• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.10
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• pp.186-192
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• 1998

This paper presents a high performance low switching PWM technique or the propulsion system of railway such as subway and high speed train. In order to achieve the continuous voltage control to six-step and s low harmonics with low switching frequency under 500Hz, the synchronous technique is combined with a space vector overmodulation and implemented by using DSP. Improved performance and a validation of proposed method are showed by the digital simulation and the experimental results using a 1.65MVA IGBT VVVF inverter and inertia load equivalent to 160 tons railway cars.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.2
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• pp.152-161
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• 2009

As follow jamming signals in a FHSS system cause malfuctioning in the code tracking circuits using early-late gates, we need a code tracking circuit that is robust against the follow jamming signals. In this paper, we propose a code tracking circuit using a linear clipper-Gaussian filter algorithm to remedy the malfunctioning due to the follow jamming signals in FHSS systems. We investigate the mechanism of the malfunctioning of the code tracking circuit and verify that the proposed linear clipper-Gaussian filter metigates the problem through mathematical analysis and computer simulations.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.3
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• pp.462-469
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• 2001

In this paper, local oscillator in K band using low frequency noise upconversion gain anaylsis was designed and measured. We extended Two Signal Method(TSM) to estimate upconversion gain and resulting phase noise. To confirm the validity of the proposed method, a free-running oscillator which had low upconversion gain was designed. The measured oscillation frequency was 23.42 GHz and phase noise at 1 MHz of offset was -105.2 dBc/Hz. Also, this oscillator was operated for subharmonic injection locked osci1lator(SILO). In this case, SILO showed ideal frequency multiplier phase noise characteristics at low subharmonic injection power level.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.3
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• pp.6-11
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• 2006

This paper describes the novel control techniques design of VSC(Voltage Sag Corrector) for the purpose of power line quality enhancement. A fast detecting technique of voltage sag is implemented through the detection of instantaneous value on synchronous rotating dq-reference frame. The first order digital filter is added in the detection algorithm to protect the insensitive characteristics against the noise. The relationship between the total detection time and cut-off frequency of the filter is described. The size of the capacitor bank used as the energy storage element is designed from the point of view of input/output energy with circuit analysis. Finally, the validity of the proposed scheme is proven through the simulated results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1357-1370
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• 2000

In this paper, we investigate the performance of asynchronous multiple-chip-rate (MCR)-DS/CDMA systems, where singles are transmitted at different chip rates, processing gains, and transmitted powers according to the required services and their own bit rates. A simplified expression for the improved Gaussian approximation (SEIGA), which is hewn for as a very accurate and simple tool for the performance evaluation, is applied to MCR systems, The correlations between chip waveforms and integrations are utilized instead of correlations between chip sequences which are used in conventional method [6] [7][8], and since this approach makes use of the system model parameter directly, we obtain more direct relationship among system parameters. Simulation results show that the performance of MCR-DS/CDMA systems can be evaluated more accurately by using the proposed procedure than by using the GA.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1383-1390
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• 2000

Pilot symbol-based coherent detection is used to increase the link capacity in CDMA systems. In order to detect data efficiently, data signals must be compensated with channel estimation values obtained by using pilot symbols. Many channel estimation schemes were published in previous literatures. However, most of these schemes have performance deterioration in fast fading because of using average vaules of several timeslots. In this paper, we propose an improved channel estimation scheme which is efficient in fast fading and also operates in slow fading satisfactorily. Through computer simulation we show that the proposed scheme has better performance than other schemes in terms of both MSE and BER in fast fading and show robustness for variation in Doppler frequencies.

• Proceedings of the KIEE Conference
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• 2005.04a
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• pp.210-212
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• 2005

최근 급속도로 발전하고 있는 산업분야에서 요구되는 서보 시스템에서 빠른 응답특성, 고도의 정밀성 그리고 안전성에 대한 요구가 커지고 있는 실정이다. 본 논문에서는 이러한 요구에 따라 5상 IPM(Five-phase IPM)의 DTC(Direct torque control)에 대해 고찰하였으며, Texas Instruments사에서 전동기 제어 전용으로 개발된 DSP칩인 TMS320F2812를 이용하여 디지털적으로 제어 알고리즘을 구성하였다. 5상 전동기는 현재 산업현장에서 일반적으로 널리 사용되고 있는 삼상 전동기에 비해 안정성이 높고, 상당 전압의 변화 없이 고정자 전류를 줄일 수 있고, 토크 맥동의 주파수를 높이고 결과적으로 토크의 크기를 감소시킬 수 있다는 여러 가지 장점을 가지고 있으며, 특히 안정성을 요구하는 항공기(Aerospace applications), 전기자동차 및 하이브리드 자동차(Electric or hybrid vehicles)등의 특수한 영역에서 요구가 계속 증가되고 있다. 따라서 본 논문에서는 5상 IPM의 DTC에 대한 특성을 실험을 통하여 확인하였다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.3
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• pp.18-27
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• 2000

Signal attenuation of Ka-band satellite communication system due to rain fading is more severe than those of conventional frequency band system, thus an efficient rain fade countermeasure technique is absolutely required. In this paper, we design an improved adaptive modulation system, which switches the modulation mode according to the channel condition, and propose the novel synchronization algorithms. We assume that the modulation scheme is M-ary PSK and the receiver is TDMA burst mode. And the transponder model is the same with KOREASAT-3. By using the adaptive modulation scheme, we satisfy the BER and mean spectral efficiency requirements, simultaneously, which is impossible by using the fixed modulation scheme.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.8
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• pp.783-789
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• 2002

In this paper, V-band MMIC coupled oscillator arrays are presented. In the proposed array, two push-pull patch antennas are synchronized by using strong electromagnetic coupling between two antennas. As a result, total size of the array is reduced and the array can be integrated in a single chip. To verify proposed array concept, two 1$\times$2 arrays are designed and fabricated using standard 0.15 um gate length pHEMT MMIC process. The circuits are mounted in an oversized waveguide and measured. The first array shows 0.5 dBm at 56.372 GHz and the second one has an output of 5.85 dBm at 60.147 GHz.

• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.29-32
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• 2015

Since the characteristics of Renewable Energy Sources like wind turbine generators are very different from those of existing thermal power generators and their response to the sudden change of the frequency are not as good as that from thermal power generators. Especially when the penetration level of the wind power generation is substantially high, the output from the WTG would be possibly limited to keep the stability of power systems. For this, this paper implements the process for calculating the dynamic penetration limit of WTG and analyze the potential application of BESS for increasing the dynamic penetration limit of WTG.