Another DIY DC controller mock - DIY Electric Car Forums
Go Back  

DIY Electric Car Forums > EV Conversions and Builds > Controllers

Register Blogs FAQ Members List Social Groups Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Display Modes
  #1  
Old 06-29-2011, 02:47 AM
valerun valerun is offline
Senior Member
 
Join Date: Nov 2010
Posts: 1,509
Blog Entries: 1
valerun is on a distinguished road
Default Another DIY DC controller mock

...there is something mystically attractive in power electronics...

so after getting my 10kW charger design to a reasonably good place, I wanted to live dangerously and have wired some 1200V, 600A IGBTs together for a quick DC controller setup. Would love to get your feedback. The idea is more about learning advanced power electronics rather than building any kind of production version (which we got covered quite well by the EVnetics guys ;-)

Having read a bunch of docs on how to design these things without having them blow up right away, I am using, among other things:
1. Laminated DC input bus with 1/4" polycarbonate between 2 large copper plates.
2. Lots of parallel caps mounted with studs on one line with IGBT leads to reduce current loop area
3. On-IGBT control boards with SMD 8A drivers (all to minimize inductance between driver and gate)
4. +/- 15V driver to ensure turn-off
5. Emitter current balancing resistors (0.3Ohm) to sync turn on and turn off of the parallel IGBTs
6. Output cables connected to the opposite sides of the controller to avoid concentration of current in one pair of devices

You can see some pics of the setup below - including my very sophisticated 'load system' - a bucket of cold water with a 5" iron powder toroid with ~80 turns of 8x14 gauge copper wire (15 mOhm, 800 microHenry at zero current; according to micrometals.com software, saturating to ~1/3 of the inductance at 100A etc).

In my first test run, I've used a 30V battery (I know, not super-impressive but hey, I didn't want to have to catch plasma balls in case something went wrong ;-), switched at 10kHz, and went to 250A 'motor' current.

Couple of scope captures attached. You can see (images numbered in order they appear - some images in the next post due to limit of 10 per post):
1.1. no ringing on gates. good thing
1.2. Turn-on/off takes ~1us. ok for 100us cycle.
2. Peak gate current of 4A both ways. Rg=5Ohm. I drive both SMD drivers by one A3120 isolated 2.5A driver.
3. There is some ringing on the +/-15V DC rail for SMB driver boards - to the tune of ~2V at ~0.5Mhz. I thought it's passable - let me know what you think.
4. Now this is where I'd REALLY love to hear your input: at 250A, I can see negative IGBT emitter spikes of -80V at turn-off (ringing back to zero within 400ns or so at ringing frequency of ~10Mhz). At the same time, I can see positive IGBT collector spikes of +40V. So the total spike swing is ~120V, or ~4x the input DC voltage - for the total voltage stress of 5x the input DC voltage. That is not cool. I made a conclusion that I am driving these IGBTs too fast for freewheeling diodes (which are same model IGBTs with shorted G and E) to catch the negative inductive undershoot from the load. So I am going to try 10Ohm Rg (now at 5Ohm) and lower the switching frequency to 5kHz. What do you guys think????

Thanks,
Valery.

PS. I am using the same control board I've developed for my charger (http://www.emotorwerks.com/cgi-bin/VMcharger.pl). Just finished adapting code to the controller duty, as well. Surprising amount of stuff seems to be reusable (current limiters, precharge circuits/logic, etc).
Attached Images
File Type: jpg DSC_5916.jpg (92.5 KB, 147 views)
File Type: jpg DSC_5922.jpg (67.4 KB, 113 views)
File Type: jpg DSC_6103.jpg (85.9 KB, 106 views)
File Type: jpg DSC_6106.jpg (85.9 KB, 97 views)
File Type: jpg DSC_6107.jpg (72.9 KB, 95 views)
File Type: jpg DSC_6110.jpg (64.7 KB, 88 views)
File Type: jpg DSC_6108.jpg (74.3 KB, 87 views)
File Type: jpg DSC_6102.jpg (95.0 KB, 84 views)
File Type: jpg DSC_6104.jpg (85.9 KB, 93 views)
File Type: jpg DSC_5926.jpg (87.8 KB, 97 views)

