MATLAB: Does the PSBFFT_SCOPE function in SimPowerSystems 3.0 (R13SP1) return the wrong phase

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I have a model and I am analyzing the output signal after the model has run using the PSBFFT_SCOPE function. In my test cases, I am comparing the results of this function with the output of the Discrete Fourier block. The magnitudes match up well, but the phase is always wrong from the PSBFFT_SCOPE function.

Best Answer

The Discrete Fourier block and your original source blocks are based on SINUS signals. The phase returned by the PSBFFT_SCOPE function is for a COSINUS signal. To convert from COSINUS to SINUS, add 90 degrees to the phase output of the PSBFFT_SCOPE function. This will make your phase outputs match.

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MATLAB: Constant Amplitude from a Sine Wave

hi Mark,

So you are talking about square wave or Pulse train, there are many ways to generate or derive that signal from Cos/Sin wave :

Let us derive an example and derive the signal by two ways :

 Fs=120;
 t=0:1/Fs:1;
 F=50;% Hz
 %Phi=1.33;
 y=2*sin(t*F);

1.Solution 1 : using a loop :

 n=length(y);
 Pulse_train=zeros(1,n);
 Max=max(y);
 Min=min(y);
 %y(y>0)=Max;
 %y(y<0)=Min;
 for x=1:n
    if y(x)>0
        Pulse_train(x)=Max;
    elseif y(x)<0
        Pulse_train(x)=Min;
    else
        Pulse_train(x)=y(x);
    end
 end
figure, plot(t,Pulse_train), axis ([0 1 -3 3])

2.Using Built-in Mathw(c) function :

 y2=2*square(t*F);
 figure, plot(t,y2), axis ([0 1 -3 3]), hold on, plot(t,Pulse_train,'r')

There are many ways , either by using the software or using Electronic devices , and by the way take a look at this Mathw(c) Example that illustrates :The Fourier series expansion for a square-wave altough this method has the disadvantage of Gibbs effect : http://www.mathworks.com/products/matlab/examples.html?file=/products/demos/shipping/matlab/xfourier.html

MATLAB: Am I unable to use a DC Controlled Voltage Source in SimPowerSystems 3.0 (R13SP1)

This bug has been fixed for Release 14 (R14). For previous releases, please read below for any possible workarounds:

This has been verified as a bug in SimPowerSystems 3.0 (R13SP1) in the way that the Controlled Voltage Source handles the DC option.

Currently, to work around this issue, you can select the AC option with zero initial frequency and phase shift.

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Related Solutions

MATLAB: Constant Amplitude from a Sine Wave

MATLAB: Am I unable to use a DC Controlled Voltage Source in SimPowerSystems 3.0 (R13SP1)

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