Power Equation

Discussion in 'Homework Help' started by ridemx, Feb 24, 2010.

  1. ridemx

    Thread Starter New Member

    Feb 24, 2010
    1
    0
    For a homework assignment I need to write a MatLab program that plots instantaneous power through a load. It is just a simple ac voltage source V=3cos(15000t) powering a load of Z=270+471.24jΩ. Attached is the output of power that I get and It seems wrong to me. Should it be just a simple sinusoidal wave, or is what I have at all correct? If it is wrong where am I making a mistake? Thank you!!!!

    My code:

    trange=30/15000;
    dt=trange/10000;
    t=0:dt:trange;

    V=3*cos(15000*t);
    Z=270+471.24j;
    I=V./Z;
    Mag=abs(I);
    Phase=angle(I);
    Iinst=Mag.*cos((15000*t)+Phase);
    P=Iinst.*V;
    plot(t,P)

    The plot:
    [​IMG]
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    I don't use Matlab but it could be the 'Phase' term.

    Since the current phase [lag] is constant, why not simply use

    Phase=-atan(Imag(Z)/Real(Z))
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Just multiply V with I to get the power.
     
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