Last edited by valerun; 06-29-2011 at 02:54 AM.
Reply With Quote
Sponsored Links
Advertisement
 
  #2  
Old 06-29-2011, 02:49 AM
valerun valerun is offline
Senior Member
 
Join Date: Nov 2010
Posts: 1,509
Blog Entries: 1
valerun is on a distinguished road
Default Re: Another DIY DC controller mock

remaining pics:
2: Rg voltage drop of ~20V max (hence the 4A max gate current)
3: +/-15V supply rail in AC scope mode
4. Emitter (top) and Collector (bottom) at turn-off
5. Same for both turn-on and -off

EDIT: added the datasheet of the IGBT I am using.
Attached Images
File Type: jpg DSC_5927.jpg (95.1 KB, 63 views)
File Type: jpg DSC_5928.jpg (80.0 KB, 56 views)
File Type: jpg DSO-2090 USB(7.0.0.0) 6282011 95009 PM.jpg (89.1 KB, 60 views)
File Type: jpg DSO-2090 USB(7.0.0.0) 6282011 95041 PM.jpg (92.2 KB, 57 views)
Attached Files
File Type: pdf IGBT 1200V 600A - CM600HA-24H.pdf (59.7 KB, 84 views)

Last edited by valerun; 06-29-2011 at 02:56 AM.
Reply With Quote
  #3  
Old 07-01-2011, 12:35 AM
valerun valerun is offline
Senior Member
 
Join Date: Nov 2010
Posts: 1,509
Blog Entries: 1
valerun is on a distinguished road
Default Re: Another DIY DC controller mock

more fun today:
1. swapped 5 Ohm Rg into 20Ohm
2. lowered switching frequency to 5 kHz
3. still 30V pack

took the thing to 600A output, which is 50% of the combined continuous rating for the 2+2 devices I am using. Spiking across the switch is now limited to just +70V. This is linear to the current so I expect ~100V at 1000A. Of course, switching transition is a bit long now - especially on turn ON - to the tune of ~5us.

So I'm thinking to use a 5 Ohm as a turn-on Rg and 20 Ohm as a turn-off Rg. Also want to hook up a shunt to measure current waveform so I can calculate the losses.

Also probably will have to take the switching frequency down a bit more. The only thing is: got to watch out the caps. Have 17000uF on the bus now which should be good for 1000A output at 300V pack voltage at 5kHz.

Some pics attached.

V
Reply With Quote
  #4  
Old 07-01-2011, 02:32 AM
jackbauer's Avatar
jackbauer jackbauer is offline
Senior Member
 
Join Date: Jan 2008
Location: Ireland
Posts: 1,319
jackbauer is on a distinguished road
Default Re: Another DIY DC controller mock

Nice work val. From what I can see you are getting stuck on the miller plateau on turn on. That HCPL3120 driver does not have near enough kick for the application. Consider a 9amp driver sucj as the mic4421 or better still a VLA501 module.

If you drive the switch too fast the freewheel diode will not recover properly before the next cycle. I had this problem when I first ran my igbt controler at 16khz. Dropping to 8khz cured this problem. Consider snubber caps. At least 2 or 3 on the dc link and one across the switch. Next be aware of the ton and toff of the device and the freewheel. A lot of older modules have terrible values.


I have a few threads on here from late '09 dealing with these exact issues. Also got some videos on the subject. Hope that helps.
__________________
Now, Cole, when you shift the gear and that little needle on the ammeter goes into the red and reads 1000 Amps, that's bad.
www.evbmw.com
www.e39ev.com
Reply With Quote
  #5  
Old 07-01-2011, 12:45 PM
valerun valerun is offline
Senior Member
 
Join Date: Nov 2010
Posts: 1,509
Blog Entries: 1
valerun is on a distinguished road
Default Re: Another DIY DC controller mock

Quote:
Originally Posted by jackbauer View Post
Nice work val. From what I can see you are getting stuck on the miller plateau on turn on. That HCPL3120 driver does not have near enough kick for the application. Consider a 9amp driver sucj as the mic4421 or better still a VLA501 module.

