• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.1
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• pp.1-8
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• 2022

Recently, photovoltaic (PV) systems have been gradually applied in eco-friendly vehicle applications to improve fuel economy. The relevant market is expected to continue to grow because the installation of large-capacity PV systems to other eco-friendly vehicles, such as electric buses and trains, is being considered. However, in a PV system, power imbalance between submodules and low power generation efficiency occur due to factors such as cell aging, contamination, and shading. To resolve this problem, various differential power processing (DPP) converters have been researched and developed. However, conventional DPP converters suffer from large volume and low efficiency. Therefore, to apply DPP converters to eco-friendly vehicles, increasing efficiency and reducing volume and price compared with existing DPP converters is necessary. In this paper, a novel DPP converter with an integrated transformer is proposed and analyzed. The proposed DPP converter uses a single magnetic component by integrating transformers and secondary sides of conventional DPP converters. Therefore, the proposed DPP converter shows high power density and high efficiency, and it is suitable for PV systems in eco-friendly vehicle applications.

• International journal of advanced smart convergence
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• v.12 no.2
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• pp.25-33
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• 2023

The purpose of this study is to evaluate the impact of intermediate features on FER performance. To achieve this objective, intermediate features were extracted from the input images at specific layers (FM1~FM4) of the pre-trained network (Resnet-18). These extracted intermediate features and original images were used as inputs to the vision transformer (ViT), and the FER performance was compared. As a result, when using a single image as input, using intermediate features extracted from FM2 yielded the best performance (training accuracy: 94.35%, testing accuracy: 75.51%). When using the original image as input, the training accuracy was 91.32% and the testing accuracy was 74.68%. However, when combining the original image with intermediate features as input, the best FER performance was achieved by combining the original image with FM2, FM3, and FM4 (training accuracy: 97.88%, testing accuracy: 79.21%). These results imply that incorporating intermediate features alongside the original image can lead to superior performance. The findings can be referenced and utilized when designing the preprocessing stages of a deep learning model in FER. By considering the effectiveness of using intermediate features, practitioners can make informed decisions to enhance the performance of FER systems.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.9
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• pp.2334-2347
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• 2023

Metaverse services generate text data, data of ubiquitous computing, in real-time to analyze user emotions. Analysis of user emotions is an important task in metaverse services. This study aims to classify user sentiments using deep learning and pre-trained language models based on the transformer structure. Previous studies collected data from a single platform, whereas the current study incorporated the review data as "Metaverse" keyword from the YouTube and Google Play Store platforms for general utilization. As a result, the Bidirectional Encoder Representations from Transformers (BERT) and Robustly optimized BERT approach (RoBERTa) models using the soft voting mechanism achieved a highest accuracy of 88.57%. In addition, the area under the curve (AUC) score of the ensemble model comprising RoBERTa, BERT, and A Lite BERT (ALBERT) was 0.9458. The results demonstrate that the ensemble combined with the RoBERTa model exhibits good performance. Therefore, the RoBERTa model can be applied on platforms that provide metaverse services. The findings contribute to the advancement of natural language processing techniques in metaverse services, which are increasingly important in digital platforms and virtual environments. Overall, this study provides empirical evidence that sentiment analysis using deep learning and pre-trained language models is a promising approach to improving user experiences in metaverse services.

• Transactions on Semiconductor Engineering
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• v.2 no.3
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• pp.6-12
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• 2024

This paper presents a study on a 2.4GHz differential cascode power amplifier(PA) fabricated using a 130nm CMOS process. This PA is designed for wireless power transmission applications and consists of two differential stages with custom-designed balun transformers for single-ended output. Balun transformers are utilized not only for the output stage but also for power match-ing between each stage. Additionally, a bias circuit with temperature compensation capability is added to maintain stable bias voltage in the 2.4GHz frequency band. As a result, it achieves an output power of 21.75 dBm with a power-added efficiency(PAE) of 40.9% at TT/40℃.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.4
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• pp.21-28
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• 2006

In this paper, the proposed full-bridge high frequency isolated zoo voltage and zero current switching phase shifted pulse width modulation(ZVZCS PS-PWM)DC-DC converter among fuel cell generation system consist of 1.2[kW] fuel cell of Nexa Power Module, full-bridge DC-DC converter to boost the fuel cell low voltage($28{\sim}43[%]$) to 380[VDC] and a single phase full-bridge inverter is implemented to produce AC output(220[VAC], 60[Hz]). A tapped inductor filter with freewheeling diode is newly implemented in the output filter of the proposed full-bridge high frequency isolated ZVZCS PS-PWM DC-DC converter to suppress circulating current under the wide output voltage regulation range, thus to eliminate the switching and transformer turn-on/off over-short voltage or transient phenomena. Besides the efficiency of $93{\sim}97[%]$ is obtained over the wide output voltage regulation ranges and load variations.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.2 s.117
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• pp.158-165
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• 2007

