Microgrid Ramp Rates and the Inertial Stability Margin

Variable power sources are becoming increasingly common in low-inertia microgrids. Inadequate amounts, however, can disrupt electric service if ramped events occur too quickly. The authors introduce an approach to predict how long microgrids can withstand ramped events as a function of local inertia. Although microgrids can ride through disturbances using local inertia and other technologies, it is not clear for how long disturbances can be tolerated-particularly when in progress. The estimated reaction times are presented, first, as stability margins to illustrate how ramp-rate magnitudes relate to local inertia. Then, use of the reaction times is demonstrated as a forward-looking capability to anticipate frequency deviation times as a microgrid model undergoes large solar ramp rates. It is shown that the available remaining times can be estimated even as disturbances and remedial actions take place.