• 전력전자학회논문지
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• 제25권4호
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• pp.319-328
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• 2020

The recent use of distributed power generation systems constructed with DC-DC converters has become extremely popular owing to the rising need for environment friendly energy generation power systems. In this study, a new single-phase five-level inverter for off-grid applications constructed with a multilevel DC-DC step-up converter is proposed to boost a low-level DC voltage (36 V-64 V) to a high-level DC bus (380 V) and invert and connect them with a single-phase 230 V rms AC load. Compared with other traditional multilevel inverters, the proposed five-level inverter has a reduced number of switching devices, can generate high-quality power with lower THD values, and has balanced voltage stress for DC capacitors. Moreover, the proposed topology does not require multiple DC sources. Finally, the performance of the proposed topology is presented through the simulation and experimental results of a 400 W hardware prototype.

• 조명전기설비학회논문지
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• 제27권5호
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• pp.95-103
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• 2013

Protection of the electrical and electronic equipment against surges in low voltage AC power distribution systems is based on wide applications of surge protective devices(SPDs). Cascade application of SPDs located at the service entrance of a building and near sensitive equipment is intended to ensure the optimal voltage protection level and energy sharing among cascade SPDs. In this paper, when surges impinge at the service entrance of the building of interest, the protection characteristics of two-stage cascade SPD systems were investigated. The influence of the distance between the upstream and downstream SPDs on the voltage protection level and energy sharing of the two-stage cascade SPD systems were analyzed experimentally. It was found that the energy sharing of two-stage cascade SPD systems strongly depends on the distance between the two SPDs and the component of SPD. As the distance between the two SPDs increases, the energy absorbed by the upstream SPD increases while the energy absorbed by the downstream SPD decreases. Consequently, it is desirable to select the upstream and downstream SPDs having the proper energy capability with due consideration of the distance between the two SPDs.

• Journal of Power Electronics
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• 제14권2호
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• pp.271-281
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• 2014

Fluctuating wind conditions necessitate the use of a variable speed wind turbine (VSWT) with a AC/DC/AC converter scheme in order to harvest the maximum power from the wind and to decouple the synchronous generator voltage and frequency from the grid voltage and frequency. In this paper, a combination of a three phase diode bridge rectifier (DBR) and a modified topology of the diode clamped multilevel inverter (DCMLI) has been considered as an AC/DC/AC converter. A control strategy has been proposed for the DCMLI to achieve the objective of grid interface of a wind power system together with local load compensation. A novel fixed frequency current control method is proposed for the DCMLI based on the level shifted multi carrier PWM for achieving the required control objectives with equal and uniform switching frequency operation for better control and thermal management with the modified DCMLI. The condition of the controller gain is derived to ensure the operation of the DCMLI at the fixed frequency of the carrier. The converter current injected into the distribution grid is controlled in accordance with the wind power availability. In addition, load compensation is performed as an added facility in order to free the source currents being fed from the grid of harmonic distortion, unbalance and a low power factor even though the load may be unbalanced, non-linear and of a poor power factor. The results are validated using PSCAD/EMTDC simulation studies.

• 조명전기설비학회논문지
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• 제13권1호
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• pp.94-101
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• 1999

본 논문은 PWM인버터 장치의 스위칭 서지에 관한 문제를 분석한 것이다. 교류 전동기의 효율적인 속도제어를 위한 가변속 구동 장치의 적용이 증가함에 따라 전동기와 가변속 구동장치에 관련된 고장이 발생한다. 산업용 전동기 설비에 PWM 드라이브의 도입은 때때로 높은 과도전압 피크에 의한 상권선 사이 절연파괴를 낳을 수 있다. 높은 스위칭 주파수와 결합한 전동기 케이블 길이는 적?한 드라이브 동작을 위한 매우 민감한 문제가 된다. 케이블 길이와 높은 스위칭주파수의 결과는 전동기와 인버터에 영향을 미칠 수 있다. 전동기 권선 절연레벨이 낮을 때, 높은 피크전압과 빠른 전압상승시간에 의해 생겨난 고장 확률은 높다. 전압반사는 전동기 용량, 여러 가변속 구동장치와 상승시간에 대해 계산하였으며 이를 도식적으로 나타내었다. 인버터 구동 교류 전동기 시스템에서 전동기 단자 과전압과 전압상승률을 줄이기 위한 필터효과도 언급하였다. 연구결과 전동기 용량과 전동기 절연정격 레벨이 낮을수록 그리고 스위칭 시간과 케이블 길이가 짧을수록 절연파괴의 가능성이 높아짐을 알 수 있었다.

