• 전기학회논문지
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• 제63권6호
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• pp.828-833
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• 2014

Grid connected transformerless solar power generation system is frequently used with the benefits of cost and efficiency. However, significant DC leakage current can flow from the DC line into the ground with dielectric breakdown in the transformerless solar power generation system. The leakage current occurred in the DC line causes accidents such as fire and electric shock on human. To resolve this problem, high sensitivity DC leakage current sensor is needed. But recently the studies on safety of DC line are not performed. In this paper, a high sensitivity DC leakage current sensor that can detect DC leakage current in solar power generation system, is proposed. Based on the studies, DC leakage current sensor is fabricated and characteristic tests are carried out. Finally, the accuracy of sensor performance is verified by leakage current experiments in solar power generation system.

• Journal of Power Electronics
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• 제16권5호
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• pp.1743-1751
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• 2016

The increasing demand for high voltage DC grids resulting from the continuous installation of offshore wind farms in the North Sea has led to the concept of multi-terminal direct current (MTDC) grids, which face some challenges. Power (current) flow control is a challenge that must be addressed to realize a reliable operation of MTDC grids. This paper presents a reduced switch count topology of a current flow controller (CFC) for power flow and current limiting applications in MTDC grids. A simple control system based on hysteresis band current control is proposed for the CFC. The theory of operation and control of the CFC are demonstrated. The key features of the proposed controller, including cable current balancing, cable current limiting, and current nulling, are illustrated. An MTDC grid is simulated using MATLAB/SIMULINK software to evaluate the steady state and dynamic performance of the proposed CFC topology. Furthermore, a low power prototype is built for a CFC to experimentally validate its performance using rapid control prototyping. Simulation and experimental studies indicate the fast dynamic response and precise results of the proposed topology. Furthermore, the proposed controller offers a real solution for power flow challenges in MTDC grids.

• 전력전자학회논문지
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• 제17권6호
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• pp.523-531
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• 2012

This paper proposes a high efficiency power conversion system for battery-ultracapacitor hybrid energy storages. The proposed system has only one bidirectional dc-dc converter for hybrid power source with batteries and ultracapacitors. The hybrid power source has bidirectional switching circuits for selecting one energy storage device. Bidirectional power flow between the energy storage device and high voltage capacitor can be controlled by one bidirectional converter. An asymmetrical switching method is applied to the bidirectional converter for high power efficiency. Switching power losses are reduced by zero-voltage switching of power switches. System operation and design considerations are presented. The experimental results are provided to verify the performance of the proposed system.

• 전기학회논문지
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• 제56권8호
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• pp.1373-1381
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• 2007

This paper presents a graphical windows-based software for the education and training of transmission network charge. The motivation for the development of the simulator is to provide students with a simple and useable tool for gaining an intuitive feel for transmission network charge. The developed simulator consists of the main module (MMI, GUI), the power flow module (PF), the power flow tracing module (PFT), and usage cost DB module (UCD). Each module has a separate graphical and interactive interfacing window. The developed simulator provides with two power system analysis methods (i.e., DC-PF and Modified DC-PF) and supports the PSS/E input data format to load input data of power system. Also, power flow tracing can be calculate using four methods such as "Felix Wu", "Modified Felix Wu", "DCLF ICRP", and "Reverse MW mile". Results of calculation for transmission usage cost are displayed and compared on the window through the table and/or chart. Therefore, the developed simulator can be utilize as a useful tool for effective education and training of transmission network charge.

• 한국재료학회지
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• 제9권5호
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• pp.533-537
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• 1999

ATO(Sb doped $SnO_2$) thin films whose thicknesses were 600, 1100 and $2100\AA$ were prepared by DC magnetron sputtering method. They showed the lowest resistivity at DC sputtering power 0.24kW and had lower resistivity with increasing thickness. The power dependence of resistivity among ATO thin films was also different with thickness. The increase of carrier concentration in ATO thin films was responsible for the decrease of resistivity with thickness increase. ATO thin films which were prepared at 30sccm oxygen flow rate showed a great change of sheet resistance under 1M HCl solution. The investigation of SAM(Scanning Auger Microprobe) revealed that oxygen atomic percentage on the surface of ATO thin films was changed. The decrease of sheet resistance also occurred when ATO thin films, prepared at 30sccm oxygen flow rate, were exposed to air for a long period of time. For this reason, it was considered that the desorption of oxygen on ATO surface was accelerated by HCl.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2015년도 전력전자학술대회 논문집
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• pp.301-302
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• 2015

