Conversion of continuous time domain model to discrete time domain model

[VenkatParticipant]

Simulunk modelling steps are to
1. Develop Simulink model from the mathematical model in continuous time domain and testing
2. Converting this model to discrete time domain model and testing
3. Converting floating point arithmetic to fixed point as per the target controller requirements.

Please provide a note on converting this model to discrete time domain model.

[cKKeymaster]

Which model ?

[VenkatParticipant]

Any model.
Looking for general steps to take to do this.

Example :
1. One need to change the Solver from XYZ to discrete.
2. Need to replace integrator with discrete Integrator.
etc….

[cKKeymaster]

Pretty much thats it. Not just integrators, you will have to replace every block you drew from continuous library with its discrete equivalent. 1/z delay/memory blocks have discrete functionality only, so don’t need to worry about them. Choosing appropriate step time will be the most crucial part. You may start with variable step simulations with specific limits on min-time step and then use trial and error for a good choice of step time Ts. Too big Ts will result in diverging simulation errors thereby producing a wrong result. Hence, to ensure integrity of simulation, I’ll make your (1) as last step (assuming you are using a fixed step solver) and choose variable step (discrete) solver to start with.

You might have to troubleshoot new issues in discrete model that didn’t pop up in continuous model, e.g. resolving algebraic loops.

[Author]

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