Certifying microgrid stability under large-signal intermittency

The uptake of high penetrations of renewable energy in microgrids is curtailed by concerns that their intermittency may cause the system to become unstable. The classic approach of small-signal stability analysis may lead to overly optimistic conclusions, because it implicitly assumes that the intermittency is small-signal in nature. Instead, LMI techniques from robust controls can be used to provide large-signal stability guarantees that overcome this limitation. In this paper, we give an illustrative example of a microgrid that is guaranteed to be stable under small-signal intermittency, and show that it can be made unstable when the intermittency becomes large-signal. Instead, we compute more conservative large-signal stability margins using Lyapunov analysis, and show that the small- and large-signal stability margins are related by the maximum allowable slew-rate of the intermittency.