• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.327-328
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• 2012

대용량 계통 연계형 태양광 인버터는 그 중요성이 부각되면서 현재는 수MW~수백MW에 이르는 발전소 개념으로 시장이 더욱 확대되고 있다. 이에 따라 본 논문에서는 대용량 태양광 발전소에 적합한 멀티 센트럴 구성 방식과 기존 토폴로지의 접근을 통한 시장의 최신 동향에 대해 기술하고자 한다.

• Proceedings of the KIPE Conference
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• 2018.11a
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• pp.173-174
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• 2018

This paper proposes the coupled inductor instead of four non-coupled inductors in each leg of the flying-capacitor modular multilevel converter (MMC) to reduce the dimension, weight and cost of the magnetic core. The simulation results have verified the effectiveness of the proposed coupled inductor.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10a
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• pp.43-48
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• 1992

The automation system oriented as one of the second year automation projects for the small and medium sized enterprises(SME) was developed for the improvement of the production rate and cut the required manpower in the field of the relay which is one of the small electric components used in various industrial fields. The objectives of this study are not only improving the international competition of the relay itself but also partially solving the technical and financial problems featured by common bottlenecks of the SME for efficient assembly automation. For the purpose of these objectives, several topics are studied as followings. - Analyzing the adjustment process and determining the specification of the automation system. - Determining the layout for the automation system to meet the determined specification. - Detail design of the automation system for relay adjustment and inspection. - Control system design - Automation system development and performance test.

• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.280-287
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• 2015

Three-level PWM rectifiers applied in medium voltage applications usually operate at low switching frequency to keep the dynamic losses under permitted level. However, low switching frequency brings a heavy cross-coupling between the current components $i_d$ and $i_q$ with a poor dynamic system performance and a harmonic distortion in the grid-connecting current. To overcome these problems, a mathematical model based on complex variables of the three-level voltage source PWM rectifier is firstly established, and the reasons of above issues resulted from low switching frequency have been analyzed using modern control theory. Then, a novel control strategy suitable for the current decoupling control based on the complex variables for $i_d$ and $i_q$ is designed here. The comparisons between this kind of control strategy and the normal PI method have been carried out. MATLAB and experimental results are given in detail.

• Journal of Power Electronics
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• v.16 no.3
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• pp.861-871
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• 2016

With high penetration of renewable energies, power electronic transformers (PETs) will be one of the most important infrastructures in the future power delivery and management system. In this study, an isolated bidirectional modular multilevel DC/DC converter is proposed for PET applications. A modular multilevel structure is adopted as switching valves to sustain medium voltages to achieve modular design and high reliability. Only one high-frequency transformer is used in the proposed converter, which significantly simplifies the circuit and galvanic insulation design. A dual-phase-shift modulation strategy is proposed to regulate the output power and achieve a simple voltage balancing control. A down-scaled (2 kW/20 kHz) prototype is constructed to demonstrate the proposed converter and verify the control strategy. The experimental results comply with the theoretical analysis well, with the highest power efficiency reaching 97.6%.

• Progress in Superconductivity and Cryogenics
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• v.13 no.1
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• pp.27-30
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• 2011

A sub-cooled liquid nitrogen cooling system is known as a most promising method to develop large scale superconducting apparatuses such as superconducting fault current limiters and superconducting cables [1]. Gaseous helium (GHe), gaseous nitrogen ($GN_2$) and sulfur hexafluoride ($SF_6$) are commonly used for designing an high voltage applied superconducting device as an injection gaseous medium [2, 3]. In this paper, the analysis on the dielectric characteristics of GHe, $GN_2$ and $SF_6$ are conducted by designing and manufacturing sphere-to-plane electrode systems. The AC withstand voltage experiments on the various gaseous insulation media are carried out and the results are analyzed by using finite element method (FEM) considering field utilization factors (${\xi}$). It is found that the electric field intensity at sparkover ($E_{MAX}$) of insulation media exponentially decreases according to ${\xi}$ increases. Also, the empirical expressions of the functional relations between $E_{MAX}$ and ${\xi}$ of insulation media are deduced by dielectric experiments and computational analyses. It is expected that the electrical insulation design of applied superconducting devices could be performed by using the deduced empirical formulae without dielectric experiments.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.1
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• pp.41-50
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• 2014

The rising penetration of renewable energy resulted in the development of grid-connected large-scale power plants. Therefore, grid stabilization, which depends on the system-type or grid of each country, plays an important role and has been strengthened by different grid codes. With this background, VDE-AR-N 4105 for photovoltaic (PV) systems connected to the low-voltage grid and the German Association of Energy and Water Industries (BDEW) introduced the medium-voltage grid code for connecting power plants to the grid and they are the most stringent certifications. In this paper, an optimal control strategy scheme for three-phase grid-connected PV system is enhanced with VDE-AR-N 4105 and BDEW grid code, where both active/reactive powers are controlled. Simulation and experimental results of 100kW PV inverter are shown to verify the effectiveness of the proposed implemental control strategy.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.5
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• pp.410-420
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• 2015

This paper provides a comparison of power converter loss and thermal description for voltage source and current source type 5 MW-class medium-voltage topologies of wind turbines. Neutral-point clamped three-level converter is adopted for a voltage source type topology, whereas a two-level converter is employed for current source type topology, considering the popularity in the industry. To match the required voltage level of 4160 V with the same switching device of IGCT as in the voltage source converter, two active switches are connected in series for the case of current source converter. Transient thermal modeling of a four-layer Foster network for heat transfer is done to better estimate the transient junction and case temperature of power semiconductors during various operating conditions in wind turbines. The loss analysis is confirmed through PLECS simulations. Comparison result shows that the VSC-based wind turbine system has higher efficiency than the CSC under the rated operating conditions.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.3
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• pp.257-267
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• 1999

This paper deals with the water cooling system of HVDC(High Voltage Direct CUlTentJ. It is generally accepted that water is a veη effective medium to remove heat losses from any type of equipment. Because of this benefits the water cooling method is used in HVDC. The water cooling system consists of a heat exchanger, circulation pump and a connecting pipe. According to thYI1stor temperature level. thyristor junction temperature is controlled by controlling the f fan of exchanger. In this paper. the water cooling system of HVDC system is analyzed and estimated.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.3
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• pp.80-86
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• 2003

A study on the insulation aging assessment and maintenance for submarine medium voltage power cable systems has been performed The purpose of this work is the economic discrimination and maintenance of bad cables which is likely to cause cable system failure. 1 have found that aging status of submarine cable systems are very poor and in progress. Therefore, we have the replacement of cable terminations and repeat the diagnostic measurement Insulation status were improved with the replacement of cable terminations. I have confirmed, with the electrical md structural analysis of terminations, that the poor aging status of cables are mainly caused not by the cable insulations but by the aging of cable terminations. From the above results, I have also confirmed that the domestic diagnostic system is successful and convenient for the discrimination and maintenance of the damaged cables economically.