How many isolated dc sorce for multilevel inverter

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kappa_am

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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.
 

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.
 

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!!!
 

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

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.
 
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
 

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.
 

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