• Journal of Power Electronics
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• 제13권1호
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• pp.59-69
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• 2013

An alternative technique to control multilevel inverters with vector approximations has been presented. The innovative control method utilizes specially designed two-dimensional hysteresis comparators to simplify the implementation and improve the resultant waveform. The multistage inverter designed with maximum number of levels is operated in such a way to approximate the reference voltage vector by exploiting the large number of multilevel inverter vectors. A three-stage inverter with the main high voltage stage made of three phase, six-switch and singly-fed inverter is considered for application to the proposed design. The proposed control concept is to maintain a higher voltage stage state as long as it can lead to a target vector. High and medium voltage stages controllers are based on surface hysteresis comparators to hold the switching state or to perform the necessary change to achieve its reference voltage with minimal switching losses. The low voltage stage controller is designed to approximate the target reference voltage to the nearest inverter vector using the nearest integer rounding and adjustment comparators. Model simulation and prototype test results show that the proposed control technique clearly outperforms the previous control methods.

• 대한조선학회논문집
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• 제51권1호
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• pp.88-98
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• 2014

A supercavitation is modern technology that can be used to reduce the frictional resistance of the underwater vehicle. In the process of reaching the supercavity condition which cavity envelops whole vehicle body, a vehicle passes through transition phase from fully-wetted to supercaviting operation. During this phase of flight, unsteady hydrodynamic forces and moments are created by partial cavity. In this paper, analytical and numerical investigations into the dynamics of supercavitating vehicle in transition phase are presented. The ventilated cavity model is used to lead rapid supercavity condition, when the cavitation number is relatively high. Immersion depth of fins and body, which is decided by the cavity profile, is calculated to determine hydrodynamical effects on the body. Additionally, the frictional drag reduction associated by the downstream flow is considered. Numerical simulation for depth tracking control is performed to verify modeling quality using PID controller. Depth command is transformed to attitude control using double loop control structure.

• Journal of Electrical Engineering and Technology
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• 제12권3호
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• pp.1195-1202
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• 2017

Induction motors often reach their maximum efficiency at the nominal load. In most applications, the machine load is not equal to the nominal load, thus reduces the motor efficiency and turns a greater percent of power into loss. In this paper, the induction motor control problem has been investigated to reduce the system losses. The Field Oriented Control method (FOC) has been employed in this paper. In this research, the mathematical equations related to system losses are calculated in relation to torque and speed, and then the q- and d-axis are summarized according to the current components. After that, the proposed method is applied along with d- and q-axis. In the recent three decades, many techniques have been suggested to improve the induction motor performance using smart and non-smart methods. In this paper, a new PSO-Fuzzy method have used in real time. The fuzzy logic method serves as speed controller in q-axis and PSO algorithm controls the optimum flux in d-axis. It will be proved that the use of this combined method will lead to a significant improvement in motor efficiency.

• Journal of Electrical Engineering and Technology
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• 제13권1호
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• pp.240-249
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• 2018

Individual DC voltage balance problem is an inherent issue for cascaded H-bridge (CHB) based converter. When the CHB-based static synchronous compensator (STATCOM) is operating at zero current mode, the software-based individual DC voltage balancing control techniques may not work because of the infinitesimal output current. However, the different power losses of each cell would lead to the individual DC voltages unbalance. The uneven power losses on the local supplied cell-controllers (including the control circuit and drive circuit) would especially cause the divergence of individual DC voltages, due to their characteristic as constant power loads. To solve this problem, this paper proposes an adaptive voltage balancing module which is designed in the cell-controller board with small size and low cost circuits. It is controlled to make the power loss of the cell a constant resistance load, thus the DC voltages are balanced in zero current mode. Field test in a 10kV STATCOM confirms the performance of the proposed method.

• Nuclear Engineering and Technology
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• 제49권3호
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• pp.484-494
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• 2017

In industrial plants such as nuclear power plants, system operations are performed by embedded controllers orchestrated by Supervisory Control and Data Acquisition (SCADA) software. A targeted attack (also termed a control aware attack) on the controller/SCADA software can lead a control system to operate in an unsafe mode or sometimes to complete shutdown of the plant. Such malware attacks can result in tremendous cost to the organization for recovery, cleanup, and maintenance activity. SCADA systems in operational mode generate huge log files. These files are useful in analysis of the plant behavior and diagnostics during an ongoing attack. However, they are bulky and difficult for manual inspection. Data mining techniques such as least squares approximation and computational methods can be used in the analysis of logs and to take proactive actions when required. This paper explores methodologies and algorithms so as to develop an effective monitoring scheme against control aware cyber attacks. It also explains soft computation techniques such as the computational geometric method and least squares approximation that can be effective in monitor design. This paper provides insights into diagnostic monitoring of its effectiveness by attack simulations on a four-tank model and using computation techniques to diagnose it. Cyber security of instrumentation and control systems used in nuclear power plants is of paramount importance and hence could be a possible target of such applications.

• 대한임베디드공학회논문지
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• 제6권4호
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• pp.209-214
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• 2011

This study suggests a Healthcare System for elderly and disabled who have mobility impairment and use a wheelchair for long time. Seating long time in a wheelchair without reducing pressure causes high risk of developing pressure sores. Pressure sores come with great deal of pain and often lead to develop complication. Not only it takes time and effort to treat pressure sores but also increases medical expenses. Therefore, we will develop a device to help to prevent pressure sores by measuring pressure distribution while seating in a wheelchair and wirelessly send information to user device to check pressure distribution in real time. The equipment to measure body pressure is composed of FSR sitting mat which is a sensor measuring part and an user terminal which is a monitoring part. The designed mat is matrix formed FSR sensor to measure pressure. The sensor send measured data to the controller which is connected to the end of the mat, and then the collected data are sent to an user terminal through a bluetooth. Developing a pressure monitoring system will help to prevent those who have mobility impairment to manage pressure sores and furthermore relieve their burden of medical expenses.

