• 한국전기전자재료학회논문지
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• 제19권4호
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• pp.350-356
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• 2006

In this study, piezoelectric transformer was manufactured at the sintering temperature of $950^{\circ}C$, and then the feasibility of application to low temperature sintering piezoelectric transformers was investigated by evaluating the electrical characteristics of it. The voltage ratio of piezoelectric transformer showed the maximum value at the resonant frequency of input part, and increased according to the increase of load resistance. The output power and efficiency of piezoelectric transformer showed the superior properties when the output impedance of it coincides with the load resistance. Piezoelectric transformer manufactured at the low temperature of $950^{\circ}C$ showed the heat generation less than $20^{\circ}C$ at the output power of 30 W, and stable driving characteristics.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.389-392
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• 2001

In this paper, we have explained electrical characteristics of a step-down Rosen type piezoelectric transformer for AC-adapter. When the electric voltage is applied to the driving piezoelectric vibrator polarized in the longitudinal direction, then output voltage is generated at the generating piezoelectric vibrator polarized in the thickness direction due to the piezoelectric effects. Output voltage and current from a 11-layered and a 13-layered piezoelectric transformer were measured under the various conditions of loads and frequencies. We measured resonant frequency from impedance curve. It was shown from experiments that output voltage has increased and resonant frequency has changed according to various resistor loads. Output current has changed inversely proportional to resistances.

• Journal of Power Electronics
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• 제16권5호
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• pp.1802-1812
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• 2016

Cross regulation is a key technical issue of single-inductor multiple-output (SIMO) DC-DC converters. This paper investigates the cross regulation in single-inductor dual-output (SIDO) Buck converters with continuous conduction mode (CCM) operation. The expressions of the DC voltage gain, control to the output transfer function, cross regulation transfer function, cross coupled transfer function and impedance transfer function of the converter are presented by the time averaging equivalent circuit approach. A small signal model of a SIDO CCM Buck converter is built to analyze this cross regulation. The laws of cross regulation with respect to various load conditions are investigated. Simulation and experiment results verify the theoretical analysis. This study will be helpful for converter design to reduce the cross regulation. In addition, a control strategy to reduce cross regulation is performed.

• 센서학회지
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• 제13권5호
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• pp.363-368
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• 2004

A reliable voltage measurement system is necessary to monitor status of power facilities in substations, which is easy to set up and is not influenced by electromagnetic interference in and around substation. In this paper, we described a voltage measurement system (VMS) which is composed of a capacitive voltage probe, an impedance converter, and an optical linker. To get a wide-band characteristic of the VMS, a high speed impedance converter was used, and the output impedance of the VMS was set at $50{\Omega}$ to match any types of observing instruments. The frequency bandwidth of the VMS. which was estimated by a step pulse, was ranges from 11.42 Hz to 13.65 MHz, and the VMS showed a good response characteristic in a high frequency domain such as impulse voltages as well as a commercial frequency voltage.

• 전력전자학회논문지
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• 제25권4호
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• pp.243-250
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• 2020

Energy harvesting is a recent technology involving the harvest and utilization of extremely small surrounding energy. Energy harvesting research is conducted in various fields. Triboelectric nanogenerators (TENGs) are energy harvesting technologies that use static electricity generated by physical movement or friction. Although TENGs generate output power in microwatt levels, they experience high internal impedance compared with other energy harvesting generators, thereby making the continuous transfer of electric power to loads difficult. This study proposes a power management system for TENGs that consists of three stages, that is, an AC/DC rectifier, an impedance coupler switch with a capacitor bank, and a DC/DC converter. In addition, the selection method of the AC/DC rectifier and DC/DC converter is proposed to maximize the amount of power transferred from energy harvesting areas. Furthermore, the impedance coupler switch and capacitor bank are discussed in detail. The validity and performance of the proposed three-stage power management system for TENGs are verified using a prototype system.

• 한국광학회지
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• 제20권2호
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• pp.65-70
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• 2009

본 논문에서는 높은 입력 임피던스를 가지는 테라헤르츠 Yagi-Uda 안테나를 제안하였다. 제안된 Yagi-Uda 안테나는 두께가 얇은 기판 위에 설계하여 기판의 비유전율에 의한 안테나의 임피던스 저하를 줄이고 Yagi-Uda 안테나 고유의 복사패턴을 가지도록 하였다. 전 파장 길이를 가지는 U-형태의 다이폴을 driver로 사용하여 공진주파수에서 $4,400{\Omega}$ 정도의 높은 입력저항을 얻을 수 있었다. 따라서 제안된 Yagi-Uda 안테나는 기존의 테라헤르츠 안테나들에 비하여 증가된 테라헤르츠파 출력을 얻을 수 있다.

