Feedforward control
High school
Consider a system that is affected by a disturbance that you can see coming. Feedforward control reacts to the disturbance before it affects the result.
Undergraduate
Consider a control system with a measured disturbance or a known reference signal. Feedforward is a control action computed from the disturbance or reference, applied before the disturbance or the change in the reference affects the output.
Examples
Examples
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Cruise control that uses both the speed error and a map of upcoming hills
High school
Cruise control that uses a map of upcoming hills is feedforward control, because it uses the map to anticipate the hills.
- Raising heater power when an outdoor thermometer reports a cold snap High school
Non-examples
Things that may be mistaken for examples.
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A thermostat
Elementary
A thermostat is not feedforward, because it reacts to the measured temperature after a disturbance has already affected it.
Properties
- Feedforward cannot correct errors it does not anticipate, such as unmeasured disturbances or model errors, so it is usually combined with feedback (a two-degree-of-freedom controller).
Distinctions involving this term
- Types of control: A controller can decide its input with or without measuring what the system is doing. Open-loop control computes the input without measuring the output, and closed-loop (feedback) control uses the measured output to correct errors. Feedforward acts on a measured disturbance or a known reference before it affects the output, and is usually combined with feedback.