• Journal of the Korean Society for Precision Engineering
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• v.31 no.9
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• pp.805-811
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• 2014

In this investigation, we constructed and demonstrated a simple Yb-doped fiber laser, of which longitudinal modes are mode-locked without any additional devices to compensate the dispersion caused by optical components. Non-linear polarization rotation (NPR) was adopted for the mode-locking mechanism and a polarization controller (PC) was used for a kind of spectral filters to restrict the bandwidth for mode-locking. As the result, the laser was successfully operated as mode-locked with the repetition rate of 42.2 MHz and the spectrum was broadened up to approximately 16 nm at 1033 nm center wavelength when the laser was mode-locked. In this paper, the operation of the developed Yb-doped mode-locked laser is explained with the concept of Lyot filter realized by a PC, which enables mode-locking under normal dispersion. In the industrial applications, this laser can be used as a seed laser of the high power lasers for optical manufacturing.

• Journal of KSNVE
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• v.8 no.1
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• pp.81-86
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• 1998

A 500Wh class high-speed Flywheel Energy Storage System (FESS) driven by a built-in BLDC motor/generator has been designed, which runs from 30000 to 60000rpm nominally. Due to the motor/generator inside, the flywheel rotor made of composites supported by PM/EM hybrid bearing system has a shape of bell or pendulum and thus requires accurate rotordynamic analysis and prediction of its dynamic behavior to secure the operating reliability. Rotordynamic analyses of the flywheel rotor-bearing system revealed that the bell shaped rotor has two conical rigid-body modes in the system operating range and the first conical mode, of which nodal point lies in the radial EM bearing position, can adversely affect the dynamic response of the rotor at the corresponding critical speed. To eliminate the possibility of wild behavior of the rotor, two guide bearings are adopted at the upper end of the rotor and motor/generator. It was also revealed that the EM bearing stiffness if 0.5~1.0E+6 N/m and damping of 2000 Ns/m are favirable for smooth operation of the system around the 2nd critical speed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.3
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• pp.131-136
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• 2013

The present study has conducted cycle design and control technology of a water source VRF heat pump system. Previously, study of a simultaneous heating and cooling in an air source VRF heat pump system has been conducted. However, performance data and design methods for simultaneous heating and cooling in a water source VRF heat pump system are limited in the literature, due to various system parameters and operating conditions. In this study, the operating characteristics and performances of a simultaneous heating and cooling heat pump system are carried out, in simultaneous operation modes. Control logics of an EEV are developed for flow rate control to the outdoor unit, and are verified. When the control logics are applied, the simultaneous cooling and heating performances are sufficiently achieved, and system COPs are increased by up to 23.4%.

• Korean Journal of Optics and Photonics
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• v.15 no.6
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• pp.503-510
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• 2004

We propose a novel vertical directional coupler switch using a vertical directional coupler with polarization independent coupling lengths employing the doublesided deep-ridge waveguide structure. This switch is composed of a switching operation induced section with symmetric structures and an extinction ratio enhanced section with asymmetric structures. We present design methods and examples for this switch with very short lengths and very high extinction ratios larger than 30 dB for both TE and TM modes in cases of both cross and bar states.

• Journal of Sensor Science and Technology
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• v.26 no.6
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• pp.402-407
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• 2017

Characteristics of various material surface plasmon resonance (SPR) chips were investigated in angular interrogation mode and intensity interrogation mode. Among five metals, silver (Ag), gold (Au), copper (Cu), chromium (Cr) and titanium (Ti), three metals, Ag, Au and Cu were paid attention to since their characteristics can be easily analyzed in angular interrogation mode by investigating the change of their reflectance curves according to refractive index change from 1.331 to 1.335. Most of SPR chips with various configurations showed the similar property in angular interrogation mode. The application of the SPR chip made of Ag, Au and Cu or their combinations depends on their reflectance properties. In intensity interrogation mode, the operation range may be limited since the variation of the intensity was not linearly related to refractive index change ranging from 1.331 to 1.335. However, the SPR chip containing high ratio of Ag may be applicable to high sensitive detection due to their sharp reflectance curves in intensity interrogation mode.

