MATLAB Answers


What is the sample time in Rapid Control Prorotyping?

Asked by Orestis
on 8 Dec 2012

Hello people!

I have just started to deal with an application of Rapid Control Prototyping in Power Electronics.

I am using a typical Matlab/Simulink PC connected to a Speedgoat real time computer which has a X301 I/O card for producing PWM clocking at 33MHz.

I already have a similar application from the previous user of the setup but I need to understand what each of the configuration parameters is.

First of all I need to know what the sample time of the simulation is and what value should it have.

As I stated above the X301 I/O card has a clock frequency of 33MHz. I suspect that the xPC has a different clock frequency than its I/O card and they are not synchronized.

I also suspect that the sample time will be the instant when the translated-into-code model runs.

My thought is that the xPC (say 1GHz clock frequency) runs the model and needs some time until the next run which has to be less than the sample time.

Is that correct? Also for real time control applications doesn't the sample time affect the control response?

FIY: I have some experience with MATLAB but very little with Simulink.

Thanks!! Orestis


1 Answer

Answer by Ryan G
on 10 Dec 2012

I think you have the right idea. The only time the power/speed of the Speedgoat components should come into play is when you hit a limit on what it can process. Otherwise your application should run at the sample time you set it at.

You can find the sample time in the configuration parameters in the solver settings.

In terms of deciding what to set your sample time, this is really dependent on the control hardware that will be used and your expectations of the system response. For a slow responding system you can set this really slow, for example an industrial chemical control can be set less than 1 hz. For something with a fast response time it can be more than 1000 hz.

The hardware running the control has to be able to handle that sample time and the algorithm has to be streamlined as to not overwork the hardware.


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