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A Motor-Driven Focusing Mechanism for Small Satellite (소형위성용 모터 구동형 포커싱 메커니즘)

  • Jung, Jinwon;Choi, Junwoo;Lee, Dongkyu;Hwang, Jaehyuck;Kim, Byungkyu
    • Journal of Aerospace System Engineering
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    • v.12 no.4
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    • pp.75-80
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    • 2018
  • The working principle of a satellite camera involves a focusing mechanism for controlling the focus of the optical system, which is essential for proper functioning. However, research on focusing mechanisms of satellite optical systems in Korea is in the beginning stage and developed technology is limited to a thermal control type. Therefore, in this paper, we propose a motor-driven focusing mechanism applicable to small satellite optical systems. The proposed mechanism is designed to generate z-axis displacement in the secondary mirror by a motor. In addition, three flexure hinges have been installed on the supporter for application of preload on the mechanism resulting in minimization of the alignment error arising due to manufacturing tolerance and assembly tolerance within the mechanism. After fabrication of the mechanism, the alignment errors (de-space, de-center, and tilt) were measured with LVDT sensors and laser displacement meters. Conclusively, the proposed focusing mechanism could achieve proper alignment degree, which can be applicable to small satellite optical system.

High-Efficiency CMOS Power Amplifier using Low-Loss PCB Balun with Second Harmonic Impedance Matching (2차 고조파 정합 네트워크를 포함하는 저손실 PCB 발룬을 이용한 고효율 CMOS 전력증폭기)

  • Kim, Hyungyu;Lim, Wonseob;Kang, Hyunuk;Lee, Wooseok;Oh, Sungjae;Oh, Hansik;Yang, Youngoo
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.30 no.2
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    • pp.104-110
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    • 2019
  • In this paper, a complementary metal oxide semiconductor(CMOS) power amplifier(PA) integrated circuit operating in the 900 MHz band for long-term evolution(LTE) communication systems is presented. The output matching network based on a transformer was implemented on a printed circuit board for low loss. Simultaneously, to achieve high efficiency of the PA, the second harmonic impedances are controlled. The CMOS PA was fabricated using a $0.18{\mu}m$ CMOS process and measured using an LTE uplink signal with a bandwidth of 10 MHz and peak to average power ratio of 7.2 dB for verification. The implemented CMOS PA module exhibits a power gain of 24.4 dB, power-added efficiency of 34.2%, and an adjacent channel leakage ratio of -30.1 dBc at an average output power level of 24.3 dBm.

A Study on Load Current and Temperature to Expect Lifetime of High-Power Cables (고전력 케이블의 잔여 수명 예측을 위한 부하 전류 및 온도 연구)

  • Um, Kee-Hong;Lee, Kwan-Woo
    • The Journal of the Institute of Internet, Broadcasting and Communication
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    • v.15 no.4
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    • pp.199-203
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    • 2015
  • With the development of industry these days, the demand for electric power increases and the larger capacity for power transfer is required. The scales of facilities should become larger; and the relative systems are required to operate with a higher degree of reliability. Therefore, stabilization of electric power systems is an important issue. The high degree of reliability required in the process of production and supply of electric power is an essential part of industrial society. Accident such as blackouts causes a hugh amount of economic losses to the high-tech industrial society dependent upon electric power. This paper is about the basic study of the relations between the load current and lifetime of power cables in operation. In order to do the research, we installed a current transformer and an equipment for measuring temperature at the 6.6. kV cables in operation. The two equipments have been installed on the cable systems in operation for the last 20 years. Since the insulation resistance of most of the cables showed the value larger than the threshold, it was not easy to tell the remaining lifetime of cables. The load current of the cables was almost constant. The surrunding temperature was $15{\sim}25^{\circ}C$, little variation of temperature values.

H-Plane 8-Way Rectangular Waveguide Power Divider Using Y-Junction (Y-Junction을 이용한 H-평면 8-Way 구형 도파관 전력 분배기)

  • Lee, Sang-Heun;Yoon, Ji-Hwan;Yoon, Young-Joong;Kim, Jun-Yeon;Lee, Woo-Sang;Park, Seul-Gi
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.23 no.2
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    • pp.151-158
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    • 2012
  • This paper proposes a H-plane 8-way rectangular waveguide power divider using Y-junction. A general N-way power divider can be composed of multi-stage T-junctions. However, if the distances of output ports are close, the matching characteristic is not improved by using only T-junctions because of space limitation. In this case, since other types of 3-port junctions should be used to final output stage, Y-junctions are used with T-junctions in this paper. The proposed Y-junction uses the tapered-line impedance transformer and inductive irises to improve impedance matching characteristic. The 8-way power divider using Y-junction is fabricated and measured. The measured return loss and insertion loss from input port to output port are -30.8 dB and -9.3 dB at operating frequency, respectively. The measured maximum phase difference is about $1^{\circ}$. Therefore, the proposed power divider will be useful to apply to various microwave systems, which need to divide the input power equally, such as feed networks for array antennas.

