An Improved Circulating Current Injection Method for Modular Multilevel Converters in Variable-Speed Drives

• Published in: IEEE transactions on industrial electronics (1982) Vol. 63; no. 11; pp. 7215 - 7225
• Main Authors: Binbin Li, Shaoze Zhou, Dandan Xu, Rongfeng Yang, Dianguo Xu, Buccella, Concettina, Cecati, Carlo
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-11-2016; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Capacitance; Capacitance dimensioning; capacitor voltage ripple; Capacitors; circulating current injection; Converters; Harmonic analysis; modular multilevel converter; Modulation; submodule (SM); Topology; Variable speed drives
• ISSN: 0278-0046; 1557-9948
• DOI: 10.1109/TIE.2016.2547899

Modular multilevel converters (MMC) represent an interesting and emerging topology in medium-voltage motor drive applications. The main challenge of using such a topology in variable-speed drives is the large voltage ripple of submodule capacitors at low speed with constant torque. In this paper, an improved circulating current injection method is proposed, which does not completely eliminate the capacitor voltage ripple, but maintains it bounded within reasonable values. As a result, magnitude of injected circulating current is reduced, leading to converter efficiency improvement and reduction of semiconductor current ratings. Dimensioning of submodule capacitance is also discussed, which is an important consideration when designing the MMCs in variable-speed drives. The proposed method has been successfully validated by simulation and experimental results.