Complementary Grid Forming: Inertia Gathered From Constrained Resources

Power-electronic contributions of inherent inertia require grid-forming (GFM) control schemes such as ‘virtual synchronous machine’. In order to minimize cost and expenditure, the available resources should be fully exploited. Constraints of the resource at/behind the DC link require an AC behaviour slightly or strongly deviating from that of a synchronous machine. For two outstanding aspects of those deviations, this article proposes clear-cut approaches. The notion ‘complementary grid forming’ (C-GFM) is proposed for contributors of inherent inertia whose full compliance with GFM requirements is at least debatable, be it very close to or very far from them. Its definition draws a sharp demarcation towards GFL (grid following) and a soft line towards full GFM. In the context of the umbrella term ‘tailored inertia’, this article proposes the P-contribution time constant TP for power-electronic inertia. The described TP framework proposes a minimal set of rules for parameterizing and operating devices that contribute tailored inertia. Utilization examples are oriented not only at constraints of resources but also at new possibilities of shaping inertia contributions in order to keep the maximum of network participants operational during extreme events. [1] in the same issue of this journal exemplifies a generic technical implementation.