• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.4
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• pp.166-175
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• 2001

The high speed tracking control of a 6-6 Stewart platform manipulator (SPM) normally requires knowledge of its complex full dynamics and measurement of its base motion when the SPM operates on a motion nit. In this study, an enhanced sliding mode control scheme has been developed, which is based on the reduced dynamics, not necessitating measurement of the base motion. The enhanced sliding mode control implemented with the perturbation compensation and modified reaching phase alleviation functions has been successfully employed for high speed tacking control of the laboratory SPM, when it is subjected to a virtual base motion.

• Journal of Electrical Engineering and information Science
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• v.2 no.3
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• pp.88-94
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• 1997

This paper presents the sliding mode observer-model following (SMO-MF) power system stabilizer(PSS) for unmeasurable state variables. This SMO-MF PSS is obtained by combining the sliding mode-model following (SM-MF) including closed-loop feedback(CLF) with the full-order observer(FOO). The control input of the proposed MO-MF PSS is derived by Lyapunov's second method to determine a control input that keeps the system stable for unmeasurable plant state variables. Simulation results show that the proposed SMO-MF PSS including CLF is able to reduce the low frequency oscillation and to achieve asymptotic tracking error between the reference mode state and the estimated plant state at different initial conditions.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.2
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• pp.169-176
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• 2005

In this paper, a DC and small-signal AC modeling for the active-clamp, ful1-bridge boost converter is described. Based on the operation principle, the ac part of the converter can be replaced by a dc counterpart. Then, a conceptual equivalent circuit is derived by rearranging the switches. The equivalent circuit for this converter consists of CCM(Continuous conduction mode) boost and DCM(Discontinuous conduction mode) buck converter. The analyses for the equivalent CCM boost and DCM buck converter are done using the model of PWM switch. The theoretical modeling results are confirmed through experiment or SIMPLIS simulation.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1750-1759
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• 2018

A complete code-package for gyrotron simulation to analyze its performance is under development in UNIST, Korea. We first time report the present status of the code-package named as UNIST Gyrotron Design Tool (UGDT). It can perform design simulations for gyrotron's interaction cavity, RF window, and the essential mode calculations including the study of mode competition. We will discuss about its salient features, theory, numerical implementation, and its calculation result for 95 GHz UNIST Gyrotron. Moreover, we will validate its capability to perform the mode competition calculation for fundamental and second harmonic modes.

• Nuclear Engineering and Technology
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• v.50 no.7
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• pp.1106-1111
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• 2018

Electromagnetic waves potentially have been used to heat overdense nuclear fusion plasmas through a double mode conversion from ordinary to slow extraordinary and finally to Electron Bernstein Wave (EBW) modes, OSXB. This scheme is efficient and has not any plasma density limit of electron cyclotron resonance heating due to cut-off layer. The efficiency of conversion depends on the isotropic launching angles of the microwaves with the plasma parameters. In this article, a two-step mode conversions of OSXB power transmission efficiency affected by the fast extraordinary (FX) loses at upper hybrid frequency are studied. In addition, the kinetic (hot) dispersion relation of a overdense plasma in a full wave analysis of a OSXB in Wendelstein 7X (W7-X) stellarator plasma has been numerically simulated. The influence of plasma dependent parameters such as finite Larmor radius, electron thermal velocity and electron cyclotron frequency are represented.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.10
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• pp.1217-1224
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• 2014

