• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.5
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• pp.420-429
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• 2004

This paper proposes a novel current control strategy on active power filters using PQR instantaneous power theory which can compensate the line current harmonics and the neutral line current under the unbalanced and/or distorted source conditions in three-phase four-wire systems. The characteristics of the inverter ac filters are analyzed and a novel digital controller are proposed to overcome the inherent time delay problem in digital controllers with designed control gain in this paper. The proposed current control method is based on a sinusoidal PWM for fully-digital implementation compared with a conventional hysteresis PWM. PSiM simulation results verify the good performance of the proposed current control strategy on shunt type APFs.

• Korean Journal of Materials Research
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• v.11 no.2
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• pp.151-154
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• 2001

The leakage current behaviors of PLZT capacitors with top electrodes of Pt, Ir, and $IrO_2$ are investigated before and after hydrogen forming gas anneal. The P-E hysteresis and fatigue properties of Pt/PLZT/Pt capacitors are almost recovered after recovery anneal in $O_2$ ambient. The leakage current mechanisms of PLZT capacitors with Pt and $IrO_2$ top electrodes are consistent with space-charge influenced injection model showing the strong time dependence irrespective of annealing conditions. On the other hand, the leakage current behavior of Ir/PLZT/Pt capacitor shows steady state independent of time because IrPb, conducting phase, formed at interface between Ir top and PLZT is a high conduction path. Teh leakage current mechanism of Ir/PLZT/Pt capacitor is consistent with Schottky barrier model.

• Journal of Korea Multimedia Society
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• v.9 no.5
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• pp.585-594
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• 2006

Due to the size limit, the voice coil motor (VCM) is adopted in most of the mobile phone camera to control auto-focus instead of step motor. The optical system using the VCM has the property that the focus values are varying even though the same current is induced. It means that an error of the lens position was taken placed due to the characteristics of the VCM. In this paper, a algorithm was proposed to compensate the lens position error using the step size and the search count of each stage. In the proposed algorithm -7 step middle searching stage is inserted the conventional searching algorithm for the fast auto-focus searching and the final searing step size was set to +1 for the precise focus control, respectively. In the experimental results, the focus values was found more fast in the proposed algorithm than the conventional. And more the image quality by the proposed algorithm was superior to that of the conventional.

• Journal of Drive and Control
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• v.12 no.3
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• pp.52-59
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• 2015

An electro hydraulic poppet valve (EHPV) and a variable orifice poppet are assembled in a single block, which is referred to as a RHINO but is also generally called a pilot-operated flow control valve. In this study, we analyzed the structure and the operating principle for a RHINO applied in a 21-ton electric excavator system. The RHINO was experimentally tested to measure the dynamic responses and the pressure energy loss. In this test, we investigated the variation in the conductance coefficient according to the increase in the supply pressure under a constant current and a variation in the flow rate according to the increase in the current. Then, the geometrical shapes and the spring stiffness of the RHINO were considered to develop an analysis model. The characteristics (current-force and hysteresis) for the solenoid based on the experimental data were reflected in the analysis model that was developed, and the reliability of the analysis model was also verified by comparing the experimental and analytical results. The developed model is thus considered to be reliable for use in a wide range of applications, including optimum design, sensitivity analysis, parameter tuning, etc.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.3
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• pp.570-576
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• 2007

In this study, the characteristics of metal-ferroelectric-semiconductor FET (MFSFET) device is investigated using field-dependent polarization and square-law FET models. From drain current with the gate voltage variation, when coercive voltages of ferroelectric thin film are 0.5 and 1V, the memory windows are 1 and 2V, respectively. When the gate voltages are 0, 0.1, 0.2 and 0.3V, the difference of saturation drain currents of the MFSFET device at two threshold voltages in ID-VD curve are 1.5, 2.7, 4.0, and 5.7mA, respectively. As a result of the analysis for drain currents after tine lapse, which is based on the simulation for hysteresis loop and the fitting of retention properties of ferroelectric thin films such as PLZT(10/30/70), PLT(10) and PZT(30/70) thin film shows excellent reliability that the decrease of saturation current is about 18% after 10 years.

• Korean Journal of Materials Research
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• v.29 no.2
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• pp.73-78
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• 2019

Lead free $(Ba_{0.7}Ca_{0.3})TiO_3$ thick films with nano-sized grains are prepared using an aerosol deposition (AD) method at room temperature. The crystallinity of the AD thick films is enhanced by a post annealing process. Contrary to the sharp phase transition of bulk ceramics that has been reported, AD films show broad phase transition behaviors due to the nano-sized grains. The polarization-electric hysteresis loop of annealed AD film shows ferroelectric behaviors. With an increase in annealing temperature, the saturation polarization increases because of an increase in crystallinity. However, the remnant polarization and cohesive field are not affected by the annealing temperature. BCT AD thick films annealed at $700^{\circ}C/2h$ have an energy density of $1.84J/cm^3$ and a charge-discharge efficiency of 69.9 %, which is much higher than those of bulk ceramic with the same composition. The higher energy storage properties are likely due to the increase in the breakdown field from a large number of grain boundaries of nano-sized grains.

