Transient Stability Assessment of PMSG Grid-Connected System With High-Dimensional Nonlinearity by Normal-Form Method

With fast penetration of renewable energy in power grids recently, transient stability problems have become very serious. Unfortunately an effective assessment method still lacks, especially when the system’s high-dimensional nonlinearity has to be considered. Therefore, taking the permanent magnet synchronous generator grid-connected system as a basic example, this paper estimates its basin boundary by the normal form method and proposes a novel algorithm for calculating the basin boundary and the critical clearing time (CCT). This paper provides a normalized method to clarify the relationship between the high-dimensional stable region and the projection of the stable region, and reveals that the phase-locked loop (PLL) phase and frequency are the dominant transient variables of the system. Based on this, the basin boundary which is originally a high-dimensional curved surface can be projected as a curved line on the two-dimensional plane consisting of the PLL phase and frequency. Hence, the transient stability can be judged on this two-dimensional plane and the CCT can be obtained accurately and effectively. Under various typical faults, the correctness of the transient stability assessment algorithm is well verified by broad simulations and experiments. Therefore, the normal-form-based method is very useful for the new-type power system transient stability analysis.