• JSTS:Journal of Semiconductor Technology and Science
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• v.3 no.2
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• pp.89-95
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• 2003

In this paper, we have designed and fabricated high conversion gain Q-band active sub-harmonic mixers for a receiver of millimeter wave wireless communication systems. The fabricated active sub-harmonic mixer uses 2nd harmonic signals of a low local oscillator (LO) frequency. The fabricated mixer was successfully integrated by using $0.1{\;}\mu\textrm{m}$GaAs pseudomorphic high electron mobility transistors (PHEMTs) and coplanar waveguide (CPW) structures. From the measurement, it shows that maximum conversion gain of 4.8 dB has obtained at a RF frequency of 40 GHz for 10 dBm LO power of 17.5 GHz. Conversion gain from the fabricated sub-harmonic mixer is one of the best reported thus far. And a phase noise of the 2nd harmonic was obtained -90.23 dBc/Hz at 100 kHz offset. The active sub-harmonic mixer also ensure a high degree of isolations, which are -35.8 dB from LO-to-IF and -40.5 dB from LO-to-RF, respectively, at a LO frequency of 17.5 GHz.

• Journal of Power Electronics
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• v.5 no.2
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• pp.160-165
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• 2005

In a parallel operation of UPS, there are two types of circulating currents between UPS. One is the low order circulating current with a fundamental frequency caused by the amplitude and phase differences of UPS output voltages, and the other is the harmonic circulating current with PWM switching frequency caused by non-synchronized PWM waveforms among UPS. The elimination of the low order circulating current is essential for optimal load sharing in parallel operations of UPS, which can be accomplished by the phase and magnitude control at each UPS. The harmonic circulating current may cause troubles and deteriorate in performance of the controller for optimal load sharing in parallel operation of UPS. This paper presents a PWM synchronizing method to eliminate the harmonic circulation current in parallel operation of UPS. The effectiveness of the proposed scheme has been investigated and verified through experiments by a 50kVA UPS.

• Journal of Power Electronics
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• v.16 no.3
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• pp.960-969
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• 2016

High-power three-level voltage-source converters are widely utilized in high-performance AC drive systems. In several ultra-power instances, the harmonics on the grid side should be reduced through multiple rectifications. A combined harmonic elimination method that includes a dual primary-side series-connected winding transformer and selective harmonic elimination pulse-width modulation is proposed to eliminate low-order current harmonics on the primary and secondary sides of transformers. Through an analysis of the harmonic influence caused by dead time and DC magnetic bias, a synthetic compensation control strategy is presented to minimize the grid-side harmonics in the dual primary side series-connected winding transformer application. Both simulation and experimental results demonstrate that the proposed control strategy can significantly reduce the converter input current harmonics and eliminates the DC magnetic bias in the transformer.

• Journal of Power Electronics
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• v.13 no.3
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• pp.458-468
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• 2013

Large capacity reactive power compensation and harmonic control in the low-voltage grid of an enterprise, are important technical means to improve power quality and reduce power loss. In this paper, the principle of an efficient power quality controller is analyzed. Then, key application technologies of the HPQC which would influence the performances of the HPQC are studied. Based on an analysis of the harmonic shunt problem, a frequency dividing control strategy of the HPQC continuous subsystem is proposed. A parameter design method of the HPQC discrete subsystem and its installation method are also proposed to ensure the system compensation effect. HPQC systems have been designed for a copper foil plant. The effectiveness of this paper has been verified by the simulation and application results.