This paper provides a practical scaling method to solve an old problem for scaling and developing the speed and resistance of a model to full-scale submarine in fully submerged underwater test. In every experimental test in towing tank, water tunnel and wind tunnel, in the first step, the speed of a model should be scaled to the full-scale vessel (ship or submarine). In the second step, the obtained resistance of the model should be developed. For submarine, there are two modes of movement: surface and submerged mode. There is no matter in surface mode because, according to Froude's law, the ratio of speed of the model to the full-scale vessel is proportional to the square root of lengths (length of the model on the length of the vessel). This leads to a reasonable speed and is not so much for the model that is applicable in the laboratory. The main problem is in submerged mode (fully submerged) that there isn't surface wave effect and therefore, Froude's law couldn't be used. Reynold's similarity is actually impossible to implement because it leads to very high speeds of the model that is impossible in a laboratory and inside the water. According to Reynold's similarity, the ratio of speed of the model to the full-scale vessel is proportional to the ratio of the full-scale length to the model length that leads to a too high speed. This paper proves that there is no need for exact Reynold's similarity because after a special Reynolds, resistance coefficient remains constant. Therefore, there is not compulsion for high speeds of the model. For proving this finding, three groups of results are presented: two cases are based on CFD method, and one case is based on the model test in towing tank. All these three results are presented for three different shapes that can show; this finding is independent of the shapes and geometries. For CFD method, Flow Vision software has been used.

• Journal of Korea Multimedia Society
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• v.11 no.10
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• pp.1392-1402
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• 2008

Home gateway is always full-powered for ubiquitous home services, and consumes much energy yearly. Power-saving algorithm to conserve this energy must reduce the energy consumption and preserve always-on services. Our algorithm predicts current idle period using the history of the past idle period when the idle period starts, and then determines whether the power mode is changed to the saving mode or not. On the power saving mode, it processes the simple protocol data for network control using proxying with no wakeup. And it changes the power mode to active mode when user's traffic exists. As the results of the simulation using real traffic, our algorithm saves the energy consumption from 14% to 49% as compared with existing method.

• Journal of electromagnetic engineering and science
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• v.4 no.1
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• pp.30-36
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• 2004

We determined equivalent circuit parameters of a 1.5 cell S-band RF gun cavity from the resonant characteristics of its decoupled cavities(half cell and full cell) using the code SUPERFISH. Equivalent circuit parameters of the 1.5 cell RF gun cavity resonated in the 0-mode were obtained easily from the circuit parameters of each decoupled cavities. In order to obtain equivalent circuit parameters for the $\pi$ -mode cavity, we calculated the differences of the resonant frequencies and the equivalent resistances between the 0- and $\pi$ -modes with slight variations of the radius and thickness of the coupling iris. From those differences, we obtained R/Q value and equivalent resistance of the $\pi$ -mode, which are directly related to the equivalent circuit parameters of the coupled cavity. Using calculated R/Q value, we can express equivalent inductance, capacitance and resistances of the RF gun cavity resonated in the $\pi$ -mode, which can be useful for analyzing coupled cavities in a steady state.

• Journal of Satellite, Information and Communications
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• v.9 no.1
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• pp.13-16
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• 2014

In applying LCD to TV application, one of the most significant factors to be improved is image sticking on the moving picture. LCD is different from CRT in the sense that it's continuous passive device, which holds images in entire frame period, while impulse type device generate image in very short time. To reduce image sticking problem related to hold type display mode, we made an experiment to drive TN-LCD like CRT. We made articulate images by fast refreshing images, and we realized the ratio of refresh time by counting between on time and off time for video signal input during 1 frame (16.7ms). Conventional driving signal cannot follow fast on-off speed, so we evaluated new signal generator using SDI (Serial Data Interface) mode signal generator. We realized articulate image generation similar to CRT by high fast full HD (High Definition) signals and TN-LCD overdriving. As a result, reduced image sticking phenomenon was validated by naked eye and response time measurement.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.11
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• pp.2613-2620
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• 2014

In this paper, we consider a full duplexing (FD) wireless cellular network where a central base station (BS) works in the FD mode while the downlink (DL) and uplink (UL) users work in the time division duplexing (TDD) mode. Since this FD system induces the inter-user interference from UL user to DL user, the main challenge for maximizing the system performances is user scheduling that makes a pair of DL user and UL user to use the same radio resource simultaneously. We formulate an optimization problem for user pairing to maximize the cell capacity and propose a suboptimal user scheduling algorithm with low complexity. This scheduling algorithm is designed in a way where the DL user with a better signal quality has a higher priority to choose its UL user that causes less interference. Simulation results show that the FD system using the proposed user scheduling algorithm achieves the optimal performance and significantly outperforms the conventional TDD system in terms of the cell capacity.