• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 한국공작기계학회 2004년도 춘계학술대회 논문집
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• pp.439-444
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• 2004

The important problem in high speed spindle is to reduce and minimize the thermal effect by motor and ball bearings. In this study. the effects of bearing preload and cooling for high speed spindle with high frequency motor are investigated. A high speed spindle is composed of angular contact ball bearings, high frequency motor, grease lubrication, oil jacket cooling, and so on. Heat generation of the bearing and the high frequency motor are estimated from the theoretical and experimental data. The thermal analyses of high speed spindle to minimize the thermal effect and maximize the cooling effect are carried out under the various cooling conditions and preload. Method of variable bearing preload and cooling can be useful to design the high speed motor spindle. The results show that the optimal preload and cooling are very effective to minimize the thermal displacement by motor and ball bearing.

• The Transactions of the Korean Institute of Electrical Engineers P
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• 제64권4호
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• pp.261-266
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• 2015

This paper presents a newly proposed prototype of voltage-fed half-bridge partial resonant zero voltage switching PWM inverter operating at a constant frequency variable power regulation scheme, which is more suitable and acceptable for induction heated(IH) cooking appliances. This application-specific high frequency inverter circuit topology using a new generation specially-designed IGBTs can operate under a principle of a fixed frequency ZVS-PWM strategy. The operating principle of a new partial resonant inverter circuit is described on the basis of its computer-aided simulation analysis, its including steady-state operating characteristics.

• The Transactions of The Korean Institute of Electrical Engineers
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• 제60권8호
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• pp.1566-1571
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• 2011

The objective of this paper is to present a quantitative analysis leading to the assessment of optimum terminating impedances in the design of active frequency multipliers. A brief analysis of the basic principal of the GaAs FET frequency multiplier is presented. The analysis is outlined in bias optimization and drive power determination. Utilizing the equivalent circuit model of GaAs FET, we have simulated the optimized load impedance for the maximum output of the active frequency multipliers. The C-class and reverse C-class frequency doublers have been fabricated and the load impedances have been measured. The experimental results are in good agreement with the estimated results in the simulation with the accuracy of 90%.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.646-651
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• 2002

The flow field around a symmetrical airfoil in a uniform flow under the generation of noise was studied by experiments and numerical simulation. The experiments are conducted by visualizing the surface flow over the airfoil with a shear-sensitive liquid-crystal coating and by measuring the instantaneous velocity field around the trailing edge of the airfoil. The results indicate that the discrete frequency noise is generated when the separated laminar flow reattaches near the trailing edge of the pressure side and the turbulent boundary layer is formed over the suction side of the airfoil near the trailing edge. The periodic behavior of vortex formation was observed around the trailing edge and it persists further downstream in the wake. The frequency of the vortex formation in the wake was consistent with that of the discrete frequency noise.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• 제25권3호
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• pp.40-49
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• 2011

This paper presents novel circuit topology of half-bridge soft-switching PWM inverter type DC-DC high power converter for DC bus feeding power plants. The proposed DC-DC power converter is composed of a typical voltage source-fed, half-bridge high frequency PWM inverter with a high frequency planar transformer link PWM control scheme and parallel capacitive lossless snubbers. The operating principle of the new DC-DC converter treated here is described by using switching mode-equivalent circuits, together with its unique features. All the active power switches in the half-bridge arms and input DC bus lines can achieve ZCS turn-on and ZVS turn-off commutation transitions. The total turn-off switching losses of the power switches can be significantly reduced. As a result, high switching frequency IGBTs can actually be selected in the frequency range of 40[kHz] under the principle of soft-switching. The performance evaluations of the experimental setup are illustrated practically.

• Proceedings of the KIEE Conference
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• 대한전기학회 2005년도 추계학술대회 논문집 전력기술부문
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• pp.9-11
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• 2005

Adequate Co-ordination between Generator Speed Governor and AGC plays major role in maintaining a Frequency Stability. Recently frequency instability cases were recorded when power system was unbalanced between generation and demand in Korea. The paper deals with the concept of Generator frequency control logic & AGC algorithm for determining generator output target. Consequently the paper presents the improvement of EMS AGC control for stable frequency recovery in case of generator disturbance.

• Proceedings of the KIEE Conference
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• 대한전기학회 2006년도 심포지엄 논문집 정보 및 제어부문
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• pp.63-65
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• 2006

As OFDM-based systems exhibits robustness over wireless channel, it is possible to consider them the next generation of the wireless communications including the mobile communications. However, there is a critical point that OFDM-based systems can receive the distorted signal due to the frequency-offset. Therefore, it is necessary to accurately estimate the frequency-offset for OFDM-based systems to be adopted as the next wireless communication systems. In this paper, the efficient frequency-offset estimation scheme based on MUSIC is presented in 802,1la WLAN systems. As shown in the simulation result, this scheme can improve and optimize the estimation performance.

• ETRI Journal
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• 제37권6호
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• pp.1055-1064
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• 2015

We demonstrate a next-generation high-capacity mobile fronthaul based on radio over fiber (RoF) technology, which links between a digital unit and a radio unit supporting two frequency assignments and $2{\times}2$ multiple input, multiple output antennas. To confirm the technical feasibility of a mobile fronthaul, we experimentally investigate its down- and uplink end-to-end performances including the optical and radio frequency (RF) signal path. Frequency-dependent performance deviations, error vector magnitude variations, overall system performance variations caused by optical to electrical conversion, and intermediate frequency to RF conversions are examined. Experimental verifications on multiple LTE uplink signals are performed for the first time. We also demonstrate several commercial mobile Internet services, YouTube video streaming, and file transfers using off-the-shelf mobile devices, through a mobile fronthaul based on RoF.

• Journal of international Conference on Electrical Machines and Systems
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• 제2권3호
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• pp.342-348
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• 2013

As a number of wind power generation systems have been installed in power systems in the world, frequency fluctuations due to output power variations from wind farms have become a serious problem. Battery systems have been studied for smoothing the output variations and decreasing the resulting frequency fluctuations. Among these studies, efficient design of battery systems is one of the most important subjects from a point of view of cost. This paper presents a comparative analysis of the smoothing effect between the conventional moving average method and a new method based on frequency response analysis.

• Journal of Electrical Engineering and Technology
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• 제6권5호
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• pp.647-657
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• 2011

The present paper proposes a sliding mode control with fixed switching frequency for three-phase three-leg voltage source inverter based four-wire shunt active power filter. The aim is to improve phase current waveform, neutral current mitigation, and reactive power compensation in electric power distribution system. The performed sliding mode for active filter current control is formulated using elementary differential geometry. The discrete control vector is deduced from the sliding surface accessibility using the Lyapunov stability. The problem of the switching frequency is addressed by considering hysteresis comparators for the switched signals generation. Through this method, a variable hysteresis band has been established as a function of the sliding mode equivalent control and a predefined switching frequency in order to keep this band constant. The proposed control has been verified with computer simulation which showed satisfactory results.