• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.1114-1116
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• 2002

The characteristics of voltage drop and THD for parallel operating 11 PCRs (Phase Controlled Rectifiers) are analysed. The PCRs are used to drive high current (1.6 kA ${\sim}$ 3.7 kADC) electromagnetic coils for electromagnets. All the PCRs operate simultaneously in pulsed mode, and the pulse shot occurs every 150 seconds. During the pulse operation the PCR output current ramps up for 4 seconds, and then keeps flat top state for 2 seconds, and finally ramps down for 4 seconds. For the flat top mode a severe voltage drop and distortion appear in the power system because transformers for the PCRs are designed considering pulsed mode operation. It is expected that the analysis method can be applied to improve the system performance including power factor and design of high power pulsed mode operating power supply systems.

• Proceedings of the KIPE Conference
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• 2003.07a
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• pp.264-268
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• 2003

This paper describes a high voltage high power DC power supply which has the ability of pulsed mode operation. The power supply Is constructed with several series connected power converters based on modified multilevel converters. The modified multilevel converters are suitable for the protection of frequent output short-circuit. The output dc power of the proposed converter can be disconnected from the load within several hundred microseconds at the instant of short-circuit fault. The rising time of the dc load voltage is as small as several hundred microseconds, and there is no overshoot of the do voltage because the dc output capacitors keep undischarged state. Analysis, simulations, and experiments are carried out to Investigate the operation and usefulness of the proposed scheme.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.208-212
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• 2003

An airborne radar is an essential aviation electronic system of the helicopter to perform various missions in all-weather environments. This paper presents the conceptual design results of the multi-mode pulsed Doppler radar system testbed model for helicopter. Due to the inherent flight nature of the hovering vehicle which is flying in low-altitude and low speed, as well as rapid maneuvering, the moving clutters from the platform should be suppressed by using a special MTD (Moving Target Detector) processing. For the multi-mode radar system model design, the flight parameters of the moving helicopter platform were assumed: altitude of 3 Km, average cruising velocity of 150knots. The multi-mode operation capability was applied such as short-range, medium-range, and long-range depending on the mission of the vehicle. The nominal detection ranges is 30 Km for the testbed experimental model, but can be expanded up to 75 Km for the long range weather mode. The detection probability of each mode is also compared in terms of the signal-to noise ratio of each mode, and the designed radar system specifications ate provided as a design results.

• Korean Journal of Optics and Photonics
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• v.5 no.1
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• pp.84-89
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• 1994

A tunable pulsed dye laser was operated in a single longitudinal mode by injection locking with a cw ring dye laser. A doubled Nd:YAG laser was used as the pumping source. Phase sensitive detection technique was applied to maintain the required match between the master laser frequency and the slave resonator cavity length. The fluctuation of the center frequency of the pulsed laser was < 10 MHz, and the pulse duration (FWHM) was 6 ns. The linewidth measured by scanning confocal interferometer was 130 MHz. When pumped by 50 mJ of the doubled Nd:YAG laser, the output energy of the pulsed dye laser was 2 mJ and the peak power was 330 kW. 30 kW.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1759-1761
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• 1996

Md:YAG laser has been used in many applications such as micromachining, nonlinear optical experiments, holography, and rangefinding. These applications quite often require operation of the laser at the $TEM_{00}$ mode since this mode produces the smallest beam divergence, the highest power density, and, hence, the highest brightness. In this study, a pinhole is put between a rod and a half mirror to make the $TEM_{00}$ mode, and then we measured the intensity distribution of the output beam as reducing the diameter of the pinhole from 6mm to 1.5mm. As a result, the optimum size of the pinhole fixed in a resonator to make the $TEM_{00}$ mode was obtained, and we found out that the output beam of the pulsed Nd:YAG laser with a single elliptical cavity has a Gaussian distribution.

