Virtual synchronous generators

TLDR

In electricity grids, frequency stability depends on the rotational inertia of synchronous generators and control algorithms, but as non‑synchronous units replace synchronous capacity, the overall inertia drops, leading to large frequency swings. The study proposes adding virtual rotational inertia to distributed generators to stabilize grid frequency. Virtual inertia is achieved by equipping any generator with short‑term energy storage and a control scheme for its power‑electronics converter. This approach lets generators behave as virtual synchronous generators for brief intervals, reducing large frequency variations and improving grid stability.

Abstract

In electricity grids the frequency of the voltage is stabilized by a combination of the rotational inertia (rotating mass) of synchronous power generators in the grid and a control algorithm acting on the rotational speed of a number of major synchronous power generators. When in future small non-synchronous generation units replace a significant part of the synchronous power generation capacity, the total rotational inertia of the synchronous generators is decreased significantly. This causes large frequency variations that can end up in an unstable grid. A way to stabilize the grid frequency is to add virtual rotational inertia to the distributed generators. A virtual inertia can be attained for any generator by adding a short-term energy storage to it, combined with a suitable control mechanism for its power electronics converter. In this way a generator can behave like a ldquoVirtual Synchronous Generatorrdquo (VSG) during short time intervals, and contribute to stabilization of the grid frequency.