Electronic Brake by wire system/regenerative braking

[Colin Mackintosh]

hello

I am doing a project for college and my project is an electronic brake by wire system with regenerative braking. the aim is to brake 4 wheels simply by a an input. the hard section which i am struggling with the designing a way to get the kinetic energy under braking in to electrical energy and store it in a bank of capacitors and then release the stored energy to produce more momentum/speed. what is the best way to capture this energy and how?

if anyone who could help me out with a schematic and data sheets for components.

 

[hevans1944]

The classic way to do this provides each wheel with a motor/generator, i.e., a motor that will also operate as a generator as well as a consumer of electricity, but not at the same time of course. The motor function provides motion to the wheels and builds up kinetic energy by virtue of the mass of the vehicle in motion. When it is time to brake, the motor becomes a generator. For non-regenerative braking the electrical energy is simply dissipated as heat in a load resistance. For regenerative braking, the electrical energy must somehow be stored, such as in a bank of capacitors as you suggested.

Energy could also be stored in a flywheel, typically spun in a vacuum to reduce windage losses, and recovered by using the flywheel energy to drive a generator or, mechanically, the drive train. The electro-mechanical details determine the overall efficiency, which is not large by any means currently employed. I believe flywheel energy storage has been tried in Europe to allow electrically powered mass transit buses to operate, with limited range, while separated from the usual overhead power lines. We have electric trolly buses here in Dayton, but none use regenerative braking to recover storable electrical energy. For "off grid" propulsion, the city uses diesel powered buses that are not equipped with electric motors for "on grid" power.

There is currently no electrical energy storage technology capable of efficient use in a vehicle. This includes electric cars with advanced battery technologies. But not to worry, automakers are "working on it" so we should see practical results "real soon now."

 

[Colin Mackintosh]

thanks for that, it really helped. Ive been looking at a way to do the regenerative part but im stuck. i am looking at capturing the energy from a pair of transistors which are connected to a motor in a H-Bridge circuit. does anyone know how i can integrate it in to a H-Bridge ?

 

[(*steve*)]

I'm not sure how advanced you are, so some of this may be overly simplistic or completely opaque.

There are several practical approaches to regenerative braking. The simplest is to connect the motor/generator to a large resistor bank. If you want to modulate the braking effort then you could use PWM or some other similar means.

If you want to use the energy for something useful then you need to go to a bit more effort. Let's assume that you want to charge some batteries.

Consider that simply connecting the motor/generator to the battery bank via a diode will provide maximum braking effort when the generator is being turned quickly, and less, and eventually none as is slows down.

In order to be able to maintain braking efficiency at lower speeds you could sacrifice braking effort at high speeds, but that seems silly.

A better approach is one which has some similarities to MPPT battery chargers. An MPPT charger is essentially a switchmode regulator which varies its operating point in order to maximise the energy transferred from the solar panels to the battery.

In a similar way, you could employ such a circuit to get the maximum braking effort possible by maximising the power drawn from the motor/generator at any speed. (However you probably don't want that either!)

If one assumes the output voltage of the MPPT regulator is constant (as it very nearly s when charging a battery) then the output current is proportional to power. In order to use this to modulate braking performance you need to track an output current proportional to brake pedal displacement rather than a maximum current.

In this case the design probably becomes much more like a constant current SMPS (e.g. a LED driver) albeit with a variable current.

You would probably want to determine when regenerative braking was no longer able to meet the braking effort defined by the displacement of the brake pedal and then to apply mechanical brakes to supplement (and eventually totally replace) the regenerative braking as the vehicle slows.