• Journal of Korea Multimedia Society
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• v.16 no.10
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• pp.1171-1179
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• 2013

Interactive audio service provide with audio generating and editing functionality according to user's preference. A spatial audio object coding (SAOC) scheme is audio coding technology that can support the interactive audio service with relatively low bit-rate. However, when the SAOC scheme remove the specific one object such as vocal object signal for Karaoke mode, the scheme support poor quality because the removed vocal object remain in the SAOC-decoded background music. Thus, we propose a new SAOC vocal harmonic extranction and elimination technique to improve the background music quality in the Karaoke service. Namely, utilizing the harmonic information of the vocal object, we removed the harmonics of the vocal object remaining in the background music. As harmonic parameters, we utilize the pitch, MVF(maximum voiced frequency), and harmonic amplitude. To evaluate the performance of the proposed scheme, we perform the objective and subjective evaluation. As our experimental results, we can confirm that the background music quality is improved by the proposed scheme comparing with the SAOC scheme.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.2 no.4
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• pp.13-18
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• 2009

This paper suggests that efficiency improvement of power amplifier to enhance harmonic suppression using a DGS line structure. A efficiency related harmonic component is an important factor to design of power amplifier. Therefor harmonic component suppress consisting coupled line using DGS after power amplifier. A DGS line with periodic slits and stubs is first designed and joined after power ampifier. Experimental measurements for efficiency of power amplifier in the WCDMA are shown to improve 6% of PAE.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.5
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• pp.778-785
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• 2017

This paper presents a control method for reducing the distortion of the grid current at a grid-connected three-level neutral point clamped (NPC) inverter. The grid current is distorted from the 5th and 7th harmonic components in the stationary frame current also the 6th harmonic component in the synchronous frame current. In this paper, the 6th harmonic component on synchronous frame is controlled by using all-pass filters (APFs) and proportional integral (PI) controllers for distortion of the grid side. When transformed the 6th harmonic component is controlled, the 5th and 7th harmonic components are reduced. The validity of the proposed control method is verified by simulation and experiment results using a 25kW three-level NPC inverter.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12B
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• pp.1076-1086
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• 2006

In providing video-on-demand (VoD) services to a number of clients through networks, the bandwidth requirements of video transmission restrict VoD services. For this reason, many significant broadcasting-based VoD schemes have been proposed to efficiently support services. However, the broadcasting-based VoD schemes approach needs frequency channel hopping, using many channels at the same time and managing many segments of a video. These make it difficult to implement. In this paper, we propose a Harmonic Staggered broadcasting scheme which has a simple structure and substantially improved VoD efficiency. The numerical results demonstrate that the viewer's waiting time of the Harmonic Staggered broadcasting scheme is close to the harmonic broadcasting scheme and the maximum buffer requirements of this can be adapted for demanding rate by adjusting the short front part of a video sizes.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05b
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• pp.500-504
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• 2004

This research is about the result of leakage current waveform about the situation of surface leakage current and environmental changes(Salt fog, clean fog and rain) by EPDM polymer insulators' amount of salt. The researcher presents the result of changing about fundamental harmonic, 3rd harmonic and 5th harmonic from starting point of supplying power to flashover. In this study, researched environmental affects (clean fog, salt fog and .am) about surface aging of polymer insulators and used frequency spectrum of leakage current waveform to develop the diagnostic technique of surface aging. When amount of salt contents changed, surface aging stage and the degree of aging (distortion factor) about 3rd and 5th harmonir waveform on low frequency harmonic wave. The distortion factor which is harmonic percentage about basic harmonic is important pointer to evaluate the surface condition of polymer insulators.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.2
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• pp.425-431
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• 2011

The harmonic distortion level may be significant in electric propulsion systems, as the main loads usually are variable speed propulsion/thruster drives. Distortion of currents and supply voltage waveforms may lead to: Increased power dissipation(losses) in equipment connected to the network, such as generators, motors, transformers, cables, etc., from the harmonic currents, may cause overheating and deterioration of the insulation, and reduced life time of the equipment. In this paper introduced the canceling method of harmonic currents by a multipulse drive with phase shifting transformer. The simulation results indicated a good speed response to the middle speed range of electric propulsion motor. And also, THD(total harmonic distortion) and torque ripple could be reduced in comparing the 12-pulse drive with 6-pulse drive.