Beyond the Critical Point: Microgrid Security Assessment

Abstract

Microgrids are a key element of decentralized energy systems, yet their operational security cannot be reliably assessed through static analysis alone. The low inertia of converter-interfaced devices, together with the variability of renewable resources, makes it necessary to account for the dynamic response of the system under disturbances. This paper proposes an integrated methodology for determining the feasibility region of a microgrid by combining load-flow analysis with dynamic fault simulations. In the first stage, a set of randomly generated operating points is subjected to static verification, and the admissible points are bounded using the Convex Hull algorithm. In the second stage, the resulting points are evaluated under fault conditions against protection thresholds in terms of voltage, frequency, and RoCoF. Points that violate these constraints are then discarded, yielding a dynamically valid region that represents the system’s actual feasible operating domain. Since the most computationally intensive steps are performed offline, online assessment of an operating condition reduces to simple low-complexity geometric operations. The methodology also quantifies, in terms of power variation, the distance of each operating point from the instability boundary, providing a useful indicator for preventive control strategies. The results show that static analysis alone systematically overestimates the secure operating domain, confirming the need for dynamic verification to obtain a complete characterization of microgrid security.