• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2099-2105
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• 2017

In a power system that has a high wind penetration, the output power fluctuation of a large-scale wind turbine generator (WTG) caused by the varying wind speed increases the maximum frequency deviation, which is an important metric to assess the quality of electricity, because of the reduced system inertia. This paper proposes a stable power-smoothing scheme of a doubly-fed induction generator (DFIG) that can suppress the maximum frequency deviation, particularly for a power system with a high wind penetration. To do this, the proposed scheme employs an additional control loop relying on the system frequency deviation that operates in combination with the maximum power point tracking control loop. To improve the power-smoothing capability while guaranteeing the stable operation of a DFIG, the gain of the additional loop is modified with the rotor speed and frequency deviation. The gain is set to be high if the rotor speed and/or frequency deviation is large. The simulation results based on the IEEE 14-bus system demonstrate that the proposed scheme significantly lessens the output power fluctuation of a WTG under various scenarios by modifying the gain with the rotor speed and frequency deviation, and thereby it can regulate the frequency deviation within a narrow range.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.218-226
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• 2022

The main characteristics of the underwater acoustic channel have varying multipath and fast fading. Especially, Frequency Shift Keying (FSK) signals with multiple frequency bands caused loss of information bits allocated on the specific frequencies due to selective fading phenomenon. Therefore, this paper proposes frequency gain control algorithm based on preamble error rates. The proposed algorithm estimates optimal gain value in the range of preamble error rate with less than 10 % for specific faded frequency. By employing turbo equalized FSK signals with rate of 1/3, the experiment was conducted on a lake in Munkyeong city with distance of 300 m to 500 m. The result confirms that packets are decoded successfully by applying proposed algorithm as increasing number of iterations.

• Water Engineering Research
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• v.1 no.1
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• pp.11-23
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• 2000

Regional flood frequency analysis has been developed by employing the nearby site's information to improve a precision in estimating flood quantiles at the site of interest. In this paper, single site and regional flood frequency analyses were compared based of the 2-parameter Weibull model. For regional analysis, two approaches were employed. The First one is to use the asymptotic variances of the quantile estimators derived based of the assumption that all sites including the site of interest are independent each other. This approach may give the maximum regional gain due to the spatial independence assumption among sites. The second one in Hosking's regional L-moment algorithm. These methods were applied to annual flood data. As the results, both methods generally showed the regional gain at the site of interest depending on grouping the sites as homogeneous. And asymptotic formula generally shows smaller variance than those from Hosking's algorithm. If the shape parameter of the site of interest from single site analysis is quite different from that from regional analysis then Hosking's results might be better than the asymptotic ones because the formula was derived based on the assumption that all sites have the same regional shape parameter. Furthermore, in such a case, regional analysis might be worse than single site analysis in the sense of precision of flood quantile estimation. Even though the selected sites may satisfy Hosking's criteria, regional analysis may not give a regional gain for specific and nonexceedance probabilities.

• Journal of the Korea Society of Computer and Information
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• v.12 no.6
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• pp.243-249
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• 2007

I propose the excess noise suppressed optical sensor network using optical CDMA with gain saturated optical amplifier in order to increase number of sensors simultaneously connected to network. Simulation analyses confirm that the maximum number of sensors simultaneously connected to the optical sensor network can be largely increased by increasing the gain of gain saturated optical amplifier owing to the pression of access noises with the assignment of sweeping frequency of optical sensors within 10MHz. In the case of the requested SNR of 20dB and the sweeping frequency of 10MHz, the maximum number of sensors simultaneously connected to the optical sensor network can be increased four times as many as the conventional system.

• Journal of the Korean Institute of Telematics and Electronics
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• v.9 no.5
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• pp.27-33
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• 1972

This paper describes the computer-aided design, fabrication and performance of high Q and high gain active filters suitable for microminiaturization in the frequency range of 10-800MHz, based on the negative resistance operation of a transistor. 48 as high as 1000 and a transducer gain as high as 35dB can readily be obtained with a single-transistor amplifier and with an inductance as small as a few nH at higher frequencies and 150 nH at lower frequencies in tile above frequency range. The gain of the proposed active filter can be stoabilized within $\pm$ 1.5 dB over the temperature range -1$0^{\circ}C$ to +5$0^{\circ}C$ and the temperature dependence of the center frequency is tapicalla 50ppm/$^{\circ}C$. An experimental FM receiver utilizing these fitters and operating at a carrier frequency of 92 MH3 was built. The whole circuit was fabricated on eight alumina substrates of by the thick-film hybrid IC technique and the coils are constructed, for miniaturization, in a spiral form of 3 or 4 turns of enamel copper wire with an overall diameter of about 5mm. The test results are also reported in this paper.

• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1780-1785
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• 2015

In this paper, the adaptive particle swarm optimization (APSO) algorithm is employed to design a gain-enhanced antenna with a reflector for energy harvesting. We placed the reflector below the main radiating element. Its back-radiated field is reflected and added to the forward radiated field, which could increase the antenna gain. We adopt the adaptive particle swarm optimization (APSO) algorithm, which improves the speed of convergence with a high frequency solver. The result shows that performance of the optimized design successfully satisfied the design goal of the frequency band, gain and axial ratio.

• Korean Journal of Optics and Photonics
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• v.6 no.2
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• pp.135-141
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• 1995

Phenomenological nonlinear gain saturation effect on the noise characteristics of a multi-electrode DBR laser, when the lasing wavelength changes continuously, is presented theoretically. Using the optical transmission line theory, noise characteristics reliant on output power are analyzed by taking into account both the spontaneous enhancement factor K due to the distribution of the spontaneous emission along the active cavity and the nonlinear gain saturation effect. Spontaneous emission rate was increased due to an increase in injected current into the passive section, which in turn lead to increase in relative intensity noise (RIN) and frequency noise. Phenomenological nonlinear gain saturation was found to have significant effect on RIN and frequency noise characteristics. However. Iinewidth was found to decrease due to a phenomenological nonlinear gain saturation effect. ffect.

• Current Optics and Photonics
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• v.5 no.2
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• pp.141-146
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• 2021

We have evaluated the suppression effect of atmospheric-turbulence-induced optical scintillation in terrestrial free-space optical (FSO) communication systems using a gain-saturated erbium-doped fiber amplifier (EDFA). The variation of EDFA output signal power has been measured with different amounts of gain saturation and modulation indices of the optical input signal. From the measured results, we have found that the peak-to-peak power variation was decreased drastically below 2 kHz of modulation frequency, in both 3-dB and 6-dB gain compression cases. Then, the power spectral density (PSD) of optical scintillation has been calculated with Butterworth-type transfer function. In the calculation, different levels of atmospheric-turbulence-induced optical scintillation have been taken into account with different values of the Butterworth cut-off frequency. Finally, the suppression effect of optical scintillation has been estimated with the measured frequency response of the EDFA and the calculated PSD of the optical scintillation. From our estimated results, the atmospheric-turbulence-induced optical scintillation could be suppressed efficiently, as long as the EDFA were operated in a deeply gain-saturated region.

• Journal of Nutrition and Health
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• v.56 no.3
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• pp.288-299
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• 2023

Purpose: This study aimed to assess the weight fluctuations in college students during the coronavirus disease 2019 (COVID-19) pandemic and identify lifestyle and dietary changes related to weight gain. Methods: An online survey was conducted on 270 college students from September 22 to October 26, 2021. A logistic regression analysis was performed to analyze the relationship of weight gain with the general characteristics, lifestyle, and dietary changes of the students. Results: Among the respondents, 42.9% of men and 44.7% of women reported weight gain. The main reasons given for weight gain were reduced activities due to restrictions during lockdown and diet changes, mainly relating to delivered or fast foods. Among the general characteristics and lifestyle factors poor perceived health (odds ratio [OR], 3.97, 95% confidence interval [CI], 1.98-7.96) and being underweight (OR, 0.19, 95% CI, 0.05-0.83) were significantly associated with weight gain. With respect to the diet, increased frequency of eating breakfasts (OR, 4.44, 95% CI, 1.76-11.21), decreased frequency of eating snacks (OR, 0.35, 95% CI, 0.16-0.77), decreased frequency of fruit intake (OR, 3.0, 95% CI, 1.32-6.80), increased frequency of carbonated and sweetened beverage intake (OR, 2.74, 95% CI, 1.26-5.99) and increased frequency of fast food consumption (OR, 2.32, 95% CI, 1.14-4.70) were significantly associated with weight gain. Conclusion: The COVID-19 pandemic affected weight gain and caused lifestyle and dietary changes. Specific health and nutrition management plans should be prepared for handling future epidemics of infectious diseases based on the results of surveys conducted on larger sample size.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.3
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• pp.138-144
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• 2017

In this paper, we propose a high frequency boosting circuits compensating for age-related hearing loss. The frequency response of this hearing loss is quite similar to that of a low-pass filter of which the critical frequency get lower with age. Therefore the voltage gain of this compensation circuits increase proportionally to the frequency of signals when the frequency is higher than the critical frequency and the voltage is constant irrespective of the frequency of signals when the frequency is lower than the critical frequency. The proposed circuits consist of a differential circuit and a unity gain amplifier. Because the critical frequency of the proposed circuits is controlled simply in the shape of a volume control lever, the aged people can adjust the high frequency boosting level easily according to one's hearing loss level. The critical frequency is continuously controllable in the whole audible frequency band and the gain of this high frequency boosting circuits is above 80dB at 10kHz.