• 대한원격탐사학회지
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• 제19권5호
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• pp.381-392
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• 2003

Multi-temporal approaches using sequential data acquired over multiple years are essential for satisfactory discrimination between many land-cover classes whose signatures exhibit seasonal trends. At any particular time, the response of several classes may be indistinguishable. A harmonic model that can represent seasonal variability is characterized by four components: mean level, frequency, phase and amplitude. The trigonometric components of the harmonic function inherently contain temporal information about changes in land-cover characteristics. Using the estimates which are obtained from sequential images through spectral analysis, seasonal periodicity can be incorporates into multi-temporal classification. The Normalized Difference Vegetation Index (NDVI) was computed for one week composites of the Advanced Very High Resolution Radiometer (AVHRR) imagery over the Korean peninsula for 1996 ～ 2000 using a dynamic technique. Land-cover types were then classified both with the estimated harmonic components using an unsupervised classification approach based on a hierarchical clustering algorithm. The results of the classification using the harmonic components show that the new approach is potentially very effective for identifying land-cover types by the analysis of its multi-temporal behavior.

• 호남수학학술지
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• 제41권2호
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• pp.301-319
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• 2019

The aim of the paper is to characterize some curves with the help of their harmonic curvature functions. First of all, we have defined harmonic curvature function of an arbitrary curve and have re-determined the position vectors of helices in terms of their harmonic curvature functions in Galilean 3-space. Then, we have investigated the relation between rectifying curves and Salkowski (or anti-Salkowski) curves in Galilean 3-space. Furthermore, the position vectors of them are obtained via the serial approach of the curves. Finally, we have given some illustrated examples of helices and rectifying curves with some assumptions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권4호
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• pp.1961-1974
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• 2019

In this letter, a harmonic-mean-based dual-antenna selection scheme at relay node is proposed in two-way relaying networks (TWRNs). With well-designed distributed orthogonal concatenated Alamouti space-time block code (STBC), a dual-antenna selection problem based on the instantaneous achievable sum-rate criterion is formulated. We propose a low-complexity selection algorithm based on the harmonic-mean criterion with linearly complexity $O(N_R)$ rather than the directly exhaustive search with complexity $O(N^2_R)$. From the analysis of network outage performance, we show that the asymptotic diversity gain function of the proposed scheme achieves as $1/{\rho}{^{N_R-1}}$, which demonstrates one degree loss of diversity order compared with the full diversity. This slight performance gap is mainly caused by sacrificing some dual-antenna selection freedom to reduce the algorithm complexity. In addition, our proposed scheme can obtain an extra coding gain because of the combination of the well-designed orthogonal concatenated Alamouti STBC and the corresponding dual-antenna selection algorithm. Compared with the common-used selection algorithms in the state of the art, the proposed scheme can achieve the best performance, which is validated by numerical simulations.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1992년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 19-21 Oct. 1992
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• pp.1051-1059
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• 1992

Two types of digital repetitive control systems are analyzed and designed to reduce the error spectrum including not only harmonic but also non-harmonic components. First, a novel gain scheduling algorithm is suggested for conventional and modified repetitive controller is scheduled to reduce the infinite norm of error in frequency domain. For this, the relative error transfer function is mewly defined as the ratio of the error spectrum for the system with a repetitive controller to the error spectrum for the system with a repetitive controller to the error spectrum for the system without a repetitive controller. Secondly, as an alternative of a repetitive control system with the gain scheduling, a repetitive control system with higher order repetitve function is analyzed and designed, where instead of equal weightings, weightings of the higher order repetitive function is determined in such a way that the infinite norm of relative error transfer function is minimized. To show the validities of proposed methods, computer simulation results are illustrated for a typical disk drive head positioning servo system.

• 전기학회논문지P
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• 제63권4호
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• pp.277-282
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• 2014

Hybrid transformer means the distribution transformer, one of multi-function transformer equipped with the enhancement function of harmonics and unbalance. In other words, since existing transformer are equipped simply with transformation function only, a separated electric facility should be additionally installed in order to reduce the mutual harmonics and unbalance. Meanwhile, since hybrid transformer can perform the reduction of harmonics and unbalance as well as transformation function simultaneously through zigzag winding, it doesn't need any additional electric facility. This study addressed the issue of developing and testing the performance of a generator that would reduce the harmonics supplied to the grid when grid-connected with the output of a photovoltaic inverter for photovoltaic generation system.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 A
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• pp.214-216
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• 2005

A magnitude of generated harmonic currents along with the operation of traction has nonlinear characteristics. The harmonic currents generated along with the operating speed of electrical railroad traction is to analyze very difficulty. This paper therefore presents probabilistic approach for the harmonic currents evaluation about the operating speed of the arbitrary single traction. To use probabilistic method for railroad system, probability density function(PDF) using measuring data based on the realistic harmonic currents per operating speed is calculated. Mean and variance of harmonic currents of single traction also are obtained the PDF of the operating speed and electrical railroad traction model. Uncertainty of harmonic currents expects to results through mean and variance with PDF. The probability of harmonic currents generated with the operating of arbitrary many tractions is calculated by the convolution of functions. The harmonics of different number of tractions are systematically investigated. It is assessed by the total demand distortion(TDD) for the railroad system.

