• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.4
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• pp.617-621
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• 2016

In addition to the energy storage facilities based on high power technologies, Electric double layer capacitors(EDLC) are today's candidate for power quality stabilization. However, its low energy density is often inhibiting factor for application of electric power industry. Hybrid supercapacitor is an promising energy storage device that positioned between conventional EDLC and Li-ion battery. This paper describes the preparation and characteristics of a hybrid supercapacitor and module for power quality stabilization. A cylindrical 3200F hybrid supercapacitor ($60{\times}74.5mm$) was assembled by using the $Li_4Ti_5O_{12}$ electrode as an anode and activated carbon as a cathode. It shows 2.5 times higher energy density than conventional EDLC with the same volume. In order to determine the characteristics of the hybrid supercapacitor Module for uninterruptible power supply (UPS), hybrid supercapacitor cells were connected in series with active balancing circuit. At even the high current density of 14A(10C), Module prepared by 18 cells showed the capacitance of 170F at 30~50V, suggesting the applicability for UPS.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.312-317
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• 1996

This paper compares the output voltage control strategies of three-phase PWM inverter for uninterruptible power supply. The feedforward control, feedforward/feedback control, and decoupled feedback control in both the synchronous reference frame and the stationary reference frame are examined. In particular, it is shown that the response of the decoupled feedback controller in the synchronous reference frame can be improved by pole-zero cancellation method. It is also shown that the pole-zero cancellation method reduces to the deadbeat control, when it is implemented with digital controller.

• Proceedings of the KIEE Conference
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• 1999.07f
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• pp.2587-2589
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• 1999

In this paper, we propose a new control scheme for a PWM inverter using digital control. Digital control has various advantages in comparison with conventional analogue control. It can achieve high frequency switching of inverter and can be little influenced for temperature variations and aging of devices. This digitally-controlled PWM inverter is implemented using a Digital Signal Processor(DSPTMS320F240). The simulation results are given to verify the DSP based PWM inverter design and implementation.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.394-396
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• 1995

This paper present fuzzy control technique for the control of output voltage and improvement of UPS wave forms. General UPS has the harmonics in carrier because of output of PWM signal using analog circuit. Output voltage is controlled by selecting PWM data to improve these problems, PWM signal discreted is written on ROM and analog circuit is removed at the system and output voltage is controlled by selecting PWM data by fuzzy controller.

• Proceedings of the KIEE Conference
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• 1999.11b
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• pp.381-383
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• 1999

In this paper a remote monitoring and control system using SNMP(Simple Network Management Protocol) for UPS (Uninterruptible Power Supply) systems is proposed. The local remote system by RS-232 or RS-485 communication code or the wide remote system by modems is used for conventional remote monitoring & control system for UPSs. But recently because of communication cost and long distance the system is changed to remote control systems through internet and information communication network. And serial communication method by RS-232 or RS-485 is used between agent and UPSs. In this study. we designed and developed the system which is able to control UPSs and to monitor errors. statuses and actual values transmitted from UPS through internet.

• Proceedings of the KIPE Conference
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• 2004.07a
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• pp.77-81
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• 2004

In this paper a novel line interactive UPS (Uninterruptible Power Supply) using the two 4-leg VSCs and AC line reactor is proposed. The 4-leg Voltage Source Converter(VSC) can use the DC link voltage effectively by the 3-D SVPWM method. Hence the DC battery voltage can be reduced by $15\%$ in comparison to that of the conventional line-interactive UPS system. One VSC is in parallel with the AC line reactor of the power source side, and the other is in series with the load. The parallel 4-leg voltage source inverter controls three-phase line voltage independently in order to control the line reactor current indirectly. It eliminates the neutral line current and the active ripple power of the source side using the pqr theory so that unity power factor and the sinusoidal source current can be achieved even though both the source and the load voltages have zero sequence components. The series 4-leg voltage source inverter compensates the line voltage and allows the load voltage to be balanced and harmonic-free. Both of parallel and series 4-leg voltage source inverters always act as independently controllable voltage sources, so that three-phase output voltage shows a seamless transition to the backup mode. The feasibility of the proposed UPS system has been investigated and verified through computer simulation results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.5
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• pp.140-145
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• 2004

In this paper, we analyzed the operational characteristics of the modified DC reactor type SFCL and derived the design condition of superconducting coil to be operated properly as power source as well as fault current limiter. It was confirmed through the simulation for the operation of this SFCL that the modified DC reactor type SFCL could be operated as both the uninterruptible power supply and the fault current limiter by controlling the duty ratio of GTO thyristor bridge.

• Journal of Electrical Engineering and Technology
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• v.9 no.3
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• pp.812-819
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• 2014

The proposed technical work attempts to compare the two key technologies of power distribution, i.e. direct current (DC) and alternating current (AC) in a fiscal manner. The DC versus AC debate has been around since the earliest days of electric power. Here, at least four types of a low voltage DC (LVDC) distribution are examined as an alternative to the existing medium voltage AC (MVAC) distribution with an economic assessment technique for a project investment. Besides, the sensitivity analysis will be incorporated in the overall economic analysis model to cover uncertainties of the input data. A detailed feasibility study indicates that many of the common benefits claimed for an LVDC distribution will continue to grow more profoundly as it is foreseen to arise with the increased integration of renewable energy sources and the proliferation of energy storage associated with the enhanced utilization of uninterruptible power supply (UPS) systems.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1413-1415
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• 2005

In paper, propose new partial resonance ZCS PWM controlled High frequency insulating Full-bridge DC/DC converter not using exciting current of high frequency transformer. It is compared with the existing principles in characteristics. It also realizes a widely stabilized ZVS operating using new On-Off control method at synchronized power rectification MOSFET of high frequency insulating transformer secondary. Finally, it is brought over 97[%] measurement -efficiency by proposed DC-DC converter. It is proved effectiveness of new methods using DC UPS PWM rectifier as switching power.

• Progress in Superconductivity and Cryogenics
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• v.10 no.1
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• pp.62-66
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• 2008

The characteristic of the superconducting magnetic energy storage(SMES) system is faster response, longer life time, more economical, and environment friendly than other uninterruptible power supply(UPS) using battery. So, the SMES system can be used to develop methods for improving power quality where a short interruption of power could lead to a long and costly shutdown. Recently, cryogen free SMES has developed using BSCCO(Bismuth Strontium Calcium Copper Oxide) wire. We fabricated and tested the conduction cooling system for the 600 kJ class HTS SMES. The experiment was accomplished for the simulation coils. The simulation coils were made of aluminium, it is equivalent to thermal mass of 600 kJ HTS SMES coil. The coil is cooled with two GM coolers through the copper conduction bar. In this paper, we report that the test results of cool-down and heat loads characteristics of the simulation coils. The developed conduction cooling system adapted to 600 kJ HTS SMES system and cope with the unexpected sudden heat impact, too.