• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.5
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• pp.385-393
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• 2020

This study introduces an analysis and control method for the variation of neutral point current in a grid-tied three-level neutral point clamped (NPC) converter under various grid imbalance operating conditions. Various fault cases with unbalanced amplitude and phase are systematically categorized and described using a unified metric called the imbalance factor. The fundamental component of neutral point current is generated under grid imbalance cases. The pattern and behavior of this fundamental component of neutral point current highly depend on the imbalance factor regardless of the particular type of grid fault cases. The control scheme for regulating the negative sequential component of AC input current effectively reduces the size of the fundamental component of neutral point current under a wide range of grid imbalance cases. The control scheme will enable a grid-tied three-level NPC converter to operate reliably and stably under various types of grid faults.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.12
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• pp.622-628
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• 2005

This paper is given a full detail of mathematical analyses of input current and output voltage for a novel active type power factor correction (PFC) converter. These are compared with harmonics components of input current for a conventional PFC converter. The proposed PFC converter is constructed in using a new loss-less snubber circuit to achieve a soft switching of control device. Also the proposed converter for discontinuous conduction mode (DCM) eliminates the complicated circuit control requirement and reduces the size of components. The input current waveform in the proposed converter is got to be a sinusoidal form of discontinuous pulse in proportion to magnitude of ac input voltage under the constant duty cycle switching. Therefore, input power factor is nearly unity and the control method is simple. Particularly, the stored energy of loss-less snubber capacitor is recovered with input side and increases input current from resonant operation. The result is that input power factor of the proposed converter is higher than that of conventional PFC converter. Some simulative results on computer and experimental results are included to confirm the validity of the analytical results.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.6
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• pp.496-503
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• 2017

This study proposes a high-performance current control algorithm for a diode-bridge-type single-phase boost power factor correction (PFC) converter. The conventional asynchronous single-phase current controllers that directly control AC-type current tend to be accompanied by steady-state errors due to their poor dynamic characteristics for the transient-state, which can be attributed to bandwidth limitations and phase delays. In the proposed algorithm, an ideal current control with minimal phase delays and steady-state errors can be achieved by using a virtual DQ synchronous reference frame and by controlling the synchronous reference frame excluding the frequency component in the single-phase system. The performance of the conventional asynchronous single-phase current controller is compared with that of the proposed algorithm through simulation and experiments, and the results have confirmed the superiority of the latter.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.2
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• pp.95-101
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• 2017

A simple and practical voltage balance method for a solid-state transformer (SST) is proposed to reduce the voltage difference of cascaded H-bridge converters. The tolerance device components in SST cause the imbalance problem of DC-link voltage in the H-bridge converter. The Max/Min algorithms of voltage balance controller are merged in the controller of an AC/DC rectifier to reduce the voltage difference. The DC-link voltage through each H-bridge converter can be balanced with the proposed control methods. The design and performance of the proposed SST are verified by experimental results using a 30 kW prototype.

• Proceedings of the KIEE Conference
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• 2003.11c
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• pp.987-990
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• 2003

산업현장에서의 인터넷환경 및 원격 제어를 위한 시스템 개발에서 신뢰성이 있고 경제적이며 지능적인 Power Supply가 요구되고 있다. 최근 통신시스템의 Power Supply는 수 kA이상의 출력전류를 가지고 있으며 최소 10개 이상의 모듈로 이루어져 있다. High-End 서버 시스템과 같이 수백 개의 마이크로프로세서를 내장한 시스템은 수십 kW의 전력을 소모한다. 이들이 사용하는 Power Supply는 별도의 시스템 제어기와의 통신으로 시스템에서 발생하는 발열, 소모전력, Total Harmonic Distortion (THD)에 대한 정보를 바탕으로 시스템이 갖는 각각의 Module에 대해 효과적이고 신뢰성 있는 전력공급을 하여야 만다. Distributed Power System (DPS)에서 가장 중요만 역할을 담당하는 Power Factor Correction (PFC) AC-DC Converter의 디지털 제어는 시스템 제어기와의 통신능력을 충분히 고려하면서 DPS를 위한 적합한 솔루션을 제공할 것이다. 본 논문에서는 Digital Signal Processor (DSP)를 사용하여 PFC 제어에 필요한 전파정류전압, 입력전류, 출력전압을 계측하여 역률개선과 THD의 저감을 위한 전류의 추종을 제어하면서 이들 제어기에서의 파라미터를 PC를 통해 모니터하여 최근의 추세를 만족시킬 수 있는 시스템을 구현할 수 있을 것으로 사료된다.

