delay Output parameter in Simulink - equivalent to function dde23

Hello,

I have a discrete-time series model, where I am confused on how to replicate the delay parameter of the output_01. As of discrete, it doesnt make sense to use the "transport delay"-block, but with the block delay I wasnt able to obtain the same signal, as one should do in Matlab by calling the function dde23; from which the closest result I obtain is when using a delay length = 1/sampleTime (sampleTime = 0.1 seconds).

A screenshot of the model:

The Matlab function block is merely the two delay differential equations i used in the dde23 function in Matlab, which delivers the correct output when applying the same concept but with the ode23 function. So my actual struggle is again with the delay/transport delay block. I had tried the transport delay block as for the continous-time series, but it is well known it shouldnt work here in a discrete time series model.

Any Questions or helpful advices are welcome. Thank you in advance.

Answer 1

[MULI]

Hi David,

I understand that you are having issues in replicating the delay behaviour observed in continuous-time models within a discrete framework. You may follow these suggestions to address this:

• Ensure the delays introduced by the “Unit Delay” blocks accurately represent the delay times intended in the original `dde23` model.
• Adjust the number of “Unit Delay” blocks or their configuration to match the discrete equivalent of the continuous delays.
• For example, a delay of 1 second in a model with a `sampleTime` of 0.1 seconds requires a configuration of 10 unit delays.
• Ensure the variable delay logic correctly interprets the Clock input and adjusts the delays in a manner consistent with the discrete timestep.
• Simplify the model to isolate and address one issue at a time. Start with modelling a single delay using a “Unit Delay” block, validate this part, and then incrementally add complexity, such as variable delays or additional differential equations, validating at each step.

Hope this answers your query!