• Journal of Power Electronics
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• 제18권1호
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• pp.160-170
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• 2018

For high power photovoltaic (PV) grid-connected converters, high order filters such as multi-tuned filters and Traps+RC filters with outstanding filtering performance have been widely researched. In this paper, the optimization of a multi-tuned filter with a low damping resistance and research on its corresponding control scheme have been combined to improve the performance of the proposed filter. Based on the characteristics of the switching harmonics produced by PWM, the proposed filter is optimized to further improve its filtering performance. When compared with the more common Traps+RC filter, the advantages of the proposed filter with low damping resistances in attenuating the major switching harmonics have been demonstrated. In addition, a simpler topology and reduced power loss can be achieved. On the other hand, to make the implementation of the proposed filter possible, on the base of the unique frequency response characteristic of the proposed filter, a digital single-loop control scheme has been proposed. This scheme is a simple and effective means to suppress the resonance peak caused by a lack of damping. Therefore, a smaller volume, better efficiency of the proposed filter, and easy implementation of the corresponding control scheme can be realized. Finally, the superiority of the proposed filter topology and control scheme is verified in experiments.

• ETRI Journal
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• 제43권2호
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• pp.232-245
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• 2021

As wireless communication continues to develop in limited frequency resource environments, it is becoming important to identify the state of spectrum utilization and predict the amount needed in future. It is essential to collect reliable information for data analysis. This paper introduces a platform that enables the gathering of the scheduling information of a long-term evolution (LTE) cellular system without connecting to the network. A typical LTE terminal can confirm its assigned resource information using the configuration parameters delivered from a network. However, our platform receives and captures only the LTE signal over the air and then enables the estimation of the data relevant to scheduling for all terminals within an LTE cell. After extracting the control channel signal without loss from all LTE subframes, it detects valid downlink control information using the proposed algorithm, which is based on the error vector magnitude of depatterned symbols. We verify the reliability of the developed platform by comparing it with real data from mobile phones and service operators. The average difference in resource block utilization is only 0.28%.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권5호
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• pp.2299-2318
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• 2019

Location-aware networks are of great importance for both civil lives and military applications. Methods based on line-of-sight (LOS) measurements suffer sever performance loss in harsh environments such as indoor scenarios, where sensors can receive both LOS and non-line-of-sight (NLOS) measurements. In this paper, we propose a data association (DA) process based on the expectation maximization (EM) algorithm, which enables us to exploit multipath components (MPCs). By setting the mapping relationship between the measurements and scatters as a latent variable, coefficients of the Gaussian mixture model are estimated. Moreover, considering the misalignment of sensor position, we propose a space-alternating generalized expectation maximization (SAGE)-based algorithms to jointly update the target localization and sensor position information. A two dimensional (2-D) circularly symmetric Gaussian distribution is employed to approximate the probability density function of the sensor's position uncertainty via the minimization of the Kullback-Leibler divergence (KLD), which enables us to calculate the expectation step with low computational complexity. Moreover, a distributed implementation is derived based on the average consensus method to improve the scalability of the proposed algorithm. Simulation results demonstrate that the proposed centralized and distributed algorithms can perform close to the Monte Carlo-based method with much lower communication overhead and computational complexity.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 C
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• pp.2014-2016
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• 2004

In order to obtain a low-loss ferroelectric phase shifter, the reflection-type phase shifter with ferroelectric defected ground structure (DGS) resonators has been designed in this paper. The proposed phase shifter is consist of a 3-dB $90^{\circ}$ branch-line hybrid coupler and terminated reflective circuit with tunable ferroelectric DGS resonator. The ferroelectric DGS unit structure can provide high Q resonator characteristic at high frequencies. The design parameters of equivalent circuit for the tunable DGS resonator are derived by using simple circuit analysis method and three-dimensional full wave finite element method. The fabricated phase shifter has an insertion loss of better than 3.4dB at 13.5GHz.

• 접착 및 계면
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• 제6권1호
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• pp.1-6
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• 2005

The high accurate simulation of very thin glue layers based on the finite element method is still connected to many problems which result from the necessity to construct a complicated mesh of essentially different sizes of elements. This can lead to a loss of accuracy, unstable calculations and even loss of convergence. However, the implementation of special transmission elements along the glue ling and special edge-elements in the near-edge region would lead to a dramatic decrease of number of finite elements in the mesh and thus, prevent unsatisfactory phenomena in numerical analysis and extensive computation time. The theoretical basis for such special elements is the knowledge about appropriate transmission conditions and the edge effects near the free boundary of the adhesive layer. Therefore, recently proposed so-called non-classical transmission conditions and the behavior near the free edge are investigated in the context of the single-lap tensile-shear test of adhesive technology.

