• Progress in Superconductivity
• /
• 제11권1호
• /
• pp.57-61
• /
• 2009

A superconductor flywheel energy storage(SFES) system is mainly act an electro-mechanical battery which transfers mechanical energy into electrical form and vice versa. SFES system consists of a pair of non-contacting High Temperature Superconductor (HTS) bearings with a very low frictional loss. But it is essential to design an efficient HTS bearing considering with rotor dynamic properties through correct calculation of stiffness in order to support a huge composite flywheel rotor with high energy storage density. Static properties of HTS bearings provide data to solve problems which may occur easily in a running system. Since stiffness to counter vibration is the main parameter in designing an HTS bearing system, we investigate HTS bearing magnetic force through static properties between the Permanent Magnet(PM) and HTS. We measured axial / radial stiffness and found bearing stiffness can be easily changed by activated vibration direction between PM and HTS bulk. These results are used to determine the optimal design for a 10 kWh SFES.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2011년도 제40회 동계학술대회 초록집
• /
• pp.288-289
• /
• 2011

Indium Tin Oxide (ITO) is a typical highly Transparent Conductive Oxide (TCO) currently used as a transparent electrode material. Most widely used deposition method is the sputtering process for ITO film deposition because it has a high deposition rate, allows accurate control of the film thickness and easy deposition process and high electrical/optical properties. However, to apply high quality ITO thin film in a flexible microelectronic device using a plastic substrate, conventional DC magnetron sputtering (DMS) processed ITO thin film is not suitable because it needs a high temperature thermal annealing process to obtain high optical transmittance and low resistivity, while the generally plastic substrates has low glass transition temperatures. In the room temperature sputtering process, the electrical property degradation of ITO thin film is caused by negative oxygen ions effect. This high energy negative oxygen ions(about over 100eV) can be critical physical bombardment damages against the formation of the ITO thin film, and this damage does not recover in the room temperature process that does not offer thermal annealing. Hence new ITO deposition process that can provide the high electrical/optical properties of the ITO film at room temperature is needed. To solve these limitations we develop the Magnetic Field Shielded Sputtering (MFSS) system. The MFSS is based on DMS and it has the plasma limiter, which compose the permanent magnet array (Fig.1). During the ITO thin film deposition in the MFSS process, the electrons in the plasma are trapped by the magnetic field at the plasma limiters. The plasma limiter, which has a negative potential in the MFSS process, prevents to the damage by negative oxygen ions bombardment, and increases the heat(-) up effect by the Ar ions in the bulk plasma. Fig. 2. shows the electrical properties of the MFSS ITO thin film and DMS ITO thin film at room temperature. With the increase of the sputtering pressure, the resistivity of DMS ITO increases. On the other hand, the resistivity of the MFSS ITO slightly increases and becomes lower than that of the DMS ITO at all sputtering pressures. The lowest resistivity of the DMS ITO is $1.0{\times}10-3{\Omega}{\cdot}cm$ and that of the MFSS ITO is $4.5{\times}10-4{\Omega}{\cdot}cm$. This resistivity difference is caused by the carrier mobility. The carrier mobility of the MFSS ITO is 40 $cm^2/V{\cdot}s$, which is significantly higher than that of the DMS ITO (10 $cm^2/V{\cdot}s$). The low resistivity and high carrier mobility of the MFSS ITO are due to the magnetic field shielded effect. In addition, although not shown in this paper, the roughness of the MFSS ITO thin film is lower than that of the DMS ITO thin film, and TEM, XRD and XPS analysis of the MFSS ITO show the nano-crystalline structure. As a result, the MFSS process can effectively prevent to the high energy negative oxygen ions bombardment and supply activation energies by accelerating Ar ions in the plasma; therefore, high quality ITO can be deposited at room temperature.

