Constant Amplitude from a Sine Wave

I am trying to transform a normal 50Hz sine wave (frequency will not change) into a constant amplitude value. I have done so with an RMS block in SimPowerSystems. But I am wondering what way would you do it? Any suggestions.

Answer 1

[Youssef Khmou]

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

[Youssef Khmou]

note : if you want to compute the Frequency you have to add the term "2*pi" inside Cos/sin and square functions !

[Mark]

Thanks for you answer, I see what you are doing.

I am using this in a power system model in Simulink (SimPowerSystems). At one of my buses I am getting an 11kV sine wave. I want to convert it to a constant amplitude value in order to use it in a proportional control system against a constant reference. Is there a way you know of using blocks in simulink do that?

[Youssef Khmou]

hi,

i Do not know exactly the function that performs that but :

1.type in the command prompt "dsplib" and take a look at the library try to find something useful .

2. Create a Embedded M file in Simulink, i think this is good solution, a M-file as function where the input is the 11Kv Sinusoid and write the conditions necessary to obtain the pulse train

i hope this helps