• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권7호
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• pp.2365-2382
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• 2014

While single-user spatial multiplexing multiple-input multiple-output (SU-MIMO) allows spatially multiplexed data streams to be transmitted to one node at a time, multi-user spatial multiplexing MIMO (MU-MIMO) enables the simultaneous transmission to multiple nodes. However, if the transmission time required to send packets to each node varies considerably, MU-MIMO may fail to utilize the available MIMO capacity to its full potential. The transmission time typically depends upon two factors: the link quality of the selected channel and the data length (packet size). To utilize the cumulative capacity of multiple channels in MIMO applications, the assignment of channels to each node should be controlled according to the measured channel quality or the transmission queue status of the node.A MAC protocol design that can switch between MU-MIMO and multiple SU-MIMO transmissions by considering the channel quality and queue status information prior to the actual data transmission (i.e., by exchanging control packets between transmitter and receiver pairs) could address such issues in a simple but in attractive way. In this study, we propose a new MAC protocol that is capable of performing such switching and thereby improve the system performance of very high throughput WLANs. The detailed performance analysis demonstrates that greater benefits can be obtained using the proposed scheme, as compared to conventional MU-MIMO transmission schemes.

• Journal of international Conference on Electrical Machines and Systems
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• 제3권3호
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• pp.241-247
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• 2014

The voltage source PWM inverter generally used to drive the air conditioning (A/C) fans has been posing a large issue that the bearings in air conditioning fan motors are highly possible to be corroded electrically. Potential difference called shaft voltage is generated between inner and outer rings of the bearings due to inverter switching. The shaft voltage causes bearing lubricant breakdown dielectrically. As a result, bearing current is caused. This current causes the bearing corrosion. In previous work, we demonstrated that the shaft voltage can be reduced by using an insulator inserted between the outer and inner cores of the rotor in an air conditioning fan motor without grounding. This paper proposes the other countermeasure for reducing the shaft voltage in fan motors. The countermeasure which adds a capacitor between the brackets and the stator core is effective even for fan motors with non-insulated rotor. The effectiveness is confirmed by both simulated and experimental results.

• 전자공학회논문지
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• 제49권10호
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• pp.142-147
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• 2012

본 논문에서는 다이나믹 주파수 스케일링 (DFS) 카운터를 사용하여 코오스, 파인 조정 기능을 갖는 CMOS 듀티 사이클 보정회로를 제시한다. DFS 카운터는 디지털-아날로그 컨버터의 비트 스위칭 글리치를 감소시키기 때문에 제안하는 CMOS 듀티 사이클 보정회로의 듀티 보정 범위를 증가시키고 지터 특성을 개선한다. 제안하는 회로는 0.18-${\mu}m$ CMOS 공정을 이용하여 설계되었다. 0.5-1.5GHz의 넓은 동작 주파수와 25-75%의 넓은 듀티 사이클 보정 범위 내에서 측정된 최대 출력 듀티 사이클 에러는 ${\pm}1.1%$이다.

• 한국전기전자재료학회논문지
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• 제33권2호
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• pp.109-113
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• 2020

A power device is a component used as a switch or rectifier in power electronics to control high voltages. Consequently, power devices are used to improve the efficiency of electric-vehicle (EV) chargers, new energy generators, welders, and switched-mode power supplies (SMPS). Power device designs, which require high voltage, high efficiency, and high reliability, are typically based on MOSFET (metal-oxide-semiconductor field-effect transistor) and IGBT (insulated-gate bipolar transistor) structures. As a unipolar device, a MOSFET has the advantage of relatively fast switching and low tail current at turn-off compared to IGBT-based devices, which are built on bipolar structures. A superjunction structure adds a p-base region to allow a higher yield voltage due to lower R_DS (on) and field dispersion than previous p-base components, significantly reducing the total gate charge. To verify the basic characteristics of the superjunction, we worked with a planar type MOSFET and Synopsys' process simulation T-CAD tool. A basic structure of the superjunction MOSFET was produced and its changing electrical characteristics, tested under a number of environmental variables, were analyzed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 심포지엄 논문집 정보 및 제어부문
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• pp.55-57
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• 2007

$CO_2$ laser sees that is most suitable to get this effect through minimum formation damage and advantage that is root enemy of effect that happen in minimum cellular tissue depth of 0.1mm is stable living body organization or internal organs institution. Formation damage by ten can be related in formation's kind or energy density, length of evaporation time. If shorten evaporation time, surroundings cellular thermal damage 200 - because happen within 400ums laser beam in rain focus sacred ground surroundings cellular, tissue without vitiation me by evaporation Poe of very small floor as is clean steam can. Application is possible to vulva cuticle cousins by a paternal aunt quantity, uterine cancer, cuticle tumor by laser system that $CO_2$ laser gets into standard in obstetrics and gynecology application. Because effect that super pulse output is ten enemies of laser if uniformity one pulse durations are short almost is decreased, most of all pulse module special quality of pulse style $CO_2$ laser for obstetrics and gynecology mode stabilization by weight very, in this research to get into short pulse duration and higher frequency density, do switching by high frequency in DC-DC Converter output DC's ripple high frequency to be changed, high frequency done current ripple amount of condenser for output filter greatly reduce can. Ripple of output approximately to Zero realization applying possible inductor realization through a special quality experiment do.

