There are many electricity transmission systems and distribution systems operating at a fixed frequency, for example, at 50 Hz or 60 Hz. Grid frequency control systems control resources such as power sources (generators) and energy storage resources.
In order to maintain grid frequency stability, grid operators send commands for controlling the amount of power withdrawn from the grid by loads and the amount of power injected to the grid by generators, storage, and renewable energy sources. The power sources and the energy storage resources control inputs or outputs of their power.
However, large delay occurs in transmission of command signals from a grid operator's computer to receivers. To overcome the delay, there is a system that creates, at a receiver side, a control signal having a grid frequency, instead of using commands sent from the grid operator (see PTL 1, for example).