Transient Synchronous Stability Evaluation of Heterogeneous Power Grids With Grid‐Following and Grid‐Forming Converters by Manifold Theory

ABSTRACT The energy function method developed from Lyapunov theory is a typical direct method to evaluate the transient synchronous stability of traditional power grids. Different from grid‐forming (GFM) converters mimicking characteristics of synchronous generators (SGs), grid‐following (GFL) converters behave like current sources. The integration of multiple GFL converters poses challenges of constructing energy functions for transient synchronous stability assessment, which is analysed in this paper. In addition, the damping terms of GFL converters are highly dependent on phase angles. Due to the indefinite damping terms of GFL converters, assessment results might be optimistic or conservative, if neglecting damping terms to construct energy functions. Thus, based on manifold theory, an alternative without constructing energy functions is proposed for transient synchronous stability assessment of multi‐converter‐based power grids. Firstly, a hybrid modelling with equivalent voltage and current sources is built to accommodate different network topologies and types of converters. Then, benefiting from the first‐order approximation of manifolds and the geometrical analysis of the region of attraction (ROA) boundary, a criterion designed by manifold theory is proposed and employed for transient synchronous stability evaluation. In addition, the transient synchronous stability margin k rel ζ is defined to avoid optimistic results. Finally, modified IEEE 4‐generator 11‐bus and IEEE 10‐generator 39‐bus systems are built on the MATLAB/Simulink platform to validate the effectiveness of the method.