• Journal of Power Electronics
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• v.19 no.3
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• pp.702-713
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• 2019

Multilevel Inverters (MLIs) are widely used in medium voltage applications due to their various advantages. In addition, there are numerous types of MLIs for such applications. However, the diode-less 3-level (3L) T-type Neutral Point Clamped (NPC) MLI is the most advantageous due to its low conduction losses and high potential efficiency. The power circuit of a 3L T-type NPC is derived by the conventional two level inverter by a slight modification. In order to explore the MLI performance for various Pulse Width Modulation (PWM) schemes, this paper examines the operation of a 3L (five level line to line) T-type NPC MLI for various types of Multi-Carriers Pulse Width Modulation (MCPWM) schemes. These PWM schemes are compared in terms of their voltage profile, total harmonic distortion (THD) and conduction losses. In addition, a 3L T-type NPC MLI is also compared with the conventional NPC in terms of number of switches, clamping diodes, main diodes and capacitors. Moreover, the capacitor-balancing problem is also investigated using the Neutral Point Fluctuation (NPF) method with all of the MCPWM schemes. A 1kW 3L T-type NPC MLI is simulated in MATLAB/Simulink and implemented experimentally and its performance is tested with a 1HP induction motor. The results indicate that the 3L T-type NPC MLI has better performance than conventional NPC MLIs.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.47-50
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• 1991

LPM(Linear Pulse Motor) provide direct and precise position control of bidirectional linear motion. LPM is not subject to the same linear velocity and acceleration limitations inherent in systems converting rotary to linear motion such as lead screws, rack and pinion, belt and pulley drives. With LPM, all the thrust force generated by the motor is efficiently applied directly to the load. And speed, distance, and acceleration are easily programmed in a highly repeatable fashion. Potential industrial and application fields of LPM include PCB assembly, industrial sewing machines, automatic inspection, coil winder, medical uses, conveyer system, laser cut and trim systems, semiconductor wafer processing, OA instruments etc. This paper describes various design parameter of LPM such as magnetic ciucuit construction methods, phase number and tooth number per pole, permanent magnet and coil mmf, tooth geometries. And to solve the problems of existing control methods, in this paper, a new control method of the LPM is proposed throughout modern control theory.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.205-206
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• 2002

In this paper we examined the contribution of mechanical and electrochemical factors in corrosive wear for Zr-alloy against $Al_2O_3$ ball in $Na_2SO_4$ solution. Normal load and the area of metallic specimen was varied to change the corrosion behavior. At the commence of sliding, the potential drop took place, which increased with load due to the great exposure of fresh surface. Wear volume was linearly proportional to load. The corrosion factor was about 15%. By increasing the Aa/Ac ratio, corrosion factor to total wear decreases and saturates above Aa/Ac=0.15.

• Journal of the Semiconductor & Display Technology
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• v.14 no.4
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• pp.72-77
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• 2015

Three-level diode clamped multilevel inverter, generally known as neutral point clamped (NPC) inverter, has an inherent problem causing neutral point (NP) potential variation. Until now, the NP potential problem of variation has been investigated and lots of solutions have also been proposed. This paper presents a neutral point voltage control technology using the anti-windup PI controller and offset technology of PWM (Pulse Width Modulation) to control the variation of NPC 3-phase three-level inverter neutral point voltage. And the proposed algorithm is tested and verified using a PLL (Phase Locked Loop) in order to synchronize the phase voltage from the line voltage of grid. It significantly improves the voltage balancing under a solar fluctuation conditions of the inverter. Experimental results show the good performance and effectiveness of the proposed method.

• Journal of the Korean Chemical Society
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• v.48 no.2
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• pp.137-143
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• 2004

The determination of 2-mercapto-1-methyl-imidazole (MMI) in 5.0${\times}10^{-2}$ M lithium perchlorate suporting electrolyte has been investigated by the differential pulse polarography. The optimum condition of MMI analysis was as follows; -0.9 volts initial potential, 0.08 mV pulse height, 2 mV/sec scan rate, and medium mercury drop size. Standard calibration curve showed a good linearlity in the range of 1.0${\times}10^{-7}M\;to\;8.0{\times}10^{-5}$ M and the detection limit has been (2.2${\pm}0.1){\times}0.1^{-9}$ M. This method was applicated for the determination of MMI in antithyroid drug without interference of additives.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.204-204
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• 1999

The plasma source ion implantation(PSII) technique which is a method using high negative voltage pulse in plasma system has the potential to change the surface properties of polymer. PSII technique increase the surface free energy by introducing polar functional groups on the surface so that it improves reactivity, hydrophilicity, adhension, biocompatability, etc. However, the mobility of polymer chains enables the modified surface layers to adapt their composition to interfacial force. This hydrophobic recovery interrupts the stability of modified surfaces to keep for the long time. In this study, poly(methyl methacrylate)(PMMA), poly(2-hydroxyethyl methacrylate)(PHEMA), and polu(2-hydroxypropyl methacylate)(PHPMA) for contact lens application, were modified to improve the wettability with PSII technique and were investigated the surface stabilities. Polymer film was prepared with solution casting(3 wt.% solution) and was annealed at 11$0^{\circ}C$ under vacuum oven to remove solvent completely and to eliminate physical ageing. The thickness of the film measured by scanning electron microscopy (SEM) and surface profilometer was about 10${\mu}{\textrm}{m}$. Polymers were treated with different kinds of gases, pulse frequency, pulse with, pulse voltage, and treatment time. Even though PMMA, PHEMA, and PHPMA have similar repeat unit structure, the optimal treatment conditions and the tendency to hydrophobic recovery were different. PHPMA, more hydrophilic polymer than PMMA and PHEMA showd better wettability and stability after mild treatment. Surface tensions were obtained by water and diiodomethane contact angle measurements to monitor the relation between hydrophobic recovery and polymer structure. Different ion species in plasma change the polar component and dispersion component of polymer surface. For better wettability surface, the increase of polar component was a dominant factor. We also characterized modified polymer surfaces using x-ray photoelectron spectroscopy(XPS), secondary ion mass spectrometry(SIMS), Fourier Transform infrared spectroscopy(FT-IR), and SEM.

