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RegGuheert
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When can we expect Nissan to move SiC MOSFETs?

Wed Feb 27, 2013 5:14 am

It seems that where efficiency is important, the trend is away from Si IGBTs to SiC MOSFETs, at least in the voltage range at which the LEAF inverter operates. They are easier to drive and have lower switching losses than IGBTs. Here is a quote from the article:
EETimes wrote:According to John Palmour, Cree founder and CTO, in typical applications, these SiC-based MOSFETS result in system efficiency gains of two percentage points; he noted that in one well-designed solar-inverter application at Fraunhofer Institute (Freiburg, Germany), efficiency increased from 96% to 98%, in an application where even fractions of a percent are considered vital.
So I wonder how long it will be before we can expect to see SiC power MOSFETs in the Nissan LEAF drivetrain as well as in other EVs. Perhaps it would take too many in parallel to be reasonable? I wonder how many IGBTs are in parallel at each location in the 3-phase H-bridge now.
Last edited by RegGuheert on Wed Feb 27, 2013 5:23 am, edited 1 time in total.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

mendenmh
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Re: When can we expect Nissan to move SiC MOSFETs?

Wed Feb 27, 2013 5:21 am

The auto industry is quite conservative about adopting new electronics, because of reliability worries. IGBTs have a lot of history behind them, and are known to be nearly indestructible. SiC is a coming technology, and promises many good things. Since SiC is a large bandgap material, it can operate at very high temperatures without large leakage currents, which is a big plus for under-the-hood operation. However, I suspect we will have to wait a couple years until enough of them have been really torture tested before they go into automobiles. It also has to get very cheap, which Si IGBTs are.

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RegGuheert
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Re: When can we expect Nissan to move SiC MOSFETs?

Wed Feb 27, 2013 5:30 am

mendenmh wrote:The auto industry is quite conservative about adopting new electronics, because of reliability worries. IGBTs have a lot of history behind them, and are known to be nearly indestructible. SiC is a coming technology, and promises many good things. Since SiC is a large bandgap material, it can operate at very high temperatures without large leakage currents, which is a big plus for under-the-hood operation. However, I suspect we will have to wait a couple years until enough of them have been really torture tested before they go into automobiles. It also has to get very cheap, which Si IGBTs are.
Agreed. Also, there needs to be multiple sources and that is not yet in place for SiC power MOSFETs.

It may also be true that at the power levels of the LEAF inverter you would have to parallel so many SiC MOSFETs devices to get to the same on-state losses of the IGBT that you would then have as much or more switching loss than you had with the IGBT. I don't know exactly where that crossover would occur.

It does appear that SiC will play a bigger and bigger role in our daily lives as time goes on. I am starting to see them being designed in in other applications.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

Herm
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Re: When can we expect Nissan to move SiC MOSFETs?

Wed Feb 27, 2013 7:02 am

in other words, avoiding warranty issues is more important and a couple extra efficiency points, one warranty repair probably wipes out any profit they managed to make.

Conservative = Good

Dealerships depend on repairs and used car sales to make a profit.. manufacturers are the opposite.

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RegGuheert
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Re: When can we expect Nissan to move SiC MOSFETs?

Wed Feb 27, 2013 8:52 am

Herm wrote:in other words, avoiding warranty issues is more important and a couple extra efficiency points, one warranty repair probably wipes out any profit they managed to make.
There is certainly no questioning the reliability of the inverter in the LEAF. That thing has been bulletproof so far!

But looking at this further, it doesn't really appear that you need the high breakdown voltage of the current SiC power MOSFETs. They are probably using 600V devices in the inverter today. If they could use Si MOSFETs, they would already be doing that, so I will guess that at these voltage and power levels, IGBTs are simply better in performance, cost and reliability.

Nothing to see here...
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

adric22
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Re: When can we expect Nissan to move SiC MOSFETs?

Wed Feb 27, 2013 9:39 am

I've often wondered how many power transistors they have in the Leaf. I've seen inside of an off-the-shelf motor controller and was surprised how many were in there. And the Leaf can deliver quite a bit more power than that thing could.
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