본 논문은 레독스 흐름 전지(Redox Flow Battery : RFB)용 양극성을 갖는 DC-DC 컨버터의 기본 동작 원리 및 최적 스위칭 기법에 관한 것이다. 양극성을 갖는 DC-DC 컨버터는 매우 낮은 배터리 전압에서도 완전 방전을 위해 고승압이 필요하고, 완전 방전 후 극성 반전이 되어 매우 낮은 전압에서도 충전이 가능하여야 한다. 본 논문에서는 이러한 동작이 요구되는 RFB용 DC-DC 컨버터의 스위칭 손실을 최소화하기 위한 스위칭 방법을 제안한다. 최종 발표 시 실험 결과를 제시하고자 한다.

• Journal of Electrical Engineering and Technology
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• 제12권1호
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• pp.478-485
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• 2017

Urban DC railways have played an important role in urban transportation, and railway operation and energy management have been emphasized to be important to achieve maximum efficiency from existing infrastructure. Fast, accurate DC railway power flow analysis is required to operate a DC railway efficiently, and this paper proposes a novel methodology to analyze the DC railway power network by implementing the participation factor (PF). The PF concept consists of a correlation between the vehicle and the substation, as explained using zones based on the position of the vehicles running on the route. Then, the DC railway powerflow is calculated using the PF concept. Finally, the usability of the proposed method was validated via case studies with actual railway operation data, and we discuss some of the advantages of the suggested methodology.

• Journal of Power Electronics
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• 제17권6호
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• pp.1625-1636
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• 2017

A power electronic transformer (PET) based on the cascaded H-bridge (CHB) and the isolated bidirectional DC/DC converter (IBDC) is capable of accommodating a large scale battery energy storage system (BESS) in the medium-voltage grid, and is referred to as a power electronic transformer based battery energy storage system (PET-BESS). This paper investigates the PET-BESS and proposes a coordinative control strategy for it. In the proposed method, the CHB controls the power flow and the battery state-of-charge (SOC) balancing, while the IBDC maintains the dc-link voltages with feedforward implementation of the power reference and the switch status of the CHB. State-feedback and linear quadratic Riccati (LQR) methods have been adopted in the CHB to control the grid current, active power and reactive power. A hybrid PWM modulating method is utilized to achieve SOC balancing, where battery SOC sorting is involved. The feedforward path of the power reference and the CHB switch status substantially reduces the dc-link voltage fluctuations under dynamic power variations. The effectiveness of the proposed control has been verified both by simulation and experimental results. The performance of the PET-BESS under bidirectional power flow has been improved, and the battery SOC values have been adjusted to converge.

• Journal of Power Electronics
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• 제16권2호
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• pp.399-413
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• 2016

This paper presents a topology for a modular power electronic transformer (PET) and a control scheme. The proposed PET consists of a cascaded H-Bridge rectifier on the primary side, a high-frequency DC/DC conversion cell in the center, and a cascaded H-Bridge inverter on the secondary side. It is practical to use PETs in power systems to reduce the cost, weight and size. A detailed analysis of the structure is carried out by using equivalent circuit. An algorithm to control the voltages of each capacitor and to maintain the power flow in the PET is established. The merits are analyzed and verified in theory, including the bi-directional power flow, variable voltage/frequency and high power factor on the primary side. The experimental results validated the propose structure and algorithm.

• Journal of Power Electronics
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• 제12권4호
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• pp.664-676
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• 2012

A phase shift algorithm based on the closed-loop control of dc-link voltage implemented on a series active voltage quality regulator (AVQR) is proposed in this paper. To avoid pumping-up the dc-link voltage, a general phase shift compensation strategy is applied. The relationships among the operation variables are discussed in detail, which is very important for guiding the design of both the main circuit and the control system. Then on the basis of an investigation of the dc-link voltage pumping-up from viewpoint of the active power flow, a novel phase shift control method based on the closed-loop of the dc-link voltage is proposed. This method can adjust the phase of the output voltage gradually and automatically according to the dc-link voltage variation without introducing a phase jump. The effectiveness of the proposed strategy is verified through simulations of a single-phase 5kVA prototype and laboratory experiments on both a single-phase 5kVA and a three-phase 15kVA prototype.