• Proceedings of the KIEE Conference
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• 1999.07c
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• pp.1327-1330
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• 1999

In this paper control hierarchy of Haenam-Cheju HVDC link are analyzed and their functional specifications are summarized related to their level. The control functions for the submarine DC transmission are implemented by software programs on 16-bit parallel processor-based machines which are composed of subunits hierarchically linked each other

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.1
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• pp.61-67
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• 2020

This study deals with the modulation index (MI) of a voltage source converter (VSC) HVDC system based on a modular multilevel converter (MMC). In the two-level converter, the purpose of the MI is to maximize the achievable AC voltage of the converter from a fixed DC voltage. Unlike that in a two-level converter, the MI in the MMC topology plays a role in making the converter a voltage source using a capacitor. The circulating current in the MMC distorts the AC voltage reference, and the distortion affects the MI. In addition, the AC network conditions, such as AC voltage variation and reactive power, affect the MI. Therefore, the MI should be optimized with consideration of internal and external factors. This study proposes a method to optimize the MI of an MMC HVDC system.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.225-230
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• 2001

In this paper, a method for optimal design of PID controller using the immune algorithm(IA) has been proposed to improve the stability of A.C.-D.C. power system. The process of this study is composed of formulation of basic controls on HVDC transmission system, mathematical model preparation for stability analysis, and supplementary signal control by an optimal PID controller using the IA. The dynamic property was verified through computer simulations regarding transient stability.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.702-703
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• 2011

Large offshore wind farms using high voltage direct current transmission system (HVDC) have been considered and exploited in many countries in the world. The maintenance of the stable operation of wind farm and interconnected system is an important issue, especially in the case of fault. To ensure the stable operation after fault clearance, the PCC voltage must be restored as soon as possible and meet the grid code requirement. This paper will evaluate the PCC voltage recovery ability of a large offshore wind farm as it is connected to a weak grid via a VSC-HVDC.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.71-72
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• 2014

This paper presents a method to find the fault location on the DC cables for the HVDC transmission systems which utilizes a hybrid topology of the diode rectifier and the voltage-source converter (VSC) in the wind farm (WF) side. First, the DC-cable fault occurring in this HVDC system is analyzed in detail. Then, the DC-cable fault location is detected from the two relative voltages located on the same section of the cable, which are estimated from a pair of DC-cable voltage and current measurements. The effectiveness of the method is verified by the simulation results.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.3
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• pp.191-197
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• 2012

This paper proposes a new synthetic test circuit (STC) to confirm the switching operation of thyristor valve in HVDC converter. The proposed STC uses a 6-pulse thyristor converter with 2-phase chopper as a high-current source to provide turn-on current to the test valve. The operation of proposed STC was verified through theoretical analysis and computer simulations. Based on computer simulations, a hardware scaled model was built and tested to confirm the feasibility of implementing a real-size test facility. The proposed system has an advantage of simple structure and operation over the existing system.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.3
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• pp.399-404
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• 2015

This paper presents the DC voltage control method in DC link of High Voltage Direct Current(HVDC) for an offshore wind farm in Low Voltage Ride Through(LVRT) situation. Wind generators in an offshore wind farm are connected to onshore network via HVDC transmission. Due to LVRT control of grid side inverter in HVDC, power imbalancing in DC link is generated and this consequentially causes rising of DC voltage. A de-loading scheme is one of the method to protect the wind power system DC link capacitors from over voltage. But the flaw of this method is slow control response time and that it needs long recovery time to pre-fault condition after fault clear. Thus, this paper proposes improved de-loading method and we analyze control performance for DC voltage in LVRT control of HVDC for an offshore wind farm.

• Journal of Power Electronics
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• v.18 no.1
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• pp.225-233
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• 2018

This paper proposes a universal system control strategy for voltage source converter (VSC) based high voltage direct current (HVDC) systems. The framework of the designed control strategy consists of five layer structures considering the topology and control characteristics of the VSC-HVDC system. The control commands sent from the topmost layer can be transmitted to the next layer based on the existing communication system. When the commands are sent to each substation, the following transmission of commands between the four lower layers are realized using the internal communication system while ignoring the communication delay. This hierarchical control strategy can be easily applied to any VSC-HVDC system with any topology. Furthermore, an integrated controller for each converter is designed and implemented considering all of the possible operating states. The modular-designed integrated controller makes it quite easy to extend its operating states if necessary, and it is available for any kind of VSC. A detailed model of a VSC-HVDC system containing a DC hub is built in the PSCAD/EMTDC environment. Simulation results based on three operating conditions (the start-up process, the voltage margin control method and the master-slave control method) demonstrate the flexibility and validity of the proposed control strategy.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.217-218
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• 2015

This paper presents an anaysis of parallel operated HVDC and AC transmissions' transient stability and control analysis by using PACAD/EMTDC program. We measured and analyzed power trasfer in case of various operating conditions including ac, dc faults to find an effects to the power system of the operating conditions. In this project, Simulation of ac/dc parallel system that maximize margins of the ac system and allow a higher power transfer is performed and analyzed.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.1289-1291
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• 2000

The operation of Back-To-Back HVDC system for asynchronous connection is described. It can exchange electric power up to 300 MW between separately operated two rower systems, making the interaction on each system minimum. The analysis is done under three different AC transmission lines interconnected to BTB HVDC.