Stability Boundary of Power System with Converter Interfaced Generation: Evolution and Transition Point

Recent studies indicate that transient instability in power systems with converter interfaced generation (CIG) is primarily related to unstable periodic orbit (UPO) rather than unstable equilibrium point (UEP). This phenomenon is noticeable in weak grids, emphasizing the importance of studying the evolution of the stability boundary's dominant, from UEP to UPO. To address this, the present study introduces a novel transient stability analysis framework for power systems, which relies on the energy-angle complex vector. Both the identification of transition point of the stability boundary and the stability margin assessment are conducted under this framework. It is revealed that variations in parameter conditions, such as an increased proportion of CIG, a decrease in system strength, and inadequate control parameters for CIG, may lead to the dominance of UPO in shaping the stability boundary. This may lead to the ineffectiveness and non-conservatism of the UEP-based criteria. Simulation results demonstrate the effectiveness of the derived conclusions. With the increasing integration scale of CIG, the growing importance of UPO-based stability characteristic will become pronounced in future power systems.