• Journal of Power Electronics
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• v.18 no.2
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• pp.547-557
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• 2018

This work proposes a control method of frequency stabilization for grid integration of large-scale wind farms via the voltage source converter-based high-voltage direct current (VSC-HVDC) technology. First, the topology of grid integration of a large-scale wind farm via the VSC-HVDC link is provided, and simple control strategies for wind turbines, wind farm side VSC (WFVSC), and grid side VSC are presented. Second, a mathematical model between the phase angle of WFVSC and the frequency of the wind farm is established. The control principle of the large-scale wind power integrated system is analyzed in theory in accordance with the mathematical model. Third, frequency and AC voltage controllers of WFVSC are designed based on the mathematical model of the relationships between the phase angle of WFVSC and the frequency of the wind farm, and between the modulation index of WFVSC and the voltage of the wind farm. Corresponding controller structures are established by deriving a transfer function, and an optimization method for selecting the parameters of the frequency controller is presented. Finally, a case study is performed under different operating conditions by using the DIgSILENT/PowerFactory software. Results show that the proposed control method has good performance in the frequency stabilization of the large-scale wind power integrated system via the VSC-HVDC technology.

• Journal of Digital Contents Society
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• v.9 no.4
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• pp.543-550
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• 2008

There exist many QoS problems such as delay and jitter for mobile streaming due to limited bandwidth. This paper proposed a transaction update method based on Fuzzy chunk to solve the problems. The proposed method updated a transaction, which is classified as a read or an update, using Fuzzy filtering. A chunk block is rearranged according to the fuzziness which is classified as better relevance for fuzziness greater than 0.8, relevance for fuzziness between 0.5 and 0.7, and less irrelevance for fuzziness less than 0.5. According to the simulation result for the rearranged chunk block, the proposed method has better performance than those of RBM(Randon Based method), DBM(Distance Based Method), and FBM(Frequency Based Method).

• Journal of Electrical Engineering and Technology
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• v.6 no.6
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• pp.776-785
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• 2011

Since the Internet-based real-time Global Positioning System(GPS) synchronized widearea power system frequency monitoring network (FNET) was proposed in 2001, it has been monitoring the power system frequency in interconnected United States power systems and numerous interesting behaviors have been observed, including frequency excursion propagation. We address the consistency of a frequency excursion detection order of frequency disturbance recorders in FNET in relation to the same generation trip, as well as the ability to recreate by power systems dynamic simulation. We also propose a new method, as an application of FNET measurement, to locate a tripped generator using power systems dynamic simulation and wide-area frequency measurement. The simulation database of all the possible trips of generators in the interconnected power systems is created using the off-line power systems dynamic simulation. When FNET detects a sudden drop in the monitoring frequency, which is most likely due to a generation trip in power systems, the proposed algorithm locates a tripped generator by finding the best matching case of the measured frequency excursion in the simulation database in terms of the frequency drop detection order and the time of monitoring points.

• Ocean Systems Engineering
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• v.13 no.1
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• pp.57-77
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• 2023

In the present study, the total hydrodynamic pressure exerted by the fluid on walls of rectangular tanks due to horizontal excitations of different frequencies, is investigated by pressure based finite element method. Fluid within the tanks is invisid, compressible and its motion is considered to be irrotational and it is simulated by two dimensional eight-node isoparametric. The walls of the tanks are assumed to be rigid. The total hydrodynamic pressure increases with the increase of exciting frequency and has maximum value when the exciting frequency is equal to the fundamental frequency. However, the hydrodynamic pressure has decreasing trend for the frequency greater than the fundamental frequency. Hydrodynamic pressure at the free surface is independent to the height of fluid. However, the pressure at base and mid height of vertical wall depends on height of fluid. At these two locations, the hydrodynamic pressure decreases with the increase of fluid depth. The depth of undisturbed fluid near the base increases with the increase of depth of fluid when it is excited with fundamental frequency of fluid. The sloshing of fluid with in the tank increases with the increase of exciting frequency and has maximum value when the exciting frequency is equal to the fundamental frequency of liquid. However, this vertical displacement is quite less when the exciting frequency is greater than the fundamental frequency.

• Journal of KSNVE
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• v.10 no.4
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• pp.648-654
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• 2000

A procedure to determine the realizable optimal positions of rigid supports is suggested to get a maximum fundamental natural frequency. a measured frequency response function based substructure-coupling technique is used to model the supported structure. The optimization procedure carries out the eigenvalue sensitivity analysis with respect to the stiffness of supports. As a result of such stiffness optimization, the optimal rigid-support positions are shown to be determined by choosing the position of the largest stiffness. The optimally determined support conditions are verified to satisfy the eigenvalue limit theorem. To demonstrate the effectiveness of the proposed method, the optimal support positions of a plate model are investigated. Experimental results indicate that the proposed method can effectively find out the optimal support conditions of the structure just based on the measured frequency response functions without any use of numerical model of the structure.