• Journal of Power Electronics
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• 제19권2호
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• pp.487-496
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• 2019

For a solid-state transformer (SST), some factors, such as signal delay, switching loss and differences in the system parameters, lead to unbalanced DC-link voltages among the cascaded H-bridges (CHB). With a control method implemented in the ${\alpha}{\beta}$ frame, the DC-link voltages are balanced, and the reactive power is equally distributed among all of the H-bridges. Based on the ${\alpha}{\beta}$ frame control, the system can achieve independent active current and reactive current control. In addition, the control method of the high-voltage stage is easy to implement without decoupling or a phase-locked loop. Furthermore, the method can eliminate additional current delays during transients and get the dynamic response rapidly without an imaginary current component. In order to carry out the controller design, the vector refactoring relations that are used to balance DC-link voltages are derived. Different strategies are discussed and simulated under the unbalanced load condition. Finally, a three-cell CHB rectifier is constructed to conduct further research, and the steady and transient experimental results verify the effectiveness and correctness of the proposed method.

• 인터넷정보학회논문지
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• 제22권6호
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• pp.1-8
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• 2021

With the rapid growth of intelligent devices and communication technologies, 5G network environment has become more heterogeneous and complex in terms of service management and orchestration. 5G architecture requires supportive technologies to handle the existing challenges for improving the Quality of Service (QoS) and the Quality of Experience (QoE) performances. Among many challenges, traffic steering is one of the key elements which requires critically developing an optimal solution for smart guidance, control, and reliable system. Mobile edge computing (MEC), software-defined networking (SDN), network functions virtualization (NFV), and deep learning (DL) play essential roles to complementary develop a flexible computation and extensible flow rules management in this potential aspect. In this proposed system, an accurate flow recommendation, a centralized control, and a reliable distributed connectivity based on the inspection of packet condition are provided. With the system deployment, the packet is classified separately and recommended to request from the optimal destination with matched preferences and conditions. To evaluate the proposed scheme outperformance, a network simulator software was used to conduct and capture the end-to-end QoS performance metrics. SDN flow rules installation was experimented to illustrate the post control function corresponding to DL-based output. The intelligent steering for network communication traffic is cooperatively configured in SDN controller and NFV-orchestrator to lead a variety of beneficial factors for improving massive real-time Internet of Things (IoT) performance.

• 정보보호학회논문지
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• 제30권4호
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• pp.745-756
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• 2020

산업제어시스템이란 전력, 수처리, 교통과 같은 주요기반시설이나, 자동화 공장, 화학 플랜트와 같이 산업분야의 프로세스를 안전하고 효율적으로 모니터링 및 제어하는 시스템을 말한다. 이러한 산업제어시스템을 대상으로 하는 사이버 공격이 성공한다면 큰 인명 피해, 경제적 피해를 유발할 수 있어, 국가단위 해커 집단들의 주요 공격 대상이 될 가능성이 높다. Stuxnet, Industroyer, TRITON과 같은 사이버 공격은 이러한 우려가 실제 현실로 드러난 사례이며, 사이버 공격으로 실제 물리적 피해를 발생시키기 위해 대상 제어시스템에 대한 깊은 지식을 기반으로 개발된 것으로 확인되었다. 따라서 산업제어시스템의 사고조사를 위해서는 사고분석가 역시 제어시스템 운영 프로세스에 대한 지식을 보유하고 제어시스템에 특화된 사고조사 기술을 확보해야 한다. 이를 위해 사이버와 물리적 경계에 위치한 임베디드 제어기기와 같이 사이버 공격의 대상이 될 수 있지만, IT분야에서 사용되지 않아 즉시 활용할 기술이 없는 장치들을 대상으로 하는 사고조사 기술 개발이 필요하다. 이러한 연구 개발의 첫 단계로써 대표적인 임베디드 제어기기인 PLC(Programmable Logic Controller) 4종을 대상으로 PLC의 로깅 기능 및 본 논문에서 제안한 공격 시나리오에서 사고조사에 활용 가능한 로그 생성 여부를 분석한 결과를 제시한다.

• 보존과학회지
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• 제30권2호
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• pp.235-241
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• 2014

본 연구에서는 활성탄의 문화재 전시 환경에 대한 습도 및 유해물질 제어 능력을 확인하고자 하였다. 흡 방습 성능 실험 결과, 저습과정(RH $30{\rightarrow}55{\rightarrow}30%$)에서는 박물관에서 주로 사용되는 Silica계 조습제에 비해 활성탄의 흡습량이 많은 반면 방습량은 적었다. 흡습속도는 활성탄이 Silica계 조습제에 비해 빠르고 방습속도는 Silica계 조습제가 빨랐다. 중습과정(RH $50{\rightarrow}75{\rightarrow}50%$)에서는 활성탄에 비해 Silica계 조습제의 흡습량이 근소하게 많았으며 방습량은 비슷하게 나타났다. 흡 방습 속도는 활성탄의 흡습 속도가 Silica계 조습제에 비해 빠르고 방습속도는 큰 차이를 보이지 않았다. 유해물질 흡착 실험에서는 활성탄을 적용한 환경이 Silica 계 조습제를 적용한 환경에 비해 Formaldehyde의 농도가 낮았다.