates the compensating phase-difference using the rotating speed which is measured by an encoder and fed back. Integral control is used to eliminate steady-state errors. Differential control for reducing overshoot is not used since the response of ultrasonic motor is prompt due to its low inertia and friction-driving characteristics. The developed controller demonstrates reasonable performance overcoming disturbing torque and the changes in material properties due to continuous usage.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.6
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• pp.938-943
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• 2008

Coupling capacitor voltage transformers(CCVTs) have been used in extra or ultra high voltage systems to obtain the standard low voltage signal for protection and measurement. For fast suppression of the phenomenon of ferroresonance, three winding CCVTs are used instead of two winding CCVTs. A tuning reactor is connected between a capacitor voltage divider and a voltage transformer to reduce the phase angle difference between the primary and secondary voltages in the steady state. Slight distortion of the secondary voltage is generated when no fault occurs. However, when a fault occurs, the secondary voltage of the CCVT has significant errors due to the transient components such as dc offset component and/or high frequency components resulting from the fault. This paper proposes an algorithm for compensating the secondary voltage of a three winding CCVT in the time domain. With the values of the measured secondary voltage of the three winding CCVT, the secondary, tertiary and primary currents and voltages are estimated; then the voltages across the capacitor and the tuning reactor are calculated and then added to the measured voltage. Test results indicate that the algorithm can successfully compensate the distorted secondary voltage of the three winding CCVT irrespective of the fault distance, the fault impedance and the fault inception angle as well as in the steady state.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.3
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• pp.285-293
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• 1999

In this paper, the novel digital frequency/phase controller, to control the invelter fed traveling wave type ultra-sonic m motor(USM) is proposed. This controller is used to control the drive frequency, phase difference and applied voltages of e each phase of the motor. Proposed digital controller has constructed with digital logic only, no more use digitallongleftarrowanalog h hybrid method of the conventional controller, in order to generate drive frequency and phase difference. Therefore, the c control system has become to velY simple structure. T\rvo types of controllers are designed, one is to control drive f frequency and phase difference, another has added voltage control function of each phase. Two full digital voltage/phase c controllers are implemented by using custom LSI and EPLD, the control pelformance and the simplicity ofthe proposed c controller is verified by expeJimental results.

• Transactions of the Korean hydrogen and new energy society
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• v.3 no.2
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• pp.63-69
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• 1992

Two unit cells were made and operated with oxygen and air as oxidants After 350 hours operation with oxygen, the open circuit voltage drop of unit cell was 30 mV and internal resistance increased. After 250 hours operation with air, the open circuit voltage drop was 130mV. And the open circuit voltage difference of two cases was 90mV. In order to improve the performance of the unit cell with air, the supplying method of the electrolyte and the mass transfer characteristics of the electrode should be studied.

• 전기의세계
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• v.28 no.1
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• pp.73-82
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• 1979

There are a great number of papers on the Townsend discharge in gases, and many of them are concerned with the effect of the cathode. It has been regarded that there are two kinds of effect of the electrodes, especially of the cathode; (a) the effect caused by the difference of the cathode material and (b) the effect by the change of the cathode surface state even in the same material. Both of them may change the secondary coefficient following after the change of the work function, and the atter may further change the primary ionization coefficient as foreign atoms on the surface may be dseorbed in sparks to decrease the purity of the gas. Thus the two effects must be investigated independently to study the roles of the cathode in gas discharges. In this report the effect of the cathode material on the sparking voltage is described. The experiment is also carried out under the condition that the desorption of impurities from the cathode be negligible. From these the new correlativity between the work function of the cathode and the sparking voltage is obtained. In addition, the interesting character of the minimum point of the Paschen's curve can be found.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.605-607
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• 2001

In this paper, an off-tine UPS with CVT(constant voltage transformer) is designed and the experimental result and problems of the designed UPS is given and discussed. This off-line UPS consists of triple-port CVT and PWM inverter which acts as charger and inverter. It can be evaluated in low price because haying simple structure. It offers high performance because CVT restricts the short current automatically about two or three times of rated current, has nearly unit power factor and constant output voltage to varying input voltage. The weak points of this UPS are that the output voltage waveform is not perfect sinusoidal and has phase difference to input voltage. The experimental result and problems of the designed UPS is given.