• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2008.05a
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• pp.419-422
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• 2008

This paper presents a novel prototype of ZCS-PFM high frequency series resonant Inverter using IGBT power module for electromagnetic induction eddy current-heated roller in copy and printing machines. The operating principle and unique features of this voltage source half bridge inverter with two additional soft commutation inductor snubber are presented Including the transformer modeling of induction heated rolling drum. This soft switching inverter can achieve stable zero current soft commutation under a discontinuous and continuous resonant load current for a widely specified power regulation processing. The experimental results and computer-aided analysis of this inverter are discussed from a practical point of view.

• Journal of KSNVE
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• v.9 no.5
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• pp.891-898
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• 1999

The purpose of Superconducting Magnetic Bearing Flywheel Energy Storage System (SMB-FESS) is to store unused nighttime electricity until it is needed during daytime. An analytical model of the SMB-FESS is necessary to identify the system behavior. At first, we have to model the superconducting magnetic bearing. Modeling the SMB is same as estimating the bearing parameter. The theoretical modal parameter is calculated through the equation of motion and the experimental modal parameter is estimated through the impact testing (modal testing). The bearing parameter is searched by using the non-linear least square method until the theoretical result corresponds to the experimental result. The suggested modeling method is verified by comparing experimental and analytical frequency response function.

• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2099-2105
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• 2017

In a power system that has a high wind penetration, the output power fluctuation of a large-scale wind turbine generator (WTG) caused by the varying wind speed increases the maximum frequency deviation, which is an important metric to assess the quality of electricity, because of the reduced system inertia. This paper proposes a stable power-smoothing scheme of a doubly-fed induction generator (DFIG) that can suppress the maximum frequency deviation, particularly for a power system with a high wind penetration. To do this, the proposed scheme employs an additional control loop relying on the system frequency deviation that operates in combination with the maximum power point tracking control loop. To improve the power-smoothing capability while guaranteeing the stable operation of a DFIG, the gain of the additional loop is modified with the rotor speed and frequency deviation. The gain is set to be high if the rotor speed and/or frequency deviation is large. The simulation results based on the IEEE 14-bus system demonstrate that the proposed scheme significantly lessens the output power fluctuation of a WTG under various scenarios by modifying the gain with the rotor speed and frequency deviation, and thereby it can regulate the frequency deviation within a narrow range.

• Journal of the Korean Academy of Clinical Electrophysiology
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• v.7 no.1
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• pp.7-10
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• 2009

Purpose : The purpose of this study was to investigate the effect of electrical stimulation applied in dominant forearm on autonomic nervous system response of both hands. Methods : Fourteen healthy subjects (women) received low frequency-high intensity electrical stimulation to one forearm. The subjects assigned to two groups; a ipsilateral stimulation group (n=7) and a contralateral stimulation group (n=7). The electrode attachment was arranged on the forearm of the dominant arm and the electricity stimulus time was set as 15 minutes. Measuring items were the skin conduction velocity, the blood flow, and the pulse rate, which were measured total 3 times (pre, post, and post 10 min.). Results : The skin conduction velocity showed a significant difference according to the change of the time in both hands, but there was no significant difference according to time in the blood flow, and the change of the pulse frequency regardless of stimulus side. Conclusion : These results demonstrate that the low frequency-high intensity electrical stimulation applied dominant forearm can increase selectively only with the skin conduction velocity, which may be helpful for the activation of the sudomotor function of both hands by the activation of sympathetic nerve.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.6
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• pp.979-986
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• 2016

At present, electric power industry around the world are being gradually changed to a new paradigm, such as electrical energy storage system, the wireless power transmission. Demand for ESS, the core technology of the new paradigm, has been growing worldwide. However, it is essential to estimate the optimal capacity of ESS facilities for frequency regulation because the benefit would be saturated in accordance with the investment moment and the increase of total invested capacity of ESS facilities. Hence, in this paper, the annual optimal mathematical investment model is proposed to estimate the optimal capacity and to establish investment plan of ESS facility for frequency regulation. The optimal mathematical investment model is newly established for each season, because the construction period is short and the operation effect for the load by seasons is different unlike previous the mathematical investment model. Additionally, the marginal operating cost is found by new mathematical operation model considering no-load cost and start-up cost as step functions improving the previous mathematical operation model. ESS optimal capacity is established by use value in use iterative methods. In this case, ESS facilities cost is used in terms of the value of the beginning of the year.

• Nuclear Engineering and Technology
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• v.56 no.4
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• pp.1254-1266
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• 2024

This study investigates the application of supercritical carbon dioxide (S-CO₂) direct-cycle micro modular reactors (MMRs) in primary frequency control (PFC), which is a scenario characterized by significant load fluctuations that has received less attention compared to secondary load-following. Using a modified GAMMA + code and a deep neural network-based turbomachinery off-design model, the authors conducted an analysis to assess the behavior of the reactor core and fluid system under different PFC scenarios. The results indicate that the acceptable range for sudden relative electricity output (REO) fluctuations is approximately 20%p which aligns with the performance of combined-cycle gas turbines (CCGTs) and open-cycle gas turbines (OCGTs). In S-CO₂ direct-cycle MMRs, the control of the core operates passively within the operational range by managing coolant density through inventory control. However, when PFC exceeds 35%p, system control failure is observed, suggesting the need for improved control strategies. These findings affirm the potential of S-CO₂ direct-cycle MMRs in PFC operations, representing an advancement in the management of grid fluctuations while ensuring reliable and carbon-free power generation.

