Ramp-Rate Limitation of Distributed Renewable Energy Sources via Supercapacitors as Preventive Action towards Frequency Disturbances

The increasing penetration of Distributed Renewable Energy Sources (DRES) has caused several issues to the electric grid, e.g., frequency instability. The Transmission System Operators (TSOs) try to solve these issues by committing huge amounts of fuel-driven Power Plants (PPs) as spinning reserves, leading to increased costs. For this reason, grid codes are posing specific limits to the DRES Ramp-Rates (RRs). However, the actual impact of the RR Limitation (RRL) on the frequency disturbances has not been investigated yet in the technical literature. In this paper, an investigation is performed in DigSilent PowerFactory using the IEEE 9-bus Transmission System to evaluate the impact of the RRL action of a DRES coupled with a Supercapacitor (SC) on the frequency disturbances, while conventional Synchronous Generators (SGs) operate as Frequency Containment Reserves and Frequency Restoration Reserves. The SC is added to the DRES so that RRL is performed without active power curtailment. Several parameters and indices are considered: the RRL value, the SC size, the SGs energy, etc.