• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 A
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• pp.185-187
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• 1995

A boost converter proposed in this paper operates with high power factor due to input current of sinusoidal waveform. If there were no input LPF, the current is got to be discontinuos form in proportion to AC input voltage magnitude under the constant duty factor switching. Thereupon, the harmonics of input current waveform is reduced and the LPF is made with few elaboration and the control circuit is simple. The switching devices in proposed circuit are operated with soft switching by the partial resonant method. The patial resonant circuit makes use of a reactor using step-up and a capacitor of loss-less snubber. The result is that switching loss is very low and efficiency of system is high.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 A
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• pp.125-127
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• 1998

Superconducting tape is being developed for electrical equipment such as superconducting transformers and generators. AC loss reduction is primary concern in the development of such high-efficiency equipment. AC losses in Bi-2223 silver-sheathed tapes, both single and multi-filamentary, were investigated by means of AC magnetization techniques. The results were compared with the hysteresis loss equation based on Bean model and the eddy current loss equation. The AC loss, of the mono-filamentary tape was the hysteresis. On the contrary, the AC loss of the multi-filamentary tape was substantially dominated by the eddy current loss in the Ag matrix.

• Journal of Electrical Engineering and Technology
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• 제13권1호
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• pp.105-113
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• 2018

This paper proposes pre-analysis on planning of high-voltage direct current (HVDC) transmission system applied to Korea electric power grid. HVDC transmission system for interface lines has been considered as alternative solution for high-voltage AC transmission line in South Korea since constructing new high-voltage AC transmission lines is challenging due to political, environmental and social acceptance problems. However, the installation of HVDC transmission system as interface line in AC grid must be examined carefully. Thus, this paper suggests three scenarios to examine the influences of the installation of HVDC transmission system in AC grid. The power flow and contingency analyses are carried out for the proposed scenarios. Power reserves in metro area are also evaluated. And then the transient stability analysis focusing on special protection scheme (SPS) operations is analyzed when critical lines, which are HVDC lines or high voltage AC lines, are tripped. The latest generic model of HVDC system is considered for evaluating the impacts of the SPS operations for introducing HVDC system in the AC grid. The analyses of proposed scenarios are evaluated by electromechanical simulation.

• Nuclear Engineering and Technology
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• 제51권6호
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• pp.1610-1615
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• 2019

Positron emission tomography (PET)/magnetic resonance (MR) scanning has the advantage of less additional exposure to radiation than does PET/computed tomography (CT). In particular, MR based attenuation correction (MR AC) can greatly affect the image quality of PET and is frequently obtained using various MR sequences. Thus, the purpose of the current study was to quantitatively compare the image quality between MR non-AC (MR NAC) and MR AC in PET images with three MR sequences. Percent image uniformity (PIU), percent contrast recovery (PCR), and percent background variability (PBV) were estimated to evaluate the quality of PET images with MR AC. Based on the results of PIU, 15.2% increase in the average quality was observed for PET images with MR AC than for PET images with MR NAC. In addition, 28.6% and 71.1% improvement in the average results of PCR and PBV respectively, was observed for PET images with MR AC compared with that with MR NAC. Moreover, no significant difference was observed among the average values using three MR sequences. In conclusion, the current study demonstrated that PET with MR AC improved the image quality and can be help diagnosis in all MR sequence cases.

• 조명전기설비학회논문지
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• 제19권8호
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• pp.116-121
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• 2005

전류모드 아날로그 회로를 이용하여 FIR(Finite Impulse Response) 필터를 설계하는 경우에 tap coefficient와 전류모드 FFT(Fast Fourier Transform) LSI의 회전인자(twiddle factor)를 실현시키기 위해서는 높은 정밀도를 갖는 전류 감쇠 회로가 필요하게 된다. 본 논문은 전류 모드 신호처리 기술에서 전류감쇠 회로의 감쇠 정밀도를 향상시킬 수 있는 기술을 소개하고자한다. 먼저 게이트 길이 비율을 조정하는(gate-ratioed) Current Mirror 회로를 사용하는 기존의 전류 감쇠 조정회로에 있어서의 DC offset 전류 에러에 대하여 분석하였으며, 다음으로 DC offset 전류 에러를 제거할 수 있는 전류감쇠 회로를 제안하였다. 회로 구성은 입력 전류를 1/N로 감쇠시킬 수 있도록 N개의 Current Mirror를 병렬로 연결하는 기본 구성을 하였으며, Kirchhoff 전류 법칙에 근거하여, 전류 감쇠가 결정되도록 설계하였다. 또한 Current Mirror 회로에서, 정전류원의 사용을 줄일 수 있는 회로설계를 제안하였다. 제안된 전류 감쇠 회로에서 정밀도는 Current Mirror의 ac 이득 에러에 의하여 제한되며 High Swing Current Mirror를 기본 Current Mirror로 사용한 경우에, 최대 정밀도는 이론상 입력 전류의 -80[dB]까지 실현가능하다.

