Minimum Loop Gain Goal
Purpose
Boost gain of feedback loops at low frequency when using Control System Tuner.Description
Minimum Loop Gain Goal enforces a minimum loop gain in a particular frequency band.
This tuning goal is useful, for example, for improving disturbance rejection at a particular
location.Minimum Loop Gain Goal imposes a minimum gain on the open-loop frequency response
(L) at a specified location in your control system. You specify the minimum open-loop gain
as a function of frequency (a minimum gain profile). For MIMO feedback loops, the
specified gain profile is interpreted as a lower bound on the smallest singular value of L.When you tune a control system, the minimum gain profile is converted to a minimum
gain constraint on the inverse of the sensitivity function, inv(S) = (I + L).The following figure shows a typical specified minimum gain profile (dashed line) and a
resulting tuned loop gain, L (blue line). The green region represents gain profile values
that are forbidden by this requirement. The figure shows that when L is much larger than
1, imposing a minimum gain on inv(S) is a good proxy for a minimum open-loop gain.10 Control System Tuning