# Is IGBT better than MOSFET for motor control, or just cheaper?



## AmpedSpeed (Mar 25, 2012)

Been reading a lot about motor control the last little while. I've built buck controllers before, only with FETs, never IGBTs, and always at 50V or less. 

So, I've been reading up on IGBTs to see what all the fuss is about, and honestly, (I'm probably missing something) I don't get it.

I've read that the IGBTs are prefered for higher voltage (250V+) mainly because as a MOSFET is manufactured with a higher Drain to Source breakdown voltage, the on resistance, (Ron) becomes proportionally higher. 

Lets look at a couple parts:

The Mitsubishi CM600HA-24A 1200V 600A IGBT ~$120 Datasheet: http://www.pwrx.com/pwrx/docs/cm600ha_24a.pdf

and the STMicro STY112N65M5 650V 96A MOSFET ~$24 Datasheet: http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00222838.pdf

Let's say we put 3 of the IGBTs in parallel to make a 1000A controller. ~$360

Same imaginary controller, but with 19 MOSFETs in parallel to have nearly the same continuous current rating. ~ $456


Looking at conduction losses for the IGBTs (3 in parallel, 33.3A each) at 25C we get about 1V saturation at 100A for roughly 100W of heat loss

At 500A there's about 1.25V saturation for ~625W loss.

At 1000A (333A each) saturation has reached about 1.7V and conduction losses are up to 1700W or so.



Now lets take a over simplified look at the MOSFET.

Using 19 MOSFETs at 100A is about 5.25A each @ 25C we get 0.018Ron each. 0.018*100*100/19 = 9.47W of heat loss.

At 500A total we have ~26A each and Ron of 0.01825 = 240W loss

At 1000A total it's 52A each, 0.019 Ron, and 1000W total loss in conduction.


Gate charge on the 19 MOSFETs would also be less than the 3 IGBTs, making them easier the drive. MOSFETs can also switch much faster and don't have a current tailing effect when turned off. Also, MOSFETs are much more easily paralleled. With a positive temperature coefficient, they will naturally balance themselves if one is drawing more current than another. IGBT are negative temperature coefficient, meaning the one drawing more current will heat up and draw more.. and possibly undergo thermal runaway.

I know there's a lot more to it than this, and that the switching losses are usually higher than conduction losses anyway, but the MOSFET also seems to switch better.... so why IGBT, other than cost? 

Even for a 400V controller, MOSFET looks better than IGBT to me, especially at lower currents where most driving is done. What am I missing?


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## bjfreeman (Dec 7, 2011)

if your lucky and get all from the same die you will not have to match them, which take time, and is money.


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## AmpedSpeed (Mar 25, 2012)

Saturation voltage won't be matched either on IGBT modules. At least with unmatched MOSFETs, the one with less resistance will draw more current, heat up, resistance raises, and current evens. Obviously extreme cases could cause problems, but it's not the same issue it is with IGBT, where you need to take extra care to make sure things are balanced.


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## AmpedSpeed (Mar 25, 2012)

Now I've really confused myself. Looking at IGBTs I wanted I see how bad the current could get out of balance with higher temps, and how well it could be brought into balance with higher temps with MOSFETs.

Looking at single IGBTs, the temp coef is negative, as the device heats up the collector-emitter voltage drops and more current can flow in comparison to another lower temp device in parallel. This compounds and you can get thermal runaway.

Now when I look at the Mitsubishi module, the collector-emitter voltage graph shows the voltage getting higher as temp gets higher, which would help them balance, what kind of sorcery is this? 

I need one of the electronic gurus around here to set me straight.


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## subcooledheatpump (Mar 5, 2012)

IGBTs mainly find use in industrial applications, IE high voltage. 

High voltage MOSFETs don't come with high current ratings, so they must be configured in parallel, which adds physical complexity. IGBTs have a higher current rating per die while maintaing high voltage operation. That means we can have a physically smaller controller and a less complex physical wiring schematic with IGBTs.

