• 한국통신학회논문지
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• 제38B권8호
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• pp.679-686
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• 2013

데이터전송 증가에 따라 제한적인 배터리를 사용하는 모바일 단말에서 효율적으로 전력을 사용하는 것은 중요하게 여겨지고 있다. 802.11 표준에 있는 Power Saving Mechanism (PSM)은 부하가 많은 네트워크에서 적합하지 않다. AP(Access Point)는 버퍼링된 프레임을 PS (Power Saving) 단말들에게 즉시 보낼 수 없어서 단말들이 깨어 있는 모드를 계속 유지함으로써 전력을 낭비하게 된다. 또한, PS단말들이 하나의 데이터 프레임을 받기 위해 AP에게 하나의 PS-POLL프레임을 전송하는 방식은 효율적이지 않다. 본 논문에서는 802.11 PSM의 성능을 향상하기 위해 PS단말들이 AP에게 데이터 받을 시간을 미리 예약하는 시분할 메커니즘을 제안한다. 제안된 메커니즘은 충돌가능성을 감소시킬 수 있으며 채널사용 효율을 높일 수 있다. 분석결과 및 시뮬레이션 결과로부터, 제안된 시분할 메커니즘은 전체 네트워크의 전력소비가 효과적으로 감소되며, PSM의 성능을 개선시킨다.

• 정보보호학회논문지
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• 제21권4호
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• pp.149-160
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• 2011

스마트그리드는 기존의 전력망과 정보통신 기술을 융합하여 에너지 효율을 최적화할 수 있는 차세대 지능형 전력망이다. 이는 소비자에게는 전력 요금의 실시간 확인을 통해 능동적인 전력소비를 유도하고, 공급자에게는 예상 발전량 측정을 통해 보다 안정적인 전력 시스템을 운용하도록 할 수 있다는 장점이 있다. 그러나 스마트그리드는 지능형 장치를 통한 양방향 통신 사이에서 데이터 노출, 데이터 도용, 프라이버시 침해와 같은 다양한 보안 위협들이 존재할 가능성이 있다. 따라서 이러한 스마트그리드의 보안 위협에 대응할 수 있는 안전한 환경을 구축하기 위해서는 보안 메커니즘 개발에 핵심이 되는 키 관리 기법이 필수적으로 요구된다. 본 논문에서는 해쉬 체인을 이용하여 계층적 구조를 갖는 스마트그리드 환경에 효율적으로 적용 가능한 그룹키 관리 메커니즘을 제안하고, 제안하는 그룹키 관리 메커니즘의 안전성 및 효율성을 분석한다.

• Journal of Electrical Engineering and Technology
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• 제12권6호
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• pp.2227-2236
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• 2017

In order to solve the neutral-point voltage fluctuation problem of three-phase three-level T-type inverters (TPTLTIs), the unbalance characteristics of capacitor voltages under different switching states and the mechanism of neutral-point voltage fluctuation are revealed. Based on the mathematical model of a TPTLTI, a feed-forward voltage balancing control strategy of DC-link capacitor voltages error is proposed. The strategy generates a DC bias voltage using a capacitor voltage loop with a proportional integral (PI) controller. The proposed strategy can suppress the neutral-point voltage fluctuation effectively and improve the quality of output currents. The correctness of the theoretical analysis is verified through simulations. An experimental prototype of a TPTLTI based on Digital Signal Processor (DSP) is built. The feasibility and effectiveness of the proposed strategy is verified through experiment. The results from simulations and experiment match very well.

• 한국소음진동공학회논문집
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• 제21권12호
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• pp.1152-1158
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• 2011

In this paper a configuration of the load evaluation device for the tilting actuator using hydraulic power is presented, which makes it possible to measure the force action on the tilting actuator. It is possible to measure only current using the conventional electro-mechanical actuator when the bogie is in the process of the tilting. This makes impossible to measure the force acting on the tilting actuator. In order to overcome this problem a kinetic mechanism test system using hydraulic cylinder is proposed. The system are consisted of hydraulic cylinder for the tilting actuation, control system to control hydraulic power, sensors to measure for force and displacement and monitoring system for the user interface.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.190-193
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• 2001

