Effect of Frequency Coupling on Stability Analysis of a Grid-Connected Modular Multilevel Converter System

Yixing Wang, Qianming Xu and Josep M. Guerrero
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Yixing Wang: College of Electrical and Information Engineering, Hunan University, Changsha 410000, China
Qianming Xu: College of Electrical and Information Engineering, Hunan University, Changsha 410000, China
Josep M. Guerrero: Department of Energy Technology, Aalborg University, 9200 Aalborg, Denmark

Energies, 2021, vol. 14, issue 20, 1-23

Abstract: Due to the internal dynamics of the modular multilevel converter (MMC), the coupling between the positive and negative sequences in impedance, which is defined as frequency coupling, inherently exists in MMC. Ignoring the frequency coupling of the MMC impedance model may lead to inaccurate stability assessment, and thus the multi-input multi-output (MIMO) impedance model has been developed to consider the frequency coupling effect. However, the generalized Nyquist criterion (GNC), which is used for the stability analysis of an MIMO model, is more complicated than the stability analysis method applied on single-input-single-output (SISO) models. Meanwhile, it is not always the case that the SISO model fails in the stability assessment. Therefore, the conditions when the MIMO impedance model needs to be considered in the stability analysis of an MMC system should be analyzed. This paper quantitatively analyzes the effect of frequency coupling on the stability analysis of grid-connected MMC, and clarifies the frequency range and grid conditions that the coupling effect required to be considered in the stability analysis. Based on the quantitative relations between the frequency coupling and the stability analysis of the grid-connected MMC system, a simple and accurate stability analysis method for the grid-connected MMC system is proposed, where the MIMO impedance model is applied when the frequency coupling has a significant effect and the SISO impedance model is used if the frequency coupling is insignificant.

Keywords: modular multilevel converters (MMC); impedance; frequency coupling; stability (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
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