There are more losses with IGBTs though, so for most making a low voltage (less than 600 volts) EV controller they choose MOSFETs. 

IGBTs come in preassembled packages too, with all of the chips already professionally layed out in the smallest package they could fit them in

Paralleling MOSFETs(or IGBTs) though only adds inductance, and since MOSFETs usually don't have high voltage ratings, the added inductance means you're more likely to blow parallel MOSFETs than you are to blow an IGBT module. 

New IGBTs can also work at higher temperatures, some up to 175 C vs 150 C with MOSFETs. I could be wrong but it looks like the only MOSFETs that can work at those temperatures are 100 volts drain-source or less, whereas 175 C rated IGBTs can go up to 1200 volts

MOSFETs though can switch faster. 

So is IGBT better than MOSFET? well that depends on what you are using them for. If you want to take the time and care to carefully design a parallel MOSFET controller with less loss, and spend the money to buy the chips then a MOSFET is probably better. 

If you want a high voltage controller that works in a high temperature environment, and is relatively eaiser to manufacture and assemble, then an IGBT is better

Also read http://www.diyelectriccar.com/forums/showthread.php/igbts-vs-mosfets-24664.html


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## AmpedSpeed (Mar 25, 2012)

I found out what the sorcery was. PT and NPT (Punch Through and Non Punch Through) IGBTs. 

The PT have negative temp coef, and NPT have a positive temp coef at most current levels.

So during conduction they will balance themselves as MOSFETs do, that's good.

The biggest thing to worry about it seems would be the time it takes for each device to turn on. Easier to take care of with 3 modules instead of 19.

The MOSFETs however would be significantly more efficient, especially at lower amperage draw during normal driving.

Subcool you are definitely correct about the MOSFETs being slighlty more delicate because of the lower voltage rating. The STY112N65M5 can take 710V max though, so you should still be able to pull off a 400V controller with some care.


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## ga2500ev (Apr 20, 2008)

AmpedSpeed,

The only reason that I'm looking at IGBTs is simplicity. Even in your example you discussed 3 modules instead of 19 individual MOSFETs. I'm planning on building a testbed controller with a single IGBT. There's simply no way to pull that off with ordinary MOSFETs.

My goal is to put together a bolt together controller, keeping it as simple a possible.

That's the reason for my choice.

ga2500ev


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## AmpedSpeed (Mar 25, 2012)

IGBT seems to be for ease of use and lower price, yet many of the cheaper controllers use MOSFETs. I suppose that could be due to people being more familiar with MOSFETs.

I've got a lot more reading and some testing to do first, but I think MOSFETs are definitely the way to go for my goals.

I'm on page 125 (of 575) of Paul and Sabrina's open source 500A controller. http://ecomodder.com/forum/showthread.php/paul-sabrinas-cheap-diy-144v-motor-controller-6404.html

I've been inspired by his project and the amount of cooperation from so many different people to make it happen. After I have read a whole lot more and started ordering some parts, I would like to start an open source project on a "performance" controller.

Paul and Sabrina have a great open source cheap controller. My goal will be a high performance controller without as much attention paid to cost.

A 400V 2000A controller will be an estimated $1500-2000 in parts.


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## bjfreeman (Dec 7, 2011)

AmpedSpeed said:


> A 400V 2000A controller will be an estimated $1500-2000 in parts.


that equals 800KW.
what vehicle needs that, unless you are a truck or bus.
the Battery pack for that is 188S10P Thats a lot of batteries.
What motor would handle that voltage and current?
What size wire would you use from the Battery to controller and from controller to motor?
765 Volts @300 amps (229.5KW) is used in commercial Electric drives.


