Help understanding a semi-controlled full rectifier

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In summary, the Vout waveform goes to zero because both controlled rectifiers (T1 and T2) are not conducting (reverse biased). The path that io is flowing is through the resistor and inductor and through diodes D1 and D2. The inductor is creating the voltage that is dropped across the resistor. Think of the path through D1 and D2 as a wire in a conventional circuit and Vo is basically putting your meter across it. FYI - diodes D1 and D2 are acting like "flyback" or "freewheeling" diodes during this part of the cycle.
  • #1
jendrix
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Hi, I'm analysing the the circuit here

http://imgur.com/a/23GUZ

And I'm having some trouble understand the Vout waveform and why it goes to 0 when when pi<wt<pi+a

If there is always an output current wouldn't there always be a voltage out? The only thing I could think would be the voltage across the inductor cancelling out the voltage across the resistor?
 
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  • #2
I swear this looks exactly like an old professor of mine hand writing (uddin?)

To answer your question - the Vout waveform goes to zero because both controlled rectifiers (T1 and T2) are not conducting (reverse biased). Are you aware that inductors oppose changes in current by creating their own current flow by using their own stored energy? that is what is happening here.

The path that io is flowing is through the resistor and inductor and through diodes D1 and D2. And you are correct, the inductor is creating the voltage that is dropped across the resistor. think of the path through D1 and D2 as a wire in a conventional circuit and Vo is basically putting your meter across it.

FYI - diodes D1 and D2 are acting like "flyback" or "freewheeling" diodes during this part of the cycle.
 

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  • #3
It could be :)I'm working through a similar problem and found the notes here

http://www.slideshare.net/maneesh001/phase-controlled-rectifiers

Thanks for clearing up the question, it's clearer now I'm a bit rusty with inductors.

I'm still a bit confused with the voltage across the thyristors, we analysed a similar circuit in the lab and I got a different waveform. I added it to the link, it is the pink line on the oscilliscope? Any idea why there is a discrepancy?
 
  • #4
Not sure where the waveforms are
 
  • #5
Hi, I added them here

http://imgur.com/a/i67f8

They bottom (pink) signal in each one is supposed supposed to be Voltage of T1, voltage of D2 and voltage of the inductor with a firing angle of 90 degrees - I think they may have been mislabeled

Yellow -Vin
Green -Vout
Blue -Iout

But I'm having trouble what was being measure on the pink signal in each
 
  • #6
It would make sense to me if the pink was the voltage across T1 and the voltage across D2, since they conduct during the positive half cycle of Vs, and do not conduct during the negative half cycle of Vs.
 
  • #7
FOIWATER said:
It would make sense to me if the pink was the voltage across T1 and the voltage across D2, since they conduct during the positive half cycle of Vs, and do not conduct during the negative half cycle of Vs.

Thanks, that sounds right to me

Do you know what the waveform would look like for the ac source current? I thought it would be the same as Iout but 0 from

0-pi

pi+a - 2pi

Or would it be negative during the period pi+a to 2pi?

Thanks
 
  • #8
Only time the source current isn't flowing (is 0) is from $$0 - \alpha$$ $$\pi - (\pi+\alpha)$$ $$2\pi - (2\pi + \alpha)$$ $$\vdots$$ Unlike the output current, the source current flows in two directions depending on which rectifiers are on
 
  • #9
Thanks for the help, all much clearer now
 
  • #10
Not a problem
 

1. What is a semi-controlled full rectifier?

A semi-controlled full rectifier is a type of rectifier circuit that uses both controlled and uncontrolled devices to convert alternating current (AC) to direct current (DC). It typically consists of a combination of diodes and thyristors, with the thyristors being used to control the flow of current.

2. How does a semi-controlled full rectifier work?

A semi-controlled full rectifier works by using uncontrolled diodes to rectify the AC input voltage, and then using controlled thyristors to regulate the output voltage. The thyristors are triggered at specific times during the AC cycle to control the flow of current, resulting in a smoother and more controlled output voltage.

3. What are the advantages of using a semi-controlled full rectifier?

One advantage of using a semi-controlled full rectifier is that it allows for more precise control of the output voltage compared to a fully uncontrolled rectifier. It also has a lower harmonic distortion, which can result in a more efficient and stable power supply.

4. What are the applications of a semi-controlled full rectifier?

Semi-controlled full rectifiers are commonly used in industrial and power electronics applications, such as in motor drives, battery chargers, and welding machines. They are also used in power supplies for electronic equipment, such as computers and televisions.

5. What are the potential challenges of using a semi-controlled full rectifier?

One potential challenge of using a semi-controlled full rectifier is the complexity of the circuit, which may require more careful design and maintenance. Another challenge is the potential for harmonic distortion, which can affect the performance of other electronic devices connected to the same power supply.

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