On-line Inertia Estimation in Presence of Distributed Energy Resources

Proper levels of inertia guarantee the stable and secure operation of power systems. Due to the increasing deployment of distributed resources, most of which are converter-interfaced sources (CISs), the inertia level is decreasing and can vary significantly depending on the connection of renewable energy sources. It is hence useful to monitor the system inertia close to real-time. This paper proposes an improved online inertia estimation method based on a non-linear least squares (LSQ) optimization technique and the Dynamic Regressor Extension and Mixing (DREM) procedure. The LSQ optimizer periodically characterizes the aggregated dynamics of the units involved in the primary frequency control, while the DREM continuously estimates the inertia of the system. Both units with directly connected synchronous generators and CISs are considered in the tests based on the 39-bus IEEE system. The CIS models include a droop control together with a virtual inertia scheme to represent their participation in the frequency regulation. The impact of rotating load dynamic is also considered.