  Conventional inertia control strategies (i.e., the VSG-based and PD-based
strategies) for the fast frequency regulation resources (FFRs) might lead to
system oscillations due to their emulations of generator dynamics. The
only-droop-based inertia control strategy is a feasible idea to address this
issue. This letter quantitatively investigates the equivalent inertia provided
by the droop control of the FFRs. First, an equivalent-scenario-based method is
proposed to evaluate the equivalent inertia provided by the droop control,
which shows that the droop control with a constant droop coefficient provides
time-variant equivalent inertia. Then, the time-variant-droop-based equivalent
inertia control (VDIC) strategy is proposed for the FFRs, which can provide the
required constant inertia support without introducing generator-like dynamics.
A case study verifies the effectiveness of the VDIC strategy.
