# Dual Regenerative Braking



## frodus (Apr 12, 2008)

Talk to the guys at Evdrive.com
I know Bob Simpson has done some vectoring with these controllers as well as regen. 

I don't think it would matter as long as there are two motors and two controllers with each having its own contactor going to a single battery.


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## ajosmer (Sep 27, 2013)

Why would this require a contactor? These are FET controlled motors.


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## ajosmer (Sep 27, 2013)

Also, thank you very much for the reference to EVDrive, they appear to be doing exactly what I am suggesting with the same motor controllers. If they haven't caught fire yet, it gives me hope.


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## dougingraham (Jul 26, 2011)

ajosmer said:


> The only part I'm concerned about is regenerative braking. We will be using lithium-ion batteries which are matched to the motor controllers by Zero, so single regen _will_ work. However, I don't know if we can safely brake with both motor controllers simultaneously, or brake with one while accelerating with the other (as in a corner for torque vectoring). I cannot think of an "ideal" electrical reason this should be dangerous, but I'm also hesitant to blow up several kWh of batteries next to our driver's tush.


The batteries don't care if there is one or two motor/controllers. The only thing you need to worry about is exceeding the limits of the battery both charging and discharging. You mentioned a 114HP limit. Is this WHP (wheel horse power) or battery horse power? If battery then we are talking about about 85 kilowatts input to the controller(s). If wheel horsepower then you are talking about 15% to 40% more battery power.

The zero kit looks like the limits are battery 102 volts and 300/500 amps discharge and 50 amp charge current.

The controller limits are 420 amps.

The motor limits are not shown on the datasheet but most likely the controller is the limiting factor short term.

Taking these limits it looks like a nominal 102 volts at 420 amps giving 42840 watts (57.4HP) which is not too far off of the claims.

Your greatest limitation is going to be charge current during regen braking. This is 50 amps so you are looking at a regen limit of 5110 watts (6.8hp).

Your best situation would be the case you are worried about, regen on one wheel while braking on the other. You could regen at the unlisted controller limits instead of the battery limits because some or all of the energy coming out of the braking wheel goes to the driven wheel instead of the battery. What the battery sees is a sum of the currents. So if the braking wheel is doing 100 amps of regen current and the driven wheel is doing 200 amps of drive this is a difference of 100 amps and the battery is still seeing 100 amps of draw.

It will take some fancy control software to take advantage of a dual motor arrangement.


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## ajosmer (Sep 27, 2013)

All of the numbers we're limited to are in electrical power (we're using 735 W/HP instead of 745, because America). The competition limits us to 85 kW peak output, and I think they measure from the main power lines, not individual controllers.

Thank you for the insight. I know Li-Ion can be finnicky about charging conditions, but after reading up on those particular packs some more, it seems that they have their own management system built-in and are controlled by CAN. If we feel really brave, we might even look at some boostcaps to buffer in some of the regen current, but since this is a racing car, the regen is mostly ancillary anyway. I was really just concerned about any weird waveforms that could be coming out of the motor controllers that might cause damage, but the batteries have cutoff circuitry already to keep that from happening.

I'm not so worried about the differential steering controls (maybe not as worried as I should be). Getting the theoretical numbers is all vectors and radii. The harder part will be making sure that the theoretical numbers are actually coming out of the motors without tearing up the tires. I think we might go for the simple feedback route of reading the speeds of the front tires and comparing them to the backs. There might be slip during braking, but that's another bridge for another time.


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