• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 B
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• pp.1377-1379
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• 1996

In this paper, each parameter was identified by the gradient descent method to overcome difficulty deciding fuzzy rules of FLC for the unknown process and the type of membership Junctions. Usually PID or optimal control theories have been mostly usee in control field so far. However, optimal control requires much time for calculation because of adaptation for disturbance and nonlinearity. And intricate technique such as MRAS which can be realized only by an expert are limited to be used in the systems requiring rapid and precise response because of comparatively longer calculating time and complicateness. Gradient descent method is a method to find Z minimizing a function about a certain vector Z. And required output of FLC is gained using gradient approaching method in order to adapt control rule parameters of FLC. Simulation proved validation of this algorithm.

• 비파괴검사학회지
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• 제34권3호
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• pp.220-225
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• 2014

초음파 비선형 특성은 일반적으로 재료 내부를 전파한 초음파의 기본주파수 및 2차 고조파 성분 크기에 의해 결정되는 비선형 파라미터 ${\beta}$로 측정되며, 재료의 미세한 변질을 평가하는데 효과적인 인자로 알려져 있다. 이에 본 연구에서는 인공시효된 Al6061-T6의 열처리 시간에 따른 초음파 비선형 특성을 평가하였다. 초음파가 시편을 투과하여 수신되는 신호를 분석하여 비선형 파라미터 ${\beta}$를 구하였고, 비선형 파라미터 측정 후 마이크로 비커스 경도를 측정하였다. 비선형 파라미터 측정 결과로부터 열처리 시간에 따른 재료 내 미세 구조적인 변화를 추정하였으며, 경도 측정 결과로부터 이러한 추정이 합당함을 증명하였다. 측정 결과 비선형 파라미터는 석출거동 메커니즘에 의한 재료 미세조직 변화와 매우 밀접한 상관관계를 나타냈다. 이로부터 초음파 비선형 파라미터를 이용하여 인공시효에 의한 재료 내 미세구조 및 상태 변화를 초음파 비선형 파라미터로 평가할 수 있음을 확인하였다.

• 비파괴검사학회지
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• 제33권2호
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• pp.193-197
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• 2013

본 연구에서는 열처리된 알루미늄 합금의 초음파 비선형 특성을 평가하였다. 초음파의 비선형성은 재료를 전파한 초음파의 2차고조파와 기본주파수 성분의 진폭비에 의존하는 비선형 파라미터 ${\beta}$로 측정하였다. 비선형 파라미터 ${\beta}$의 측정은 접촉식 탐촉자를 이용하여 동일 평면상에서 시편저면에서 반사된 신호로부터 구하였다. 열처리(시효)는 $300^{\circ}C$에서 1시간부터 50시간까지 다양한 유지시간동안 수행하였다. 인장시험으로부터 인장강도와 연신율을 구하고 비선형 파라미터와 비교하였다. 비선형 파라미터 ${\beta}$는 시효시간 5시간에서 피크를 나타내고 이후는 감소하였다. 이는 인장강도와 연신율의 변화와 밀접한 관련이 있는 것으로 나타났다. 또한 비선형 파라미터가 피크를 나타낸 열처리 시간과 인장곡선에서 최대변화가 나타난 열처리 시간이 일치하였다. 이 같은 결과는 알루미늄합금의 시효처리로 인한 강도 변화를 모니터링 하는데 초음파의 비선형성이 유용할 수 있음을 보여준다.

• Journal of the Optical Society of Korea
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• 제8권2호
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• pp.59-64
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• 2004

The response of a single-mode fiber to a sinusoidally modulated input has been studied to see its utility in measuring system performance in the presence of fiber nonlinearities. The sinusoidally modulated signal models an alternating bit sequence of ones and zeros in on-off keying. The sinusoidal response of normally dispersive fiber shows a strong correlation with eye-opening penalty (EOP) over a wide range of the nonlinearity parameter N (0.1 ＜ N$^2$＜ 100). This result implies that the measurement of the sinusoidal response can be an alternate way of measuring EOP without having a long sequence of randomly modulated input bits. But in the anomalous dispersion region, the sinusoidal response has a much more limited range of application to estimate system performance.

