Small-Signal Stability Assessment of Heterogeneous Grid-Following Converter Power Systems Based on Grid Strength Analysis

The increasing penetration of renewable resources into the power network through grid-following converters has increased the risks of small-signal instability resulting from the interaction between the converters and the power network. It is challenging to assess the small-signal stability in a power system with high penetration of renewable resources due to the complex interaction between a large number of grid-following converters and 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 such challenges, this paper proposes a method for assessing the small-signal stability in a heterogeneous multi-grid-following-converter system based on grid strength analysis. It is first theoretically proved that the small-signal stability of a heterogeneous multi-grid-following-converter system can be characterized by an equivalent homogeneous one, where all interconnected grid-following converters have the same control configurations and parameters. The equivalent homogeneous system can be decoupled into a set of subsystems for reducing the complexity of the small-signal stability assessment of the original heterogeneous system. On this basis, it is derived that the small-signal stability and stability margin of the heterogeneous system can be estimated based on the generalized short-circuit ratio (gSCR), and the critical gSCR (CgSCR). As a result, a gSCR-based method is proposed for assessing the small-signal stability of heterogeneous multi-converter systems. The efficacy of the proposed method is validated by both modal analysis and electromagnetic transient simulations on two heterogeneous multiple-converter systems with different network topologies and a large-scale practical power system.