Enforced Coherent Dynamic Interaction of Grid-Forming Inverters in Low Inertia Systems

The primary focus of this dissertation is to address the challenges for stable and resilient operation of low inertia power systems (LIPS) dominated by grid-forming inverters (GFMI) with inherent heterogeneity. A cluster of droop controlled GFMI with heterogeneous parameters such as dissimilar filter parameters, different power ratings, and varying controller gains is analyzed to investigate the dynamic behavior of this heterogeneous cluster. Moreover, the shortcomings of existing control schemes for heterogeneous GFMIs are analyzed during disturbances and transients. Then a forced enclave homogenization (FEH) scheme is proposed to enforce coherent dynamics within the heterogeneous cluster. This control method involves autonomously determining the equivalent inertia of the cluster and then adjusting the droop characteristics to enforce coherency in the cluster of heterogeneous GFMIs. The proposed FEH scheme is validated via multiple case studies that involve various levels of grid disturbance and cluster reconfigurations. It is demonstrated that the proposed FEH scheme is able to effectively enforce coherency in heterogeneous cluster of GFMIs that enables resilient operation of LIPS dominated by GFMIs. Additionally, the seamless merging of two heterogeneous clusters of GFMIs is achieved with minimal synchronization time and without significant frequency and voltage fluctuations after closing the breaker between the clusters.