• 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.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1467-1476
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• 2019

Grid unbalanced faults can cause core saturation of power transformer and produce lower-order harmonics. These issues increase the electrical stress of power electronic devices and can cause a tripping of an entire HVDC system. In this paper, based on the positive-sequence and negative-sequence impedance model of a VSC-HVDC system as seen from the point of common connection (PCC), the resonance problem is analyzed and the factors determining the resonant frequency are obtained. Furthermore, to suppress over-voltage and over-current during resonance, a novel method using a virtual harmonic resistor is proposed. The virtual harmonic resistor emulates the role of a resistor connected in series with the commutating inductor without influencing the active and reactive power control. Simulation results in PSCAD/EMTDC show that the proposed control strategy can suppress resonant over-voltage and over-current. In addition, it can be seen that the proposed strategy improves the safety of the VSC-HVDC system under unbalanced faults.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.161-162
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• 2015

최근 세계적으로 전력계통의 대륙 간 연계나 신재생에너지, 분산전원의 계통 연계를 위해 HVDC(High voltage Direct Current)에 대한 연구가 활발히 진행되고 있다. 대용량, 장거리 송전이 필요한 경우 HVAC에서의 전력손실과 송전거리의 한계를 극복하기 위하여 HVDC가 새로운 대안으로 떠오르고 있으며, LCC(Line commutated Converter)와 VSC(Voltage Source Converter)의 기술발전이 비약적으로 이뤄지고 있다. 특히, DC Grid화를 위해서 유럽에서는 해상풍력을 연계한 Windfarm을 DC Grid화 하는 프로젝트가 활발히 진행되고 있다. 이러한 신재생 에너지의 계통 연계를 위해서 DC Grid가 본격적으로 논의가 되고 있고 관련분야에서는 기술개발을 앞다퉈 진행하고 있는 상황이다. DC Grid 구현을 위해 VSC HVDC가 최근 주목받고 있으며, VSC로 연계된 DC Grid의 AC 계통과의 연계를 위해 가장 필요한 것이 바로 DC 차단기라고 할 수 있겠다. 본 논문에서는 DC Grid의 고장분석을 위한 기초연구로써 MMC(Modular Multilevel Converter) VSC를 기반으로 한 Point-to-Point HVDC Grid에서의 DC 고장에 대한 분석을 실시하였으며 그 특징을 분석하였다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.1
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• pp.121-127
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• 2015

Recently, LVDC(Low Voltage Direct Current) has been came into the newly spotlight with HVDC(High Voltage Direct Current) and as increasing digital load, DC power supply and high quality of demand is also getting extended. In accordance with the report of EPRI(Electric Power Research Institute), they expect digital load will grow to 50% of whole load in 2020. Subsequently, the use of DC equipment will grow dramatically. Therefore, the careful adoption of LVDC standardization policy is urgently required for the safety of people, prevention of confusion and occupancy of the market.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.1
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• pp.49-57
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• 2016

A modular multilevel converter is widely adapted for a high-voltage direct current power transmission system. This study proposes a design methodology for a novel digital control that mitigates the negative effects caused by time delay, including communication transport delay for a modular multilevel converter. The modeling and negative effect of time delay are analyzed theoretically in a frequency domain, and its compensation methodology based on an inverse model is described fully with practical considerations. The proposed methodology is verified through several simulation results using a modular 21-level converter system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.229-231
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• 2005

HVDC(High Voltage Direct Current) is an underwater cable between Jeju Island and Haenam in main land and supplies approximately 50% of electrical usage in Jeju Island. If there is any power failure due to HVDC, it will cost approximately 50,000 US dollars per day including Thermal Electrical Generation. Therefore it is absolutely necessary to recover the problem in rapid timely basis. In conclusion, evaluation methode of HVDC cable is needed urgently to upgrade current HVDC underwater cable repair technique in Korea to minimize the cost and time factors.

• Journal of Electrical Engineering and Technology
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• v.13 no.6
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• pp.2319-2328
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• 2018

This paper introduces a control method for a transformerless MMC-HVDC system. The proposed method can effectively control the grid currents of the MMC-HVDC system under unbalanced grid conditions such as a single line-to-ground fault. The proposed method controls the currents of the positive sequence component and the negative sequence component without separating algorithms. Therefore, complicated calculations for extracting the positive sequence and the negative sequence component are not required. In addition, a control method to regulate a zero sequence component current under unbalanced grid conditions in the transformerless MMC-HVDC system is also proposed. The validity of the proposed method is verified through PSCAD/EMTDC simulation.

• Proceedings of the KIPE Conference
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• 2013.11a
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• pp.133-134
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• 2013

현재 LS산전과 한국전력공사의 공동 개발을 통하여 60MW급 ${\pm}80kV$ 전류형 HVDC(High Voltage Direct Current) Transmission System 내 알고리즘 국산화 개발을 진행하고 있다. 제어 알고리즘 여러 레벨(AC Yard Control, Master Control, Pole Control, Phase Control)에서 운전하기 전 여러 고려사항 중 DC Yard 내 DC Switch의 투입/개방의 조건이 있다. 본 논문에서는 이러한 DC Line에 DC Switch의 상태를 효율적으로 제어하는 방법에 대해 소개하고자 한다.

• Proceedings of the KIPE Conference
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• 2015.11a
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• pp.111-112
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• 2015

MMC HVDC(Multi-level Modular Converter High Voltage Direct Current)는 현재 차세대 전력망으로써 각광을 받고 있고 그에 대한 연구가 활발하게 진행 중이다. 본 논문에서는 모듈형 멀티레벨 컨버터를 이용한 전압형 HVDC 시스템의 AC 전류제어기에 대하여 기술하고자 한다. 일반적으로 사용되는 회전변환을 통한 DQ전류제어와 PR제어를 사용하여 응답특성을 PSCAD/EMTDC를 통하여 비교 검증하고자 한다.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.748-749
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• 2007

HVDC(High Voltage Direct Current) is an underwater cable between Jeju Island and Haenam in main land and supplies approximately 50% of electrical usage in Jeju Island. If there is any power failure due to HVDC, it will cost approximately 50,000 US dollars per day including Thermal Electrical Generation. Therefore it is absolutely necessary to recover the problem in rapid timely basis. In conclusion, jointing methode of HVDC cable is needed urgently to upgrade current HVDC underwater cable repair technique in Korea to minimize the cost and time factors.