Control theory
![A block diagram of a negative feedback control system. Illustrates the concept of using a feedback loop to control the behavior of a system by comparing it's output to a desired value, and applying the difference as an error signal to dynamically change the output so it is closer to the desired output](/Images/godic/202501/27/Feedback_loop_with_descriptions.svg3301.png")
![Centrifugal governor in a Boulton & Watt engine of 1788](/Images/godic/202501/27/Boulton_and_Watt_centrifugal_governor-MJ3301.jpg")
![](/Images/godic/202501/27/Simple_feedback_control_loop2.svg3301.png")
Control theory is an interdisciplinary branch of engineering and mathematics that deals with the behavior of dynamical systems with inputs, and how their behavior is modified by feedback. The usual objective of control theory is to control a system, often called the plant, so its output follows a desired control signal, called the reference, which may be a fixed or changing value. To do this a controller is designed, which monitors the output and compares it with the reference. The difference between actual and desired output, called the error signal, is applied as feedback to the input of the system, to bring the actual output closer to the reference. Some topics studied in control theory are stability (whether the output will converge to the reference value or oscillate about it), controllability and observability.