  Frequency performance has been a crucial issue for islanded microgrids. On
the one hand, most distributed energy resources (DER) are converter-interfaced
and do not inherently respond to frequency variations. On the other hand,
current inertia emulation approach cannot provide guaranteed response. In this
paper, a model reference control based inertia emulation strategy is proposed
for diesel-wind systems. Desired inertia can be precisely emulated through the
proposed strategy. A typical frequency response model with parametric inertia
is set to be the reference model. A measurement at a specific location delivers
the information about the disturbance acting on the diesel-wind system to the
reference model. The objective is for the speed of the diesel generator to
track the reference so that the desired inertial response is realized. In
addition, polytopic parameter uncertainty will be considered. The control
strategy is configured in different ways according to different operating
points. The parameters of the reference model are scheduled to ensure adequate
frequency response under a pre-defined worst case. The controller is
implemented in a nonlinear three-phase diesel-wind system fed microgrid using
the Simulink software platform. The results show that exact synthetic inertia
can be emulated and adequate frequency response is achieved.
