• 전자공학회논문지B
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• 제33B권8호
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• pp.124-133
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• 1996

This paper presents the implementation of variable structure control system for a linear or nonlinear system using neural networks. The overall control system consists of neural network controller and a reaching mode controller. While the former approximates the equivalent control input on the sliding surface, the latter is used to bring the entire system trajectories toward the sliding surface. No supervised learning procedures are needed and the weights of the neural network are tuned on-line automatically. The neural netowrk-based variable structure control system is applied to a nonlinare unstable inverted pendulum system through computer simulations, and implemented using a microcomputer (80486-50MHz) and applied to the DC servomotor position control system. Simulation and experimental results show the expected approximation sliding property is occurred. The proposed controller is compared with a PID controller and shows better performance than the PID controller in abrupt plant parameter change.

• 전자공학회논문지B
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• 제32B권8호
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• pp.1119-1126
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• 1995

The construction of rule-base for a nonlinear time-varying system, becomes much more complicated because of model uncertainty and parameter variations. Furthemore, FLC does not have an ability of adjusting rule- base in responding to some sudden changes of control environments. To cope with these problems, an auto-tuning method of the fuzzy rule-base is required. In this paper, the GA-based Fuzzy-Neural control system combining Fuzzy-Neural control theory with the genetic algorithm(GA), which is known to be very effective in the optimization problem, will be proposed. The tuning of the proposed system is performed by two tuning processes(the course tuning process and the fine tuning/adaptive learning process). The effectiveness of the proposed control system will be demonstrated by computer simulations using a two degree of freedom robot manipulator.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권8호
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• pp.500-508
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• 2004

This paper presents a new sensorless vector control system for high performance induction motor drives fed by a matrix converter with non-linearity compensation and disturbance observer. The nonlinear voltage distortion that is caused by commutation delay and on-state voltage drop in switching device is corrected by a new matrix converter modeling. The lumped disturbances such as parameter variation and load disturbance of the system are estimated by the radial basis function network (RBFN). An adaptive observer is also employed to bring better responses at the low speed operation. Experimental results are shown to illustrate the performance of the proposed system.

• 대한기계학회논문집B
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• 제20권8호
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• pp.2572-2592
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• 1996

A low-Reynolds-number second moment turbulence closure was developed with the aid of DNS data. Model coefficients of nonlinear return to isotropy term were derived by use of Cayley-Hamilton theorem and two component turbulence limit condition as the functions of invariances of anisotropy and turbulent Reynolds number. Launder and Tselepidakis' cubic mean pressure strain model was modified to fit the predicted pressure-strain components to the DNS data. Two component turbulence limit condition was the precondition to be satisfied in developing the second moment turbulence closure for the realizable Reynolds stress prediction. But the satisfactions of Reynolds stress level and pressure-strain level of each component were compromised because the satisfaction of both levels was impossible.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권7호
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• pp.468-474
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• 2000

This paper presents an investigation of the parameter modeling on the basis of Finite Element (FE) analysis in which the variable frequency characteristic in field weakening is considered in Interior Permanent Magnet Synchronous Motors (IPMSM). The parameters of IPMSM have nonlinear characteristics not only in accordance with the load variation but also with the current phase angle of a system fed inverter. From the results of FE analysis, the performances of torque and speed-power are simulated and the validity of the proposed FE analysis is compared with experimental results.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권11호
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• pp.763-770
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• 2000

The speed and position information of the rotor are required in the speed control of SRM(Switched Reluctance Motors). This information is generally provided by shaft encoder or resolver. It is weak in the dusty, high temperature, and EMI environment. Consequntly, much attention has been given to SRM control for eliminationating the position and speed sensors. In this paper, a new estimation algorithm for the rotor position and speed for SRM drives is described. The algorithm is implemented by the sliding mode observer. The stability and robustness of the sliding observer for the parameter variations of the SRM are proved by variable structure control theory. Speed control of the SRM is accomplished by the estimated speed and position. Experiment results verify that the mode observer is able to estimate the speed and position well.

