• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1540-1551
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• 2015

The detection of position and speed in BLDC motors without using position sensors has meant many efforts for the last decades. The aim of this paper is to develop a sensorless technique for detecting the position and speed of BLDC motors, and to overcome the drawbacks of position sensor-based methods by improving the performance of traditional approaches oriented to motor phase voltage sensing. The position and speed information is obtained by computing the derivative of the terminal phase voltages regarding to a virtual neutral point. For starting-up the motor and implementing the algorithms of the detection technique, a FPGA board with a real-time processor is used. Also, a versatile hardware has been developed for driving BLDC motors through pulse width modulation (PWM) signals. Delta and wye winding motors have been considered for evaluating the performance of the designed hardware and software, and tests with and without load are performed. Experimental results for validating the detection technique were attained in the range 5-1500 rpm and 5-150 rpm under no-load and full-load conditions, respectively. Specifically, speed and position square errors lower than 3 rpm and between 10º-30º were obtained without load. In addition, the speed and position errors after full-load tests were around 1 rpm and between 10º-15º, respectively. These results provide the evidence that the developed technique allows to detect the position and speed of BLDC motors with low accuracy errors at starting-up and over a wide speed range, and reduce the influence of noise in position sensing, which suggest that it can be satisfactorily used as a reliable alternative to position sensors in precision applications.

• Journal of Power Electronics
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• 제12권1호
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• pp.208-214
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• 2012

This paper presents a novel approach based on the loci of instantaneous symmetrical components called "Wing Shape" which requires the measurement of three input stator currents and voltages to diagnose interturn insulation faults in three phase induction motors operating under different loading conditions. In this methodology, the effect of unbalanced supply conditions, constructional imbalances and measurement errors are also investigated. The sizes of the wings determine the loading on the motor and the travel of the wings while their areas determine the degree of severity of the faults. This approach is also applied to detect open circuit faults or single phasing conditions in induction motors. In order to validate this method, experimental results are presented for a 5 hp squirrel cage induction motor. The proposed technique helps improve the reliability, efficiency, and safety of the motor system and industrial plant. It also allows maintenance to be performed in a more efficient manner, since the course of action can be determined based on the type and severity of the fault.

• 한국지진공학회논문집
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• 제10권5호
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• pp.1-9
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• 2006

본 논문에서는 탄소섬유관으로 구속된 무근 콘크리트 원형 및 각형 기둥에 대한 축하중 및 횡하중 재하 실험을 수행하고, 실험결과를 바탕으로 하여 몬테카를로 해석을 이용한 신뢰성 해석을 수행함으로써 탄소섬유관으로 구속된 무근 콘크리트 원형 및 각형 기둥과 탄소섬유관으로 구속된 철근 콘크리트 원형 및 각형 기둥의 두 가지 경우에 대한 강도저감계수를 예측하였다. 해석 결과, 무근의 경우에는 강도저감계수가 0.7로 예측되었고, 철근이 삽입된 경우에는 강도저감계수가 0.85로 예측 되었다. 이러한 계수값은 원형과 각형인 경우 모두 같은 계수값을 보여주었다.

• 대한기계학회논문집A
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• 제24권4호
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• pp.858-865
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• 2000

It is well recently recognized that quench is one of the serious problems for the integrity of superconducting magnets, which is mainly attribute to the rapid temperature rising in the magnet due to some extrinsic factors such as conductor motion, crack initiation etc. In order to apply acoustic emission(AE)echnique effectively to monitor and diagnose superconducting magnets, it is essential to identify the sources of acoustic emission. In this paper, an acoustic emission technique has been used to monitor and diagnose quenching phenomenon in racetrack shaped superconducting magnets at cryogenic environment of 4.2K. For these purposes special attention was paid to detect AE signals associated with the quench of superconducting magnets. The characteristics of AE parameters have been analyzed by correlating with quench number, winding tension of superconducting coil and charge rate by transport current. In addition, the source location of quench in superconducting magnet was also discussed on the basis of correlation between magnet voltage and AE energy.

• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.1107-1113
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• 2015

Test temperature is an important factor affecting the measurement results of dielectric response of field power transformers. In order to better apply the polarization and depolarization current (PDC) to the condition monitoring of oil-paper insulation system in power transformers, the influences and elimination method of test temperature on PDC characteristic spectroscopy (PDC-CS) were investigated. Firstly, the experimental winding sample was measured by PDC method at different test temperatures, then the PDC-CS was obtained from the measurement results and its changing rules were discussed, which show that the PDC-CS appears a horizontal mobility with the rise of temperature. Based on the rules, the “time temperature shift technique” was introduced to eliminate the influence of test temperature. It is shown that the PDC-CS at different test temperatures can be converted to the same reference temperature coincident with each other.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제28회 춘계학술대회논문집
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• pp.185-188
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• 2007

액체 및 고체추진기관의 내열부품으로 사용하기 위하여 Liquid Silicon Infiltration(액체 실리콘 함침) 공정이 적용된 C/SiC 복합재료를 개발하였다. 탄소섬유 및 탄소직물을 사용하여 필리멘트 와인딩, 테이프 롤링 및 인벌루트 적층 공법이 사용된 다양한 탄소 프리폼이 제작되었다. 내열 부품으로써의 열구조 성능을 극대화시키기 위하여 SiC 함유량, 열처리 조건, 수지 및 기상 함침 조건을 변화시키면서 시편을 제작하고 평가하였다. C/SiC 복합재료를 액체 및 고체추진기관의 내열부품으로 사용하기 위하여 연소시험을 수행하였으며 내열 성능 해석을 위한 수학적 삭마 모델이 개발되었다.

• Tribology and Lubricants
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• 제32권6호
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• pp.201-206
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• 2016

In this study, we attempt to produce a semi-elliptical riblet with a shark skin-like surface using wire electrical discharge machining (WEDM) and micro molding techniques. Our design for the production of the semi-elliptical mold includes an electrode, a winding roller, and a guide on the WEDM system. A replication mold with negative riblets is machined using WEDM, and a shark skin inspired surface with positive riblets is fabricated using a micro molding technique. For a comparison with the original shark skin, a shark skin replica is also produced using the micro molding technique directly from a shark skin template. Droplet contact angles on a flat surface, the shark skin replica, and the epoxy resin-based micro riblet shark skin-like surface are evaluated. The effect of a Teflon coating on the contact angles for the three different surfaces is also investigated. The results show the micro riblet with a shark skin-like surface has a similar contact angle as the shark skin replica, which means that the simplified riblet shark skin surface strongly influences the performance of wettability. This study confirms the effectiveness of using the WEDM method to prepare hydrophobic surfaces with diverse surface patterns.

• Composites Research
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• 제12권6호
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• pp.22-30
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• 1999

$Nb_3Sn$ 복합초전도 테이프는 금속간 화합물로서 다른 초전도 재료에 비하여 임계밀도가 높아 MRI등에 널리 이용되고 있다. 한편 $Nb_3Sn$층은 화합물이므로 bending이나 winding등의 코아 제작시 테이프 도체에 응력이 작용하면 화합물층에 취성으로 인한 크랙이 발생하여 부분적으로 파단이 일어나 임계전류 특성이 열화하며 무응력 상태에 비하여 크게 저하된다. 따라서 이와 같은 $Nb_3Sn$복합초전도 테이프의 실질적인 적용을 위해서는 선재의 제조과정 뿐만 아니라 가동 중에 기계적 응력에 대한$Nb_3Sn$복합 초전도 테이프의 미시적 거동 특성을 필히 이해하여야 할 필요가 있다. 본 연구에서는 음향방출기법(Acoustic Emission)을 이용하여 $Nb_3Sn$ 복합초전도 테이프에 대해서 일정변형속도(constant extension rate)제어로 인장하중이 작용할 경우 발생하는 AE 신호특성과 이에 대응하는 각 화합물층의 미시적 변형거동 특성과의 상관관계를 분석하였다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 추계학술대회 논문집
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• pp.13-14
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• 2013

Multiple output converters (MOCs) are widely used for applications which require various kinds of the output voltages due to its advantages in cost, volume, and efficiency. However, most of the MOCs developed so far can regulate only one output tightly and require as many secondary windings in the transformer as the number of the outputs. In this paper, a novel Time Division Multiple Control (TDMC) method to regulate all the outputs in high precision is proposed and applied to the double ended forward converter for the multiple battery charger. Additional benefit of the proposed topology is to require only one secondary winding in the transformer for all the outputs. The proposed converter can charge two different kinds of batteries or same kind of batteries in different state of charges (SOCs) by CC/CV mode independently with the even degree of tight regulation, thereby satisfying the ripple requirements for each battery.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 추계학술대회 논문집 학회본부
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• pp.101-104
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• 1991

Design characteristics of Interior Permanent Magnet Synchronous Motors are induced. In order to maximize the efficiency of the motor, the objective function is taken stator winding and core losses. And using Sequential Unconstrained Minimization Technique, the dimensions of the motor are obtained which minimize the objective function. Characteristics of the motor which is designed as above are compared with the conventional one.