• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.263-266
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• 2005

The critical speeds and mode shapes are most important to determine the behaviors of rotor in designing rotating machinery. As the capacity and the span of turbine-generator increases, the turbine-generator system has many components such as bearings, pedestal, turbine and baseplates etc. and it is getting flexible and has many critical speeds. Especially, the characteristics of bearing-pedestal are very complicated and then they affect the entire vibration characteristics of turbine-generator system. In this paper, it is observed how to determine the equivalent dynamic stiffness of bearing-pedestal by analytic and experimental method.

• Proceedings of the KIEE Conference
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• 2001.04a
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• pp.227-230
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• 2001

This paper deals with a bidirectional ac-dc converter used in ups system application. We propose a Voltage-Source-Charge-Pump-Power-Factor-Correction(VS-CPPFC) ac-dc converters. First of all, we propose a charge pump power-factor-correction converter. Secondly, we derive and analyse a unity power factor condition. The proposed topology is based on a half-bridge for the primary and a current-fed push pull for the secondary side of a high frequency isolation transformer. The advantage of bidirectional flow of power achieved by using the same power components is that the circuit is simple and efficient. And the galvanically isolated topology is specially attractive in battery charge/discharge circuits in ups system. We design equivalent model for the steady-state circuit and analyse operation waveforms for each mode. We show that the proposed model can be applied to ups system by simulation processes.

• Journal of Power Electronics
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• v.18 no.6
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• pp.1844-1854
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• 2018

Isolated power systems (IPS) are often characterized by a weak grid due to small power grids. The grid side voltage is no longer equivalent to an ideal voltage source of an infinitely big power grid. The conversion control of new energy sources, parameter perturbations as well as the load itself can easily cause the system voltage to oscillate or to become unstable. To solve this problem, increasing the energy-storage power sources is usually used to improve the reliability of a system. In order to provide support for the voltage, the energy-storage power source inverter needs an method to control the voltage source. Therefore, this paper has proposed the active damping control of a voltage source inverter (VSI) based on virtual compensation. By simplifying the VSI double closed-loop control, two feedback compensation channels have been constructed to reduce the VSI output impedance without changing the characteristics of the voltage gain of a system. This improvement allows systems to operate stably in a larger range. A frequency-domain analysis, and simulation and experimental results demonstrate the feasibility and effectiveness of the proposed method.

• Transactions of the Korean hydrogen and new energy society
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• v.17 no.3
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• pp.338-346
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• 2006

In this paper, the test results of medium-size(120 kW class) PV system which was installed in the Taeahn thermal power station of Korea Western Power Co., Ltd., were summarized for developing the practical technology to applicate high voltage grid connection PV system. The 120 kW photovoltaic system which was consisted of 1,300 modules, PCS, and 150 kVA transformer station has been operated since Aug. 05, 2005. For verifying the modeling results of PV system, the operation data was compared with modeling results which was executed commercial PSCAD/EMTD and Psim tools. An equivalent circuit model of a solar cell has been also used for solar array modeling. A series of parameters required for array modeling have been estimated from general specification data of a solar module. A PWM voltage source inverter(VIS) and its current control scheme have been analyzed by using P&O (perturbation and Observation) MPPT algorithms technique.

• Proceedings of the KIEE Conference
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• 2005.10b
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• pp.496-498
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• 2005

This paper presents intelligent digital redesign method of global approach for hybrid state space fuzzy-model-based controllers. For effectiveness and stabilization of continuous-time uncertain nonlinear systems under discrete-time controller, Takagi-Sugeno(TS) fuzzy model is used to represent the complex system. And global approach design problems viewed as a convex optimization problem that we minimize the error of the norm bounds between nonlinearly interpolated linear operators to be matched. Also by using the power series, we analyzed nonlinear system's uncertain parts more precisely. When a sampling period is sufficiently small, the conversion of a continuous-time structured uncertain nonlinear system to an equivalent discrete-time system have proper reason. Sufficiently conditions for the global state-matching of the digitally controlled system are formulated in terms of linear matrix inequalities (LMIs).

