• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.15-16
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• 2010

This paper is study on a high efficiency DC-DC converter of discontinuous conduction mode (DCM) added electric isolation. The converters of high efficiency are generally made that the power losses of the used semiconductor switching devices is minimized. To achieve high efficiency system, the proposed converter is constructed by using a quasi resonant circuit. The control switches using in the converter are operated with soft switching by quasi resonant method. The control switches are operated without increasing their voltage and current stresses by the soft switching technology. The result is that the switching loss is very low and the efficiency of the system is high. The proposed converter is also added electric isolation which is used a pulse transformer. When the power conversion system is required electric isolation, the proposed converter is adopted with the converter system development of high efficiency. The soft switching operation and the system efficiency of the proposed converter are verified by digital simulation and experimental results.

• Journal of Power Electronics
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• v.16 no.3
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• pp.840-848
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• 2016

A primary-side regulation AC-DC converter operating in the PFM (Pulse Frequency Modulation) mode with a high precision output current is designed, which applies a novel inductance compensation technique to improve the precision of the output current, which reduces the bad impact of the large tolerance of the transformer primary side inductance in the same batch. In this paper, the output current is regulated by the OSC charging current, which is controlled by a CC (constant current) controller. Meanwhile, for different primary inductors, the inductance compensation module adjusts the OSC charging current finely to improve the accuracy of the output current. The operation principle and design of the CC controller and the inductance compensation module are analyzed and illustrated herein. The control chip is implemented based on a TSMC 0.35μm 5V/40V BCD process, and a 12V/1.1A prototype has been built to verify the proposed control method. The deviation of the output current is within ±3% and the variation of the output current is less than 1% when the inductances of the primary windings vary by 10%.

• Journal of Power Electronics
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• v.13 no.1
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• pp.20-30
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• 2013

This paper presents a soft switching DC/DC converter for high voltage application. The interleaved pulse-width modulation (PWM) scheme is used to reduce the ripple current at the output capacitor and the size of output inductors. Two converter cells are connected in series at the high voltage side to reduce the voltage stresses of the active switches. Thus, the voltage stress of each switch is clamped at one half of the input voltage. On the other hand, the output sides of two converter cells are connected in parallel to achieve the load current sharing and reduce the current stress of output inductors. In each converter cell, a half-bridge converter with the asymmetrical PWM scheme is adopted to control power switches and to regulate the output voltage at a desired voltage level. Based on the resonant behavior by the output capacitance of power switches and the transformer leakage inductance, active switches can be turned on at zero voltage switching (ZVS) during the transition interval. Thus, the switching losses of power MOSFETs are reduced. The current doubler rectifier is used at the secondary side to partially cancel ripple current. Therefore, the root-mean-square (rms) current at output capacitor is reduced. The proposed converter can be applied for high input voltage applications such as a three-phase 380V utility system. Finally, experiments based on a laboratory prototype with 960W (24V/40A) rated power are provided to demonstrate the performance of proposed converter.

• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.908-910
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• 1998

Modern AC electric car has PWM(Pulse Width Modulation) -controlled converters, which give rise to higher harmonics. The current harmonics injected from AC electric car is propagated through power feeding circuit. As the feeding circuit is a distributed constant circuit composed of RLC, the capacitance of the feeding circuit and the inductance on the side of power system cause a parallel resonance and a magnification of current harmonics at a specific frequency. The magnified current harmonics usually brings about various problems. That is, the current harmonics makes interference in the adjacent lines of communications and the railway signalling system. Furthermore, in case it flows on the side of power system, not only overheating and vibration at the power capacitors but also wrong operation at the protective devices can occur. Therefore, the exact assessment of the harmonic current flow must be undertaken at design and planning stage for the electric traction systems. From these point of view, this study presents an approach to model and to analyse traction power feeding system focused on the amplification of harmonic current. The proposed algorithm is applied to a standard AT(Auto-transformer)-fed test system in which electric car with PWM-controlled converters is running.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.12
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• pp.691-700
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• 1999

This paper proposes a novel switching strategy of 1Mvar STATCON using cascade multilevel H-bridge inverter(HBI) for FACTS application. To control the reactive power instantaneously, the d-q dynamic system model is described and analyzed. A single pulse pattern based on the SHEM(Selective Harmonic Elimination Method) technique is determined from the look-up table to reduce the line current harmonics and a rotating fundamental frequency switching scheme is presented to adjust the DC voltage of each inverter capacitor at the same value. So the voltage unbalance problem between separately DC bus voltage is improved by using the proposed switching scheme. As a result, the presented inverter configuration not only reduces the system complexity by eliminating the isolation at the AC input side transformer but also improves the dynamic response to the step change of reactive power.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.8
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• pp.39-47
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• 2011