• Korean Journal of Metals and Materials
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• v.50 no.8
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• pp.613-618
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• 2012

We report on electrical and mechanical properties of silicon nitride ($SiN_x$) films deposited by a plasma enhanced chemical vapor deposition (PECVD) method at $200^{\circ}C$ from $SiH_4$ highly diluted in $N_2$. The films were also prepared from $SiH_4$ diluted in He for comparison. The $N_2$ dilution was also effective in improving adhesion of the $SiN_x$ films, fascilitating construction of thin film transistors (TFTs). Metal-insulator-semiconductor (MIS) and Metal-insulator-Metal (MIM) structures were used for capacitance-voltage (C-V) and current-voltage (I-V) measurements, respectively. The resistivity and breakdown field strength of the $SiN_x$ films from $N_2$-diluted $SiH_4$ were estimated to be $1{\times}10^{13}{\Omega}{\cdot}cm$, 7.4 MV/cm, respectively. The MIS device showed a hysteresis window and a flat band voltage shift of 3 V and 0.5 V, respectively. The TFTs fabricated by using these films showed a field-effect mobility of $0.16cm^2/Vs$, a threshold voltage of 3 V, a subthreshold slope of 1.2 V/dec, and an on/off ratio of > $10^6$.

• Journal of Drive and Control
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• v.18 no.4
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• pp.19-27
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• 2021

A bunker bed is a type of furniture that efficiently utilizes a narrow indoor space by having a high bed and using the empty space below as a living and storage space. The demand for multi-purpose furniture is increasing due to the recent increase in single-person households and wide-spread shared accommodation. According to the consumer research, one of the major drawbacks of a bunker bed was to get on and off the bed through a ladder or stairs. In order to overcome these problems, it was confirmed that the height adjustment function that can easily adjust the minimum and maximum heights of the bed was necessary. In this study, a height adjustable bunker bed was designed by using a gas spring that generates a repulsive force by the compressed gas inside. The design process consisted of the following three steps: Firstly, the hysteresis characteristics due to a friction and spring constant of a commercial gas spring were confirmed by measuring the repulsive force vs. compressed displacement. Secondly, requirements of the vertical lifting force exerted on the bed against gravity force were derived. Finally, the height-adjustable bed using the four-bar link mechanism was designed with 4 parameters so that the bed weight of 60-70 kgf could be adjusted to 800 mm in height by an affordable initial operation force. The performance was verified through prototype production and the results of vertical displacement and force to move were nearly the same as designed. In addition, an electrically operated height-adjustable bed was also designed with linear actuators and the performance was proved with the prototype.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.339-339
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• 2002

In the RABiTS approach to coated conductor development, successful (both economic and technological) depends on the refinement and optimization of each of three important components: the metal tape substrate, the buffer layer(s), and the HTS layer. Here we will report on the ORNL approach and progress in each of these areas. - Most applications will require metal tapes with low magnetic hysteresis, mechanical strength, and excellent crystalline texture. Some of these requirements are competing. We report on progress in obtaining a good combination of these characteristics on metal alloys of Ni-Cr and Ni-W. - The deposition of appropriate buffer layers is a crucial step. Recently, base research has shown that the presence of a stable sulfur superstructure present on the metal surface is needed for the nucleation and epitaxial growth of vapor-deposited seed buffer layers such as YSZ, CeO$_2$ and SrTiO$_3$. We report on the details and control of this superstructure for nickel tapes, as well as recent results for Cu and Ni-13%Cr. - Processes for deposition of the HTS coating must economically provide large values of the figure-of-merit for conductors, current x length. At ORNL, we have devoted efforts to a precursor/post-annealing approach to YBCO coatings, for which the deposition and reaction steps are separate. We describe motivation for and progress toward developing this approach. - Finally, we address some issues for the implementation of coated conductors in real applications, including the need for texture control and electrical stabilization of the HTS coating.

• Elastomers and Composites
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• v.58 no.1
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• pp.32-43
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• 2023

The worldwide use of polyurethane foam products generates large amounts of waste, which in turn has detrimental effects on the surroundings. Hence, finding an economical and environmentally friendly way to dispose of or recycle foam waste is an utmost priority for researchers to overcome this problem. In that sense, the glycolysis of waste flexible polyurethane foam (WFPF) from automotive seat cushions using different industrial-grade glycols and potassium hydroxide as a catalyst to produce recovered polyol was investigated. The effect of different molecular weight polyols, catalyst concentration, and material ratio (PU foam: Glycols) on the reaction conversion and viscosity of the recovered polyols was determined. The obtained recovered polyols are obtained as single or split-phase reaction products. Besides, the foaming characteristics and physical properties such as cell morphology, thermal stability, and compressive stress-strain nature of the regenerated flexible foams based on the recovered polyols were discussed. It was observed that the regenerated flexible foams displayed good seating comfort properties as a function of hardness, sag factor, and hysteresis loss compared to the reference virgin foam. With the growing demand for a sustainable and circular economy, a global valorization of glycolysis products from polyurethane scraps can be realized by transforming them into profitable substances.