• 한국자동차공학회논문집
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• 제19권1호
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• pp.139-146
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• 2011

In present study, it aims to compare the noise and vibration characteristics between magnesium alloy and steel hood panel. The AZ31 magnesium hood panel was fabricated through warm forming process, and the noise and vibration characteristics between both hood panels was compared through the measurement of engine radiation noise and transmission loss, as well as FRF on modal analysis. The sound insulation performance of magnesium alloy was wholly superior to that of steel hood panel, even though the transmission loss of magnesium alloy is lower than that of steel due to mass effect primarily. The FRF characteristics on modal analysis indicates that the resonance frequency of magnesium hood panel is remarkably increased to higher value than that of steel hood panel. The radiation and interior noise of magnesium panel even without acoustic hood insulation were remarkably lower than those of steel hood panel with acoustic insulation, in particular, at a range below 4,000 rpm.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -1
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• pp.654-657
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• 2002

This paper introduces the design and implementation of 40-㎓-band low noise amplifier (LNA) with ultra low gain flatness for wide-band wireless multimedia and satellite communication systems. The 40-㎓-band 4-stage LNA MMIC (Monolithic Microwave Integrated Circuit) demonstrates a small signal gain of more than 20 ㏈, an input return loss of 10.3 ㏈, and an output return loss of 16.3 ㏈ for 37$\square$42 ㎓. The gain flatness of the 40-㎓-band 4-stage LNA MMIC was 0.1 ㏈ for 37$\square$42 ㎓. The noise figure of the 40 ㎓-band LNA was simulated to be less than 2.7 dB for 37~42 ㎓. The chip size of the 4-stage LNA MMIC was 3.7${\times}$1.7 $\textrm{mm}^2$.

• 전기학회논문지
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• 제67권4호
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• pp.538-542
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• 2018

In order to generate a clock source with low cost and high performance in system on chip(SoC), a relaxation oscillator with stable output characteristics according to PVT(process, voltage and temperature) fluctuation require a low area and a low power. In this paper, we propose a solution to reduce the current loss caused by parasitic components in the conventional relaxation oscillator. Since the slew rate of the bias current and the capacitor are adjusted to be the same through the proposed solution, a relaxation oscillator with low area characteristics is designed for the same clock source frequency implementation. The proposed circuit is designed using the TSMC CMOS 0.18um process. The Simulation results show that the relaxation oscillator using the proposed solution can prevent the current loss of about $279{\mu}A$ and reduce the total chip area by 20.8% compared with the conventional oscillator in the clock source frequency of 96 MHz.

• Journal of Electrical Engineering and Technology
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• 제12권2호
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• pp.654-664
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• 2017

This paper proposed an unified dual-phase-shift (UDPS) control for dual active bridge (DAB) converters in order to improve efficiency for a wide output power range. Different operating modes of UDPS are characterized with respect to the reactive current distribution. The proposed UDPS has the same output power capability with conventional phase-shift (CPS) method. Furthermore, its implementation is simple since only the change of the leading phase-shift direction is required for different operating power range. The proposed UDPS control can minimize both the inductor rms current and the circulating reactive current for various voltage conversion ratios and load conditions. The optimal phase-shift pairs for two bridges of DAB converter are derived with respect to the comprehensive reactive power loss model, including the reactive components delivered from the load and back to the source. Simulation and experimental results are illustrated and explained with details. The effectiveness of the proposed method is verified in terms of reactive power losses minimization and efficiency improvement.

• 센서학회지
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• 제25권4호
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• pp.280-284
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• 2016

For an arc-flash protection system, the selection of arc-flash sensor in implementation is largely dependent on the coverage area and the spatial resolution. Typically, a point sensor is used to accurately measure an arc event within a very narrow region; whereas, a loop or a line sensor can cover several electrical compartment at the same time, but with a poor resolution. In this work, a novel scheme for an arc-flash sensor was developed by making use of the transmission loss of plastic optical fibers (POFs) to cover a broad range with a high spatial resolution. By relating the amplitude ratio of the arc-signals at the ends of the POF with the arc-location, arc events could be located with a resolution of ~5 cm within a spatial range of 10 m, which has not been reported yet.