• Journal of Power Electronics
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• 제14권1호
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• pp.125-134
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• 2014

This paper presents a robust and speed-sensorless stator flux estimation for induction motor direct torque control. The proposed observer is based on sliding mode approach. Stator electrical equations are used in the rotor orientation reference frame to eliminate the observer dependence on rotor speed. Lyapunov's concept for systems stability is adopted to confine the observer gain. Furthermore, the sensitivity of the observer to parameter mismatch is recovered with an adaptation technique. The nonlinearities of the pulse width modulation voltage source inverter are estimated and compensated to enhance stability at low speeds. Therefore, a new method based on the model reference adaptive system is proposed. Simulation and experimental results are shown to verify the feasibility and effectiveness of the proposed algorithms.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.699-703
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• 2004

The autopilot system targets decreasing labor, working environment, service safety security and elevation of service efficiency. Ultimate purpose is minimizing number of crew for guarantee economical efficiency of shipping service. Recently, being achieving research about Course Keeping Control, Track Keeping Control, Roll-Rudder Stabilization, Dynamic ship Positioning and Automatic Mooring Control etc. which compensate nonlinear characteristic using optimizing control technique. And application research is progressing using real ship on actual field. Relation of Rudder angle which adjusted by Steering Machine and ship-heading angle are non-linear. And, Load Condition of ship acts as non-linear element that influence to Parameter of ship. Also, because the speed of a current and direction of waves, velocity and quantity of wind etc. that id disturbance act in non-linear form, become factor who make service of shipping painfully. Therefore, service system of shipping requires robust control algorithm that can overcome nonlinearity. In this paper, Using GA algorithm,design autopilot system of ship that could overcome the non-linear factor of ship and disturbance and examined result through simulation.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.627-630
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• 2004

The PID type controller has been widely used in industrial application due to its simply control structure, ease of design, and inexpensive cost. However, control performance of the PID type controller suffers greatly from high uncertainty and nonlinearity of the system, large disturbances and so on. This paper presents a hybrid fuzzy logic proportional plus conventional integral derivative controller (fuzzy P+ID). In comparison with a conventional PID controller, only one additional parameter has to be adjusted to tune the fuzzy P+ID controller. In this case, the stability of a system remains unchanged after the PID controller is replaced by the fuzzy P+ID controller without modifying the original controller parameters. Finally, the proposed hybrid fuzzy P+ID controller is applied to BLDC motor drive. Simulation results demonstrated that the control performance of the proposed controller is better than that of the conventional controller.

• Journal of Power Electronics
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• 제15권5호
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• pp.1358-1366
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• 2015

This study focuses on an advanced second-order sliding mode control strategy for a variable speed wind turbine based on a permanent magnet synchronous generator to maximize wind power extraction while simultaneously reducing the mechanical stress effect. The control design based on a modified version of the super-twisting algorithm with variable gains can be applied to the cascaded system scheme comprising the current control loop and speed control loop. The proposed control inheriting the well-known robustness of the sliding technique successfully deals with the problems of essential nonlinearity of wind turbine systems, the effects of disturbance regarding variation on the parameters, and the random nature of wind speed. In addition, the advantages of the adaptive gains and the smoothness of the control action strongly reduce the chatter signals of wind turbine systems. Finally, with comparison with the traditional super-twisting algorithm, the performance of the system is verified through simulation results under wind speed turbulence and parameter variations.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.1924-1929
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• 1991

The conventional sliding mode control and variable structure control (VSC) of nonlinear uncertain system are well known for their robust property and simplity of control law. However, the use of them is only pardonable on the assumption that the upper-bound of parameter variation or nonlinearity is known and that the complete information about state is available. Though the former has been solved with adaptive robust control theory recently, the latter seems not to be solved. In this paper, we try to solve this problem using the technique of VSS adaptive robust control theory. That is, we propose a VSS adaptive observer and a sliding mode control incorporated with this observer. We can prove the robust stability of the closed system applying the Lyapunov's second method.

• 천문학회보
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• 제40권2호
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• pp.33.2-33.2
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• 2015

The color distribution functions (CDFs) of globular clusters (GCs) in individual early-type galaxies show great diversity in their morphology. Based on the conventional "linear" relationship between colors and metallicities of GCs, the inferred GC metallicity distribution functions and thus their formation histories should be as diverse as they appear. In contrast, an alternative scenario rooted in the "nonlinear" nature of the color-to-metallicity transformation finds the various CDFs pointing systematically to a simple picture, i.e., such a high degree of variety stems predominately from only one parameter, the mean metallicity of GCs. The simulated CDFs of GCs aimed to reproduce 67 massive early-type galaxies from the ACS Virgo & Fornax Cluster Survey show that over 70% of the CDFs concur fully with the nonlinearity scenario. We discuss our new findings in terms of early-type galaxy formation in the cluster environment.