Why does the error message "Plant model cannot be a pure direct feed-through system without additional dynamics error" appear when configuring MPC Controller?

I am adding an "MPC Controller" block to my Simulink model and configured it using "MPC Designer". I have mapped the "Manipulated Variables" and "Measured Outputs" to Simulink signals in my model. When I click "Import", the following error message appears:

Plant model cannot be a pure direct feed-through system without additional dynamics error.

How can I resolve this error?

Answer 1

[MathWorks Support Team]

MPC Controllers include a linearized model of the plant. MPC design thus involves linearizing the Simulink model with an input at the "Measured Outputs" signal, and an open-loop output at the "Manipulated Variable" signal. If the model linearizes to "ss(0, 0, 0, 0)", then the above error message will appear. To resolve this error, please follow the following steps:

1. Try placing an input and open-loop output linearization point at these signals, such as shown in:

https://www.mathworks.com/help/slcontrol/ug/linearize-simulink-model.html

2. Create an operating point at different time points in your model using the "findop" function and choose a time point that is indicative of standard operating conditions of your plant model. Please refer to the following documentation for details on using the "findop" function:

https://www.mathworks.com/help/slcontrol/ug/findop.html

3. Linearize your model, and ensure that the linearization does not equal "ss(0, 0, 0, 0)".

4. Go back to the "MPC Designer". Go the "Simulink Operating Point" section, and and use the previously used time point as your operating point, as shown in:

https://www.mathworks.com/help/mpc/gs/designing-a-model-predictive-controller-for-a-simulink-plant.html