• 전력전자학회:학술대회논문집
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• 전력전자학회 2017년도 전력전자학술대회
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• pp.24-25
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• 2017

In this paper, a low cost bridgeless interleaved power factor correction topology for electric vehicle charger application is proposed. With the proposed topology the number of switches, inductors, current sensors and associated circuits can be reduced, thereby reducing the cost of the system as compared to the conventional bridgeless PFC circuit. The reduced input current ripple by the proposed interleaved topology makes it suitable for high power applications such as electric vehicle chargers since it can reduce the size of the inductor core and the Electro Magnetic Interference (EMI) problem. In the proposed topology only one current sensor is required. All the boost inductor currents can be reconstructed by sampling the output current and used to control the input current. Therefore the typical problem caused by the unequal current gain of each current sensor inherently does not exist in the proposed topology. In addition the current sharing between converters can be achieved more accurately and the high frequency distortion is decreased. The performance of the proposed converter is verified by the experimental results with a prototype of 6.6kW bridgeless interleaved PFC circuit.

• 한국위성정보통신학회논문지
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• 제6권2호
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• pp.10-14
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• 2011

본 논문은 최근 급증하는 ISM(Industrial Scientific Medical) 기기 및 무선기기의 사용 증가에 따라 ISM 기기와 무선기기가 인접한 공간에서 운용될 경우 상호간에 간섭이 예측되는 상황에서, ISM 기기와 무선기기 상호간에 간섭 없이 양립할 수 있도록 ISM 기기의 방사 한계치 산출 방법을 제시하였다. ISM 기기의 방사 한계치는 원하는 무선기기의 신호에 무선기기 보호를 위해 요구되는 보호비를 적용하고 이에 보정 요소를 고려하여 산출한다. 이어서 한계치 산출이 요구되는 시나리오를 제시함과 동시에 Matlab GUI(Graphical User Interface)를 이용한 방사 한계치 산출 S/W를 구현하였다. 본 논문에서 제시한 ISM 기기의 방사 한계치 산출 방법은 ISM 기기로부터 무선기기를 보호하기 위한 방안으로 활용될 것으로 기대된다.

• 한국산학기술학회논문지
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• 제8권5호
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• pp.979-983
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• 2007

본 논문에서는 액정용 실드 케이스 (Shield Case)의 스트립 레이아웃 도 작성하였다. 프레스 금형에 있어서 스트립 레이아웃 도는 제품 양산을 결정하는 중요 요인이다. 장착되는 다른 부품과의 간섭요인을 용이하게 수정하기 위하여 3D CAD/CAM 시스템을 적용하였다. 블랭크 레이아웃을 최적화하고 광폭배열로 스트립 레이아웃 하여 재료 이용률을 60.17%로 향상시켰다. 또한 얇은 소재두께로 인해 변형 발생이 예상되는 노칭부위에 집중적으로 비딩공정을 추가하여 제품의 평탄도를 요구사항에 맞게 적용하였다. 사용된 3D CAD/CAM 소프트웨어는 Unigraphics NX 3.0이며 12개 공정으로 스트립 레이아웃 도를 작성하였다.

• Nuclear Engineering and Technology
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• 제49권6호
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• pp.1287-1300
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• 2017

Based on the observation that ignoring the angle dependency of multigroup resonance cross sections within a fuel pellet would result in nontrivial underestimation of the spatial self-shielding of flux, a parametrized spectral superhomogenization (SPH) factor library (PSSL) method is developed as a practical means of resolving the problem. Region-wise spectral SPH factors are calculated by the normal and transport corrected SPH iterations after ultrafine group slowing down calculations over various light water reactor pin-cell configurations. The parametrization is done with fuel temperature, U-238 number density, fuel radius, moderator source represented by ${\Sigma}_{mod}V_{mod}$, and the number density ratio of resonance nuclides to that of U-238 in a form of resonance interference correction factors. The parametrization is successful in that the root mean square errors of the interpolated SPH factors over the fuel regions of various pin-cells are within 0.1%. The improvement in reactivity error of the PSSL method is shown to be superior to that by the original SPH method in that the reactivity bias of -200 pcm to -300 pcm vanishes almost completely. It is demonstrated that the environment effect takes only about 4% in the reactivity improvement so that the pin-cell based PSSL method is effective in the assembly problems.

• Journal of Power Electronics
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• 제19권1호
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• pp.278-287
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• 2019

In this study, a zero-crossing spike current issue in a totem-pole bridgeless power factor correction (PFC) converter is comprehensively investigated for the first time. Spike current occurs when input voltage crosses zero, becomes a noise source, and causes severe common mode emission issues. A generation mechanism for electromagnetic interference (EMI) is presented to investigate the EMI problem caused by zero-crossing issue, and a noise spectrum due to this issue is predicted by a theoretical analysis based on the Fourier coefficient of an approximate spike current waveform. Furthermore, a noise reduction method is proposed and then improved to reduce the spike current. Experimental measurements are implemented on a GaN-based totem-pole bridgeless PFC converter, and the spike current can be effectively suppressed through the proposed method. Furthermore, the noise spectrums measured without and with the reduced zero-crossing spike current are compared. Experimental results validate the analysis of the noise spectrum caused by the zero-crossing spike current issue.

