• Journal of Power Electronics
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• 제16권5호
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• pp.1821-1832
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• 2016

This study presents a strategy using the synchronized output regulation method (SOR) for controlling inverters operating in stand-alone and grid-connected modes. From the view point of networked dynamic systems, SOR involves nodes with outputs that are synchronized but also display a desirable wave shape. Under the SOR strategy, the inverter and grid are treated as two nodes that comprise a simple network. These two nodes work independently under the stand-alone mode. An intermediate mode, here is named the synchronization mode, is emphasized because the transition from the stand-alone mode to the grid-connected mode can be dealt as a standard SOR problem. In the grid-connected mode, the inverter operates in an independent way, in which the voltage reference changes for generalized synchronization where its output current satisfies the required power injection. Such a relatively independent design leads to a seamless transfer between operation modes. The closed-loop system is analyzed in the state space on the basis of the output regulation theory, which improves the robustness of the design. Simulations and experiments are performed to verify the proposed control strategy.

• 한국유체기계학회 논문집
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• 제13권4호
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• pp.31-36
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• 2010

Free energy based lattice Boltzmann method (LBM) has been used to simulate the rising bubble flows with large density ratio. LBM with compact discretization is able to reduce the spurious current of the static bubble test and be satisfied with the Laplace law. The terminal rise velocity and shape of the bubbles are dependent on Eotvos number, Morton number and Reynolds number. For single bubble flows, simulations are executed for various Eotvos number, Morton number and Reynolds number, and the results are agreed well with the experiments. For multiple bubbles, the bubble flow characteristics are related by the vortex pattern of the leading bubble. The coalescence of the bubbles are simulated successfully and the subsequent results are presented. The present method is validated for static, dynamic bubble test cases and compared to the numerical, experimental results.

• Journal of Magnetics
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• 제7권4호
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• pp.160-164
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• 2002

A new discovery of the super-giant magneto-impedance (SGMI) effect was found out in a LC-resonator consisted of a glass-coated amorphous $CO_{83.2}B_{3.3}Si_{5.9}Mn_{7.6}$ microwire. The measurement was carried out at high frequency range from 100 MHz up to 1 GHz of an ac-current flowing along the wire and at varying axial dcmagnetic field in its range of $\pm$120 Oe. The wires, about 16${\mu}m$ in diameter, were fabricated by a glass-coated melt spinning technique. The shape of the impedance curves plotted vs. a dc-field is changing dramatically with the frequency. The phase angle was also strongly dependent on this field. The external dc-magnetic field changes the circumferential permeability as well as the penetration depth, both in turn change the impedance of the sample. The drastic increments of SGMI at high frequency can be understood in terms of the LC-resonance phenomena. The sudden change of the phase angle, as large as $180^{\circ}$ evidenced the occurrence of the resonance at a given intensity of the external dc-field. The maximum ratio of SGMI reached in the experiment by precise tuning frequency equals 450,000％ at the frequency of around 551.9075 MHz.

• Current Photovoltaic Research
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• 제1권2호
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• pp.109-114
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• 2013

$Cu_2ZnSnS_4$ (CZTS) nanoparticles were synthesized by a solvothermal method using copper (II) acetate, zinc acetate, tin chloride, and sulfur in diethylenetriamine solvent. Binary sulfide particles such as CuS, ZnS, SnS, and $SnS_2$ were obtained at $180^{\circ}C$; single-phase CZTS nanoparticles were obtained at $280^{\circ}C$. CZTS nanoparticles with spherical shape and grain size of 40 to 60 nm were obtained at $280^{\circ}C$. In the middle of 180 and $280^{\circ}C$, CZTS and ZnS phases were found. The time variation of reaction at $280^{\circ}C$ revealed that an amorphous state formed first instead of binary phases and then the amorphous phase was converted to crystalline CZTS state; it is different reaction path way from conventional solid-state reaction path of which binary phases react to form CZTS. CZTS films deposited and annealed from single-phase nanoparticles showed porous microstructure and poor adhesion. This indicates that a combination of CZTS and other flux phase is necessary to have a dense film for device fabrication.

