I dunno about that, it could be an active brake, using more juice to stop until it finally switches direction. If that's how it works out it's not a total loss, would be a nice feature to have if the brakes fail!
This made me think of something though.. if it's passive only then it's being rectified through the FET diodes. You'll be in for a bad surprise as those diodes suck!! high drop and terrible reverse recovery. Back them up with something substantial, one across each FET (a 3 phase rectifier).
Well, I ought to tell you why I went there.
I'm starting to think that the ideal motor would be more like a giant repurposed alternator. The control code would be based on brushless DC instead of induction, but the rotor field would be adjustable for the purpose of controlling torque (throttle or brake). So I'd need another PWM source there for the field. It should also be possible to replace the slip rings with a rotating transformer of sorts but really they aren't nearly as troublesome as brushes on a DC motor to begin with.
At first I figured it would be nice to get a stronger field than magnets or induction will do, DC's main advantage.. but the other benefits are nice. If doing a hybrid field+magnet I guess only modest magnets would do well to lower the static field current without causing too much EMF at light load.
someone at the diy board posted this:
Induction Versus DC Brushless Motors | Blog | Tesla Motors
Your controller should be able to drive brushless DC with only software modification (assuming the position encoder that comes with the motor is compatible).
So.. if you start tinkering in that area could you save an extra PWM out?