The motion of a conductive spherical particle under uniform electric field is investigated in order to find a suitable method for removing the conducting solid impurities contained in liquid plastic. When the positive dc voltage applied to the upper electrode, the vertical up-and-down motion of a charged particle by electrostatic force is observed by a charge-coupled device (CCD) camera or a high-speed video camera. The experimental data of the static threshold voltage by which the particle starts to move toward the counter electrode in air or silicone oil are in good agreement with theoretical value. When the applied voltage is larger than the static threshold voltage, the particle motion pattern in silicone oil consists of four stages: upward motion, stopping at the upper electrode, downward motion and stopping at the lower electrode. The stopping motion on the electrode is thought to be caused by the liquid flow accompanied by the particle motion. The particle charge calculated by integrating the pulse current, which is generated by the charge exchange between the electrode and the particle, is approximately 0.1~0.25 times of the theoretical value. This study is expected to help understand the electric properties of microparticles in oil circuit breaker (OCB) and oil transformer and improve their performance and longevity.

• Journal of Power Electronics
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• v.5 no.3
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• pp.224-232
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• 2005

A new three phase three-level Pulse Width Modulation (PWM) Switched Voltage Source (SVS) inverter with zero neutral point potential is proposed. It consists of three single-phase inverter modules. Each module is composed of a switched voltage source and inverter switches. The major advantage is that the peak value of the phase output voltage is twice as high as that of a conventional neutral-point-clamped (NPC) PWM inverter. Thus, the proposed inverter is suitable for applications with low voltage sources such as batteries, fuel cells, or solar cells. Furthermore, three-level waveforms of the proposed inverter can be achieved without the switch voltage imbalance problem. Since the average neutral point potential of the proposed inverter is zero, a common ground between the input stage and the output stage is possible. Therefore, it can be applied to a transformer-less Power Conditioning System (PCS). The proposed inverter is verified by a PSpice simulation and experimental results based on a laboratory prototype.

• Journal of Power Electronics
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• v.14 no.3
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• pp.478-487
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• 2014

This study presents a new interleaved three-level zero-voltage switching (ZVS) converter for high-voltage and high-current applications. Two circuit cells are operated with interleaved pulse-width modulation in the proposed converter to reduce the current ripple at the input and output sides, as well as to decrease the current rating of output inductors for high-load-current applications. Each circuit cell includes one half-bridge converter and one three-level converter at the primary side. At the secondary side, the transformer windings of two converters are connected in series to reduce the size of the output inductor or switching current in the output capacitor. Based on the three-level circuit topology, the voltage stress of power switches is clamped at $V_{in}/2$. Thus, MOSFETs with 500 V voltage rating can be used at 800 V input voltage converters. The output capacitance of the power switch and the leakage inductance (or external inductance) are resonant at the transition interval. Therefore, power switches can be turned on under ZVS. Finally, experiments verify the effectiveness of the proposed converter.

• Journal of Power Electronics
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• v.6 no.2
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• pp.131-138
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• 2006

An active clamp ZVS PWM forward converter using a secondary synchronous switch control is proposed in this paper. The proposed converter is suitable for low-voltage and high-current applications. The structure of the proposed converter is the same as a conventional active clamp forward converter. However, since it controls the secondary synchronous switch to build up the primary current during a very short period of time, the ZVS operation is easily achieved without any additional conduction losses of magnetizing current in the transformer and clamp circuit. Furthermore, there are no additional circuits required for the ZVS operation of power switches. Therefore, the proposed converter can achieve high efficiency with low EMI noise, resulting from soft switching without any additional conduction losses, and shows high power dens~ty, a result of high efficiency, and requires no additional components. The operational principle and design example are presented. Experimental results demonstrate that the proposed converter can achieve an excellent ZVS performance throughout all load conditions and demonstrates significant improvement in efficiency for the 100W (5V, 20A) prototype converter.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.1
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• pp.55-60
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• 2017

Capacitor Charging Power Supply(CCPS) is one of the most important components of a pulsed power system. The CCPS is widely used in source of lasers, accelerators and plasma generators. This paper presents design of a dead time control circuit and operation characteristics for stable high repetition rate of high voltage CCPS. The CCPS consists of battery, high voltage transformer and controller with a dead time control circuit. A dead time control circuit was simulated by PSpice. The performance test of the CCPS was carried out with a 7[nF] load capacitor at output voltage of 50[kV] and a pulse repetition frequency of 100[Hz]. As a result, we can verify that charging and discharging waveform is stable at 100[Hz]. The experiment results indicate that 3[ms] dead time made it possible for stable high repetition rate of 100[Hz]. This paper paves the way for designing an advanced CCPS which is more applicable outside experiments.