• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.5-10
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• 2005

We deal with the sliding mode control using the time delay estimation. The time delay estimation is able to weaken the need for obtaining a quantitative plant model analogous to the real plant so the sliding mode control with a time delay estimation (SMCTE) is very suitable for plant such as SMA actuators whose quantitative model is difficult to obtain. We have already studied the application of the time delay control (TDC) to SMA actuators in other literature. Based on the previous study on the TDC, we developed the gain tuning method for the SMCTE, which results were nearly the same as the TDC. With respect to the step response, the SMCTE proved its predominance in a comparison with other control schemes such as the PID control and the relay control. As well as the contribution of the above control methodology, the model identification for SMA actuators has also been studied. The dynamics for an SMA actuator was newly derived using the modified Liang's model. The derived dynamics showed a continuity at the change of the phase transformation process but the original Liang's model could not.

• 전기학회논문지
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• 제63권6호
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• pp.786-796
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• 2014

This paper presents a new approach to design a robust tracking controller for linear time-invariant systems with uncertain time-delay. By introducing the model following control (MFC) structure which consists of two loops in nature, we show that the controller is capable of having a predictive control action and effectively tracking the reference output with a desired transient response as well. Three design techniques to achieve good tracking performance are suggested. It is also analytically shown that the tracking performance of the proposed scheme is more robust than that of typical single-loop feedback structure. An illustrative example is given to compare the tracking performances of the proposed methods with a single loop method.

• 한국정보처리학회논문지
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• 제6권2호
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• pp.449-458
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• 1999

실시간 시스템에서 정확한 응답 시간과 통신상의 지연이 최소화 될 것이 요구된다. 그러나, 현재의 SNMP 프로토콜은 주기적인 자료 요청을 하는데 많은 통신량을 유발하며, 네트워크 자원을 비효율적으로 사용한다. 본 논문은 현재 사용중인 SNMP에 시간적 제약 조건을 수용할 수 있도록 확장한 실시간 SNMP의 구현에 대한 논문이다. 실시간 SNMP는 기존에 사용하던 SNMP가 주기적 요구 (periodic request)를 수행할 때 발생하는 통신상의 비효율성을 개선하였다. 이를 위해서는, 기존의 SNMP의 서버/클라이언트 방식의 기법에 변화를 주지 않고, 관리국 (Management station)이 Real-Time SNMP PDU를 에이전트에게 전송하며, 실시간 SNMP 에이전트 측에서 관리국에서 요청한 MIB에 대한 정보를 주기적으로 관리국으로 정보를 제공할 수 있게 하였다. 이러한 설계를 바탕으로 관리국과 에이전트 사이의 요구에 대한 정확한 응답 시간(response time)을 제공할 수 있게 하여, 네트워크 관리의 효율을 높일 수 있는 방법을 본 논문에서는 제시하고, 실제 구현 환경에서의 실험을 통하여 성능이 개선됨을 보였다.

• 대한기계학회논문집A
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• 제21권12호
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• pp.2081-2089
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• 1997

Accurate positioning of the throttle valve of a gasoline engine is required to implement various systems such as traction control system(TCS), cruise control system and drive-by-wire system. In this research, position control system has been developed for the throttle actuator system that uses one throttle actuation for small volume and DC servo motor for fast response. In order to drive the DC motor, PWM signal generator and PWM amplifier were built and interfaced to the motor and controller. Also, time delay control(TDC) law has been used as a basic control algorithm. A method of varying the reference model of the TDC according to the size of change in target throttle angle is proposed here. The simulation and experimental results show that both overshoot prevention and fast response are achieved by the TDC technique with this variable reference model.

• Smart Structures and Systems
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• 제13권2호
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• pp.305-318
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• 2014

This paper numerically investigates the feasibility of an active mass damper (AMD) system using the time delay control (TDC) algorithm, which is one of the robust and adaptive control algorithms, for effectively suppressing the excessive vibration of a building structure under wind loading. Because of its several attractive features such as the simplicity and the excellent robustness to unknown system dynamics and disturbance, the TDC algorithm has the potential to be an effective control system for mitigating the vibration of civil engineering structures such as buildings and bridges. However, it has not been used for structural response reduction yet. In this study, therefore, the active control method combining an AMD system with the TDC algorithm is first proposed in order to reduce the wind-induced vibration of a building structure and its effectiveness is numerically examined. To this end, its stability analysis is first performed; and then, a series of numerical simulations are conducted. It is demonstrated that the proposed active structural control system can effectively reduce the acceleration response of the building structure.