• JSTS:Journal of Semiconductor Technology and Science
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• v.7 no.4
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• pp.267-273
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• 2007

A fractional-N frequency synthesizer supports quadruple bands and multiple standards for mobile broadcasting systems. A novel linearized coarse tuned VCO adopting a pseudo-exponential capacitor bank structure is proposed to cover the wide bandwidth of 65%. The proposed technique successfully reduces the variations of KVCO and per-code frequency step by 3.2 and 2.7 times, respectively. For the divider and prescaler circuits, TSPC (true single-phase clock) logic is extensively utilized for high speed operation, low power consumption, and small silicon area. Implemented in $0.18-{\mu}m$ CMOS, the PLL covers $154{\sim}303$ MHz (VHF-III), $462{\sim}911$ MHz (UHF), and $1441{\sim}1887$ MHz (L1, L2) with two VCO's while dissipating 23 mA from 1.8 V supply. The integrated phase noise is 0.598 and 0.812 degree for the integer-N and fractional-N modes, respectively, at 750 MHz output frequency. The in-band noise at 10 kHz offset is -96 dBc/Hz for the integer-N mode and degraded only by 3 dB for the fractional-N mode.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.8
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• pp.90-97
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• 2014

This paper presents a compensation method of unbalanced phase currents in interleaved bi-directional converters. Phase currents in interleaved bi-directional converter are apt to be unbalanced due to circuit parameter error and switch operation difference. This problem causes the switch element failure and the reduced efficiency of the converter. Therefore, it is necessary that a certain balance control algorithm is provided in interleaved bi-directional converter system. In this paper, a balance control algorithm based on the circular chain control method is proposed. Further, in order to reduce the number of phase current sensors, this paper shows a simple method in which phase currents can be extracted indirectly through a DC-link current sensor in both charging and discharging modes. The validity and the effectiveness of the proposed phase currents balance control algorithm are illustrated through the simulation results.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.381-384
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• 2008

This paper presents an operational technique to maximize profit of a cogeneration power plant. To minimize errors in a loss and gain analysis of a cogeneration power plant, the energy sale profit in the cost-based-pool electric power trade market, the heat sale profit, and the supplementary fund profit for electric power industry are taken into consideration. The objective is to optimize the heat-electric power ratio to maximize profit of a cogeneration power plant. Furthermore, the constrained bidding technique to optimize heat-electric power ratiocan be obtained. Profits from of a cogeneration power plant are composed of three categories, such as the energy sale profit in the cost-based-pool electric power trade market, the heat sale profit, and the supplementary fund profit for electric power industry. Profits of a cogeneration power plant are varied enormously by the operation modes. The profits are mainly determined by the amount of constrained heat generation in each trading time. And the three profit categories arecoupled tightly via the heat-electric power ratio. The result of this case study can be used as a reference to a cogeneration power plant under the power trading system considered in this case.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.6
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• pp.769-777
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• 1999

This paper presents models for the dynamic simulation of a regenerative gas turbine and describes dynamic behaviors of a small regenerative engine. A quasi-steady model is introduced where the inertia of the working fluid is assumed to be negligible compared with the mechanical inertia of the rotating shaft. Based on this quasi-steady model, the transient model for the heat exchanger is employed to simulate the unsteady heat exchange in the recuperator. The effect of the thermal inertia of the recuperator metal on transient behaviors is analyzed by comparing the predicted results of the transient and steady state heat exchanger models. For several load change modes such as sudden increase, decrease and periodic variation, engine dynamic characteristics are investigated by applying a fuel control logic for the constant shaft speed. It is found that the thermal inertia of the recuperator metal has a dominant effect on the whole engine dynamic behavior.

• The Journal of the Acoustical Society of Korea
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• v.20 no.5
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• pp.54-60
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• 2001

This paper investigates the equivalent circuit analysis method for the multi-functional device in mobile telephones, which works both as a buzzer and a vibrator in a single unit form. With a representative multi-functional device, we construct the corresponding equivalent circuits for the buzzer mode and the vibrator mode of the device, respectively, and analyze the performance of each of the modes. For proper construction of the circuit, we analyze the structure and operation mechanism of the device, and develop a computer simulation tool to simulate the behavior of the device. Validity of the analysis method is verified through comparison of the analysis results with experimental measurement results, which shows good agreement between the two sets of data.