• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.4
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• pp.341-349
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• 2004

A parallel operation of Uninterruptible Power Supply(UPS) systems is used to increase power capacity of the system or to secure higher reliability at critical loads. In the conventional parallel operation, the load-sharing control to maintain the current balance is the most important, since the load-sharing is very sensitive to discord between components of each module, amplitude/phase difference, line impedance, output LC filter, and so on. To solve these problems various control algorithms are researching. However, these methods cannot apply to the different ratings of UPS. In the case, master and slave control algorithm for parallel operation is adequate. However, if the UPS ratings are different, the value of passive filters L, C is different, and it affects the sharing of current. This paper presents general problems of conventional parallel operation systems, and control strategy for parallel operation with different ratings. The validity of the proposed control strategy is investigated through simulation and experiment in the parallel operation system with two 3-phase UPS systems.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.29 no.2
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• pp.365-375
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• 2019

A PLC (Programmable Logic Controller) is a highly-reliable industrial digital computer which supports real-time embedded control applications for safety-critical control systems. Real-time operating systems such as uC/OS have been used for PLCs and must meet real-time constraints. As PLCs have been widely used for industrial control systems and connected to the Internet, they have been becoming a main target of cyberattacks. In this paper, we propose an execution code sanitizer to enhance the security of PLC systems. The proposed sanitizer analyzes PLC programs developed by an IDE before downloading the program to a target PLC, and mitigates security vulnerabilities of the program. Our sanitizer can detect vulnerable function calls and illegal memory accesses in development of PLC programs using a database of vulnerable functions as well as the other database of code patterns related to pointer misuses. Based on these DBs, it detects and removes abnormal use patterns of pointer variables and existence of vulnerable functions shown in the call graph of the target executable code. We have implemented the proposed technique and verified its effectiveness through experiments.

• Nuclear Engineering and Technology
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• v.41 no.1
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• pp.71-78
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• 2009

One of main concepts involved in regional small nuclear reactors is unmanned remote control. Internet-based virtual private networks provide environments for the remote monitoring and control of geographically-dispersed systems, and with the advances in communication technologies, the potential of networks for real time control and automation becomes enormous. However, networked control has some problems. The most critical is delay in signal transmission, which degrades system stability and performance. Therefore, a networked control system should be designed to account for delay. This paper proposes some design approaches for a delay-tolerant system that can guarantee predetermined stability margins and performance. To accomplish this, the reactor plant is modeled with consideration of uncertainties. With this model, three kinds of controllers are developed using different methods. The designed systems are compared with respect to stability and performance, and a second-order controller designed using the table lookup method was found to give the most satisfactory results.

• Journal of the Korean Solar Energy Society
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• v.36 no.4
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• pp.31-40
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• 2016

The demands for photovoltaic systems on a large scale have grown dramatically and require new technologies to get the high efficiency and reliable operations of power conversion systems. These needs can be realized by the cost-effective and high performance digital revolutions and faster semiconductor switching devices. However, the new power systems have been more sophisticated and their reliability becomes critical issues. In this paper, a new fault-tolerance power conversion scheme for the photovoltaic systems is proposed. The proposed fault-tolerant scheme is able to supply energy from solar panels to loads intermittently in spite of a front boost converter open failure, and its voltage and current controllers are designed to improve the transient performance by using an average model design scheme. The proposed approach is verified both by simulations. The results will enable more timely and wide usage of alternative/renewable energy systems resulting in increased energy security.

• The Journal of Korean Physical Therapy
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• v.11 no.3
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• pp.23-36
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• 1999

The very definitions of posture and balance have changed, as has our understanding of the underlying neural mechanisms, In rehabilitation science, there awe at least two different conceptual theories to describe the neural control of posture and balance : the reflex/hierarchical theory and system theory. A reflex/hierarchical theory suggests the posture and balance result from hierarchically organized reflex responses triggered by independent sensory systems. The systems approach suggests that action emerges from an interaction of the individual with the task and environment. That is to say, the systems approach implies that the ability to control our body's position in space emerges from a complex interaction of musculoskeletal and neural systems, collectively referred to as the postural control system. The specific organization of postural systems determined both by the functional task and the environment in which it is being performed, The postural control system is divided into three basic functional components for assessment : 1) musculoskeletal components, 2) motor coordination components, and 3) sensory organization components. It is proposed that a systemic functional understanding of human balance is critical to effective programs for balance rehabilitation. Thus, this article briefly reviews the basic functional components to consider in designing treatment plan and for the benefit of the balance assessment.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.2
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• pp.65-71
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• 2008

