How does the 2 stage regenerative braking work?

[Zaverx]

Hello, just wanted to ask a question about how the 2 stage regenerative braking (low vs standard regen braking).

I believe I understand how regenerative braking works and what it does, but I would like to know how these cars have 2 stages to the regen.

Thanks!

 

[Tessaract]

Not really 2 stages. Just more or less regenerative deceleration (with more or less regeneration). All determined by SW control of the motor phase voltages.

 

[jdcollins5]

A difference in the regen limit setting in software. Standard allows max regen. Low allows a lower regen limit.

Some people do not like the feel of full regen and prefer the lower setting.

 

[theothertom]

Here's an in depth discussion on the subject. It's for the Chevy Bolt but I imagine the same principals would apply.
Help me understand how regen works - Chevrolet Bolt EV Forum

 

[Zaverx]

Here's an in depth discussion on the subject. It's for the Chevy Bolt but I imagine the same principals would apply.
Help me understand how regen works - Chevrolet Bolt EV Forum

Ok, I believe I understand the concept now. So, in actuality, it has to do with the motor controller getting different frequencies and voltages... right? To me that makes some sense, I saw a video on the topic by the WeberAuto youtube channel, and he explained it well, but in his demonstration he used a resistor to create load. I think thats what I was confused about. Thank you for the link!

EDIT: Ok, so did a little more thinking and the easiest way I can simplify this is... by taking more voltage, you're stressing more load on the motor, which then slows down the wheels. So in a sense, all the different modes are doing is either taking a lot of voltage from the motor, or taking little voltage from the motor. Makes sense to me now.

 

[Tessaract]

Ok, I believe I understand the concept now. So, in actuality, it has to do with the motor controller getting different frequencies and voltages... right? To me that makes some sense, I saw a video on the topic by the WeberAuto youtube channel, and he explained it well, but in his demonstration he used a resistor to create load. I think thats what I was confused about. Thank you for the link!

EDIT: Ok, so did a little more thinking and the easiest way I can simplify this is... by taking more voltage, you're stressing more load on the motor, which then slows down the wheels. So in a sense, all the different modes are doing is either taking a lot of voltage from the motor, or taking little voltage from the motor. Makes sense to me now.

The explanation involving frequency is sort of correct.

In reality, in a synchronous motor, the frequency of the rotor and stator magnetic fields/voltages/currents are always identical (that's why it's called synchronous). What really happens is the "slip angle" between the rotating magnetic field of the rotor and the rotating magnetic field of the stator is varied. When the rotating stator mag field "leads" (is "ahead of") the rotor mag field, then "forward" torque is developed by the motor, and current is pulled from the battery (through the electronic invertor circuitry). When the rotating stator mag field "lags" (is "behind") the rotor mag field, then "reverse" torque is developed by the motor, and current is pushed into the battery (through the electronic invertor circuitry operating "in reverse"). The amount of slip angle determines how much forward or reverse torque is developed, and consequently how much current is drawn from or pushed into the battery.

The somewhat counterintuitive thing here is that the voltage of the electric drive waveforms to the motor do not change in voltage, just in the "slip angle" changes. How much current (and whether the current direction is into or out of the battery) is drawn, is merely a consequence of the slip angle. And that's why there are really no different modes at work here. Motor torque amount and direction are all controlled by one thing: the slip angle.

 

[user212_nr]

Ok, I believe I understand the concept now. So, in actuality, it has to do with the motor controller getting different frequencies and voltages... right?

When you power the motor, it works by increasing the frequency of the A/C current, hence putting more power.

When the motor is used for regen, those same settings produce more or less power, hence less regen.

The confusing thing is that the battery is DC power and the motor is AC power. You probably need to learn about how an inverter/rectifier works, and it probably gets pretty complicated before you can follow how it works.

 

[Zaverx]

The explanation involving frequency is sort of correct.

In reality, in a synchronous motor, the frequency of the rotor and stator magnetic fields/voltages/currents are always identical (that's why it's called synchronous). What really happens is the "slip angle" between the rotating magnetic field of the rotor and the rotating magnetic field of the stator is varied. When the rotating stator mag field "leads" (is "ahead of") the rotor mag field, then "forward" torque is developed by the motor, and current is pulled from the battery (through the electronic invertor circuitry). When the rotating stator mag field "lags" (is "behind") the rotor mag field, then "reverse" torque is developed by the motor, and current is pushed into the battery (through the electronic invertor circuitry operating "in reverse"). The amount of slip angle determines how much forward or reverse torque is developed, and consequently how much current is drawn from or pushed into the battery.

The somewhat counterintuitive thing here is that the voltage of the electric drive waveforms to the motor do not change in voltage, just in the "slip angle" changes. How much current (and whether the current direction is into or out of the battery) is drawn, is merely a consequence of the slip angle. And that's why there are really no different modes at work here. Motor torque amount and direction are all controlled by one thing: the slip angle.

Yeah. The way that that one guy described it in the Bolt forums that when you take current from the motor, it slows it down because of resistance. Basically, what I'm thinking here is, in Low regen mode, its taking less current from the motor, and then in Standard mode its taking a decent amount of power from the motor, hence producing more negative torque.

 

[Tessaract]

Yeah. The way that that one guy described it in the Bolt forums that when you take current from the motor, it slows it down because of resistance. Basically, what I'm thinking here is, in Low regen mode, its taking less current from the motor, and then in Standard mode its taking a decent amount of power from the motor, hence producing more negative torque.

Essentially, the notion of taking more or less power (more or less current, in reality) from the motor is correct. And the amount of current taken is infinitely variable (including going from negative to positive or "taken from" to "putting in"), so that's really why there aren't different modes, just different amounts of the same thing.

The Bolt forum explanation is a little untidy, and easy to misunderstand. Because electric resistance and mechanical resistance (as it's commonly understood) are different things, despite having the same name, and therefore easily confounded. Synchronous motors, with their 3-phase rotating magnetic fields are not easy to visualize, but when you do, everything falls in to place.

 

[Zaverx]

Essentially, the notion of taking more or less power (more or less current, in reality) from the motor is correct. And the amount of current taken is infinitely variable (including going from negative to positive or "taken from" to "putting in"), so that's really why there aren't different modes, just different amounts of the same thing.

The Bolt forum explanation is a little untidy, and easy to misunderstand. Because electric resistance and mechanical resistance (as it's commonly understood) are different things, despite having the same name, and therefore easily confounded. Synchronous motors, with their 3-phase rotating magnetic fields are not easy to visualize, but when you do, everything falls in to place.

Yeah, electric resistance is way different from mechanical resistance. Anyway, thank you for the help!