Author Topic: 100KW wireless EV charging at 96% efficient using polyphase electromag coupling?  (Read 57917 times)

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Online T3sl4co1l

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The numbers are realistic, the economics are TBD. It's not going to be cheap, but that can come down if it's deployed in scale.

Tim
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Offline Marco

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A couple decades ago the efficiency of modern switching power supplies would have looked magic too.

All the resonating energy in the coils will take a lot of expensive litz though, no way around that with magnetics with poor coupling.

PS. I wonder if the stray fields are within legal limits.
« Last Edit: April 02, 2024, 05:17:30 pm by Marco »
 

Offline mikeselectricstuff

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Not totally implausible in theory, but how accurately does it need to be aligned ?
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Offline johansen

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What happens if a soda or other metallic trash can rolls into the air gap?
 

Online T3sl4co1l

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Not totally implausible in theory, but how accurately does it need to be aligned ?

Would imagine within half to full the height range. Give or take some tradeoff in the two parameters, maybe it needs to be closer as it's less aligned.  Could also be on an arm or table to adjust it if needed.


What happens if a soda or other metallic trash can rolls into the air gap?

It rolls away faster than it rolled in.  Unless they're at some MHz (which is possible; I saw a proposal at 6MHz ISM for e.g. forklift charging, based on layered resonant semi-rings), the Lorentz force will be pretty significant.  If held there, it would melt or burn; a can or sheet would melt in a mossy/fractal pattern, much like microwaving a CD.  Aluminum foil wrappers might be thin enough not to ignite or melt, but most other things should get pretty toasty.

The rotating field is peculiar, because it induces a torque; not anything that could move a car, certainly, but I'm guessing they do it more to get continuous power output -- in other words, no reason you can't do multi-phase converters, or multi-pulse rectifiers (and inverters driving the other side) at-frequency, you just see it more often at mains frequency.

Very hand-waved guess at field strength, but the power level and Q factor can't be too far off from industrial induction heating purposes for example.  Loaded Q will be pretty high for the dimensions shown (>50, 100?), which makes the efficiency figure that much more impressive; the coils will indeed have to be quite finely divided.  This probably favors high, but not super high frequencies (fractional MHz?), unless they are in fact doing it at some MHz with resonant structures.

Tim
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Offline Marco

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I can surmise some very poor reasons why journalists don't include citations with their pieces, but why is it so common place for academic press releases? It's so bloody stupid. Any way, here's the paper :
https://www.osti.gov/servlets/purl/1876291

It works at 84 KHz (not in the text, need to look at the pictures). So the rolling can will see around 100k cycles rolling through the field, not much of a DC component to give it momentum. Eddy current heating is more of an issue, but you could put an IR sensor under the car?
 

Offline coppercone2

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i wonder if potato chip bag explodes under these conditions
 
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Offline mikeselectricstuff

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Can't tell from the pic what year that Kona is, but until very recently they could only charge at 77kW....
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Offline Kim Christensen

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Imagine the lawsuit when someone with a medical implant dies after walking near this while it's in operation.  :palm:
 

Offline mikeselectricstuff

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Imagine the lawsuit when someone with a medical implant dies after walking near this while it's in operation.  :palm:
Inverse square law takes care of that.

I do wonder about a curious cat with metal on a collar, or RFID implant though.
That 4kw of waste heat is going to make the area nice and cosy warm
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Offline Marco

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Imagine the lawsuit when someone with a medical implant dies after walking near this while it's in operation.  :palm:
InductEV has 300 kW systems in use for buses at publicly accessible locations.
 

Online EEVblog

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Offline coppercone2

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lol the obsession for not having cables is ridiculous

I stopped using wireless charging for the phone after 2 of em broke (from quality manufacturers). The high price of a car with this added gimmick just decrease reliability and ensures you won't retire before 85

and it still sucks compared to the cable, because its millions of cars. that is alot of waste. 96 sounds good but its alot of losses compared to a good cable.
 

Offline mikeselectricstuff

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There are some niche cases where it may make sense - bus stops, taxi ranks etc. and there will always be the rich gadget fans who'd want it, but solely the fact that it needs a significantly modified vehicle makes it impractical for most cases.
Car makers aren't going to offer it as a standard option, and won't be likely to approve third-parties modifying the HV system to accommodate it outside of quantity fleet buyers.
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Online T3sl4co1l

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I mean... there are many reasons to do it.  Maybe not great reasons, but remember, this is for the great unwashed masses, it has to be convenient and fancy and magic to adopt or sell.  If you can do something that no other method has done before, might as well go for it for the bragging rights.

You can't transmit fuel wirelessly.  Hoselessly.  Well.  You shouldn't.  Please, for the love of god, don't.......

...But electricity, it's not a huge problem.  An engineering problem, sure, but a soluble one.  The equipment will be more expensive, but the capital cost pales in comparison to the electricity flowed through it over its lifetime.  Even a fraction of it, because, you know, we've gotta take our cut of your charge bill.

