Re: AC drives

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:

> DC Brushless motors are really misnamed. THEY are truly

synchronous

> motors. AC servo motors
> are VERY similar to ordinary AC induction motors, and they ARE
> asynchronous, as they have to be
> for the induction principle to excite the rotor.

I've been confused between DC Brushless and AC synchronous Servo
motors and thought I'd sorted this out, but now I'm confused again.

The MAC AC Servo motors by Indramat (now Bosch Rexroth) are described
as synchronous but they are not similar to ordinary ac induction
motors. They have a wound stator, electronic commutation, and a rotor
comprised of 6 (or another multiple of 3 presumably) permanent
magnets, rather than the squirrel cage of conductors which form the
normal induction motor rotor. As far as I can see there is no
induction involved - the stator produces a rotating magnetic field
and the magnetic rotor follows it. What makes it synchronous is the
commutation which signals the servo drive to supply the correctly
phased stator drive.

How would you describe that type of motor?