What is feedforward control and how does it differ from feedback control?

Feedforward control measures disturbances before they affect the process and applies corrective action preemptively. Unlike feedback control that reacts to error after it occurs, feedforward anticipates disturbances using a process model. Example: measuring feed rate change to a heat exchanger and adjusting steam flow before outlet temperature changes. Feedforward provides faster disturbance rejection but requires good disturbance measurement and accurate process model. Often combined with feedback control.