• Journal of the Korean Institute of Telematics and Electronics B
• /
• v.30B no.4
• /
• pp.130-137
• /
• 1993

In this paper, A progressive coding of mean difference pyramid by Hadamard transform of the difference between two successive pyramid levels has been studied. A block adaptive bit allocation method based on ac energy of each sub-block has been proposed, which efficiently reduces the final distortion in the progressive transmission of image parameters. In our scheme, the dc energy equals the sum of the quantization errors of the Hadamard transform coefficients at previous level. Therefore proposed allocation method includes the estimation of dc energy at each pyramid level. Computer simulation results show some improvements in terms of MSE and picture quality over the conventional fixed allocation scheme.

• Journal of the Korean Institute of Telematics and Electronics B
• /
• v.31B no.1
• /
• pp.72-80
• /
• 1994

In this paper, a new variable block-size transform coding algorithm using information of segmentation is proposed. In general variable block-size transform coding algorithms, the information which is used to form variable blocks is thrown away, but in the proposed algorithm, the information of segmentation which is composed of texture and contour information is maintained for efficient coding. That is, the number of blocks can be reduced by contour information, a DC component of block can be predicted by texture information, and the region compensation, which reduces mean difference between regions, using texture and contour information can diminish the magnitude of AC components. The result is that the proposed algorithm has improved highly the coding efficiency of DC and AC components.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.35D no.11
• /
• pp.46-54
• /
• 1998

A planar Bi-Sb multijunction thermal converter, which is consisted of a linear or bifilar thin film NiCr-heater and a thin film Bi-Sb thermopile, has been fabricated, and its ac-dc transfer characteristics were examined in a frequency range from 10 Hz to 10 KHz. In order to increase the thermal sensitivity and to decrease the ac-dc transfer error of a thermal converter, the heater and the hot junctions of a thermopile were prepared on a Si$_3$N$_4$/SiO$_2$/Si$_3$N$_4$-diaphragm which acts as a thermal isolation layer, and the cold junctions on the Si$_3$N$_4$/SiO$_2$/Si$_3$N$_4$-thin film supported with the silicon rim which functions as a heat sink. The respective thermal sensitivities in air and in a vacuum of the converter with a built-in bifilar heater were about 14.0 ㎷/㎽ and 54.0 ㎷/㎽, and the ac-dc voltage and the current transfer difference ranges in air were about $\pm$0.60 ppm and $\pm$0.11 ppm, respectively, indicating that the ac-dc transfer accuracy of the converter are much higher than that of a commercial 3-dimensional multijunction thermal converter. However, the output thermoelectric voltage fluctuation of the converter was rather high.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.12 no.4
• /
• pp.551-561
• /
• 2001

In this paper, the large signal unified model is established for H4O GaAs pHEMT of GEC-Marconi using modified Curtice model. This unified model includes DC characteristic, small signal, and noise characteristic as various bias. Particularly, the model can simply and physically explain trans-conductance $(g_m)$ of pHEMT using modified Curtice model, and can tell the difference $g_m$, $R_ds$ at DC and these at AC through inclusion of internal RF-choke. The results of the established model built up using SDD in HP-Eessof show good agreement to the S/W measured data in DC, small signal, and noise characteristic. This model can also be applied to various computer aided analysis, such as linear simulation, 1-tone harmonic balance simulation, and multi-tone harmonic balance simulation, so the LNA(Low Noise Amplifier), oscillator, and mixer design has been shown using this model library.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.22 no.2
• /
• pp.95-101
• /
• 2017

A simple and practical voltage balance method for a solid-state transformer (SST) is proposed to reduce the voltage difference of cascaded H-bridge converters. The tolerance device components in SST cause the imbalance problem of DC-link voltage in the H-bridge converter. The Max/Min algorithms of voltage balance controller are merged in the controller of an AC/DC rectifier to reduce the voltage difference. The DC-link voltage through each H-bridge converter can be balanced with the proposed control methods. The design and performance of the proposed SST are verified by experimental results using a 30 kW prototype.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.64 no.8
• /
• pp.1193-1201
• /
• 2015

This paper presents a study of circulating current of modular multi-level converter (MMC) based a high voltage direct current (HVDC) system under unbalanced grid conditions. Due to the connection of a dependent DC source in each phase, the MMC system inherently generates the power ripple of double-line-frequency components in the AC-side and as a result, the additional sinusoidal current named circulating current flows through the each arm. Reliability improvement of HVDC system under an unbalanced grid condition is one of the important criteria. Generally, the modeling of the circulating current is based on the power relation between DC-side and AC-side. However, the method is not perfectly matched in the MMC system due to the difference of the structural characteristic. In this paper, improved modeling method of circulating current is proposed, which is based on the inner arm power. The proposed method is verified by several simulations to have good agreement of the circulating current components.

• Smart Media Journal
• /
• v.5 no.3
• /
• pp.25-29
• /
• 2016

This paper presents research for non-contact gesture recognition system using EPS(Electronic Potential Sensor) for measuring the human body of electromagnetic fields. It implemented a signal acquisition and signal processing system for designing a system suitable for motion recognition using the data coming from the sensors. we transform AC-type data into DC-type data by applying a 10Hz LPF considering H/W sampling rate. in addition, we extract 2-dimensional movement information by taking difference value between two cross-diagonal deployed sensor.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.18 no.5
• /
• pp.663-674
• /
• 1993

In this paper, a DCT image coding algorithm using the human visual property is proposed. Human visual is relatively sensitive to noise in the darker region, insensitive to noise in the brighter region. This property was proved by Weber's law through psycovisual experiment. Weber's law states that the just noticeable difference (j.n.d.) is proportional to intensity. Therefore, the implication of this observation for image processing is that reducing noise in the darker region is more important than reducing noise in the brighter region. In this proposed coding scheme AC coefficients in the darker region are more finely quantized than those in the brighter region. Results showed that, at low bit rate, the subjective quality of reconstructed images by proposed coding scheme is improved than that of coding scheme without considering human visual property.

• Journal of Electrical Engineering and Technology
• /
• v.13 no.4
• /
• pp.1682-1691
• /
• 2018

Natural ester is a suitable substitute for mineral oil and has been widely used in AC transformer in many countries. In order to further application of natural ester in direct current (DC) equipment, it is needed to investigate its long term insulation property under DC condition. In this paper, a thermal ageing experiment was conducted for both mineral oil-paper and natural ester-paper insulation. The DC breakdown and space charge characteristics of insulation paper impregnated with natural ester and mineral oil was compared. Results show that the resistivity of the paper immersed in natural ester and mineral oil both increase as the ageing goes on. While insulation paper impregnated with natural ester has higher resistivity and DC breakdown voltage than the paper impregnated with mineral oil. The DC breakdown voltage for the oil impregnated insulation paper being DC pre-stressing is higher than that without pre-stressing. The average DC breakdown field strength difference between the test with pre-stressing and without pre-stressing clearly shows that there is an apparent enhancement effect for the homo-charge injection on the DC breakdown.

• Proceedings of the KIEE Conference
• /
• 1994.07a
• /
• pp.369-372
• /
• 1994

In this paper, a voltage type dual PWM converter which achives the bidirectional power flow between a AC supply and a DC bus voltage is described. In PWM modulator, there exist a time difference between the sampling time and carrier wave, it achieves stable modulation even the disturbance in the synchronous AC source voltage. And this paper proposes the compensation method and the control method related a disturbance of synchronous signal using the low pass filter and phase shifter for the stable modulation. As a result the voltage type dual PWM converter makes the imput current wave as sinusoid, and performs the high power factor driving.