• Journal of Electrical Engineering and Technology
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• v.5 no.3
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• pp.477-483
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• 2010

This paper is studied on a novel buck-boost isolated converter for high efficiency and high power factor. The switching devices in the proposed converter are operated by soft switching technique using a new quasi-resonant circuit, and are driven with discontinuous conduction mode (DCM) according to pulse width modulation (PWM). The quasi-resonant circuit makes use of a step up-down inductor and a loss-less snubber capacitor. The proposed converter with DCM also simplifies the requirement of control circuit and reduces a number of control components. The input ac current waveform in the proposed converter becomes a quasi sinusoidal waveform in proportion to the magnitude of input ac voltage under constant switching frequency. As a result, it is obtained by the proposed converter that the switching power losses are low, the efficiency of the converter is high, and the input power factor is nearly unity. The validity of analytical results is confirmed by some simulation results on computer and experimental results.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.1342-1344
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• 2000

This paper presents a microcontroller-based control circuit for color variation of high brightness RGB LEDs in $8{\times}8$ matrix array. The control circuit is comprised of an AT89C52 chip, D Flip-flops, and transistors for switching, and is used to adjust the number of LEDs operated for color variation. For a stable operation, it is required that the input current to each LED should be maintained to a normal value irrespective of the number of LEDs operated.

• Journal of Electrical Engineering and Technology
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• v.7 no.3
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• pp.358-365
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• 2012

A new third harmonic injection circuit for light-emitting diode (LED) drivers is proposed to eliminate electrolytic capacitors and thereby extend the lifetime of LED drivers. When a third harmonic current is injected to the input current of the LED driver, the required capacitance of the driver can be reduced. The proposed circuit can control an injection ratio and has simple circuitry. The synchronous third harmonic is generated by a phase locked loop (PLL), a 1/3 counter, and op-amps and applied to a power factor correction circuit. Thus, the storage capacitor can install film capacitors instead of the electrolytic capacitor. The value of storage capacitance can be reduced to 78% compared to an input power factor of 100%. The proposed circuit is applied to the 80W prototype LED driver to experimentally verify the performances.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.11
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• pp.1575-1583
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• 2017

With the development of DC distribution, DC circuit breaker is required to ensure the stability of the DC grid. Unlike a mechanical circuit breaker that blocks after several tens of milliseconds, a DC SSCB(Solid-State Circuit Breaker) can break the fault well within 1 [ms], so it can prevent the damage of accident. However, the previous DC SSCB requires a lot of switching elements for charging commutation capacitors, and the control is complicated. Therefore, this paper proposes a new DC SSCB suitable for DC grid. The proposed DC SSCB is simple to control for charging commutation capacitors, and it can perform the rapid breaking and operating duty of reclosing and rebreaking. The proposed DC SSCB was designed to 380 [V] and 5 [kW] class which is suitable for residential DC distribution, and the operating characteristics of the proposed DC SSCB were verified by simulations and experiments. It is anticipated that the proposed DC SSCB may be utilized to design and realize DC grid system.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.1
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• pp.23-33
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• 2002

A hysteresis control is widely used to control output current of inverter. A hysteresis bandwidth is affected by system parameters such as source voltage, device on/off time, load inductance and resistance. The frequency limiter is used to protect switching devices overload. In the conventional hysteresis controller, a lock-out circuit with D-latch and timer is used to device protection circuit. But switching delay time and harmonic components are appeared in output current. In this paper the performance of lock-out circuit is tested, and new circuit for switching device fault protection is proposed ad it's performance is simulated.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.6
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• pp.495-499
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• 2012

Recently, DC distribution systems become hot issues since DC type loads increase rapidly according to the expansion of IT equipment such as computers, servers, and digital devices; DC type loads will cover 50% for all electricity loads in 2020 which was mere 10% in 2000. DC distribution systems are also accelerated by the expansion of renewable power systems since they are easy to be interfaced with DC grids rather than AC grids. However, removing the fault current in DC grids is comparably difficult since the current in DC grids has non zero-crossing point like in AC grids. Thus, developing dedicated DC circuit breakers for DC grids is necessary to get safety for human and electrical facilities. Magnet arc extinguishing method is proper to small size DC circuit breakers. However, simple Magnet arc extinguishing method is not enough to break inductive fault currents. This paper proposed a novel DC circuit breaker against inductive fault current defined by IEEE C37.14-2004 Standard for Low-Voltage DC Power Circuit Breakers Used in Enclosures. The performance of the proposed DC circuit breaker was verified by an experimental circuit breaker test system built in this research.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.6
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• pp.927-935
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• 1994

Detailed analysis of the commutation circuit of the proposed wide-frequency current source inverter is given. In this inverter a spike-limit circuit and a precommutation circuit are used. The spike-limit circuit is intended to limit spike voltage which is arising during commutation time in a current source inverter, and the precommutation circuit to reuse the energy which flows from main inverter to spike-limit circuit during commutation time to aid commutation. Thus voltage stress of main thyristor is minimized. Since this inverter can be made up of thyristors for phase control, it has some advantage in high voltage and high power application.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.11
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• pp.2089-2092
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• 2010

There are many cases that interrupt the production process because of malfunctions caused by electronic circuit boards which control equipment, but it is difficult to distinctly identify the causes in many cases. Especially, CMOS devices with the control logic circuit return automatically to normal state after their own faults. Therefore it is not easy to analyze the problems with electronic circuit boards. Recently, nuclear power plant experienced a failure due to the malfunction of electronic circuit boards and it was identified that the reason of the malfunction was because of latch-up phenomenon caused by external surge in electronic devices. This paper presents the causes and the phenomenon of latch-up by experiment and also a way using counter EMF diodes, noise filters and surge protective devices to prevent latch-up phenomenon from electronic circuit boards, finally confirms the effectiveness of the result by experiment.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.09a
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• pp.82-88
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• 2001

Manufactured easy elevator can drives from the first floor to fifth floor as sequence control circuit in cause opening than existing equipment of experiment and practice, the structure of in the first implementation process are hand-worked control component with push-button, L/S and relay, it is structured a lamp to express that the door open and moving of cage by mechanical action of For/Rev motor-braker of which load. The second structure of implement process to control from the first floor to the fifth floor with the PLC elevator program can control by the sensor of hand-operated function of L/Sl~L/S5 in time that the S/Wl~S/W5 of PLC control panel operates to the For/Rev. The function of two kind process that an elevator is driven by PLC program and the sequence control relay circuit is a mechanical relay sequence control field and it is equipment apparatus of it to get appropriately the technology of For/Rev in that mechanical operating cause of a load using the PLC program. Also the wring circuit using a plug, dissembly. the circuit and the principle of component, and PLC program with the function test can be used the implementation field to the total technology theory about FA.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.80-82
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• 1988

This paper proposed a new equivalent circuit and parameter estimation for I.M, which is different from T type and L type equivalent circuits. By using this circuit, we can analyze the torque of I.M, such as seperately exited D.C Motor, further more, we think that this equivalent circuit is effective to the vector control system for I.M.