• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.7
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• pp.647-651
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• 2005

We studied the external pressure-stable advanced frnge field switching (FFS) pixel design with 3 slit sructue. In this mode, a patterned pixel slit is partitioned into 3 areas, namely, two edges and a center, where the edge slit angle is larger than the center slit angle. Thus the reverse twist region in the pixel edge is reduced comparing to the conventional FFS mode so that the LC dynamics in this region becomes very stable. And also, when the external pressure is applied to the panel at the high voltage, the disclination lines (DLs) were barely intruded into active area. Therefore, the structure is use for the pen based system such as the tablet personal computer (PC), personal digital asistant (PDA).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.312-313
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• 2008

A transflective liquid crystal displays associated with fringe field switching (FFS) mode of new concept is proposed. The device utilizes unique characteristic of the FFS mode in which the rotation angle of LC director is strongly dependent on electrode position in on state. We use the liquid crystal with negative dielectric anisotropy. Also we are look for optimized electrode size and the optimization of pixel electrode width and distance between them, the LC director could rotate about $22.5^{\circ}$ and $45^{\circ}$ depending on electrode positions. Consequently, we get high transmittance and high reflection on the optimized electrode condition. Respectively, a high image quality transflective display with single gap and single gamma characteristics realized.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.629-632
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• 2009

We have proposed a novel viewing angle controllable display of in-plane switching (IPS) mode with single panel. One pixel of this device is divided to two regions, in which main pixel shows image and sub pixel for viewing angle control. In initial state, the liquid crystal of sub pixel is homogeneous aligned on substrate for wide viewing angle mode. On the other hand, after applying voltage, the liquid crystal of sub pixel tilts up for narrow viewing angle mode. The proposed device has advantage for the function for simple manufacturing process and good viewing angle control with single panel.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.7
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• pp.754-759
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• 2004

We have studied the fringe field switching (FFS) mode with the positive dielectric anisotropy for the fast response time. The factors such as the physical properties of the LC, the cell gap, and the rubbing angle were critical for the fast response time of the FFS mode. The response time became 10 ms faster when the rotational viscosity of the new LC is 20 mPa.s lower than the conventional LC. When the cell gap changed from 3.6 ${\mu}{\textrm}{m}$ to 3.0 ${\mu}{\textrm}{m}$, it was possible to achieve the total response time and response times associated with grey-to-grey transitions under 16 ms. And the response times including grey-to-grey transitions become fast as the rubbing angle decreases.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.8
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• pp.1854-1860
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• 2014

In this paper, the energy saving on mobile communication repeater is studied. DB(Dual Band) small repeater, which is currently used in the field for indoor coverage, is adopted as a test unit. For reducing the power consumption, PFC (Power Factor Correction) is included on SMPS (Switching Mode Power Supply) of the DB small repeater. The test results show that approximately 38.9% of the power consumption is reduced comparing with the repeater without PFC. It means that approximately 230.43kWh per unit can be saved annually.

• Journal of Power Electronics
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• v.19 no.4
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• pp.907-921
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• 2019

This paper presents two advanced hybrid pulse-width modulation (PWM) strategies for multilevel inverters (MLIs) that provide both common-mode voltage (CMV) elimination and current ripple reduction. The first PWM utilizes sequences that apply one switching state at the double ends of a half-carrier cycle. The second PWM combines the advantages of the former and an existing four-state PWM. Analyses of the harmonic characteristics of the two groups of switching sequences based on a general switching voltage model are carried out, and algorithms to optimize the current ripple are proposed. These methods are simple and can be implemented online for general n-level inverters. Using a three-level NPC inverter and a five-level CHB inverter, good performances in terms of the root mean square current ripple are obtained with the proposed PWM schemes as indicated through improved harmonic distortion factors when compared to existing schemes in almost the entire region of the modulation index. This also leads to a significant reduction in the current total harmonic distortion. Simulation and experimental results are provided to verify the effectiveness of the proposed PWM methods.

• Transactions on Control, Automation and Systems Engineering
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• v.4 no.2
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• pp.169-175
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• 2002

A sliding mode control of spacecraft attitude tracking with actuator, especially reaction wheel, is presented. The sliding mode controller is derived based on quaternion parameterization for the kinematic equations of motion. The reaction wheel dynamic equations represented by wheel input voltage are presented. The input voltage to wheel is calculated from the sliding mode controller and reaction wheel dynamics. The global asymptotic stability is shown using a Lyapunov analysis. In addition the robustness analysis is performed for nonlinear system with parameter variations and disturbances. It is shown that the controller ensures control objectives for the spacecraft with reaction wheels.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.379-382
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• 1996

Evolution Strategy is used as an effective search algorithm in optimization problems and Sliding Mode Control is well known as a robust control algorithm. In this paper, we propose a Sliding Mode Control Method for robot manipulator using Evolution Strategy. Evolution Strategy is used to estimate Sliding Mode Control Parameters such as sliding surface gradient, continuous function boundary layer, unknown plant parameters and switching gain. Experimental results show the proposed control scheme has accurate and robust performances with effective search ability.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2000.05a
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• pp.51-54
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• 2000

In variable structure control algorithm, sliding mode makes the closed loop system insensitive to modelling uncertainties and external disturbances. However due to imperfections in switching, the system trajectory chatters, which is very undesirable. And the insensitivity property of a sliding mode controller is present only when the system is in the sliding mode. To overcome these shortcomings, in this paper, new sliding mode control algorithm using time-varying sliding surface and fuzzy PI structrue is proposed.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.1148-1150
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• 2003

Power conversion system must be increased switching frequency in order to achieve a small size, a light weight and a low noise. However, the switches of converter are subjected to high switching power losses and switching stresses. As a result of those, the power system brings on a low efficiency. To improved these, a large number of soft switching topologies included a resonant circuit has been prosed. But these circuits increase number of switch in circuit and complicate sequence of switching operation. In this paper, the authors propose a high power factor and high efficiency DC-DC converter using single-pulse soft switching by partial resonant switching node. The switching devices in a prosed circuit are operated with soft switching by the partial resonant method, that is, Partial Resonant Switch Mode Power Converter. The partial resonant circuit makes use of a inductor using step up and a condenser of loss-less snubber. The result is that the switching loss is very low and the efficiency of system is high. Also the proposed converter is deemed the most suitable for high power applications where the power switching devices are used. Some simulative results on computer results are included to confirm the validity of the analytical results.