• 전력전자학회:학술대회논문집
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• 전력전자학회 2003년도 춘계전력전자학술대회 논문집(1)
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• pp.424-429
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• 2003

A reciprocating compressor with a rotary motor used in a refrigerator has low efficiency, because it has the large mechanical losses due to the crank mechanism. The linear compressor which has the free piston driven by a linear motor, was developed to increase the efficiency of compressor by reducing mechanical losses. The TRIAC has been widely used for controlling the piston, because it has simple structure. However, as it is able to control only stator voltage, it is very difficult to obtain good efficiency. Recently, PWM inverter which is able to control the voltage as well as the frequency, is applied to linear compressor drive system to overcome above problem. In this paper, the variations for efficiency and power factor of linear compressor are investigated by changing both the mechanical resonant frequency and electrical resonant frequency of linear compressor, and also the inverter frequency The optimum relationships between both resonant frequencies and the inverter frequency is derived in order to obtain the maximum efficiency and also good power factor.

• 한국소음진동공학회논문집
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• 제14권5호
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• pp.410-415
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• 2004

To ensure a safe operation of the prototype KGT-74 kW small gas turbine, vibrational reliabilities of the compressor 1st, 2nd, and 3rd stages and turbine blades have been estimated and reviewed. FE analyses have been carried out to obtain the natural vibration characteristics of the blades, and impact modal testings have been performed on every each one of the blades to measure their 1st natural frequencies. Then, the Campbell diagram analyses have been carried out to judge the safety of the blades from resonant failures up to 6k harmonics. Results show that the compressor 1st stage blade is exposed to a potential resonant failure with 3k harmonic around a rated speed of 30,000 rpm but that the other compressor 2nd and 3rd stages and turbine blades are safe from resonant failures. Finally, 27,900 rpm is selected as the safe operation limit for the KGT-74 ㎾ gas turbine relative to the blade vibrations.

• Journal of Advanced Marine Engineering and Technology
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• 제9권4호
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• pp.307-316
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• 1985

Nowadays, the natural frequencies and their relative amplitudes of torsional vibration for the marine diesel engine shafting are usually calculated by the Holzer method and also its resonant amplitudes are estimated by the energy method, that is, by equating the exciting energy to the damping one. Therefore, the forced vibration amplitudes out of the resonant points can not be calculated by the above-mentioned method. And so, the reasonable barred-ranges of torsional vibration can not be set and also the flank of resonant point which locates near the calculation limit can not be estimated. For such problems, the equation of forced vibration with damping must be solved directly and these results can be utilized to derive the synthesized torsional vibration of the marine diesel engine propulsion shafting. In this study, the equation of forced vibration with damping for the marine diesel engine propulsion shafting is derived and its steady-state vibration is calculated by the mechanical impedance method. For numerical calculation of the actual propulsion shafting a computer program is developed. In order to prove the reliability of this program, an actual ship's propulsion shafting whose torsional vibration was measured is analyzed and the calculated propulsion shafting whose torsional vibration was measured is analyzed and the calculated results are compared with the measured ones. And also, they are compared with the calculated results which were obtained by the modal analysis.

• 한국전자파학회논문지
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• 제23권4호
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• pp.507-514
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• 2012

본 논문에서는 함체 내부의 PCB에 있는 트레이스 파원에 의한 함체의 공진 특성 해석법을 제안하고 있다. 함체 내부의 전자계를 계산하기 위해 PCB 트레이스에 형성되는 전류 분포 및 PCB 유전체의 경계면에서 만족하는 경계면 전계 분포에 관한 연립 적분방정식을 유도하였으며, 연립 적분방정식의 해는 Galerkin의 모멘트 법으로 구하고 있다. 그 결과, 함체의 공진 특성은 실험 결과 및 HFSS 툴에 의한 시뮬레이션 결과와도 잘 일치하고 있으며, 함체의 공진 주파수는 PCB 트레이스의 위치에 의해 달라진다는 것을 확인하고 있다. 이론 해석의 타당성을 검증하기 위해 반사 계수의 이론치를 측정치와도 비교하고 있다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.297-302
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• 2003

To ensure a safe operation of the prototype KGT-74 ㎾ small gas turbine, vibrational reliabilities of the compressor 1st, 2nd. and 3rd stages and turbine blades have been estimated and reviewed. FE analyses have been tarried out to obtain the natural vibration characteristics of the blades, and impact modal testings have been performed on every each one of the blades to measure their 1st natural frequencies. Then, the Campbell diagram analyses have been carried out to Judge the safety of the blades from resonant failures up to 6k harmonics. Results show that the compressor 1st stage blade is exposed to a potential resonant failure with 3k harmonic around a rated speed of 30,000rpm but that the other compressor 2nd and 3rd stages and turbine blades are safe from resonant failures. Finally. 27,900 rpm Is selected as the safe operation limit for the KGT-74 ㎾ gas turbine relative to the blade vibrations.

