Small-Signal Stability Assessment of Heterogeneous Grid-Following Converter Power Systems Based on Grid Strength Analysis
Yuhan Zhou, Huanhai Xin, Di Wu, Feng Liu, Zhiyi Li, Guanzhong Wang, Hui Yuan, Ping Ju
Abstract
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.