Extreme Event-Triggered Islanding Control of Urban Sub-Transmission Systems Considering Frequency Security Constraints

Urban power systems are featured by high density of critical loads. There is an urgent need to enhance their resilience. This paper proposes an islanding control method for urban power sub-transmission system to ensure a smooth transition to islanded operation under extreme events. An optimal islanding control problem is formulated, aiming to minimize the total control costs subject to dynamic frequency security constraints. An improved system frequency response model considering limiters, switches, and time delays is established to emulate dynamic frequency under large disturbances. Through discretization and linearization, the frequency-related constraints involving nonlinear differential-algebraic equations are converted into linear forms, and the islanding control problem is transformed into a mixed-integer linear program. The selection method of discretization is specially investigated. Finally, a two-stage solution method is designed to accelerate the computation of large-scale mixed-integer linear program by prefixing some integer variables. Simulation results show that the proposed method can maintain system transient frequency security during the islanding process and keep static node voltages in a reasonable range in islanded operation. In addition, the discretization method has high accuracy, and the proposed solution method can speed up the computation.