RMS of a current

Hi,

I have a Simulink-Model of a level 2 Back to Back converter, and I need one value of the root mean square value of a current from the model.

There is a RMS Block in Simulink, but it gives me a curve (vector), but I need one value (the overall value of the RMS from that one current).

So in this example, phase a of the input current. The scope gives following:

And here all the input currents:

I tried exporting the RMS value as timeseries to Matlab and simply using

Rms = mean(Ia_in);

Another option I found was sending the raw value (without the RMS block) of the current to the workspace and then

          Ia_in_rms = sqrt(mean(Ia_in.^2));

They don't give the same result. Which one is the "true" RMS value?

Sorry but my understanding of this is quite limited.

Answer 1

[Naman Chaturvedi]

Hi Marino,

Select the correct RMS block from the library: 'DSP System Toolbox/Statistics'. Check the 'Running RMS' option in the block parameters dialogue box of your RMS block. The last value of the timeseries signal output by the RMS block will give you the desired RMS of the whole signal. Hope this helps.