RMS Value:
In a dynamic system simulation you can readily generate an instantaneous
power value that can be recorded simply by using a volts*current
product or any other dimensionally equivalent product.
If however you want to do some averaging of the power level then you
must have a record of that instantaneous value and do the averaging
over the length of the record, which your request implies you have and
therefore implies a post processing operation. You can partition the
record into whatever shorter lengths you want and generate true RMS
values over those time segments. But beware, if the model is simulating
a fixed frequency (e.g.50Hz) power system then the periods must be
integer multiples of the cycle time.
If you want a value that appears like a metered value might appear then
you can put the product term through a 1st order lag (exponentially
weighted effect)
G(s)=1/(1+sT) // xdot=(1/T)*(Input- x);
and imitate the behaviour of a meter. All you have to do is chose the
"time constant",T, of the meter. e.g several cycles.
The MATLAB (2017a) Moving RMS includes the exponential weighting option
and the true moving window version as well. I expect it could be
replicated in XCOS with a SciLab function.
Mike.
==================
On 19/05/2017 05:51, Sachverständigenbüro Niedermaier Holger wrote:
Dear all,
by simulating an electrical power circuit I’d like to plot the voltage and the
current over time, which is easy to perform by using the scope block.
In addition to the signal recorded I’d like to calculate the TRMS value of the
plotted current and voltage signal.
Unfortunately Xcos does not include a TRMS block like e.g. Simulink do.
Because I’m so far not so familiar with Xcos and Scilab I’d like to ask the
community for support.
Does anybody have a good idea or advise how to get the TRMS value of the
recorded signal?
Thanks and nice weekend
Holger
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Dr.M.J.McCann,MJMcCann-Consulting
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