• Journal of Power Electronics
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• 제18권6호
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• pp.1889-1900
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• 2018

Harmonic current mitigation is vital in power distribution networks owing to the inflow of nonlinear loads, distributed generation, and renewable energy sources. The active power filter (APF) is the current electrical equipment that can dynamically compensate for harmonic distortion and eliminate asymmetrical loads. The compensation performance of an APF largely depends on the control strategy applied to the voltage source inverter (VSI). Model predictive control (MPC) has been demonstrated to be one of the effective control approaches to providing fast dynamic responses. This approach covers different types of power converters due to its several advantages, such as flexible control scheme and simple inclusion of nonlinearities and constraints within the controller design. In this study, a finite control set-MPC technique is proposed for the control of VSIs. Unlike conventional control methods, the proposed technique uses a discrete time model of the shunt APF to predict the future behavior of harmonic currents and determine the cost function so as to optimize current errors through the selection of appropriate switching states. The viability of this strategy in terms of harmonic mitigation is verified in MATLAB/Simulink. Experimental results show that MPC performs well in terms of reduced total harmonic distortion and is effective in APFs.

• 대한전자공학회논문지
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• 제26권5호
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• pp.60-70
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• 1989

본 연구는 인버터로 구동되는 유도전동기에서 발생되는 토오크 맥동을 표현하는, 고조파 토오크 함수 HTF(harmonic torque function)를 제안하고, 컴퓨터 시뮬레이션과 실험을 통하여 HTF의 타당성을 입증하였다. 제안된 HTF는 고조파 전류의 크기 뿐만 아니라 위상까지 고려하므로서 부하변동에 무관한 고조파 토오크 함수가 되었으며, 이를 six-step. SPWM 및 TPWM의 펄스 폭 제어 인버터에 적용하여 비교하였다. 그 결과 PAWM 인버터에서의 우수한 제어방법이 선택되었다. 한 주기당 펄스수가 9이하에서는 six-step이, 출력전압 크기와 토오크 맥동의 측면에서, SPWM 및 TPWM보다 우수함을 알 수 있었다.

• 대한기계학회논문집A
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• 제31권3호
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• pp.365-372
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• 2007

Revisited in this paper are Green's functions for unit concentrated forces in an infinite orthotropic Kirchhoff plate. Instead of obtaining Green's functions expressed in explicit forms in terms of Barnett-Lothe tensors and their associated tensors in cylindrical or dual coordinates systems, presented here are Green's functions expressed in two quasi-harmonic functions in a Cartesian coordinates system. These functions could be applied to thin plate problems regardless of whether the plate is homogeneous or inhomogeneous in the thickness direction. With a composite variable defined as $z=x_1+ipx_2$ which is adopted under the necessity of expressing the Green's functions in terms of two quasi-harmonic functions in a Cartesian coordinates system Stroh-like formalism for orthotropic Kirchhoffplates is evolved. Using some identities of logarithmic and arctangent functions given in this paper, the Green's functions are presented in terms of two quasi-harmonic functions. These forms of Green's functions are favorable to obtain the Newtonian potentials associated with defect problems. Thus, the defects in the orthotropic plate may be easily analyzed by way of the Green's function method.

• 전기학회논문지
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• 제62권7호
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• pp.913-917
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• 2013

During the restoration process of primary restorative transmission system, some over voltages may happen due to nonlinear interaction between unloaded transformers and transmission systems. These over voltages caused by harmonic resonance can be suppressed by inserting damping loads before energizing transformers. But it is very difficult to predict the occurrence possibility of harmonic resonance and complex simulation must be repeated to estimate the sufficient damping loads. This paper presents a damping loads prediction system to prevent harmonic resonance. Detailed analysis of the relationship between harmonic resonance and the amount of damping loads is discussed. The prediction system is developed using a curve fitting and a neural network based on this relationship. A curve fitting used a Gaussian function based on non-linear least square method and multi-layer back-propagation neural network is applied. The system is applied to primary restorative transmission lines in korean power system and the result showed satisfactory performance.