Microstructure and Electrical Properties of Pb[(Mg,Mn)Nb]O3-Pb(Zr,Ti)O3 Piezoelectric Ceramics

  • Kim, Jin-Ho;Kim, Jong-Hwa;Baik, Seung-Woo
    • Transactions on Electrical and Electronic Materials
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    • v.6 no.5
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    • pp.202-209
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    • 2005
  • Phase evolution, microstructure and the electrical properties such as $k_p$ and $Q_m$ of $Pb(Mg_{1/3}Nb_{2/3})O_3[PMN]-Pb(Mn_{1/3}Nb_{2/3})O3[PM'N]-PbZrO_3[PZ]-PbTiO_3[PT]$ quaternary system were investigated within the compositional ranges $0{\leq}y{\leq}0.125$, y+z=0.125, and $0.39{\leq}x{\leq}0.54$ of the formula $Pb_{0.97}Sr_{0.03}[Mg_{1/3}Nb_{2/3})_y\;(Mn_{1/3}Nb_{2/3})_z\;(Zr_{x}Ti_{1-x})_{1-(y+z)}]O_3$. In the case of increasing Mn/(Mg+Mn) ratio for a fixed Zr/Ti ratio of 47.5/52.5, phase relation remained unchanged but the grain size drastically decreased, and the electrical properties changed as following: both $k_P$ and $Q_m$ reached the peak values at $Mn/(Mg+Mn)\cong0.3l7$ and gradually decreased; $\varepsilon33^T$ showed a monotonic decrease; P-E hysteresis loop gradually changed to asymmetrical one, and $E_i$ increased in correspondence. With increasing Zr/Ti ratio for a fixed Mn/(Mg+Mn) ratio of 0.317, on the contrary, the cell parameter $(\alpha^2c)^{1/3}$ gradually increased, and tetragonal-rhombohedral morphotropic phase boundary appeared in the range of $51/49{\leq}Zr/Ti{\leq}54/46$. the meantime, the grain size substantially increased, and the electrical properties changed as following: $k_P$ and $\varepsilon33^T$ reached peak values at Zr/Ti=51/49 and 48/52, respectively, and then gradually decreased; change of $Q_m$ was adverse to $k_P$; both $E_C\;and\;E_i$ considerably decreased while $P_S$ moderately increased. For the system 0.125(PMN+PM'N)-0.875PZT studied, the composition Mn/(Mg+Mn)=0.3l7 and Zr/Ti=51/49 revealed some promising electrical properties for piezoelectric transformer application such as $k_P=0.58,\;Q_m\cong1000$, and $\varepsilon^T_{33}=970$, as well as dense and fine-grained microstructure.

3-Phase Power Quality Disturbance Generator with Phase Jump Function (위상급변 기능을 갖는 3상 전력품질 외란발생기)

  • Lee, B.C.;Choi, S.H.;Paeng, S.H.;Park, S.D.;Choi, N.S.;Kim, I.D.;Chun, T.W.;Kim, H.G.;Nho, E.C.
    • The Transactions of the Korean Institute of Power Electronics
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    • v.11 no.5
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    • pp.463-470
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    • 2006
  • This paper deals with a new 3-phase power quality disturbance generator. The proposed generator can provide phase jump as well as voltage sag, swell, outage, unbalance, and over and under voltage. The operating principle of the generator is described in each mode of disturbance. The magnitude of the phase jump is analysed and it is found that the magnitude is the function of the turn-ratios of the transformers consisting the generator. The scheme has simple structure compared with the conventional one, and the major components of the proposed scheme are SCR thyristor and transformer, which guarantees high reliability and cost-effective implementation of the generator. Furthermore, high efficiency can be obtained because there is no PWM switching of the semiconductor devices, and it is easy to control the system. Simulations are carried out to confirm the operation in each disturbance mode, and experiments has been done with 5kVA power rating. The usefulness of the proposed scheme is verified through simulation and experimental results. It is expected that the scheme can be applied to the performance test of the custom power devices such as UPS, DVR, DSTATCOM, and SSTS with cost-effective system.

On the Design of Multi-layered Polygonal Helix Antennas (다각 다단 구조 헬릭스 안테나 설계)

  • Choo Jae-Yul;Choo Ho-Sung;Park Ik-Mo;Oh Yi-Sok
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.17 no.3
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    • pp.249-258
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    • 2006
  • In this letter, we propose a novel printed helix antenna for RFID reader in UHF band. The printed strip line of the antenna is first wound up outside a polygonal shaped layer and then the winding continues on an inner layer to control the overall gain and the radiation pattern. In addition, the winding pitch angles on each layer have either negative or positive values resulting in the broad CP bandwidth. The detail structure of the antenna was optimized using Pareto genetic algorithm(GA), so as to obtain excellent performances for RFID reader antennas. The optimized two-layered polygonal helix was fabricated on the cardboard of a flexible substrate and the performances were measured and compared with the simulations. The fabricated antenna was made up of copper tape which can adhere to a flexible cardboard and had 21.4 % matching bandwidth, 31.9 % CP bandwidth, readable range of $5.5m^2$ with kr=3.2. Also based on the current distribution of the strip line of the antenna and sensitivity of the antenna bents points, we confirmed that the antenna has the quarter-wave transformer near the feed for the broad matching bandwidth and radiates the traveling wave for the broad CP bandwidth using the bent strip line.