• 조명전기설비학회논문지
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• 제18권6호
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• pp.230-237
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• 2004

본 논문에서는 인버터에서 발생하는 맥동전류가 양자 교환막형 연료전지에 미치는 영향을 임피던스 모델을 통하여 분석한다. 제안된 방법은 주파수 응답 분석법을 이용하여 연료전지 스택의 등가 임피던스를 유도하고, 유도된 모델을 이용하여 맥동전류의 영향을 분석한다. 모델을 통해 계산된 결과는 상용 연료전지 스택을 사용한 실험을 통하여 증명된다. 실험결과는 인버터에 의해 발생한 맥동전류로 인해 최대 10(%)까지 연료전지 스택의 출력이 감소할 수 있음을 보인다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.352-353
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• 2005

In this paper, an ultrasonic level limit sensor with a new structure utilizing the acoustic impedance matching is proposed to be able to check it out a change of water-level. 2 PZT resonators with the same property are bonded directly on the polyethylene plate. One is for transmitter as an ultrasonic transducer, the other one is for receiver. In this case, a polyethylene plate will operate as an acoustic guider to transmit a transverse wave between 2 PZT resonators in air. While in the water, a polyethylene plate having a similar acoustic impedance with the water will be emitted an acoustic energy into the water as a longitudinal wave. According to this mechanism, there was a wide difference of acoustic signal output between underwater and in air. As a summary, it is believed that this proposed level limit sensor could be used as a new one with strong toughness from the external electrical and mechanical noise.

• 한국ITS학회 논문지
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• 제9권2호
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• pp.51-59
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• 2010

본 논문에서는 입력신호의 Peak to Average Power Ratio (PAR) 에 따라 원하는 출력전력 백-오프 (Output Power Back-Off, OPBO) 구간에서 최적의 효율특성을 가지는 반전 타입의 비대칭 도허티 전력증폭기의 설계 방법을 제안하였다. 원하는 OPBO 구간에서 비대칭 도허티 전력증폭기의 최적 효율특성을 얻기 위해 주 증폭기와 피킹 증폭기의 피크 전력비를 결정하였고 피크 전력비에 따른 $90^{\circ}$ 임피던스 변환기의 정확한 임피던스 값을 도출 하였다. 또한 비대칭 도허티 전력증폭기 설계시 최적의 성능을 얻기 위해 오프셋 라인의 길이와 전력 분배비를 계산하였다. 측정결과, 비대칭 도허티 전력증폭기는 CDMA 2000 1x 3-FA 테스트 신호에 대해서 평균 출력 전력 48.7 dBm에서 40%의 전력 효율과 -35 dBc의 인접 채널전력비를 얻었다.

• Journal of Electrical Engineering and Technology
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• 제9권6호
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• pp.2224-2236
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• 2014

The performance of an isolated high voltage full bridge converter is improved using a voltage doubler. In a conventional high voltage full bridge converter, the diode of the transformer secondary voltage undergoes a voltage spike due to the leakage inductance of the transformer and the resonance occurring with the parasitic capacitance of the diode. In addition, in the phase shift control, conduction loss largely increases from the freewheeling mode because of the circulating current. The efficiency of the converter is thus reduced. However, in the proposed converter, the high voltage dual converter consists of a voltage doubler because the circulating current of the converter is reduced to increase efficiency. On the other hand, in the proposed converter, an input current is distributed when using parallel input / serial output and the output voltage can be doubled. However, the voltages in the 2 serial DC links might be unbalanced due to line impedance, passive and active components impedance, and sensor error. Considering these problems, DC injection is performed due to the complementary operations of half bridge inverters as well as the disadvantage of the unbalance in the DC link. Therefore, the serial output of the converter needs to control the balance of the algorithm. In this paper, the performance of the conventional converter is improved and a balance control algorithm is proposed for the proposed converter. Also, the system of the 1.5[kW] PCS is verified through an experiment examining the operation and stability.