• Journal of Power Electronics
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• v.14 no.2
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• pp.362-368
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• 2014

This paper proposes a harmonic reduction approach for a pulse width modulation (PWM) AC-AC converters using Bee Colony Optimization (BCO). The optimal switching angles are provided by BCO to minimize harmonic distortions. The sequences of the PWM switching angles are considered as a technical constraint. In this paper, simulation results from various optimization techniques including BCO, Genetic Algorithm (GA), and Particle Swarm Optimization (PSO) are compared. The test results indicate that BCO can provide a better solution than the others in terms of power quality and power factor improvement. Lastly, experiments on a 200W AC-AC converter confirm the performance of the proposed switching pattern in reducing harmonic distortions of the output waveform.

• Journal of Power Electronics
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• v.17 no.4
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• pp.860-873
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• 2017

The present article reports an analysis and investigation of a direct AC-AC quasi-resonant converter. A bidirectional power device, whose switching frequency is lower than the frequency of the current passing through the load, is used for its realization. The zero voltage switching mode is described when zero voltage on the power device is available by measuring it with the control system. The continuous current in the resonant inductance by switching the power device at zero voltage is considered, and it is characterized by two sub-modes. A mathematical analysis of the processes has been made and comparative results from the computer simulation and experimental study have been brought. The converter can be used in a wide areas of power electronics: induction heating, wireless power transfer, AC-DC converters, etc.

• Korean Journal of Chemical Engineering
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• v.35 no.11
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• pp.2207-2219
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• 2018

Activated carbon (AC) was synthesized from Phoenix dactylifera stones and then modified by $CoFe_2O_4$ magnetic nanocomposite for use as a Cr(VI) adsorbent. Both $AC/CoFe_2O_4$ composite and AC were fully characterized by FTIR, SEM, XRD, TEM, TGA, and VSM techniques. Based on the surface analyses, the addition of $CoFe_2O_4$ nanoparticles had a significant effect on the thermal stability and crystalline structure of AC. Factors affecting chromium removal efficiency like pH, dosage, contact time, temperature, and initial Cr(VI) concentration were investigated. The best pH was found 2 and 3 for Cr adsorption by AC and $AC/CoFe_2O_4$ composite, respectively. The presence of ion sulfate had a greater effect on the chromium sorption efficiency than nitrate and chlorine ions. The results illustrated that both adsorbents can be used up to seven times to adsorb chromium. The adsorption process was examined by three isothermal models, and Freundlich was chosen as the best one. The experimental data were well fitted by pseudo-second-order kinetic model. The half-life ($t_{1/2}$) of hexavalent chromium using AC and $AC/CoFe_2O_4$ magnetic composite was obtained as 5.18 min and 1.52 min, respectively. Cr(VI) adsorption by AC and $AC/CoFe_2O_4$ magnetic composite was spontaneous and exothermic. In general, our study showed that the composition of $CoFe_2O_4$ magnetic nanoparticles with AC can increase the adsorption capacity of AC from 36 mg/L to 70 mg/L.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.2
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• pp.216-223
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• 1996

The active power factor control AC/DC converter needs a current loop compensator to obtain better dynamic characteristics and power factor performance, but the optimal design of a current loop compensator is difficult because the AC/DC converter is a nonlinear system having periodically varying poles and zeros. The predictive current control scheme generates a control input using the dynamic equations of the AC/DC converter so that the dynamic of the AC/DC converter is included in the controller and the necessary bandwidth and the gain characteristics of the current control loop are satisfied. And as a result, a compensator becomes unnecessary and the current loop shows the improved current loop characteristics. In this paper, a power factor controller without current loop compensator by adopting a predictive current control scheme is designed and the designed power factor controller is modelled by using a small signal perturbation modelling technique, and simulated to investigate its small signal characteristics. A 200 W power factor control AC/DC converter is built to verify the effectiveness of the proposed power factor controller.

• The Journal of the Acoustical Society of Korea
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• v.15 no.2
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• pp.12-20
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• 1996

A real-time Dolby AC-3 decoder has been implemented using a 20-bit fixed point general purpose DSP chip. It is shown that AC-3 decoder of this paper has same performance as decoder of C-simulator on PC. And also, it is applied to DVD player. Especially, in this paper, we proved that it has shorter latency time than that of previous AC-3 decoder.