A Study on the ZVZCS Three Level DC/DC Converter without Primary Freewheeling Diodes (1차측 환류 다이오드를 제거한 ZVZCS Three Level DC/DC 컨버터에 관한 연구)

  • Bae, Jin-Yong;Kim, Yong;Baek, Soo-Hyun;Kwon, Soon-Do;Kim, Pil-Soo;Gye, Sang-Bum
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.16 no.6
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    • pp.66-73
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    • 2002
  • This paper presents ZVZCS(Zero-Voltage and Zero-Current Switching) Three Level DC/DC Converter without primary freewheeling diodes. The new converter presented in this paper used a phase shirt control with a flying capacitor in the primary side to achieve ZVS for the outer switches. A secondary anxiliary circuit which consists of one small capacitor, two small diodes and one coupled inductor, is added in the secondary to provide ZVZCS conditions to primary switches, ZVS for outer switches and ZCS for inner switches. Many advantages include simple secondary auxiliary circuit topology, high efficiency, and low cost make the new converter attractive for high power applications. Also the circulating current flows through the circuit so that it causes the needless coduction loss to be occurred in the devices and the transformer of the circuit The new converter has no primary auxiliary diodes for freewheeling current. The principle of operation, feature and design considerations are illustrated and verified through the experiment with a 1[㎾] 50[KHz]IGBT based experimental circuit.

Analysis on the Deformation Characteristics of a Pillar between Large Caverns by Burton-Bandis Rock Joint Model (Barton-Bandis 절리 모델에 의한 지하대공동 암주의 변형 특성 연구)

  • 강추원;임한욱;김치환
    • Tunnel and Underground Space
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    • v.11 no.2
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    • pp.109-119
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    • 2001
  • Up to now single large cavern was excavated for each undergroud hydraulic powerhouse in Korea. But the Yangyang underground hydraulic powerhouse consists of two large caverns; a powerhouse cavern and main transformer cavern. In this carte, the structural stability of the caverns, especially the rock pillar formed between two large caverns, should be guaranteed to be sound to make the caverns permanently sustainable. In this research, the Distinct Element Method(DEM) was used to analyze the structural stability of two caverns and the rock pillar. The Barton-Bandis joint model was used as a constitutive model. The moot significant parameters such as in-site stress, JRC of in-situ natural joints, and spatial distribution characteristics of discontinuities were acquired through field investigation. In addition, two different cases; 1) with no support system and 2) with a support system, were analysed to optimize a support system and to investigate reinforcing effects of a support system. The results of analysis horizontal displacement and joint shear displacement proved to be reduced with the support system. The relaxed zone in the rock pilar also proved to be reduced in conjunction with the support system. Having a support system in place provided the fact that the non zero minimum principal stresses were still acting in the rock pillar so that the pillar was not under uniaxial compressive condition but under triaxial compressive condition. The structural stability f an approximately 36 m wide rock pillar between two large caverns was assured with the appropriate support system.

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A Three-phase Current-fed DC-DC Converter with Active Clamp (연료전지용 3상 전류형 능동클램프 DC-DC 컨버터)

  • Cha, Han-Ju;Choi, Jung-Wan;Yoon, Gi-Gab
    • The Transactions of the Korean Institute of Power Electronics
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    • v.12 no.6
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    • pp.456-464
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    • 2007
  • This paper proposes a novel three-phase current-fed active clamp DC-DC converter for fuel cells. A single common active clamp branch is used to limit transient voltage across the three-phase full bridge and to realize zero-voltage switching(ZVS) in all switches. To apply for the power generation system current-fed type has been combined with the three-phase power conversion system. The proposed approach has the following advantages: an increase (by a factor of three) of input current and output voltage chopping frequencies; lower RMS current through the inverter switches with higher power transfer capability; reduction in size of reactive later components and the power conditioning system; better transformer utilization; increase of the system reliability. Therefore, the proposed three-phase current-fed active clamp DC-DC converter is appropriate for the boost type DC-DC converter for fuel cells and also applicable for the photovoltaic and battery charge system. The paper details the analysis, simulation and hardware implementation of the proposed system. Finally, experimental results with the proposed PWM strategy demonstrate the feasibility of the proposed scheme on a 500W prototype converter.