If you drive the switch too fast the freewheel diode will not recover properly before the next cycle. I had this problem when I first ran my igbt controler at 16khz. Dropping to 8khz cured this problem. Consider snubber caps. At least 2 or 3 on the dc link and one across the switch. Next be aware of the ton and toff of the device and the freewheel. A lot of older modules have terrible values.


I have a few threads on here from late '09 dealing with these exact issues. Also got some videos on the subject. Hope that helps.
Thanks Damien!

I am using a 3120 only for isolation - it then drives the bigger 8A drivers - one per IGBT. My problem is I can't unleash their full power - even with Rg of 5Ohm (and peak gate current of 4A) the IGBTs switch off too fast (and, as you very correctly noted, exceed the recovery speed of the freewheeling diode). So I needed to slow down the turn-off and it helped a ton for toff spike. But now my t-on is muddling through the miller plateau for too long as you correctly noted. So I am thinking of doing a 5 Ohm Rg for turn-on to keep the speed but 20 Ohm for turn off.

I have read most of your threads and your posts on ecomodder - they've been a great help! Not fully up to speed on the videos, though ;-)

BTW, what is the value of the snubber cap you are using across the switch? All the snubber design docs I have read talk about RCD snubbers for high power applications... Also, how did you connect the caps across the DC link given that + and - connections to IGBT and freewheeling diode much be ~10cm apart (I think you are also using single IGBT modules, right?)

Thanks!!
V
Reply With Quote
  #6  
Old 07-01-2011, 01:45 PM
jackbauer's Avatar
jackbauer jackbauer is offline
Senior Member
 
Join Date: Jan 2008
Location: Ireland
Posts: 1,319
jackbauer is on a distinguished road
Default Re: Another DIY DC controller mock

Right now the controller i have in the car is running a pair of Fuji 800amp single igbts. One as the switch the other with its g-e shorted as the freewheel diode. They are joined with a piece of 20x10mm copper bar. Thats a bad idea in theory as the link can ring like a bell and i go shooting down the road trailing flames like a dragster with a blown engine. In practice its worked fine. Remember that app notes are based on ideal conditions with unlimited resources and infinte development times. They are a guide at best.

I used a piece of standard copper clad pcb board , roughly routed on the drill press to cary the link caps. Kind of a poor man's laminated busbar. I used a 1uf RC snubber across the switch as i was seeing some alarming ringing on turn on if i remember rightly. My advice would be to use 2 resistors and a schottky diode to shape the turn on and turn off. You really need a hard turn on to punch through the miller knee.

What is the ton and toff of the devices your using? Are you using emitter resistors?
__________________
Now, Cole, when you shift the gear and that little needle on the ammeter goes into the red and reads 1000 Amps, that's bad.
www.evbmw.com
www.e39ev.com
Reply With Quote
  #7  
Old 07-01-2011, 01:57 PM
valerun valerun is offline
Senior Member
 
Join Date: Nov 2010
Posts: 1,509
Blog Entries: 1
valerun is on a distinguished road
Default Re: Another DIY DC controller mock

Quote:
Originally Posted by jackbauer View Post
I used a 1uf RC snubber across the switch as i was seeing some alarming ringing on turn on if i remember rightly. My advice would be to use 2 resistors and a schottky diode to shape the turn on and turn off. You really need a hard turn on to punch through the miller knee.
yes, will try that tonight. For the RC snubber, what did you use as R? And how you heatsinked that? From my calculations, at 200V and 8kHz, you would have to dissipate C*U^2*f=10^-6 * 4*10^4 * 8*10^3 = 320W on a resistor (:-0). I can't find anything close to that in a non-inductive package...

