• Proceedings of the KIPE Conference
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• 2003.11a
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• pp.85-89
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• 2003

Many single-stage PFC(power-facto.-correction) ACHC converters suffer from the high link voltage at high input voltage and light load condition. In this paper, to suppress the link voltage, a novel high power factor high efficiency PFC AC/DC converter is proposed using the single controller which generates two gate signals so that one of them is used far gate signal of the flyback DC/DC converter switch and the other is applied to the Boost PFC stage. A 130w prototype for LCD monitor adapter with universal input $(90-265V_{rms})$ and 19.5V 6.7A output is implemented to verify the operational principles and performances. The experimental results show that the maximum link voltage stress is about 450V at 270Vac input voltage. Moreover, efficiency and power factor are over $84\%$ and 0.95, respectively, under the full load condition.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.65 no.4
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• pp.285-291
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• 2016

A light-emitting diode (LED) has been increasingly applied to various industrial fields and general lightings because of its high efficiency, low power consumption, environment-friendly characteristic and long lifetime. To drive the LED lighting, a power converter with the constant output current is needed. Among many power converters, the flyback converter is chosen by many converter designers due to high power density, structural simplicity, and miniaturization. In this converter, an electrolytic capacitor is generally chosen for the stabilization of the DC voltage because of having the large capacitance and the low price. However, the disadvantages are the short expected life time and 120Hz ripple currents on the converter output node. In this paper, a single-stage dimmable PFC DCM flyback converter without the electrolytic capacitor is proposed to prolong the lifetime of the LED driver. For the long lifetime of the converter, the polyester film capacitor with the small capacitance is substituted for the electrolytic capacitor on the output node and an LC resonant filter is added to damp 120Hz ripple current. The proposed converter is verified through the simulation and the experimental works.

• Journal of Electrical Engineering and Technology
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• v.10 no.5
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• pp.2031-2039
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• 2015

In the LED lighting industry, the dimming function in the LED lamp is required by demands of many consumers. To drive this LED lighting, various types of power converters have been applied. Among them, an LLC resonant converter could be applied for high power LED lighting because of its high efficiency and high power density, etc. The function of power factor correction (PFC) might be added to it. In this paper, a dimmable single-stage asymmetrical LLC resonant converter is proposed. The proposed converter performs both input-current harmonics reduction and PFC using the discontinuous conduction mode (DCM). Also, the lower voltage stress across switching devices as well as the zero voltage switching (ZVS) in switching devices is realized by the proposed topology. It can reduce cost and has high efficiency of the driver. In addition, the regulation of the output power by variable switching frequency can vary the brightness of a light. In the proposed converter, one of the attractive advantages doesn’t need any extra control circuits for the dimming function. To verify the performance of the proposed converter, simulation and experimental results from a 300W prototype are provided.

• Proceedings of the KIPE Conference
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• 2002.07a
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• pp.519-524
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• 2002

This paper presents a soft-switching technique of single-stage power conversion Matrix Converter of AC-AC converters. Conventional hard-switching method is limited to operate at low switching frequency due to increased switching loss. In this paper, by additional auxiliary switch circuits, it is shown that the main switch of the matrix converter operate as a zero-voltage switches, and the auxiliary switch operate as a zero current switch. Finally, the soft-switching technique with auxiliary switches is compared with conventional hard-switching technique, and Is analyzed by simulation.

• 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.

• Journal of Power Electronics
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• v.19 no.5
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• pp.1099-1107
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• 2019

A soft switching converter with wide voltage range operation is investigated in this paper. A series resonant converter is implemented to achieve a high circuit efficiency with soft switching characteristics on power switches and rectifier diodes. To improve the weakness of the narrow voltage range in LLC converters, an alternating current (ac) power switch is used on the primary side to select a half-bridge or full-bridge resonant circuit to implement 4:1 voltage range operation. On the secondary-side, another ac power switch is adopted to select a full-wave rectifier or voltage-doubler rectifier to achiever an additional 2:1 output voltage range. Therefore, the proposed resonant converter has the capacity for 8:1 (320V~40V) wide output voltage operation. A single-stage hybrid resonant converter is employed in the study circuit instead of a two-stage dc converter to achiever wide voltage range operation. As a result, the study converter has better converter efficiency. The theoretical analysis and circuit characteristics are verified by experiments with a prototype circuit.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.3
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• pp.263-269
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• 2013

