Abstract
Electrical machines are designed to operate at a fixed electrical frequency.Consequently, maintaining the electrical frequency is a critical task for electrical utilities.
This task is made more difficult by the increasing penetration of inverter-based resources, as they lack the inertia of traditional synchronous generators.
This has led to an interest in recent years to pair renewable generation with energy storage devices to mimic the inertia of synchronous machines.
In this work, it is suggested that this way of thinking is inverted.
Instead, this work considers that the inertia of synchronous machines \emph{is} energy storage.
Historically, this built-in storage has been taken for granted but is essential for power system stability.
This work shows how inefficiently this stored energy is utilized during contingencies and formalizes it in a way that facilitates direct comparisons with grid-scale energy storage systems.
Next is presented a method to enhance the amount of useful energy that can be extracted from a rotating mass by leveraging the concept of a variable moment of inertia.
This concept is then further explored by presenting designs for various variable moment of inertia devices.
The main contribution of this work, however, is a novel type of vMOI device designed specifically for frequency stability applications.
The viability of this design is validated by assessing the various design parameters that would need to be considered to construct a physical device.
Finally, the performance of this device is characterized in a low inertia case study featuring a 12-bus power system model.