• Journal of applied mathematics & informatics
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• 제17권1_2_3호
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• pp.361-377
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• 2005

A mathematical model dealing with a prey-predator system with disease in the prey is considered. The functional response of the predator is governed by a Hoilling type-2 function. Mathematical analysis of the model regarding stability and persistence has been performed. The effect of delay and diffusion on the above system is studied. The role of diffusivity on stability and persistence criteria of the system has also been discussed.

• International journal of advanced smart convergence
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• 제9권3호
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• pp.137-140
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• 2020

Orthogonal time frequency space (OTFS) modulation is considered as one of the solutions to cope with high mobility channel environments. It converts the time-varying channel to the near-constant channel response in the delay-Doppler domain. This modulation scheme also benefits from the diversity in two-dimensional modulation. According to recent researches, this method outperforms the conventional OFDM modulation, especially in high-speed channel conditions. In this paper, to investigate the performance of OTFS in a practical system, channel estimation in the delay-Doppler domain is compared with the conventional method in the time-frequency domain at different mobile speeds. Simulation results confirm that the delay-Doppler domain channel estimation brings a better performance compared to the conventional one under the same overhead rate.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제50권4호
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• pp.170-178
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• 2001

Deadbeat technique has been proposed as a digital controller for an UPS inverter to achieve the fast, response to a load variation and to conserve a very low THD under a nonlinear load condition. This scheme contains a fatal drawback, sensitivity against parameter variation and calculation time delay. This paper proposes a second order deadbeat controller, which fundamentally solves the calculation time delay problem and certainly guarantees the robustness of the parameter's variation. RLP(Repetitive Load Predictor) which predicts the load current ahead of two sampling time and FVR(Fundamental Voltage Regulator) which eliminates the fundamental errors of the output voltage are also proposed for the second order deadbeat controller to apply to UPS inverter systems. These are shown theoretically and practically through simulation and experiment.

• 한국콘텐츠학회논문지
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• 제2권4호
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• pp.51-58
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• 2002

전자상거래 사용자의 폭발적인 증가는 전자상거래 시스템의 급격한 로드 증가와 네트워크 트래픽을 증가시키고 있다. 또한 전자상거래 시스템에서 동영상을 포함한 자료가 점차 늘어나고 있고 이에 따라 인터넷 서비스 제공업자들은 시스템의 관리와 회선의 유지를 위해 막대한 비용을 지불하고 있다. 이러한 시스템의 로드와 네트워크의 트래픽 증가는 웹 고객의 서비스 요청에 대한 응답 속도의 지연을 가져오게 되며 이는 고객만족도를 감소시켜 e-비지니스 기업의 경쟁력을 떨어뜨리는 중대한 요인으로 작용하고 있다. 본 연구에서는 마이크로소프트사의 최신 버전인 닷넷을 기반으로 한 전자상거래 시스템에서, 응답 지연 속도를 개선한 전자상거래 시스템을 설계하고 실험을 통해 성능을 분석하였다. 실험 결과 제안한 시스템은 웹 고객의 다양한 요구에 대해 개선된 응답 속도와 빠른 적응성을 가질 수 있으며, 특히 전자상거래 시스템에 대해 동시에 발생하는 다수의 다중 사용자의 요구로 인해 발생되는 응답 속도의 지연을 막을 수 있을 것으로 기대된다.

• Journal of applied mathematics & informatics
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• 제33권5_6호
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• pp.559-578
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• 2015

Human Immune Deficiency Virus (or simply HIV) induces a persistent infection that leads to AIDS causing death in almost every infected individual. As HIV affects the immune system directly by attacking the CD4+ T cells, to exterminate the infection, the natural immune system produces virus-specific cytotoxic T lymphocytes(CTLs) that kills the infected CD4+ T cells. The reduced CD4+ T cell count produce reduced amount of cytokines to stimulate the production of CTLs to fight the invaders that weakens the body immunity succeeding to AIDS. In this paper, we introduce a mathematical model with discrete time-delay to represent this cell dynamics between CD4+ T cells and the CTLs under HIV infection. A modified functional form has been considered to describe the infection mechanism. Characteristics of the system are studied through mathematical analysis. Numerical simulations are carried out to illustrate the analytical findings.