What is the purpose of these diodes?

What is the purpose of these didoes? I couldn't find it because I don't know it's name.

Thank you.

simulate this circuit – Schematic created using CircuitLab

• Which diodes? The SCRs or the two rectifiers? Do you mean "What is the purpose of this circuit"? – TimWescott Jul 8 at 19:41
• Which didoes? D1 and D2? Their purpose depends on what the circuit is driving. Can you edit your question to add some context? Where did you see a circuit like this? – Transistor Jul 8 at 19:42
• @TimWescott not the SCRs, two rectifiers – Das D. Jul 8 at 19:43
• @Transistor it’s a rectifier used for both load supply and battery charge – Das D. Jul 8 at 19:44
• @Transistor DC bus is divided into two outputs, one for battery charge and other is for supplying a load – Das D. Jul 8 at 19:48

On the left is a full-bridge fully-controlled thyristor rectifier. With that circuit it's possible to turn DC into AC if the outer DC voltage is ever higher than the rectified AC voltage. The current flow is reversed then.

D1 stops this reversed current from the DC connector.

In addition, D2 and D1 function as a crowbar for reversed polarity on the DC connector.

There is no real reason to have D1, though, because the ability to turn DC into AC relies on firing the thyristors in the correct pattern. One could simply forbid the control logic to use that pattern.

• Thank you so much, does these process have a specific name? – Das D. Jul 8 at 19:53
• @DasD. Rectification... – KingDuken Jul 8 at 19:54
• Thank you but I don’t mean that, I mean the name of preventing reverse current – Das D. Jul 8 at 19:57
• It's preventing reverse current. – Janka Jul 8 at 19:58
• @DasD. I apologize :) I don't mean to sound like a smarta** but rectification does prevent reverse current. – KingDuken Jul 8 at 20:41