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## subcooledheatpump (Mar 5, 2012)

Maybe he's making a racer using ultracapacitors?

that kind of current would require 400 MM2 cables


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## Ziggythewiz (May 16, 2010)

bjfreeman said:


> that equals 800KW.
> what vehicle needs that, unless you are a truck or bus.
> the Battery pack for that is 188S10P


That's amazing that you can calculate that independent of any battery statistics.


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## bjfreeman (Dec 7, 2011)

Ziggythewiz said:


> That's amazing that you can calculate that independent of any battery statistics.


I always figure someone needs to get from point a to point b and use some general distance and speed for a conventional car.
I may be hi on the number of 188 series cells needed in parallel. But he seems to be going for top level so I gave him some lea way.


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## AmpedSpeed (Mar 25, 2012)

bjfreeman said:


> that equals 800KW.
> what vehicle needs that, unless you are a truck or bus.
> the Battery pack for that is 188S10P Thats a lot of batteries.
> What motor would handle that voltage and current?
> ...





subcooledheatpump said:


> Maybe he's making a racer using ultracapacitors?


Why are you being rude? There's no need poke fun at me and type as if I'm not in this thread myself. 

Have neither of you heard of running a 9" motor at 1000A? Or the possibility of using 2 at the same time in parallel? You're both acting like I'm talking about building a spaceship.

Some of the 11"s and the 13"s can take 2000A for a short burst as well.

With 6/0 cable you'll drop 0.24V ever 2 feet, big whoop. We're not talking about constant current 2000A long range transmission lines here. It wouldn't be seeing 2000A for extended periods. 

A 400V 2000A controller doesn't mean 800kW output. I'm just going with the flow, it seems motor controllers for EVs are stated with battery input voltage, and then motor output current. It means the controller take take a fully charged 3.6Vx110S pack voltage (396V) that will sag to 308V under heavier loads.

As for the cell pack, a somewhat modest pack of 110S 4P of the A123 20Ah cells would be able to produce 220V/2000A output from 308V input @ 90% controller efficiency. I'm just throwing out numbers... But it's not the far fetched dream you're making it out to be.


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## bjfreeman (Dec 7, 2011)

Not making fun of you.
I have a 200KW 3 phase Controller I use.
Yes I saw where between the controller and motor there was 1000 amps, just not continuous
I raised some questions, if you have them solved, then go for it.


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## Ziggythewiz (May 16, 2010)

AmpedSpeed said:


> it's not the far fetched dream you're making it out to be.


Microsoft designs their OSs for hardware that will hit the market in 2-3 years. A controller doesn't get designed or built in a day, and if cost isn't much of a concern you'll want it to fully utilize whatever makes A123 obsolete.


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## AmpedSpeed (Mar 25, 2012)

bjfreeman said:


> Yes I saw where between the controller and motor there was 1000 amps, just not continuous
> I raised some questions, if you have them solved, then go for it.


Not really sure what you're saying here, but I'm not claiming I have anything solved. Just that it could be a fun open source project. Open source always produces the best, most adaptable products in their field, such as Linux, or Megasquirt.



Ziggythewiz said:


> Microsoft designs their OSs for hardware that will hit the market in 2-3 years. A controller doesn't get designed or built in a day, and if cost isn't much of a concern you'll want it to fully utilize whatever makes A123 obsolete.


Not quite sure what you're getting at. I just used an A123 pack as an example because Subcool said something about Ultracapacitors. When better power sources become available you'll be able to use less/spend less on them for the same performance.


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## Ziggythewiz (May 16, 2010)

I'm saying you're smart to not limit your controller's design based on the power that typical people can afford to put in their cars today.

My car is 120V and I considered building an open revolt to take it up to 144V, but decided that was shortsighted as I would likely later want to go beyond 150V, so having the 144V controller would be a waste. Open Revolt would have been a great place to start, but since I already have a controller it's better to spend more and do one that can do 180 or 200.


