• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.05a
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• pp.467-472
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• 2005

In this paper, design and control of the novel SEPIC-Flyback converter(SF converter) is developed as a possible converter for fuel cell system. This output characteristic of SF converter is similar to Buck-Boost converter in that it can step-up or step-down the voltage. With the small signal equivalent circuit modeling of SF converter, control-to-output transfer function is obtained. SF converter couples up the inductive type converter to capacitive type converter with one transformer, which has less ripple current than its respective one does. To verify the validity of the proposed converter, 500W, 100kHz converter is designed and tested. ZVS switching and active clamping are also tested in practice.

• Journal of Electrical Engineering and Technology
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• v.11 no.4
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• pp.860-868
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• 2016

A bidirectional DC-DC converter (BDC) is an indispensable electrical unit for the electric vehicles (EVs). High efficiency, high power density, isolation, light weight and reliability are all essential requirements for BDC. In this paper, a 3 kW BDC for the battery charger of EVs is proposed. The proposed converter consists of a half-bridge structure on the primary side and an isolation transformer and a synchronous rectifier structure on the secondary side. With this topology, minimum number of switching devices are required for bidirectional power flow between the two dc buses of EVs. The easy implementation of the synchronous rectification gives advantages in terms of efficiency, cost and flexibility. The proposed BDC achieves high efficiency when operating in both modes (step-up and step-down). A 3 kW prototype is implemented to verify theoretical analysis and the performance of the proposed converter.

• Journal of Power Electronics
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• v.14 no.6
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• pp.1166-1177
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• 2014

A new type of topology with medium-frequency-transformer (MFT) isolation for medium voltage wind power generation systems is proposed in this paper. This type of converter is a high density power conversion system, with high performance features suitable for next generation wind power systems in either on-shore or off-shore applications. The proposed topology employs single-phase cascaded multi-level AC-AC converters on the grid side and three phase matrix converters on the generator side, which are interfaced by medium frequency transformers. This avoids DC-Link electrolytic capacitors and/or resonant L-C components in the power flow path thereby improving the power density and system reliability. Several configurations are given to fit different applications. The modulation and control strategy has been detailed. As two important part of the whole system, a novel single phase AC-AC converter topology with its reliable six-step switching technique and a novel symmetrical 11-segment modulation strategy for two stage matrix converter (TSMC) is proposed at the special situation of medium frequency chopping. The validity of the proposed concept has been verified by simulation results and experiment waveforms from a scaled down laboratory prototype.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.1
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• pp.108-114
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• 2008

Recently, there have been several instances that the nuclear power plants were shut down due to the mechanical faults in the main transformer of the plants. These mechanical faults are primarily originated from the electromagnetically induced mechanical vibrations. Magnetostriction is identified to be the main cause of the mechanical vibration after analyzing the vibration data of the main transformers in nuclear power plants. In this study, we derived a mathematical model of the magnetostriction based on the Jiles-Atherton hysteresis model. The validity of the model is checked by matching the simulations with the experimental observations. The magnetostriction model used in this study will be the first step toward developing a design tool far the transformers that have minimal mechanical vibrations and are robust to mechanical faults.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1358-1360
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• 2005

본 논문에서는 비접촉 전원장치와 같이 누설인덕턴스가 큰 공진형 컨버터에서 스위치단과 공진 탱크 사이에 강압형 매칭 트랜스포머를 삽입하여 스위치의 공진 전류를 줄이는 방법을 제안하였다. 누설인덕턴스가 큰 공진형 컨버터에 강압형 매칭 트랜스포머를 추가함으로써, 일차측의 입력 임피던스를 증가시켜 동일 전압에 대하여 전류의 크기를 작게 하고, 또한 전압과 전류의 위상을 거의 일치시켜 무효 전력 성분을 감소시킬 수 있다. 본 논문에서는 비접촉 트랜스포머의 파라메타 측정을 통하여 비접촉 트랜스포머의 등가화 회로를 구현하였고, 일반 비접촉 트랜스포머와 강압형 매칭 트랜스포머를 추가한 트랜스포머의 전압 이득과 입력 임피던스 특성을 해석하였다. 강압형 매칭 트랜스포머의 특성을 검증하기 위하여 30kW급 비접촉 전원장치를 제작하여 실험하였다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.2
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• pp.75-81
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• 2015

