• 전력전자학회논문지
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• 제12권4호
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• pp.318-323
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• 2007

본 논문에서는 영구자석형 5상 전동기(Five-phase permanent magnet motor)의 약계자 제어에 대한 연구를 수행한다. 제안된 전동기는 집중권 방식의 권선분포를 가지고 있고 사다리꼴 형태의 역기전력을 나타내고 있으며, 사다리꼴 형태의 전류를 인가하기 위하여 사인파의 기본파 성분에 3고조파 성분을 첨가하였다. 따라서 BLDC 전동기(Brushless dc motor)와 등가적으로 같은 평균토크를 발생시키면서 BLDC 전동기의 단점을 극복할 수 있었다. 전동기 전류의 토크성분과 자속성분은 다중 레퍼런스 프래임을 이용하여 분리할 수 있었으며, 결과적으로 쉽게 벡터제어가 이루어질 수 있었다. 사용된 전동기는 고속영역에서부터 저속영역까지 BLDC 전동기와 같이 높은 토크 밀도를 가지며, 약계자 영역이나 고속영역에서 영구자석형 전동기와 같이 제어의 용이함을 가진다는 장점을 가지고 있으며 실험결과를 통하여 제안된 전동기와 알고리즘을 검증하였다.

• 전력전자학회논문지
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• 제4권5호
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• pp.462-473
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• 1999

디지털 제어 방식으로 구동되는 모든 교류 전동기 벡터제어시스템의 근간을 이루는 전류 측정에 관한 문제를 다룬다. 일반적인 펄스폭 변조 방식 교류 전동기 구동 시스템에서 전동기 전류에 포함된 인버터 스위칭 노이즈를 없애기 위하여 저역 통과 필터를 사용하는데 이러한 필터는 필연적으로 측정된 신호의 시간 지연을 유발하게 된다. 따라서 샘플링한 전류값에는 기본파 성분 뿐만아니라 고조파 리플 성분이 포함된다. 본 논문에서는 3상 대칭 펄스폭 변조시 기준 전압 벡터의 위치에 다른 전류 샘플링 오차를 해석적으로 구하고 이러한 샘플링 오차를 최소화하기 위한 기법을 제안한다. 제안된 지연 보상 샘플링 기법을 사용하면 정상 상태 전류 측정 오차를 최소화할 수 있고 보다 정확한 토오크 제어가 가능하게 됨을 시뮬레이션과 실험을 통해 보였다.

• 전기학회논문지
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• 제63권10호
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• pp.1377-1383
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• 2014

This paper deals with eddy current loss of magnetic coupling with radial permanent magnet (PM) using analytical method such as a space harmonic method. Superposition of two kinds analysis model is used to analyze eddy current loss induced in inner PM and outer PM of magnetic coupling. When the eddy current is induced, the environmental temperature increases, and the permanent magnet(PM) characteristics are degraded because the performance of PM is greatly influenced by temperature rise. Hence, the calculation of eddy current loss becomes an important factor in the magnetic coupling. In order to analyze eddy current loss, first, on the basis of the magnetic vector potential and two-dimensional(2-D) polar-coordinate system, the magnetic field solutions of the radial magnetized PM are obtained. And we obtain the analytical solutions for the eddy current density produced by permanent magnet. Lastly, analytical solutions for eddy current loss are derived by using equivalent, electrical resistance calculated from magnet volume and analytical solution for eddy current density. This analytical results are validated by comparing with the 2-D finite element analysis (FEA).

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.561-562
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• 2008

The numerical analysis of sound radiation by vibrating structure is a well known and mature technology used in many industries. Accurate methods based on the boundary or finite element method have been successfully developed over the last two decades and are now available in standard CAE tools. These methods are however known to require significant computational resources which, furthermore, very quickly increase with the frequency of interest. The low speed of most current methods is a main obstacle for a systematic use of acoustic CAE in industrial design processes. In this paper we are going to present a set of innovative techniques that significantly speed-up the calculation of acoustic radiation indicators (acoustic pressure, velocity, intensity and power; contribution vectors). The modeling is based on the well known combination of finite elements and infinite elements but also combines the following ingredients to obtain a very high performance: o a multi-frontal massively parallel sparse direct solver; o a multi-frequency solver based on the Krylov method; o the use of pellicular acoustic modes as a vector basis for representing acoustic excitations; o the numerical evaluation of Green functions related to the specific geometry of the problem under investigation. All these ingredients are embedded in the ACTRAN/AR CAE tool which provides unprecedented performance for acoustic radiation analysis. The method will be demonstrated on several applications taken from various industries.

• 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.

