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Compute Steady-State Gain

This example shows how to analyze a Model Predictive Controller using cloffset. The function computes the closed-loop, steady-state gain for each output when subjected to a sustained, 1-unit disturbance added to each output. It assumes that no constraints will be encountered.

For example, consider the controller operating at the final steady-state of the nonlinear CSTR of the previous section. To compute its gain, type

cloffset(MPCobj)

which gives the result:

ans =

    1.0000   14.5910
   -0.0000   -0.0000

The interpretation is that the controller doesn't react to a sustained disturbance of 1 unit in the first output (the reactor temperature). Recall that we assigned zero weight to this output in the controller design, so the controller ignores deviations from its setpoint. The same disturbance has no effect on the second output (the 2,1 element is zero).

If there is a 1-unit disturbance in the second output, the controller reacts, and the first output increases 14.59 units. This is again due to the zero weight on this output. The second output stays at its setpoint (the 2,2 element is zero).

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