• Current Optics and Photonics
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• v.2 no.4
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• pp.332-339
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• 2018

A new multi-frequency fringe projection method is proposed to reduce the nonlinear phase error in 3-D shape measurements using an adaptive compensation method. The phase error of the traditional fringe projection technique originates from various sources such as lens distortion, the nonlinear imaging system and a nonsinusoidal fringe pattern that can be very difficult to model. Inherent possibility of phase error appearing hinders one from accurate 3-D reconstruction. In this work, an adaptive compensation algorithm is introduced to reduce adaptively the phase error resulting from the fringe projection profilometry. Three different frequencies are used for generating the gratings of projector and conveyed to the four-step phase-shifting procedure to measure the objects of very discontinuous surfaces. The 3-D shape results show that this proposed technique succeeds in reconstructing the 3-D shape of any type of objects.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.46.1-46.1
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• 2016

The formation process of a current sheet is important for solar flare from a viewpoint of a space weather prediction. We therefore derive the temporal development of the spatial and statistical distribution of electric current density distributed in a flare-producing active region to describe the formation of a current sheet. We derive time sequence distribution of electric current density by applying a nonlinear force-free approximation reconstruction to Active Region 12158 that produces an X1.6-class flare. The time sequence maps of photospheric vector magnetic field used for reconstruction are captured by a Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamic Observatory (SDO) on 10th September, 2014. The spatial distribution of electric current density in NLFFF model well reproduce observed sigmoidal structure at the preflare phase, although a layer of high current density shrinks at the postflare phase. A double power-law profile of electric current density is found in statistical analysis. This may be expected to use an indicator of the occurrence of a solar flare.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.8
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• pp.1186-1192
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• 2015

This paper proposes an economical method that the phase currents can be measured and reconstructed by means of the leg-shunt resistors in the 3-leg 2-phase vector-controlled inverter for 2-phase induction motor. In general, the phase currents of 2-phase induction motor have been measured using two Hall current sensors. However, because Hall current sensors are expensive, economically disadvantageous to apply in low power applications. The proposed method is verified by computer simulations and experiments to show the good performance of the vector control.

• Journal of Power Electronics
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• v.16 no.2
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• pp.621-630
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• 2016

In this paper, a single current sensor technique (SCST) is proposed for single-phase full-bridge inverters. The proposed SCST measures the currents of multiple branches at the same time, and reconstructs the average inductor, capacitor, and load current in a single switching cycle. Since all of the branches' current in the LC filter and the load are obtained using the SCST, both the inductor and the capacitor current feedback schemes can be selectively applied while taking advantages of each other. This paper also analyzes both of the current feedback schemes from the view point of the closed-loop output impedance. The proposed SCST and the analysis in this paper are verified through experiments on a 3kVA single-phase uninterruptible power supply (UPS).

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.8
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• pp.440-447
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• 1999

This paper proposes a control method for three-phase PWM rectifier with only single current sensor in DC link side. A PWM modulation strategy for reconstructing three phase currents from the DC link current is given. The states of the retifier switch are modified so that all phase currents can be reconstructed in a switching period although one or two of active vectors is applied only for a short time. Therefore, a new current control using an adjustment scheme of the modulation signal for three-phase PWM rectifier will be discussed, and verified the experimental results.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.4
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• pp.343-350
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• 2016

Generally, the average phase current is sampled at the midpoint of a PWM signal for the vector control of an AC motor. The three-phase current can also be reconstructed from a DC-link shunt resistor by sampling the shunt voltage during the active vectors of the SVPWM. However, the reconstructed current is different from the average current because of the deviation of the sampling point from the midpoint of the PWM signal. This paper proposes an algorithm to estimate the average current from the reconstructed current in a single-shunt inverter. The proposed method is derived from the phase current slopes based on switching states and corresponding switching time. In addition, the proposed method is generalized for all the six sectors of the space vector hexagon. The validity of the proposed algorithm is verified with simulations and experiments.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.55 no.2
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• pp.110-114
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• 2006

This paper describes the accident analysis by modelling the current transformer mounting in a metal-clad switchgear at 22.9kV. In analyzing the accident, the reconstruction at the current transformer mounting(VCB connecting guide) has to be taken into account. The accident was modelled as a 3-phase ground fault occurring between the end plate of 22.9kV lines and the safety shutter at the current transformer mounting of the VCB inside the metal clad switchgear. Since the outside maintenance of the metal clad switchgear is restricted by the enclosed compartments, Its circumference has to be kept clean. Through the reconstruction results, it was confirmed that the fault of the enclosed switchboard could be reduced when the shutter made of Fe material was chanted into an insulation.

• Current Optics and Photonics
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• v.6 no.6
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• pp.598-607
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• 2022

In this paper, a simple nondestructive technology is used to investigate unstained biological blood cells in three dimensions (3D). The technology employs a reflective phase-only spatial light modulator (SLM) for displaying the phase hologram of the object being tested, and a Fourier lens for its reconstruction. The phase hologram is generated via superposing a digital random phase on the 2D image of the object. The phase hologram is then displayed by the SLM with 256 grayscale levels, and reconstructed by a Fourier lens to present the object in 3D. Since noise is the main problem in this method, the windowed Fourier filtering (WFF) method is applied to suppress the noise of the reconstructed object. The quality of the reconstructed object is refined and the noise level suppressed by approximately 40%. The technique is applied to objects: the National Institute of Standards (NIS) logo, and a film of unstained peripheral blood. Experimental results show that the proposed technique can be used for rapid investigation of unstained biological blood cells in 3D for disease diagnosis. Moreover, it can be used for viewing unstained white blood cells, which is still challenging with an optical microscope, even at large magnification.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.193-200
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• 2009

Recently, there have been efforts to construct hybrids among the existing methodologies for multiphase flow such as VOF, Level Set, and Front Tracking with the intention of facilitating simulations of general three-dimensional problems. As one of the hybrid method, we have developed the Level Contour Reconstruction Method (LCRM) for general three-dimensional multiphase flows including phase change. The main idea was focused on simplicity and a robust algorithm especially for the three-dimensional case. It combines characteristics of both Front Tracking and Level Set methods. While retaining an explicitly tracked interface using interfacial elements, the calculation of a vector distance function plays a crucial role in the periodic reconstruction of the interface elements in the LCRM method to maintain excellent mass conservation and interface fidelity. In addition, compact curvature formulation is incorporated for the calculation of the surface tension force thereby reducing parasitic currents to a negligible level.

• Current Optics and Photonics
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• v.7 no.6
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• pp.692-700
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• 2023

We present a method for improving the accuracy of the modal wavefront reconstruction in the radial shearing interferometers (RSIs). Our approach involves expanding the reduced radial terms of Zernike polynomials to high-order, which enables more precise reconstruction of the wavefront aberrations with high-spatial frequency. We expanded the reduced polynomials up to infinite order with symbolic variables of the radius, shearing amount, and transformation matrix elements. For the simulation of the modal wavefront reconstruction, we generated a target wavefront subsequently, magnified and measured wavefronts were generated. To validate the effectiveness of the high-order Zernike polynomials, we applied both low- and high-order polynomials to the wavefront reconstruction process. Consequently, the peak-to-valley (PV) and RMS errors notably decreased with values of 0.011λ and 0.001λ, respectively, as the order of the radial Zernike polynomial increased.