• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.1
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• pp.80-90
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• 2014

This paper suggests loss analysis and calculation methods for efficiency improvement of power conversion equipment in detail. The detailed loss analysis and calculation has been conducted for 3.3kW On-board Battery Charger considering temperature condition. The validity of the analysis and calculation method is verified by simulation model.

• KIEE International Transactions on Electrophysics and Applications
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• v.4C no.6
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• pp.272-275
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• 2004

A balanced single side-band (SSB) mixer employing a sub-harmonic configuration is designed for up and down conversions in K-band. The designed mixer uses anti-parallel diode (APD) pairs to effectively eliminate even harmonics of the local oscillator (LO) spurious signal. To reduce the odd harmonics of LO at the RF port, we employ a balanced configuration for LO. The fabricated chip shows 12$\pm$2dB of conversion loss and image-rejection ratio of about 20dB for down conversion at RF frequencies of 24-27.5GHz. As an up-conversion mode, the designed chip shows 12dB of conversion loss and image-rejection ratio of 20 ～ 25 dB at RF frequencies of 25 to 27GHz. The odd harmonics of the LO are measured below -37dBc.

• Journal of the Korea Society for Simulation
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• v.6 no.2
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• pp.1-14
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• 1997

The characteristics of the flow and energy conversion in OMACON liquid-metal MHD system are investigated. Numerical simulation of two-phase flow in the OMACON system without magnetic field was carried out by the Phoenics code and the energy conversion characteristics are studied in association with the fact that the mechanical energy loss at the nozzle of the OMACON system are to be converted into electrical energy. In this system, working fluid (gas) is injected through the mixer located at the bottom of the riser, and is mixed with hot liquid metal. Therefore in the riser two-phase flow is developed under the influence of the gravity. In this study, the interaction between the gas and liquid is considered by the use of IPSA(InterPhase Slip Algorithm) where standard drag coefficient has been used. It has been assumed that in the flow regime the liquid is continuous and the gas is dispersed. For the liquid and gas, the continuity equations, momentum equations and energy equations are solved respectively in association with void fraction in the flow field. In order to calculate the energy conversion efficiency, firstly the ratio of the mechanical energy loss of liquid metal flow at the nozzle to the input thermal energy is considered. Secondly flow pattern of liquid metal in the generator has been analyzed, and the characteristics of the conversion of the mechanical energy into the electrical energy has been investigated. For an representative case where Hartmann number is 540 and magnetic field is 0.35 T, the present analysis shows that the energy conversion efficiency is 0.653. This result is considered to be reasonable in comparison with published experimental results.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.3
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• pp.475-485
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• 2017

This paper develops a conversion function and method transforming from daily peak load curve used $LOLE_D$ [days/year] to hourly load curve used $LOLE_H$[hours/year]and describes relationship between $LOLE_D$ [days/year] and $LOLE_H$ [hours/year]. The indices can not only be transformed just arithmetically but also have different characteristics physically because of using their different load curves. The conversion function is formulated as variables of capacity and forced outage rate of generator, hourly load daily load factor and daily peak load yearly load factor, etc. Therefore, the conversion function (${\gamma}={\varphi}$(.)) can not be simple. In this study, therefore, the function is formulated as linear times of separated two functions. One is an exponential formed conversion function of daily load factor. Another is formulated with an exponential typed conversion function of daily peak load yearly load factor. Futhermore, this paper presents algorithm and flow chart for transforming from $LOLE_D$[days/year] to $LOLE_H$[hours/year]. The proposed conversion function is applied to sample system and actual KPS(Korea Power System) in 2015. The exponent coefficients of the conversion functions are assessed using proposed method. Finally, assessment errors using conversion function for case studies of sample system and actual system are evaluated to certify the firstly proposed method.

• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.857-860
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• 2005

We reported 94 GHz, low conversion loss, and high isolation single balanced active-gate mixer based on 70 nm gate length InGaAs/InAlAs metamorphic high electron mobility transistors (MHEMTs). This mixer showed that the conversion loss and isolation characteristics were 2.5 ${\sim}$ 2.8 dB and under -30 dB, respectively, in the range of 93.65 ${\sim}$ 94.25 GHz. The low conversion loss of the mixer is mainly attributed to the high-performance of the MHEMTs exhibiting a maximum drain current density of 607 mA/mm, a extrinsic transconductance of 1015 mS/mm, a current gain cutoff frequency ($f_t$) of 330 GHz, and a maximum oscillation frequency ($f_{max}$) of 425 GHz. High isolation characteristics are due to hybrid ring coupler which adopted dielectric-supported air-gapped microstrip line (DAML) structure using surface micromachined technology. To our knowledge, these results are the best performance demonstrated from 94 GHz single balanced mixer utilizing GaAs-based HEMTs in terms of conversion loss as well as isolation characteristics.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.2
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• pp.50-54
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• 2015

