Regen circuit questions

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edoc

Member
Joined
Apr 8, 2022
Messages
6
Not sure how to ask this sensibly....but here goes.....Does the regen power (AC) go straight thru the inverter (AC to DC) and then flow straight to the battery ? are there a controller / activator/ breakers in the path ? From the inverter does it simply use the same HV wire back to the battery that the HV uses going to the inverter to power motor?
Bottom line of this question is ....if I have a continuous DC power source (Genset/ Power plant/ etc) ONBOARD , where would be the best place to "cut it into" the system to continually replenish the battery supply while the Leaf is being driven ?
My understanding is that safety design prevents the car from moving/starting while the charge ports are being active , so that makes that "entry point" difficult.
This all regards my guinea pig 11SV ...
Thanks for any and all thoughts.
 
Only 2 high voltage cables go to the battery(1 positive, 1 negative). The same wires power the motor and send power back to the battery. these are also the same wires that charging power is sent through. this youtube video shows you a guy making an adapter to T into(tap into) the high voltage cable going into the battery.

https://www.youtube.com/watch?v=UcGoSO_uRXs
 
Thanks mohammad,
That was great info and video, I had seen many (too many) Utubes but not that one !
It also led to others in a series.....so thanks

The problem I see is there are contactors, capacitors, etc in control of elec flow and setting off error codes shutting down the whole system.

ie " tapped in to the contactor lines that have entered the battery pack. So find the line to the P contactor and tap that to your own relays. You also need to sense the N contactor line, in case that drops first. So one diode to the P line and another diode to the N line, then connect together in a 'Y', and then use an appropriate resistor to connect to the auxiliary relay, such that if either N or P drops, the relay opens. To install a timer, add a mosfet and a capacitor, and use a voltage divider - but make sure that this does not introduce a delay in cutting off, when N or P drops!"

thats why I think if I can get a diagram of the regen circuit to tap into that would be safest. (maybe)

PS...... also learning the "precharge circuit" is a car killer if not dealt with .....hmmm

PPS ......further bog down points ....mostly for my future reference (ha!!)
" a Leaf that developed the same problem (P0AA1 main contactor error), and I was able to fix it without a trip to the dealer.

Thanks to the awesome work of Jim Pollock (Turbo3 on mynissanleaf) and creator of the LeafSpy app, there is now a non-Consult option to clear this code. He was able to determine the CAN message procedure to clear the P0AA1 code that was preventing my contactor from closing.

As this video demonstrates, this error that is likely to be encountered by folks hacking additional batteries or a vehicle to grid connection to their Leaf. If you make the mistake of applying high voltage to the switched side of the contactor when the car does not expect it to be closed, this hard error will be triggered (because it thinks the contactor has been welded shut) and the regular LeafSpy DTC clear function will not clear it. Consult III+ equipment is typically needed to reset (once any physical damage to the car is repaired).

I was very lucky. None of the parts were physically damaged in my car (precharge resistor still measured 30 ohms), but you should really check things out using the service manual procedure for this error before clearing the code.

Jim is going to add the P0AA1 clear feature to future versions of Leaf Spy,"
 
In Regen mode the motor is being back-driven thru the gearbox, and the spinning magnets of the rotor induce an EMF in the 3 phase windings. The body diodes (aka freewheeling or flyback diodes) of the 6 power IGBTs in the inverter rectify this and current flows back to the pack thru the + and - cables between the pack and the inverter.

Maybe this diagram from the Laef FSM will help you

HTFAvxY.png
 
Whoa.....Thanks
Is this the Leaf itself or a generic schematic ??

I'm pretty sure the leaf regen occurs by just a controlled polarity switch at the motor, with motor still moving in same direction forward...... but how the backfeed of the regened current is routed is my dilemma
 
There is not a single switch for the polarity of the motor since it is a 3-phase motor. The drivers for each motor phase are synchronized to the rotational position of the motor. The timing of when these drivers are turned on/off relative to the motor's position controls the various modes of the motor: drive, regen or coast.
 
yes thanks.....that was a much clearer statement then my mumblings....but as i said, what is the circuitry for that regen power? Guess obviously to the inverter first, but then how is it regulated back to the battery pack??
 
According to the schematic above there isn't much in the circuit between the motor and the battery except the IGBT. That is a bit of a black box since there obviously has to be more inside that component than a single IGBT but I wouldn't be surprised if it is fairly simple.

In general, regen is much more limited than normal charging so it doesn't need to be as well regulated. It's possible the regen current has quite a bit of ripple on it since it probably isn't allowed to reach the voltages supplied by a normal charging process.
 
edoc said:
what is the circuitry for that regen power? Guess obviously to the inverter first, but then how is it regulated back to the battery pack??
It's all in the gate action. There is no different path for regen power compared to motor power; regen power is just motor power with a negative sign. The current merely flows into the battery instead of out from it.

