• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.1
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• pp.66-74
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• 2012

This paper propose a improved direct torque control(DTC) system for improving operation of five-phase squirrel-cage induction motor(IM). A five-phase IM drives present unique characteristics due to the additional degrees of freedom and also drives possess many others advantage compared with the traditional three-phase motor drive system, such as reducing a amplitude of torque pulsation and increasing the reliability. In order to maximize the torque per ampere, the proposed motor has concentrated windings and the produced back-electromotive force(EMF) is almost trapezoidal, and the motor is supplied with the combined sinusoidal plus third harmonic of currents, there is necessary to controlled 3rd harmonic current. Also a DTC method is advantageous when it is applied to the five-phase IM, because the five-phase inverter provides 32 space vectors in comparison to 8 space voltage vectors into the three-phase inverter drive system. For presenting the superior performance of the proposed DTC, experimental results of speed control are presented using a 32-bit fixed point TMS320F2812 DSP with 1.5[hp] IM.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.57.2-57.2
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• 2017

KVN is a millimeter VLBI array composed of three 21m-diameter radio telescopes at Seoul, Ulsan and Jeju island in Korea. KVN has unique simultaneous multi-frequency receiving systems, which enable us to correct phase fluctuation of troposphere by transferring phase solution of low frequency data to higher frequency data. Although KVN can achieve very high performance up to 130 GHz through multi-frequency technique, imaging capability is highly limited because of lack of the number of baselines. In order to enhance imaging capability and maximizing multi-frequency capability, we plan to extend KVN baselines from 3 to 10 (or more) by constructing new KVN stations. This talk introduce expected performances, science cases, required budgets and periods of the Extended-KVN.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.34.2-34.2
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• 2010

We built 7 potential extra-terrestrial planets including the full 3D Earth model with various surface types and 6 planet models, each with uniform surface characteristics. The surface types include ice, tundra, forest, grass, ground and ocean. We then imported these 7 planets into integrated ray tracing(IRT) model to compute their disk averaged spectra and to understand the spectral behavior depending on the geometrical view, illumination phase and seasonal change. The IRT computation show that the 6 planets with uniform surfaces exhibit clear spectral differences from that of the Earth. We then built a phase and seasonal DAS database for the 6 uniform surface planets and used them for parametric spectral decomposition technique to derive the Earth DAS. This computation resulted in the first potential solution to the surface type ratio of the Earth compared to the measured earth surface type ratio. The computational details and the implications are discussed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.12
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• pp.1215-1218
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• 2013

A 90-deg phase shifter using corrugated square waveguide structure for 86 GHz band VLBI(Very Long Baseline Interferometry) dual-circular polarization observation has been developed. The 90-deg phase shifter was designed to have two corrugated walls inside the square waveguide so that the vertically and horizontally polarized waves at the output port have phase differences of $90{\pm}3.3$ deg across 85~115 GHz. Measurements show that the return and insertion losses for the both polarizations are better than 17 dB and 0.25 dB, respectively. The axial ratio is estimated to be less than 0.6 dB within the required frequency band.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.1
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• pp.1-16
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• 2009

In this paper, we introduce two-phase versions of RoeM and AUSMPW+ schemes. Both schemes are originally developed for the gas dynamic problems, and have shown superior accuracy, efficiency and robustness. A new shock discontinuity sensing term is derived from the mixture equation of state, which is commonly used in the RoeM and AUSMPW+ schemes for the stable numerical flux calculation. The developed two-phase versions of the schemes are applied to several liquid-gas, large property discrepancy two-phase test problems, including several shock stability test problems. The results show that both schemes maintain the merits exhibited in gas dynamic problems even in two-phase flows.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.3
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• pp.251-256
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• 2018

In the case of a radar repeater that used for the trajectory tracking of a high-speed aircraft, it emits pulses of short width. For phase displacement of these signals a branch type phase shifter is used. The phase on the transmission line is changed by utilizing the variable reactance at the end of the displacement branch transmission line. Further, it is easy to control the high output signal, and there is an advantage that the insertion loss is not large even when the reactance fails. In this paper, we will discuss the fabrication test results of a 400 W class phase shifter that sequentially displaces the phase at $0^{\circ}$, $30^{\circ}$, $60^{\circ}$, $90^{\circ}$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.10 s.101
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• pp.1043-1049
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• 2005

In OFDM system suitable for high capacity high speed broadband transmission, ICI caused by phase noise degrades system performance seriously by destroying the orthogonality among subcarriers. In this paper, a new STFBC method combining ICI self cancellation scheme and antenna, time, frequency diversity is studied to reduce ICI effectively. CPE and ICI are analyzed by the phase noise linear approximation method in the proposed STFBC OFDM system. CIR, PICR and BER are discussed to compare the system performance degraded by phase noise of PLL. As results, STFBC method significantly reduces ICI. Furthermore, the SCI that usually happens in the traditional STBC, SFBC diversity coding method can be easily avoided.

• Proceedings of the KIPE Conference
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• 1999.07a
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• pp.307-310
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• 1999

This paper proposes a novel current control method of three-phase PWM rectifiers without phase current sensors. The features of this method are to reconstruct phase currents by using switching pattern of space vector modulation and to estimate phase currents by a predictive state observer for practical applications. Simulation results show that the performance of the proposed system is nearly the same as that of sensor-based system.

• Journal of Electrical Engineering and Technology
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• v.2 no.2
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• pp.231-240
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• 2007

This paper presents an advanced modeling and simulation technique applied to DC/DC power electronic converters fed through renewable energy power sources. The distributed generation (DG) system at the Illinois Institute of Technology, which employs a phase-l system consisting of a photovoltaic-based power system and a phase-2 system consisting of a fuel cell based primary power source, is studied. The modeling and simulation of the DG system is done using the generalized state space averaging (GSSA) method. Furthermore, the paper compares the results achieved upon simulation of the specific GSSA models with those of popular computer aided design software simulations performed on the same system. Finally, the GSSA and CAD software simulation results are accompanied with test results achieved via experimentation on both, the PV-based phase-l system and the fuel cell based phase-2 power system.

• The Bulletin of The Korean Astronomical Society
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• v.31 no.1
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• pp.24-24
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• 2006