In this paper, the circularly polarized $4{\times}4$ array antenna is proposed for the X-band. A single antenna consists of square patch and unequal cross-aperture coupled feeding. The RHCP(Right Handed Circularly Polarization) is generated by unequal cross-aperture coupled feeding. By reducing space among elements of way antenna from 0.8 ${\lambda}_0$ to 0.45 ${\lambda}_0$, the mounting area of array antenna is miniaturized. The $2{\times}2$ array antenna is designed using sequential rotation feeding network. The good level of gain, axial ratio, and impedance bandwidth are achieved. The $4{\times}4$ array antenna is extended by ${\lambda}/4$ transformer and T-junction power divider. The simulated maximum radiation gain is 15.09 dBi at 10 GHz. The simulated 3 dB Axial Ratio bandwidth is from 9.05 to 10.4 GHz(13.5%). Also the measured impedance bandwidth($VSWR{\leq}2$) of manufactured $4{\times}4$ array antenna is from 8.45 to 11.84 GHz(33.9%). The measured maximum radiation gain is 11.10 dBi at 10 GHz. The measured 3 dB Axial Ratio bandwidth is from 9.42 to 10.47 GHz(10.5%).

• Journal of the Korean Vacuum Society
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• v.15 no.6
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• pp.587-593
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• 2006

The circuit of the EEFL system and the inverter has been analyzed into the resistance RL, the capacitance C of the EEFL-backlight system, and the inductance of transformer in the inverter. The lamp resistance and capacitance are deter-mined from the phase difference is between the lamp current and voltage and from the Q-V diagram, respectively. The single Lamp of EEFL for 32' LCD-BLU has the resistance of $66\;k\Omega$ and the capacitance of 21.61 pF. The resistance, which is connected by parallel in the 20-EEFLS BLU, is $3.3\;k\Omega$ and the capacitance is 402.1 pF. The matching frequency in the operation of lamp system is noted as $\omega_M=1/\sqrt{L_2C(1-k^2)}$, where $L_2$ is the inductance of secondary coil and k is the coupling coefficient between primary and secondary coil. The lamp current and voltage has maximum value at the matching frequency in the LCD BLU system. The results of analytic solutions are in good agreement with the experimental results.

• Food Engineering Progress
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• v.15 no.4
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• pp.398-403
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• 2011

A dielectric barrier discharge plasma (DBDP) treatment system was fabricated and the optimum operating conditions for the plasma generation were determined in order to explore the potential of cold plasma as a non-thermal proessing technology. The microbial inactivation performance of the system was also evaluated against Staphyloocus aureus. The system consisted of power supply, transformer, electrode assembly and sample treatment plate. The input power was 220 V single phase AC and amplified to 10.0-50.0 kV on a transformer. A pulsed sine wave of frequency 10.0-50.0 kHz was introduced to the electrode embedded in ceramic as a dielectric barrier material in order to generate plasma at atmospheric pressure. Higher currents and consequently greater power were required for the plasma generation as the frequencies increased. A homogeneous and stable plasma was generated at currents of 1.0-2.0, and frequencies of 32.0-35.3 kHz. The optimum electrode-gaps for the plasma generation were 1.85 mm without loaded samples. More power was consumed as the electrode-gaps increased. The practically optimum electrode- gap was, however, 2.65 mm when samples were treated on slide-glasses for microbial inactivation. The maximum temperature increase after 10 min treatment was less than 20$^{\circ}C$, indicating no microbial inactivation effect by heat and thereby insuring a non-thermal method. The DBDP inactivation effect against Staphyloocus aureus increased linearly with treatment time up to 5 min, but plateaued afterward. More than 5 log reduction was achieved by 10 min treatment at 1.25 A.

• Journal of the Korean Society of Marine Environment & Safety
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• v.15 no.3
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• pp.257-262
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• 2009

The unified power flow controller(UPFC) is one of the most effective devices in the FACTS family. This paper concerns about a filtering technique for reducing the computer calculation to determine the optimal location of UPFC in a power system. The sensitivities of the power generation cost for UPFC control parameters are evaluated. This technique requires that only one optimal power flow is run to get UPFC sensitivities for all possible transmission lines. To find out a optimal locating of a single UPFC in power system, an ideal transformer model which consists of a complex turns ratio and a variable shunt admittance was used. In this model, the UPFC control variables do not depend on UPFC input and output currents and voltages. The sensitivity method was tested on a 5-bus system derived from the IEEE 14-bus system and IEEE 14-bus system to establish its effectiveness.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.3
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• pp.330-333
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• 2016

In this paper, we propose 77 GHz power amplifier for long range automotive collision avoidance radar using 65 nm CMOS process. The proposed circuit has a 3-stage single power amplifier which includes common source structure and transformer. The measurement results show 18.7 dB maximum voltage gain at 13 GHz 3 dB bandwidth. The measured maximum output power is 10.2 dBm, input $P_{1dB}$ is -12 dBm, output $P_{1dB}$ is 5.7 dBm, and maximum power add efficiency is 7.2 %. The power amplifier consumes 140.4 mW DC power from 1.2 V supply voltage.