用于评估跟网型与构网型变流器并网系统小信号同步稳定性的电网强度评估方法

Oscillations caused by small-signal instability have been widely observed in AC grids with grid-following(GFL)and grid-forming(GFM)converters.The generalized short-cir-cuit ratio is commonly used to assess the strength of GFL con-verters when integrated with weak AC systems at risk of oscilla-tion.This paper provides the grid strength assessment method to evaluate the small-signal synchronization stability of GFL and GFM converters integrated systems.First,the admittance and impedance matrices of the GFL and GFM converters are analyzed to identify the frequency bands associated with nega-tive damping in oscillation modes dominated by heterogeneous synchronization control.Secondly,based on the interaction rules between the short-circuit ratio and the different oscilla-tion modes,an equivalent circuit is proposed to simplify the grid strength assessment through the topological transformation of the AC grid.The risk of sub-synchronization and low-fre-quency oscillations,influenced by GFL and GFM converters,is then reformulated as a semi-definite programming(SDP)mod-el,incorporating the node admittance matrix and grid-connect-ed device capacities.The effectiveness of the proposed method is demonstrated through a case analysis.