I'll have a go at this:

A brushless DC motor is essentially an inverted DC motor. Normal DC motors
have a field on the outside (either coils for big motors or permanent
magnets for PM motors) and a winding in the center rotating bit, the
armature. The brushes conduct power to the armature via a commutator, a
banded or slotted copper tube connected to the armature. As the motor
spins, the commutator essentially reverses the poles on the fly, allowing
the armature to alternatl\ely push or pull at the fixed field, creating
rotation.

In a brushless DC motor, there is no commutator. The armature is the fixed
magnetic structure and the windings are on the outside. Something needs to
tell the controller the position of the armature so it can adjust or
regulate the windings. This is typically a hall-effect sensor, so most
brushless DC drives require that feedback, although more sophisticated new
models can sense position without feedback. These wires are usually called
Hall A, Hall B and Hall C, with one or more common leads. Thus, a brushless
DC drive is a bit more complicated than a regular DC drive. The advantages
to brushless a no wearing brushes, elimination of drag from the brushes,
and ability to reasonably sense position and speed, although not with the
accuracy of an encoder for feedback.

In a brushless AC design, the speed is proportional to frequency, unlike DC
drives where is is proportional to voltage. You would need a three-phase
system and a VFD to take advantage of these motors for speed control. Some
inverters do allow single-phase inputs and can control three-phase motors -
look around and you'll find them, although they are much less common and
more expensive due to the additional electronics involved.

Good luck!

Damian

"elitkh" wrote in message
oups.com...
what is the different betwean AC brushless motor and DC brushless
motor?
see this link: http://www.hnmotor.com/main/productlist.aspx
this company produce 2 product lines:AC brushless and DC brushless.
does AC mean i should use inverter to oparate the motor?
thank you
eli