Capacitor Inertia Enhanced Control Strategy of Three-Port Grid-Forming Converters

In the three-port grid-forming (TP-GFM) converter system, the DC capacitor can provide fast short-time inertia support power for the system, which has the advantages of fast response and sensitivity to small disturbances. However, existing studies still pay insufficient attention to the capacitive inertia in this system. In this paper, a capacitor inertia enhanced (CIE) control is proposed for TP-GFM converter. This strategy reduces the rate of change of frequency (RoCoF) of the system during disturbances by establishing the coupled relationship between the DC capacitor voltage and the system frequency, which induces the DC capacitor to participate in the system frequency response. Then, for TP-GFM converter system, an equivalent Philips- Heffron model is constructed and its system inertia is quantified using the equivalent inertia constant. Finally, the effectiveness of the proposed control strategy and the reasonableness of the inertia analysis method are verified using a TP-GFM converter based simulation.