• 전기학회논문지
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• 제66권8호
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• pp.1215-1221
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• 2017

Parametric array transducers are used for highly directional speaker in an air environments. Piezoelectric micromachined ultrasonic transducers for parametric array transducers need DC-biased voltage driving signals in order to get high-directional quality-sound features. The existing power amplifier such as class A amplifiers has low efficiency and require large volume heatsinks. To overcome the above-mentioned disadvantages of the conventional amplifier, this paper proposes a new power amplifier system. The proposed power amplifier system ensures high linearity of output characteristic by utilizing the push-pull class B type amplifier. Furthermore, the proposed power amplifier system gets high efficiency because it contains the DC-DC converter-type power supply which can perform energy recovery and envelope tracking function. Also the paper suggests the detailed circuit topology. Its characteristics are verified by the detailed experimental results.

• 동력기계공학회지
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• 제18권5호
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• pp.88-93
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• 2014

In this paper, the performance analysis of condensation and evaporation capacity, turbine work and efficiency of the OTEC power system using vapor-liquid Ejector is presented to offer the basic design data for the operating parameters of the system. The working fluid used in this system is $CO_2$. The operating parameters considered in this study include the vapor quality at heat exchanger outlet, pressure ratio of ejector and inlet pressure of low turbine, mass flow ratio of separator at condenser outlet. The main results were summarized as follows. The efficiency of the OTEC power cycle has an enormous effect on the mass flow ratio of separator at condenser outlet. With a thorough grasp of these effects, it is possible to design the OTEC power cycle proposed in this study.

• Journal of Power Electronics
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• 제16권3호
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• pp.1163-1175
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• 2016

In recent years, microgrids have been the focus of considerable attention in distributed energy distribution. Microgrids contain a large number of power electronic devices that can potentially cause negative impedance instability. Harmonic impedance is an important tool to analyze stability and power quality of microgrids. Harmonic impedance can also be used in harmonic source localization. Precise measurement of microgrid impedance and analysis of system stability with impedances are essential to increase stability. In this study, we introduce a new square wave current injection method for impedance measurement and stability analysis. First, three stability criteria based on impedance parameters are presented. Then, we present a new impedance measurement method for microgrids based on square wave current injection. By injecting an unbalanced line-to-line current between two lines of the AC system, the method determines all impedance information in the traditional synchronous reference frame d-q model. Finally, the microgrid impedances of each part and the overall microgrid are calculated to verify the measurement results. In the experiments, a simulation model of a three-phase AC microgrid is developed using PSCAD, and the AC system harmonic impedance measuring device is developed.

• 전력전자학회논문지
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• 제21권2호
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• pp.160-167
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• 2016

An energy storage system (ESS) is applied to increase the energy efficiency of large plants or buildings that consume much energy, to improve the power quality of power systems, and to stabilize renewable energy source such as photovoltaic or wind turbine. The ESS is composed of a power conditioning system (PCS) and an energy storage. The battery is used as the energy storage. The battery is needed to design and verify a hardware and control system of PCS. Usually, a battery simulator is used instead of a battery, which is costly and hard to manage. In this paper, the development of the battery simulator for performance verification of the MW-class PCS is described. The battery simulator simulates the charging and discharging characteristics of batteries to design and verify the hardware and control system of PCS.

• 동아시아식생활학회지
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• 제19권5호
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• pp.776-782
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• 2009

This study was conducted to develop functional soybean paste with krill (Euphausiacea) as compared to a conventional soybean paste (S1). Soybean containing 10%, 20% and 30% (w/w) krill (S2~S4, respectively) was prepared and quality characteristics (moisture, crude fat, crude protein, ash, reducing sugar, pH, titratable acidity, total acidity and buffering power) were assessed during fermentation for 150 days. As well, antioxidative activities of krill soybean paste were compared to those of control soybean paste based on total phenolic compound content and free radical scavenging activity, including the 1,1-diphenyl-2-picryl-hydrazil (DPPH) scavenging activity and the thiobarbituric acid value (TBA value). The moisture content of all samples decreased to 41.91~53.47% during fermentation, while the crude fat increased to 1.98~5.21% with increasing addition of krill. Additionally, crude protein increased slightly to 8.24~14.08% with increasing addition of krill after 120 days of fermentation. Ash content was 15.96~18.92%. The reducing sugar content of S2, S3 and S4 was higher than those of S1 with increasing length of fermentation. S2, S3, and S4 displayed progressive decreases in pH and progressive increases in titratable acidity compared to S1. The total acidity of all samples was increased, while the buffering power was decreased with increasing fermentation. Especially, the buffering power of S1 was lower than that of S2, S3 and S4. DPPH radical scavenging activity of lipophilic extracts from S2, S3 and S4 was slightly higher than those of S1. However, the radical scavenging activity of hydrophilic extracts from all samples had similar tendencies, regardless of the krill content or fermentation period. Total phenolics increased with increasing fermentation time and TBA value increased with increasing fermentation time and krill content.

