# A/C inverter as charger?



## DJBecker (Nov 3, 2010)

It's using the motor as the inductor for a buck-boost circuit.

It's clever when you first see it, but nothing new in the power conversion world.


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## bruceme (Dec 10, 2008)

DJBecker said:


> It's using the motor as the inductor for a buck-boost circuit.
> 
> It's clever when you first see it, but nothing new in the power conversion world.



That is a handy coil! Is there a name for this?

-Bruce


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## bruceme (Dec 10, 2008)

What keeps the motor from moving? Or is it mechanically locked while charging.

-Bruce


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## rmay635703 (Oct 23, 2008)

I assume the motor doesn't move because the field control isn't tuned/coordinated to move.


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## bruceme (Dec 10, 2008)

rmay635703 said:


> I assume the motor doesn't move because the field control isn't tuned/coordinated to move.


So it would just "hum" a little at best. Ok, this makes sense. So it really is that simple? Software and a few switches, why don't all A/C controllers do this?


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## Coulomb (Apr 22, 2009)

bruceme said:


> Software and a few switches, why don't all A/C controllers do this?


I believe that it's mainly because for real mains (240 V phase to neutral) has a peak to peak value of some 680 V, so you need 1200 V silicon; commonly used 600 V silicon (for up to 400 V packs) is not enough.

The hopefully forthcoming 1200 V silicon (up to 900 V DC bus) Tritium controller is planned to offer fast charging, but I believe it will require some external (to the motor and controller) inductors, which will add some cost and bulk, reducing the attractiveness of the idea.


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## Nathan219 (May 18, 2010)

The E-Tracers were pretty quiet while charging I only thing they had a cooling fan on some of the time, and boy do they look nice like a luxury car inside, watching them go around the skid pad was a bit scary though, their driver had more guts than I do. 
1200V IGBTs are pretty common, and if you have 460V input to the charger you would need to buck, right which would just use the fly back diodes of the IGBTs to rectify the AC and the controller would then just need to limit the charge current and voltage. Is that how it is supposed to work? I bet there is a thread on this already.


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## Coulomb (Apr 22, 2009)

Nathan219 said:


> ... if you have 460V input to the charger you would need to buck, right?


No. Even 460 VAC is less than the pack voltage for part of the waveform, and for decent "power factor" (low harmonics) you need to be using the mains for the whole cycle.



> which would just use the fly back diodes of the IGBTs to rectify the AC ...


Again, you can't just rectify the peaks if you want low harmonics and good use of the mains power.

The controller can readily boost to the pack voltage; that's ordinary regen operation. I don't think you can buck from the controller's output (which is really an input now, connected to the mains via an inductance) back to the pack. So that's the other catch: the pack voltage needs to be higher than the highest expected peak mains voltage, which would be about 375 V minimum, or something like 480 V nominal at least. This is common where industrial controllers are used, but many AC systems are still around the 320 to 400 V range.

If the pack was a lower voltage than the mains peak, then the IGBT diodes would rectify the mains and charge the pack in an uncontrolled manner. It's been a while since I looked at this, so I could be misremembering.


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## Nathan219 (May 18, 2010)

So we should rectify mains and put them on the DC bus and while the DC buss is disconnected from the battery pack and then the motor control IGB pair can pwm the DC to charge the pack. Seams simple enough, until someone really smart tells us we are all missing something. For 2 phase two of the output IGBT modules be used to rectify mains say 240V AC and the remaining IGBT be used to charge the pack using one of the motor coils to filter along with a filter CAP to stabilize the output to the pack? 
For three phase an extra IGBT to control the charge or a rectifier module. The issue would be the PWM channels they one would have to be switched to the charge IGBT but this would allow three phase charging then, with the addition of only a IGBT or Mosfet which could be smaller, a output CAP, and a contactor.


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## DJBecker (Nov 3, 2010)

bruceme said:


> So it would just "hum" a little at best. Ok, this makes sense. So it really is that simple? Software and a few switches, why don't all A/C controllers do this?


Besides the issues already mentioned (possibly needing higher voltage devices, extra components for input conditioning), you also need a DPDT contactor that can handle the full motor current. I don't know the market for these, but simple SPST contactors are expensive. DPDT contactors might cost more than the components for a stand-alone charger.

Using the motor as an inductor is likely to cause armature hum. This has the potential to cause excessive bearing and gear wear. Checking the design or adding an armature lock would be a simple pre-production step, but a big hassle for a one-off.


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## Nathan219 (May 18, 2010)

Contactor expensive, it would probably just be easier and more cost effective to build a charger into a controller design rather than multitasking drive components. The motor controller is a good place for a charger to live; it is also a good place for the DC/DC converter IMO. Is anyone building high power circuits for EV applications?


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