Originally Posted by
joeavaerage
Hi,
I suspect it IS a servo, which has a permanently magnetized armature surrounded by a three phase winding. Matecs test will confirm that within seconds.
If it is the there is NO VFD that will give you satisfactory torque control. The best VFDs are vector controlled, and vector control relies on the drive being able to determine
the rotor position (magnetically) by an 'estimator' which uses the current caused by the slip of an induction motor. With a synchronous motor there is no, or should not be, any
slip. Ergo the 'estimator' fails, and the vector drive becomes no more than a complicated V/F drive.
There are a couple of superb videos by Texas Instruments on 'Field Oriented Control' which will expand on Matecs description very well. There is yet more videos in the series
explaining the 'estimator' control strategy, also called vector control. It has its uses, but synchronous motors are not it.
You may be familiar with BLDC motors, they commonly have Hall sensors rather than an encoder to detect rotor position, and are used to 'commutate' the stator windings.
Such a device would work better with your motor, assuming you retrofitted Hall sensors in the correct arrangement, than a VFD. The resultant torque is lumpy though, but you
would get torque control.
I would recommend you watch the video, or even more than one, then you'll be much better prepared to make an informed decision regarding whether a VFD will work well
enough for your purpose.
I experimented with several VFDs and a largish (3kW) servo some years ago and was very underwhelmed. The video tells me why.
Craig