• 전기의세계
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• 제29권4호
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• pp.247-255
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• 1980

In this study, an application of Finite Element Method which, in principle, based on variational calculus has been presented for the two-dimensional analysis of magnetic flux distribution in the shell type core of single phase transformer. The necessary stationarity condition of energy functional and boundary conditions were determined under the assumptions that the electromagnetic field considered is stationary and that the effect of eddy current is negligible. In the process of application the domain of magnetic field was divided into triangle subsectional elements and then the matrix equations were constructed for the respective triangular element and for those of all after the manipulation of minimization process to the vector potential of magnetic field at the each vertex of the element. Furthermore the numerical computation for the equations was guided by the Gaussian Elimination Methods. As the results obtained, it is found that the aspect of magnetic flux distribution inside the core as well as the leakage flux profile at the vicinity of the inner leg of the core is not much different from the well-known distribution profile of magnetic flux, however, the procedure shows to possess the merit of the uniquely deterministic nature for the flux distribution at the desired points.

• 동력기계공학회지
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• 제21권2호
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• pp.48-56
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• 2017

The steady-state, incompressible and three-dimensional numerical analysis was carried out to evaluate the velocity fields around the seabed tiller used for the improvement of the seabed soil and the pulling force and buoyancy generated by driving the seabed tiller. The turbulence model used in this study is a realizable $k-{\varepsilon}$ well known to be excellent for predicting the performance of the flow separation and recirculation flow as well as the boundary layer with rotation and strong back pressure gradient. As a results, a typical vortex pair appears near the adjacent rotor vane tip. When the current is stopped, there is no force when pulling the seabed tiller, but when the current flows at 1.2 knots, the force acts on the downstream side and the pulling force is much greater. In stationary currents, the buoyancy of the seabed tiller acts more strongly towards the seabed as the number of rotations of the rotor increases, but acts more strongly toward the sea surface at 1.2 knots of current.

• Journal of Power Electronics
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• 제9권5호
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• pp.781-790
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• 2009

This paper presents an implementation of a direct active and reactive power control for a doubly fed induction generator (DFIG), which is applied to a wind generation system as an alternative to the classical field-oriented control (FOC). The FOC has a complex control structure that consists of a current controller, a power controller and frame transformations. The performance of the FOC depends highly on parameter variations of the rotor and stator resistances and the inductances. The proposed direct power control (DPC) method produces a fast and robust power response without the need of complex structure and algorithms. One drawback, however, is its high power ripple during a steady state. In this paper, active and reactive power controllers and space-vector modulation (SVM) are combined to replace hysteresis controllers used in the original DPC drive, resulting in a fixed switching frequency of the power converter. Simulation results with the FOC and DPC for a 3kW DFIG are given and discussed, and the experimental results of a test involving identical machines are presented to illustrate the feasibility of the proposed control strategy.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2014년도 춘계학술대회
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• pp.391-394
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• 2014

본 논문에서는 DSP(TMS320F28335)를 이용하는 홀센서 타입의 다극 BLDC 전동기의 벡터 구동을 위한 회전자의 절대위치를 결정하는 방법을 소개하고, 기존 방법의 문제점을 보완하기 위한 알고리즘을 구현 한다. 모터의 각 상에 원하는 교류 전류를 공급하기 위한 전압원 인버터의 스위칭 방법으로 공간벡터 변조방식을 이용하였다. 또한 속도 영역의 증가를 위해 약계자 제어 기법을 사용 하였다. 제안된 알고리즘을 검증하기 위해 보상 전후의 계산된 Iqe, Ide 및 상전류를 비교한다.

• 대한원격탐사학회지
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• 제26권2호
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• pp.209-220
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• 2010

해양현상을 이해하기 위한 관측분야의 노력 중에서 해류 정보의 생산은 가장 어려운 작업 중의 하나이다. 이를 극복하기 위한 대안으로서 연속 화상 자료로부터 해류벡터를 추정하려는 많은 연구들이 진행 되고 있다. 본 연구에서는 한반도 주변의 SeaWiFS (Sea-viewing Wide Field-of-view Sensor) chlorophyll-a 해색 자료와 AVHRR/SST 를 이용하여 연속 화상 사이의 유사한 형태를 추적하는 최대상 관계수법을 사용한 표층 유속 벡터의 추정을 시도하였다. 한국의 남해역에서 적용한 유속 벡터 결과는 해면 고도계를 이용한 지형류, ADCP 관측 결과와 비교하여 유속은 약 15% 정도 작고, 유향은 약 $36^{\circ}$의 차이로 근접하여 기존 연구 결과에 비해 양호하게 나타났다. 이는 향후 GOCI 자료의 응용적 측면에서 매우 고무적이다.