Simulink Control Design™ - MathWorks

where is the loop transfer function measured at the disturbance entry point. The

gain of is the disturbance attenuation factor, the ratio between the open- and

closed-loop sensitivities to the disturbance. Its reciprocal is the sensitivity

at the disturbance input.

Figure 1: Sample feedback loop.

The TuningGoal.Rejection requirement specifies the disturbance attenuation as a

function of frequency. The attenuation factor is greater than one inside the control

bandwidth since feedback control reduces the impact of disturbances. As a rule of thumb,

a 10-times-larger attenuation requires a 10-times-larger loop gain. For example

R1 = TuningGoal.Rejection('u',10);

R1.Focus = [0 1];

specifies that a disturbance entering at the plant input "u" should be attenuated by a

factor 10 in the frequency band from 0 to 1 rad/s.

viewGoal(R1)

13 Control System Tuning Examples