• Proceedings of the KIEE Conference
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• 2007.11c
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• pp.108-111
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• 2007

A novel voltage sag compensator with hi-directional DC/DC converter of Electric double layer capacitor is proposed. Recently, the double-layer capacitor which is drawn attention as a new energy storage element has a lot of advantage such as no maintenance, long lifetime and quick charge/discharge characteristics with large current. This DC/DC converter is used to control the charging current to the double-layer capacitor and also used to keep the DC link voltage constant for discharge of the double-layer capacitor. Therefore, the proposed DC/DC converter has the high-efficiency controller, dynamic compensator of voltage sag is driven by this converter. Finally, experimental results show the validity of the control scheme and the ability of the dynamic voltage compensator.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.38 no.4
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• pp.269-278
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• 1989

When the induction motor is operated by CSI, the commutation capacitance in the CSI circuit is increased according to the increase of large capacitor system. The output voltage spikes are generated at the moment of charge and discharge of the commutation capacitor. Also, since output current comprise a great number of harmonics, torque ripples of the motor are generated, having bad effects on the motor. In this study, by adopting the 18-phase multiple high Frequency Current Source Inverter (HFCSI), torque ripples generated by the voltage spikes are mostly eliminated except the 17th and 19th harmonics. To reduce the voltage spikes comprised in the output voltage, particularly, the methods of eliminating the cause of bad effect upon the motor are proposed in this paper. In the proposed method, by using additional voltage Clamping Curcuit (VCC), it is possible to select the values of commutation capacitor energy loss in commutating, the commutating capacitor, and the capacitor in the clamping circuit.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.7
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• pp.338-346
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• 2001

In this paper, dc link currents for the three-phase diode rectifiers and PWM inverters are analyzed and an algorithm of estimating the life of dc link electrolytic capacitors using the analyzed ripple current is presented. Since the capacitor life is dependent on the operating temperature, the power dissipation in capacitors should be calculated. For this, the ESR(equivalent series resistance) model of the capacitor is derived and ripple currents through the capacitor are analyzed. Relating the power dissipation and the heat transfer equation, the internal operating temperature is calculated. Then, the capacitor life can be predicted by using Arrhenius's equation. An example for applications is given for the practical system.

• Journal of the Korean Ceramic Society
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• v.34 no.10
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• pp.1060-1066
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• 1997

In this paper, the effects of La addition of PLZT thin film prepared by sol-gel method on the capacitor characteristics are investigated for gigabit generation DRAM applications. The addition of La on the PLZT capacitor results in a trade-off between charge storage density(Qc') and leakage current density(Jl). As La content increases, Qc' and permeability(εr) at 0V are reduced while Jl is significantly decreased. It is demonstrated that 5% La doping of PZT can substantially reduce Jl and also improve resistance to fatigue while incurring only minimal degradation of Qc'. Very low leakage current density (5×10-7 A/㎠ even at 125℃) and high charge storage density (100fC/㎛2) under VDD/2=1V conditions are achieved using 5% La doped PZT thin films for gigabit DRAM capacitor dielectrics. In addition, the fatigue and TDDB measurements indicate good reliability of the PLZT capacitors.

• Journal of Power Electronics
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• v.13 no.3
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• pp.329-338
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• 2013

In this paper, the charging characteristics of series resonant type high voltage capacitor chargers considering the transformer stray capacitance have been studied. The principles of operation for the four operational modes and the mode changes for the four different switching frequency sections are explained and analyzed in the range of switching frequency below the resonant frequency. It is confirmed that the average charging currents derived from the above analysis results have non-linear characteristics in each of the four modes. The resonant current, resonant voltage, charging current, and charging time of this capacitor charger as variations of the switching frequency, series parallel capacitance ratio ($k=C_p/C_s$), and output voltage are calculated. From the calculation results, the advantages and disadvantages arising from the parallel connection of this stray capacitance are described. Some methods to minimize charging time of this capacitor charger are suggested. In addition, the results of a comparative test using two transformers whose stray capacitances are different are described. A 1.8 kJ/s prototype capacitor charger is assembled with a TI28335 DSP controller and a 40 kJ, 7 kV capacitor. The analysis results are verified by the experiment.

