alternative to sample function with varying sampling range

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南笙 2021-01-21 03:08

Is there an alternative to the sample function in Openmodelica, which accepts arguments which are not of type parameter? That is, the alternative should pe

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  • 2021-01-21 03:49

    Some possible solutions (you probably should check my math and just use them for inspiration; also check the RootMeanSquare block in the standard library which for some reason samples the Mean block):

    Running RMS from beginning of time (no frequency).

    model RMS
      Real signal = sin(time);
      Real rms = if time < 1e-10 then signal else sqrt(i_sq / time /* Assume start-time is 0; can also integrate the denominator using der(denom)=1 for a portable solution. Remember to guard the first period of time against division by zero */);
      Real i_sq(start=0, fixed=true) "Integrated square of the signal";
    equation
      der(i_sq) = signal^2;
    end RMS;
    

    With a fixed window, f:

    model RMS
      constant Real f = 2*2*asin(1.0);
      Real signal = sin(time);
      Real rms = if time < f then (if time < 1e-10 then signal else sqrt(i_sq / time)) else sqrt(i_sq_f / f);
      Real i_sq(start=0, fixed=true);
      Real i_sq_f = i_sq - delay(i_sq, f);
    equation
      der(i_sq) = signal^2;
    end RMS;
    

    With a variable window, f (limited by f_max):

    model RMS
      constant Real f_max = 2*2*asin(1.0);
      constant Real f = 1+abs(2*asin(time));
      Real signal = sin(time);
      Real rms = if time < f then (if time < 1e-10 then signal else sqrt(i_sq / time)) else sqrt(i_sq_f / f);
      Real i_sq(start=0, fixed=true);
      Real i_sq_f = i_sq - delay(i_sq, f, f_max);
    equation
      der(i_sq) = signal^2;
    end RMS;
    

    Variable time for sampling in synchronous Modelica: https://trac.modelica.org/Modelica/ticket/2022

    Variable time for sampling in older Modelica:

    when time>=nextEvent then
      doSampleStuff(...);
      nextEvent = calculateNextSampleTime(...);
    end when;
    
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