• Journal of Power Electronics
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• 제15권4호
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• pp.1139-1147
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• 2015

In this paper, an algorithm based on a model analysis of the online calculation of the root-mean-square (RMS) value of welding current for single-phase AC resistance spot welding (RSW) was developed. The current is highly nonlinear and typically non-sinusoidal, which makes the measuring and controlling actions difficult. Though some previous methods focused on this issue, they were so complex that they could not be effectively used in general cases. The electrical model of a single-phase AC RSW was analyzed, and then an algorithm for online calculation of the RMS value of the welding current was presented. The description includes two parts, a model-dependent part and a model-independent part. Using a previous work about online measurement of the power factor angle, the first part can be solved. For the second part, although the solution of the governing equation can be directly obtained, a lot of CPU time must be consumed due to the fact that it involves a lot of complex calculations. Therefore, a neural network was employed to simplify the calculations. Finally, experimental results and a corresponding analysis showed that the proposed algorithm can obtain the RMS values with a high precision while consuming less time when compared to directly solving the equations.

• Journal of Power Electronics
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• 제15권4호
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• pp.1006-1017
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• 2015

This paper presents a finite control set model predictive control (FCS-MPC) strategy for the AC/DC matrix converter used in grid-connected battery energy storage system (BESS). First, to control the grid current properly, the DC current is also included in the cost function because of input and output direct coupling. The DC current reference is generated based on the dynamic relationship of the two currents, so the grid current gains improved transient state performance. Furthermore, the steady state error is reduced by adding a closed-loop. Second, a Luenberger observer is adopted to detect the AC input voltage instead of sensors, so the cost is reduced and the reliability can be enhanced. Third, a switching state pre-selection method that only needs to evaluate half of the active switching states is presented, with the advantages of shorter calculation time, no high dv/dt at the DC terminal, and less switching loss. The robustness under grid voltage distortion and parameter sensibility are discussed as well. Simulation and experimental results confirm the good performance of the proposed scheme for battery charging and discharging control.

• Journal of Power Electronics
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• 제18권6호
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• pp.1920-1929
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• 2018

In order to provide a source for nine phases suitable for 18-pulse ac to dc power, this paper proposes a new structure for a step-up asymmetrical delta-connected transformer for converting three-phase ac power to nine-phase ac power. The design allows for symmetry between the nine output voltages to improve the power quality of the supply current and to minimize the THD. The results show that this new structure proves the equality between the output voltages with $40^{\circ}-{\alpha}$ and $40^{\circ}+{\alpha}$ phase shifting and produces symmetrical output currents. This result in the elimination of harmonics in the network current and provides a simulated THD that is equal to 5.12 %. An experimental prototype of the step-up asymmetrical delta-autotransformer is developed in the laboratory and the obtained results give a network current with a THD that is equal to 5.35%. Furthermore, a finite element analysis with a 3D magnetic field model is made based on the dimensions of the 4kVA, 400 V laboratory prototype three-phase with three-limb delta-autotransformer with a six-stacked-core in each limb. The magnetic distribution flux, field intensity and magnetic energy are carried out under open-circuit operation or load-loss.

• 조명전기설비학회논문지
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• 제21권10호
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• pp.66-72
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• 2007

이 논문은 직류+60[Hz] 교류 중첩전압에서 신품과 노후된 18[kV] 산화아연 서지피뢰기의 누설전류와 전력손실에 대하여 기술하였다. 최대 50[kV]의 직류+60[Hz] 교류를 발생시킬 수 있는 중첩전압발생장치가 설계되고 제작되었다. 피뢰기의 I-V 특성곡선은 전압중첩률 K의 함수로 측정된다. DC와 AC 전압이 중첩된 I-V, R-V 특성곡선은 순수한 직류와 교류곡선 사이에 있고 저전류 영역에서 교차현상이 나타난다. 그 결과 중첩 전압에서 직류 성분의 증가는 ZnO 피뢰기의 전체 누설전류의 저항성분의 증가를 유발한다. 또한 같은 인가전압에서 피뢰기를 통해 흐르는 누설전류는 상용전원에서 장시간 스트레스 받은 피뢰기가 신품 피뢰기에 비해서 높게 나타났다.

• 조명전기설비학회논문지
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• 제17권6호
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• pp.105-112
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• 2003

AC/DC 전력변환장치로서 위상제어 컨버터나 출력전압을 제어할 수 없는 다이오드 정류기는 역률저하 및 저차고조파 발생의 문제점을 가진다. 본 논문에서는 역률개선 및 고조파 감소의 문제점을 극복하기 위하여 3상 PWM AC/DC Boost 컨버터에 대해 연구하였다. 제안한 컨버터의 특성은 입력 단에 전류 센서 없이 전압 센서만을 사용하여 입력전류의 위상을 조정하는 비교적 간단한 알고리즘으로 단위역률을 구현하였으며, 일정 주파수로 스위칭 소자를 구동시키는 정현 PWM 방식을 채용하여 불규칙한 스위칭 주파수 방식에서 나타나는 입력필터의 설계 및 스위칭 소자 선정에 대한 어려움을 극복하였다. 본 논문에서 제안한 제어알고리즘을 시뮬레이션 한 결과 부하영역 및 발전영역에서도 단위역률이 잘 이루어졌으며 DC link 단의 출력전압이 거의 리플 없이 다이나믹한 응답특성을 보였다. 또 시뮬레이션으로 얻어진 회로정수를 바탕으로 인덕터 및 커패시터의 용량을 적절한 크기로 산정하여 실험 에 적용한 결과 같은 부하조건에서 다이오드 정류기와 비교하여 역률 및 저차 고조파가 현저하게 개선되었음을 알 수 있었다.