The flyback converter has been applied widely in isolated DC/DC power converters because this converters employ a single MOSFET switch. The leakage inductance should be minimized for high efficiency of flyback converter. but in reality, it is very difficult. Namely, The Snubber circuit is essential to recover the leakage inductance stored energy when the switch is turn off. Flyback Converter typically operates in DCM mode and when switch is turn off in hard switching, this hard switching action results in a high power losses and switching stresses. In order to overcome these problems, a novel soft switching flyback converter using resonant snubber circuit is proposed in this paper. The resonant snubber circuit is composed of the transformer leakage inductance and a capacitor. To verify and confirm the proposed resonant snubber circuit, PSIM simulation and hardware prototype are implemented. Simulation and Experimental results indicate that the proposed resonant snubber circuit is effective.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.2
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• pp.282-289
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• 2008

To improve the efficiency of PDP TV, it should minimize the power losses transpired during AC-to-DC power conversion and PDP driving process. Generally the input power supply for PDP driving employes a two-stage power factor corrected converter, and it needs additional DC-to-DC converters to supply driving power for reset circuit ed sustain driver, which has high power consumption. However, such a circuit configuration has a difficulty for the PDP market requires low cost. To alleviate this problem, a new circuit composition is presented. It integrates input power supply with reset and sustain driver in a single power stack The input power supply of the proposed circuit has a single-stage structure to minimize power conversion loss, and it directly supplies power to the sustain driver so as to reduce the system size and cost.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.5
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• pp.343-354
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• 2009

In this paper, a magnetic-less dc-dc switching converter realizing an integrable power conversion system is described. Instead of magnetic devices, the inductive impedance range of piezoelectric transducers is utilized to store and resonate the energy for soft-switching. Piezoelectric devices have no windings and deliver the power by the electrodes, which lead to mass product through semiconductor-manufacturing process. This paper presents a resonant-type step-up dc-dc power converter employing a disk-type piezoelectric transducer, analyzing the operation principles and the frequency control characteristics. Also, a topology extension of the single stage converter into cascaded multi-stage is presented and analyzed with the operation principles and control characteristics. For verification of the analysis, a 10W output dc-dc power converter hardware was implemented. The hardware experiments shows a good frequency control and power efficiency greater than 96% in the single stage. A hardware prototype of the extended multi-stage one was also realized and tested. The results shows that the converter has the same frequency control performance and high efficiency such as 93%.

• Journal of Electrical Engineering and Technology
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• v.3 no.3
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• pp.391-400
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• 2008

Multi-pulse topology of converters using elementary six-pulse GTO - VSC (gate turn off based voltage source converter) operated under fundamental frequency switching (FFS) control is widely adopted in high power rating static synchronous compensators (STATCOM). Practically, a 48-pulse ($6{\times}8$ pulse) configuration is used with the phase angle control algorithm employing proportional and integral (PI) control methodology. These kinds of controllers, for example the ${\pm}80MVAR$ compensator at Inuyama switching station, KEPCO, Japan, employs two stages of magnetics viz. intermediate transformers (as many as VSCs) and a main coupling transformer to minimize harmonics distortion in the line and to achieve a desired operational efficiency. The magnetic circuit needs altogether nine transformers of which eight are phase shifting transformers (PST) used in the intermediate stage, each rating equal to or more than one eighth of the compensator rating, and the other one is the main coupling transformer having a power rating equal to that of the compensator. In this paper, a two-level 48-pulse ${\pm}100MVAR$ STATCOM is proposed where eight, six-pulse GTO-VSC are employed and magnetics is simplified to single-stage using four transformers of which three are PSTs and the other is a normal transformer. Thus, it reduces the magnetics to half of the value needed in the commercially available compensator. By adopting the simple PI-controllers, the model is simulated in a MATLAB environment by SimPowerSystems toolbox for voltage regulation in the transmission system. The simulation results show that the THD levels in line voltage and current are well below the limiting values specified in the IEEE Std 519-1992 for harmonic control in electrical power systems. The controller performance is observed reasonably well during capacitive and inductive modes of operation.