In this paper, we report on a high performance 94 GHz MMIC mixer module using 0.1-um metamorphic high electron mobility transistors (MHEMTs). A modified resistive mixer with a RF amplifier was proposed in this work for low conversion loss and high LO-RF isolation. The MMIC mixer module was fabricated using a MMIC chip and CPW-waveguide transitions. The fabricated mixer chip and module showed a low conversion loss of 6.3 dB and 9.5 dB, and LO-RF isolations of 24.8 and 30.4 dB at 94 GHz, respectively. This results are superior to those of previously W-band (75-110 GHz) MMIC mixers.

• Journal of Korean Society of Rural Planning
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• v.22 no.4
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• pp.37-47
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• 2016

The purpose of this study was to analyze the loss of open space of schools in Ulaanbaatar city and found out main causes of the conversion trend of open space to suggest alternatives. 76 designated sites were selected from 118 public schools within 6 districts of Ulaanbaatar city. These 76 schools were eligible for analysis of the open space change between 2005 and 2015 with Google Earth Pro. The results showed that $175,048m^2$ open space was developed and two dominant types of open space conversion were found; 1) constructions of school facilities such as soccer field, extended school buildings, parking lot, sidewalk, and square, and 2) constructions of apartment buildings and service facilities such as community center, pedestrian, sports facilities, and parking lot. Apartment complex development has commonly happened in all districts and caused bigger open space loss than other types of development. Chingeltei district is located in the center of Ulaanbaatar city, and schools in this district lost the biggest open space, $50,036m^2$/35.24% over 10 years. The rate of open space loss seemed to be related to the distance from the urban center and open space loss was an ongoing event in Ulaanbaatar city. This trend would not be improved without a strong regulation, so, in this study, making strict regulations that prevent conversions of open space were suggested to conserve open space in Ulaanbaatar city.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.6
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• pp.127-132
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• 2018

In this paper, a high conversion gain cascode mixer was designed in W-band and verified by the fabrication and measurements. In the high frequency band such as a W-band, the conversion loss of a mixer is increased because of the poor performance of transistors. This high conversion loss of the mixer requires additional circuits which can give an extra gain such as an RF buffer amplifier, and this can affects the linearity and stability of the overall systems. Therefore, it is necessary to maximize the conversion gain of the mixer. To maximize the conversion gain of the mixer, biases of the transistor were optimized, and output load impedance was optimized by the load-pull simulations. The designed mixer was fabricated in $0.1-{\mu}m$ GaAs pHEMT technology and verified by the measurements. The measurement results shows a maximum conversion gain of -4.7 dB at W-band and an input 1-dB compression point of 2.5 dBm.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.12
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• pp.166-172
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• 1995

A novel passive TE/TM polarization mode converter is fabricated by using poled polymer waveguides. The optic axis of the poling induced waveguide is slowly rotated by using a slowly varying structure of poling electrodes. Thus the polarization conversion is achieved as the guided mode propagates through the waveguide. The proposed device is simulated by a full vectorial beam propagation method (VBPM) for anisotropic medium. For the rotation length of 1 mm, the TE polarization of the guided mode is successfully converted to the TM polarization with negligible loss. Based on the simulation results, we fabricated the polarization converter which is tested by using 1.3 $\mu$m laser diode. TE to TM mode conversion is observed with a polarization extinction ratio higher than 30 dB, and the excess loss is less than 1 dB. The polarization conversion is relatively insensitive to wavelength since the device contains no periodic structures. These devices are easier to fabricate than others containing periodic structures.

• JSTS:Journal of Semiconductor Technology and Science
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• v.4 no.1
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• pp.74-81
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• 2004

We propose a novel scheme to transmit high center frequency RF signals using electroabsorption devices (EADs) as frequency converters at the transmitter and the receiver. In this approach frequency heterodyning is employed for obtaining high center frequency. With the EAD as a detector/mixer at the receiver we demonstrated a smaller conversion loss than that of the conventional modulator/mixer. With EAD as a modulator/mixer at the transmitter and with two heterodyned lasers to generate an optical local oscillator (LO), we demonstrated a large reduction (${\sim}23dB$) in conversion loss, and the transmission is not limited by the optical saturation of the EAD. This transmission scheme has optical single-side-band transmission feature which greatly relieves the fiber dispersion effect.