Quote:
Originally Posted by jackbauer View Post
What is the ton and toff of the devices your using? Are you using emitter resistors?
ton: 700 ns
toff: 350 ns
I figured if I want to keep switching time to <1% of the cycle, this would mean <10kHz frequency. Now, since I can't really use that blazing toff speed anyway, I have to reduce the frequency to keep the dissipation under control. I hope I can use 5 kHz.

EDIT: oh, yes, I am using emitter resistors.

V

Last edited by valerun; 07-01-2011 at 09:25 PM.
Reply With Quote
  #8  
Old 07-01-2011, 09:24 PM
valerun valerun is offline
Senior Member
 
Join Date: Nov 2010
Posts: 1,509
Blog Entries: 1
valerun is on a distinguished road
Default Re: Another DIY DC controller mock

added a 5 Ohm turn-on resistor parallel with the 20Ohm I already have. Turn on now takes 700-800ns as it should. no additional ringing so I am happy.

took it to 800A today. a bit scary.

turn-off spike is ~80V at 800A. It was fun to put one end of the scope on one end of the DC+ bar and slide the second end along the bar - the further apart I took it, the more voltage spike I saw ;-) ~30V along the 5" of a bar. Power electronics is fun ;-)

Measured voltage spikes across DC link and across freewheel diode separately to understand what drives voltage stress. DC link spike only ~1/4-1/3 of the overall C-E spike on the switch so not really a problem. So if I want to reduce the spike, I have to deal with the diode part. How's this for an idea: using a smaller u-fast diode (say, 60A 1200V part) in parallel with the big one? It will turn back on much faster and will conduct for the first 200ns while the large diode ramps up. Yes, the initial current will be close to the IGBT current (say, 500A if I push 1000A through the controller) but this will go on for just 200ns and the remaining 200 micro-seconds it will be chilling. So I would definitely not exceed the power dissipation ratings. Is this a crazy idea?

EDIT: also, any ideas how to confirm whether my IGBTs share the current evenly or not?

V

Last edited by valerun; 07-01-2011 at 11:23 PM.
Reply With Quote
  #9  
Old 07-01-2011, 11:29 PM
valerun valerun is offline
Senior Member
 
Join Date: Nov 2010
Posts: 1,509
Blog Entries: 1
valerun is on a distinguished road
Default Re: Another DIY DC controller mock

ok tried the parallel diodes. Largely good news - the turn-off [C-E on the switch] spiking goes down to ~40V at 800A output (from ~80V).

However, there is now some new small (~20V) spiking and ringing on turn-on. I guess the reverse recovery is too fast / snappy and sets off the ringing... Just can't bloody have it all, huh? ;-)

Also, there is quite a bit of power dissipated on the smaller diodes. Looks like they share some good part of the freewheeling current. Just looked up the forward voltage vs. current dependency: at 600A, the large diode drops ~2.5V. At the same 2.5V drop, the small diode would have to conduct ...250A. So looks like up to 1/3 of the total current can be going through the poor little diode. Not good. Perhaps something like 0.02-0.03 Ohm resistor in series with the smaller diode would cure it. Initial spike of 500A would result in 10-15V drop on a resistor, which would add to a voltage spike on a switch. But then during steady state, every 10A through small diode would generate 0.2-0.3V - enough to force on the current to go through the large diode... Although it's becoming to look a bit complex now ;-) Maybe I should just give up and use a snubber...
Reply With Quote
  #10  
Old 07-01-2011, 11:45 PM
aeroscott aeroscott is offline
Senior Member
 
Join Date: Jan 2008
Posts: 1,223
aeroscott is on a distinguished road
Default Re: Another DIY DC controller mock

great work , teacher !
Reply With Quote
Reply

Share or Bookmark this

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

 
Support DIY Electric Car
Sponsors

All times are GMT -6. The time now is 09:25 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.

Ad Management by RedTyger