The fact that it's AC makes it a bit more difficult to visualise, but the principle is the same. So consider a battery and a permanent magnet DC motor, with a magical "DC transformer" between the battery and the motor. This "DC transformer" is the DC equivalent of the AC inverter and its motor controller. At stand still, the motor has no back-emf, so the "DC transformer" has to be at nearly zero volts output to get the motor started. As the motor speeds up, the back emf increases, and the "transformer" has to be careful to closely track the back emf, but stay just above it to keep power flowing into the motor. The back-emf (emf = Electro Motive Force) is a real voltage caused by the motor acting as a generator.

Now we're at cruising speed. For simplicity, let's ignore the power needed to keep the vehicle at speed, or imagine that we are going down a hill such that we need zero power to maintain that speed. The "transformer" arranges for the voltage across the motor to be equal to the back emf. The two voltages cancel, so there is no power flow, and no current out of or into the battery.

Now we want to slow down. The controller/"transformer" arranges for the motor voltage to now be slightly less than the back emf. That causes current to flow from the higher voltage source towards the lower voltage source (the battery), so power flows towards the battery.

At any time, if the controller goes crazy and tries to put a voltage across the motor that is very different to that of the back emf, then wild currents will flow, and safety systems have to cut in to prevent damage and/or burning the cables.

So "all" the motor controller computer has to do is to turn on and off about 6 gates at just the right time, thousands of times per second, to cause the accelerator pedal to produce expected torques (positive and negative).
 
Using figure 5 of the Texas Instruments datasheet, which represents the typical motor controller of an EV,

https://www.ti.com/lit/an/slua963a/slua963a.pdf?ts=1650513375551

one will notice the parallel diode within each of the six IGBTs, which gets forward biased when an EV enters its
re-gen mode (motor voltage greater than the battery voltage). Each winding of the motor will then conduct
a charging current back into the battery thru the upper and the lower IGBT diodes. The controller (MCU)
determines which mode the IGBT operates in by controlling its gate signal.
 
lorenfb said:
... one will notice the parallel diode within each of the six IGBTs, which gets forward biased when an EV enters its
re-gen mode (motor voltage greater than the battery voltage).
Err, not quite. If the vehicle goes so fast that the back-emf exceeds the entire battery voltage, then indeed the vehicle will hit a speed wall and can't exceed it without regenerating back to the point where the battery voltage is not exceeded.

But in normal operation, that doesn't happen. Back to the DC case, it's when the back-emf exceeds the "transformed" battery voltage that regeneration will happen. At cruising speed, in a properly designed vehicle, this will be way lower than 100% of the battery voltage, so you have some head room to go faster.

Of course, for simplicity, I'm ignoring field weakening, which effectively reduces the motor's back-emf (but also torque) so that the motor can enter a relatively constant power region for most of its operating speeds (like >= ~50 mi/h).
 
coulomb said:
lorenfb said:
... one will notice the parallel diode within each of the six IGBTs, which gets forward biased when an EV enters its
re-gen mode (motor voltage greater than the battery voltage).
Err, not quite. If the vehicle goes so fast that the back-emf exceeds the entire battery voltage, then indeed the vehicle will hit a speed wall and can't exceed it without regenerating back to the point where the battery voltage is not exceeded.

The motor controller prevents that.

coulomb said:
But in normal operation, that doesn't happen. Back to the DC case, it's when the back-emf exceeds the "transformed" battery voltage that regeneration will happen. At cruising speed, in a properly designed vehicle, this will be way lower than 100% of the battery voltage, so you have some head room to go faster.

Of course, for simplicity, I'm ignoring field weakening, which effectively reduces the motor's back-emf (but also torque) so that the motor can enter a relatively constant power region for most of its operating speeds (like >= ~50 mi/h).

Correct.
 
Thanks guys for all the feedback....so with the complexities of the regen circuit .......
In my case of trying to feed additional external on board DC to the battery , looks like I will need to feed the battery directly somehow (after the "protection breakers")
 
there isn't much in the circuit between the motor and the battery except the IGBT

This is a simplified schematic. There is a lot of stuff inside the IGBT block. There are six groups of insulated gate bipolar transistors (IGBTs). Each group has many IGBTs connected in parallel. The IGBT gates are connected to amplifiers called gate drivers. The gate drivers are connected to a microprocessor. The microprocessor has inputs for the accelerator position and the motor's encoder or position sensor. The microprocessor will determine the frequency, magnitude and phase of the three phase AC power needed for the motor. The phase can be adjusted to power the motor or make it regenerate. The current path for regeneration is the same as for accelerating.

I used to design electrical systems for electric fork lift trucks. The Leaf is similar to the newer AC forklift trucks.
 
How different or similar is the inverter/driver on an EV compared to a basic permanent magnet DC brushless motor driver using 3 H-bridges? I've used those before but I thought there was more going on with an EV type motor.
 
goldbrick said:
How different or similar is the inverter/driver on an EV compared to a basic permanent magnet DC brushless motor driver using 3 H-bridges? I've used those before but I thought there was more going on with an EV type motor.

The typical H-Bridge circuitry actually reverses the voltage to the stator to reverse the rotor direction,
where an EV PM motor controller (inverter) just changes the phases of the drive signals to reverse rotor direction.

https://electronics.stackexchange.com/questions/372215/a-question-about-servo-motor-direction-control
 
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