• 대한기계학회논문집B
• /
• 제38권3호
• /
• pp.243-254
• /
• 2014

고속 저토크 표면 부착 영구자석형 동기 전동기의 운전 안정성 확보를 위하여 과속도 및 과부하 영역에서 전동기 코일 온도 예측이 필수적이다. 0.35mm 의 S18, S08 등급인 35PN440, 35PN220 그리고 0.15mm 의 저손실 재료인 15HTH1000 으로 제작된 고정자 철심을 포함하는 전동기의 정격 구동 조건에서 손실 및 코일 온도를 측정하여 과속도 및 과부하 영역의 손실 및 열저항을 예측하고 열전달 모델링을 수행하였다. 이의 검증을 위하여 무부하 과속도 영역에서 계산된 코일 온도와 실험값을 비교하여 6.4%이하로 일치하였다. 35PN440 을 적용한 전동기에 비하여 15HTH100 을 적용한 전동기는 무차원 회전속도 0.9, 부하율 3.0 일 때 철손실이 84.4% 로 감소하였고, 무차원 코일 온도 1.0 을 기준으로 출력이 85.2% 향상되었다. 정격 구동 영역의 손실 측정 및 열전달 모델링으로 과부하 및 과속도 영역에서 철심재질에 따른 코일 온도 변화 및 전동기 출력 개선량을 정확하게 예측할 수 있음을 알 수 있다.

• 전력전자학회논문지
• /
• 제17권5호
• /
• pp.401-408
• /
• 2012

A simple on-line elimination strategy of the dead time and inverter nonlinearity using the current slope information is presented for a PWM inverter-fed IPMSM (Interior Permanent Magnet Synchronous Motor) drive. In a PWM inverter-fed IPMSM drive, a dead time is inserted to prevent a breakdown of switching device. This distorts the inverter output voltage, resulting in a current distortion and torque ripple. In addition to the dead time, inverter nonlinearity exists in switching devices of the PWM inverter, which is generally dependent on operating conditions such as the temperature, DC link voltage, and current. The proposed scheme is based on the fact that the d-axis current ripple is mainly caused by the dead time and inverter nonlinearity. To eliminate such an influence, the current slope information is determined. The obtained current slope information is processed by the PI controller to estimate the disturbance caused by the dead time and inverter nonlinearity. The overall system is implemented using DSP TMS320F28335 and the validity of the proposed algorithm is verified through the simulation and experiments. Without requiring any additional hardware, the proposed scheme can effectively eliminate the dead time and inverter nonlinearity even in the presence of the parameter uncertainty.

• 조명전기설비학회논문지
• /
• 제20권4호
• /
• pp.56-64
• /
• 2006

PM BLDC 전동기를 구동하려면 회전자 위치를 검출하는 센서가 필수적으로 요구된다. 그러나 주변 온도나 습도 등 작업 환경에 제한을 받는 곳에서는 센서의 고장 및 오동작으로 인한 전동기의 운전 정지 및 회전자 위치 검출오차에 의한 제어의 어려움이 발생할 수 있다. 따라서 3상 PM BLDC 전동기의 경우 3개의 센서를 이용하는 것이 일반적인 방법으로 사용되고 있지만 본 논문에서는 기존의 회전자 위치 검출 시 1개 또는 2개의 홀 센서만을 사용하여 기존의 방법과 동일한 성능을 가질 수 있는 알고리즘을 제안하였다. 그 결과 기존의 방법과 동일한 성능을 가지며 저가격, 보호회로 역할의 효과를 기대할 수 있다.

• 한국인터넷방송통신학회논문지
• /
• 제17권6호
• /
• pp.83-88
• /
• 2017

본 논문에서는 유도무기용 탐색기의 송신 시 고 전력 송수신 신호 분리를 위한 Ka-대역 밀리미터파 3-포트 도파관 순환기를 설계, 제작하였으며 상온에서의 S-parameter 시험, 고 전력 시험, 운용 온도 시험을 통해 성능을 검증하였다. 탐색기 안테나와의 인터페이스 설계 및 소형, 경량화를 위한 표준 도파관 높이의 half-size 설계를 적용하였다. 전기적 성능 구현을 위해 시뮬레이션을 통한 구성 부품인 영구자석, 페라이트 최적 형상 설계 및 포트 별 튜닝 유전체 적용을 통해 성능을 최적화 하였다. 설계된 도파관 순환기는 중심 주파수 Fc 기준 ${\pm}1000MHz$의 대역에서 -20 dB 이하 반사 손실, 0.5 dB 이하 삽입 손실, -23 dB 이하 분리도 특성을 가지며, 측정 결과는 설계 결과와 유사함을 확인하였다.

