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  #1  
Old 07-20-2008, 12:55 AM
etischer etischer is offline
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Default IGBT firing circuit, building my own 90hp AC drive.

Im in the process of trying to upgrade a 2 hp AC drive to 90 hp. Im doing this by using bigger external IGBTs.

I'm making progress. The IGBT's I have won't be easy to integrate, but I have been learning.

Here is what the firing signal looks like. This is a PWM version of the top half of a sine wave being fed into the drives IGBT Pack



Zoomed in it looks like a square wave with varying width pulses. This is with no IGBT connected, the voltage increased from 14v to 18v because the load was removed.



Here I have my external "big" IGBT connected, and the firing circuit falls on its face, only 5v pk-to-pk.



I think I have sourced some IGBT's with less trigger current requirements, and hope to have my motor turning soon! Checking to see if anyone has and free advice they'd like to share =)


Here is the IGBT I took out.



Last edited by etischer; 07-20-2008 at 12:58 AM.
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  #2  
Old 07-20-2008, 01:11 AM
Nate Nate is offline
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Default Re: IGBT firing circuit, building my own 90hp AC drive.

Your big IGBT module has way to much gate capacitance for the factory 2HP drivers to handle. You may need to hook a much bigger driver to the IGBT module then fire this driver with the 2HP driver output.
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Old 07-20-2008, 08:56 AM
etischer etischer is offline
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Default Re: IGBT firing circuit, building my own 90hp AC drive.

Wow, there are some smart people in this forum, I wasn't expecting to get an answer.

It makes sense that the capacitance is too large, instead of an instantaneous rise, it is slowly ramping up as the cap charges. This also explains why my IGBT was acting like a latch.

I didn't see a capacitance spec on the data sheet for this device. I think the "smart power module" I'm planning to buy will work better than an IGBT. The power module has the 7 igbts and some extra circuitry to fire the igbts. We'll see next week if it works!

thanks for a quick reply.
Eric.
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Old 07-20-2008, 09:05 AM
TheSGC TheSGC is offline
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Default Re: IGBT firing circuit, building my own 90hp AC drive.

I want that Fluke meter you have..... I have built a DC controller that uses an IGBT and it seems to work on all my bench tests.

Definately check out the specs on the driver. I ended up with a homemade driver using transistors to drive up the voltage. It's crude, but it works.
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Old 07-20-2008, 12:20 PM
etischer etischer is offline
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Default Re: IGBT firing circuit, building my own 90hp AC drive.

I bought the fluke scopemeter on ebay for $425 after shipping. Looks like it was never used. I even used it for a couple hours using the battery. They are on there all the time, the Fluke 123 scopemeter was what I really wanted, but got such a good deal on this, I don't mind the bigger size.

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Originally Posted by TheSGC View Post
I want that Fluke meter you have..... I have built a DC controller that uses an IGBT and it seems to work on all my bench tests.

Definately check out the specs on the driver. I ended up with a homemade driver using transistors to drive up the voltage. It's crude, but it works.
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Old 07-20-2008, 04:34 PM
Nate Nate is offline
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Default Re: IGBT firing circuit, building my own 90hp AC drive.

Yes there are some very smart people here! I don't consider myself to be one of them though. I just know those big modules have some large gate capacitance but then they are very high amperage. The gate capacitance is actually filtering your output signal and trying to make a smoother DC out of it.

I like your meter also! I will have to check with eBay, $425 for a Fluke Scopemeter is a very good price.
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Old 07-20-2008, 04:46 PM
aeroscott aeroscott is offline
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Default Re: IGBT firing circuit, building my own 90hp AC drive.

Quote:
Originally Posted by Nate View Post
Yes there are some very smart people here! I don't consider myself to be one of them though. I just know those big modules have some large gate capacitance but then they are very high amperage. The gate capacitance is actually filtering your output signal and trying to make a smoother DC out of it.

I like your meter also! I will have to check with eBay, $425 for a Fluke Scopemeter is a very good price.
a little peace of very smart is great , then we just keep adding to that, great work in helping me understand ,thanks
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Old 07-20-2008, 07:01 PM
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lazzer408 lazzer408 is offline
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Default Re: IGBT firing circuit, building my own 90hp AC drive.

Try sticking a TC4422 or 4452 in line with your gate signal.
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Old 07-20-2008, 09:49 PM
etischer etischer is offline
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Default Re: IGBT firing circuit, building my own 90hp AC drive.

Awesome, I'll try that first.

...actually, not sure this will work because I need an floating output. The trigger voltage for the IGBT is applied between the collector & emitter. For 3 IGBT's the emitter is ref. to ground. The other 3 IGBT's have the emitter tied to the motor leads (300V).

Would probably work great for a DC motor, but 3 phase introduces more complexity. Guess thats why most AC drives use a "smart power module" instead of 7 IGBT's.


Last edited by etischer; 07-20-2008 at 09:53 PM.
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Old 07-20-2008, 10:35 PM
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lazzer408 lazzer408 is offline
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Default Re: IGBT firing circuit, building my own 90hp AC drive.

Ah yeh. The high side igbts need X volts (say ~15+) above their B+ rail aka. emitters. -doh!-

Does the 2hp unit provide that supply? If so maybe the 4422s will work but their grounsd needs to be tied to each emitter instead of B- ?

What are those 7pin ICs (I assume) shown in your first post. Gate drivers? Could they be replaced with a better driver? Wp Vp and Up inputs I would guess are the pwm input signal to the IC?
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Last edited by lazzer408; 07-20-2008 at 10:42 PM.
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