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## subcooledheatpump (Mar 5, 2012)

@AmpedSpeed, I was actually talking to the others who were questioning your motives for making/using such a high powered controller, not trying to come across as rude. I was being completely serious when I said maybe you were trying to go for an electric racecar. Personally I think it would be awesome to have such high power in an EV. It may not be completely pratical, but if you want do it then I say go for it


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## johnsiddle (Jun 22, 2011)

Does anyone have any experience with FREDFETS found them in the RS catalogue and the write up I have read indicate they are supposed to be the next generation for switching big stuff.
John


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## ga2500ev (Apr 20, 2008)

AmpedSpeed said:


> IGBT seems to be for ease of use and lower price, yet many of the cheaper controllers use MOSFETs. I suppose that could be due to people being more familiar with MOSFETs.


I don't think that's the issue. IGBT's are not as efficient. They will convert much more energy to heat than MOSFETs. Also standard IGBT's cannot be paralleled easily, so when one starts picking a single unit, the costs go up.


> I've got a lot more reading and some testing to do first, but I think MOSFETs are definitely the way to go for my goals.
> 
> I'm on page 125 (of 575) of Paul and Sabrina's open source 500A controller. http://ecomodder.com/forum/showthread.php/paul-sabrinas-cheap-diy-144v-motor-controller-6404.html
> 
> ...


That is certainly a load. Good luck with that.

ga2500ev


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## piotrsko (Dec 9, 2007)

you may want to also search this forum for Tessaract and his trials / tribulations/ discoveries back about 3 to 4 years ago while he was designing the Sol1.

Lot of weird things not covered in electronics 502 when you run high watts through circuits.

Come to think of it, Valerun for the same thing, also Jack Bauer


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## AmpedSpeed (Mar 25, 2012)

subcooledheatpump said:


> @AmpedSpeed, I was actually talking to the others who were questioning your motives for making/using such a high powered controller, not trying to come across as rude. I was being completely serious when I said maybe you were trying to go for an electric racecar. Personally I think it would be awesome to have such high power in an EV. It may not be completely pratical, but if you want do it then I say go for it


I seemed as though there was some sarcasm involved with your ultracapacitor racecar statement, but it's not always easy to tell with text. 

As for being practical, I don't see the issue. More power capability won't hinder me from driving around town slow with ease as it would with an ICE.




ga2500ev said:


> I don't think that's the issue. IGBT's are not as efficient. They will convert much more energy to heat than MOSFETs. Also standard IGBT's cannot be paralleled easily, so when one starts picking a single unit, the costs go up.
> 
> 
> That is certainly a load. Good luck with that.
> ...


That's why I created this thread. To ask why IGBTs seem to be the switch of choice in many controllers even though MOSFETs are much more efficient.

NPT IGBTs can be paralleled just as easily as MOSFETs, except there are many more of them, which makes it more difficult. Look up a few posts for an explanation about PT, and NTP IGBTs and why they can be paralleled like MOSFETs.

IGBT is also easier to use because of the layout issues that can arise with multiple parallel MOSFETs.


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## AmpedSpeed (Mar 25, 2012)

Thanks piotrsko.

Read through Valerun's thread but hasn't been any activity for quite a while in there now. I'll check out Tesseract and Jack's builds as well.
http://www.diyelectriccar.com/forums/member.php?u=401


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## bga (May 25, 2009)

Hi AmpedSpeed,
I am in the process of building a control system for a 500volt induction motor drive, along the same lines as the paul and sabrina 3 phase controller project.

The FET (STY112N65M5) you have identified is certainly the best I've seen and would give IGBTs a run for their money!.

Generally, voltage and current are consideration factors in choosing one over the other.

IGBTs excel in high voltage systems, particularly above 300 volts and essential in systems with 500 volt or higher buses. A significant amount of headroom is needed to cope with inductive switching spikes, so 1200 volt IGBTs are a good fit for a 600 volt battery.

