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help on discrete time control system

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lady bird
lady bird on 5 May 2015
Commented: lady bird on 10 May 2015
hello all
I'm currently working on the design of a discrete time sliding mode controller, i discretized the continuous model of the system using ZOH and started designing the controller.
At this point, i'm really confused about the results i got.
My question is, since i'm working in discrete time , am i supposed to have the control law in the form of staircase plot?
And how can i apply the sample and hold principle in simulation discrete time systems ?
Thank you so much
Looking to read from you

Answers (1)

Sriram Narayanan
Sriram Narayanan on 7 May 2015
The control law would purely depend on the desired closed-loop system behavior. Can you be more descriptive about what you mean by "apply the sample and hold principle"?
The ZOH block lets you hold the input for the desired number of samples that you specify. One thing that you should be careful about when designing a discrete control system is the correct value of the sample time for the controller. Since the controller should capture the complete system dynamics, the sample time should generally be smaller than 1/20 times the closed-loop system bandwidth.
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lady bird
lady bird on 10 May 2015
Thank you Sriram Narayanan for your answer
what i meant by sample and hold is the staircase plot format of the control law
In fact, i designed a sliding control law for the discretized model of my system, but i noticed that this control doesnt not have the staircase plot format, so it doesn't hold the same control value between two samples. Is this correct in the context of designing discrete time control laws (sliding control)
Best regards

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