How many isolated dc sorce for multilevel inverter

[kappa_am]

just a basic question.
I am going to implement a hybrid multilevel inverter, how can I calculate how many isolated dc source that are needed to drive IGBTS?
I know it depends on structure of inverter but I'm not sure how to assess the number of isolated dc sources.

 

[mtwieg]

So long as multiple IGBTs share an emitter node, they can use the same gate driver supply. So basically for each node with IGBT emitters, you need a gate drive supply.

 

[kappa_am]

Thanks for your reply
so a simple 3-phase inverter needs 4 isolated gate drive DC sources? A question is risen: so how a compact driver for a 3-phase inverter works just by a single dc source?
another question is that: is there any way to reduce these sources? I assessed, and it seems I need 22 isolated DC sources!!!

 

[FvM]

so how a compact driver for a 3-phase inverter works just by a single dc source?

It probably uses a bootstrap circuit. A capacitor is charged through a diode while the low-side switch is closed.

Usual high power IGBT drivers are combining the drive and error signal isolation with an isolated DC/DC converter.

 

[mtwieg]

Correct, on most high power (like >10hp) drives I've seen, actual isolated DC supplies are normally used for every IGBT (except maybe parallel IGBTs may share a gate drive supply), and the bridge is completely isolated from the control electronics.

 

[kappa_am]

so it means I have to use 22 isolated DC source for my circuit! wow. could you possibly share a simple dc source schematic suitable for 300V 5A IGBTs?

thank you very much

 

[mtwieg]

The supplies don't need to be very well regulated, so you can use a multi-output flyback topology. I've seen up to 6 outputs per flyback generated like this, but you need a good transformer with appropriate isolation ratings.