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.190-191
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• 2016

국제 핵융합실험로인 ITER 장치의 초전도자석 전원장치용 CCU/L(Correction Coil Upper/Lower), CCS(Correction Coil Side) 그리고 VS1($1^{st}$ Vertical Stabilization) 형식 등 각 변압기 초도품의 제작을 완료하고 공장시험(FAT, Factory Acceptance Test)을 실시하였다. 이 변압기들은 각 형식별로 2대에서 6대를 제작하지만 각 형식별 초도품 1대에 대해서는 Type Test를 실시하고 나머지 후속물량에 대해서는 Routine Test로 공장시험을 실시하도록 계획되어 있다. 따라서 이 초도품 변압기들에 대해서는 Type Test로 공장시험으로 실시하였고, 그 대표적인 시험항목으로는 단락시험, %임피던스 시험, 뇌임펄스 시험, 정격전류 온도상승시험, 상용주파수 내전압시험 등이 있다. 이들 중 CCU/L, CCS 각 형식의 초도품에 대해서는 2015년도 공장시험을 실시하여 요건에 부합됨을 확인하였고, 본 논문에서는 VS1 컨버터 변압기 초도품에 대하여 Type Test로 실시한 공장시험 내용과 그 결과를 보여준다.

• Proceedings of the KIPE Conference
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• 2018.11a
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• pp.62-64
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• 2018

In two-stage single-phase inverters, inherent double line frequency component is present at both input and output of the front-end converter. Generally large electrolytic capacitors are required to eliminate the ripple. It is well known that the low frequency ripple shortens the lifespan of the capacitor hence the system reliability. However, the ripple can hardly be eliminated without the hardware combined with an energy storage device or a certain control algorithm. In this paper, a novel power-decoupling control method is proposed to eliminate the double line frequency ripple at the front-end converter of the DC/AC power conversion system. The proposed control algorithm is composed of two loop, ripple rejection loop and average voltage control loop and no extra hardware is required. In addition, it does not require any information from the phase-locked-loop (PLL) of the inverter and hence it is independent of the inverter control. In order to prove the validity and feasibility of the proposed algorithm a 5kW Dual Active Bridge DC/DC converter and a single-phase inverter are implemented, and experimental results are presented.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.1
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• pp.135-140
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• 2022

In addition to the stack that directly generates electricity by the reaction of hydrogen and oxygen, the fuel cell power generation system has a reformer that generates hydrogen from various fuels such as methanol and natural gas. It also consists of a power converter that converts the DC voltage generated in the stack into a stable AC voltage. The fuel cell output of such a system is direct current, and in order to be used at home, an inverter device that converts it into alternating current through a power converter is required. In addition, a DC-DC step-up converter is used to boost the fuel cell voltage to about 30~70V, which is the inverter operating voltage, to about 380V. The DC-DC step-up converter is a DC voltage variable device that exists between the fuel cell output and the inverter. Accordingly, since a constant output voltage of the converter is generated in response to a change in the output voltage of the fuel cell, the inverter can receive constant power regardless of the voltage change of the fuel cell. Therefore, in this paper, we discuss the detailed hardware design of the full-bridge converter, which is the main power source of the inverter that receives the fuel cell output voltage (30~70V) as an input and is applied to the grid among the members of the fuel cell power generation system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.491-499
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• 2019

Recently, there has been increasing demand for power quality in power supply devices. The IEC 61000-3-2 standard requires that the AC / DC power supply for lighting meet the specifications for the power factor (PF) and total waveform distortion (THD). In addition, advanced countries in Europe are regulating the ripple rate as 15 ~ 30% for the flicker phenomenon caused by the change in the amount of foot energy due to the change in current of the output terminal. Therefore, domestic standards and regulations are being updated. This study adopted the Flyback converter to satisfy the PFC standard, and has the circuit first and second insulation function. To reduce the low frequency ripple of the LED current, Flyback, Coupled Inductor, LC parallel resonance filter, LLC resonance filter, and Cuk were simulated by PSIM to mimic each LED driving circuit. A coupled LC resonant circuit with a coupled inductor on the primary side and LC resonance on the secondary side was also proposed for output side ripple reduction.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.4
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• pp.21-28
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• 2006

In this paper, the proposed full-bridge high frequency isolated zoo voltage and zero current switching phase shifted pulse width modulation(ZVZCS PS-PWM)DC-DC converter among fuel cell generation system consist of 1.2[kW] fuel cell of Nexa Power Module, full-bridge DC-DC converter to boost the fuel cell low voltage($28{\sim}43[%]$) to 380[VDC] and a single phase full-bridge inverter is implemented to produce AC output(220[VAC], 60[Hz]). A tapped inductor filter with freewheeling diode is newly implemented in the output filter of the proposed full-bridge high frequency isolated ZVZCS PS-PWM DC-DC converter to suppress circulating current under the wide output voltage regulation range, thus to eliminate the switching and transformer turn-on/off over-short voltage or transient phenomena. Besides the efficiency of $93{\sim}97[%]$ is obtained over the wide output voltage regulation ranges and load variations.