View Single Post
Old 12-20-2009, 10:04 PM   #177 (permalink)
adamj12b
Master EcoModder
 
Join Date: Apr 2009
Location: Charlton MA, USA
Posts: 463

EVVette - '71 Chevy Corvette Coupe
Thanks: 31
Thanked 183 Times in 94 Posts
OK,

Im a little late on this post...I was hanging christmas lights....LOL

Im going to try to clear up some of the questions about the Isolation and power converters for the IPM's and IGBT's.

First off, Isolation is mandatory with and AC system...Its mandatory for a DC system as well. Anyways, without isolation, the control logic and power stages would share a common ground, and with that, you have basically created a common ground between the traction battery and the 12V car system battery. This is VERY dangerous. So if you were to touch any of the positive terminals on the battery while touching the frame of the car...

OK, so the isolation uses a minimum of 4 isolated DC-DC converters. One for the 3 low sides and 1 for each high side. They way this work, is because of the internal configuration of the IPM. The low side of the IGTB is connects to the negative battery terminal, this is also connected to the negative supply terminal for the logic of the IPM.

So a little off track for the High side. The way the bootstrap caps work is they charge when the phase is pulled to the negative side of the pack. Since this is common to the negative supply of the logic, the cap charges with 15VDC. when the IGBT goes high, the logic uses the power stored in the caps to power the gate.

Now the reason for not having a common isolated supply for the whole module has to do with the internal wiring distance, delay and inductance. So when you have 3 IGBT's it is not possible to pick a common point to tie the the supply to, So you use 3 so they are all powered at the same time with the same delay, because they are all symmetrical.

So, with the Ebay IGBT modules, you will need 2 small isolated DC-DC converters to power each one. One for High side and one for Low side. There will be two opto-isolator's, One for High and one for Low. Each will get its power from the respective DC-DC converter.

Thats what I have for now. Some time tomorrow, I will post a schematic showing what I mean.

-Adam
__________________
www.EVVette.com - 1971 Corvette Coupe Conversion to all Electric!
www.AdamBrunette.com - Machining, CNC, Robotics and Electronics.

You can download RTD Explorer for the Cougar controllers at www.EVVette.com
  Reply With Quote
The Following 3 Users Say Thank You to adamj12b For This Useful Post:
lapwing (12-30-2009), mpgmike (01-25-2022), sangito (08-24-2014)