Revisiting Small-Signal Dynamic Stability Assessment of Multi-Inverter Interfaced Grids

Procedures for developing small-signal dynamic models of multiple inverter-interfaced power grids are well-established in the literature. For grids consisting of multiple buses in such models, the definition of node voltages is however dealt arbitrarily by use of high virtual resistance ($R_{v}$) between the corresponding node and the ground. The selection of $R_{v}$ obviously has an impact on the resultant eigenvalues of the system under consideration. This article proves that even the selection of arbitrarily higher $R_{v}$ leaves the scope of unacceptable errors in obtaining true system modes. The stability conclusion obtained thereby is also questionable. To address this fundamental gap, a novel approach to redefine node voltages as the functions of system states and known parameters is proposed. The resultant system matrix is free from any random characterization in terms of $R_{v}$. The improved and detailed small-signal model of multiple grid-feeding inverters is used to validate the consistency and superiority of the proposed method.