• Bulletin of the Korean Chemical Society
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• v.14 no.5
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• pp.567-574
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• 1993

Mordant Red 19(MR19) is reduced at mercury electrode at -0.67 V vs. Ag/AgCl with two electrons per molecule in pH 9.2 buffer by differential pulse polarography and linear sweep voltammetry. The peak potential is dependent on the pH of solution. The exhaustive electrolysis, however, gives 4 electrons per molecule because of the disproportionation of the unstable hydrazo intermediate. The electrochemical reduction of lanthanide-MR19 complexes is observed at more cathodic potential than that of free ligand. The difference in peak potentials between complex and free ligand varies from 75 mV for $La^{3+}$ to 165 mV for $Tb^{3+}$ and increases with increasing the atomic number of lanthanide. The electrochemical reduction of lanthanide complexes with MR19 is due to the reduction of ligand itself, and it can be potentially useful as an indirect method for the determination of lanthanides. The shape of i-E curves and the scan rate dependence indicates the presence of adsorption and the adsorption was confirmed by potential double-step chronocoulometry and the effect of standing time. Also the surface excess of the adsorbed species and diffusion coefficients are determined. The composition of the complex is determined to be 1 : 2 by spectrophotometric and electrochemical methods.

• Earthquakes and Structures
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• v.7 no.6
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• pp.1223-1240
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• 2014

Seismic isolation has been established as an effective earthquake-resistant design method and the lead rubber bearings (LRBs) are among the most commonly used seismic isolation systems. In the scientific literature, a sharp bilinear model is often used for capturing the hysteretic behaviour of the LRBs in the analysis of seismically isolated structures, although the actual behaviour of the LRBs can be more accurately represented utilizing smoothed plasticity, as captured by the Bouc-Wen model. Discrepancies between these two models are quantified in terms of the computed peak relative displacements at the isolation level, as well as the peak inter-storey deflections and the absolute top-floor accelerations, for the case of base-isolated buildings modelled as multi degree-of-freedom systems. Numerical simulations under pulse-like ground motions have been performed to assess the effect of non-linear parameters of the seismic isolation system and characteristics of both the superstructure and the earthquake excitation, on the accuracy of the computed peak structural responses. Through parametric analyses, this paper assesses potential inaccuracies of the computed peak seismic response when the sharp bilinear model is employed for modelling the LRBs instead of the more accurate and smoother Bouc-Wen model.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.32 no.5
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• pp.164-169
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• 1983

A method to control the luminous colour of a gaseous discharge tube has been investigated by using the saw-tooth wave of which rise-time was controlled by an electronic circuit. The luminous colour of a Ne - Hg lamp was changed from red to blue continuously and vice versa, and it's luminous characteristics are as follows: (a) With D.C. potentials, it showed blue colour and the relative intensity of the colour is increased first and saturated at about 17 mA as the discharge current is increased. (b) When the rise-time of the saw-tooth wave is about 10 $\mu\textrm{s}$, the red colour which is caused by Ne - excitation is dominant, and when about 200 $\mu\textrm{s}$, only the blue colour which is caused by Hg - excitation is shown. (c) With saw-tooth pulse, the relative intensity of blue is increased similarly as that with D.C. potential as the current peak of each pulse is increased, while that of red is increasing continuously and it's intensity shows about twice than blue. (d) The spectrum of red colour contains Ne - excitation lines and Hg - blue lines, but the apparent luminous colour is red because Ne - red lines are more plenty than Hg-blue lines. The spectrum of blue colour presents only Hg-blre lines.

• Progress in Superconductivity and Cryogenics
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• v.24 no.2
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• pp.1-6
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• 2022

This paper reviews the literature that has been published since 1980s related to cryogenic refrigeration systems for quantum computing. The reason why such a temperature level of 10-20 mK is necessary for quantum computing is that the superconducting qubit is sensitive to even very small thermal disturbances. The entanglement of the qubits may not be sustained due to thermal fluctuations and mechanical vibrations beyond their thresholds. This phenomenon is referred to as decoherence, and it causes an computation error in operation. For the stable operation of the quantum computer, a low-vibration cryogenic refrigeration system is imperative as an enabling technology. Conventional dilution refrigerators (DR), so called 'wet' DR, are precooled by liquid helium, but a more convenient and economical precooling method can be achieved by using a mechanical refrigerator instead of liquid cryogen. These 'dry' DRs typically equip pulse-tube refrigerators (PTR) for precooling the DRs around 4 K because of its particular advantage of low vibration characteristic. In this review paper, we have focused on the development status of 4 K PTRs and further potential development issues will be also discussed. A quiet 4 K refrigerator not only serves as an indispensable precooler of DR but also immediately enhances the characteristics of low noise amplifiers (LNA) or other cryo-electronics of various type quantum computers.