• Journal of Power Electronics
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• v.15 no.3
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• pp.730-740
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• 2015

This paper presents model reference adaptive system speed estimators based on Type-1 and Type-2 fuzzy logic controllers for the speed sensorless direct torque and flux control of an induction motor drive (IMD) using space vector pulse width modulation. A Type-1 fuzzy logic controller (T1FLC) based adaptation mechanism scheme is initially presented to achieve high performance sensorless drive in both transient as well as in steady-state conditions. However, the Type-1 fuzzy sets are certain and cannot work effectively when a higher degree of uncertainties occurs in the system, which can be caused by sudden changes in speed or different load disturbances and, process noise. Therefore, a new Type-2 FLC (T2FLC) - based adaptation mechanism scheme is proposed to better handle the higher degree of uncertainties, improve the performance, and is also robust to different load torque and sudden changes in speed conditions. The detailed performance of different adaptation mechanism schemes are performed in a MATLAB/Simulink environment with a speed sensor and sensorless modes of operation when an IMD is operates under different operating conditions, such as no-load, load, and sudden changes in speed. To validate the different control approaches, the system is also implemented on a real-time system, and adequate results are reported for its validation.

• Journal of Digital Convergence
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• v.11 no.8
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• pp.331-340
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• 2013

Depaysement, suggested by the well-known surrealist Rene Magritte, has been used for and applied to many media. Application of depaysement through various media such as TV, commercial, and advertisement, attempted to provide interest by deviation from fixed ideas and visual shock, placing common objects in new and strange environment. The study applied screen projection mapping using a transparent screen and objet for different purposes to projection mapping media, applying depaysement to the artwork 'Illusion' in order to suggest visual pleasure, possibility as a new media, and projection mapping using transparent screen and objet. The work cases were suggested by applying expressive methods and effects according to three classifications - modulation of space, combination of conflicting images, and transformation and change of objects - in depaysement, and analyzed by types based on classification of the layout, typography, image, color, and time. Through 'Illusion,' new objet and characteristics of the media are applied and expanded by using projection mapping and depaysement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.11
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• pp.1341-1348
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• 2016

In this paper, we propose method to enhance security performance using HT-STBC with artificial noise under Wier-Tap channel model that exist with legitimate receiver and illegal eavesdropper. Conventional STBC with artificial noise scheme has a weakness that a limited increase in the BER of the difference between the receiver and an eavesdropper, when used over QPSK modulation. To solve this problem, we suggest HT-STBC combining hadamard transform and STBC with artificial noise for reduce BER of receiver than the conventional scheme and demonstrated through simulation that also increased BER difference between the receiver and an eavesdropper. By the simulation results, when used proposed scheme, showed approximately 3dB improvement in performance compared to the conventional scheme.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.3
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• pp.292-298
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• 2003

Most of the three phase inverters for adjustable speed drive of AC machines are equipped with two or three current sensors for measurement of three phase current. One method to reduce the number of current sensors is that single current sensor measures the DC link current, then three phase current is reconstructed using the measured value and the switching status. To improve the measurement accuracy, switching state should be maintained for more than minimum switching time. Many papers have been published, which focused on the readjustment of pulse width and compensation of voltage distortion. Those methods are suitable for space vector modulation. But there are some difficulties in applying these methods to carrier-based PWM which is widely used in industry. In this paper, new current measurement method and voltage compensation method are proposed which are suitable for carrier-based PWM, then, the validity of proposed method is confirmed through experiment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.1
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• pp.61-70
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• 1996

M-ary differential phase shift keying(DPSK)is a bandwidth efficient digital modulation technique and recently has attracted increased attention in mobile satellite communication application where the available radio bandwidth is limited. Coherent detection offers good BER performance in AWGN channel. However, it requires long acquisition times in fading environment. In this paper, we analyze the BER performance of M-ary DPSK signal using the Multiple Differ- ential Feedback Detection(MDFD) technique in Rician fading and shadowed Rician fading channel. MDFD is an efficient scheme to decrease the performance gap between differential and coherent reception by increasing the complexity of the conventional differential receiver to some extent. Compared to the multiple symbol maximum likelihood detection technique, the multiple differential feedback detection technique has a much simpler structure for hardware implementation. Espe- cially, this technique has application to land mobile satellite channel which can vary in time and space between AWGN and rapidly fading channel.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.10
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• pp.4561-4568
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• 2011

