Constraints violation in MPC design

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Osamah Ali Mohammed Saad 2023-10-24

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评论： Osamah Ali Mohammed Saad 2023-12-8

I am building a mpc on MATLAB/Simulink. I applied some equality and inequality constraints to the controller (states and unputs); however, there are inequality state constraints that are violated. What might be the reason behind that?

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Emmanouil Tzorakoleftherakis 2023-10-27

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The more constraints you are adding, the smaller the solutions space, the harder it gets for the solver to find a solution. If your constraints are too restrictive, you may be asking the controller to solve an infeasible optimization problem. You can easily check if that's the case by making sure that your constraints are soft. And always make sure to check the exit flag status to see if the controller was actually able to solve the problem or not.

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Jordan Olson 2023-12-7

@Osamah Ali Mohammed Saad Thanks for uploading your files! I took a look through them and simulated the controller on my end, and I'm not seeing any constraint violation. State 3 (SOC) is the only state with constraints in the code you provided, it looks like all the others are commented out. State 3 stays within its hard constraints ([0.1, 1]) during the entire simulation.

All the constraints on the MVs appear to be satisfied as well, except for some very small violations of the RateMin constraint on MV 3 (mass flow), which is a soft constraint.

Could you elaborate on what constraint violations you are seeing on your end?

Osamah Ali Mohammed Saad 2023-12-8

Thank you Jordan for your response. A custom inequalities constraints file is used to apply softened state constraints. These constraints are violated, but the slack variable value remains unchanged (0 = unused). However, when I reduce the sampling time, the solver is able to detect the constraints violation and uses the slack variable accordingly.

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