Transient Stability Assessment of Prone-to-Trip Renewable Generation Rich Power Systems Using Lyapunov's Direct Method

Utilities across the world are seeing increased penetration of inverter-based renewable generation (RG) in their systems. These RGs have ride through curves programmed in them which define operating conditions that need to be satisfied during electrical disturbances. If they are violated, the RGs are tripped offline. In systems with large amounts of RGs tightly coupled electrically, there can be disturbances that cause sudden loss of a large number of RGs, which will then considerably exacerbate the stability of the system. Such a phenomenon is not captured by the existing direct methods for TSA. In this paper, by treating RG-rich systems as non-linear switched systems as opposed to the traditional approach of treating this tripping phenomenon as an instability, an approach utilizing multiple low voltage ride through constrained stability regions (CSRs) is proposed for capturing unstable fault clearing times. The CSRs are estimated through Lyapunov functions found using sum of squares programming. The effectiveness of the proposed technique is demonstrated using a three-machine system.