• Journal of Power Electronics
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• 제17권4호
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• pp.972-982
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• 2017

The Park's vector of stator current is a popular technique for the detection of induction motor faults. While the detection of the faulty condition using the Park's vector technique is easy, the classification of different types of faults is intricate. This problem is overcome by the Multiple Park's Vector (MPV) approach proposed in this paper. In this technique, the characteristic fault frequency component (CFFC) of stator winding faults, rotor winding faults, unbalanced voltage and bearing faults are extracted from three phase stator currents. Due to constructional asymmetry, under the healthy condition these characteristic fault frequency components are unbalanced. In order to balanced them, a correction factor is added to the characteristic fault frequency components of three phase stator currents. Therefore, the Park's vector pattern under the healthy condition is circular in shape. This pattern is considered as a reference pattern under the healthy condition. According to the fault condition, the amplitude and phase of characteristic faults frequency components changes. Thus, the pattern of the Park's vector changes. By monitoring the variation in multiple Park's vector patterns, the type of fault and its severity level is identified. In the proposed technique, the diagnosis of faults is immune to the effects of unbalanced voltage and multiple faults. This technique is verified on a 7.5 hp three phase wound rotor induction motor (WRIM). The experimental analysis is verified by simulation results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 C
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• pp.1593-1598
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• 1994

Recently rotary-arc, thermal expansion and their composite interrupters are widely used in the distribution power system because they have lots of advantages in making the larger interrupting capacity, the smaller size, the lighter weight and the less surge. A model interrupter of rotary-arc type, which has constant stroke and thermal expansion volume, was studied by varying the design parameters, i.e. the number of turns of the driving coil, the inner diameter of the moving contact, the gas pressure and the shape of the fixed contact for this project. Short cicuit current interrupting tests were conducted to the model interrupters by varying the requirements from 42% to 175% of the test voltage, interrupting current and transient recovery voltage for the test duty No.4 of 7.2kV 12.5kA single phase test. The pressure rise, minimum and maximum arcing times were analyzed for each model interrupter. All types of model interrupters showed good interrupting performances and sufficient design margins for the ratings.

• 대한기계학회논문집B
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• 제20권3호
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• pp.1050-1060
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• 1996

Recently, attention has been paid to the flame diagnostic by noncontact methods which dose not deform the flame shape. One of them is a method which is using the radical luminous intensity. Generally, this diagnostic method using radical luminous has been investigated its reliability by applying to laminar flame. This study, however, investigated each radical luminous signals through stocastical analysis like auto-correlation, cross-correlation, phase and coherence which were acquired from measuring radical luminous intensity of OH, CH, $O_{2}$, radicals in turbulent diffusion flame. To compare radical luminous intensity in flame with temperature, ion current and concentration , radious distribution of each properties was investigated and considered. In radical luminous intensity, correlation in the reaction zone of flame was higher than in correlation in combusted gas zone. And radious distribution of radical luminous intensity was corresponded with radious distribution of temperature, ion current and concentration. The result of the study confirms that a radical luminous flame diagnosis is possible in the turbulent diffusion flame.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.83-85
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• 1996

Major cause of defects in steam generator tubes at nuclear power plant is the accumulation of magnetite and other byproducts of corrosion in the crevice gap between support plates and tubes. Since damaged tubes result in contamination of the secondary coolant by the radioactive primary coolant, they represent a safety hazard. Early detection of magnetite buildup is, therefore, imperative in order to take remedial measures such as chemical flushing. Although the eddy current testing is being used for the inspection of steam generator tubes, the interpretation of resulting signals is generally a difficult task. This paper uses the phase of sensor coil emf as the test signal to find a way of easier signal interpretation. Numerical study using FEM shows that the shape of resulting signal is good for identifying the relative position of the probe to the support plate, and for discreminating the different shapes and degrees of magnetite buildup in the crevice gap region.

• 전기전자학회논문지
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• 제15권2호
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• pp.129-133
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• 2011

A spread spectrum clock generation is an efficient way to reduce electro-magnetic interference (EMI) radiation in modern mixed signal chip systems. The proposed circuit generates the spread spectrum clock by directly injecting the modulation voltage into the voltage-controlled oscillator (VCO) current source for SATA II. The resulting 33KHz modulation profile has a Hersey-Kiss shape with a rounded peak. The chip has been fabricated using $0.18{\mu}m$ CMOS process and test results show that the proposed circuit achieves 0.509% (5090ppm) down spreading at 1.5GHz and peak power reduction of 10dB. The active chip area is 0.36mm ${\times}$ 0.49mm and the chip consumes 30mW power at 1.5GHz.

• 한국항공운항학회지
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• 제23권4호
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• pp.36-41
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• 2015

The cyclone separator is a simple device, which causes the centrifugal separation of materials such as droplets or particles in a fluid stream. The cyclone separator utilizes the energy obtained from fluid pressure and linear motion to create rotational fluid motion. This rotational motion leads the materials suspended in the fluid to separate from the fluid quickly due to the centrifugal force. The rotation is produced by the tangential or involuted introduction of fluid into the vessel. These materials may be droplets of fuel in blow-by gas through an engine. Droplets suspended in the feed liquid may separate according to size, shape, or density. And the change of part dimension in a cyclone separator can yield the its performance variation. The current study shows the influence of design parameters on the performance of a cyclone separator for blow-by gas.