RoCoF Constrained Regional Inertia Security Region: Formulation and Application

The regional inertia, which determines the regional rate of change of frequency (RoCoF), should be kept in a secure status in renewable-penetrated power systems. To break away from mapping the regional maximum RoCoF with regional inertia in a linearized form, this paper comprehensively studies the regional inertia security problem from formulation to applications. Firstly, the regional inertia security region (R-ISR) is defined, whose boundary is non-linear and non-convex. Then, a local linearized method is devised to calculate the global maximum of regional RoCoF. The non-convex ISR boundary is expressed by multiple simple boundaries corresponding to each local solution, which can be obtained by a simple search-based method. Finally, the convexified R-ISR constraint is formed by convex decomposition and embedded in an inertia optimal adjustment model. The results on a 3-region system show some counter-intuitive findings, such as increasing the inertia of one region may worsen its RoCoF.