• Journal of Institute of Control, Robotics and Systems
• /
• v.13 no.1
• /
• pp.1-5
• /
• 2007

Many nonlinear controllers for the power system are based on nonlinear models involving the power angle as an element of the state, and therefore the reference value for the power angle is needed. As this reference value is not generally available, it is difficult to apply such nonlinear control methods in practice. To deal with this problem, we present an input-output feedback linearizing control scheme by selecting the output as a combination of the squared voltage and the relative frequency. It is shown that the internal dynamics are locally stable with controllable damping, and that the frequency remains bounded for all time. Simulations illustrate the effectiveness of the proposed method.

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.39 no.10
• /
• pp.1029-1036
• /
• 1990

This paper presents a systematic study for control loops in the induction motor drive system employing a load commutated current source inverter (LCCSI) which has appeared since the early 1980's, and their effects on the dynamic stability of the system. A set of dq equations which amalgamate the overall system is developed, and from the equations it is revealed that the steady state characteristics of the LCCSI-induction motor system are between VSI and ASCI. When the speed control loop is constructed without a speed sensor, the evaluation of the pole/zero locations and the assessment of the stability for the added loops are investigated. We also show that the V/F loop is essential in this type of drive without the speed sensor.

• Proceedings of the KIEE Conference
• /
• 2002.11c
• /
• pp.35-38
• /
• 2002

In this paper, the design of explicit rate-based congestion control in high speed communication networks is considered. The goal of congestion control is to achieve high link utilization, low packet loss, low delay, and fairness among the best-effort sources. To deal with the propagation delays associated with the best effort sources, An MPC technique is employed to solve the congestion problem[1] here. However, the problem with this method is that the closed loop performance relies highly on the knowledge of average service rate. This paper focuses on coping with the problem described above by using a CARIMA model for service rate(available rate).

• Proceedings of the KIEE Conference
• /
• 2002.11c
• /
• pp.54-57
• /
• 2002

In this paper model reference adaptive control (MRAC) of linear time-varying(LTV) systems is considered. MRAC for a linear time invariant(LTI) system does not assure the boundedness of the output and parameter estimation errors in the presence of time variations of the parameters. However, changing the adaptive laws such as use of $\sigma$-modification can result in the boundedness of the output and parameter estimation errors[5]. Together with the $\sigma$-modification in the adaptive law, we also modify the control law by adding an additional term to the standard control law. The additional term leads to smaller bounds of the output and parameter estimation errors when compared to the case where only the standard control law is applied.

• Proceedings of the Korean Society of Computer Information Conference
• /
• 2017.07a
• /
• pp.178-179
• /
• 2017

우리나라의 최대 철강회사인 포스코는 2005년부터 품질개선을 위해서 포스코 자체의 혁신방법론인 QSS+(Quick Six Sigma)을 개발하여 실시하고 있다. QSS+는 회사 전체 직원이 개선 실천 학습을 하고, 지속적인 낭비제거를 통해 부가가치를 창출하는 활동으로 '일상개선 활동, 과제 활동, 솔선/격려활동, 인재양성' 4개의 축으로 운영되고 있다. 또한 QSS+는 오랜 시간에 걸쳐 정착되어 정부 기관, 기업, 그룹사, 외주파트너사, 공급사 및 다양한 분야에서 우수 혁신 활동 사례로 벤치마킹을 실시하고 있다. 매년 현장에서 활동하는 포스코 QSS+ 현 수준을 정확히 판단하고 향후 방향성을 제시하는 QSS+ 충실도 평가 기준을 개선하기 위하여 AHP 분석 방법을 통해 평가 항목을 분석하고 현장이 반영된 'QSS+ 평가 기준'을 제시하고자 한다.

• Proceedings of the KIEE Conference
• /
• 1987.11a
• /
• pp.351-354
• /
• 1987

In this paper, an adaptive control scheme is applied to the speed control system of a synchronous AC servo motor. The adaptive control system using Ioannou's modified adaptation law is shown to be robustly stable in the presence of current control error and load torque disturbance. The computer simulation demonstrates the rapid compensation of rotor speed deviation due to load torque disturbance.

• Proceedings of the KIEE Conference
• /
• 2001.07a
• /
• pp.109-111
• /
• 2001

Modern power grids are becoming more and more stressed with the load demands increasing continually. Therefore large stressed power systems exhibit complicated dynamic behavior when subjected to small disturbance. Especially, it is needed to analyze special conditions which make small signal stability structure varied according to operating conditions. This paper shows that the relation between small signal stability and operating conditions can be predicted well using node-focus point and 1:1 resonance point. Also, the weak point which limits operating range can be identified by the analysis of resonance condition. The proposed method is applied to test systems, and the results illustrate its capabilities.

• Proceedings of the KIEE Conference
• /
• 1997.07a
• /
• pp.115-117
• /
• 1997

본 논문에서는 유도전동기의 적응 비선형 제어에 대해 논한다. 제어 목적은 회전자저항의 불확실성에도 불구하고 유도전동기의 속도 및 자속을 분리하여 제어하는 것이며, 이를 위해 백스테핑(Backstepping) 기법을 사용한 비선형제어기와 회전자 저항 추정기를 결합한다. 제안된 적응제어시스템은 내부의 모든 변수가 유계(Bounded)되어 있다는 점에서 안정하며, 더불어 그 개선된 성능을 모의실험을 통해 보인다.

• Journal of the Korea Society for Simulation
• /
• v.12 no.3
• /
• pp.83-94
• /
• 2003

For 24 hours-7 days service on distributed systems, a great deal of efforts are investigated on high availability for seamless operation. In this paper, we propose a dynamic reconfiguration framework of distributed systems, called "hot-swapping" framework. This framework allows us to upgrade and exchange a number of modules of a distributed system without stopping running service as well as the system itself. In order to hide the state of service operation, the framework employes the "proxy" design pattern. Our framework provides two types of proxies: a static proxy and a dynamic proxy, Static proxies can achieve fast execution time, but they need to be changed whenever any minor change exists in the related swappable module. Meanwhile, dynamic proxies takes longer execution time, but do not need to be changed under minor changes of swappable modules. We compare performances of static and dynamic proxies and also apply the framework to a real situation with security management modules. management modules.

• Proceedings of the Korea Society for Simulation Conference
• /
• 2003.06a
• /
• pp.115-119
• /
• 2003

It requires a great deal of efforts to maintain a distributed system. What is important here is that we should be able to upgrade/maintain a distributed system without stopping the system in operation. For this, what we need is a dynamic reconfigurable framework for highly available distributed systems. In this paper, we propose objects-hot-swapping methods as a solution to our problem. These methods permit us to dynamically upgrade/expand a system without stopping the system in operation. In addition, we analyze these methods and show that an approach based on proxy is the most efficient. Furthermore, we propose two proxy-based approaches: the first one based on the static proxy provides for a fast execution time but it is difficult to implement. The second one based on the dynamic proxy provides for a slow execution time but it is easier to implement. Finally, we propose a hot swapping framework for these static and dynamic proxy.