• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.352-353
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• 2011

This paper proposes a cascaded boost type inverter system to compensate the voltage sag. If the voltage sag has appeared in input voltage, a cascaded boost converter would be operated to compensate voltage sag. The output voltage is kept constant by a direct-quadrature frame controller in the single-phase PWM inverter. The validity of proposed system is verified by simulation on the 300W cascaded boost type inverter system.

• Journal of Korean Society for Quality Management
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• v.32 no.4
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• pp.208-219
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• 2004

This paper considers a nonparametric estimation of lifetime distribution for ramp stress tests with stress bound under intermittent inspection. The test items are inspected only at specified time points an⊂1 so the collected observations are grouped data. Under the cumulative exposure model, two nonparametric estimation methods of estimating the lifetime distribution at use condition stress are proposed for the situation which the time transformation function relating stress to lifetime is a type of the inverse power law. Each of items is initially put on test under ramp stress and then survivors are put on test under constant stress, where all failures in the Inspection interval are assumed to occur at the midi)oint or the endpoint of that interval. Two proposed estimators of quantile from grouped data consisting of the number of items failed in each inspection interval are numerically compared with the maximum likelihood estimator(MLE) based on Weibull distribution.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.5
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• pp.403-408
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• 2012

In this paper, we propose useful load flow algorithms called FEDL (fast enhanced decoupled load flow). The proposed load flow method can improve the convergence characteristics particularly when the P-Q coupling becomes significant and the power system operating states deviate from the conditions required for stable convergence of the FDL by reflecting in part the effects of the off-diagonal terms in the Jacobian. In our test with IEEE AEP-30 bus system and RTS-96 73-bus system, it converge even when the fast decoupled load flow (FDL) and its variations keeping load flow matrices constant experience convergence problems. Test results show promising performances of the proposed algorithms in their convergence characteristics both in number of iterations and overall convergence speeds.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.699-702
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• 1992

A miniature size electrostatic induction motor have been constructed and studied by applying a three phase ac power source with a maximum voltage of 5 KV and a variable frequency ranged 0.0 - 150 Hz. A maximum no load speed of the motor tested was about 7600 RPM at the applied voltage of 4330 volt and the frequency of 130 Hz for the case of the rotor surface material of polyprophylene sheet screen-printed $TiO_2$ powder on it. It is found that there are 3 different regions of the motor operation, a rotor stop region, a stable operation region and a high speed abnormal region. And it is also found that the motor speed is influenced greatly by the charge relaxation time constant of the rotor surface materials, which however was changed by the means of vapour-deposited Ti or Ni and screen-printed $TiO_2$ powder on the surface of the rotor material, polyprophylene.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.710-713
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• 1992

An AVR for OLTC controls motor tap in transformer in order to supply constant power source. Recently for society which is higher informative and more automatic, in our research, the digital AVR for OLTC is developed that can perform more functions and higher functions ( mesurement, display, protection, control ) using microprocessor in a different control method than the conventional AVR. The experiment result is also present.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1084_1085
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• 2009

This paper proposes a novel maximum power point tracking(MPPT) control algorithm considering insolation to improve efficiency of PV system. The propoed algorithm is composed perturb and observe(PO) method and constant voltage(CV) method. PO method is simple to realize and CV method is possible to tracking MPP with low insolation. Response characteristics of proposed algorithm is compared to conventional PO method with insolation variation. This paper proves the validity of proposed algorithm through the analysis result.

• Proceedings of the KIEE Conference
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• 2007.04c
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• pp.5-7
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• 2007

This paper deals with design and analysis of thrust magnetic bearing for 300HP class high speed motor. Using the solutions obtained from equivalent magnetic circuits, we predicts the electromagnetic characteristics such as thrust, time constant and power loss according to design parameters. And then, using non-linear finite element analysis, a detailed design is performed considering saturation in order to meet requirements.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3219-3226
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• 1994

A model is constructed to evaluate the stress intensity factors for a center crack subjected to polynomial anti-symmetric loading in a layered material. A Fredholm integral equation is derived by Fourier integral transform method. The integral equation is numerically analyzed to evaluate the effects of the ratios of shear modulus, Poisson's ratio and crack length to layer thickness as well as the number of layers on the stress intensity factor. The stress intensity factors are approached to constant values as the number of layers increase and decrease as the polynomial power of the loading increase. In case of the E-glass/Epoxy composite, dimensionless stress intensity factor is affected by cracked-resin layer thickness.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.9
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• pp.733-740
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• 2007

Microchannel heat sink shape optimization is performed using Kriging method. Design variables relating to microchannel width, depth and fin width are selected, and thermal resistance has been taken as objective function. Design points are selected through a three-level fractional factorial design of sampling method. Navier-Stokes and energy equations for laminar flow and conjugate heat transfer are solved at these design points using a finite volume solver. Solutions are carefully validated with experimental results. Using the numerically evaluated objective function, a surrogate model (Kriging) is constructed and optimum point is searched by sequential quadratic programming. The process of shape optimization greatly improves the thermal performance of microchannel heat sink under constant pumping power.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.14 no.1
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• pp.1-7
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• 2018

Materials in nuclear power plants can be embrittled by neutron irradiation. According to existing studies, the effect of the material property by irradiation embrittlement can be approximately simulated by cold working (pre-strain). In this study, finite element damage analysis method using the stress-modified fracture strain model is proposed to predict J-Resistance curves of irradiated SUS316 stainless steel. Experimental data of pre-strained SUS316 stainless steel material are obtained from literature and the damage model is determined by simulating the tensile and fracture toughness tests. In order to consider damage caused by the pre-strain, a pre-strain constant is newly introduced. Experimental J-Resistance curves for various degrees of pre-strain are well predicted.