FETS in the 600V+ territory have previously had significant RdsON values, which limit the current and efficiency at high currents. Even the FET mentioned above will have a Vds of about 2 volts at 96 amps, or about the same as the Vce of an IGBT, but will have much lower Vds at typical operating currents and will be more efficient at those lower currents.

(IGBTs aren't all that bad, with many having VceON of about 1.5V at lower currents, but it's effectively a darlington transistor, so the VceON will never get lower than that, not so good at 24V, but more or less OK 150V, though - 1% conduction loss) 

One significant difference with big IGBT modules is the packaging, which is much simpler than multiple TO247 FETs. The power section bolts together onto bus bars and plate heatsinks.

I am using CM300DY-24A dual IGBTs (300A/1200V) to make the power section simpler.

Contrary to other opinions above, parallel FETs will share current effectively in a well designed circuit. This is because VdsON is about 2 Volts at maximum current, so even 0.5 volt difference down the row of devices won't make a dramatic difference to the current sharing.

Device power dissipation is an issue; 100 Amps at 2V is 200 watts being dissipated in each TO-247. This is likely to be tricky to get the heatsink to cope with, so it would be wise to derate the device 50 amps so the dissipation per device becomes about 50 watts, easier to deal with in the heatsink, also this allows for some mismatch in current sharing.


Something else that I have been concerned about is the flyback diode that is needed in addition to the active driving IGBT/FET. This is an essential component of the buck converter that the motor+controller becomes.

An often overlooked issue is that at low PWM ratios (low speed and transistor mostly off) and high current (accelerating at the lights), the diode is doing most of the of the conducting during the discharge phase of the inductor (motor), so will do a lot more work than the transistor at low speed and blow up if inadequate.


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## aeroscott (Jan 5, 2008)

bga said:


> Hi AmpedSpeed,
> I am in the process of building a control system for a 500volt induction motor drive, along the same lines as the paul and sabrina 3 phase controller project.
> 
> The FET (STY112N65M5) you have identified is certainly the best I've seen and would give IGBTs a run for their money!.
> ...


interesting stuff. thanks


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## fireblade (Aug 20, 2012)

I want to say thanks to all of you. You are a treasure trove of information.

After reading this thread I did a little homework and found that:
In order to minimize the power consumption of the IGBT you will have to put the current across the device as close to the knee of the transfer function. Since it is a bipolar the minimum voltage drop will be ~.6 to .7 volts. And since the transfer function is almost a straight line it will not be a linear power reduction with increasing IGBTs.

The IGBTs have the much higher voltage rating from 600 to 1200 as in the case of the powerex module referenced.

Powerex also has modules that has additional features such as current and temperature sensing built in (http://www.pwrx.com/pwrx/app/PWRX%20Transfer%20Molded%20GBT4EV%20Propulsion.pdf)

MOSfets operate at the 600 and below voltage however because MOSfets are resistance devices lessening the current flow also lessens the power dissipation. To elaborate, 4 MOSfets will deliver the same current with 1/4 the total dissipation of the same MOSfet . Since power W, is ( I^2)*R and resistance in parallel is (1/(1/r1+ 1/r2+...)).

Good news is that Powerex had a 1200V,100A Mosfet. (http://www.pwrx.com/pwrx/docs/qjd1210007.pdf). Price is unknown


In comparison the CM1000DXL-24S is $787.52 (http://www.pwrx.com/Product/CM1000DXL-24S)

I computed the current and power dissipation between these two devices and some interesting findings. As the current went up in either a single or multiple MOSfet device configuration the power went up significantly. This can be ameliorated by adding more devices.

In contrast the rate of change for the IGBT was not as drastic and was lower than the MOSfet configuration.

To summarize, the operating current and the voltage should be determined, meaning what will be the most often current draw. Then a price per current for each device determined. And lastly how complex, meaning how many devices can the driver stage drive. There is no one answer but both types of devices should be considered with the goal of having the lowest overall dissipation for a given circuit design.


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