• Korean Journal of Optics and Photonics
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• v.28 no.6
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• pp.351-355
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• 2017

In this paper, we conduct a simulation of manipulating various pulsed laser operations through tuning the modulation depth of the saturable absorber in a laser cavity. The research, showing that various pulsed operations could be manipulated from Q-switching through Q-switched mode locking to mode locking by tuning the modulation depth of the saturable absorber in a cavity, has been studied by experimental means. We conduct a simulation with the Haus master equation to verify that these experimental results are consistent with expectations from theory. The time dependence of the gain was considered to express Q-switching fluctuation through applying a rate equation with the Haus master equation. Laser operation was manipulated from mode locking through Q-switched mode locking to Q-switching as modulation depth was increased, and this result agreed well with the theoretical expectation.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.4
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• pp.265-272
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• 2018

This paper proposes a new control method for the supercapacitor (SC) to compensate the pulsed load and to enhance the power quality of the DC microgrid. By coordinating the operating frequency, the SC is controlled to handle the surge current, while the low-frequency current component is dealt with by the remaining sources in the system. The operation mode of the SC unit is automatically changed based on the state of charge and DC bus voltage level. Meanwhile, the mismatch in the power demand is covered by the SC unit by regulating the DC bus voltage level. The effectiveness of the proposed method is verified experimentally by the prototype with two distributed generators and one SC unit.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.12
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• pp.624-630
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• 2001

The trend of the regulations on environmental issues are getting tight. Responding to this trend new technologies such as moving electrodes, wide pitch and pulsed power supply are also introduced in the electrostatic precipitator(EP) systems. The introduction of wide pitch and moving electrodes enhances the system performance of the EPs by improving air-flow and by improving the ash reentrainment on rapping. The power supplies for the EPs developed up to date include thyristor-based dc or intermittent type, SMPS(switching mode power supply) type and the pulsed-power supply type. The use of the pulsed ones is known to improve dust-collecting efficiency of high resistivity ash and reduces back corona occurrence in the collecting plate. There are two kinds of pulsed-power supplies; one with pulsed transformers and the other with direct dc switching devices. The latter uses rotary spark gap switches or semiconductor switches. Both have the merits and demerits: the spark gap switches are simple and robust but has short life time, hence, high maintenance cost, whereas the semiconductor switches have long life time but are costly. In this study, A high voltage power supply with superimposing voltage pulse on dc source was developed for EPs. This study describes circuit topology, operating principle of the scheme, and analysis of experimental results on Dong-Hae Power Plant. The pulsed power supply consists of a variable dc power supply with ratings of 60kV, 800mA and pulse generator which is made of high voltage thyristor-diode switch strings, an LC resonant tank and a blocking inductor. The pulse generator generates variable pulse-voltage up to 70kV using a high frequency resonant inverter with a variable dc source. Two prototypes were built and tested on 250MW DongHae power plant to verify the possibility of the commercial use and the normal operation in the transient states.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.53 no.1
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• pp.47-54
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• 2004

A new high voltage DC power supply is proposed. The proposed power supply is constructed with several power converters connected in series. It is easy to obtain high DC voltage for the same structure of each power converter. The output DC power of the proposed power supply can be disconnected from the load within several hundred microseconds at the instant of a load short-circuit fault. The rising time of the output DC voltage is also as small as several hundred microseconds, and there is no overshoot of the voltage because all of the output filter capacitors keep undischarged state even in load short-circuit condition. Therefore, the proposed scheme is suitable for the protection of frequent output short-circuit and fast on/off switching of output DC voltage. The proposed power supply has improved features such as simple structure, high power factor, and reduced size and volume compared with the conventional schemes. The operating principle is described and the validity of the proposed scheme is proved through simulations and experiments.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1665-1670
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• 2023

It is shown that in the IBR-2M reactor by the end of the reactor cycle, changes in dynamics are observed associated with a strong weakening of the fast power feedback (PF), as a result of which the reactor becomes oscillatorily unstable. After each week of zero-power operation the negative changes in reactor dynamics disappear and the stability of the reactor is restored. Thus, the reactor undergoes cyclic changes in the oscillatory instability. The correlation between of a fast PF and a slow PF is experimentally observed, which makes it possible to almost completely eliminate the cyclic component of instability by changing the control mode of rods of the control system.