Drive range questions

[rfguy]

I recently watched a very cool you tube video from Weber Sate University called a deep dive into chevy bolt drive unit. One of things I was curious about that was not covered is what happens in L range and R range. I have a theory that reverse is accomplished in the single power 3 phase inverter where any 2 phases are reversed via a contactor which would reverse motor rotation. I would like to know if this is true or not. Also I would like to know how L range increases the regenerative braking. In town we always drive in L range as the service brakes are not needed as long as the battery is not fully charged. Thanks for any comments.

 

[WetEV]

I recently watched a very cool you tube video from Weber Sate University called a deep dive into chevy bolt drive unit. One of things I was curious about that was not covered is what happens in L range and R range. I have a theory that reverse is accomplished in the single power 3 phase inverter where any 2 phases are reversed via a contactor which would reverse motor rotation. I would like to know if this is true or not. Also I would like to know how L range increases the regenerative braking. In town we always drive in L range as the service brakes are not needed as long as the battery is not fully charged. Thanks for any comments.

The motor is 3 phase, and is driven by 3 inverters, which are controlled in 6 logical phases, and is computer controlled. The computer will energize phases, one at a time, to make the car move. If the computer energizes 1,2,3,4,5,6,1,2,3,4,5,6,... the car goes forwards. If the computer energizes 1,6,5,4,3,2,1,6,5,4,3,2,1,... the car goes backwards. If the phases are moving at the same speed as the car, there is no acceleration or braking. If the phases move slower, the motor brakes the car. "L range" is just a software command to the computer to tell it to work harder slowing the car.

(Edit) I had read a paper on the firmware that does the logical control of the motor, and was confused. Sorry for any confusion I spread.

 

[SeanNelson]

The motor is 6 phase, and is computer controlled. The computer will energize phases, one at a time, to make the car move. If the computer energizes 1,2,3,4,5,6,1,2,3,4,5,6,... the car goes forwards. If the computer energizes 1,6,5,4,3,2,1,6,5,4,3,2,1,... the car goes backwards.

Exactly. There are no gears to change, and no contactors to open or close. It's not a DC motor where the current needs to be reversed in order to switch directions, it's an AC motor where motor speed and direction are controlled by the timing and strength of the current being applied to the various coils.

 

[Telek]

The motor is 6 phase, and is computer controlled. The computer will energize phases, one at a time, to make the car move. If the computer energizes 1,2,3,4,5,6,1,2,3,4,5,6,... the car goes forwards. If the computer energizes 1,6,5,4,3,2,1,6,5,4,3,2,1,... the car goes backwards. If the phases are moving at the same speed as the car, there is no acceleration or braking. If the phases move slower, the motor brakes the car. "L range" is just a software command to the computer to tell it to work harder slowing the car.

Sorry I'm a bit confused -- How do you figure that it's 6-phase when it's 3-phase AC power that runs it?

 

[WetEV]

The motor is 6 phase, and is computer controlled. The computer will energize phases, one at a time, to make the car move. If the computer energizes 1,2,3,4,5,6,1,2,3,4,5,6,... the car goes forwards. If the computer energizes 1,6,5,4,3,2,1,6,5,4,3,2,1,... the car goes backwards. If the phases are moving at the same speed as the car, there is no acceleration or braking. If the phases move slower, the motor brakes the car. "L range" is just a software command to the computer to tell it to work harder slowing the car.

Sorry I'm a bit confused -- How do you figure that it's 6-phase when it's 3-phase AC power that runs it?

The battery is DC.

No AC power is connected while the car is moving. The battery is all DC, all the time.

Electronics ("the inverter") switch the DC from the battery through the phases of the motor. These electronics make 6 phases, at the frequency and voltage needed to match the speed of the motor, and at currents needed to provide the torque needed.

The control of the motor is 6 phase. There are three sets of coils that make a magnetic field to push the rotor around, connected to the 3 phases output from the inverter. A complete cycle of the inverters has 6 zero crossings, one per logical phase.

(Edit) I had read a paper on the firmware that does the logical control of the motor, and was confused. Sorry for any confusion I spread.

 

[theothertom]

Here's another discussion on the subject:
http://www.mychevybolt.com/forum/viewtopic.php?f=11&t=8424

 

[Pigwich]

The motor is 6 phase. This means there are six sets of coils that make a magnetic field to push the rotor around, connected to the 6 phases output from the inverter.

eh.... I might have to disagree on the details of this, and sometimes stray a tad off topic, sorry, and I know you're knowledgeable, so a lot of this will be "no **** sherlock" to you, but for the benefit of others, I'll try to make some clever analogies.

The motor is three phase, the inverter is 3 phase, there are three AC cables running between these two components. This is set in stone.

The motor itself is an 8 pole motor, which is related to the number of times the coils and magnets are repeated around the rotor and stator.

More poles = slower speed at any given frequency, a lot like teeth on a gear. Frequency means how many teeth you can pass per second, and phases are how many intermediate steps there are in the passing of a single tooth..more or less. More phases = smoother. Smoother is better, but once you start moving at high speed, it stops mattering and three is plenty, and as we can clearly see (by driving the car) that even at extremely slow speeds, three phase is plenty smooth because the coils aren't driven at full or zero power, but rather in a set of three, synchronized sine waves offset by 120º. Some low speed motors, like stepper motors, are usually considered 2 phase, and definitely benefit from more phases. There are plenty of 3 and 5 phase steppers out there, and they're slick and fancy and expensive and overkill for most applications. 2 is usually fine, especially when the inverters (or drives in their cases) put out cute little sine waves.

Now on to that inverter. So say the internets, the inverter has a six step control scheme, which looks like it's just a way of them diddling the current and waveform (those sine waves again) to be more efficient at different speeds. Kinda like valve / ignition timing etc. But that number isn't phases. Again, going back to stepper motors, often, at low speeds they drive them with sine waves, but as the speed increases, the drive current can morph into a square wave to give more torque at higher speeds. Here's the other thing about inverters... Adding more phases means adding more transistors (IGBTs or whatever) which are probably the most expensive single components in there, and you need six for a bare minimum 3-phase inverter. And more for more phases.

 

[Telek]

The motor is 6 phase. This means there are six sets of coils that make a magnetic field to push the rotor around, connected to the 6 phases output from the inverter.

eh.... I might have to disagree on the details of this, and sometimes stray a tad off topic, sorry, and I know you're knowledgeable, so a lot of this will be "no **** sherlock" to you, but for the benefit of others, I'll try to make some clever analogies.

The motor is three phase, the inverter is 3 phase, there are three AC cables running between these two components. This is set in stone.

The motor itself is an 8 pole motor, which is related to the number of times the coils and magnets are repeated around the rotor and stator.

Pigwich is right and I agree with his analysis. I'm looking at the design documents right now to confirm - 8 pole, 3 phase AC, permanent magnet motor. The inverter has 3 phase AC output, 3 cables to the motor.

 

[WetEV]

Pigwich is correct. Thanks for the correction.