• Journal of Power Electronics
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• 제18권4호
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• pp.1268-1277
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• 2018

A relatively high operating frequency is required for efficient wireless power transfer (WPT). However, the alternating current (AC) resistance of coils increases sharply with operating frequency, which possibly degrades overall efficiency. Hence, the evaluation of coil AC resistance is critical in selecting operating frequency to achieve good efficiency. For a Litz wire coil, AC resistance is attributed to the magnetic field, which leads to the skin effect, the proximity effect, and the corresponding conductive resistance and inductive resistance in the coil. A numerical calculation method based on the Biot-Savart law is proposed to calculate magnetic field strength over strands in Litz wire planar spiral coils to evaluate their AC resistance. An optimized frequency can be found to achieve the maximum efficiency of a WPT system based on the predicted resistance. Sample coils are manufactured to verify the resistance analysis method. A prototype WPT system is set up to conduct the experiments. The experiments show that the proposed method can accurately predict the AC resistance of Litz wire planar spiral coils and the optimized operating frequency for maximum efficiency.

• 한국소음진동공학회논문집
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• 제24권12호
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• pp.992-998
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• 2014

Acoustic radiation efficiency is one of the important factors in the prediction of underwater radiated noise of ships. A ship has much equipment to operate successful mission in a ship. Most of equipment is running simultaneously as multi-excitation and becomes the source of underwater radiated noise. In many cases of multi-excitation, phase difference between multi-excitation is not considered. Because vibration response under multi-excitation is the vector sum of each single excitation, acoustic radiation efficiency based on surface velocity field can be affected by phase of excitation. In this study, acoustic radiation efficiency of a plate on air and a stiffened cylindrical model in water under multi-excitation with phase difference is investigated.

• 대한전자공학회논문지SD
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• 제44권8호
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• pp.8-15
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• 2007

본 논문에서는 산화된 다공질 폴리실리콘을 이용하여 전계 방출 소자를 제작하여, 각각의 픽셀에 따른 전기적 특성과 형광체의 발광 특성을 조사하였다. 실제 대면적 디스플레이 소자에 적용하기 위해서 PM 방식을 이용해서 소자를 픽셀별로 동작하였고, 상부금속 전극의 어레이에 따른 두께와 폭의 공정조건을 확립하였다. 산화된 다공질 폴리실리콘의 미세 구조를 분석하고, 각각의 픽셀에 따른 전계방출 특성을 조사해 보았다. 상부금속 전극의 두께와 폭에 따른 전자방출 특성을 조사해 본 결과 Ti/pt(2nm/7nm)가 가장 적절한 두께라는 것을 확인 할 수 있었고, 2.5 mm 이상 폭에서 전자방출 효율이 증가하는 모습을 확인 할 수 있었다. 각 픽셀에 따른 소자의 전기적 특성은 픽셀마다 조금씩의 차이는 있지만 거의 동일한 누설 전류와 방출 전류가 나타남을 확인할 수 있었고, 동일한 크기의 효율도 관찰할 수 있었다. 누설 전류와 방출 전류는 시간이 증가함에 따라 감소하는 모습이 나타나긴 하였으나, 모든 픽셀이 거의 동일하게 감소하였다. 각각의 픽셀에 따른 휘도는 큰 차이가 없음을 확인할 수 있었고, 20 V에서 $700cd/m^2$ 이상의 높은 휘도를 나타내었으므로 실제 디스플레이 소자로도 응용이 가능할 것이다.

• 지질공학
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• 제25권1호
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• pp.131-148
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• 2015

본 연구는 지열시스템 열교환 효율의 개선방안을 모색하기 위한 것으로 금속재질의 열교환기인 동관 및 스테인레스관과 기존 지열시스템에 많이 적용되는 PE관을 이용하여 지열열교환기의 재질에 따른 열전달 효율을 비교 분석하였다. 또한 지하매질의 지하수에 포함되어 있는 지하수열을 동시 활용할 경우의 열전달 효율 변화를 평가하고 그 적용성을 검토하였다. 열교환기 내의 유속, 유량 및 열교환기의 구경을 조절함으로써 열교환기의 재질에 따른 열전달 효율을 평가 후 현장실증시험 설계인자를 도출하였다. 열교환 효율과 유효 열전도도는 현장 열전달 효율 시험 및 열응답 시험을 통해 변화양상을 분석하였다. 분석결과 금속재질이 PE관에 비해 높은 열전달 효율을 보였으며, 유량에서의 구경증대에 따른 열전달효율은 크지 않았으나 유속에서의 구경증대에 따른 열전달효율은 높아지는 것을 확인하였다.

• 수산해양기술연구
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• 제47권4호
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• pp.290-299
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• 2011

Field tests were carried out with five different mesh sizes (86.6, 101.0, 121.2, 137.7, 151.5mm) to study the relative efficiency of monofilament and multifilament gill net for Marbled sole, Pleuronectes yokohamae, in the western sea of Korea, 2007-2009. The relative efficiency was analyzed by length distribution, catch in number, catch in weight and weight per individual for Marbled sole. Statistical T-test was done to verify the efficiency between two gears. In the field tests, the total body length range, catch in number and weight of Marbled sole was 15.8-48.2cm, 728 and 254,939g, respectively. During the field tests, Marbled sole less than 15cm length which is prohibition size of fishing was not caught, but the caught number of Marbled sole less than 19.5cm length which is first maturity length was 13 (1.8%) and the caught number of Marbled sole more than 19.5cm was 715 (98.2%). Catches of monofilament gill net was average 1.4 times more efficient than multifilament gill net. The weight per individual and total length by mesh sizes in the two gears tended to gradually increase according to mesh size increasing. But there was little difference of weight per individual and total length by mesh sizes between two gears.

