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Feedback Control vs Feedforward Control-Difference between Feedback Control and Feedforward Control

This page compares Feedback Control vs Feedforward Control and mentions difference between Feedback Control and Feedforward Control. It mentions advantages and disadvantages of Feedback Control system and Feedforward Control system.

Feedback Control System

Feedback Control

• In feedback control system, the output of the process is continuously compared with input of the process. If there is any deviation between them, the error signal is generated which is sent to the controller.
• The controller tries to bring back the process to the desired level with the help of final control element. The figure-1 depicts generalized process in a feedback control loop.

Advantages of Feedback Control System

Following are the advantages of Feedback control system:
➨It does not require identification and measurement of any disturbance.
➨It is insensitive to modeling errors.
➨It is insensitive to parameter changes.

Disadvantages of Feedback Control System

Following are the disadvantages of Feedback control system:
➨It waits until the effect of the disturbances has been felt by the system before control action is taken.
➨It is unsatisfactory for slow processes or with significant dead time.
➨It may create instability in the closed loop response.

Feedforward Control System

Feedforward Control

• A feedforward control configuration measures the disturbance directly and takes the control action to eliminate its impact on the proces output. The figure-2 depicts feedforward control action.

In case of feedforward control, the effect of disturbance is completely eliminated as it is already sensed and corrected before reaching the process. The feedforward acts beforehand in an anticipatory manner.

Advantages of Feedforward Control System

Following are the advantages of Feedforward control system:
➨Acts before the effect of a disturbance has been felt by the system.
➨It is good for slow system or with significant dead time.
➨It does not introduce instability in the closed loop.

Disadvantages of Feedforward Control System

Following are the disadvantages of Feedforward control system:
➨It requires identification of all possible disturbances and their direct measurement.
➨It can not cope with unmeasured disturbances.
➨It is sensitive to process parameter variations.
➨It requires good knowledge of the process model.

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