• Journal of Communications and Networks
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• 제14권6호
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• pp.597-605
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• 2012

With the smart grid coming near, wide-area supervisory control and data acquisition (SCADA) becomes more and more important. However, traditional SCADA systems are not suitable for the openness and distribution requirements of smart grid. Distributed SCADA services should be openly composable and secure. Event-driven methodology makes service collaborations more real-time and flexible because of the space, time and control decoupling of event producer and consumer, which gives us an appropriate foundation. Our SCADA services are constructed and integrated based on distributed events in this paper. Unfortunately, an event-driven SCADA service does not know who consumes its events, and consumers do not know who produces the events either. In this environment, a SCADA service cannot directly control access because of anonymous and multicast interactions. In this paper, a distributed security framework is proposed to protect not only service operations but also data contents in smart grid environments. Finally, a security implementation scheme is given for SCADA services.

• 한국지진공학회논문집
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• 제8권4호
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• pp.51-62
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• 2004

사장교의 지진응답 제어를 위한 퍼지관리제어기법에 대하여 연구하였다. 제시하는 방법은 복합제어방법의 하나로서, 여러 개의 최적제어기로 이루어진 하부제어기와 퍼지관리자로 구성되는 계층적인 구조를 가진다. 하위제어기들은 사장교의 주요 지진응답들을 저감시키도록 각각 독립적으로 설계되며, 퍼지관리자는 설계된 하위제어기들의 참여율을 조절함으로써 향상된 제진성능을 확보한다. 이는 하위제어기의 정적 제어이득을 퍼지추론과정에 기반하여 실시간으로 변화하는 동적 제어이득으로 변화함으로써 이루어진다. 제안하는 방법으리 적용성을 평가하기 위하여 Dyke 등이 제안한 사장교의 벤치마크 제어문제를 설계 예로 고려하였으며, 사장교 지진응답제어를 위한 제어변수로는 주탑하부의 전단력과 휨모멘트, 주탑상부의 수평변위 및 테크 주탑간 상대변위, 그리고 케이블의 장력을 선정하였다. 벤치마크 사장교에 대하여 제안한 퍼지관리제어기 및 최적제어이론에 기반한 LQG 제어기의 제어성능 비교로부터 제시하는 기법의 효율성을 검증하였다.

• Journal of Electrical Engineering and Technology
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• 제9권3호
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• pp.1096-1103
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• 2014

This paper proposes a novel strategy for attenuating the output power fluctuation of the wind farm (WF) in a range of tens of seconds delivered to the grid, where the kinetic energy caused by the large inertia of the wind turbine systems is utilized. A control scheme of the two-level structure is applied to control the wind farm, which consists of a supervisory control of the wind farm and individual wind turbine controls. The supervisory control generates the output power reference of the wind farm, which is filtered out from the available power extracted from the wind by a low-pass filter (LPF). A lead-lag compensator is used for compensating for the phase delay of the output power reference compared with the available power. By this control strategy, when the reference power is lower than the maximum available power, some of individual wind turbines are operated in the storing mode of the kinetic energy by increasing the turbine speeds. Then, these individual wind turbines release the kinetic power by reducing the turbine speed, when the power command is higher than the available power. In addition, the pitch angle control systems of the wind turbines are also employed to limit the turbine speed not higher than the limitation value during the storing mode of kinetic energy. For coordinating the de-rated operation of the WT and the storing or releasing modes of the kinetic energy, the output power fluctuations are reduced by about 20%. The PSCAD/EMTDC simulations have been carried out for a 10-MW wind farm equipped with the permanent-magnet synchronous generator (PMSG) to verify the validity of the proposed method.

• 디지털산업정보학회논문지
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• 제5권2호
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• pp.123-131
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• 2009

Process Control Systems (PCSs) or Supervisory Control and Data Acquisition (SCADA) systems have recently been added to the already wide collection of wireless sensor networks applications. The PCS/SCADA environment is somewhat more amenable to the use of heavy cryptographic mechanisms such as public key cryptography than other sensor application environments. The sensor nodes in the environment, however, are still open to devastating attacks such as node capture, which makes designing a secure key management challenging. Recently, Nilsson et al. proposed a key management scheme for PCS/SCADA, which was claimed to provide forward and backward secrecies. In this paper, we define four different types of adversaries or attackers in wireless sensor network environments in order to facilitate the evaluation of protocol strength. We then analyze Nilsson et al. 's protocol and show that it does not provide forward and backward secrecies against any type of adversary model.

