Circulating Current Control in MMC Under the Unbalanced Voltage

• Published in: IEEE transactions on power delivery Vol. 28; no. 3; pp. 1952 - 1959
• Main Authors: MOON, Ji-Woo, KIM, Chun-Sung, PARK, Jung-Woo, KANG, Dae-Wook, KIM, Jang-Mok
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.07.2013; Institute of Electrical and Electronics Engineers
• Subjects: Applied sciences; Circulating current; Current control; dual vector current control (DVCC); Electrical engineering. Electrical power engineering; Electrical machines; Exact sciences and technology; Frequency control; HVDC transmission; modular multilevel converter (MMC); Moon; negative sequence; positive sequence; Power conversion; Power electronics, power supplies; Regulation and control; Testing. Reliability. Quality control; Voltage control; zero sequence; Performance evaluation; Power converter; modular multilevel converter (MMC); Control system; Unbalanced conditions; Power electronics; zero sequence; Voltage control; Balanced conditions; Current control; dual vector current control (DVCC); Vector control; negative sequence; Circulating current; System simulation; Control method; Effectiveness factor; Multilevel system; positive sequence; Alternating current
• ISSN: 0885-8977; 1937-4208
• DOI: 10.1109/TPWRD.2013.2264496

This paper proposes a control method for circulating currents in modular multilevel converters (MMCs) under unbalanced voltage conditions. Under balanced voltage conditions, only negative-sequence circulating currents exist. Consequently, the conventional method has considered only negative-sequence circulating currents in MMC. However, under unbalanced voltage conditions, there are positive-sequence circulating currents, zero-sequence circulating currents, and negative-sequence circulating currents in MMC. Thus, under unbalanced voltage conditions, a control method should consider all of these components. This study adopts a dual vector current controller as an ac-side current controller to reduce the ac-side active power ripple under unbalanced voltage. It analyzes the effect of the unbalanced voltage on circulating currents in MMC and then proposes a control method considering each component of circulating currents under the unbalanced voltage. The effectiveness of the proposed controlling method is verified through simulation results using PSCAD/EMTDC.