• E2M - 전기 전자와 첨단 소재
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• 제7권5호
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• pp.417-424
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• 1994

PbNb$_{2}$O$_{6}$ piezoelectric ceramics have good properties, but the applications of them have been limited due to the problems of microstructures. In the present study, effects of additives on the phase stability, microstructure, and electrical proper-ties of ferroetectric phase were investigated. La$_{2}$O$_{3}$, Nd$_{2}$O$_{3}$ and Sm$_{2}$O$_{3}$ were added with the amounts of 1, 3, 5 mol% respectively. The results showed that single orthorhombic(ferroelectric phase) phase compared with the mixed phase of pure PbNb2O6 was obtained. In the case of 5 mol% Nd$_{2}$O$_{3}$ addition, relative density of >95% and dense microstructure with -2.mu.m grain size were obtained.d.

• Journal of Electrical Engineering and Technology
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• 제2권3호
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• pp.289-293
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• 2007

The fault current limiting characteristics of the separated and the integrated three-phase flux-lock type superconducting fault current limiters (SFCLs) were analyzed. The three-phase flux-lock type SFCL consisted of three flux-lock reactors and three $high-T_c$ superconducting (HTSC) elements. In the integrated three-phase flux-lock type SFCL, three flux-lock reactors are connected on the same iron core. On the other hand, three flux-lock reactors of the separated three-phase flux-lock type SFCL are connected on three separated iron cores. The integrated three-phase flux-lock type SFCL showed the different fault current limiting characteristics from the separated three-phase flux-lock type SFCL that the fault phase could affect the sound phase, which resulted in quench of the HTSC element in the sound phase. Through the computer simulation applying numerical analysis for its three-phase equivalent circuit, the fault current limiting characteristics of the separated and the integrated three-phase flux-lock type SFCLs according to the ground fault types were compared.

• 한국정보통신학회논문지
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• 제11권10호
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• pp.1894-1898
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• 2007

본 연구는 산업체에서 널리 사용되어지고 있는 기존의 3상 AC-DC 컨버터에서 무게와 부피를 획기적으로 줄일 수 있는 고역율 3상 AC-DC컨버터를 제안하였다. 제안된 고역율 3상 AC-DC 컨버터는 LC 필터를 제거 한 상태에서 효율성과 다탕성을 검증함으로써 경량화는 물론 저 비용을 실현할 수 있게 된다. 또한 LC 필터를 제거하였음에도 불구하고 성능 면에서 볼 때 기존의 AC-DC 컨버터와 비슷한 성능을 얻을 수 있으므로 고전력 밀도 및 고역율이 요구되는 항공 우주 분야에 응용이 가능해 질 것으로 기대된다.

• 한국세라믹학회지
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• 제26권2호
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• pp.249-257
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• 1989

Dielectric properties and the stability of the perovskite phase in the Pb(Mg1/3Nb2/3)O3 system have been investigated as a function of amount of BaTiO3 and firing temperature. In the specimens fired at 120$0^{\circ}C$, the pyrochlore phase was eliminated by the addition of 10-15m/o BaTiO3 and also the dielectric constant increased. However, the dielectric constant decreased with further addition of BaTiO3 even though no pyrochlore phase was found to be present. The reducing tendency of the pyrochlore phase decreased with lowering the firing temperature in the system of Pb(Mg1/3Nb2/3)O3 with BaTiO3. Dielectric properties in PMN ceramics were affected by the character of the BaTiO3 rather than the pyrochlore phase.

• Journal of Power Electronics
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• 제16권3호
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• pp.982-993
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• 2016

A method for the fault-tolerant vector control of star-connected 3-phase Induction Motor (IM) drive systems based on Field-Oriented Control (FOC) is proposed in this paper. This method enables the control of a 3-phase IM in the presence of an open-phase failure in one of its phases without the need for control structure changes to the conventional FOC algorithm. The proposed drive system significantly reduces the speed and torque pulsations caused by an open-phase fault in the stator windings. The performance of the proposed method was verified using MATLAB (M-File) simulation as well experimental tests on a 1.5kW 3-phase IM drive system. This paper experimentally compares the operation of the proposed fault-tolerant vector controller and a conventional vector controller during open-phase fault.

• 전력전자학회논문지
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• 제7권3호
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• pp.224-236
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• 2002

PWM기법의 성능을 비교하고 있다. 랜덤 펄스 위치 PWM기법은 2상 또는 3상 펄스들을 변조 구간내의 임의의 위치에 랜덤하게 배치하고 인버터 스위칭에 의하여 고조파의 스펙트럼을 광역화하는 RPWM기법이다. 시뮬레이션과 실험에 의하여 인버터 출력 전압의 고조파 스펙트럼과 맥동 전류 파형 그리고 모터의 가청 스위칭 소음의 저감 효과를 비교 검토하였다. 스위칭 손실 및 연산시간 그리고 구현의 용이성에서 3상 RPWM보다는 2상 RPWM이 양호하며, 고조파의 광대역화 측면에서는 3상 RPWM이 보다 좋은 성능을 지니고 있음을 알 수 있었다. 또한 가청 스위칭 소음저감은 2상 RPWM과 3상 RPWM이 거의 유사한 성능을 갖고 있음이 확인되었다.