• Progress in Superconductivity
• /
• 제10권1호
• /
• pp.55-59
• /
• 2008

A Superconductor Flywheel Energy Storage System(SFES) mainly consists of a pair of non-contacting High Temperature Superconductor(HTS) bearings that provide very low frictional losses, a composite flywheel with high energy storage density. The HTS bearings, which offer dynamic stability without active control, are the key technology that distinguishes the SFES from other flywheel energy storage devices, and great effort is being put into developing this technology. The Superconductor Journal Bearing(SJB) mainly consists of HTS bulks and a stator, which holds the HTS bulks and also acts as a cold head. Static properties of HTS bearings provide data to solve problems which may occur easily in a running system. Since stiffness to counter vibration is the main parameter in designing an HTS bearing system, we investigate SJB magnetic force through static properties between the Permanent Magnet(PM) and HTS. We measure stiffness in static condition and the results are used to determine the optimal number of HTS bulks for a 100kWh SFES.

• 전력전자학회논문지
• /
• 제10권1호
• /
• pp.52-60
• /
• 2005

펄스 폭 변조 전압원 인버터에서는 전압 명령과 실제 전압 사이에 전압 차 또는 전압 왜곡이 존재한다. 이 전압 왜곡은 동작 온도, DC 링크 전압, 및 상전류 수준에 따라 달라진다. 또한 전압 왜곡은 전류 왜곡, 전동기 토크 맥동, 그리고 제어 성능에 영향을 미친다. 본 논문에서는 펄스 폭 변조 전압원 인버터의 전압 왜곡을 분석하고, 모델기준 적응 시스템(Model Reference Adaptive System)을 기반으로 하여 영구자석 동기 전동기의 파라미터 변화에 강인한 새로운 실시간 전압 왜곡 관측 기법을 제안한다. 그리고 제안된 전압 왜곡 관측 및 보상 기법에 대한 모의실험 및 실험을 통해서 그 효용성을 증명한다.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
• /
• pp.100-101
• /
• 2012

