• Journal of the Korean Society for Precision Engineering
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• v.33 no.3
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• pp.173-181
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• 2016

This paper reports on the development of a roller-cam clutch mechanism. This mechanism can transfer bidirectional torque with high backdrivability, as well as increase actuation energy efficiency, in electrical exoskeleton robots. The developed mechanism was installed at the robot knee joint and unclutched during the swing phase which uses less metabolic energy, thereby functioning as a passive joint. The roller-cam clutch aimed to increase actuation energy efficiency while also producing high backdrivability by generating zero impedance for users during the swing phase. To develop the mechanism, mathematical modeling of the roller-cam clutch was conducted, with the design having more than three safety factors following optimization. Titanium (Ti-6AL-4V) material was used. Finally, modeling verification was done using ANSYS software.

• Korean Management Science Review
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• v.29 no.1
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• pp.33-56
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• 2012

Domestic LCD TV market is composed of two groups of products produced by major firms and small and medium enterprises. The major companies make the price relatively high, but the other makes lower in the same sizes. The model of the low price products does not make consumers choice when they choose LCD TV. This makes the questions of capability between difference price products. The reason above mentioned, the firms that include group of comparatively lower price, are worried about not increasing sale because of prejudice. This study is to find any interrelationship and evaluate the efficiency between the products using performance, exterior and brand power of product. In order to do this, a hybrid AHP/DEA evaluation model for comparison/valuation of LCD TV products is developed. The proposed process is; first, to derive hierarchy structure of LCD TV evaluation criteria using axiomatic design, second, to calculate the score of each LCD TV product through AHP analysis including weight calculation of evaluation criteria, and last, to evaluate the efficiency of LCD TV product by applying DEA by defining product scores as output and prices as input. It concludes that the high price products shows good efficiency, but there are some products with good exterior and brand power, not performance, also presenting good efficiency.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2006.10a
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• pp.4-5
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• 2006

This paper represents modeling and optimization techniques for solar cell process on single-crystalline float zone (FZ) wafers with high efficiency; There were the four significant processes : i)emitter formation by diffusion, anti-reflection-coating (ARC) with silicon nitride using plasma-enhanced chemical vapor deposition (PECVD); iii)screen-printing for front and back metallization; and iv)contact formation by firing. In order to increase the performance of solar cells, the contact formation process is modeled and optimized. This paper utilizes the design of experiments (DOE) in contact formation to reduce process time, fabrication costs. The experiments were designed by using central composite design which is composed of $2^4$ factorial design augmented by 8 axial points with three center points. After contact formation process, the efficiency of the solar cell is modeled using neural networks. This model is used to analyse the characteristics of the process, and to optimize the process condition using genetic algorithms (GA). Finally, find optimal recipe for solar cell efficiency.

• Journal of Power Electronics
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• v.14 no.3
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• pp.468-477
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• 2014

This study proposes an optimized design of a dual active bridge converter for a low-voltage charger in a military uninterrupted power supply (UPS) system. The dual active bridge converter is among various bi-directional DC/DC converters that possess a high-efficiency isolated bi-directional converter. In the general design, the zero-voltage switching(ZVS) region is reduced when the battery voltage is high. By contrast, efficiency is low because of high conduction losses when the battery voltage is low. Variable switching frequency is applied to increase the ZVS region and the power conversion efficiency, depending on battery voltage changes. At the same duty, the same power is obtained regardless of the battery voltage using the variable switching frequency. The proposed method is applied to a 5 kW prototype dual active bridge converter, and the experimental results are analyzed and verified.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.40-41
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• 2016

The inverter resistance welder requires AC/DC converter of high efficiency because the converter changes a commercial ac power source to low voltage dc power source. Harmonic components that occur in the conversion process of converter decrease system power factor and deal great damage in electric power system. To improve such problems, this paper proposes a high efficiency AC/DC converter for inverter resistance welder. The switching devices in the proposed converter are operated by soft switching technique using a new quasi-resonant circuit. As a result, the proposed AC/DC converter obtains low switching power loss and high efficiency.