• 한국운동역학회지
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• 제16권4호
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• pp.115-124
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• 2006

This study was conducted to investigate the running motion in the max-velocity phase(150-160m) and the fatigue phase(350-360m) during 400m sprint by performed elementary school athletes. Eighteen elementary school male athletes who achieved at least the 3rd place in the sprint at the Korea Gangwon-Do elementary school track and field meetings during 2004 and 2005 were selected as subjects. The running motions performed by the subjects were recorded using two 8mm high speed cameras at the nominal speed of 100 frames per second. The Direct Linear Transformation technique was adopted from the beginning of filming to the final stage of data extraction. KWON 3D motion analysis package program was used to compute the 3 Dimensional coordinates, smoothing factor in which lowpass filtering method was used and cutoff frequency was 6.0 Hz. The movement patterns during foot touchdown and takeoff for the running stride were related with the biomechanical consideration. Within the limitations of this study it is concluded: In order to increase running velocity, several conditions must be fullfilled at the instant of leg touchdown and takeoff during the fatigue phase(350-360m). First, the body C.O.G(Center of Gravity) height should be raised at the instant of leg touchdown and takeoff during the fatigue phase. Second, the foot contact time should be shortened and the takeoff distance should be increased at the foot takeoff during the fatigue phase. Third, the shank angular velocity with respect to a transverse axis through the center of gravity should be increased during the leg touchdown and takeoff in the fatigue phase. Forth, the active landing style described as clawing the ground with the sole of the foot should be performed during the leg touchdown and takeoff in the fatigue phase) phase. Fifth, In order to increase running velocity in the fatigue phase while taking a slightly greater leg knee angle and body lean angle within the range of the subject's running motion during the fatigue phase would result in greater flight distance.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.187-189
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• 2007

In this paper, the cascade 3-phase IHMCL inverter using two low frequency transformers is proposed. The proposed inverter is constructed by connecting a 3-phase IHCML inverter. the cascade 3-phase IHCML inverter has several advantages. One advantage is that only one input power source is required because of using transformers to isolate. Another advantage is that the switching frequency of the high power switches is almost fundamental frequency of reference and the other the switching frequency of the low power switches is higher. It can be known that cascade 3 phase IHCML inverter has the excellent efficiency and the outstanding electric quality. lastly, we tested the 5kW cascade 3-phase IHCML inverter to clarify the proposed electric circuit and reasonableness of control signal for the proposed inverter.

• 한국전자통신학회논문지
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• 제16권2호
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• pp.261-270
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• 2021

본 연구에서는 계통 연계 3상 인버터를 위한 LCL 필터를 설계 방법론을 연구하였다. 먼저, 대표적인 필터 구조들에 대해서 3상 인버터의 계통 연계를 위한 필터로서의 적용 시 장단점을 분석하였다. 다음, 3상 인버터의 계통 연계를 위한 필터 설계 방법론들을 분석하여 그리드 연계 시 고조파 요구 조건을 만족할 수 있는 효과적인 필터 설계 방법론을 결정하였다. 그리고 설계 방법론의 유효성을 확인하기 위해서 EMTP-RV를 이용하여 3상 인버터, LCL 필터 그리고 필터의 성능을 평가하기 위한 성능 평가 시스템을 모델링 하였다. 끝으로, 하나의 3상 인버터에 대한 LCL 필터를 설계하였으며, EMTP-RV 시뮬레이션 작업을 통해 3상 인버터의 출력 전류 리플의 크기가 제한됨을 확인함으로서 설계 방법론의 유효성을 검증할 수 있었다.

• 한국태양에너지학회 논문집
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• 제32권spc3호
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• pp.228-234
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• 2012

This paper presents the algorithm of the compensation of the grid current distortion caused by the grid voltage unbalance and distortion in 3-phase bi-directional DC to AC inverter. Usually 3-phase grid system has unbalance and distortion because of connecting 1-phase and non-linear load with 3-phase load using same input node. Controlling 3-phase inverter by general method under the unbalanced and distorted grid voltage, the grid current has distortion. This distortion of the grid current cause the grid voltage distortion again. So, it need to control the grid current balanced and non-distorted, even the grid voltage gets unbalanced and distorted. There are some complex method to compensate the gird current distortion. it sugest simple method to solve the problem. PSIM simulation is used to validate the proposed algorithm.