Small-Signal Modeling and Analysis of MMC Under Unbalanced Grid Conditions Based on Linear Time-Periodic (LTP) Method

• Published in: IEEE transactions on power delivery Vol. 36; no. 1; pp. 205 - 214
• Main Authors: Zhu, Jianhang, Hu, Jiabing, Wang, Sicheng, Wan, Minhui
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.02.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Analytical models; Converters; Eigenvalue locus; Eigenvalues; Eigenvalues and eigenfunctions; floquet-lyapunov theory; linear time periodic (LTP); modular multilevel converters (MMC); Monte Carlo methods; Phase locked loops; Power system dynamics; Stability analysis; Steady-state; Unbalance; unbalance grid conditions
• ISSN: 0885-8977; 1937-4208
• DOI: 10.1109/TPWRD.2020.2976776

As in grid-tied Modular Multilevel Converters (MMC), the steady-state operation under asymmetric grid conditions is rather general, especially for the overhead line of the AC network. Therefore, the small-signal dynamics of MMC under unbalanced grid conditions have become a great important research topic. In this paper, the inherent periodic time-varying characteristic of MMC's original relationships is given priority consideration. Based on the linear time-periodic (LTP) method, a general small-signal LTP model under unbalanced grid conditions is built considering the internal dynamic of submodules (SMs). Then based on the eigenvalue locus analysis method from Floquet- Lyapunov theory, the effects of controller parameters and interactions between different controllers on small-signal dynamics are studied, respectively. Finally, the results from the detailed nonlinear MMC model are provided to verify the effectiveness of the proposed analysis.