• Journal of electromagnetic engineering and science
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• v.16 no.1
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• pp.13-18
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• 2016

This paper presents a design of an impedance transformer (IT) with high frequency selectivity characteristics. The frequency selectivity can be controlled by even- and odd-mode impedance of a shunt coupled transmission line (TL). For experimental validation, a 50- to $20-{\Omega}$ IT was implemented at a center frequency ($f_0$) of 2.6 GHz for the long-term evolution signal. The measured results were in good agreement with the simulations, showing a return loss higher than 19 dB over a passband bandwidth of 0.63 GHz (2.28-2.91 GHz) and good sharp frequency selectivity characteristic near to the passband. The series coupled TL provides a transmission zero at 5.75 GHz, whereas the shunt coupled TL provides three transmission zeros located at 2 GHz, 3.1 GHz, and 7.14 GHz.

• Journal of Power Electronics
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• v.13 no.3
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• pp.329-338
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• 2013

In this paper, the charging characteristics of series resonant type high voltage capacitor chargers considering the transformer stray capacitance have been studied. The principles of operation for the four operational modes and the mode changes for the four different switching frequency sections are explained and analyzed in the range of switching frequency below the resonant frequency. It is confirmed that the average charging currents derived from the above analysis results have non-linear characteristics in each of the four modes. The resonant current, resonant voltage, charging current, and charging time of this capacitor charger as variations of the switching frequency, series parallel capacitance ratio ($k=C_p/C_s$), and output voltage are calculated. From the calculation results, the advantages and disadvantages arising from the parallel connection of this stray capacitance are described. Some methods to minimize charging time of this capacitor charger are suggested. In addition, the results of a comparative test using two transformers whose stray capacitances are different are described. A 1.8 kJ/s prototype capacitor charger is assembled with a TI28335 DSP controller and a 40 kJ, 7 kV capacitor. The analysis results are verified by the experiment.

• Transactions on Electrical and Electronic Materials
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• v.1 no.3
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• pp.1-5
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• 2000

This paper presents a new sort of multilayer piezoelectric ceramic transformer for switching regulation power supplies. This piezoelectric transformer operate in the second thickness resonant vibration mode. Accordingly its resonant frequency is higher than 1 NHz, Because output power is low if input and output part of transformer are consisted of single layer, this research suggests a new method, which is consisted of both input and output part of transformer have 2-layered piezoelectric ceramics, The size of transformer is 20 mm in width and length, and 1.4 mm in thickness, respectively, To design a high efficient switching circuit of the transformer, internal circuit parameters were measured and then weve calculated a parameter of inductor nd capacitor to design a driving circuit, Weve used a MISFET and its driver circuit modified a calp oscillator circuit as the primary switching circuit.

• Journal of Power System Engineering
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• v.4 no.4
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• pp.59-64
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• 2000

Especially, demands for the noise reduction of mold transformer has been becoming an common issue because it has been used mainly at the residence area such as building and ship. So, this paper investigates the noise source and countermeasure of mold transformer radiated high noise abnormally. The result of impact hammering test for core of transformer ascertains the core resonance by harmonics of line frequency and high noise can be reduced to avoid core resonance by changing torque strength of tie rod. Magnetic field analysis is performed to identify the reason that noise of V-phase is higher than U and W-phase in the normal condition. It is the cause that flux density and magnetic force of V-phase is higher than the other phase respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05a
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• pp.18-22
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• 2000

The partial discharge testing is widely used in insulation property measurement because it gives low stress to high voltage equipment which is undertaken tests. Therefore it is very useful method compare to previous destructive methods and effective diagnosis method in power transformer that requires live-line diagnosis. But partial discharges have very complex characteristics of discharge pattern so it is required continuous research to development of precise analysis method. In recent, the study of partial discharge is carrying out discover of initial defect of power equipment through condition diagnosis and system development of degradation diagnosis using HFPD(High Frequency Partial Discharge) detection. In this study, simulated transformer is manufactured and HFPD occurred from transformer is measured with broad band antenna in real time, the degradation grade of transformer is analyzed through produced patterns in simulated transformer according to applied voltages.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05a
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• pp.29-32
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• 2000

The partial discharge testing is widely used in insulation property measurement because it gives low stress to high voltage equipment which is undertaken tests. Therefore it is very useful method compare to previous destructive methods and effective diagnosis method in power transformer that requires on-line & on-site diagnosis. But partial discharges have very complex characteristics of discharge pattern so it is required continuous research to development of precise analysis method. In recent, the study of partial discharge is carrying out discover of initial defect of power equipment through condition diagnosis and system development of degradation diagnosis using HFPD(High Frequency Partial Discharge) detection. In this study, simulated transformer is manufactured and PD/HFPD occurred from transformer is measured with broad band antenna in real time, the degradation grade of transformer is analyzed through produced patterns in simulated transformer according to applied voltages.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.4
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• pp.351-355
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• 2016

Welding machines are high-capacity systems used in a low-frequency range using IGBT. As their system is similar to a large transformer, most welding machines suffer a great loss because of hard switching and vast leakage inductance. A voltage-balancing circuit is designed to overcome these shortcomings. This circuit can reduce the transformer size by making it into a high frequency and reducing the input voltage by half and by adopting a serial structure that connects two full-bridges in a series to use a MOSFET with a good property at high frequency. In addition, a Schottky diode is used in the primary rectifier to overcome the low efficiency of most welding machines. To use the Schottky diode with a reliably relatively low withstanding voltage, an active snubber is adopted to effectively limit the ringing voltage of the diode cut-off voltage.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.12
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• pp.520-526
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• 2005

Demands for the noise reduction of a transformer has been becoming an common issue because it has been used mainly at the residence area such as an apartment complex. This paper shows 2 trouble shooting examples that high noise sources were found out structural resonance of a transformer by 120Hz exciting frequency caused from magnetostrictive vibration of core. This paper presents that vibration data are very important to find noise source and how to avoid natural frequency of core and tank wall

• Proceedings of the KSR Conference
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• 2003.10c
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• pp.513-518
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• 2003

Noises are defined as unwanted sound and invoke the physical harm and unconvenience. The higher the noise level is, the more damage peoples have. Low frequency noise is less harmful than high frequency one. In case of train, noises inside of train which is isolated from outer circumstances reduce the convenience of passenger very much. This paper reviewed the noise standard of train for urban subway and investigated the main transformer as the main noise source of train and suggested the method to diminish the noise resulted from main transformer of train and compared the measured results of before and after the improvement of main transformer.

• Journal of Power Electronics
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• v.15 no.5
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• pp.1402-1408
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• 2015

A MOSFET's gate driver based on magnetic coupling is investigated. The gate driver can meet the demands in applications for wide range of duty cycles and high frequency. Fully galvanic isolation can be realized, and no auxiliary supply is needed. The driver is insensitive to the leakage inductor of the isolated transformer. No gate resistor is needed to damp the oscillation, and thus the peak output current of the gate driver can be improved. Design of the driving transformer can also be made more flexible, which helps to improve the isolation voltage between the power stage and the control electronics, and aids to enhance the electromagnetic compatibility. The driver's operation principle is analyzed, and the design method for its key parameters is presented. The performance analysis is validated via experiment. The disadvantages of the traditional magnetic coupling and optical coupling have been conquered through the investigated circuit.