Power electronics - Rectifier help required

Discussion in 'Homework Help' started by izzy, Dec 6, 2008.

  1. izzy

    Thread Starter New Member

    Jul 12, 2008
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    Hello forum members,

    I am trying to prepare for my final exam, and I am confused about one of the rectifier problem which might be asked in the final. I would really appreciate if anyone can help me on this!

    Here is the problem

    Schematic:
    http://img370.imageshack.us/my.php?image=17823553lk1.jpg


    [​IMG]

    Vsource = V mag Sin(wt+ a)

    a = Commencement angle; a>0
    β = Conduction angle; β<2 pi


    1. Find i(t)

    2.At what time does D1 current falls to 0?

    3.At what time does inductor current falls to 0?

    4. What is the DC current flowing through the source?

    5. How much power is delivered to the battery?

    6. What is the power factor of the source?



    Thanks in advance!
    Jacky
     
  2. izzy

    Thread Starter New Member

    Jul 12, 2008
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    Anyone? Please?
     
  3. mik3

    Senior Member

    Feb 4, 2008
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    where is β in the equation?

    where is i(t) in the circuit?
     
  4. izzy

    Thread Starter New Member

    Jul 12, 2008
    8
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    Thanks for you reply.

    i(t) is the current through the inductor.

    I am not sure about beta. All I know is it is the conduction angle.:(

    I think the beta only tell us that the current is continious or something.
     
    Last edited: Dec 7, 2008
  5. mik3

    Senior Member

    Feb 4, 2008
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    If you assume ideal diodes (no voltage drop across them when they conduct), then D1 will conduct when V3 exceeds 8V (battery voltage). Thus to find the conduction angle of D1 calculate at which angle Vsource = V mag Sin(wt+ a) equals 8V. Also, D2 will conduct when V3 reaches its peak value (12V) and starts to decrease.
     
  6. izzy

    Thread Starter New Member

    Jul 12, 2008
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    Thanks for your reply once again.

    Yes I tried that before But I couldnt get the right answer.

    First of all let me make sure I have the right equation for i(t)

    i(t) = -(Vm /Lω) Cos(120*pi*t + a) - Vs/L + (Vm /Lω) Cos(a)

    Right?

    Ok now for
    2.At what time does D1 current falls to 0?

    I set V3 = V4

    12 Sin(120*pi*t + a) = 8
    Sin(120*pi*t + a) = 2/3
    120*pi*t + a = arc Sin (2/3)
    120*pi*t + a = 0.72

    Now what should I do? I am not sure.


    Any idea on no. 3 and no. 4?


    BTW, I found

    a = the angle in radians at which the source current begins to flow

    β = is the angle at which the source current ceases
     
    Last edited: Dec 7, 2008
  7. izzy

    Thread Starter New Member

    Jul 12, 2008
    8
    0
    Any thoughts?
     
  8. izzy

    Thread Starter New Member

    Jul 12, 2008
    8
    0
    I have Final exam tomorrow, I would appreciate of anyone could help me here.
     
  9. izzy

    Thread Starter New Member

    Jul 12, 2008
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    No one? :(
     
  10. izzy

    Thread Starter New Member

    Jul 12, 2008
    8
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    Will the answer for both of these questions be same?


    2.At what time does D1 current falls to 0?

    3.At what time does inductor current falls to 0?
     
  11. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You need to make circuit analysis to find these values.
     
  12. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    If you don't know how to analyze it, simulate it with a simulation software to see what is going on.
     
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