Closed-loop controller: Difference between revisions

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{{Short description|Feedback controller}}

[[File:Industrial control loop.jpg|thumb|300px|Example of a single industrial control loop; showing continuously modulated control of process flow.]]

[[File:Closed Control Loop.svg|thumb|300px|Illustration of a Closed Loop Control consisting of [[Setpoint (control system)|Set Point]] <math>w(t)</math>, [[Feedback|Measured Output]] <math>y_m(t)</math>, Measured Error <math>e(t)</math>, Controller Output <math>u(t)</math>, System Input <math>u_s(t)</math>, Disturbance <math>d(t)</math>, and System Output <math>y(t)</math>]]

A '''closed-loop controller''' or '''feedback controller''' is a [[control loop]] which incorporates [[feedback]], in contrast to an ''[[open-loop controller]]'' or ''non-feedback controller''.

A closed-loop controller uses feedback to control [[state (controls)|states]] or [[Negative feedback#Overview|outputs]] of a [[dynamical system]]. Its name comes from the information path in the system: process inputs (e.g., [[voltage]] applied to an [[electric motor]]) have an effect on the process outputs (e.g., speed or torque of the motor), which is measured with [[sensor]]s and processed by the controller; the result (the control signal) is "fed back" as input to the process, closing the loop.<ref>{{Cite journal |last=Bechhoefer |first=John |date=2005-08-31 |title=Feedback for physicists: A tutorial essay on control |url=https://link.aps.org/doi/10.1103/RevModPhys.77.783 |journal=Reviews of Modern Physics |volume=77 |issue=3 |pages=783–836 |doi=10.1103/RevModPhys.77.783|url-access=subscription }}</ref>

In the case of linear [[feedback]] systems, a [[control loop]] including [[sensor]]s, control algorithms, and actuators is arranged in an attempt to regulate a variable at a [[Setpoint (control system)|setpoint]] (SP). An everyday example is the [[cruise control]] on a road vehicle; where external influences such as hills would cause speed changes, and the driver has the ability to alter the desired set speed. The [[PID algorithm]] in the controller restores the actual speed to the desired speed in an optimum way, with minimal delay or [[Overshoot (signal)|overshoot]], by controlling the power output of the vehicle's engine.

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* reduced sensitivity to parameter variations

* improved reference tracking performance

* improved rectification of random fluctuations<ref>{{Cite journal |last=Cao |first=F. J. |last2=Feito |first2=M. |date=2009-04-10 |title=Thermodynamics of feedback controlled systems |url=https://link.aps.org/doi/10.1103/PhysRevE.79.041118 |journal=Physical Review E |volume=79 |issue=4 |pages=041118 |doi=10.1103/PhysRevE.79.041118|arxiv=0805.4824 }}</ref>

In some systems, closed-loop and open-loop control are used simultaneously. In such systems, the open-loop control is termed ''[[feed forward (control)|feedforward]]'' and serves to further improve reference tracking performance.

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==PID feedback control==

{{main|PID controller}}

[[File:PID en.svg|right|thumb|400x400px|A [[block diagram]] of a PID controller in a feedback loop,; {{math|''r''(''t'')}} is the desired process value or "set point", and {{math|''y''(''t'')}} is the measured process value.]]

A proportional–integral–derivative controller (PID controller) is a [[control loop]] [[feedback mechanism]] control technique widely used in control systems.