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Discussion Starter #1
First of all, I apologise if it's the wrong section.

Ok, now the question :)

I have uploaded the picture of an rectifier that is operating in inverter mode, from a PDF that I'm reading.

During V(source)'s positive cycle the current goes through T1 through the motor and then back to T4. So far so good but...

at some point it says that when V(source) changes polarity and is now negative the current will change direction through the motor(sustained by the back EMF of the motor) but keep it's direction through the inverter structure. Now I'm a beginner and I do not understand how this happens. How can it change the direction through the motor yet not change direction through the inverter structure? I don't see what path it could take.

I understand it has something to do with the fire angle of the thyristors beiing over 90 degrees. So I guess, and please correct me if I'm wrong that by changing the firing angle of a thyristor-pair you can make the current change it's direction through the motor but what makes it keep it's direction through the inverter structure?(the path allowed by thyristors).

If possible please explain the fire angle with a clear explanation(keep in mind I'm no expert :) ).

Thank you for reading!
 

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Light Emitting Decoration
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I think it's like a self resetting DPDT switch that rests in the middle.
Every drop to zero turns them all off. When you throw the switch in reverse every "mountain", you'll make DC.
http://www.reliance.com/mtr/images/mtdfig6.gif


if you connected the ends of DPDT and middle connected to battery, you can change the polarity of output.
 

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Just trying to get home
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T3. Look at the polarities on the transformer secondary. T1...T3..T1...T3...etc.
 

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Discussion Starter #4
Thank you for the answers. I think I got it. It was ambigous explanation the current doesn't change direction through the motor(it would be impossible as it's a DC current motor). The back EMF of the motor gets a higher potential when V source gets negative polarity so the current will now go from motor-t4t1-source instead of source-t1t4-motor...
 

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Light Emitting Decoration
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However my question stands why does an increased fire angle of a thyristor means lower current???
Like a light dimmer. Each "mountain" is 180degrees and you reach the summit at 90 degrees of delay (firing angle). The further you delay, the less power delivered.
 

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By the way, this is not an "inverter", it is a DC drive feeding a DC motor. The delaying of the firing angle has to do with changing the voltage going to the motor, nothing else. If you look up the term "phase angle firing of SCRs"you should be able to find out more details on the general technique.

I'm not sure where you got all the other stuff.
 

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Sparks fly from my finger
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All it is is a bridge rectifier that you can control the turn on point of the diodes. The diodes have been replaced with scrs and circuitry added to fire them.
 

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I think he means pushing the power back into the power source in regenerative mode.
 
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