Regen circuit questions

[lorenfb]

Using figure 5 of the Texas Instruments datasheet, which represents the typical motor controller of an EV,

https://www.ti.com/lit/an/slua963a/slua ... 0513375551

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.

[coulomb]

So you think thats the actual Leaf Schematic ??

Yes.

[coulomb]

... 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).

[lorenfb]

... 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.

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.

[edoc]

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")

[RNeil]

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.

[goldbrick]

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.

[lorenfb]

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/q ... on-control