predisturbance

Predisturbance is a concept in control theory and signal processing that refers to techniques which apply a compensating action before a disturbance affects a system, with the aim of maintaining the desired output. It is a form of disturbance rejection implemented in a feedforward fashion and is often described as pre-compensation or disturbance pre-cancellation. Unlike feedback control, which corrects errors after they appear, predisturbance relies on a model or measurements of the disturbance to cancel its effect at the plant input or state.

Implementation typically requires an estimate or measurement of the disturbance signal and a model of how that disturbance propagates through the system. The predisturbance signal is designed so that, when combined with the control input, the resulting effect at the output is minimized or nullified. Variants include static pre-compensation, dynamic pre-compensation using a dynamic model, disturbance observers that estimate the disturbance in real time, and model predictive control that optimizes input trajectories under predicted disturbances.

Common applications appear in aerospace (compensating for gusts), robotics (payload changes or external forces), process control (flow or feed disturbances), and power electronics (load or impedance variations). Challenges include the need for an accurate disturbance model, sensitivity to measurement noise, unmeasured disturbances, and ensuring robustness when disturbances deviate from the model.

Predisturbance is often used in combination with feedback control to provide both proactive and reactive disturbance rejection, offering improved performance in the presence of repeatable or measurable disturbances.