At the end of the 19th century, Edison's DC power system and Tesla's AC power system was debated in power market. Finally, AC system became the primary system of the power market because both step-up and step-down of voltage by using transformer and long-distance power transmission are easily possible. However, nowadays the power market takes some action for introducing DC system. Both domestic and foreign researchers are conducting the study on the DC system as well. Some researchers have conducted the studies on power quality and economic evaluation of the DC distribution system but DC distribution system is still controversial in terms of the effectiveness and reliability. In this paper, we calculate the reliability indices of the Low Voltage Direct Current(LVDC) distribution system considering arrangement of power electronics, layout of the distribution system, and distance between load points.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2007.11a
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• pp.195-197
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• 2007

This paper presents experimental results on the safety of persons due to a ground fault in 22.9 kV-Y distribution system In order to evaluate the touch voltages due to internal ground faults in a step down transformer based on the newly prescribed KS C IEC 60364 standard series, the verification tests in a 22.9 kV multi-grounded neutral system were carried out From the experimental results, it was found that there will be significant potential rise jeopardizing LV equipment insulation in case of separate grounding between HV and LV system and the effective measures against hazardous touch voltages due to a IN side ground fault in the common grounding system between HV and LV system are proposed. As a consequence, it was found that the equipotential bonding is an important prerequisite for the effectiveness of the protective measures for the safety of persons in the common ground system between 22.9 kV-Y and low-voltage grounding system.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.932_933
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• 2009

A technology based on thyristors will be used to manufacture the super-conducting coil AC/DC converters because of the low ratio of cost over installed power compared to a design based on GTO or similar technology. But phase-controlled converter suffers from fundamental disadvantage. They inject current harmonics into the input ac mains due to their nonlinear characteristics, thereby distort the supply voltage waveform, and demand reactive power from the associated ac power system at retarded angles. To overcome this disadvantage, in the case of two series converters at the DC side, connected to the same step-down transformer, apply for the sequence control. It is the most simple and efficient way to reduce the reactive power consumption at low cost. Analytical sequence control algorithm is suggested, the validity of the proposed scheme has been verified by experimental results with the small-scaled International Thermonuclear Experimental Reactor (ITER) Power Supply to minimize reactive power consumption.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.4
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• pp.748-757
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• 2007

This paper is intended to solve the technical problem that fails in large-capacity induction motor starting due to serious voltage drop during starting period. One induction motor that is established already can reach in steady-state using reactor starting method but the voltage magnitude of PCC (point of common coupling) has dropped down a little. When the same capacity induction motor is installed additionally in the PCC, where the existing induction motor is operating, voltage drop becomes more serious by starting of additional induction motor. As a result, the additional induction motor fails in starting. Therefore, voltage compensation method is proposed so that all of two induction motors can be started completely. First, modeling technique is described in order to implement starting characteristics of large induction motor. And then, this paper proposes strategic starting scheme by proper voltage compensation that use no-load transformer tap control (NLTC) and step voltage regulator (SVR) for starting of two large induction motors successfully and improving the feeding network voltage profile during the starting period. The induction motor discussed in this paper is the pumped induction motor of 2500kVA capacity that is operating by KOWACO (Korea Water Resources Corporation). Modeling and simulation is conducted using PSCAD/EMTDC software.

• Journal of Power Electronics
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• v.15 no.2
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• pp.555-566
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• 2015

A TRIAC dimming LED driver that can control the brightness of LED arrays for a wide range of source voltage variations is proposed in this paper. Unlike conventional PWM LED drivers, the proposed LED driver adopts a TRIAC switch, which inherently guarantees zero current switching and has been proven to be quite reliable over its long lifetime. Unlike previous TRIAC type LED drivers, the proposed LED driver is composed of an LC input filter and a variable switched capacitance, which is modulated by the TRIAC turn-on timing. Thus, the LED power regulation and dimming control, which are done by a volume resistor in the same way as the conventional TRIAC dimmers, can be simultaneously performed by the TRIAC control circuit. Because the proposed LED driver has high efficiency and a long lifetime with a high power factor (PF) and low total harmonic distortion (THD) characteristics, it is quite adequate for industrial lighting applications such as streets, factories, parking garages, and emergency stairs. A simple step-down capacitive power supply circuit composed of passive components only is also proposed, which is quite useful for providing DC power from an AC source without a bulky and heavy transformer. A prototype 60 W LED driver was implemented by the proposed design procedure and verified by simulation and experimental results, where the efficiency, PF, and THD are 92%, 0.94, and 6.3%, respectively. The LED power variation is well mitigated to below ${\pm}2%$ for 190 V < $V_s$ < 250 V by using the proposed simple control circuit.