How to write StateFcn in Nonlinear MPC Controller

Nowdays, I am doing some works about visual servoing. But there are some troubles with the nonlinear MPC Controller. I have read the example named 'Control Quadruple-Tank Using Passivity-Based Nonlinear MPC'. There is a code nlobj.Model.StateFcn = "stateFcnQuadrupleTank".

I opened it, and the content shows as a picture as follows. It looks like the example uses code to express the dynamic system. I want to know if I can use a Simulink model, which is already done, to replace the code.

Thank a lot for your help!

Answer 1

[Shubham]

Hi Frank,

I understand that you want to use a Simulink model as a state function of a Nonlinear MPC Controller.

To use a Simulink model instead of a code to express dynamic system, say for example "stateFcnQuadrupleTank", you need to follow these steps:

• Ensure that your Simulink model correctly represents correct dynamics of the system
• The model should have input and outputs corresponding to the states and control inputs
• Generate an S-Function from your Simulink model using Simulink Encoder (if the model is simple, then directly use MATLAB Function block to define state conditions directly) which is given below:

% Load the Simulink model 
load_system('model_name'); 

% Generate the S-Function 
rtwbuild('model_name'); 

• You can use the "nlmpc" object in MATLAB to define the state function using the generated S-Function:

% Define the Nonlinear MPC object 
nlobj = nlmpc(4, 1); % Assuming 4 states and 1 output for the quadruple-tank system 

% Define the state function using the generated S-Function 
nlobj.Model.StateFcn = 'model_name_sfcn'; 

Please refer to the following documentation link for more information on how to use S-Function:

https://mathworks.com/help/rtw/ug/generate-code-for-a-model-with-simulink-functions.html?searchHighlight=s%20function%20for%20simulink%20model&s_tid=srchtitle_support_results_1_s%20function%20for%20simulink%20model