• Journal of the Semiconductor & Display Technology
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• v.19 no.1
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• pp.42-48
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• 2020

As global warming accelerates, eco-friendly electric cars are being developed to reduce carbon dioxide emissions, and power conversion inverters are used to drive motors. Among inverter components, DC-link capacitor is heated by high current usage, which causes problems such as performance and life-saving of inverter. Although metal cases with good thermal performance have been used to solve this problem, it is difficult to apply them in practice due to insulation problems with other parts. In this paper, the Heat-Generation influence factor of DC-link capacitor is analyzed. Variables on heat-generation are set at 3 levels for film width, inductance, and film thickness. Box-Behnken to 13 tests using the design and minimal deviations, e.g. through the experiment three times by each level. The surface of the film k type by attaching the sensor current is measured temperature. Capacitance was set to a minimum level of 200 ㎌ and had a frequency of 16 kHz with Worst case, ambient temperature of 85℃ and a ripple current of 50 Ams was applied. The temperature at the measurement point was collected in the data logger after sampling at 1 minute intervals for 2 hours after saturation with the ambient temperature. This experiment confirmed that setup factors are correlated with heat-generation.

• Journal of Electrical Engineering and Technology
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• v.8 no.4
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• pp.808-812
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• 2013

Multilayer capacitors with high ripple current and high capacitance were manufactured. The electrical properties of these capacitors were characterized for potential application for DC-link capacitors in hybrid electric vehicle inverters. Internal electrode structures were designed to achieve high capacitance and reliability. A single multilayer capacitor showed $0.46{\mu}F/cm^3$ of capacitance, 0.65% of dielectric loss, and 1450 V to 1650 V of dielectric breakdown voltage depending on the design of the internal electrode. The capacitor module designed with several multilayer capacitors gave a total capacitance of $450{\mu}F$, which is enough for hybrid electric vehicles. In particular, an equivalent series resistance of $4.5m{\Omega}$ or less will result in 60 $A_{rms}$, thereby reaching the allowed ripple current for hybrid electric vehicles.

• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2317-2323
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• 2017

Recently, linear compressors of cooling systems such as refrigerators, which have a free piston driven by a linear motor, have attracted much attention because of their high efficiency. For structural reasons, linear compressors applied in refrigerators should use an AC capacitor to ensure stable control. However, AC capacitors are expensive and bulky. In this paper, we propose a new method to realize stable control without a real AC capacitor by implementing a virtual AC capacitor with software. To realize a virtual AC capacitor, a pure integral is calculated. Nonetheless, if an offset current exists, the calculation may diverge to infinity. To solve this problem, a high-pass filter is applied and the compensation for the phase angle and magnitude are realized with a new method. Finally, a virtual AC capacitor enables variable frequency operations. Hence, in case of a lack of voltage, we can compensate by running the linear compressor in high-frequency operations. To improve efficiency, we may optimize the operation frequency. The validity of a virtual AC capacitor has been verified through simulations and experimental results.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.1103-1105
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• 2002

A conventional AC-DC boost converter has much variation of input current as more increased the load or output voltage by the hysterical control method that is comparing area of current pulse by using PWM method and integration to sinusoidal input current. To improve the problems. in this paper, we propose the single-phase voltage doubler AC-DC converter circuit using the capacitor for boost:confirm characteristics of normal and transition state by using simulation, be stabilized voltage of doubler capacitor for boost, and Identify to get the sinusoidal input current with unity power factor.

• Proceedings of the KIEE Conference
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• 1997.07f
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• pp.1999-2001
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• 1997

The main two drawbacks of the Sin91e Stage PFC (SS-PFC) converters employing a DCM Boost PFC cell are relatively high voltage stress on the bulk capacitor and the input current harmonic distortion. The high voltage stress on bulk capacitor makes the SS-PFC converter impractical in a universal input application and the input current harmonic distortion lowers power factor. In this paper a selective variable frequency control that reduces the voltage stress on the bulk capacitor and the input current harmonic distortion is proposed. Computer simulation results of the proposed control method are presented.