controlsystems

Control systems are devices or sets of devices that regulate the behavior of other systems. A control system measures a process variable, compares it with a desired reference, and uses the resulting error to adjust actuating inputs in order to drive the process toward the desired result. The overall arrangement is often described as a plant (the system to be controlled), a controller, sensors, and actuators, connected in a feedback loop. Disturbances and model uncertainty are typical challenges.

In an open-loop system, the output is not measured; adjustments are made solely on the basis of input. In a closed-loop system, feedback from the output is used to reduce error, improving accuracy and robustness but potentially introducing dynamics like delay or instability.

Control systems can be analog or digital, continuous-time or discrete-time, linear or nonlinear. Linear time-invariant systems are commonly analyzed with transfer functions in the Laplace domain or with state-space models. Stability and performance are assessed with criteria such as Nyquist, Bode plots, root locus, or Lyapunov-based methods.

Design aims include stability, fast settling, minimal overshoot, disturbance rejection, and robustness to model uncertainty. Classical methods (PID control, frequency-domain design) and modern methods (optimal control, state feedback, observers, model predictive control) are used.

Control systems are central to process industries, robotics, aerospace, automotive systems, and consumer electronics.

Early developments in automatic control emerged in electrical engineering and steam engines; foundational concepts were advanced by Nyquist, Bode, and later Kalman in the 1960s-70s; algorithms and digital implementations expanded in the late 20th century.