• 대한기계학회논문집B
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• 제24권2호
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• pp.251-259
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• 2000

The ionic wind formed in a nonuniform electric field has been recognized to have a significant effect on particle collection in an electrostatic precipitator(ESP). Under normal operating conditions the effect of ionic wind is not pronounced. However, as the flow velocity becomes smaller, the ionic wind becomes pronounced and induces secondary flow, which has a significant influence on the flow field and the particle collecting efficiency. In this paper, experiments for investigating the effect of secondary flow on collection efficiencies were carried out by changing the flow velocities in 0.2-0.7m/s and the applied voltages in 9-11kV/cm. The particle size distributions and concentrations are measured by DMA and CNC. To analyze the experimental results, numerical analysis of electric filed in ESP was carried out. It shows that particle collection is influenced by two independent dimensionless numbers, $Re_{ehd}\;and\;Re_{flow}$ not by $N_{ehd}$ alone. When $Re_{flow}$, decreases for constant $Re_{ehd}$, the secondary flow prohibits the particle collection. But when $Re_{ehd}$ increases for constant $Re_{flow}$, it enhances the particle collection by driving the particles into the collection region.

• 한국도로학회논문집
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• 제10권2호
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• pp.229-239
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• 2008

콘크리트 슬래브를 공장에서 제작하여 도로포장의 신설 또는 보수에 사용하는 공법인 프리캐스트 콘크리트 포장의 하중전달 성능을 평가하기 위하여 연구를 수행하였다. 실내실험을 통해 다웰바 연결 부분의 그라우팅 효과를 측정할 수 있는 방법을 고안하였으며 이러한 실험을 위해 실험체를 제작하여 실험하였다. 실험을 수행한 결과 그리우팅을 한 다웰바의 전단강도는 콘크리트와 일체식으로 된 다웰바의 전단강도에 비해 떨어지지 않음을 알 수 있었다. 이울러 현장에서의 시험시공을 통해 설치된 보수용 프리캐스트 콘크리트 포장에 대해서도 FWD 시험을 실시하여 하중전달 성능을 평가하였다. 현장 실험 결과 기존 콘크리트 포장에 비해 슬래브 중앙부에서의 처짐은 다소 크게 나타나나, 줄눈부에서의 하중전달율은 거의 유사한 것으로 나타났다.

• 전기학회논문지
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• 제65권11호
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• pp.1827-1834
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• 2016

This paper presents a high efficient generator with PM(Permanent Magnet) exciter. The proposed PM exciter for the generator can produce a linear output voltage according to the engine speed. This output voltage is directly used to control the field current of the generator to adjust the generator output voltage. In the proposed generator system, since the field winding current can be supplied by the PM exciter, the generator can self-start without any battery or an external power supply due to the low residential flux. Furthermore, the operating efficiency of the generator is higher than a conventional winding exciter. The main problem of the proposed generator system, the field winding current controller has to be embedded inside the generator, and it rotates according to the generator shaft. In this paper, the proper embedded current controller is designed for the proposed generator system. Due to the embedded controller cannot be connected to the outside the generator controller, the measured instantaneous output voltage of the generator is transferred by the photo isolated communication using shaft aligned infrared transmitter and receiver to keep the constant generator output voltage. In this paper, 10kW, 380V engine generator with PM exciter and the embedded DAVR(Digital Automatic Voltage Regulator) are described. The proposed high efficiency generator is simulated and tested to verify the effectiveness.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2000년도 제1회 학술대회 논문집
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• pp.169-170
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• 2000

The conventional AC PDP has a relatively low efficiency which is close to 1.5 lm/W. If the AC sustain period is replaced by the RF sustain period, due to oscillating and low electric field, almost 60% of the supplied energy is spent by Xe excitation [1]. The efficiency of RF PDP can be $4{\sim}5$ times higher than that of AC PDP. In this paper, we will present the RF PDP that is a new type of PDP. A new display method in PDP using RF pulses is suggested and applied on a 4-inch-diagonal Panel (hereinafter 4" panel). Even though there were many researches in RF discharge, there was not enough research for display application. Now we propose the RF PDP that is a new display field and we will expect to do more research in this field.

• Journal of international Conference on Electrical Machines and Systems
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• 제2권2호
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• pp.216-224
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• 2013

This paper describes dual inverter drive for a fractional-slot concentrated winding permanent magnet synchronous machine (PMSM). PMSMs are widely used in many applications from small servo motors to few megawatts generators thanks to its high efficiency and torque density. Especially, fractional-slot concentrated winding PMSM is very popular in the applications where wide operation range is required because it shows very wide constant power speed ratios. High speed operation, however, requires lots of negative daxis current for reducing back-EMF regardless of output torque. Field weakening current does not contribute to the torque generation in surface mounted PMSM case and causes inverter and copper loss. To reduce the losses from field weakening current, this paper proposes PMSM with split stator and parallel dual inverter drive. Proposed parallel dual inverter drive reduces back-EMF and enables efficient drive at high speed and light load situation. Control strategy of proposed dual inverter system is established through loss analysis and simulation. Proposed concept is verified with practical experiment.