• Journal of Magnetics
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• v.15 no.4
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• pp.213-220
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• 2010

Since the hypothalamus immediately reacts to a nerve by processing all the information from the human body and the external stimulus being conducted, it performs a significant role in internal secretion; thus, a diverse and rapid stimulus pulse is required. By detecting Zero Detector accurately via the application of AVR on-Chip (ATMEL) using commercial electricity, chopping generates a stimulus pulse to the brain using an IGBT gate to designate a new magnetic stimulation following treatment and diagnosis. To simplify and generate a diverse range of stimuli for the brain, chopping can be used as a free magnetic stimulator. Then, commercial frequency (60Hz) is chopped precisely at the first level of the leakage transformer to deliver an appropriate stimulus pulse towards the hypothalamus when necessary. Discharge becomes stable, and the chopping frequency and duty-ratio provide variety after authorizing a high-pressure chopping voltage at the second level of the magnetic stimulator. These methods have several aims. The first is to apply a variable stimulus pulse via accurate switching frequency control by a voltaic pulse or a pulse repetition rate, according to the diagnostic purpose for a given hypothalamus. Consequently, the efficiency tends to increase. This experiment was conducted at a maximum of 210 W, a magnetic induced amplitude of 0.1~2.5 Tesla, a pulse duration of $200{\sim}350\;{\mu}s$, magnetic inducement of 5 Hz, stimulus frequency of 0.1~60 Hz, and a duration of stimulus train of 1~10 sec.

• Journal of Advanced Navigation Technology
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• v.6 no.1
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• pp.44-51
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• 2002

This paper describes the performance evaluation and analysis of an Orthogonal Frequency-Division Multiplexing (OFDM) system having the least Inter Symbol Interference (ISI) in a multi-path fading channel environment. Wireless Local Area Network (W-LAN) in accordance with IEEE 802.11a and IEEE 802.11b provides high-speed transmission to universities, businesses and other various places. In addition, service providers can offer a public W-LAN service on restricted areas such as a subway. The proliferation of W-LAN has led to greater W-LAN service demands, but problems are also on the rise in offering a good W-LAN service. In particular, urban areas with high radio wave interference and many buildings are vulnerable to deteriorated QoS including disconnected data and errors. For example, when high-speed data is transmitted in such areas, the relatively high frequency generates ISI between Access Points (AP) and Mobile Terminals (such as a notebook computer), leading to a frequency selective fading channel environment. Consequently, it is difficult to expect a goodW-LAN service. The simulation proves that the OFDM system enables W-LAN to implement QoS in high-speed data transmission in a multi-path fading channel environment. The enhanced OFDM performance with 52 sub-carriers is verified via data modulation methods such as BPSK, QPSK and 16QAM based on IEEE 802.11a and punched convolutional codes with code rate of 1/2 and 3/4 and constraint length of 7. Especially, the simulation finds that the OFDM system has better performance and there is no data disconnection even in a mobile environment by applying a single tap equalizer and a decision feedback equalizer to a mobile channel environment with heavy fading influence. Given the above result, the OFDM system is an ideal solution to guarantee QoS of the W-LAN service in a high-speed mobile environment.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3464-3466
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• 2007

Power uprate is the process of increasing the maximum power level at which a commercial nuclear power plant may operate. Power uprate applications(113 units) for NPPs(Nuclear Power Plants) were recently approved in the United States. Utilities have been using power uprates since the 1970s as a way of increasing the power output of their nuclear plants. To increase the power output of a reactor, typically more highly enriched uranium fuel and/or more fresh fuel is used. This enables the reactor to produce more thermal energy and therefore more steam, driving a turbine generator to produce electricity. In this paper, the propriety of power uprate is explained through the review on the power uprate method and the changes of the physical parameters due to power uprate. The analysis results showed that the CDF(Core Damage Frequency) and LERF(Large Early Release Frequency) are affected in the current probabilistic safety assessment (PSA) model.

• ETRI Journal
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• v.40 no.2
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• pp.167-179
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• 2018

This paper proposes an IEEE 802.15.4m compliant TV white-space orthogonal frequency-division multiplexing (TVWS)-(OFDM) radio frequency (RF) transceiver that can be adopted in advanced metering infrastructures, universal remote controllers, smart factories, consumer electronics, and other areas. The proposed TVWS-OFDM RF transceiver consists of a receiver, a transmitter, a 25% duty-cycle local oscillator generator, and a delta-sigma fractional-N phase-locked loop. In the TV band from 470 MHz to 698 MHz, the highly linear RF transmitter protects the occupied TV signals, and the high-Q filtering RF receiver is tolerable to in-band interferers as strong as -20 dBm at a 3-MHz offset. The proposed TVWS-OFDM RF transceiver is fabricated using a $0.13-{\mu}m$ CMOS process, and consumes 47 mA in the Tx mode and 35 mA in the Rx mode. The fabricated chip shows a Tx average power of 0 dBm with an error-vector-magnitude of < 3%, and a sensitivity level of -103 dBm with a packet-error-rate of < 3%. Using the implemented TVWS-OFDM modules, a public demonstration of electricity metering was successfully carried out.