ZnO varistors have been widely used to protect power system and electronic system against overvoltages based on their excellent nonlinearity. In order to increase their protection capability, the fracture and protection technologies of arresters have to study according to their applications, namely ImA DC voltage, leakage currents, impulse residual voltages, withstanding capability to impulse surge, and energy absorption capability. ZnO varistors which have nonlinear current-voltage characteristic name a number of failure mechanism when ZnO elements absorb surge energies. Failure mode by thermal stress and Pin hole are among the most common failure mechanism at the high current surge current. In this study, the fracture mechaism of power arresters are introduced and protection technologies are researched. In particular the effect of thermal stress by surge currents to ZnO elements and methods against arc surge energy through withstand structure design of arrester are discussed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 학술대회 논문집 정보 및 제어부문
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• pp.421-423
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• 2005

Power transmission lines have been playing a key role as the mainstay of national industry. When a power failure occurs, it can have severe effects on national security as well as national industry and economy. In this paper, we consider an insulator failure, which is one of the main causes of such a power failure. In spite of its importance, however, a shortage of manpower in the insulator maintenance field is getting more serious due to working environments with a high voltage and a high place. For this reason, a new active maintenance technique using a robot system is required to prevent such an insulator failure. In this paper, a new robot mechanism for insulator cleaning and inspection was developed. We confirmed its effectiveness through experiments.

• 전기학회논문지
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• 제60권2호
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• pp.416-422
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• 2011

Smart grid is the next generation intelligent power grid that combines the existing electric power infrastructure and information infrastructure. It can optimize the energy efficiency in both directions, suppliers and power consumers to exchange information in real time. In smart grid environments, with existing network security threats due to the smart grid characteristics, there are additional security threats. In this paper, we propose a security mechanism that provides mutual authentication and key agreement between a remote user and the device. The proposed mechanism has some advantages that provides secure mutual authentication and key agreement and secure against a replay attack and impersonation attacks.

• 전기학회논문지P
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• 제61권4호
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• pp.161-167
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• 2012

Energy conversion systems such as power inverters and converters are basically significant in establishing photovoltaic power systems to enhance power effectiveness. This paper proposes a new converter control method by using the Lyapunov redesign approach. We construct the proposed control mechanism linearly composed of nominal control and auxiliary control laws. The former is generally designed through a well-known power electronic technology and the latter is implemented to compensate real-time control error due to uncertain natures of converter systems in practice. For realizing adaptive control capability in the proposed control mechanism, a control parameter vector is estimated by utilizing a steepest descent based optimization method. We carry out numerical simulation with Matlab(c) software to demonstrate reliability of the proposed converter control system and conduct a comparative study to prove its superiority by comparing with a generic converter control methodology.

• 한국시스템다이내믹스연구
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• 제6권2호
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• pp.25-35
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• 2005

This paper describes the mechanism for new investment to appear in waves of boom and bust causing alternative periods of over and under supply of electricity in Korean market. A system dynamics model was developed to describe the dynamic behavior of new investment in Korean market. The simulation results show the boom and bust cycle in the new investments. When the market price is high, investors decide to build new power plants. However, it takes some delay time to complete new power plants. When the new power plants are being added into the grid, the supply increases and the wholesale price begins to decrease. This causes the cancellation of new power plant or delay the construction. This mechanism causes the boom and bust cycle in new investment.

• Nuclear Engineering and Technology
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• 제54권4호
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• pp.1185-1194
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• 2022

The maintenance of condenser main pipe is the key to achieve film-forming amine maintenance effectiveness. In this work, oxygen content, pH and temperature of the solution were controlled to simulate the condition of condenser main pipe, and magnetite coated carbon steel sample was prepared by pre-oxidization. CAM was used to characterize the hydrophobicity of film formed samples. Hydrophobic film was formed on pre-oxidized carbon steel samples when octadecylamine concentration reaches 20 mg/kg. SEM, EDS, EIS, and PD were used to characterize the influence of octadecylamine concentration on maintenance effectiveness. It was found that the maintenance effectiveness was enhanced and the corrosion rate was suppressed with the increase of octadecylamine concentration. FIB and TEM were used to detect the adsorbed octadecylamine film thickness founding that octadecylamine adsorbed onto the surface of pre-oxidized carbon steel by multi-layer adsorption mechanism.