• Journal of Power Electronics
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• v.11 no.1
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• pp.64-73
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• 2011

The stability of PWM rectifiers with a deadbeat current controller is seriously influenced by computation time delays and low-pass filters inserted into the current-sampling circuit. Predictive current control is often adopted to solve this problem. However, grid current predictive precision is affected by many factors such as grid voltage estimated errors, plant model mismatches, dead time and so on. In addition, the predictive current error aggravates the grid current distortion. To improve the grid current predictive precision, an improved deadbeat current controller with a repetitive-control-based observer to predict the grid current is proposed in this paper. The design principle of the proposed observer is given and its stability is discussed. The predictive performance of the observer is also analyzed in the frequency domain. It is shown that the grid predictive error can be decreased with the proposed method in the related bode diagrams. Experimental results show that the proposed method can minimize the current predictive error, improve the current loop robustness and reduce the grid current THD of PWM rectifiers.

• Journal of Welding and Joining
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• v.33 no.4
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• pp.24-29
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• 2015

The current waveform was analysed to monitor the weld quality in real time process. The acquired current waveform was discretely analysed for the top and bottom limits of peaks as well as the pulse frequency measurement. Fast Fourier Transform was implemented in the program to monitor the pulse frequency in real time. The developed algorithm or program was tested for the validation purpose. The cross-section of weld profile was compared to the current waveform profile to correlate the monitored signal and the actual parts. Pulse frequency was also used as auxiliary tool for the quality monitoring. Based on the results, it was possible to evaluate the quality of welding by measure the current waveform profile and frequency measurement.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.2
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• pp.137-142
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• 2003

Two existing continuous-time models for the current-mode control have presented noticeable differences in their small-signal predictions. As an attempt to clarify the origin of these disparities, this paper presents an alternative way of deriving a continuous-time model for the current-model control. The results of this paper would provide insights to comprehend the dissimilarity in the modeling method and final results of the earlier models of current-mode control models.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.05c
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• pp.161-163
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• 2001

We present the basic properties of a superconducting current limiting fuse (SCLF) based on YBCO/Au films. The SCLFs consists of YBCO stripes covered with Au layers for current shunt. Under the source voltage of 100 $V_{rms}$, the longer the duration time of fault current was, the shorter its discharge time was. The duration time of fault current and its discharge time were reduced by increased voltages in the range of 200 - 300 $V_{rms}$. We thought that this was because the quench propagation was limited by local melting generated with higher voltage.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.2
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• pp.184-190
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• 2009

One of the purposes of arc control is to change its state to the diffuse state before current zero as soon as possible. This can provide optimal conditions for full extinction of arc by minimizing the quantity of residual plasma between contacts near current zero. TRV(transient recovery voltage) occurs at current zero at the same time with current interruption. If there is substantial residual plasma near current zero it can cause 'post arc current' by the interaction of its conductance with TRV. In this paper, arc control ability as a function of configuration of spiral type VI contacts was compared on the criteria of the time taken for arc to reach to the diffuse state.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.247-248
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• 2006

In this study, the morphology of the change of primary Al phase in A356 alloy by two kinds of electromagnetic stirrers(vertical and horizontal) were investigated to obtain the globular structure. The effects of the stirring current, the stirring time and the pouring temperature were determined. The greater stirring current and longer stirring time were to get the finer the Al phase. However, over a certain stirring current and stirring time, the primary Al was merged together and was increased. The reason is the degree of breakdown of initial dendrites has been decreased by the collision and coalescence of particles with increasing stirring current and stirring time. The optimum conditions and difference of the two kinds of electromagnetic stirrers have been investigated for rheology forming with controlled solid fraction.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.3
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• pp.219-225
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• 2005

In this paper, a new discrete-time small signal model of an average current mode control is proposed to predict the inductor current responses. Compared to the peak current mode control, the analysis of the average current mode control is difficult because of its presence of an compensation network. By utilizing sampler model, a new discrete-time small signal model is derived and used to predict the behaviors of an inductor current of average current mode control employing generalized compensation networks. In order to show the usefulness of the proposed model, prediction results of the proposed model are compared to those of the circuit level simulator, PSIM and experiment.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.59 no.4
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• pp.477-480
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• 2010

Fault current in power system is expected to increase by demand of power capacity. Therefore, when the fault occurred, fault current was increased in the power system. Many studies have been progressed to limit the fault current. Superconducting fault current limiter (SFCL) is one of them which has been studied in worldwide. In this paper, we will analyze characteristics of a transformer-type SFCL by reclosing operation when the voltage increases. Twice opening times in the reclosing of circuit breaker were set as the 0.5 and 15 seconds, respectively. Turn's number of primary and secondary coils set 4:2 and we increased voltages from 120V to 280V for each experiment. By the current waveform, maximum fault current in second and third cycles was lowered when the voltage was increased. In the recovery waveform, recovery time was increased as the voltage was increased. The reason was that power burden of the SFCL increased when consumption power was increased, so the time to get back to SFCL took longer. We compared the characteristics of a resistive-type and transformer-type SFCL. As a result, we found that the fault current of a transformer-type was lower than resistive-type and recovery time of the SFCL was shorter. Consequently, transformer-type SFCL was more profitable for limitation of fault current and recovery time under the same condition for reclosing operation.

• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.481-482
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• 2011

New discrete time domain models for the peak current controlled (PCC) power LED drivers in continuous conduction mode include for the first time the effects of time delay in the pulse-width-modulator. Realistic amounts of time delay are found to have significant effects on the average output LED current and on the critical inductor value at the boundary between two conduction modes. Especially, the time delay can provide an accurate LED current for the PCC buck converter with a wide input voltage. The models can also predict the critical inductor values at the mode boundary as functions of the input voltage and the time delay.

• Journal of Institute of Control, Robotics and Systems
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• v.6 no.5
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• pp.367-375
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• 2000

It is proposed that the rotor time constant and inductance are compensated at the same time in the indirect vector control method of an induction motor. The proposed scheme compensates the rotor time constant using the difference between the Q-axis real stator current and estimated current that is calculated from the terminal voltage and current, and compensates inductance by using the difference between the D-axis real stator flux and estimated stator flux in the synchronous rotating reference frame. Although the rotor time constant and inductance vary at once, the proposed method compensates the rotor time constant and inductance with accuracy. In addition to, two variables can be compensated not only at the steady state condition, but also at the transient state, where the torque varies in a rectangular pulse waveform. Therefore, the performance of vector control is greatly improved as verified by experiment.