• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.5
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• pp.343-349
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• 2020

This study proposes a new single inductor converter for DC grid systems. A conventional system is composed of two independent converters for controlling battery and load. This system is simple but it has two inductors that affect power density and efficiency. The proposed converter can reduce the number of inductors by integrating the two converters and relieve voltage stress on switches by using a battery switching cell. Accordingly, power density and efficiency can be improved using a single inductor and lower voltage-rated switches. A prototype of a 500 W converter is built, and each mode is experimented on to confirm the validity of the proposed converter.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.2
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• pp.97-103
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• 2015

This paper introduces two on-going projects for DC high temperature superconducting (HTS) cable systems in South Korea. This study proposes the application of DC HTS cable systems to enhance power transfer limits of a grid-connected offshore wind farm. In order to develop the superconducting DC transmission system model based on HTS power cables, the maximum transfer limits from offshore wind farm are estimated and the system marginal price (SMP) calculated through a Two-Step Power Transfer (TSPT) model based on PV analysis and DC-optimal power flow. The proposed TSPT model will be applied to 2022 KEPCO systems with offshore wind farms.

• Journal of Power Electronics
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• v.18 no.1
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• pp.171-184
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• 2018

Unbalanced and distorted grid voltages cause the grid side current of a current source PWM rectifier to be heavily distorted. They can also cause the DC-link current to fluctuate with a huge amplitude. In order to enhance the performance of a current-source PWM rectifier under unbalanced and harmonic grid voltage conditions, a mathematical model of a current-source PWM rectifier is established and a flexible multi-objective control strategy is proposed to control the DC-link current and grid-current. The fundamental positive/negative sequence, $5^{th}$ and $7^{th}$ order harmonic components of the grid voltage are first separated with the proposed control strategy. The grid current reference are optimized based on three objectives: 1) sinusoidal and symmetrical grid current, 2) sinusoidal grid current and elimination of the DC-current $2^{nd}$ order fluctuations, and 3) elimination of the DC-current $2^{nd}$ and $6^{th}$ order fluctuations. To avoid separation of the grid current components, a multi-frequency proportional-resonant controller is applied to control the fundamental positive/negative sequence, $5^{th}$ and $7^{th}$ order harmonic current. Finally, experimental results verify the effectiveness of proposed control strategy.

• Journal of Power Electronics
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• v.13 no.2
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• pp.313-321
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• 2013

This paper describes the operation analysis results of a communication-based DC micro-grid using a hardware simulator developed in the lab. The developed hardware simulator is composed of distributed generation devices such as wind power, photovoltaic power and fuel cells, and energy storage devices such as super-capacitors and batteries. Whole system monitoring and control was implemented using a personal computer. The power management scheme was implemented in a main controller based on a TMS320F28335 chip. The main controller is connected with the local controller in each of the distributed generator and energy storage devices through the communication link based on a CAN or an IEC61850. The operation analysis results using the developed hardware simulator confirm the ability of the DC micro-grid to supply the electric power to end users.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.5
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• pp.417-422
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• 2008

In this paper, a novel DC/DC low-voltage high-current converter circuit is proposed to improve the efficiency of power converter used in the grid-connected fuel-cell generator system. We proposed a novel high efficiency grid-connected power conditioning system for RPG fuel cell. On the result of that, the loss of system was decreased rapidly by driving stack within the condition of maximum efficiency. The peak currents of the current-type inductor and the transformer's coil are reduced by synchronizing switching frequency of Buck-type converter is increased twice as the Push-Pull converter's switching frequency. The novel structure of DC/DC converter is able to realize ZVS-ZCS in fuel-cell system is proposed. The proposed switching component of Push-Pull converter has the ZVS and ZCS function by using the circuit of new passive clamp.

• Journal of Power Electronics
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• v.18 no.5
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• pp.1357-1368
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• 2018

In this paper, a novel high gain bidirectional modular dc-dc converter (BMC) with unipolar and bipolar structures for dc network interconnections is proposed. When compared with traditional dc grid-connecting converters, the proposed converter can achieve a high voltage gain with a simple modular transformerless structure. A sub-modular structure for the BMC is proposed to eliminate the unbalanced current stress between the different power units (levels) in the BMC. This can realize current sharing and standardized production and assembling. In addition, phase-interval operation is introduced to the sub-modules to realize low voltage and current ripple in both sides of the converter. Furthermore, two types of bipolar topologies of the sub-modular BMC were proposed to extend its application in bipolar dc network connections. In addition, the control system was optimized for grid-connection applications by providing various control strategies. Finally, simulations of a 3-level unipolar sub-modular BMC and a 4-level bipolar sub-modular BMC were conducted, and a 1-kW experimental 3-level unipolar prototype was developed to verify the effectiveness of the proposed converter.

• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.91-93
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• 2020

In recently days using distributed power generation systems constructed with boost type dc-dc converters is being extremely popularized because of the rising need of environment friendly energy generation power systems. In this paper a new constructed An efficient Step-Up DC-DC Converter for DC Grid Applications s proposed to boost a low level DC voltage(36-80V) to high DC bus (380V) level. When comparing to other step-up converters, the proposed topology has a reduced number of switching devices, can make high quality power with lower input current ripple and has wider input DC voltage range. Finally, the performance of the proposed topology is presented by simulation results with 350W hardware prototype.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.5
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• pp.377-387
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• 2012

A single-phase grid-connected PV system is known as suitable for housing of less than 3 kW. The DC link voltage in a single-phase PV system has necessarily twice component of fundamental wave. It makes high THD in the grid current. According to the problem, power quality is lower. Many engineers have studied about this problem. The most simple method is to use low pass filter on DC link voltage control. However it is affected by DC link voltage control bandwidth. If cutoff frequency is reduced to increase the performance of low pass filter, it also lowers DC link voltage control bandwidth. Second method is using band stop filter, it works good on steady state but not good on transient state. This paper proposes the new method for removing ripple voltage to get an exact current reference. It improves the responses on steady state and transient state. The performance was verified through computer simulation using MATLAB and actual experiments.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.2
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• pp.150-157
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• 2021

Nowadays, a DC microgrid that can link various distributed power sources is gaining much attention. Accordingly, research on fault situations, such as line-to-line and line-to-ground faults of the DC microgrid, has been conducted to improve grid reliability. However, the blackout of an AC system and the oscillation of a DC bus voltage have not been reported or have not been sufficiently verified by previous research. In this study, a 20 kW DC microgrid testbed using a power HIL simulation technique is proposed. This testbed can simulate various fault conditions without any additional grid facilities and dangerous experiments. It includes the blackout of the DC microgrid caused by the AC utility grid's blackout, a drastic load increment, and the DC bus voltage oscillation caused by the LCL filter of the voltage source converter. The effectiveness of the proposed testbed is verified by using Opal-RT's OP5707 real-time simulator with a 3 kW prototype three-port dual-active-bridge converter.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.705-711
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• 2005

In DC traction substation with 12-pulse diode rectifiers, the DC line voltage tends to rise above noload voltage because it can't absorb the regenerative power caused by electric brakes of train. To solve this problem, an IGBT regenerative inverter should be installed and recycles the surplus regenerative power by delivering it. to the supply grid. In this paper, the DC traction substation equipped with a IGBT regenerative inverter is studied using computer simulation. Matlab/simulink is used to simulate the operation of regenerative inverter which injects the regenerative power into the supply grid and stabilizes the DC line voltage. It is confirmed that the high quality regenerative power is delivered to the supply grid thorough computer simulation.