Hey guys. I'm just curious if you guys have ever taken a peak inside the more beefy inverters?

Do they still use IGBTs? Do some of them start using more exotic silicon?

What's the cutoff?

Just now, Adagio said:

Hey guys. I'm just curious if you guys have ever taken a peak inside the more beefy inverters?

Do they still use IGBTs?

Yes.

Yes.

Just now, Adagio said:

Do some of them start using more exotic silicon?

No.

41 minutes ago, Adagio said:

Do they still use IGBTs?

IGBTs don't parallel well, unlike MOSFETs. But MOSFETs typically can't do the higher voltage, at least not at higher power. So you end up with giant IGBTs. They can be in modules the size of cigarette packets, where the connections bolt to the semiconductor.

Here are some IGBT modules from a Prius hybrid car:

Often the snubber capacitors are film capacitors with really stiff tabs that bold directly to the IGBT. Layout is critical in all inverters, but even more so at higher power levels, since the magic smoke is stored at higher pressure. Often interconnections are via bus bars, or sometimes specially shaped flat conductors:

 

https://forums.aeva.asn.au/uploads/689/controller_mods_002_sm.jpg

 

Edited October 7, 20223 yr by Coulomb

7 hours ago, Coulomb said:

IGBTs don't parallel well, unlike MOSFETs. But MOSFETs typically can't do the higher voltage, at least not at higher power. So you end up with giant IGBTs. They can be in modules the size of cigarette packets, where the connections bolt to the semiconductor.

Here are some IGBT modules from a Prius hybrid car:

Often the snubber capacitors are film capacitors with really stiff tabs that bold directly to the IGBT. Layout is critical in all inverters, but even more so at higher power levels, since the magic smoke is stored at higher pressure. Often interconnections are via bus bars, or sometimes specially shaped flat conductors:

 

https://forums.aeva.asn.au/uploads/689/controller_mods_002_sm.jpg

 

Ah yes. I've seen those.

Thanks Coulomb.

I was just curious.

19 hours ago, Coulomb said:

IGBTs don't parallel well

Interesting point you bring up, but there is an interesting hack:

Since with IGBTs, current capacity is usually not a concern in 230VAC inverters, you want to share power dissipation between devices. (This is because if you select devices with suitable power dissipation capabilities, the current rating will usually be much higher than required).

So what you can do is to interleave the IGBTs - use one for one cycle, another for the next, and you can repeat that with quite a number of devices. This also reduces switching losses, as each IGBT is effectively switching at a much lower frequency. It does complicate the design quite a bit, so it is definitely easier to just opt for bigger devices.

But because the larger devices usually have lower Vce at a given current level, you have to run the numbers and weigh the tradeoffs. That said, I have not seen a design like this in the wild - probably because of the more complicated PWM hardware requirements.