Hybrid times, subsystems and model referencing

Hi all,

I created a Simulink model where a first-order process is controlled by a PI controller. The process is continuous-time, while the PI controller is discrete-time with a certain period (=0.05). By including both the process and the PI controller in two distinct subsystems, I do not get any warning or error, even when it is used the ODE45 Solver.

I tried to do the same by using model referencing, namely the process and the PI controller are saved in different models. However, in this case, I get the following warnings:

Warning: Inconsistent sample times. Sample time ([0, 1]) of signal driving input port 1 of 'ModRefDT/Model1' differs from the expected sample time ([0.05, 0]) at this input port.

Warning: Inconsistent sample times. Sample time ([0, 1]) of signal driving input port 2 of 'ModRefDT/Model1' differs from the expected sample time ([0.05, 0]) at this input port.

Warning: Inconsistent sample times. Sample time ([0.05, 0]) of signal driving input port 1 of 'ModRefDT/Model' differs from the expected sample time ([0, 0]) at this input port.

Such warnings can be avoided if using a fixed-step solver. Now I wonder why ODE45 works fine if I use subsystems, and it doesn't ( I get warnings) when using model referencing. Could you help me, please? Thanks

Ubaldo

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Answer 1

[Nirmal Gunaseelan]

The model reference instances have to be compatible with the solver type specified in the top model. Take a look at these requirements that might help configuring your top model and references.

[Ubaldo Tiberi]

That's right. The problem seems also to be solved by using Rate Transition blocks at the input and at the output of the PI controller block.