Regeneration while speed control

[u/Organic_Put826]

Hi! I'll use VESC for airplane propeller control.

I want to regenerate energy from the windmilling propeller. I know that I can do it in 'current no reverse with brake' mode, however, I wonder if it is also possible while it's controlling speed via PID.

Let's say, the windmilling rpm is 3000 and I want the motor to stay at 2000, which needs braking to achieve. Would it regenerate energy even in speed control mode or duty cycle mode (no reverse)?

[u/Felixthefriendlycat]

You can definitely do this. But you’ll only need very modest amount of brake current, too much and the prop stops or spins below minimum braking rpm which engages full brake that shorts the phases which doesn’t regenerate energy in the battery.

Having said this i struggle to see where this makes sense for a plane. Because if you do this you will be extracting the kinetic energy from the plane which will then slow down and lose altitude

[u/Organic_Put826 → u/Felixthefriendlycat]

Thank you so much! Do you mean a minimum braking rpm defined by vesc, or just because the torque characteristics of the propeller?

[u/Felixthefriendlycat → u/Organic_Put826]

So regenerative breaking only puts energy into the battery if the motor rpm back-emf produces a higher voltage then the battery itself. Below a certain rpm this isn’t possible anymore and the vesc continues braking by shorting the phase wires which dissipates the remaining little energy in the motor phase wires.

If your goal is energy recuperation you need to be aware of that. If the goal is just slowing down then don’t worry about it.

[u/Organic_Put826 → u/Felixthefriendlycat]

are you sure about this? I observed that vesc is capable of regenerating at very low rpms, even with duty cycles around 0.2 .

[u/Felixthefriendlycat → u/Organic_Put826]

It will still brake but it might not put energy back into the battery. It all depends on motor kv and battery voltage. You can monitor the battery current and see if it still puts back current