Enforcing Coherency in the Cluster of Grid-forming Inverters in Power Electronics-Dominated Grid

This paper presents a control scheme for realization of coherency in a cluster of grid-forming inverters with heterogenous characteristics. Growing penetration of distributed generation (DG) leads the conventional grid towards more complex and disperse network known as power electronics dominated grid (PEDG). The complex structure of PEDG due to sparse nature requires an accurate model that can mimic the large-scale network dynamics. This will help to perform various analysis such as optimal coordination of controllers and real-time stability assessment. However, the inverters in PEDG have different parameters such as controller gains, filter parameters and power ratings. Thus, the inverters with heterogenous characteristics poses a challenge in obtaining accurate aggregate model of the PEDG. To enforce the homogeneity in the inverter's dynamic response, this paper proposes a coherency enforcement scheme that will shape the dynamic frequency response such that inverters with heterogenous characteristics behave coherently under various disturbances. Moreover, this will aid in deriving the accurate aggregate model of the PEDG. Several case studies under different disturbances are presented to validate the proposed coherency enforcement control. Furthermore, an aggregated model for grid-forming inverter after enforcing coherency is developed and dynamic response of the model is compared with actual circuit model.