# AC induction motor regen



## vwdevotee (Mar 8, 2008)

I've been looking at motor controllers and I can see how for a three phase induction motor the DC power goes into an IGBT bridge and three phase power comes out. My question is, are there any hardware changes needed to allow regen? It looks as though when the motor goes into generator mode the current would just be pushed backward through the diodes. This would turn it back from three phase to DC power. I'm pretty sure there has to be some slick control with the IGBTs to control the rate of regen and the current pushed into the pack. Thanks!


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## etischer (Jun 16, 2008)

Regen can be done in simple volts/hz control mode. It's free, you don't have to do anything to make it work! 

Just make sure you have a way to disable the drive, or limit regen torque so you don't blow up caps or batteries. 

I could easily go from 320v to 450 with regen, now I taper off regen torque when the voltage reaches 350v. 




vwdevotee said:


> I've been looking at motor controllers and I can see how for a three phase induction motor the DC power goes into an IGBT bridge and three phase power comes out. My question is, are there any hardware changes needed to allow regen? It looks as though when the motor goes into generator mode the current would just be pushed backward through the diodes. This would turn it back from three phase to DC power. I'm pretty sure there has to be some slick control with the IGBTs to control the rate of regen and the current pushed into the pack. Thanks!


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## vwdevotee (Mar 8, 2008)

This might be something else that sounds simple but is really a devil, but depending on how much control of the current and voltage one has in regen, could the regen system be used to provide part of the functionality of a really high power charger? I would think that the controller wouldn't care if the AC power is coming from the motor in regen or from a wall in charging mode.


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## major (Apr 4, 2008)

vwdevotee said:


> This might be something else that sounds simple but is really a devil, but depending on how much control of the current and voltage one has in regen, could the regen system be used to provide part of the functionality of a really high power charger? I would think that the controller wouldn't care if the AC power is coming from the motor in regen or from a wall in charging mode.


Take your diagram from post #1. Get rid of T1, R, & T2. Put a 3 phase input to points U, V, & W. Put a battery across P+ & N-. 

Now get a schematic of a 3 phase battery charger and compare the two.

You'll see some similarity, and some differences. It isn't easy, or I'd say smart, to try to combine the two functions.

Regards,

major


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## vwdevotee (Mar 8, 2008)

I can see how it wouldn't be easy, but why would you say it's not smart? Other than making the entire system unusable if there is a part failure, I don't see any safety problems with it.


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## major (Apr 4, 2008)

vwdevotee said:


> I don't see any safety problems with it.


Isolation???

By "not smart", I wasn't necessarily referring to safety, but the added complexity and other issues which in my opinion make it unwise to combine functions on major components.

Not everyone agrees with me. ACPropulsion has their reductive charging system built into the controller.

Actually, I think the DC motor controller looks a lot more like a battery charger than an AC controller. How many combo unit have you ever seen on the market? Maybe the companies making controllers and charger agree with me.

Regards,

major


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## vwdevotee (Mar 8, 2008)

I'm not trying to be arguementitive, but how is isolation lost any more than with seperate units? I think I can see how the control circuitry could get a lot more complicated depending on how much additional functionality is added. I suppose I never thought about why more integrated options aren't available, I just went with the fact that frequently the chargers and controls were made by different company.

Thanks Major!


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## major (Apr 4, 2008)

vwdevotee said:


> but how is isolation lost any more than with seperate units?


I realize that at least one popular battery charger brand is not isolated, but most are, certainly ones that carry that UL logo. And that requires an isolation transformer, a component not found in motor controllers. You plug the charger into the wall, and do not do that with motor controllers.


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## frodus (Apr 12, 2008)

Exactly. With switch mode power supplies or PFC chargers, AC is rectified and put into what is essentially the DC-Link (Bus). Then its PWM'd through an isolation transformer to the final stage.


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