• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.3
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• pp.207-214
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• 2019

In this study, discrete-time domain analysis is proposed to investigate the input current of a buck AC/DC light-emitting diode (LED) driver. The buck power factor correction converter can operate in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM). Two discontinuous and two continuous conduction operating modes are possible depending on which event terminates the conduction of the main switch in a switching cycle. All four operating modes are considered in the discrete-time domain analysis. The peak current-mode control with slope compensation is used to design a low-cost AC/DC LED driver. A slope compensation design of the buck AC/DC LED driver is described on the basis of a discrete-time domain analysis. Experimental results are presented to confirm the usefulness of the proposed analysis.

• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1495-1502
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• 2017

The Theory of operation of switched reluctance motors (SRM) depends on the reluctance torque, where energy is transferred to stator winding only. Although its construction is simple, the electrical design is complex, due to the switching configuration needed to deliver power to stator coils. However, because of the nonlinearly of magnetic circuit, SRM has torque ripple. This paper proposes a new strategy to drive SRM from a single-phase AC supply. Each stator winding is connected to AC-DC or AC-AC converters, which is called branch. All branches are connected in parallel to a single-phase AC supply. A shaft encoder allows current production in stator winding during the positive torque production region and terminates it during the negative torque production region. A magnetic flux is produced between stator poles when current is supplied from AC supply to stator coil and repeats many cycles as long as the rate of change of stator inductance is positive. Different possibilities for the configurations of AC-AC or AC-DC converters are introduced to drive SRM from the single-phase AC supply. A case study is presented for a SRM fed from AC supply through semi-controlled AC-DC converter is presented. A simulation model is introduced and verified by experimental rig for two-phase SRM.

• Progress in Superconductivity and Cryogenics
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• v.15 no.2
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• pp.34-38
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• 2013

AC Losses for face to face stacks of four identical coated conductors (CCs) were numerically calculated using the H-formulation combined with the E-J power law and the Kim model. The motive sample was the face to face stack of four 2 mm-wide CC tapes with 2 ${\mu}m$ thick superconducting layer of which the critical current density, $J_c$, was $2.16{\times}10^6A/cm^2$ on IBAD-MgO template, which was suggested for the mitigation of ac loss as a round shaped wire by Korea Electrotechnology Research Institute. For the calculation the cross section of the stack was simply modeled as vertically aligned 4 rectangles of superconducting (SC) layers with $E=E_o(J(x,y,t)/J_c(B))^n$ in x-y plane where $E_o$ was $10^{-6}$ V/cm, $J_c$(B) was the field dependence of current density and n was 21. The field dependence of the critical current of the sample measured in four-probe method was employed for $J_c$(B) in the equation. The model was implemented in the finite element method program by commercial software. The ac loss properties for the stacks were compared with those of single 4 cm-wide SC layers with the same critical current density or the same critical current. The constraint for the simulation was imposed in two different ways that the total current of the stack obtained by integrating J(x,y,t) over the cross sections was the same as that of the applied transport current: one is that one fourth of the external current was enforced to flow through each SC. In this case, the ac loss values for the stacks were lower than those of single wide SC layer. This mitigation of the loss is attributed to the reduction of the normal component of the magnetic field near the SC layers due to the strong expulsion of the magnetic field by the enforced transport current. On the contrary, for the other case of no such enforcement, the ac loss values were greater than those of single 4cm-wide SC layer and. In this case, the phase difference of the current flowing through the inner and the outer SC layers of the stack was observed as the transport current was increased, which was a cause of the abrupt increase of ac loss for higher transport current.

• Journal of Electrical Engineering and Technology
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• v.3 no.2
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• pp.235-242
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• 2008

In this paper, a 24-pulse AC-DC converter is designed, modeled, simulated, and developed to feed non-isolated varying loads. The proposed AC-DC converter configuration consists of an auto-transformer based on zigzag connection to overcome current harmonic problems in AC mains. It improves power quality at AC mains and it meets IEEE-519 standard requirements at varying loads. A set of power quality indices on input AC mains and on DC buses for a load fed from 6-pulse and 12-pulse AC-DC converters is also given to compare their performance. It is observed that input current total harmonic distortion(THD) of less than 8% is possible with the proposed topology of AC-DC converter at varying loads.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.3
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• pp.433-438
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• 2008

This paper analyses current densities induced inside a worker using AC arc welder. Applying the boundary element method, we calculate current densities induced in organs inside a worker in case he was located at 1cm, 3cm, 5cm, 10cm, 15cm, 20cm far from a power cable of AC arc welder. As results of study, we find a maximum current density induces at a heart surface and may be higher than $10mA/m^2$ of ICNIRP guideline if he works within 15cm from a power cable.

• Proceedings of the KIEE Conference
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• 2007.10c
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• pp.56-58
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• 2007

AC transport current losses is an important factor in the development of superconducting tapes and superconducting power applications. In this paper we compared measurement, calculation and Norris equation of AC transport current loss in BSCCO single and multi stacked wire. And present a distribution flux density and current density in the HTS single wire and multi stacked wire. The result of Measurement and calculation of Ac transport current loss show that the same. And show that HTS characteristic of inside HTS wire.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.1103-1104
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• 2008

In this paper, authors propose a novel step-up AC-DC chopper operated with power factor correction (PFC) and with high efficiency. The proposed chopper behaves with discontinuous current control (DCC) of input current. The input current waveform in the proposed chopper is got to be a discontinuous sinusoid form in proportion to magnitude of ac input voltage under the constant duty cycle switching. Therefore, the input power factor is nearly unity and the control method is simple. In the general DCC chopper, the switching devices are turned-on with the zero current switching, but turn-off of the switching devices is switched at current maximum value. To achieve a soft switching of the switching turn-off, the proposed chopper is used a new partial resonant circuit. The result is that the switching loss is very low and the efficiency of chopper is high.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.9
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• pp.118-125
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• 1997

This paper proposed a new partial resonant 3.PHI. AC-DC boost converter of high efficiency using lossless snubber. The proposed converter, DCM (Discontinuous Current Mode) has a merit of simple controlled circuit because the input current control discontinuously. But turned off switching loss and stress of the switching device increase when the switch turned off at the peak of current. Therefore, the paper improves efficiency by adopting the PRS$^{2}$(Partial Resonant Soft Switching) in 3.PHI. AC-DC boost converter and makes the unity power factor. The PRS$^{2}$ is reduced a current/voltage stresses of switching devices. Also, a DCMPRS$^{2}$M(Discontinuous Conduction Mode Partial Resonant Soft Switching Method) appear the current and voltage equation of this circuit. The paepr examine in a 3.PHI. AC-DC boost converter and show the result of that.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.9
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• pp.445-452
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• 2001

Two switching signal patterns are proposed to prevent short circuit of PWM ac choppers. The voltage detection method and the current detection method are proposed to execute two switching signal patterns. In the voltage detection method, the dead-time has to be inserted to the switching signals after polarity of input voltage is checked by voltage transducer at input side. In the current detection method, the direction of load current is checked by current transducer at output side, and the dead-time delay is not considered. Controlling circuit built by current detection method is simple because the dead-time delay is considered. The experimental results are presented to prevent short circuit of ac chopper safely.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.49-50
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• 2012

Maximum power point tracking(MPPT) algorithm is needed in PV AC module power conditioning system because of the nonlinear current-voltage characteristics. Conventional MPPT algorithm is required to know PV-module output current and voltage. Thus, PV-AC module must have voltage and current sensor. In this paper, a current-sensorless MPPT algorithm, which uses only the voltage sensor, is presented for Flyback inverter.