Simulink Control Design™ - MathWorks

• Inject disturbances at the following locations

Select one or more signal locations in your model at which to measure the disturbance

attenuation. To constrain a SISO response, select a single-valued location. For

example, to attenuate disturbance at a location named 'y', click Add signal to

list and select 'y'. To constrain a MIMO response, select multiple signals or a vector-

valued signal.

• Evaluate disturbance rejection with the following loops open

Select one or more signal locations in your model at which to open a feedback loop for

the purpose of evaluating this tuning goal. The tuning goal is evaluated against the

open-loop configuration created by opening feedback loops at the locations you

identify. For example, to evaluate the tuning goal with an opening at a location named

'x', click Add signal to list and select 'x'.

TipTo highlight any selected signal in the Simulink model, click. To remove a signal

from the input or output list, click. When you have selected multiple signals, you can

reorder them using and. For more information on how to specify signal locations

for a tuning goal, see “Specify Goals for Interactive Tuning” on page 10-39.

Rejection Performance

Specify the minimum disturbance attenuation as a function of frequency.

Enter a SISO numeric LTI model whose magnitude represents the desired attenuation

profile as a function of frequency. For example, you can specify a smooth transfer function

(tf, zpk, or ss model). Alternatively, you can sketch a piecewise minimum disturbance

rejection using an frd model. When you do so, the software automatically maps the

profile to a smooth transfer function that approximates the desired minimum disturbance

rejection. For example, to specify an attenuation factor of 100 (40 dB) below 1 rad/s, that

gradually drops to 1 (0 dB) past 10 rad/s, enter frd([100 100 1 1],[0 1 10 100]).

If you are tuning in discrete time, you can specify the attenuation profile as a discrete-

time model with the same sampling time as you use for tuning. If you specify the

attenuation profile in continuous time, the tuning software discretizes it. Specifying the

attenuation profile in discrete time gives you more control over the profile near the

Nyquist frequency.

10 Control System Tuning