jcan
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Onboard inverter

Mon May 20, 2013 4:57 pm

I haven't been able to find any info on this. I was speaking with someone the other day about the car only charging at 3.3kw vs the 6.6kw. When I go
down a hill (mountain) I can get 20 - 30kw charging from the motor sustained for 10- 15 minutes. If the inverter can handle that, what's stopping someone from
using that inverter to charge the car at the 6.6kw or even higher?

I'm sure there's a simple reason otherwise it would have been done by now. I'd just like to know.

Jeff

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Re: Onboard inverter

Mon May 20, 2013 6:33 pm

There is plenty of prior art here, but the main issue is the lack of galvanic isolation between the AC line and the car's HV system. (Safety)

Then you have the need to install large and expensive contractors between the motor and the inverter, and between the inverter and the AC power line.

Don't forget that the inverter uses the inductance of the motor windings to buck/boost, so you'd then need auxiliary magnetics anyway. (If you want good efficiency).

Since semiconductors are really not all that expensive compared to a bunch of big contractors, why bother?

-Phil
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jcan
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Re: Onboard inverter

Tue May 21, 2013 8:33 am

Holly cow! Of course the Capacitance multiplier coupled with the Diode matrix would never be enough to handle the Supply voltage supervisor. LOL
Sounds good though, thanks for the input. I'm glad there are people smarter than me :)

smkettner
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Re: Onboard inverter

Tue May 21, 2013 8:52 am

Seems viable to me but it would have to be part of the design. And then you need three phase power input......
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fooljoe
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Re: Onboard inverter

Tue May 21, 2013 9:00 am

And one reason it's not part of the design is such a system is patented by AC Propulsion.
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Re: Onboard inverter

Tue May 21, 2013 10:16 am

smkettner wrote:Seems viable to me but it would have to be part of the design. And then you need three phase power input......
Did you see my response? If you avoid the safety implications, it still doesn't make sense in the $ department. It would also make the drivetrain less reliable. Back 15 years ago, this equation was different, but now cheap IPM's have changed this equation.

And you are also wrong about requiring 3-phase. Nothing "requires" 3-phase, it just reduces single phase current in most cases. You don't even need 3-phase for a 3-phase motor anymore, as the LEAF's inverter will happily demonstrate. (DC --> 3-Phase)

-Phil
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smkettner
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Re: Onboard inverter

Tue May 21, 2013 10:46 am

Yes I read your reponse.

I thought the inverter produced 3 phase power to drive the electric motor. And likewise the motor produces 3 phase power that is used to charge the battery during regenerative braking.

My thought (along with the OP) would be to feed the inverter with 3 phase power from the wall vs from the motor. Yes I assume much would need to be changed. If the inverter could be fed with single phase, I don't know.

Not sure of the galvanic isolation differences between the inverter/charger feeding the battery vs the regular OBC. Need a transfer relay to disconnect the motor. Contacts would not have to switch under load.

Sure it would cost some. But then so does the QC equipment. A 3 phase outlet at the rest stop might be easier to impliment. Might also work across brands vs the current proprietory systems. I like the OP's idea as it could get EVs away from the gas station/gas pump mentality.
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LEAF traded at 45,400 miles for a RAV4-EV
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Re: Onboard inverter

Tue May 21, 2013 2:04 pm

Having a large on-board charger is the route Renault took with Leaf's sister; Zoe. In Europe where they use the 3-phase Mennekes standard, even for home charging, this makes a lot of sense. Still, they did not add a bunch of relays and use the same inverter.

The cost of the relays (large contactors) is more than adding another IPM, so there is no point in doing so, and you'd still have the safety implications to deal with.

You cannot feed 3-Phase AC into the inverter without adding inductance. In drive mode, The inverter uses the inductance of the motor windings to achieve buck/boost power conversion. If you fed grid AC into the LEAF's inverter without series inductance, you would likely destroy the IPM in a big fireball. ACP used the motor windings rewired to provide the inductance, which presents significant problems, the least of which is reduced efficiency and yet another set of contactors. So adding external magnetics is the preferred way, then it's all solid-state, and you can preserve galvanic isolation.

If you did have added magnetics and contactors, and did this properly, it would accept single-phase fine, albeit at reduced maximum power levels.

-Phil
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adeyo
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Re: Onboard inverter

Thu Jun 06, 2013 9:06 pm

everyone here is way smarter than me, but this seemed like the right people to comment on my question. so, without trying to hijack (what appears to be a quieted thread)....here goes:

when it comes the the battery putting out dc voltage somewhere in the range of 350 volts, would it ever be possible to use a "Sunny Boy" sma inverter (the SB8000US accepts a dc voltage b/w 300-600 volts and spits out 240 volts AC) to power items in my home? The leaf inverter would need to be bypassed. For that matter, one could theoretically use the sunny boy to charge the leaf directly via Solar Panels feeding into the inverter -just like a solar battery bank and then when needed, take that power back for home use during the night?

How complex would this be really? I mean, if i could get my hands on a salvaged leaf (or void the warranty on a new leaf :) couldn't this be accomplished in a rather straightforward manner?

any replies please keep them simple, b/c i am dumber than you are :)

fooljoe
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Re: Onboard inverter

Thu Jun 06, 2013 10:10 pm

adeyo wrote:would it ever be possible to use a "Sunny Boy" sma inverter (the SB8000US accepts a dc voltage b/w 300-600 volts and spits out 240 volts AC) to power items in my home?
Yes, that should be possible, with the caveat that it's probably a grid-tied inverter and so would need to be connected to the grid to work - you can't just plug things into it on an "island" (but there are standalone inverters that can do this). I've thought of trying this with an old Leaf battery when they become available, if I can get my hands on one. You'd just have to access the main DC lines to the battery (which I believe you can find connected to the charger - but please don't mess with that if you don't know what you're doing). And I think the car would have to be on.
adeyo wrote:For that matter, one could theoretically use the sunny boy to charge the leaf directly via Solar Panels feeding into the inverter -just like a solar battery bank and then when needed, take that power back for home use during the night?
No, the sunny boy can't charge the Leaf directly. I suppose you could charge the pack directly by taking the DC from the panels through a DC-DC converter, to match the pack voltage, but that seems like a bad idea -you probably want some more sophisticated electronics (like a real charger than can accept DC input) to charge the battery instead of just a "dumb" DC-DC converter, but I'm not sure about this.

If you mean plugging the Leaf charger into the AC output of the sunny boy, again there's the grid-tied issue - since the inverter probably has to be connected to the grid anyway, plugging directly into the sunny boy output is indistinguishable from plugging in to any outlet in your home. And if you're talking about a standalone inverter, I'm guessing the Leaf's charger would not be happy with the wildly fluctuating power that would be produced by your solar panels, but again I'm not sure about that.

Anyway, the next question is why would you want to do this? With a grid-tied solar setup, it makes way more sense to charge your car from the grid when it's cheap overnight and sell power to the utility during the day with it's worth more (you should go on time-of-use metering if you haven't already). With a standalone solar setup, you're probably much better off using the equipment out there that's specifically designed for this purpose instead of "hacking" a Leaf and inverter to do it. Although I suppose you could use a Leaf battery in lieu of standard lead-acid batteries for such a setup, assuming the electronics will work with the pack voltage.
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