• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.3
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• pp.255-260
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• 2023

In order to spread LED lighting, LED lighting technology directly driven by alternating current (AC) commercial power has recently been introduced. Since current does not flow at a voltage lower than the threshold voltage of the LED, a non-conductive section occurs in the current waveform, and the higher the threshold voltage of the LED, the more discontinuous current waveforms are generated. In this paper, multi-LED modules are connected in series so that the threshold voltage can be adjusted according to the number of LED modules. A small number of LED modules are driven at a low instantaneous rectified voltage, and a large number of LED modules are driven at a high instantaneous rectified voltage to lengthen the overall lighting time of AC-LED lighting, thereby minimizing the luminance deviation of AC-LED lighting. In addition, the load current flowing through the LED module is adjusted to be the same as the design current even at the maximum rectified voltage higher than the design voltage, so that the light brightness of the LED module is kept constant. Therefore, even if the rectified voltage applied to the LED module changes, the AC-LED lighting in which the light brightness is constant and the luminance deviation is minimal has been realized.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.3
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• pp.358-364
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• 1996

Recently, much power demand from domestic power consumer is weakening the allowable power reserve margin in summer, especially at midday for one day due to a steep increase of air cooling loads such as air conditioner. Therefore solar airconditioning system can'be considered as one of the best remedies to meet the increase of peak power. Generally in solar air conditioning system, the diode rectifier is used to build up DC link voltage from AC source. The diode rectifier is simple and cheap but it brings out the problems of low power factor and plentiful harmonics at the AC source. Also It can derate the utilization rate of solar energy because the reverse of power flow cannot be made. Hence, in this paper to overcome the peak power problem in summer and to endure good AC input characteristics, solar air conditioning system using the PWM converter is proposed. As results, obtained are the characteristics of the PWM converter such as low distorted current waveform, high power factor and bidirectional power control. And also the stability of proposed system is verified by examining the dynamics of step load change and power reversal testing. (author). refs., figs., tabs.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.431-432
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• 2014

Recently, the demand of LED(light-emitting diode) lighting is gradually enlarged by governmental saveenergy policy, which the LED lighting has been established compulsorily in new buildings, public institutions, and residential installations etc.. The LED lighting is driven by SMPS (switching mode power supply). The SMPS requires high efficiency because the SMPS changes a commercial ac power source to low voltage dc power source. Harmonic components that occur in the conversion process of SMPS decrease system power factor and deal great damage in electric power system. To improve such problems, this paper proposes a SMPS of high efficiency. The switching devices in the proposed SMPS are operated by soft switching technique using a new quasi-resonant circuit. The input ac current waveform in the proposed SMPS becomes a quasi-sinusoidal waveform proportional to the magnitude of input ac voltage under constant switching frequency. As a result, the proposed SMPS obtains low switching power loss and high efficiency, and its input power factor is nearly in unity.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.553-555
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• 1994

Various nonlinear loads such as diode rectifiers, and phase controlled converters connected to at source cause harmonic pollutions in ac mains. Recently some filters have been proposed to minimize the potential problems. This study describes a method to improve the performances of a voltage source active filter. Two feedback loops are used in the scheme : one for reactive power compensation and the other for harmonic eliminations.

• Proceedings of the KIPE Conference
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• 2004.07a
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• pp.260-264
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• 2004

In this paper the novel converter topology for the switched reluctance motor drives is proposed, which is composed of the minimum switch per phase and is connected to the single-phase voltage inverter for ac voltage source. The proposed converter topology is divided into two types according to the voltage source inverter of half bridge type and full bridge type. Proposed converters of two types are proposed, analyzed and compared with each other. The SRM using proposed converter maintain the hi인 efficiency though the power switches are reduced.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.413-416
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• 1998

This paper presents a dAC calibration technique for high resolution and monolithic operation. The calibration technique consists of basic source, current memory cell (C.M) and current substrator. Current memory supplies the error current to basic source. Current substrator extracts the error current from the main source. It is simple and needs no special calibration period. The proposed current cell has high calibration performance and guarantees 100MHz operation.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.4
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• pp.388-393
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• 2018

In this paper, We developed a high efficiency reflector integrated type 50W AC direct connection type engine to realize miniaturization and weight reduction of product without using SMPS and to design a multistage varistor circuit Reduced costs by reducing the number of parts High reliability is achieved by using a circuit structure that does not use an electrolytic capacitor, thus increasing the lifetime of the LED. In addition, it is possible to manufacture an AC direct-coupled type driving device by using an IC semiconductor and apply an AC direct-coupled type driving device integrated with a reflector so that the lifetime of the device can be fully utilized for the lifetime of the LED, A light source having a plurality of light emitting diode channels including a plurality of light emitting diode channels arranged in series is driven with a rectified voltage.

• Korean Journal of Materials Research
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• v.20 no.8
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• pp.429-433
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• 2010

In this study, activated carbon (AC) as a carbon source was modified with different concentrations of cobalt chloride ($CoCl_2$) to prepare a Co-AC composite, and it was used for the preparation of Co-AC/$TiO_2$ composites with titanium oxysulfate (TOS) as the titanium precursor. The physicochemical properties of the prepared Co-AC/$TiO_2$ composites were characterized by $N_2$ adsorption at 77 K, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis. The photocatalytic treatments of organic dyes were examined under an irradiation of visible light with different irradiation times. $N_2$ adsorption data showed that the composites had decreased surface area compared with the pristine AC, which was $389\;m^2/g$. From the XRD results, the Co-AC/$TiO_2$ composites contained a mixturephase structuresof anatase and rutile, but a cobalt oxide phase was not detected in the XRD pattern. The EDX results of the Co-AC/$TiO_2$ composites confirmed the presence of various elements, namely, C, O, Ti, and Co. Subsequently, the decomposition of methylene orange (MO, $C_{14}H_{14}N_3NaO_3S$) and rhodamine B (Rh.B, $C_{28}H_{31}ClN_2O_3$) in an aqueous solution, respectively, showed the combined effects of an adsorption effect by AC and the photo degradation effect by $TiO_2$. Especially, the Co particles in the Co-AC/$TiO_2$ composites could enhance the photo degradation behaviors of $TiO_2$ under visible light.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.357-358
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• 2015

This paper provides a comparison of power converter loss and thermal description for voltage source and current source type 5MW-class medium voltage topologies of wind turbines. Neutral-point clamped three-level converter is adopted for voltage source type topology while two-level converter is employed for current source type topology considering the popularity in the industry. In order to match the required voltage level of 4160V with the same switching device of IGCT as in voltage source converter, two active switches are connected in series for the case of current source converter. The loss analysis is confirmed through PLECS simulations. In addition, the loss factors due to di/dt and dv/dt snubber and ac input filter are presented. The comparison result shows that VSC-based wind turbine system has a higher efficiency than that of CSC under the rated operating conditions.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.588-590
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• 1996

An AC induction motor or constant speed characteristics has been widely used as power source because of simple structure and low maintenance cost in industrial field. The variable frequency AC source with a conventional inverter which is composed or power semi-conductors and drive systems contains much noises in sine wave current due to high speed switching or direct current. In this paper, the low pass LC filter for a variable speed induction motor driven by a full bridge inverter is introduced to solve EMI problem originated by much noise current. The modified LC filter based on the 3rd order Butterworth LC filter is used for the computer simulations and real experiments. The characteristics or proposed LC filter are investigated through FET analysis.