Recently, many critical control systems are developed using formal methods. When software applied to such systems is developed, the employment of formal methods in the software requirements specification and verification will provide increased. assurance for such applications. Earlier error of overlooked requirement specification can be detected using formal specification method. Also the testing and full verification to examine all reachable states using model checking to undertake formal verification are able to be completed. In this paper, we propose an eclectic approach to incorporate Z(Zed) formal language and 'Statemate MAGNUM' which is formal method tools using Statechart for applying to the railway signaling systems.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.8
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• pp.107-112
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• 2016

Safety Critical Instrumentation and Control Systems perform those functions to maintain nuclear power plants' parameters within acceptable limits established for a design basis events and anticipated operating occurrence to ensure safety function. Those digitalized systems shall protect inadvertent and non-malicious behavior to ensure the reliable operation of systems, known as a Secure Development and Operational Environment(SDOE). SDOE would be established through managerial and technical controls. The objective of this paper is to evaluate the effectiveness of Cyclic Redundancy Checksum diagnostic, which is one of technical controls for SDOE, that can confirm the integrity of software of I&C systems to establish the secure environment. The results of this assessment would be the practical implementation of design and safety review of nuclear I&C systems.

• International Journal of Control, Automation, and Systems
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• v.6 no.5
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• pp.722-730
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• 2008

This paper proposes two novel algorithms enabling mobile robots to cooperate with each other in a reliability-based system and a time-critical system. In the reliability-based cooperative system, the concepts of a mobile ad hoc network (MANET) and an object entropy are adopted in order to coordinate a specific task. A logical robot group is created based on the exchange of request and reply messages in a robot communication group whose organization depends on transmission range. In the time-critical cooperative system, relational entropy is used to define the relationship between mobile robots. A group leader is selected based on optimizing power consumption. The proposed algorithm has been verified based on the computer-based simulation and soccer robot experiment. The performance metrics are defined. The metrics include the number of messages needed to make a logical robot group and to obtain the relationship of robots and the power consumption to select a group leader. They are verified by simulation and experiment.

• The Journal of Information Systems
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• v.19 no.1
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• pp.97-116
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• 2010

Failures of super large projects like IT Upgrade of Shinhan Financial Group can be a heavy blow not only to the company but even to the national economy. Research on the practices of risk management in those projects will provide invaluable lessons, enhancing capabilities and chances of successfully executing mission critical projects of the companies and the national economy as a whole. This paper analyzes the risk management of the Core Systems Reconstruction which was the most critical component of IT Upgrade. The analysis covers risk management plans, and identification and evolution, and control and monitoring of risk factors. This study confirms the major results of previous research on risk management in Korea. However, the analysis found as well some discrepancies of practices from the previous research results. This research also tracked the trajectories of evolution of risk factors and management. In particular, in depth analysis of control and monitoring is the first research in Korea on the "management" of risks in IT projects. The result of this research is expected to be a useful guide for theory development and practices of risk management in the future.

• Korean Chemical Engineering Research
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• v.60 no.4
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• pp.492-498
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• 2022

Process control systems used in most domestic petrochemical corporates today are based on the Windows platforms. As technology leans toward opened environment, the exposure risk of control systems is increasing. However, not many companies are preparing for various cyberattacks due to lack of awareness and misunderstanding of cyber intrusion. This study investigated the extent of how much exposed the petrochemical process control system is to security threats and suggested practical measures to reduce OT cybersecurity vulnerabilities. To identify the cyber threat status of process control systems, vulnerabilities of the Windows platform, a principal cyber threat factor, have been analyzed. For research, three major DCS providers in Korea and the discontinuation of Windows platform of 635 control systems were investigated. It was confirmed that 78% of the survey subjects were still operating in the discontinued windows platforms, and those process control systems were operated in a state vulnerable to cyber intrusions. In order to actively cope with these cyber threats, legal regulations such as designation of critical infrastructure for major petrochemical facilities which is implemented in advanced countries such as the United States are needed. Additionally, it is necessary to take the initiative in eradicating security threats to the process control systems by aggressively introducing security solutions provided from existing DCS suppliers. This paper was submitted to Professor Ko JaeWook's retirement anniversary issue.