• ETRI Journal
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• v.34 no.4
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• pp.527-535
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• 2012

A general equivalent circuit model is developed for a wireless energy transfer system composed of multiple coils via coupled magnetic resonances. To verify the developed model, four types of wireless energy transfer systems are fabricated, measured, and compared with simulation results. To model a system composed of n-coils, node equations are built in the form of an n-by-n matrix, and the equivalent circuit model is established using an electric design automation tool. Using the model, we can simulate systems with multiple coils, power sources, and loads. Moreover, coupling constants are extracted as a function of the distance between two coils, and we can predict the characteristics of a system having coils at an arbitrary location. We fabricate four types of systems with relay coils, two operating frequencies, two power sources, and the function of characteristic impedance conversion. We measure the characteristics of all systems and compare them with the simulation results. The flexibility of the developed model enables us to design and optimize a complicated system consisting of many coils.

• Journal of the Institute of Convergence Signal Processing
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• v.3 no.4
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• pp.74-78
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• 2002

For human detecting pyroelectric infrared sensor system using more than 2 sensor devices. By new top and bottom electrode design, 1 sensor can sensing human instead of using 2 sensor system. The poled P(VDF/TrFE) film used for sensor pyroelectric materials. The fabricated sensors NEP (noise equivalent power) and specific detectivity D$^*$ of the device were 9.62 $\times$ 10$10^5$ V/W, 3.95 $\times$ 10$10^-175$ W and 5.06 $\times$ 10$10^5$W under emission energy of 13 ${\mu}W/cm^2$ respectively and It's result is almost same result that using more than 2 sensor system for human detecting.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.452-457
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• 1998

This paper deal with problems of leakage current, shaft voltage, bearing current, and EMI, in valiable-speed AC drives. The originating mechanism is illustrated with a high-frequency equivalent circuit. Reduction methods are classified in to six categories based on the equivalent circuit. Some experimental results show that a common-mode transformer (CMT) and a common-noise canceler (ACC) can solve the problems, which have been proposed the authors.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.388-393
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• 1988

New circuit D-Q transformation concept is introduced to analyze AC converters such as inverters, rectifiers and cyclo-converters with ease. The equivalent linear time invariant circuit is obtained by substituting switches with equivalent turn-ratio variable transformers and changing balanced AC reactors into equivalent DC reactors combined by gyrators. This circuit enables us to utilize the powerful linear system analysis techniques such as Laplace transform otherwise which could not be applied to the time varying switching systems. Direct substitution of switches of DC converters with transformers is shown as a preliminary. Then the modeling procedure is shown for a controlled rectifier-inverter circuit. Finally an analysis example is proposed for a buck-boost inverter and the result is compared with the conventional approach. This approach is applicable to all AC converter families to determine the AC transfer functions and the DC operating points. It is identified that the switching systems are equivalent to the RLC filter circuits with transformers and gyrators.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.9
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• pp.71-77
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• 2022

In times of war or emergencies, weapon systems, such as radars, must receive stable power. This can be achieved using improved onboard portable power systems made of steel containers. However, a breakdown can occur in the event of random vibration during transportation via a vehicle or train. Electrical-power shortages or restrictions pose a significant threat to security. In this study, Composite Wheeled Vehicle(CWV) data and rail cargo data with Acceleration Spectral Density(ASD), specified in MIL-STD-810H METHOD 514.8, were interpreted as input data of the three-axis random vibration method using ANSYS 19.2. Modal analysis was performed up to 500 Hz, and deformations in modes 1 to 117 were calculated to utilize all ASD data. The maximum equivalent stress in the three-axis direction was obtained using a random vibration analysis. Similarly, the margin of safety was calculated using the derived equivalent stress and material properties. Overall, the analysis verified that the portable container designed for the power supply system satisfied the required vibration demands.