Transient Stability Analysis of the CIG-Embedded Power Systems Considering Multiple Stable Equilibrium Points

The present research focuses on the transient stability of power systems embedded with a high penetration of converter-interfaced generation (CIG). It is investigated that under large disturbances, power systems with CIGs may exhibit the characteristic of multiple stable equilibrium points (SEPs). This characteristic and its associated stability potential have not been thoroughly studied in conventional power systems, primarily due to the prevalent assumption of a single SEP constrained by the physical limitations of the large-capacity synchronous generator. Since the critical clearing time (CCT) is no longer able to determine system transient stability with multiple SEPs, the absolute instability boundary (AIB) condition is proposed. It is found that if the trajectory surpasses the AIB, the power system will be unable to maintain stability after large disturbances. In what follows, an energy function is introduced to assess transient stability considering multiple SEPs. At the end of the study, the impact of CIG's frequency limiters on transient stability is studied, and a transient stability enhancement method is derived based on the AIB condition and safety constraints. This provides a basis for CIGs with millisecond-level dynamics to respond to power systems with near-second dynamics. Numerical simulations demonstrate the effectiveness of the proposed theoretical results.