Minimal energy storage required for stability of low inertia distributed sources

Recently there have been extensive research efforts to identify possible adverse effects of distributed sources and power electronics based devices when integrated into existing power grids, where two main challenges are low rotational inertia and stability. This paper studies the dynamics and stability of two simple systems: an ideal power source and a simple synchronous machine, both connected to an infinite bus. The objective in both cases is to determine analytically the minimal storage device that is necessary for stability. One objective of this analysis is educational - to demonstrate the crucial function of local energy storage as part of any power source, and specifically to show that ideal power sources are unstable when no local energy storage is present. Another objective is to approximate the size of local storage devices in practical designs, using simple analytic expressions and limited data.