• 제어로봇시스템학회:학술대회논문집
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• 1995.10a
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• pp.360-363
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• 1995

In this paper, we describe the composition of frequency response bands based on experimental data of plants (controlled systems) with uncertainty and nonlinearity, and the robust stability evaluation of feedback control systems. Analysis and design of control systems using the upper and lower bounds of such experimental data would be effective as a practicable method which is not heavily dependent upon mathematical models such as the transfer function. First, we present a method to composite gain characteristic bands of frequency response of cascade connected plants with uncertainty and a recurrent inequality for the composition. Next, evaluation methods of the robust stability of multi-loop control systems obtained through feedback from the output terminals and multi-loop control systems obtained through feedback into the input terminals are described. In actual control systems, experimental data of frequency responses often depends on the amplitude of input. Therefore, we present the evaluation method of the nominal value and the width of the frequency response band in such a case, and finally give numerical examples based on virtual experimental data.

• Speech Sciences
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• v.12 no.4
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• pp.53-70
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• 2005

A Vowel of speech signals are multicomponent signals composed of AM-FM components whose instantaneous frequency and instantaneous amplitude are time-varying. The changes of emotion states cause the variation of the instantaneous frequencies and the instantaneous amplitudes of AM-FM components. Therefore, it is important to estimate exactly the instantaneous frequencies and the instantaneous amplitudes of AM-FM components for the extraction of key information representing emotion states and changes in speech signals. In tills paper, firstly a method decomposing speech signals into AM - FM components is addressed. Secondly, the fundamental frequency of vowel sound is estimated by the simple method based on the spectrogram. The estimate of the fundamental frequency is used for decomposing speech signals into AM-FM components. Thirdly, an estimation method is suggested for separation of the instantaneous frequencies and the instantaneous amplitudes of the decomposed AM - FM components, based on Hilbert transform and the demodulation property of the extended Fourier transform. The estimates of the instantaneous frequencies and the instantaneous amplitudes can be used for modification of the spectral distribution and smooth connection of two words in the speech synthesis systems based on a corpus.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.12 no.1
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• pp.58-71
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• 2019

This paper proposes architecture of a cognitive radio engine platform and the allowable frequency channel reasoning method that enables acquisition of the allowable channels for the military tactical network environment. The current military tactical wireless communication system is increasing need to secure a supplementary radio frequency to ensure that multiple wireless networks for different military wireless devices coexist, so that tactical wireless communication between the same or different systems can be operated effectively. This paper presents the allowable frequency channel reasoning method based on cognitive radio engine for realizing DSA(Dynamic Spectrum Access) as an optimal available frequency channel. To this end, a case-based allowable frequency channel reasoning method for cognitive radio devices is proposed through modeling of primary user's traffic status and calculation of channel occupancy probability. Also through the simulation of the performance analysis, changing rate of collision probability between the primary users' occupancy channel and the available channel acquisition information that can be used by the cognitive radio device was analysed.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.12
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• pp.544-548
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• 2006

The instantaneous frequency gives a frequency value at a time instance. Thus, it is natural to use the instantaneous frequency for detecting disturbances of voltage signal in power line. Various instantaneous frequency estimators are introduced. By applying to different types of disturbed signals, we show the estimators' ability to classify flickers. Also, the computational costs are compared between different instantaneous frequency estimators. The Prony's method (PRONY) and the modified covariance method (MCOV) need relatively smaller amount of calculation than the Teaser-Kaiser energy operator based estimator (DESA II). For an AM-FM modulated signal, the tracking performance of different instantaneous frequency estimators is also compared. Through simulation, it is shown that MCOV produces less variant frequency estimation values than DESA II and PRONY method.

• Speech Sciences
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• v.12 no.4
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• pp.17-29
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• 2005

Time-frequency representation reveals some useful information about instantaneous frequency, instantaneous bandwidth and boundary of each AM-FM component of a speech signal. In many cases, the instantaneous frequency of each component is not constant. The variability of instantaneous frequency causes degradation of resolution in time-frequency representation. This paper presents a method of adaptively adjusting the transform kernel for preventing degradation of resolution due to time-varying instantaneous frequency. The transform kernel is the form of frequency modulated function. The modulation function in the transform kernel is determined by the estimate of instantaneous frequency which is approximated by first order polynomial at each time instance. Also, the window function is modulated by the estimated instantaneous. frequency for mitigation of fringing. effect. In the proposed method, not only the transform kernel but also the shape and the length of. the window function are adaptively adjusted by the instantaneous frequency of a speech signal.