• Journal of Adhesion and Interface
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• v.17 no.3
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• pp.104-109
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• 2016

Compare AC corona and DC corona treatment effects, polyester fabrics were AC corona treated with different current intensity (5, 10, 15 A) and feeding speed (5, 10, 15 m/min) as the same DC corona treatment conditions of the preceding research. We confirmed the surface change of polyester fabrics using scanning electron microscopy (SEM) and X-ray photoelectron spectrometer (XPS), and the change of physical properties through measuring the dry and wet bonding strength. The surface changes of polyester fabrics by treating in air atmosphere with AC corona discharge are shown similar tendency with DC corona discharge. Generally dry bonding strength were increased with increasing current intensity and feeding speed, but wet bonding strength were increased with increasing current intensity and decreasing feeding speed in both AC and DC corona treatment. When the current is 20 A, carbonization occurs in DC corona discharge but carbonization does not occur in DC corona discharge.

• Journal of Power Electronics
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• v.6 no.3
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• pp.214-225
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• 2006

The design and performance analysis of a reduced rating autotransformer based thirty-pulse AC-DC converter is carried out for feeding a vector controlled induction motor drive (VCIMD). The configuration of the proposed autotransformer consists of only two single phase transformers, with their windings connected in a T-shape, resulting in simplicity in design, manufacturing and in a reduction in magnetics rating. The design procedure of the autotransformer along with the newly designed interphase transformer is presented. The proposed configuration has flexibility in varying the transformer output voltage ratios as required. The design of the autotransformer can be modified for retrofit applications, where presently a 6-pulse diode bridge rectifier is used. The proposed thirty-pulse AC-DC converter is capable of suppressing less than $29^{th}$ harmonics in the supply current. The power factor is also improved to near unity in the wide operating range of the drive. A comparison of different power quality indices at AC mains and DC bus is demonstrated in a conventional 6-pulse AC-DC converter and the proposed AC-DC converter feeding a VCIMD. A laboratory prototype of the proposed autotransformer based 30-pulse AC-DC converter was developed with test results validating the proposed design and system.

• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2089-2098
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• 2017

Microgrid is a convenient, reliable, and eco-friendly approach for the integration of Distributed Generation (DG) sources into the utility power systems. To date, AC microgrids have been the most common architecture, but DC microgrids are gaining an increasing interest owing to the provision of numerous benefits in comparison with AC ones. These benefits encompass higher reliability, power quality and transmission capacity, non-complex control as well as direct connection to some DG sources, loads and Energy Storage Systems (ESSs). In this paper, main challenges and available approaches for the protection of AC and DC microgrids are discussed. After description, analysis and classification of the existing schemes, some research directions including coordination between AC and DC protective devices as well as development of combined control and protection schemes for the realization of future hybrid AC/DC microgrids are pointed out.

• Proceedings of the KIEE Conference
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• 2000.11a
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• pp.132-135
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• 2000

Direct current corrosion have being investigated by lots of scientists but Alternating current corrosion was ignored because the corrosion rate by AC was very small. Recently however, AC corrosion accidents have been reported in many other countries. So the study of AC corrosion is to be necessary in these days. In this paper, several experiments which intentionally imposed the AC or DC to the specimens also imposed AC and DC at the same time was carried out in the laboratory to examine the AC corrosion characteristics and in addition applied the same way in the field. Moreover, while the field investigations of the abnormal corrosion failures. It was the AC that caused one of corrosion failures.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.2
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• pp.84-91
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• 2019

This study proposes a AC/DC railway vehicle control algorithm that enables simultaneous driving of AC and DC power supply sections. In the Seoul metropolitan region, trolley voltage for railway vehicle is divided into AC and DC power supplies. Therefore, AC/DC railway vehicle algorithm is essential for driving on the outskirts of the region. This study analyzes resonance and beat phenomena for simultaneously running in AC and DC power supply sections, and proposes a control algorithm for railway vehicles with the application of damping and beatless controls based on this analysis. The performance of the proposed algorithm is verified by simulation and analysis of actual driving results.