What is feedforward control and how does it complement feedback?

Feedforward control measures disturbances and compensates before they affect output, rather than waiting for output deviation like feedback. It requires knowledge of disturbance effect on output. Perfect feedforward cancels disturbance completely, but model errors leave residual effect. Feedforward is combined with feedback: feedforward handles measured disturbances quickly, feedback corrects model errors and unmeasured disturbances. Common in process control where major disturbances (load changes) are measurable.