• Progress in Superconductivity and Cryogenics
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• v.19 no.1
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• pp.26-29
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• 2017

We studied the distribution of the current density and its magnetic-field dependence in GdBCO coated conductors with AC bias currents using low temperature scanning Hall probe microscopy. We selectively measured magnetic field profiles from AC signal obtained by Lock-in technique and calculated current distributions by inversion calculation. In order to confirm the AC measurement results, we applied DC current corresponding to RMS value of AC current and compared distribution of AC and DC transport current. We carried out the same measurements at various external DC magnetic fields, and investigated field dependence of AC current distribution. We notice that the AC current distribution unaffected by external magnetic fields and preserved their own path on the contrary to DC current.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.390-394
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• 2001

A dynamic simulation model for the brush less dc (BLDC) motor drives using Matlab is presented. In this model, an entire BLDC motor drive, including power conversion unit, BLDC motor, and speed/torque control system, is investigated. Especially, the PWM inverter is modeled using switching function concept, so that the detailed voltage and current waveforms, such as line-to-line voltages, inverter input current, ac line current, and switch/diode currents, can be obtained and average/rms ratings of the components can be easily calculated. Also, the proposed model is made into modular blocks and it can be easily extended to other ac motor applications with a little modification. The detailed modeling method is explained and its actual implementation is described. The validity of the proposed model is verified by various simulation results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.9
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• pp.54-60
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• 2006

Large steel industries have time-varying nonlinear loads such as electric arc furnaces. These nonlinear loads generate harmonic currents and create distortions on the sinusoidal voltage of the power system. The main objective of the static var compensator is to maintain the rms voltage at the point of common coupling within the limit. In this research, harmonic mitigation studies were conducted with and without the SVC, and time-varying harmonics were evaluated according to the international harmonic standards (IEC 61000-3-6 and IEEE Std. 519) using a cumulative probabilistic approach.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.708-710
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• 2001

In this paper, back commutation phenomena for iron chute chamber in AC low testing. For this experimental we used high speed camera and carried out with same prospective currents up to 10kA RMS. Hybrid arc quenching chambers which are composed with iron plate and insulating materials tested for reducing back commutation phenomena in interrupting process. It is shows that hybrid chambers which are various narrow slot path width reduces back commutation. As a result, a new type arc quenching chamber is to force the arc rapidly into a narrow insulating slot with iron plate. By this means the arc is lengthened and squeezed between insulating walls. Using this model, the behavior of the arc squeezed in the hybrid chamber and characteristics of arc voltage are also investigated.

• Proceedings of the KIEE Conference
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• 2000.11a
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• pp.55-57
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• 2000

This paper presents the measurement of phasor angle of power system using Synchronized Phasor Measurement System(SPMS). SPMS includes the GPS receiver, so it can add the exact time information to the data acquired from the power system by SPMS. Using that data, we can compare the difference of phasor angles of voltages currents acquired at the exactly same time, and monitor the RMS values of voltage and current. In this paper, we present the difference of voltage angles between 345kV Sinjechon S/S and 345kV Asan S/S, where two SPMS were installed separately, and prove their performance by comparing to simulation result of PSS/E.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.3
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• pp.331-338
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• 2014

A charge-pump circuit using a current-bypass technique, which suppresses charge sharing and reduces the sub-threshold currents, helps to decrease phase-locked loop (PLL) jitter without resorting to a feedback amplifier. The PLL shows no stability issues and no power-up problems, which may occur when a feedback amplifier is used. The PLL is implemented in 0.11-${\mu}m$ CMOS technology to achieve 0.856-ps RMS and 8.75-ps peak-to-peak jitter, which is almost independent of ambient temperature while consuming 4 mW from a 1.2-V supply.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.50 no.9
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• pp.417-423
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• 2001

This paper proposes a technique for fault detection and classification for both LIF(Low Impedance Fault)s and HIF(High Impedance Fault)s using Adaptive Network-based Fuzzy Inference System(ANFIS). The inputs into ANFIS are current signals only based on Root-Mean-Square(RMS) values of 3-phase currents and zero sequence current. The performance of the proposed technique is tested on a typical 154 kV Korean transmission line system under various fault conditions. Test results show that the ANFIS can detect and classily faults including (LIFs and HIFs) accurately within half a cycle.

• Proceedings of the KIPE Conference
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• 2007.07a
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• pp.211-213
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• 2007

The electrical parameters are used to calculate gains in the current regulator as well as to determine the reference currents of speed controller in various control strategies of Synchronous Reluctance Motors (SynRMs). Many methods of measuring or estimating the electrical parameters of SynRM have been proposed by other authors. But almost papers only measure or estimate in the limited conditions without fully considering the effects of inverter, connecting wire and magnetic saturation. The parameter results are usually different from the real system parameters. The drive performance, therefore, can not be good if using inaccurate parameters. In this paper, several methods used to measure the electrical parameters are introduced. The first method is LCR meter. And then, a method determining inductances by measuring AC current and voltage from AC power supply is presented. A new method with high reliability is proposed to measure the electrical parameters of SynRM. The experiment results verify the effectiveness of the new proposed method.

• Corrosion Science and Technology
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• v.20 no.5
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• pp.231-241
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• 2021

The objective of this study was to evaluate total current under steady-state conditions for a material undergoing corrosion using the electrochemical frequency modulation (EFM) technique, taking into account the presence of solution resistance and double layer capacitance. The analysis involving linearization of the Tafel curve allowed for the estimation of corrosion parameters. Results showed that the output signal was dependent on fundamental frequencies and their multiples. In addition, the output signal almost manifested itself at frequencies that were sums of fundamental frequencies of the applied sinusoidal signal. The harmonics calculated showed a significant shift from the principal frequency of input signals. The investigation involved the influence of corrosion current and anode-to-cathode Tafel slope ratio on faradaic and non-faradaic currents (including the average and RMS). The model presented showed both qualitative and quantitative improvements over the previously developed EFM technique that ignored the influence of solution resistance and the double layer capacitance while assuming the applied DC potential corresponded to the corrosion potential of the corroding material.

• Journal of Power Electronics
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• v.15 no.3
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• pp.685-694
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• 2015

The power loss of the controllable switches in modular multilevel converter (MMC) HVDC transmission systems is an important factor, which can determine the design of the operating junction temperatures. Due to the dc current component, the approximate calculation tool provided by the manufacturer of the switches cannot be used for the losses of the switches in the MMC. Based on the enabled probabilities of each SM in an arm, the current analytical models of the switches can be determined. The average and RMS currents can be obtained from the corresponding current analytical model. Then, the conduction losses can be calculated, and the switching losses of the switches can be estimated according to the upper limit of the switching frequency. Finally, the thermal resistance model of the switches can be utilized, and the junction temperatures can be estimated. A comparison between the calculation and PSCAD simulation results shows that the proposed method is effective for estimating the junction temperatures of the switches in the MMC.