• The Transactions of the Korean Institute of Power Electronics
• /
• v.22 no.2
• /
• pp.118-125
• /
• 2017

In this paper, we propose a smart transformer for a smart transformer miniature model, which can replace a 60 [Hz] single-phase transformer installed in an electric vehicle. The proposed smart transformer is lighter than a conventional transformer, can control instantaneous voltage, and can be expected to improve power quality through harmonic compensation. The proposed intelligent transformer consists of an incoming part, an AC/DC converter, and a dual active bridge. Only the incoming part and the AC/DC converter are described in this paper. The proposed intelligent transformer has 75 kVA 3.3 kV input and 750 V DC output, which are verified by simulation and experiment.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.15 no.2
• /
• pp.280-285
• /
• 2015

A fully integrated high-efficiency linear CMOS power amplifier (PA) is developed for 802.11n WLAN applications using the 65-nm standard CMOS technology. The transformer topology is investigated to obtain a high-efficiency and high-linearity performance. By adopting a 2:2 output transformer, an optimum impedance is provided to the PA core. Besides, a LC harmonic control block is added to reduce the AM-to-AM/AM-to-PM distortions. The CMOS PA produces a saturated power of 26.1 dBm with a peak power-added efficiency (PAE) of 38.2%. The PA is tested using an 802.11n signal, and it satisfies the stringent error vector magnitude (EVM) and mask requirements. It achieves -28-dB EVM at an output power of 18.6 dBm with a PAE of 14.7%.

• Smart Media Journal
• /
• v.13 no.4
• /
• pp.9-15
• /
• 2024

Tree-based algorithms have been the dominant methods used build a prediction model for tabular data. This also includes personal credit data. However, they are limited to compatibility with categorical and numerical data only, and also do not capture information of the relationship between other features. In this work, we proposed an ensemble model using the Transformer architecture that includes text features and harness the self-attention mechanism to tackle the feature relationships limitation. We describe a text formatter module, that converts the original tabular data into sentence data that is fed into FinBERT along with other text features. Furthermore, we employed FT-Transformer that train with the original tabular data. We evaluate this multi-modal approach with two popular tree-based algorithms known as, Random Forest and Extreme Gradient Boosting, XGBoost and TabTransformer. Our proposed method shows superior Default Recall, F1 score and AUC results across two public data sets. Our results are significant for financial institutions to reduce the risk of financial loss regarding defaulters.

• Journal of the Korean Society for Railway
• /
• v.19 no.5
• /
• pp.617-628
• /
• 2016

This paper proposes the structure of a smart transformer to improve the performance of the 60Hz main power transformer for rolling stock. The proposed smart transformer is a kind of solid state transformer that consists of semiconductor switching devices and high frequency transformers. This smart transformer would have smaller size than the conventional 60Hz main transformer for rolling stock, making it possible to operate AC electrified track efficiently by power factor control. The proposed structure employs a cascade H-Bridge converter to interface with the high voltage AC single phase grid as the rectifier part. Each H-Bridge converter in the rectifier part is connected by a Dual-Active-Bridge (DAB) converter to generate an isolated low voltage DC output source of the system. Because the AC voltage in the train system is a kind of medium voltage, the number of the modules would be several tens. To control the entire smart transformer, the inner DC voltage of the modules, the AC input current, and the output DC voltage must be controlled instantaneously. In this paper, a control algorithm to operate the proposed structure is suggested and confirmed through computer simulation.

• Journal of Electrical Engineering and Technology
• /
• v.11 no.1
• /
• pp.257-264
• /
• 2016

In this paper, new electric railway feeding system which has active transformer is modeled for evaluating the steady state analysis using PSCAD/EMTDC. Equivalent models including power supply, feeder, train and transformers are proposed for simplifying the model of the feeding system in high speed electric railway. In case study, simulation results applied to proposed model are compared with the conventional and new systems through the catenary voltage, three-phase voltage of PCC (Point of Common Coupling) and the efficiency of regenerative braking energy.

