Frequency Stability Improvement in Weak Grids by Storage Systems

This chapter is focused on the improvement of the frequency stability in weak grids by advanced storage sys-tems interfaced with power converters. Weak grids suffer of a reduced inertia of the rotating generators; this in-creases the variations of the frequency due to large variations of the load. The frequency collapse can be avoided by the Automatic Load Shedding (ALS) disconnecting some loads but it causes consequences on the economic activities and service continuity. Moreover, since the rapid increase of the use of renewable energy systems (RES) with wind and photovoltaic (PV) generation plants connected to the grid reduces the inertial response, in perspective it could represent a potential limit to the maximum penetration of RES and to their inherent benefits in terms of greenhouse and dependence from fossil fuel resources reduction. After a discussion on the frequency variation issues in presence of PV and wind generation systems, the use of storage systems for dynamic grid support is analyzed. Simulations show the frequency drop caused by a reduced inertia and the benefits of the adoption of storage systems to perform a dynamic support. The specific power converters for storage systems grid interfacing are studied with reference to Superconducting Magnetic Energy Storage (SMES), flywheels energy storage (FES), supercapacitors and batteries. Finally some case studies are presented.