Simulink Control Design™ - MathWorks

magnitude represents the desired weighting function. For example, enter tf(1,[1

0.01]) to specify a high weight at low frequencies that rolls off above 0.01 rad/s.

If the tuning goal constrains a MIMO transfer function, scalar or SISO weighting

functions automatically expand to any input or output dimension. You can specify different

weights for each channel by specifying matrices or MIMO weighting functions. The

dimensions H(s) must be commensurate with the dimensions of WL and WR. For example,

if the constrained transfer function has two inputs, you can specify diag([1 10]) as

WR.

If you are tuning in discrete time, you can specify the weighting functions as discrete-time

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

functions in continuous time, the tuning software discretizes them. Specifying the

weighting functions in discrete time gives you more control over the weighting functions

near the Nyquist frequency.

Options

Use this section of the dialog box to specify additional characteristics of the weighted

gain goal.

• Stabilize I/O transfer

By default, the tuning goal imposes a stability requirement on the closed-loop transfer

function from the specified inputs to outputs, in addition to the gain constraint. If

stability is not required or cannot be achieved, select No to remove the stability

requirement. For example, if the gain constraint applies to an unstable open-loop

transfer function, select No.

• Enforce goal in frequency range

Limit the enforcement of the tuning goal to a particular frequency band. Specify the

frequency band as a row vector of the form [min,max], expressed in frequency units

of your model. For example, to create a tuning goal that applies only between 1 and

100 rad/s, enter [1,100]. By default, the tuning goal applies at all frequencies for

continuous time, and up to the Nyquist frequency for discrete time.

• Apply goal to

Use this option when tuning multiple models at once, such as an array of models

obtained by linearizing a Simulink model at different operating points or block-

parameter values. By default, active tuning goals are enforced for all models. To

10 Control System Tuning