Re: VFD: sensorless vector vs v/hz models

--- In CAD_CAM_EDM_DRO@y..., "motovidia" <motovidia@a...> wrote:

> For a full size mill (bp clone), what makes the sensorless vector
> vfd superior or better than the "standard" volt/hertz types?
> TIA
> Femi

In theory, sensorless will give you better torque and control at
very low speeds (less than 10% of nominal speed). In practice,
I believe that on machine tools, gears or belts should be used
for radical speed variations, and VFDs used for moderate changes
only. I wouldn't run a machine tool motor less than about 1/4
of nominal speed, if only because of the loss of power.

(When you slow down a spindle using belts or gears, torque goes
up as speed goes down, and available power remains the same.
When you slow down a motor using a VFD, torque remains constant
as speed goes down, and available power drops in proportion to
speed.)

So, given that I would not run the motor much below 25% speed,
the better performance at low speed of a sensorless drive
doesn't mean much. I've had enough "mysterious" problems that
were caused by complex controls that I tend to prefer simple
V/Hz whenever it can deliver adequate performance.

John Kasunich