How does regenerative braking vary the load?

[noagname]

TL;DR

They all are able to regulate the braking force based on angle of the brake pedal but what is changing in the circuitry to enable that.

Lately, I've been reading about the electronics required for driving motors and naturally that transitioned into braking. I think I have a decent grasp on resistive braking but I do not fully grasp regenerative braking.

This plus googling gaps in my knowledge have been my primary sources.

Looking at the diagram in section 4, I can see how the battery would be recharged while the generator is outputting a voltage greater than the battery's voltage. The thing I do not understand is, how do vehicles vary the amount of regenerative braking? They all are able to regulate the braking force based on angle of the brake pedal but what is changing in the circuitry to enable that.

 

[Baluncore]

The thing I do not understand is, how do vehicles vary the amount of regenerative braking?

The simple circuit shown requires more transistors to make it bi-directional.

The battery voltage is reasonably fixed so the braking is controlled by regulating the motor generated current flowing to the battery.

 

[noagname]

Ah ok, this makes more sense.

Follow up question, Does the regenerative braking circuit split that current between going back into the motor and into the battery? If so, is maximum braking force when all of the current goes back into the motor and minimum braking force when all of the current goes into the battery?

 

[DaveE]

You can think of the motor braking as similar to acceleration. The amount is determined by the voltage applied. If "positive" voltage accelerates, then "negative" voltage will brake (for a given motor direction).

It is the control circuit's job to apply the correct voltage to the motor. This is usually done in a PWM fashion where 40% braking is applied as 100% braking for 40% of the time at a frequency that's high enough that the motor doesn't respond to the ripple.

 

[noagname]

Hi Dave,

Ok, I think I see what you are saying. By sending the voltage from the generator to the battery in a PWM style, we can effectively control the load on the motor. Where is the voltage going during the off periods? Back to the motor?

Also, if you have any books or guides, I'm more than happy to read them.

 

[anorlunda]

Does the regenerative braking circuit split that current between going back into the motor and into the battery?

The braking system is not separate. The motor becomes the generator during braking. Same device for driving and braking.

You need to clarify the scale you are thinking about. A locomotive and an electric bicycle don't necessarily use the same methods.
.

 

[hutchphd]

To my understanding one serious problem with regenerative brakes is any good brake needs to be able skid the tires (or rather supply enough force to "not quite" do so). Conversely then the motor needs to be able to "burn rubber" when accelerating (even at speed)! This power is usually not available and I believe this fundamental problem increases significantly the added weight and complexity particularly on a bicycle for instance..

 

[noagname]

The braking system is not separate. The motor becomes the generator during braking. Same device for driving and braking.

Sorry, I worded that poorly. I do understand that the motor becomes the generator

In terms of scale, I'm thinking about E-bikes/scooters territory but I'm curious in general.

Really, I'm just looking for a guide about the circuitry for regenerative braking.

 

[jrmichler]

Try searching four quadrant drive, then adding some of the following: Siemens, Allen Bradley, power electronics. You might not find what you want online. In that case, look for a power electronics book.

 

[noagname]

Ah, thank you this is exactly what I was looking for!

 

[Windadct]

The - interesting, or challenging thing to think about - is in an AC motor drive, the inverter, always has the potential to act like a brake, because the Inverter inherently will act like a passive rectifier. So the case when the motor voltage (peak) is higher than the battery voltage then it will act like a brake.

Luckily this is essentially never the case - so what about when the Motor Voltage is less then the Battery(most common)

Then the inverter needs to be run as a boost mode rectifier(or active rectifier), where the inverter effectively shorts the motor to generate current, and then turns off - and current is dumped into the battery. The Controller / PWM cycle manages the current which is proportal to the torque.

 

[noagname]

Try searching four quadrant drive, then adding some of the following: Siemens, Allen Bradley, power electronics. You might not find what you want online. In that case, look for a power electronics book.

Thanks for giving me the right search term! I went down the road of H bridges and then half bridges and then I found this excellent guide!