• 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 KIEE Conference
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• 2015.07a
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• pp.237-238
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• 2015

This paper analyzed the impact of Voltage Sourced Converter High Voltage Direct Current(VSC HVDC) connected an offshore wind power on the Jeju Island electrical power system. Wind power output fluctuates with the changing of wind speed. By changing wind power output occupancy into 100%, 60%, 10% respectively, we can understand the bus voltage distribution controlled by VSC HVDC. PSS/E is used to analyze steady-state simulation results which show effectiveness of the VSC HVDC for Jeju Island power system.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.5
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• pp.664-668
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• 2012

This paper presents the operation strategy of KEPCO(Korea Electric Power COporation) ${\pm}80kV$ 60MW Bipole HVDC system that will be applied between Guemak C/S(converter station) and Hanlim C/S in Jeju island. Unlike intertie HVDC system, this system is located in AC power grid inside. Therefore, the enhancement of system security related with line flow and bus voltages can be major operation strategy. In this paper, in particular, the optimal operation algorithm in the abnormal(not steady state) power system is presented and simulated.

• Journal of Electrical Engineering and Technology
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• v.13 no.3
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• pp.1052-1059
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• 2018

This paper deals with commutation failure of the line-commutated converter high voltage direct current (LCC HVDC) system caused by a three phase fault in the ac power system. An analytic calculation method is proposed to estimate the maximum permissible voltage drop at the LCC HVDC station on various operating point and to assess the area of vulnerability for commutation failure (AOV-CF) in the power system based on the residual phase voltage equation. The concept is extended to multi-infeed HVDC power system as the area of severity for simultaneous commutation failure (AOS-CF). In addition, this paper presents the implementation of a shunt compensator applying to the proposed method. An analysis and simulation have been performed with the IEEE 57 bus sample power system and the Jeju island power system in Korea.

• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.303-304
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• 2019

본 논문에서는 모듈러 멀티레벨 컨버터(Modular Multilevel Converter, MMC) 고압직류송전(High Voltage Direct Current, HVDC)의 전도 손실 계산을 위한 반도체 스위치 V-I 특성 곡선 근사 방법을 제안한다. 일반적으로 V-I 특성 곡선은 정격 전류 구간에 대해서만 선형화하여 사용하지만, MMC HVDC의 경우 암 전류의 직류 오프셋에 의해 V-I 특성 곡선의 비선형 구간에서 손실 계산에 오차가 크게 나타난다. 따라서 본 논문에서는 암 전류의 부호에 따라 별도의 V-I 특성 곡선 근사를 적용하여 MMC HVDC의 전도 손실 계산의 정확성을 향상하는 방안을 제안한다. 전도 손실 계산 결과는 PSCAD 시뮬레이션으로 취득한 손실 값과 비교하여 결과를 검증하였다.

• 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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• 1999.11b
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• pp.395-397
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• 1999

This paper presents a method of improving the power factor and the waveform of A.C line currents and the out waveforms of AC to DC fully bridge converter systems which is achieved by connecting converters in series and parallel. The results of simulation show that the power factor and the source voltage and current waveforms are improved by the method of connecting converter in series, and the controlled input voltage and current waveform using a current limit controller.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.1
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• pp.8-15
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• 2018

New methodology for probabilistic reliability based grid expansion planning of HVDC in power system including Wind Turbine Generators(WTG) is developed in this paper. This problem is focused on scenario based optimal selection technique to decide best connection bus of new transmission lines of HVDC in view point of adequacy reliability in power system including WTG. This requires two kinds of modeling and simulation for reliability evaluation. One is how is reliability evaluation model and simulation of WTG. Another is to develop a failure model of HVDC. First, reliability evaluation of power system including WTG needs multi-state simulation methodology because of intermittent characteristics of wind speed and nonlinear generation curve of WTG. Reliability methodology of power system including WTG has already been developed with considering multi-state simulation over the years in the world. The multi-state model already developed by authors is used for WTG reliability simulation in this study. Second, the power system including HVDC includes AC/DC converter and DC/AC inverter substation. The substation is composed of a lot of thyristor devices, in which devices have possibility of failure occurrence in potential. Failure model of AC/DC converter and DC/AC inverter substation in order to simulate HVDC reliability is newly proposed in this paper. Furthermore, this problem should be formulated in hierarchical level II(HLII) reliability evaluation because of best bus choice problem for connecting new HVDC and transmission lines consideration. HLII reliability simulation technique is not simple but difficult and complex. CmRel program, which is adequacy reliability evaluation program developed by authors, is extended and developed for this study. Using proposed method, new HVDC connected bus point is able to be decided at best reliability level successfully. Methodology proposed in this paper is applied to small sized model power system.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.151-152
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• 2013

Multilevel Voltage Source Converter HVDC presents a new method for the energy transmission, The multilevel requires the converter bridge includes more than 100 converter modules, for the EMT simulation file, the simulation time increases to several hours; it can depress the research process. In the paper, author describes a method to simulate the multilevel arm based on time-varying equivalent. The result shows the extremely calculation time reduced with almost the same accuracy.

• KIPE Magazine
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• v.21 no.1
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• pp.31-39
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• 2016