• 제어로봇시스템학회논문지
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• 제7권5호
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• pp.375-383
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• 2001

As many industrial systems become more complex, it becomes extremely difficult to diagnose the cause of failures. This paper presents a failure diagnosis approach based on discrete event system theory. In particular, the approach is a hybrid of event-based and state-based ones leading to a simpler failure diagnoser with supervisory control capability. The design procedure is presented along with a pump-valve system as an example.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2008년도 한국컴퓨터종합학술대회논문집 Vol.35 No.1 (B)
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• pp.473-478
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• 2008

산업계에서의 제어시스템(Control System)은 크게 SCADA(Supervisory Control And Data Acquisition) 시스템, 분산 제어시스템(Distributed Control System, DCS), PLC 시스템 (Programmable Logic Controller System)으로 분류할 수 있다. 특히 전력분야의 SCADA 시스템은 목적상 실시간의 대규모 측정 정보 취득을 목적으로 운영되며, 실시간 및 이력 데이터베이스, 원격 데이터 취득, 다양한 데이터 처리, Supervisory Control 등 복잡한 기능과 다양한 전력시스템과의 정보교환이 요구된다. 다양한 전력시스템과의 정보 교환을 위한 표준화 요구에 부응하여, 향후 전력시스템은 표준화되고 공개된 정보모델을 활용한 통합시스템 개발이 요구된다. 본 논문에서는 전력 공통정보모델(CIM)과 애플리케이션 통합 정보기술을 이용한 전력시스템의 메시지 통합버스 설계에 대하여 기술하고자 한다.

• 제어로봇시스템학회논문지
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• 제15권4호
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• pp.396-399
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• 2009

This paper presents the notion of time-coobservability as a core condition far the existence of a decentralized supervisor achieving a given language specification in a timed discrete event system (TDES). A TDES is modeled by the framework of Brandin & Wonham [5], and the decentralized supervisory control architecture presented is extended from the untimed architecture of Yoo & Lafortune [1]. To develop the time-coobservability of a language specification, specifically this paper presents the C&P time-coobservability and D&A time-coobservability in the consideration of the event tick and forcing mechanism of decentralized supervisors.

• Journal of information and communication convergence engineering
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• 제7권4호
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• pp.521-524
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• 2009

Park proposed a forward & backward Secure key management scheme in wireless sensor networks for Process Control Systems (PCSs) or Supervisory Control and Data Acquisition (SCADA) systems [7]. The scheme, however, is still vulnerable to an attack called "sandwich attack": two nodes captured at times $t_1$ and $t_2$, respectively, surrenders all the group keys used between times $t_1$ and $t_2$. In this paper, we propose a fix to the scheme, which can limit the vulnerable time duration to an arbitrarily chosen time span while keeping the forward and backward secrecy of the scheme untouched.

• Journal of information and communication convergence engineering
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• 제7권2호
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• pp.98-106
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• 2009

Process Control Systems (PCSs) or Supervisory Control and Data Acquisition (SCADA) systems have recently been added to the already wide collection of wireless sensor networks applications. The PCS/SCADA environment is somewhat more amenable to the use of heavy cryptographic mechanisms such as public key cryptography than other sensor application environments. The sensor nodes in the environment, however, are still open to devastating attacks such as node capture, which makes designing a secure key management challenging. In this paper, a key management scheme is proposed to defeat node capture attack by offering both forward and backward secrecies. Our scheme overcomes the pitfalls which Nilsson et al.'s scheme suffers from, and is not more expensive than their scheme.

• 제어로봇시스템학회논문지
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• 제20권10호
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• pp.995-1001
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• 2014

In the aftermath of the financial crisis of 2008, while numerous members of the general public lost their homes and jobs, many of the largest banks held responsible for the crisis have been successfully rescued by bailouts. In this paper, through the analysis of income inequality, unemployment, tax cuts, and bailouts, we show that the interests of the general public are different from the interests of politicians and bankers. While the small elite group of politicians and bankers could set the deregulation policies with inordinate power based on full information, most people were ignorant and unconcerned about the policies, and hence did not oppose them. Specifically, we model the credit change in the financial markets of the United States by a finite state machine, and design three local supervisors representing three groups with different interests. It is then shown that the deregulation policies were adopted according to the difference of the supervisors' powers.