• 전력전자학회논문지
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• 제21권3호
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• pp.267-274
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• 2016

In this study, a fast charger for electric vehicle with wide charging voltage range is proposed. To achieve high efficiency, three-level topologies are employed for the AC-DC and DC-DC converters. Given that the output range of the DC-DC converter in fast chargers is quite wide, the circulating current of conventional three-level converter will increase under low voltage condition. The proposed hybrid switching method mitigates this issue. When a coupled inductor is used on the output side, the circulating current is further reduced, and the switches $S_2$, $S_3$, $S_6$, and $S_7$ achieve turning-off under the ZCS condition. Experimental results from a 50 kW prototype are provided to validate the proposed charger, and a rated efficiency of 95.9% is obtained.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권9호
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• pp.403-406
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• 2005

Precise measurement of extremely low resistance shunt is important for characterization and calibration of high current instruments. We tested resistance measurement method for extremely high current shunt (up to 140 kA), where resistance is determined by precise measurement of voltage drop at 10 A test current in the frequency range of 40 Hz to 10 kHz. For the extremely low ac voltage to be precisely measured, a verification of the measurement method was also carried, where the inherent noise is systematically evaluated. The measurement uncertainty was estimated to be $1\;\%\;at\;95\;\%$ confidence level (k=2) for about 50 $\mu\Omega$.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제5B권4호
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• pp.358-365
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• 2005

In induction machine drive without a speed sensor, the estimation of the motor flux and speed often becomes deteriorated at low speeds with low back EMF. Our analysis shows that, in addition to the state resistance variation, the estimated value of field orientation angle is often corrupted by accumulative errors from the integration of voltage variables at motor terminals that have low signal/noise ratio at low frequencies. A repetitive loop path of integration in the feedback can amplify this type of error, thus speeding up the degradation process. The control system runs into information starvation due to the loss of correct field orientation. The machine's spiral vectors are controlled only in a reduced dimension in this situation. A novel control scheme is developed to improve the control performance of motor's current, torque and speed at low frequencies. The scheme gains a full-dimensional vector control and is less sensitive to the combined effect of the error sources at the low frequencies. Experimental tests demonstrate promising performances are achievable even below 0.5 Hz.

• 대한전기학회논문지:시스템및제어부문D
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• 제53권3호
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• pp.161-165
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• 2004

In this paper, we have designed the ground faults detection and interrupting controller at normal condition of AC 120v to 240v rating voltage. Ground faults in electrical network have the characteristics of low current, 60㎐ frequency to 2㎑frequency. The load condition are no load and 20A load. The trip level of the controller is 6㎃ with ground faults. The Controller algorithm is implemented using pic16c71 microprocessor.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2010년도 추계학술대회
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• pp.213-214
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• 2010

The Arc fault is primary reason of electric fire. so we must detect. the purpose of this study is to extend our knowledge of AC-arc characteristics and detect. The Arcs are produced by separating two electrodes made with graphite and copper. A very low separation speed allows arcs to reinitiate, as in arc fault in wires. Power is 220Vrms-60Hz and the load is light bulbs and capacities are 220W, 660W and 1100W. I measured Arc voltage and current. and defined voltage and current Max level, voltage plateau and Arc-power at each cycle.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.1788_1789
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• 2009

본 논문에서는 핵폭발과 같은 고준위방사선환경에서의 전자부품소자의 피해평가분석을 통하여 군용전자장비의 내방사선화를 하기 위한 기반기술의 확립을 위한 연구의 일환으로 74AC04(Inverter) IC에 대한 고준위감마선조사시험을 통하여 Co-60 Gamma-ray 선원을 사용하여 총 400Krad[si] 누적 선량에 대한 74AC04 소자의 동작특성 및 전기적 파라메터의 변화분석을 진행하였다. 시험평가 방법 및 절차는 MIL-STD-883G 1019.7[1] 및 ESA/SCC Basic Specification No.22900[2] 절차를 기준으로 하여 동일 lot에 대한 5개의 샘플을 이용하여 동작특성에 영향을 미치는 주요한 전기 적파라메터인 정지소비전류, 입력누설전류, VIL(Maximum Low Level Input Voltage)에 대한 변화추이를 분석하였다. 이번 조사시험을 통하여 입력게이트에서의 누적선량에 따른 TID(Total Ionizing Dose) 효과로 인한 VIL의 감소 추이를 확인 할 수 있었으며 총 누적선량 160Krad 이상에서의 VIL은 허용기준치이하로 감소하였고 정지소비전류의 경우 누적선량에 따른 점진적 증가 현상과 200Krad부근에서의 설계스펙허용치를 초과하는 결과를 확인하였다.