loopview(G,C) plots
characteristics of the following positive-feedback, multi-input, multi-output
(MIMO) feedback loop with plant G and controller C.

Use loopview to analyze the performance
of a tuned control system you obtain using looptune.

Note:
If you are tuning a Simulink^{®} model with looptune through
an slTuner interface, analyze the performance
of your control system using loopview for slTuner (requires Simulink Control Design™).

loopview plots the singular values of:

Open-loop frequency responses G*C and C*G

Sensitivity function S = inv(1-G*C) and
complementary sensitivity T = 1-S

Maximum (target), actual (tuned), and normalized MIMO
stability margins. loopview plots the multi-loop
disk margin (see loopmargin).
Use this plot to verify that the stability margins of the tuned system
do not significantly exceed the target value.

For more information about singular values, see sigma.

loopview(G,C,info) uses
the info structure returned by looptune. This syntax also plots the
target and tuned values of tuning constraints imposed on the system.
Additional plots include:

Singular values of the maximum allowed S and T.
The curve marked S/T Max shows the maximum allowed S on
the low-frequency side of the plot, and the maximum allowed T on
the high-frequency side. These curves are the constraints that looptune imposes
on S and T to enforce the
target crossover range wc.

Target and tuned values of constraints imposed by
any tuning goal requirements you used with looptune.

Use loopview with the info structure
to assist in troubleshooting when tuning fails to meet all requirements.

Input Arguments

G

Numeric LTI model or
tunable genss model representing
the plant in a control system. The plant is the portion of a control
system whose outputs are sensor signals (measurements), and whose
inputs are actuator signals (controls).

You can obtain G as an output argument
from looptune when you tune your control system.

C

genss model representing
the controller in a control system. The controller is the portion
of your control system that receives sensor signals (measurements)
as inputs and produces actuator signals (controls) as outputs.

You can obtain C as an output argument
from looptune when you tune your control system.

info

info structure returned by looptune during control system tuning.

Tune a control system, and use loopview to examine the performance of the tuned controller.

s = tf('s');
G = 1/(75*s+1)*[87.8 -86.4; 108.2 -109.6];
G.InputName = {'qL','qV'};
G.OutputName = 'y';
D = ltiblock.gain('Decoupler',eye(2));
PI_L = ltiblock.pid('PI_L','pi');
PI_L.OutputName = 'qL';
PI_V = ltiblock.pid('PI_V','pi');
PI_V.OutputName = 'qV';
sum = sumblk('e = r - y',2);
C0 = (blkdiag(PI_L,PI_V)*D)*sum;
wc = [0.1,1];
options = looptuneOptions('RandomStart',5);
[G,C,gam,info] = looptune(-G,C0,wc,options);
loopview(G,C,info)

Final: Peak gain = 0.859, Iterations = 24
Achieved target gain value TargetGain=1.

The first plot shows that the open-loop gain crossovers fall close to the specified interval [0.1,1]. This plot also includes the tuned values of the sensitivity function S = inv(1-G*C) and complementary sensitivity T = 1-S. These curves reflect the constraints that looptune imposes on S and T to enforce the target crossover range wc.

The second and third plots show that the MIMO stability margins of the tuned system fall well within the target range.