• 천문학회지
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• 제33권1호
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• pp.47-55
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• 2000

Nonpotential characteristics of magnetic fields in AR 5747 are examined using Mees Solar Observatory magnetograms taken on Oct. 20, 1989 to Oct. 22, 1989. The active region showed such violent flaring activities during the observational span that strong X-ray flares took place including a 2B/X3 flare. The magnetogram data were obtained by the Haleakala Stokes Polarimeter which provides simultaneous Stokes profiles of the Fe I doublet 6301.5 and 6302.5. A nonlinear least square method was adopted to derive the magnetic field vectors from the observed Stokes profiles and a multi-step ambiguity solution method was employed to resolve the $180^{\circ}$ ambiguity. From the ambiguity-resolved vector magnetograms, we have derived a set of physical quantities characterizing the field configuration, which are magnetic flux, vertical current density, magnetic shear angle, angular shear, magnetic free energy density, a measure of magnetic field discontinuity MAD and linear force-free coefficient. Our results show that (1) magnetic nonpotentiality is concentrated near the inversion line in the flaring sites, (2) all the physical parameters decreased with time, which may imply that the active region was in a relaxation stage of its evolution, (3) 2-D MAD has similar patterns with other nonpotential parameters, demonstrating that it can be utilized as an useful parameter of flare producing active region, and (4) the linear force-free coefficient could be a evolutionary indicator with a merit as a global nonpotential parameter.

• 한국정보통신학회논문지
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• 제7권2호
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• pp.276-283
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• 2003

본 논문은 IMT-2000 단말기용 전력증폭기의 선형성을 증가시키기 위해 기존의 선형화 기법을 사용하는 대신 선형성이 우수한 Infineon 사의 SiGe HBT를 이용하여 IMT-2000 단말기용 2단 전력증폭기를 설계하고 제작하였다. HBT의 비선형 모델은 Gummel-Poon 모델을 이용하였으며, 등가모델을 이용하여 회로 시뮬레이터인 ADS를 사용하여 DC I-V 특성과 입ㆍ출력측의 S-파라미터 특성을 살펴보았다. 시뮬레이션한 S-파라미터를 이용하여 2단 전력증폭기의 첫째단은 고이득 조건으로 정합하고, 둘째단은 고출력 조건으로 정합하였다. 시뮬레이션 결과를 바탕으로 hybrid 형태로 제작한 2단 전력증폭기는 IMT-2000 상향 주파수 대역인 1920∼1980MHz에서 27.1dBm의 출력전력과 18.9dB의 전력이득, 20dB의 ACLR, 34%의 전력부가효율을 얻었다.

• 정보처리학회논문지B
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• 제12B권5호
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• pp.567-576
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• 2005

다중영상으로부터 투사 선분을 이용하여 3D 모델을 생성하고 각 면의 텍스쳐를 획득하는 구조 복원 기법을 제안한다 사용자는 매우 단순한 절차를 통해 정확한 3D 모델 데이터를 획득할 수 있다. 모델 파라메터 추정을 위해 내재된 비선형 최적화 방법은 사용자 지정 영상 선분과 모델의 투사 선분의 거리를 최소화하는 방법에 기반하고 있다. 모델링 기법의 기능적 주요 목표는 형상이 포함된 다중 영상으로부터 그 형상의 3차원 구조를 복원하고 각 면의 텍스쳐를 생성하는 것이다. 본 연구에서는 3D 정형체를 사용하여 사용의 편리성을 증대시킬 수 있고 정형체의 파라메터의 오차를 최소화하여 복원된 구조의 정확성을 높이는 방법을 제시한다. 제안된 방법은 유한 선분에 기반한 오차 함수를 도입하여 무한 직선에 기반한 방법보다 정확한 모델링이 가능하다. 제안된 방법을 다양한 실제 영상에 적용한 실험 결과를 제시하고 다중 영상기반 모델링 도구의 개발 과정에서의 기술적인 문제점과 해결책을 기술한다.

• 대한수학회보
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• 제55권6호
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• pp.1891-1908
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• 2018

In this paper, we investigate the existence of an S-shaped connected component in the set of positive solutions of the Dirichlet problem of the one-dimension Minkowski-curvature equation $$\{\(\frac{u^{\prime}}{\sqrt{1-u^{{\prime}2}}}\)^{\prime}+{\lambda}a(x)f(u)=0,\;x{\in}(0,1),\\u(0)=u(1)=0$$, where ${\lambda}$ is a positive parameter, $f{\in}C[0,{\infty})$, $a{\in}C[0,1]$. The proofs of main results are based upon the bifurcation techniques.