Hello all,
I am trying to make a prototype of regenerative braking in PMDC motor. I am using a 150 W, 24V, 2A PMDC motor.
Now in case of an actual electric vehicle, during braking the weight of the vehicle keeps the wheel in motion for sometime, till the vehicle comes to a complete halt.
I do not have the vehicle, so i was planing to use a heavy wheel. The problem is how should i calculate the amount of current drawn by the motor in terms of the weight of wheel. I mean how much current will be drawn from the battery for a particular weight of wheel?
Dear Jil,
not having a vehicle, putting all the necessary weight to a wheel does not seem to make sense.
Given that a real vehicle will carry an amount of energy E=0.5*m*v² you could calculate the wheels inertia I from Erot=0.5*I*wrot2 but the inertia depends on the wheel's geometry.
The current drawn from or regenerated to the battery depends on how long you need to transfer the energy stored. No matter if accelerating the wheel or recovering energy to the battery, Power is energy per time and the correlating current depends on the battery's instantaneous voltage.
Instead of using a fixed wheel, I'd suggest to connect the motor to a second electrical machine and simulate the countertorque using proper control. This would allow emulating various scenarios while the fixed wheel restricts you to a single case study only. This sort of setup also inherently is safer to operate.
Cheers - Martin
Dear Martin,
Thanks..That was helpful..
The experimental setup i wish to establish would be a Battery connected to the low voltage side of a Bi-Directional DC-DC converter and motor connected to high voltage side. Right now i am not using a converter and was simply trying to measure the time i would get for flowing the power back to battery. What i noticed was that without load, if i stop giving the supply to the PMDC motor, the back emf reduces to 0 from 24 V in 1 sec. Than I connected a light weight wheel to the shaft of motor as load and repeated the same thing, this time the back emf reduces from 19 V to 0 V in 2 sec. Both the time the current drawn was 0.20 for no load and 0.220 with load. so i thought of adding a heavy wheel to simulate vehicle effect. once i use a converter i can control the output voltage going to battery by controlling the duty cycle of the converter.
If I use an electric machine then I have to couple the shaft of the motor to a generator, will it then be same as above condition? or will I have to then increase the speed of generator greater than motor , just like the condition when vehicle is travelling down a slope to get regenerative action?
Regards,
Jil
Dear Jil,
the observation in your experiment when adding a wheel to the motor seems reasonable. However, the only thing the wheel changes is the inertia of the drive and thus the energy stored in the moving masses.
If instead you have a setup like:
Battery - Motor inverter - Motor - Generator - inverter - battery (or grid)
you can work the Generator in any of the four quadrants.
This way, the generator can drive or load the motor which reflects injecting energy into it.
This energy can be considered the kinetic energy of the moving vehicle.
If the inverter connected to the generator is well controlled, the generator will accurately appear to be the mass of the moving vehicle.
Inside the four quadrants of operation, this can easily simulate any point of operation your vehicle can experience.
As you can apply torque and speed in both directions, you can do
- Idling at any speed applying torque zero
- Uphill accelerating (spped>0, torque >0)
- Downhill accelerating (speed>0, torque >0)
- Downhill braking (speed>0, torque
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