# 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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0
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

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?

Jacky

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Jul 12, 2008
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3. ### mik3 Senior Member

Feb 4, 2008
4,846
63
where is β in the equation?

where is i(t) in the circuit?

4. ### izzy Thread Starter New Member

Jul 12, 2008
8
0

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
4,846
63
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
8
0

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.

Jul 12, 2008
8
0
No one?

10. ### izzy Thread Starter New Member

Jul 12, 2008
8
0
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.