Frequency Response
Most electric systems use alternating current with a nominal frequency of 50 or 60 Hz (hertz) to deliver energy produced by electrical generators to the electricity consumers. When the amount of electric power produced by the generators exceeds the power used by the customers, the frequency of the electricity rises. Conversely, when the amount of electric power produced is less than what is consumed, the frequency drops. Therefore frequency is an accurate indicator of the system-wide (called global) balance between supply and demand. Without grid-friendly frequency response, the rate at which the frequency changes is dependent principally on the system's total inertia (which is not very controllable) and the aggregate response of the generators' control systems (which can only be controlled relatively slowly). In contrast, grid-friendly devices can act very quickly.
A grid-friendly device can respond to changes in frequency by reducing or interrupting the demand for electric power (called load) when the frequency drops below a certain threshold, and/or increasing load when the frequency rises. Although a single grid-friendly device may be a very small load, the fraction of the total load that can be controlled by frequency at any time is usually sufficient to provide under-frequency protection to the system before more drastic measures like black-outs are required.
The advantage of grid-friendly frequency response is that frequency is ubiquitous on an electric system. When a generator shuts down in one part of the system, all the loads everywhere in the system can simultaneously detect the change and respond instantly and appropriately without the need for a control system to detect the problem, a control center to make a decision, or a telecommunications network to deliver commands to millions of devices. This type of behavior changes frequency from a simple electrodynamic and control systems input to an emergent property. While there is still some controversy on the subject, it is believed that complex systems utilizing self-regulation through emergence are generally more resilient and flexible than are simpler top-down command and control systems.
Read more about this topic: Grid Friendly
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