• 재활복지공학회논문지
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• 제8권1호
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• pp.41-46
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• 2014

본 논문에서는 잡음 상황에서 강인한 음성 특성을 나타내는 TE (teager energy) 기반의 특징벡터를 이용한 음성 검출 알고리즘을 제안하였다. 입력 신호에 TEO (teager energy operator)를 적용하고, 이를 이용하여 음성 검출 알고리즘에서 우수한 성능을 보여주는 파워 스펙트럼 편차를 구하였다. 또한, 제안된 음성 검출 알고리즘의 성능 향상을 위하여 통계적 모델 기반의 우도비를 TE 기반의 파워 스펙트럼 편차의 가중치 요소로 적용하였다. 제안된 알고리즘의 성능 검증을 위해서 전체 오차율, ROC (receiver operating characteristics), PESQ (perceptual evaluation of speech quality)와 같은 객관적 실험을 수행하였다. 실험결과 5dB SNR 이하의 낮은 SNR을 갖는 비 정상 잡음 환경에서 제안한 음성 검출 알고리즘이 약 2.6%의 전체 오차율 감소와 약 0.053의 PESQ 점수 향상을 나타내었다.

• Transactions on Electrical and Electronic Materials
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• 제13권5호
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• pp.245-247
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• 2012

In this study, ZnO films have been grown on PES (polyethersulfone) of flexible polymer substrate by PLD (pulsed laser deposition) and characterized for crystalline and optical properties. Growing conditions were changed with substrate temperatures ranging from 50 to $200^{\circ}C$ and laser power density ranging from 0.2 to $0.4J/cm^2$. When ZnO thin films are deposited at low temperature with a small laser power density, the (002) peaks of XRD to signify the crystal quality of ZnO thin films appear to be very weak and the (101) peaks to signify the chemical composition of oxygen and zinc are strong. The (002) peaks increase with the substrate temperature and laser power density because the energy needed for the supply of the combination regarding zinc and oxygen has increased. In this study, the best condition for growing ZnO thin film on PES is at a substrate temperature of $200^{\circ}C$ and with a laser density of $0.3J/cm^2$. The characteristics of PL were measured by UV and green luminescence.

• 한국정밀공학회지
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• 제25권7호
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• pp.116-123
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• 2008

In the fossil power plant, the reliability of the components which consist of the many welded parts depends on the quality of welding. The residual stress is occurred by the heat flux of high temperature during weld process. This decreases the mechanical properties as the strength of fatigue and fracture or causes the stress corrosion cracking and fatigue fracture. Especially, the accidents due to the residual stress occurred at the weld parts of high-temperature and high-pressure pipes and steam headers. Also, the residual stress of the welded part in the recently constructed power plants has been brought into relief as the cause of various accidents. The aim of this study is the measurement of the residual stress using the x-ray diffraction method. The merits of this are more accurate and applicable than other methods. The materials used for the study is P92 steel for the use of high temperature pipe on super critical condition. The variables of tests are the post-weld heat treatment, the surface roughness and the depth from the original surface. The test results were analyzed by the distributed characteristics of the full width at half maximum intensity (FWHM) in x-ray diffraction intensity curve and by the relation of hardness with FWHM.

• 조명전기설비학회논문지
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• 제20권3호
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• pp.12-19
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• 2006

마이크로소스는 1[kW]${\sim}$수[MW] 사이의 전력을 공급하고, 기존의 대규모 발전설비보다 높은 신뢰도와 에너지 효율을 가지는 고품질의 전력을 공급할 수 있다. 본 논문에서는 마이크로소스의 스위칭레벨 모델을 개발하였으며, 다수의 마이크로소스가 전력시스템과 연계되어 마이크로그리드를 형성할 경우의 특성에 대하여 연구하였다. 마이크로소스는 인버터의 효율을 극대화 할 수 있도록 공간벡터 펄스폭변조(Space Vector PWM, SVPWM) 기법을 채용하였으며, 마이크로소스의 제어시스템 파라미터 특성 및 마이크로소스 상호작용에 관하여 연구하였다. 마이크로소스는 PSCAD/EMTDC를 이용하여 구현하였으며 이를 이용해 마이크로그리드를 구성하여 시뮬레이션하였다. 사례 연구를 통하여 제안된 모델의 효용성을 확인하였다.

• 전기학회논문지
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• 제62권6호
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• pp.762-766
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• 2013

Interest in Wireless Power Transmission (WPT) technology has been increasing worldwide recently. This trend is proved by commercialized products such as electric toothbrush, wireless razor, and wireless charger for mobile phone battery. Studies for enhancing the applicability of the technology have been continuously conducted. Currently the WPT technology is based on the technologies using microwave, inductively coupling, and magnetic resonance. In the meantime, development of the microwave-based WPT faces difficulty due to health hazards involved in the technology, and application of the WPT technology using inductively coupling is restricted by area due to the problem of transmission length. In comparison, the WPT technology using magnetic resonance draws attention in terms of efficiency and transmission length. In this study, the sending coil based on the WPT technology using magnetic resonance system was replaced with an HTS coil to enhance transmission efficiency. Since the HTS coil has a zero resistance, power transmission loss can be minimized. At the same time, size of the current density could be increased to 100 times or more than typical coils. In addition, through impedance matching of LC device, maximal resonance properties were induced and consequently, frequency selection quality characteristics or Q was enhanced. As a result, the WPT type using the HTS coil showed a longer transmission length and better transmission efficiency compared with the WPT type using typical coils.