error when fixing these tunable parameters is insufficient to enforce zero feedthrough.
In such cases, you must modify the requirement or the control structure, or manually
fix some tunable parameters of your system to values that eliminate the feedthrough
term.When the constrained transfer function has several tunable blocks in series, the
software’s approach of zeroing all parameters that contribute to the overall
feedthrough might be conservative. In that case, it is sufficient to zero the feedthrough
term of one of the blocks. If you want to control which block has feedthrough fixed to
zero, you can manually fix the feedthrough of the tuned block of your choice.To fix parameters of tunable blocks to specified values, see “View and Change Block
Parameterization in Control System Tuner” on page 10-26.- This tuning goal also imposes an implicit stability constraint on the closed-loop
transfer function between the specified inputs to outputs, evaluated with loops opened
at the specified loop-opening locations. The dynamics affected by this implicit
constraint are the stabilized dynamics for this tuning goal. The Minimum decay rate
and Maximum natural frequency tuning options control the lower and upper
bounds on these implicitly constrained dynamics. If the optimization fails to meet the
default bounds, or if the default bounds conflict with other requirements, on the
Tuning tab, use Tuning Options to change the defaults.
Algorithms
When you tune a control system, the software converts each tuning goal into a normalized
scalar value f(x). Here, x is the vector of free (tunable) parameters in the control system.
The software then adjusts the parameter values to minimize f(x) or to drive f(x) below 1 if
the tuning goal is a hard constraint.For Variance Goal, f(x) is given by:fx = Attenuation⋅Ts,x 2.T(s,x) is the closed-loop transfer function from Input to Output. ⋅ 2 denotes the H 2
norm (see norm).For tuning discrete-time control systems, f(x) is given by:fx =
Attenuation
TsTz,x
2.
10 Control System Tuning