Control Design of Series-Connected PV-Powered Grid-Forming Converters via Singular Perturbation

Rahul Mallik, Branko Majmunovic, Soham Dutta, Gab-Su Seo, Dragan Maksimovic, Brian Johnson

Research output: Contribution to journalArticlepeer-review

8 Scopus Citations


Modular architectures that consist of several series-connected dc-ac converters have been a focal point of recent innovations in transformerless medium-voltage applications. In this article, we consider an architecture consisting of dc-ac modules containing a quadruple active bridge dc-dc converter, which generates three floating dc links that feed grid-side dc-ac inverters. Practical implementation of such a converter module in photovoltaic systems requires a variety of controllers that collectively achieve maximum power point tracking, dc-link regulation, and ac-side power control. Design of such multiloop systems is generally quite challenging due to the potential for destabilizing interactions among loops. Here, we propose a design approach where singular perturbation theory is used to decompose the timescales at which each control loop operates and provides a systematic framework for parametric selection. Our approach also ensures system stability of multiple modules with identical controls connected in series across a grid. This article concludes with experimental results of three 1000-W series-connected converter modules across a stiff grid.

Original languageAmerican English
Pages (from-to)4306-4322
Number of pages17
JournalIEEE Transactions on Power Electronics
Issue number4
StatePublished - 2023

Bibliographical note

Publisher Copyright:
© 1986-2012 IEEE.

NREL Publication Number

  • NREL/JA-5D00-83960


  • Cascaded converters
  • control design
  • grid-forming
  • modular inverters
  • singular perturbation
  • stability


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