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DOI:10.35833/MPCE.2019.000213
Analysis on Circulating Current and Split Capacitor Voltage Balance for Modular Multilevel Converter Based Three-phase Four-wire Split Capacitor DSTATCOM
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Author: Lei Lin1,2,Jialu He1,2,Chen Xu1,2

Author Affiliation: 1.State Key Laboratory of Advanced Electromagnetic Engineering and Technology;2.School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China

Foundation:
This work was supported in part by the National Natural Science Foundation of China （No. 51807073）.
Abstract: We propose a modular multilevel converter (MMC) based three-phase four-wire (3P4W) split capacitor distribution static synchronous compensator (DSTATCOM), aiming at compensating unbalanced and reactive load currents. Due to the zero-sequence current compensation, the circulating current characteristics of 3P4W MMC-DSTATCOM are different from conventional MMCs. Moreover, the distinct working principle of MMC would affect the features of split capacitor voltage. The decoupled positive-, negative- and zero-sequence second-order and DC components of the circulating current are deduced explicitly. Two proportional-integral controllers with dual dq transformation are employed to suppress the positive- and negative-sequence components of second-order circulating current, while quasi proportional-resonance controller is designed to eliminate the zero-sequence component. Besides, the phenomenon of the unbalanced split capacitor voltages is revealed, and fast-tracking balancing method by controlling zero-sequence current flowing through the split capacitors is provided. Digital simulation results verify the accuracy of the analysis and the feasibility of the suppression methods.

Keywords:
Circulating current ; modular multilevel converter (MMC) ; distribution static synchronous compensator (DSTATCOM) ; split capacitor ; three-phase four-wire (3P4W).
Received:December 12, 2019               Online Time:2021/05/19
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