They aren't used for their cost, rather it's the fact that they are synchronous that is advantageous. It's possible to use an induction motor but it's much mor

They aren't used for their cost, rather it's the fact that they are synchronous that is advantageous. It's possible to use an induction motor but it's much more complex and because of that less accurate. A reluctance motor and PM motor with the same pole count can be driven at the same speed, whereas the speed of an induction motor depends heavily on the voltage driving it, the current speed, and the torque on it. You can only solve the drive equations accurately at zero load. Commutated DC motors could also be used but they are low efficiency.