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 HSL=2.5 s (when np=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 HSL 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.