What is Feedforward control?

Control that measures disturbances or setpoint changes and, before they affect the controlled variable, applies a manipulated variable calculated from a model of the plant. It does not wait for an error to appear, so it responds quickly, but it cannot correct model errors or unmeasured disturbances, so it is usually combined with feedback control. Its path lies outside the loop, so it does not change the stability of the feedback loop. In semiconductor fabs, adjusting the conditions of a process step based on measurements from an earlier step is also called feedforward control.

Japanese name: フィードフォワード制御

Feedforward control appears in 1 practice question across 1 topic, including Control Engineering Basics.

Field: Control Engineering Basics

Try it: questions about Feedforward control

Which of the following is the correct reason for combining feedforward control with feedback control?

AFeedforward can respond to measurable disturbances and setpoint changes before an error appears, but it cannot correct unmeasured disturbances or model errors, so feedback takes care of the rest
BAdding feedforward changes the gain and phase of the loop transfer function and increases the phase margin, so the loop stays stable even with a larger feedback gain
CWith feedback alone a steady-state error always remains even with integral action, so feedforward is essential to bring the steady-state error to a constant setpoint or disturbance to zero

Show answer and explanation

Answer: A. Feedforward can respond to measurable disturbances and setpoint changes before an error appears, but it cannot correct unmeasured disturbances or model errors, so feedback takes care of the rest

Feedforward control measures disturbances or setpoint changes and, before they affect the controlled variable, applies a manipulated variable calculated from a model. It does not wait for an error to appear, so it responds quickly, but it assumes an accurate model and measurable disturbances. A common combination is therefore to let feedforward handle the main disturbances and setpoint tracking and to let feedback correct the remaining deviation. The feedforward path lies outside the loop, so it does not change the stability of the loop (the phase margin and so on).

Feedforward control in the explanations

Feedforward control measures disturbances or setpoint changes and, before they affect the controlled variable, applies a manipulated variable calculated from a model.
Which of the following is the correct reason for combining …