Determination of modular multilevel converters admittances and their impacts on HVDC power system stability

• Published in: International journal of electrical power & energy systems 2024-01, Vol.155, p.109561, Article 109561
• Main Authors: Giudice, D. del, Bizzarri, F., Linaro, D., Brambilla, A.
• Format: Article
• Language: English
• Subjects: Modular multilevel converters; periodic small-signal analysis; shooting method; Small-signal impedance/admittance model
• ISSN: 0142-0615; 1879-3517
• DOI: 10.1016/j.ijepes.2023.109561

This paper deals with the determination of the complex admittances and trans-admittances of power converters in general and in particular of two modular multilevel converters (mmcs) connected by a high-voltage direct current (hvdc) link to two distinct ac systems. With the term trans-admittances we mean the cross admittance “seen” between the points of common coupling of the two mmcs in the two ac grids. These quantities show how the hvdc link couples the two seemingly separated ac systems. The accurate computation of admittances and trans-admittances requires careful consideration of several frequency harmonics and frequency up-conversion/down-conversion phenomena through the hvdc link. To determine them, we exploit the periodic small-signal (pac) analysis that we briefly introduce from a theoretical perspective. Results show how ac and dc instabilities can be induced by mmcs and how they propagate through the hvdc link. •Presentation of the periodic small signal analysis (PAC) as a powerful tool to compute the small-signal impedance of power converters for stability analyses.•PAC can be applied to complex conveter three-phase models such as those of modular multilevel converters (MMC).•PAC is applied to an HVDC link composed of two MMCs to check small signal stability on both the AC and DC sides in different working conditions.•PAC consider the mutual interactions between the two separated AC systems connected by the HVDC link.•Accurate frequency dependent models of DC lines are considered.