Non-characteristic harmonics in modular multilevel converters—An analytical approach

• Published in: Electric power systems research Vol. 212; p. 108510
• Main Authors: Sakinci, Özgür Can, Beerten, Jef
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2022
• Subjects: Dynamic phasors; Harmonics; HVdc systems; Modular multilevel converter; State-space modeling; HVdc systems; Harmonics; Modular multilevel converter; Dynamic phasors; State-space modeling
• ISSN: 0378-7796; 1873-2046
• DOI: 10.1016/j.epsr.2022.108510

This paper analyzes the harmonic content of the arm currents and voltages of the modular multilevel converter (MMC) by using the dynamic phasor (DP) theory. DP modeling of the MMC facilitates a study without relying on simplifying assumptions on the harmonic content of the currents and voltages. In doing so, the DP-MMC model used in this paper reveals generalized conditions under which non-characteristic harmonics can exist. These conditions offer a detailed insight into the transient behavior of harmonics in the MMC. An open-loop DP model of the MMC is developed, which has the harmonics of the arm currents and voltages as independent state variables. The linearized state-space matrices of the DP model are assessed under different grounding options at the ac side of the MMC, and the relationship between characteristic and non-characteristic harmonics of the MMC voltages and currents is discussed. •An open-loop dynamic phasor model of the modular multilevel converter is developed.•Generic conditions for the existence of non-characteristic harmonics are revealed.•The proposed approach does not rely on simplifying assumptions on harmonic content.•Non-characteristic harmonics are excited when the converter arms are asymmetrical.•Dc voltage imbalances can excite non-characteristic output current harmonics.