Modeling and Mitigation Control of the Submodule-Capacitor Voltage Ripple of a Modular Multilevel Converter under Unbalanced Grid Conditions

Songda Wang, Danyang Bao, Gustavo Gontijo, Sanjay Chaudhary and Remus Teodorescu
Additional contact information
Songda Wang: Department of Energy Technology, Aalborg University, 9220 Aalborg East, Denmark
Danyang Bao: Shenzhen Polytechnic, Xili University Town, Shenzhen 518055, China
Gustavo Gontijo: Department of Energy Technology, Aalborg University, 9220 Aalborg East, Denmark
Sanjay Chaudhary: Department of Energy Technology, Aalborg University, 9220 Aalborg East, Denmark
Remus Teodorescu: Department of Energy Technology, Aalborg University, 9220 Aalborg East, Denmark

Energies, 2021, vol. 14, issue 3, 1-17

Abstract: A modular multilevel converter’s (MMC’s) submodule (SM)-capacitor voltage will increase under unbalanced grid conditions. Depending on the imbalance level, the voltage ripple can be considerably high, and it can exceed the pre-defined safe limits. If this occurs, the converter will trip, which can lead to serious stability problems for the grid. This paper first proposes an analytical solution for deriving the three-phase imbalanced SM ripple of an MMC under an unbalanced grid. With this analytical tool, the imbalance mechanism of the SM voltage ripple can be easily understood. What is more, the symmetrical component method is first applied to analyze the three-phase SM capacitor ripple, and the positive-/negative-/zero-sequence components of the three-phase SM voltage ripple are easily identified by the proposed analytical method. Then, based on this powerful analytical tool, the proper circulating-current profile to be injected can be obtained, allowing for the right compensation of the voltage ripple. Based on this approach, two new voltage ripple compensation methods are proposed in this paper. Simulations were carried out to validate the analytical description of the submodule-capacitor voltage ripple proposed in this paper. Moreover, simulation and experimental results are provided to validate the new compensation techniques introduced in this paper.

Keywords: modular multilevel converter; submodule-capacitor voltage ripple; unbalanced grid conditions (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (7)

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