• Journal of Electrical Engineering and Technology
• /
• v.13 no.4
• /
• pp.1425-1437
• /
• 2018

In this paper, a methodology was proposed to reduce the electrical level and spatial size of the smart grid with distributed generations (DGs) to a scale in which the electrical phenomena and control strategies for disturbances on the smart grid could be safely and freely experimented and observed. Based on the design methodology, a micro smart grid simulator with a substation transformer capacity of 190VA, voltage level of 19V, maximum breaking current of 20A and size of $2{\times}2m^2$ was designed by reducing the substation transformer capacity of 45MVA, voltage level of 23kV and area of $2{\times}2km^2$ of the smart grid to over one thousandth, and also reducing the maximum breaking current of 12kA of the smart grid to 1/600. It was verified that the proposed design methodology and designed micro smart grid simulator were very effective by identifying how all of the fault currents are limited to within the maximum breaking current of 20A, and by confirming that the maximum error between the fault currents obtained from the fault analysis method and the simulation method is within 1.8% through the EMTP-RV simulation results to the micro smart grid simulator model.

• Journal of Electrical Engineering and Technology
• /
• v.7 no.3
• /
• pp.320-329
• /
• 2012

The Load Tap Changing (LTC) transformer and Shunt Capacitor (SC) bank are major devices for voltage and reactive power control in a distribution substation. Thus, the coordination operation of a LTC transformer and a SC bank is required to achieve better voltage and reactive power compensation at a distribution substation in the same time. This paper proposes coordinate control method of LTC transformer and SC bank to achieve better voltage and reactive power compensation and operation times of these two devices in the same time. The mathematical formulations of the proposed coordinate control method are introduced. Sample case studies are shown to verify the effectiveness of the proposed coordinate control method.

• Journal of the Korean Society for Railway
• /
• v.19 no.6
• /
• pp.727-735
• /
• 2016

Smart transformers are effective at reducing the weight and increasing the efficiency of traction systems for railroad applications. A smart transformer generally consists of rectifier modules and the Dual-Active-Bridge (DAB) converter modules. The efficiency of the smart transformer depends on not only the electrical characteristics, but also on the control method of the converter modules. Especially, a DAB converter has a high order degree of freedom of voltage modulation to control the power transferred through the high frequency transformer, and a voltage modulation method, are very critical for the efficiency of the DAB converter. This paper proposes a new voltage modulation method for the DAB converter to increase the efficiency in the low/medium power transfer condition. The proposed modulation method controls the reactive power in the high frequency transformer, making it zero. And, the switching loss is dramatically reduced by using the received converter module as a diode rectifier. The feasibility of the proposed modulation method is verified by computer simulation of the 900Vdc DAB converter power control.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.63 no.4
• /
• pp.333-338
• /
• 2014

This paper concerns the development of the transformer that can reduce harmonics supplied to the system if the output of photovoltaic inverter in the photovoltaic system is grid-connected, and suggests that problems of harmonics and power factor degradation in the grid-connected photovoltaic system can be improved. In this study, the burden of increasing the investment in new facilities and securing their installation space due to harmonics has been substantially eased through the development of a hybrid transformer possessing unbalanced function and harmonics reduction function using zig-zag coils, and most of all, it is expected that the development of such high efficiency hybrid transformer possessing functions of transformation and reducing harmonics can improve the power quality as well as prevent damages caused by harmonics, leading to suppress unnecessary loss of electric power and thereby contribute to energy savings.

• Smart Media Journal
• /
• v.12 no.9
• /
• pp.28-37
• /
• 2023

The main factor affecting the decline in rice yield is damage caused by localized heavy rains or typhoons. The method of analyzing the rice lodging area is difficult to obtain objective results based on visual inspection and judgment based on field surveys visiting the affected area. it requires a lot of time and money. In this paper, we propose the method of estimation and diagnosis for rice lodging areas using a Vision Transformer-based Segformer for RGB images, which are captured by unmanned aerial vehicles. The proposed method estimates the lodging, normal, and background area using the Segformer model, and the lodging rate is diagnosed through the rice field inspection criteria in the seed industry Act. The diagnosis result can be used to find the distribution of the rice lodging areas, to show the trend of lodging, and to use the quality management of certified seed in government. The proposed method of rice lodging area estimation shows 98.33% of mean accuracy and 96.79% of mIoU.