Performance Limits of Low Inertia Power Systems Based on Minimum Energy Control

It is currently recognized that integration of renewable sources is tightly linked to the behavior of low-inertia power systems. In this light, our aim in the current study is to find a lower bound on the energy storage required for reliable operation of a small network. A central idea in the proposed analysis is the ideal dq storage device-a conceptual device capable of unlimited control over its AC voltage. We use this so-called device to explore what is the minimal locally stored energy that allows the system to operate reliably, such that the voltage stays within an acceptable range during a transient. We show that this problem can be posed as an optimal control problem, and propose a suboptimal solution based on minimum energy control. The results provide a conservative lower bound on the locally stored energy.