Simple regenerative generator/motor system

[shott92]

hi guys mechanical engineer here, with no electrical knowledge at all (sorry i know i must give engineers a bad name lol) however I am wanting to design/ price up a hybrid go-kart system (essentially to save on fuel)
basically what i am trying to figure out is the basic principles and equations for a regeneritive motor system
i have decided the simplest solution would be the following
engine -> generator -> batteries <-> motor
so engine to create power for the generator/alternator what have you, that charges the batteries should they become low, and the batteries power the motor to go in one direction but also acts as a generator (as i have heard this is simply a case of the magnets will force the current the opposite way??)
there are no parameters but I am thinking a 48 volt system would be best as i figure it lowers the current needed,
and i would like around 40Kilowatts (KW) output from the motor (also for efficentcy reasons and longevity i am inclined to use a BrushLess DC motor) apparently a mirco controller will be needed to do this (something i also know nothing about)
basically the things that need to be calulated are the engine power, alternator output (Amps, volts watts) (will a regulator or rectifier be needed) batteries how big will the bank off batteries i need be (amp hours, amps volts watts) i would like to do about an hour on just batteries from fully charged.and finally what sort of drive motor will i be looking at (will a BLDC motorwork the way i want and what consupmtion will it have ect)
i know this is a huge vague question but i really am interested in learning and since my knowledge is so vague google is not being much help :'(
thanks in advance you awesome people :D

 

[Baluncore]

i would like around 40Kilowatts (KW) output from the motor

Firstly, have you found a reasonably priced 48V, 40kW DC motor ?

 

[NascentOxygen]

the motor to go in one direction but also acts as a generator

Are you going to require the motor to operate simultaneously as a generator?

 

[shott92]

Firstly, have you found a reasonably priced 48V, 40kW DC motor ?

well I am not sure if they are the best ones or the best price - I've spend a good while looking and the short list ended up as either of these two

http://www.cloudelectric.com/product-p/mo-me1003.htm
http://www.thunderstruck-ev.com/motenergy-brushless-ii-pmac-me0913.html
if anybody has a recommendation suitable I am open to suggestion, although budget may be an issue
my alternative is if there is a good way of fixing a few of these together
http://www.hobbyking.com/hobbyking/store/__21969__Hobbyking_X_Car_4976_1740KV_Sensorless_Brushless_Motor.html
was thinking that trying to connect a few of these would cause plenty of problems in itsself though so unlikely i will go this route

Are you going to require the motor to operate simultaneously as a generator?

and do you mean generating power while powing the kart at the same time?? - if so then no. i am hoping to recover braking losses by using the motor as a brake (essentially engine braking) I am under the impression if you can control how much power you want to draw back from the wheels at a given point then you can control the deceleration, thinking maybe it would need a second controller to do this, that's if it is possible

 

[zoki85]

About principles and architectures for HEVs designs: http://groups.engin.umd.umich.edu/vi/w5_workshops/Chris_Mi_handout.pdf

 

[Svein]

i am hoping to recover braking losses by using the motor as a brake (essentially engine braking) I am under the impression if you can control how much power you want to draw back from the wheels at a given point then you can control the deceleration, thinking maybe it would need a second controller to do this, that's if it is possible

Hm. I recall an old Volvo Penta that had a "Dynastart", a starter motor that worked as a dynamo when the diesel engine had started. So it is possible...

 

[NascentOxygen]

i am hoping to recover braking losses by using the motor as a brake (essentially engine braking)

Does the driver do a lot of heavy braking? Is your foot at any moment in time either planted on the accelerator or on the brake? This is pertinent, because only if there's a lot of energy to be recovered would it be a worthwhile proposition.

 

[Baluncore]

The maximum regenerative braking, (deceleration), will be the same as the maximum vehicle acceleration from the electric motor.
You will therefore need some alternative form of brakes.

 

[shott92]

well the actual decelleration rate i would like to achive does not have to be to race standards and i would like to recover as much as possible for the purpose of this project, if this means that i would need to change my driving style then that would be OK, and if it can recover 25kw of braking effort then considering the wieght of the vehicle that should be plenty adiquate, and it should be a worth while proposition as if i was able to recover all braking losses then i would be able to recover all acceleration losses mean the only power i would need is that required to overcome air resistance and rolling resistance this should have a huge impact on the amount of energy used.
and i have been considering a mechanical KERsystem using a flywheel however the mass of the flywheel seem like it may become counter intuitive

 

[NascentOxygen]

A flywheel sounds like a great idea, until you look into it closely. A group at my university were working on a small vehicle project but it was abandoned after someone pointed out the car would flip over sideways when going up a hill. Slowing down the flywheel's spin poduces equal torque wanting to spin the vehicle frame in an opposite rotation.

Don't forget a heavy fast-spinning mass will have gyroscopic effects, causing weird steering and road handling. (I'm unsure whether a pair of flywheels will anull these effects.)

 

[Svein]

The maximum regenerative braking, (deceleration), will be the same as the maximum vehicle acceleration from the electric motor.
You will therefore need some alternative form of brakes.

Yes... The actual amount of regenerative braking depends on the charge status of the battery.

 

[Windadct]

IMO 40KW (rated) seems pretty big - note most vehicle rate their motors at peak power- but electrical motors are rated continuous - and at 48V... that is 833Ams! - Looking around there vehicle conversion kits at 15KW and 38KW Peak(for autos!) . Your topology seems OK, but for each element you add you increase the complexity dramatically because you have to consider the interaction of the sub-systems. I would start with Battery only - with the mechanical space for the Motor-Gen in the design for the future.
A pretty good site for info is http://www.diyelectriccar.com/ - lots of projects to look over and sources of parts and info.
As for the braking - the cart needs fully capable brakes (in addition to relying on regen).

 

[Mike_In_Plano]

I've designed many a brushless motor controller, and it's not something suitable for a novice. There will be any number of IC vendors that will sell you micro-controllers, but the first time such a part hangs up or "goes in the weeds," you'll end up with burnt junk for a drive and possibly a destroyed motor. Thus more effort is spent designing a safety system to protect the drive and motor than is typically spent on making the motor spin. If your shipping a consumer grade drive, than you can pull all that safety out and let the subsequent damages become warranty calls and scrap.There are also great hazards associated with the energies you're discussing. Yes, 48 VDC is unlikely to electrocute you, but try disconnecting a 48VDC line 500 amps going through it and you'll quickly realize that no normal switch will do this. For that matter, if your source capable of a sustained delivery in the 850 amp range, it will have a fault current in the many thousands or even tens of thousands of amps. No common fuse will break this . DC is much more difficult to break than AC, and the fuse must quench the highest possible fault current without simply arcing over and becoming a conductive path. UV flashes destroying eyes, jewelry melting on flesh, arcs spewing molten metal, components detonating. There are all manner of evil things waiting to happen at these energy levels.