# IGBT Choice



## jackbauer (Jan 12, 2008)

I'm looking for a little advice or pointers on choosing a good IGBT for my motor controller. I'm not a fan of using lots of mosfets due to the fact if one fails it will cause a cascade and also heatsinking lots of parts is generally difficult. 

I'm running a compound wound forklift motor at 96v. So far i've looked at these two devices:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=260472383397
and:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=260472742122

Ideally i'd like 500amp capacity and am not afraid of watercooling. I know IGBTs have a higher Vce on than mosfets Rds on and will tend to dissipate more heat but i can live with that. So other parameters to look out for would be gate cap , gate charge , Vce , Ic ... anything else?


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## SimonRafferty (Apr 13, 2009)

These are the kind of thing I use! Go for double the required voltage and current (give or take) you require and they will be fine!

Si


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## jackbauer (Jan 12, 2008)

That was my general plan. I figure to use an 800amp device at 400amps etc. Ideally i'd like to use only one igbt that way i don't have drive or parameter mismatch problems.


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## samborambo (Aug 27, 2008)

jackbauer said:


> That was my general plan. I figure to use an 800amp device at 400amps etc. Ideally i'd like to use only one igbt that way i don't have drive or parameter mismatch problems.


I assume you mean 400V, not 400A?

What voltage/current is the shunt field winding? If you can, drive the shunt field winding independently to give you a wider power band across the rev range. At low RPM you want full field strength to give you more back EMF - that'll mean less amps / more volts for the same torque, essentially allowing more torque. At the high end you want the field weaker so that the BEMF doesn't approach your battery voltage and cause torque to tail off.

A well designed controller with independent field control would allow you to run the drive train in a single gearing.

Sam.


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## jackbauer (Jan 12, 2008)

Sam are you fairly sure i could use one gear? I'm looking for parts to handle up to 144v and 500amps plus hence my interest in the igbts. I'm using paul holmes open source control board.

The shunt windings are 18ohms. Major helped me out with this in the fork motor thread and we discovered its 50/50 shunt series. I'll be using one of the small pwm controllers for the shunt portion. I did a few crude experiments and found i had good speed control just varying the field strength.

You now have me thinking i could ditch the gearbox and use a single reduction gear straight to the drive shaft. Here's a few vids of the motor:
http://www.youtube.com/watch?v=6SAtDzFfrWU
http://www.youtube.com/watch?v=_RTIb_dUeO0


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## samborambo (Aug 27, 2008)

It's very probable that you could run through a fixed reduction gear. My conversion I'm working on at the moment (Toyota MR2) is a fixed gear reduction with AC induction motors running each rear wheel. The motors have 200Nm peak torque each up to the base speed of 3000RPM and then constant power as the torque tails off from there up to 6000RPM. I can plug your data into my model and show you what the 0-60 acceleration will be like. I need some data from you in order to work that out:


The donor car CdA, running weight, diff ratio and tyre diameter. I may have the CdA data on hand if it's a car prior to 1996 (or an equivalent body shape).
Motor peak torque. There's a few ways to measure this if you don't have the information on hand. You could mount a large smooth heavy disc with a known moment of inertia on the motor shaft. Spin up the motor to an arbitrary speed below your voltage limit on maximum current (on both field windings). Record the time taken to reach a certain RPM and calculate the torque.
Motor base speed. The lowest speed at which the motor hits maximum voltage and maximum current.
Motor top speed. There will be a trade off between acceleration and vehicle top speed if you have some diff ratio options.
Sam.


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## blackpanther-st (Apr 4, 2009)

samborambo said:


> If you can, drive the shunt field winding independently to give you a wider power band across the rev range. At low RPM you want full field strength to give you more back EMF - that'll mean less amps / more volts for the same torque, essentially allowing more torque. At the high end you want the field weaker so that the BEMF doesn't approach your battery voltage and cause torque to tail off.
> 
> A well designed controller with independent field control would allow you to run the drive train in a single gearing.
> 
> Sam.


ahh now I understand why field weakening in a sepex causes the free speed to rise! thanks for posting this.


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