The plasma damage free and room temperature processedthin film deposition technology is essential for realization of various next generation organic microelectronic devices such as flexible AMOLED display, flexible OLED lighting, and organic photovoltaic cells because characteristics of fragile organic materials in the plasma process and low glass transition temperatures (Tg) of polymer substrate. In case of directly deposition of metal oxide thin films (including transparent conductive oxide (TCO) and amorphous oxide semiconductor (AOS)) on the organic layers, plasma damages against to the organic materials is fatal. This damage is believed to be originated mainly from high energy energetic particles during the sputtering process such as negative oxygen ions, reflected neutrals by reflection of plasma background gas at the target surface, sputtered atoms, bulk plasma ions, and secondary electrons. To solve this problem, we developed the NBAS (Neutral Beam Assisted Sputtering) process as a plasma damage free and room temperature processed sputtering technology. As a result, electro-optical properties of NBAS processed ITO thin film showed resistivity of $4.0{\times}10^{-4}{\Omega}{\cdot}m$ and high transmittance (>90% at 550 nm) with nano- crystalline structure at room temperature process. Furthermore, in the experiment result of directly deposition of TCO top anode on the inverted structure OLED cell, it is verified that NBAS TCO deposition process does not damages to the underlying organic layers. In case of deposition of transparent conductive oxide (TCO) thin film on the plastic polymer substrate, the room temperature processed sputtering coating of high quality TCO thin film is required. During the sputtering process with higher density plasma, the energetic particles contribute self supplying of activation & crystallization energy without any additional heating and post-annealing and forminga high quality TCO thin film. However, negative oxygen ions which generated from sputteringtarget surface by electron attachment are accelerated to high energy by induced cathode self-bias. Thus the high energy negative oxygen ions can lead to critical physical bombardment damages to forming oxide thin film and this effect does not recover in room temperature process without post thermal annealing. To salve the inherent limitation of plasma sputtering, we have been developed the Magnetic Field Shielded Sputtering (MFSS) process as the high quality oxide thin film deposition process at room temperature. The MFSS process is effectively eliminate or suppress the negative oxygen ions bombardment damage by the plasma limiter which composed permanent magnet array. As a result, electro-optical properties of MFSS processed ITO thin film (resistivity $3.9{\times}10^{-4}{\Omega}{\cdot}cm$, transmittance 95% at 550 nm) have approachedthose of a high temperature DC magnetron sputtering (DMS) ITO thin film were. Also, AOS (a-IGZO) TFTs fabricated by MFSS process without higher temperature post annealing showed very comparable electrical performance with those by DMS process with $400^{\circ}C$ post annealing. They are important to note that the bombardment of a negative oxygen ion which is accelerated by dc self-bias during rf sputtering could degrade the electrical performance of ITO electrodes and a-IGZO TFTs. Finally, we found that reduction of damage from the high energy negative oxygen ions bombardment drives improvement of crystalline structure in the ITO thin film and suppression of the sub-gab states in a-IGZO semiconductor thin film. For realization of organic flexible electronic devices based on plastic substrates, gas barrier coatings are required to prevent the permeation of water and oxygen because organic materials are highly susceptible to water and oxygen. In particular, high efficiency flexible AMOLEDs needs an extremely low water vapor transition rate (WVTR) of $1{\times}10^{-6}gm^{-2}day^{-1}$. The key factor in high quality inorganic gas barrier formation for achieving the very low WVTR required (under ${\sim}10^{-6}gm^{-2}day^{-1}$) is the suppression of nano-sized defect sites and gas diffusion pathways among the grain boundaries. For formation of high quality single inorganic gas barrier layer, we developed high density nano-structured Al2O3 single gas barrier layer usinga NBAS process. The NBAS process can continuously change crystalline structures from an amorphous phase to a nano- crystalline phase with various grain sizes in a single inorganic thin film. As a result, the water vapor transmission rates (WVTR) of the NBAS processed $Al_2O_3$ gas barrier film have improved order of magnitude compared with that of conventional $Al_2O_3$ layers made by the RF magnetron sputteringprocess under the same sputtering conditions; the WVTR of the NBAS processed $Al_2O_3$ gas barrier film was about $5{\times}10^{-6}g/m^2/day$ by just single layer.

• 한국재료학회지
• /
• 제22권11호
• /
• pp.569-574
• /
• 2012

Large single grain $Gd_{1.5}Ba_2Cu_3O_{7-y}$ (Gd1.5) bulk superconductors were fabricated by a top-seeded melt growth (TSMG) process using an $NdBa_2Cu_3O_{7-y}$ seed. The seeded Gd1.5 powder compacts with a diameter of 50 mm were subjected to the heating cycles of a TSMG process. After the TSMG process, the diameter of the single grain Gd1.5 compact was reduced to 43 mm owing to the volume contraction during the heat treatment. The superconducting transition temperature ($T_c$) of the top surface of the single grain Gd1.5 sample was as high as 93.5 K. The critical current densities ($J_cs$) at 77 K and 1T and 1.5 T were in ranges of 25,200-43,900 $A/cm^2$ and 10,000-23,000 $A/cm^2$, respectively. The maximum attractive force at 77 K of the sample field-cooled using an Nd-B-Fe permanent magnet (surface magnetic field of 0. 527 T) was 108.3 N; the maximum repulsive force of the zero field-cooled sample was 262 N. The magnetic flux density of the sample field-cooled at 77 K was 0.311T, which is approximately 85% of the applied magnetic field of 0.375 T. Microstructure investigation showed that many $Gd_2BaCuO_5$ (Gd211) particles of a few ${\mu}m$ in size, which are flux pinning sites of Gd123, were trapped within the $GdBa_2Cu_3O_{7-y}$ (Gd123) grain; unreacted $Ba_3Cu_5O_8$ liquid and Gd211 particles were present near the edge regions of the single grain Gd1.5 bulk compact.