The weight of the receiver is maybe the bigger problem; that's a lot of ferrite and copper to lug around, and it can't exactly be detached without "see problem #1".  Less of a problem at least with regenerative braking, but still that incremental cost on bearing and wheel load.

Can be more defensible, too; especially until such time as this ever-rising inequality is actually fucking addressed, theft will only intensify, and very bolt-cutter-able charge cables are an attractive target.  Everything stuffed into a concrete and metal block, HDPE or whatever impact shield, epoxy potting; that's a bit harder to do.  Likewise if integrated into the car's floor pan, it's less cuttable than a catalytic converter.


There are some niche cases where it may make sense - bus stops, taxi ranks etc. and there will always be the rich gadget fans who'd want it, but solely the fact that it needs a significantly modified vehicle makes it impractical for most cases.
Car makers aren't going to offer it as a standard option, and won't be likely to approve third-parties modifying the HV system to accommodate it outside of quantity fleet buyers.

Yeah, the added purchase price, and mostly having to engineer it into the system from the start, are two of the bigger reasons against it.  The easiest "in" would be as an aftermarket add-on, but I'm guessing no one makes a charging port in the trunk or whatever, so you'd have to have the cable hanging out all the time (which, see above problems) and that just looks stupid, also the unit itself would be less defensible (see above again), at best bolted on, but maybe more realistically just strapped in place somehow.  Hopefully not double-stick-taped(!!).

Tim
« Last Edit: April 03, 2024, 10:34:42 am by T3sl4co1l »
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Online Haenk

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So you have two technologies, competing on the "lowest point of the car" - either you raise the battery pack (not by a lot, due to seating, very bad for the handling of the car), or you lower the coil. Which is not ideal, either, unless you can lower it mechanically when charging.

Not sure how to solve this conflict.
 

Offline twospoons

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96% sounds like a pile of BS to me. Highly optimized buck converters ( i.e. no isolation) seem to top out around 97% so with this non-optimal magnetic coupling I'm wondering if its a typo and the real efficiency is 69%.
Used to work with Qi chargers, at 2mm gap with 50mm coils and you could get maybe 75% on a good day.

Yeah, yeah, resonant coupling and all that, but that just means large circulating currents in your LC tanks (I2R losses).

Color me skeptical.
 

Offline Marco

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Qi is not from the modern GAN ZVS+ZCS era, E²Watt is for instance.

InductEV also uses the simple trick of working from rectified but non smoothed mains.
 

Offline Berni

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Sounds like it could work if you ask me.

The high power systems tend to have higher efficiencies purely from the standpoint that at these powers the design has to be focused towards efficiency a lot more, as every % of loss quickly results in a ton of heat would threaten to blow stuff up. So high efficiency is no longer a 'nice to have' aspect in the engineering tradeoffs, but instead becomes a vital requirement for the system to even work.

That being said. Is this practical? Probably not. This incentivizes the pickup coils to be as close as possible, compromising on the ground clearance, not a problem on a race car, but not great for a every day commuter car that goes over speedumps, curbs, road derbies, road construction zones..etc

Then there is also the weight and expense of this system. You basically need to fit a 100kW DC fast charger inside the car. All of those power electronics are not cheap, take up a lot of space and adds a lot of weight, on top of the wireless pickup coils that are also needed. Well sure cars already need a fair bit of power electronics to run the motor. However look at what this complicated system is competing against.... a single high current connector on the side of the car. That charging port probably costs 10$ to produce and a 5$ contractor.

All of this, just so you don't have to plug it in.

Tho it might make more sense to aim for ~10kW charging for at home if people are really lazy.
 

Online Haenk

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I'm wondering if its a typo and the real efficiency is 69%.

That would be fantastic - producing 30kW+ of heat while charging. Enough to keep your house and your car and the pavement warm  >:D
 

Online SiliconWizard

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That's all ok, because
Quote
ORNL didn't explain how its "polyphasing" differs from the phased electromagnetic fields in traditional inductive charging, but did say "rotating magnetic fields generated by the coil phase windings boost the power."
 

Online EEVblog

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So you have two technologies, competing on the "lowest point of the car" - either you raise the battery pack (not by a lot, due to seating, very bad for the handling of the car), or you lower the coil. Which is not ideal, either, unless you can lower it mechanically when charging.
Not sure how to solve this conflict.

When you have a couple of kW heater right next to your battery pack...  :scared:
 

Offline coppercone2

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I noticed something interesting over the years. Its usually heaters that catch on fire.
 

Online SiliconWizard

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Tesla Model S can allegedly evacuate 10-20 kW of heat from the battery pack at steady state on the highway.

These numbers showing us that an EV on the highway has nowhere near the efficiency some dream about. :bullshit:
 


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