• Proceedings of the KIPE Conference
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• 2007.11a
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• pp.21-23
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• 2007

In this paper a high efficiency bi-directional DC-DC converter for hybrid vehicles is proposed. The proposed converter a three-phase half-bridge interleaved ZVS converter, is designed to have high efficiency in the main operation range. The component ratings are calculated, the actual devices are selected, and the efficiency analysis has been performed to determine optimal ZVS range. The input and output current ripples are significantly reduced due to the interleaved operation. The dual loop control for the interleaved three-phase converter is also presented. To confirm the proposed convert ter, The simulation and experimental results are presented.

• JSTS:Journal of Semiconductor Technology and Science
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• v.12 no.1
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• pp.88-98
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• 2012

In this paper, the relationship between the bandwidth (BW) and power efficiency of a source follower based (SFB) filter is quantitatively analyzed, and a design methodology for a SFB filter for optimized BW - power consumption is introduced. The proposed design methodology achieves a maximum BW at a target quality (Q) factor for the given power consumption constraint by controlling design factors individually. In order to achieve the target BW from the maximized BW, a tuning method is introduced. Through the proposed design methodology, a fourth order Butterworth filter was implemented in 0.18 ${\mu}m$ CMOS technology. The measured BW, power consumption, and IIP3 are 100 MHz, 33 ${\mu}W$, and 9 dBm, respectively. Compared with other filter structures, the measured results show high BW - power efficiency.

• ETRI Journal
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• v.39 no.1
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• pp.51-61
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• 2017

This paper demonstrates a systematic approach for the design of broadband, high efficiency, high power, Class-AB RF amplifiers with high gain flatness. It is usually difficult to simultaneously achieve a high gain flatness and high efficiency in a broadband RF power amplifier, especially in a high power design. As a result, the use of a computer-aided simulation is most often the best way to achieve these goals; however, an appropriate initial value and a systematic approach are necessary for the simulation results to rapidly converge. These objectives can be accomplished with a minimum of trial and error through the following techniques. First, signal gain variations are reduced over a wide bandwidth using a proper pre-matching network. Then, the source and load impedances are satisfactorily obtained from small-signal and load-pull simulations, respectively. Finally, two high-order Chebyshev low-pass filters are employed to provide optimum input and output impedance matching networks over a bandwidth of 100 MHz-500 MHz. By using an EM simulation for the substrate, the simulation results were observed to be in close agreement with the measured results.

• Nuclear Engineering and Technology
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• v.53 no.2
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• pp.637-646
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• 2021

The free-piston Stirling engine (FPSE) has been widely used in aerospace owing to its advantages of high efficiency, high reliability, and self-starting ability. In this paper, a 20-kW FPSE is proposed by analyzing the requirements of space nuclear power reactor. A code was developed based on an improved simple analysis method to evaluate the performance of the proposed FPSE. The code is benchmarked with experimental data, and the maximum relative error of the output power is 17.1%. Numerical results show that the output power is 21 kW, which satisfies the design requirements. The results show that: a) reducing the pressure shell's thickness can improve the output power significantly; b) the system efficiency increases with the wire porosity, while the growth of system efficiency decreases when the porosity is higher than 80%, and system efficiency exhibits a linear relationship with the temperatures of the cold and hot sides; c) the system efficiency increases with the compression ratio; the compression ratio increases by 16.7% while the system efficiency increases by 42%. This study can provide valuable theoretical support for the design and analysis of FPSEs for space nuclear power reactors.

• Journal of Hydrogen and New Energy
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• v.30 no.4
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• pp.303-311
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• 2019

Reversible solid oxide fuel cell (RSOFC) has become a prospective device for energy storage and hydrogen production. Many studies have been conducted around the world focusing on system efficiency improvement and realization. The system should have not only high efficiency but also a certain level of simplicity for stable operation. External waste steam utilization was proved to remarkably increase the efficiency at solid oxide electrolysis system. In this study, RSOFC system coupled with waste steam was proposed and optimized in term of simplicity and efficiency. Ejector for fuel recirculation is selected due to its simple design and high stability. Three system configurations using ejector for fuel recirculation were investigated for performance of design condition. In parametric study, the system efficiencies at different current density were analyzed. The system configurations were simulated using validated lumped model in EBSILON(R) program. The system components, balance of plants, were designed to work in both electrolysis and fuel cell modes, and their off-design characteristics were taken into account. The base case calculation shows that, the system with suction pump results in slightly lower efficiency but stack can be operated more stable with same inlet pressure of fuel and air electrode.