Representing controller in z-domain and plant in continuous domain

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Background: For a particular plant transfer function (dc-dc converter), I have calculated the transfer function of my controller based on my desired poles and zero locations. I plan to build the entire system on hardware and intend to use a microcontroller to implement the controller. For this reason, I want to simulate continuous-domain plant function in close loop with a discrete-domain controller transfer function.
Question: On Simulink (or MATLAB), please advise about how can I be able to cascade my plant transfer function (which is in s-domain) with the controller transfer function (which is in z-domain in the form of a difference equation). Eventually I want to see the step response of the closed loop system. I built a program in Simulink but eventually the presence of both continuous and z-domain transfer function pops up an error. How can I achieve this? Any other solution (outside Simulink) are also welcome.

Answers (1)

Arkadiy Turevskiy
Arkadiy Turevskiy on 25 Aug 2015
Simulink model should not be creating any errors if you are combining continuous and discrete blocks. Here is a model with a simple continuous-time transfer function and discrete-time PID Controller. It simulates fine, no errors.
  1 Comment
Anubhav
Anubhav on 26 Aug 2015
Hi Arkadiy, Thank you for our quick response. Looking at your file it seems I am lacking the correct settings. Please have a look at my attached simulink file. You would need to run the MATLAB file first (to populate the Workspace) before running the Simulink file.
When I run the file, I see the error "The 'VariableStepDiscrete' solver cannot be used to simulate block diagram 'DifferenceEqnSim' because it contains continuous states". I tried with 'Fixed Step' setting too but it doesnt help. Further, I am unable to find any settings to assign Integrator and/or Filter Method to 'Forward Euler'.
Please advise.

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