TY - GEN
T1 - A switching frequency reduction and a mitigation of voltage fluctuation of Modular Multilevel Converter for HVDC
AU - Lee, Hak Jun
AU - Jung, Jae Jung
AU - Sul, Seung Ki
N1 - Publisher Copyright:
© 2014 IEEE.
PY - 2014/11/11
Y1 - 2014/11/11
N2 - A switching loss of Modular Multilevel Converter(MMC) might increase drastically in HVDC system because the number of sub-module(SM) is proportional to the DC-link voltage. And, a special strategy for reducing switching frequency has been significant research issue in terms of overall operating efficiency of MMC for HVDC system. The voltage fluctuation of capacitor in SM, however, increases as the switching frequency decreases, and the capacitor with large capacitance which is the main portion of equipment cost for SM is required to mitigate the voltage fluctuation. In this paper, the switching frequency reduction strategy is proposed using the sorting method with a virtual capacitor voltage of individual SMs. In addition, this paper presents the 2nd order harmonic circulating current injection to suppress the voltage fluctuation. By numerical loss analysis, it is identified that the 2nd order harmonic current injection does not incur severe additional loss. Thanks to the harmonic current injection, the capacitance of SM capacitor could be reduced by 33% at the cost of only 0.05 % efficiency degradation in the given simulation condition. To evaluate the effectiveness of the proposed strategies, the computer simulation with 400 kV, 400MA, 221-level MMC has been performed and the results are discussed. Additionally, validity of the proposed strategies has been verified by 7-level down scaled prototype experimental setup.
AB - A switching loss of Modular Multilevel Converter(MMC) might increase drastically in HVDC system because the number of sub-module(SM) is proportional to the DC-link voltage. And, a special strategy for reducing switching frequency has been significant research issue in terms of overall operating efficiency of MMC for HVDC system. The voltage fluctuation of capacitor in SM, however, increases as the switching frequency decreases, and the capacitor with large capacitance which is the main portion of equipment cost for SM is required to mitigate the voltage fluctuation. In this paper, the switching frequency reduction strategy is proposed using the sorting method with a virtual capacitor voltage of individual SMs. In addition, this paper presents the 2nd order harmonic circulating current injection to suppress the voltage fluctuation. By numerical loss analysis, it is identified that the 2nd order harmonic current injection does not incur severe additional loss. Thanks to the harmonic current injection, the capacitance of SM capacitor could be reduced by 33% at the cost of only 0.05 % efficiency degradation in the given simulation condition. To evaluate the effectiveness of the proposed strategies, the computer simulation with 400 kV, 400MA, 221-level MMC has been performed and the results are discussed. Additionally, validity of the proposed strategies has been verified by 7-level down scaled prototype experimental setup.
KW - HVDC
KW - MMC
KW - Modular Multilevel Converter
KW - Switching frequency reduction
UR - http://www.scopus.com/inward/record.url?scp=84934281365&partnerID=8YFLogxK
U2 - 10.1109/ECCE.2014.6953433
DO - 10.1109/ECCE.2014.6953433
M3 - Conference contribution
AN - SCOPUS:84934281365
T3 - 2014 IEEE Energy Conversion Congress and Exposition, ECCE 2014
SP - 483
EP - 490
BT - 2014 IEEE Energy Conversion Congress and Exposition, ECCE 2014
PB - Institute of Electrical and Electronics Engineers Inc.
ER -