Stability Analysis of Grid-Forming Converters Under DC-Side Current Limitation in Primary Frequency Response Regime

The Stability of grid-forming converters (GFCs) interfacing renewable resources in a power system with multiple synchronous generators (SGs) is studied in the context of primary frequency response. The GFCs are divided into two classes based on the control methods - class-A: droop control, dispatchable virtual oscillator control (dVOC), and virtual synchronous machine (VSM); and class-B: matching control. First, averaged phasor models of these GFC classes are developed, which can be seamlessly integrated with positive sequence fundamental frequency planning models. Next, simplified averaged models are derived to study the stability of the dc-link voltage of the GFCs under dc-side current limitation in a generic multimachine system during primary frequency response. To that end, sufficiency conditions for stability of both classes and that of instability for class-A GFCs are established. Finally, the proposed stability conditions are verified using detailed switched models of two small systems and phasor models of a 4-machine and a 16-machine IEEE benchmark systems.