Virtual Inertia From Smart Loads

The inertia of future power systems is expected to decrease with increasing penetration of renewable energy resources. Sufficient inertia is required to avoid large fluctuations in grid frequency and also limit the excessive rate of change of frequency (RoCoF). Unlike many previous works focusing on virtual inertia on the power supply side, this paper studies and quantifies potential virtual inertia from the load side. The analysis shows that, voltage-dependent loads coupled with electric spring (ES) technology can be operated as smart loads (SL) within the +/-5% tolerance of the ac mains voltage and offer virtual inertia. Following the U.K. National Grid frequency requirements, it is shown that the ES based SL can provide virtual inertia up to an inertia coefficient of H
_SL
= 2.5 s (when n
_p
= 2) with respect to its load power rating. The effectiveness of such virtual inertia extraction from SL has been verified by the simulation study on a CIGRE benchmark microgrid with high-resolution domestic demand model. The value of H
_SL
is shown to be around 1.3 s during the most part of the day and can increase the overall system inertia coefficient by 0.53 s if all the domestic loads are transformed into the proposed smart loads.