Unified Virtual Inertia for ac and dc Microgrids: And the Role of Interlinking Converters

Abstract

In physics, inertia is defined as the tendency of an object to resist changes in its state of motion: in other words, the tendency to resist changes in speed and direction. It is a property of matter to remain at rest or uniform motion unless an external force is applied to it. In classical electric power systems, the system frequency is directly coupled to the rotational speed of all rotating equipment directly connected to the grid (as in the cases of synchronous and induction generators, induction motors of big industrial drives, pumps, fans, and so on). Therefore, we can define the inertia of a power system as the resistance of the system to variations in its frequency, which is directly related to the resistance to variations in the angular rotating speed of all of the rotating mass connected to the system. It is then evident that the inertia of the power system is determined by the total rotating inertia directly connected to it.