• 대한기계학회논문집A
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• 제32권1호
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• pp.7-12
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• 2008

The vacuum interrupter (VI) is used for medium-voltage switching circuits due to its abilities and advantages as a compacted environmental friendly circuit breaker. In general, the application of a sufficiently strong axial magnetic field (AMF) permits the arc to be maintained in a diffused mode to a high-current vacuum arc. A full understanding of the vacuum arc physics is very important since it can aid to improve the performance of vacuum interrupter. In order to closely examine the vacuum arc phenomena, it is necessary to predict the magnetohydrodynamic (MHD) characteristics by the multidisciplinary numerical modeling, which is coupled with the electromagnetic and hydrodynamic fields, simultaneously. In this study, we have investigated the effect of changing geometrical parameters for electromagnetic behaviors of high-current vacuum arcs with two different types of AMP contacts, which are coil-type and cup-type, using a commercial finite element analysis (FEA) package, ANSYS. The present results are compared with those of MAXWELL 3D, a reliable electromagnetic analysis software, for verification.

• 한국재료학회지
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• 제17권11호
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• pp.569-573
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• 2007

The static and dynamic hydrophobicities of the water droplets placed on a hydrophobic surface coated using a fluoroalkylsilanes monolayer with different molecular chain lengths were investigated through direct observation of the actual droplet motion during the sliding process. The surface roughness of both was found to be less than 1 nm. The static contact angles of the coated FAS-3 and FAS-17 were respectively $80^{\circ}$ and $108^{\circ}$ at $150^{\circ}C$, 1 h. The slope of sliding acceleration against the water droplet mass exhibited an inflection point, thus suggesting the switching of the dominant sliding mode from slipping to rolling. While their sliding angles were similar in value, notable differences were exhibited in terms of their sliding behavior. This can be understood as being due to the contribution of the shear stress difference at the interface between the solid surface and water during the sliding process. These results show that the sliding acceleration of the water droplets depends strongly on the balance between gravitational and retentive forces on the hydrophobic surface.

• 전력전자학회논문지
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• 제5권2호
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• pp.176-183
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• 2000

본 논문에서는 단일 스위치 3상 승압형 컨버터 입력전류의 왜형을 개선하기 위한 6고조파 주입 PWM 방식이 제안디었다. 주기적인 6고조파 전압이 한 스위칭 사이클 내에 컨버터 스위치의 듀비티를 가변하도록 제어회로에 주입되었다. 그 결과 입력 상전류는 입력전압을 따라가고 거의 1에 가까운 역률을 얻었다. 실험결과는 3상 입력 AC 140∼220V, 400V∼6kW 저항부하와 3상 AC 220V, 비선형 부하인 CO2 아크 용접기에 의하여 입증하였다.

• 전력전자학회논문지
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• 제7권5호
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• pp.437-442
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• 2002

본 논문에서는 벅-부스트 형태에 기초한 전류형 PWM 인버터를 제안하고, 이를 태양광과 계통 연계를 위한 인터페이스 회로로서의 타당성을 검증하였다. 제안하는 회로는 다섯 개의 스위칭 소자를 가지게 되는데, 이 중 단 하나의 스위치만이 쵸핑 동작을 수행하게 되고, 나머지 스위치들은 출력단의 정·부 방향을 결정짓는데 이용된다. 따라서, 스위칭에 의한 손실을 상당히 저감시킬 수 있고, 입력단의 인덕터 전류를 전류 불연속 모드로 동작시켜 별도의 입력 전류의 검출이 없이도 출력단을 단위 역률화 할 수 있는 장점을 가진다. 제안하는 계통 연계형 인버터에 대한 동작을 이론적으로 분석하고 DSP TMS320F241을 이용한 150[W]급 시작품의 실험 결과로부터 제안하는 인버터의 타당성을 검증하였다.

• 전력전자학회논문지
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• 제6권2호
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• pp.158-163
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• 2001

PWM 모드로 동작하는 전류형 인버터(CSI)는 구형파 제어형 CSI에 비해 구조가 복잡하여 가격이 비싸지고 공진발생 가능성이 크며 스위칭 손실, EMI등에 의해 동작 효율이 낮다. 그러나 구형파 제어모드의 CSI는 출력전류에 저차 고조파가 다량으로 함유되어 있기 때문에 모터의 토크 맥동이 발생된다. 따라서 본 연구에서는 CSI구동 유도 모터의 토크 맥동을 감소하기 위해, CSI와 유도모터 사이에 능동전력필터를 설피하여 유도모터의 입력전류에 함유되어 있는 고조파 성분을 보상하는 시스템을 제안하였다. 고조파를 보상하기 위한 알고지름으로는 연산과정에 전압이 필요치 않는 노치 필터법을 사용하였으며 PSIM 시뮬레이션에 의해 제안된 시스템의 타단성을 입증할 수 있었다.