Substitution of synchronous generator based instantaneous frequency control utilizing inverter-coupled DER

This paper describes how inverters can stabilize the grid frequency in an interconnected system. The grid frequency is currently mainly controlled by synchronous generators. With the further increase of distributed generation, inverters need to provide more grid support services. In particular, instantaneous frequency control is still exclusively provided by generators, though grid-forming inverters are already state of the art for off-grid applications and can be adapted to substitute synchronous generators. In this paper, the dynamic behavior of synchronous generators is analyzed and a control algorithm for inverters is presented which emulates the principle behavior of synchronous machines and which is able to support inertia to the grid and reduces frequency gradients. Several tests based on simulations and laboratory measurements demonstrate that inverters with adequate control algorithms are able to maintain or even improve the dynamic frequency stability.