• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.35 no.12
• /
• pp.586-593
• /
• 1986

Ringing during the scan time deteriorates the picture quality of television receiver. By tuning the stray reactance of the flyback transformer(FBT)to harmonics of the retrace pulse, the ringing can be suppressed and this is, what is called, the harmonic tuning methed. But finding the conditions for the ringing to cease in lossy FBT and satisfying these conditions at design stage require much time and experience. In this paper, the conditions for the ringing to cease in loss-included equivalent circuit are derived and a new method, unharmonic-tuning method, is suggested.

• Proceedings of the KIPE Conference
• /
• 1997.07a
• /
• pp.101-110
• /
• 1997

The circuit effects due to the transformer primary side series equivalent inductance in the Zero Voltage Switching Pulse Width Modulated Half Bridge DC/DC Converter and its impact on the effective duty are analyzed. The steady state equations and the small signal model of the converter are derived incorporating the effects of the complementary control and the utilization of transformer primary side series equivalent inductance. The open plant dynamics are analyzed on the basis of the model derived. The model predictions are confirmed by experimental measurements.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.7 no.6
• /
• pp.563-569
• /
• 2002

This paper proposes an inverter for the grid-connected photovoltaic system based on the transformer-less inverter. This system consists of a high frequency DC-DC converter, high frequency transformer, diode bridge rectifiers, a DC filter, a low frequency inverter, and an AC filter. The 20kHz switched high frequency converter is used to generate bipolar PWM pulse, and the high frequency transformer transforms its voltage twice, which is subsequently rectified by diode bridge rectifiers for a full-wave rectified 60 Hz sine wave power output. Even though the high frequency link system needs more power semiconductors, a reduced size, light weight, and saved parts cost make this system more comparative than other power conditioning systems due to elimination of 60Hz transformer.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.54 no.3
• /
• pp.120-126
• /
• 2005

The Korean Superconducting Tokamak Advanced Research (KSTAR) tokamak device is being constructed to perform long-pulse, high-beta, advanced tokamak fusion physics experiments. The long-pulse operation requires the non-inductive current drive system such as the Lower-Hybrid Current Drive (LHCD) system. The LHCD system drives the non-inductive plasma current by means of C-band RF with 2-MW CW power and 5-GHz frequency. For the LHCD test experiments, an RF test system is developed. It is composed of a 5-GHz, 1.5-MW pulsed magnetron and a compact pulse modulator with $4\;{\mu}s$ of pulse width. The pulse modulator provides the maximum output voltage of 45 kV and the maximum current of 90 A. It is composed of 7 stages of Pulse Forming Network (PFN), a thyratron tube (E2V, CX1191D), and a pulse transformer with 1:4 step-up ratio. In this paper, the detailed design and the performance test of the pulse modulator are presented.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.13 no.3
• /
• pp.73-81
• /
• 1999

Measurements of ultrasonic signals caused by partial discharges were perlonnrl by using an ultrasonic measurement technique to diagnose the electrical treeing deterioration in an epoxy mold-type power transformer. We also examined the characteristics of tree growth, partial discharge magnitude and ultrasonic pulse number with the increase of the deterioration time. From these results, it was found that the shape of the tree was a branch-type, and the rates of the tree growth were examined when ac voltages of 16[kV] and 20[kV] were applied Ultrasonic pulse number and discharge magnitude were rapidly increased as the length of the tree grows after the middle stage of the deterioration time, and it appeared that ultrasonic pulse number was proportional to discharge magnitude. Attenuation, time-delaying and directivity characteristics of ultrasonic signals propagated into epoxy resin by using ultrasonic oscillation and receiving systems are also re[prted as a basic data of ultrasonic mesasurements in mold-type power transformer.former.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.7 no.4
• /
• pp.332-338
• /
• 2002

High current coil power supply for superconductivity coil of tokamak requires fast dynamics performance of di/dt and smooth change over of current direction. To meet the specification high performance DSP-based controller Is designed for 12-pulse thyristor dual converter with interphase transformer(IPT). Not only the total current of Y and $\Delta$ converter units but also the difference for those should be regulated fast and accurately. Proportional and integral controller is designed for current difference control and the controller output is compensated to $\Delta$ converter. The source voltage phase angle detection and gate pulse generation algorithm are implemented in software for higher reliability of current control. The current error Is reduced by selection of appropriate initial gating angle during the transient of change over of current direction between thyristor converters.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.14 no.1
• /
• pp.23-30
• /
• 2009

A new high performance and low cost unified power system is proposed through investigating conventional Power-Integrated Drive(PID) system and Power-Separated Drive(PSD) system applied to LCD TV. Since the proposed system consists of two stage, namely power and inverter stage it features high efficiency and cost effectiveness. To satisfy the safety standard of the High voltage transformer, 1:1 transformer is employed between inverter and high voltage transformer. Moreover, to ensure the Zero Voltage Switching(ZVS) of all power switches and the Pulse Count Modulation(PCM) method is employed, which controls the number of pulse at the fixed frequency and fixed duty cycle. Therefore, it features high efficiency, improved heat generation, cost effectiveness and good EMI performance including no additional current balancing coil. To confirm the validity of proposed system, comparison of conventional system, verification of experimental results are presented.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.54 no.11
• /
• pp.508-514
• /
• 2005

In this paper, it was investigated the characteristics of PD(partial discharge) pulse shapes in oil and the possibility of TF(Time-Frequency) analysis for the discrimination of air corona in on-site PD measurement of oil transformers. For the purpose, single and multiple discharges combined with oil discharges and air corona were generated and measured by use of artificial models through the HFPD pulse detector and the oscilloscope. PD pulse shapes were different according to the type of defects, especially including air corona- pulses. Also, through the TF analysis, data clusters could be classified each other in the TF Map, even in the case of multiple discharges. Therefore, it is known that TF analysis could be aprlied for the improvement of on-site PD measurement in oil transformers.

• Proceedings of the KIPE Conference
• /
• 2001.12a
• /
• pp.164-165
• /
• 2001

An IGBT driver for serially connected pulse switching IGBTS was contructed and tested. The IGBT driver has ten output pulses with 1 ${\mu}ysec$ pulse width Its pulse repetition-rate can adjusted from 0 to 20 kHz. The output pulses was insulated from 10 kV high voltage by a pulse transformer. Their voltage amplitude are 18 V, voltage rising time 250 nsec., and voltage falling time 200 nsec when IGBT gates with 12 nF input capacitance are connected.

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.39 no.6
• /
• pp.545-556
• /
• 1990

A design method of a current source using 12-pulse phase-controlled rectifier (PCR) is presented. The critical inductance of the 12-pulse PCR is derived and it is shown that the critical inductance can be reduced using a current source. The control circuit of the 12-pulse PCR with an inner fast dynamic loop is proposed to give the frequency synchronism and to reduce the subharmonics due to the unbalance of the transformer of the power line. This circuit is analyzed and its dynamic loop is optimized. The optimal constant PIMF (proportional, integral and measurable variable feedback, and feedforware) controller is also designed using the time-weighted quadratic performance index. It is shown via experimental results that the proposed design method gives high dynamic and static performance of the current source using the 12-pulse PCR.