Small-signal Stability Assessment of Heterogeneous Multi-converter Power Systems

The increasing penetration of renewable resources into the power network through grid-following converters has increased the risks of oscillation instability. In such a power system, it is challenging for assessing the small-signal stability due to the complex interaction among converters interconnected through the power network. Moreover, the assessment complexity is further increased in a heterogeneous multi-converter system, where the interconnected converters have different control configurations or parameters from different manufacturers. To tackle the challenges, this paper proposes a method for the small-signal stability analysis of a heterogeneous multi-converter system. To this end, it is first theoretically proved that the small-signal stability of a heterogeneous system can be characterized by an equivalent homogeneous one, where all interconnected converters have the same control configurations and parameters. This can reduce the complexity of the small-signal stability assessment of the original heterogeneous system by decoupling the equivalent homogeneous system into a set of subsystems. To further reduce the assessment complexity, it is derived that the small-signal stability and stability margin of the heterogeneous system can be estimated based on the smallest eigenvalue of a weighted Laplacian matrix of the power network. Based on the analysis results, a scalable method is developed for assessing the small-signal stability of heterogeneous multi-converter systems. The efficacy of the proposed method is validated by performing both modal analysis and time-domain simulations on two heterogeneous multiple-converter systems with different network sizes and converter numbers.