• 전기전자학회논문지
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• 제5권1호
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• pp.91-99
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• 2001

공기 갭을 갖는 이방성 매질의 기판과 덮개층 구조에서 사각 마이크로스트립 안테나 공진 주파수의 파수 영역에 대해 해석하였다. 일축성 매질의 특성을 나타내는 텐서의 구성 관계식으로부터 파수영역에서의 다이애딕 그린 함수를 유도하였으며 이 결과를 푸리에 변환을 사용하여 공간에서의 전계 적분 방정식으로 수식화하였다. 캘러킨 모멘트법을 사용하여 적분 방정식을 이산화하였으며 기저함수로는 정현적 함수를 선택하였다. 수치해석 결과의 타당성을 검증하기 위해 기존의 결과와 비교, 일치된 결과를 얻었으며 공기 갭의 두께, 패치 길이 그리고 덮개층의 비유전율과 이방성 덮개층의 이방성 비의 변화에 따른 공진 주파수의 변화가 제시되고 분석되었다.

• Journal of Magnetics
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• 제16권3호
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• pp.246-252
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• 2011

A high-voltage power supply has been built for activation of the brain via stimulation using a Full Wave Cockroft-Walton Circuit (FWCW). A resonant half-bridge inverter was applied (with half plus/half minus DC voltage) through a bidirectional power transistor to a magnetic stimulation device with the capability of producing a variety of pulse forms. The energy obtained from the previous stage runs the transformer and FW-CW, and the current pulse coming from the pulse-forming circuit is transmitted to a stimulation coil device. In addition, the residual energy in each circuit will again generate stimulation pulses through the transformer. In particular, the bidirectional device modifies the control mode of the stimulation coil to which the current that exceeds the rated current is applied, consequently controlling the output voltage as a constant current mode. Since a serial resonant half-bridge has less switching loss and is able to reduce parasitic capacitance, a device, which can simultaneously change the charging voltage of the energy-storage condenser and the pulse repetition rate, could be implemented. Image processing of the brain activity was implemented using a graphical user interface (GUI) through a data mining technique (data mining) after measuring the vital signs separated from the frequencies of EEG and ECG spectra obtained from the pulse stimulation using a 90S8535 chip (AMTEL Corporation).

• Journal of Power Electronics
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• 제7권3호
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• pp.222-232
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• 2007

This paper presents the application of a single phase AC-to-DC converter using a three-phase series parallel (SPRC) resonant converter to variable speed dc-drive. The improved power quality converter gives the input power factor unity over a wide speed range, reduces the total harmonic distortion (THD) of ac input supply current, and makes very low ripples in the armature current and voltage waveform. This soft-switching converter not only possesses the advantages of achieving high switching frequencies with practically zero switching losses but also provides full ranges of voltage conversion and load variation. The proposed drive system is the most appropriate solution to preserve the present separately excited de motors in industry compared with the use of variable frequency ac drive technology. The simulation and experimental results are presented for variable load torque conditions. The variable frequency control scheme is implemented using a DSP- TMS320LF2402. This control reduces the switching losses and current ripples, eliminates the EMI and improves the efficiency of the drive system. Experimental results confirm the consistency of the proposed approach.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.1825-1831
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• 2011

One of the major trends in traction power electronics is increasing the switching frequencies. The advances in the frequency elevation have made it possible to reduce the total size and weight of the passive components such as capacitors, inductors and transformers in the DC/DC converter and hence to increase the power density. The traction dynamic performance is also improved. This document describes several aspects relating to the design of resonant DC/DC converter operating at high frequency(10KHz) and the converter topologies and the control method of MAGLEV, which result in soft switching, are discussed.

• 한국해양공학회지
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• 제29권1호
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• pp.1-8
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• 2015

An analytical model of liquid sloshing is developed to consider the energy-loss effect through a partially submerged porous baffle in a horizontally oscillating rectangular tank. The nonlinear boundary condition at the porous baffle is derived to accurately capture both the added inertia effects and the energy-loss effects from an equivalent non-linear drag law. Using the eigenfunction expansion method, the horizontal hydrodynamic force (added mass, damping coefficient) on both the wall and baffle induced by the fluid motion is assessed for various combinations of porosity, submergence depth, and the tank's motion amplitude. It is found that a negative value for the added mass and a sharp peak in the damping curve occur near the resonant frequencies. In particular, the hydrodynamic force and free surface amplitude can be largely reduced by installing the proper porous baffle in a tank. The optimal porosity of a porous baffle is near P=0.1.