A Time-Domain Analysis Model for Modular-Multilevel-Based Grid-Forming Converters in Isolated Power Supply

Abstract

The modular multilevel based grid-forming converter (MMGC) is considered to be a viable solution in isolated island power supply. However, the existing analysis model cannot meet the requirement of its performance evaluation and circuit parameters design. This paper proposes a high-accurate time-domain steady-state analysis model for MMGC, where the coupled relationships among the load, the MMGC, and the dc-side system can be fully reflected; the amplitudes and phase angles of electrical quantities, including their harmonic components, can be directly calculated. Then, the influence of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> filters on submodule capacitor are studied. The study found that the submodule capacitance is highly correlated to the filter capacitance and almost uncorrelated to the filter inductance. It is also found that the filter capacitance selection should consider the load characteristic; a larger filter capacitance is required in the inductive load supply scenario. Finally, the studies are verified by both simulation and experiment.