• Journal of Positioning, Navigation, and Timing
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• 제10권2호
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• pp.153-158
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• 2021

In order to mitigate the vulnerability of the satellite navigation system against radio frequency interference, South Korea has been developing advanced terrestrial navigation system (eLoran) technology since 2016. The eLoran system synchronizes the transmission time of the pulse used in the existing Loran-C system with UTC and transmits correction information that can improve the position error. The eLoran system is known to reduce the position error of about 460 m of the existing Loran-C system to 20 m, and for this, the transmitter must be able to transmit eLoran signals according to more stringent standards. For this reason, an international standard that further developed the Loran-C signal standard established by US Coast Guard was established by Society of Automotive Engineers (SAE) International. In this paper, based on the analysis of the SAE9990 document, the international standard for eLoran transmission signals, a standard inspection process was produced to check whether the eLoran transmitter is transmitting signals in accordance with the standard.

• Nuclear Engineering and Technology
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• 제54권2호
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• pp.462-468
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• 2022

The selection and effective utilization of peak-fitting software for conventional gamma-ray spectrum analysis is significant for accurate determination of the mass fraction of elements, particularly in complex peak regions. Majority of the peak-fitting programs can derive similar peak characteristics for singlet peaks, but very few programs can deconvolute multi-peaks in a complex region. The deconvolution of multi-peaks requires special peak-fitting functions, such as left and right-skew distributions. In the this study, 843.76 keV (²⁷Mg) peak area from the complex region (840 keV-850 keV) determined and compared using four different peak-fitting programs, namely, GammaVision, Genie2000, HyperLab, and HyperGam. The 843.76 keV peak interfered with 841.63 keV (^152mEu) and 846.81 keV (⁵⁶Mn). The total Mg concentration was determined through k₀-instrumental neutron activation analysis by applying the isotopic interference correction factor ²⁷Al(n,p)²⁷Mg through the simultaneous determination of Al concentration. HyperLab and HyperGam peak-fitting programs reported consistent peak areas, and resultant concentrations agreed with the certified values of matrix-certified reference materials.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권9호
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• pp.2927-2941
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• 2022

The primary task of machine fault diagnosis is to judge whether the current state is normal or damaged, so it is a typical binary classification problem with mutual exclusion. Mutually exclusive events and out-of-domain detection have one thing in common: there are two types of data and no intersection. We proposed a fusion model method to improve the accuracy of machine fault diagnosis, which is based on the mutual exclusivity of events and the commonality of out-of-distribution detection, and finally generalized to all binary classification problems. It is reported that the performance of a convolutional neural network (CNN) will decrease as the recognition type increases, so the variational auto-encoder (VAE) is used as the primary model. Two VAE models are used to train the machine's normal and fault sound data. Two reconstruction probabilities will be obtained during the test. The smaller value is transformed into a correction value of another value according to the mutually exclusive characteristics. Finally, the classification result is obtained according to the fusion algorithm. Filtering normal data features from fault data features is proposed, which shields the interference and makes the fault features more prominent. We confirm that good performance improvements have been achieved in the machine fault detection data set, and the results are better than most mainstream models.

• ETRI Journal
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• 제45권2호
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• pp.213-225
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• 2023

Physical layer security (PLS) can improve the security of both terrestrial and nonterrestrial wireless communication networks. This study proposes a simplified framework for nonterrestrial cyclic prefixed orthogonal variable spreading factor (OVSF)-encoded multiple-input and multiple-output nonorthogonal multiple access (NOMA) systems to ensure complete network security. Various useful methods are implemented, where both improved sine map and multiple parameter-weighted-type fractional Fourier transform encryption schemes are combined to investigate the effects of hybrid PLS. In addition, OVSF coding with power domain NOMA for multi-user interference reduction and peak-toaverage power ratio (PAPR) reduction is introduced. The performance of $\frac{1}{2}$-rated convolutional, turbo, and repeat and accumulate channel coding with regularized zero-forcing signal detection for forward error correction and improved bit error rate (BER) are also investigated. Simulation results ratify the pertinence of the proposed system in terms of PLS and BER performance improvement with reasonable PAPR.

• Journal of Positioning, Navigation, and Timing
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• 제11권1호
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• pp.23-28
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• 2022

The eLoran system is a high-power terrestrial navigation system that is recognized as the most appropriate alternative to complement the GNSS's vulnerability to radio frequency interference. Accordingly, Korea has conducted eLoran technology development projects since 2016. The eLoran system developed in Korea provides 20 m positioning accuracy to maritime user in Incheon and Pyeongtaek harbor. To accurately calculate the position with the eLoran signal, it is necessary to apply a compensation method that mitigates the propagation delay. In this paper, we develop the compensation method to mitigate the eLoran signal propagation delay and evaluate the positioning performance in Incheon harbor. The propagation delay due to the terrain characteristics is pre-surveyed and stored in the user receiver. Real-time fluctuations in propagation delay compared to the pre-stored data are mitigated by the temporal correction generated at a nearby differential Loran station. Finally, two performance evaluation tests were performed to verify the positioning accuracy of the Korean eLoran system. The first test took place in December 2020 and the second in April 2021. As a result, the Korean eLoran service has been confirmed to provide 20 m location accuracy without GPS.