In this paper, carrier comparison PWM method for voltage control of Vienna rectifier is discussed. In general, in industrial and communications applications, the two-level rectifier is used. However, this two-level rectifier has the limit of high THD and low efficiency. So, the studies of three-level rectifier has been carried out so far, and the Vienna rectifier circuit is the representative. The space vector pulse width modulation(SVPWM) method is generally used for Vienna rectifier, in which voltage vectors and duration time are calculated from the voltage reference. However, this method require very sophisticated and complex calculations, so realizing this method by software is very difficult. To overcome this disadvantage, simple carrier comparison PWM method for Vienna rectifier is proposed which is modified from the carrier comparison method for 3 level inverter. Furthermore, to verify the usefulness of the Vienna rectifier carrier comparison PWM the simulation and experiment are carried out.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.3
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• pp.291-297
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• 2014

Due to the rapid increase in demand for transportation of human and freight in modern railway systems, the CBTC system has been proposed, which is the solution for improvement of the line capacity that has been limited by the conventional track circuit based train control system. In the CBTC system, higher reliability of the communication system should be guaranteed for the safety of passengers and trains. However, due to the inherent characteristics of the wireless channel environment, performance degradations are inevitable. The diversity techniques can increase the reliability of data transmission using multiple antennas. In this paper, we investigate the performance of the STBC in the railway channel environment. Rician fading model is used for the viaduct scenarios which take important roles in the railway system. Also, considered is the Doppler effect which is an important factor in the mobile communication system. Simulations are performed to analyze the performance of the STBC in various channel environments. Results show that the performance degradation due to the phase error in viaduct scenarios is independent of the diversity order but is affected by the constellation of the modulation.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.2
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• pp.138-147
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• 2005

This paper presents a SPMSM(Surface-mounted Permanent Magnet Synchronous Motor) servo drive system using high performance TMS320F2812 DSP for the industrial application. The DSP(Digital Signal Processor) Controller enables an enhanced real time algorithm and cost-effective design intelligent for only exclusively motor drives which can be yield enhanced operation, fewer system components, lower control system cost, increased efficiency and high performance. The suggested system contain speed and current sensing circuits, SVPWM(Space Vector Pulse Width Modulation) and I/O interface circuit. The developed servo drive control system showns a good response characteristics results and high performance features in general purposed 400[w] machine. This system can achieve cost reduction and size minimization of controllers.

• Journal of Astronomy and Space Sciences
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• v.11 no.1
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• pp.71-80
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• 1994

It is generally known that the measurement of the ionospheric total electron content(TEC) by GPS can more accurately monitor the broader area of the ionosphere than other current methods. \Ve measured the TEC along a slant path considering the arrival time differences of P-code which is transmitted from GPS satellites with the modulation on two L-band carrier frequencies, L1 (1574.42MHz) and L2 (1227.60MHz). Under the assumptions that the ionosphere is uniformly distributed and its average height is 350km, we transformed the slant TEC to the vertical TEC at the point that the line-of-sight direction to GPS satellite cut across the average height of the ionosphere. Because there is no dual frequency P-code GPS receiver in Korea, we used the data observed at the TAIW GPS station ($N25^{\circ},E121.5^{\circ}$) in Taiwan which is one of the core stations in International GPS and Geodynamics Services (IGS). The TEC values obtained in this work showed a typical daily variation of the ionosphere which is high in the daytime and low in the nighttime. Our results are found to be consistent with the SOLAR-DAILY data of NOAA and the Klobuchar's model for the ionospheric correction of GPS. In addition, in the cornparision with SOLAR-DAILY data, we estimated the precision of our TEC measurement as 2 TEC.

• Journal of Aerospace System Engineering
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• v.12 no.4
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• pp.64-74
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• 2018

Small high-resolution Earth observation satellites require precise optical alignment at the submicron level. However, misalignments can occur due to the influence of external factors during the launch and operation despite the sufficient alignment processes that take place before the launch. Thus, satellites need to realign their optical elements in orbit in what is known as a refocusing process to compensate for any misalignments. Refocusing algorithms developed for satellites have only considered de-space, which is the most sensitive factor with respect to image quality. However, the existing algorithms can cause correction error when inner and external forces generate tilt amount in an optical system. The present work suggests an improved online refocusing algorithm by considering the tilting effect for application in the case of a de-spaced and tilted optical system. In addition, the algorithm is considered to be efficient in terms of time and cost because it is designed to be used as an online method that does not require ground communication.