[DennisCNC]

Will a 3PH VFD run a AC servo?
Will it run all of them or only some?

I'm thinking it will, but making sure.

[HuFlungDung]

Good question, and I don't really know the answer.

One difference that I can think of, is that a servo amplifier depends on the existence of a feedback positional error between its current position and the commanded position, in order for the amp to output a current to move the motor towards 'zero error'.

A VFD on the other hand, more or less runs a motor to an infinite position, since it never stops running (until the drive is commanded to stop), so I do not know if it is using an error loop to stimulate the output of a current.

Al or some of the other guys likely could tell you how an AC servo provides feedback to the amp via some kind of Hall effect transistors or something, and I am not sure a regular VFD can accept that kind of feedback signal.

[DennisCNC]

Forgot to mention: I just want to run the servo as a spindle motor. I think that servos are built better than most 3ph motors so they will last longer and go faster. I got a 400Hz VFD and wana see the 400hz being used

[ESjaavik]

AC Servo?
If it's a Permanent Magnet type it must be run synchronously. You could probably make it run using a VFD, but not using it's full torque. Reason is that the VFD does not know if the motor is in synch (it has no resolver or encoder input to verify this). So if you load the motor until it misses synchronism, it will not be able to recover and it will stop. If you know how a PM stepper works, the PM servo (BLDC) can be regarded as a stepper with very few steps/rev, and feedback to the drive.

[unterhaus]

ESjaavik, that's the way I like to think of brushless servos. I hooked a brushless servo up to an AMC control that will run without feedback and it spun it just fine. I didn't think it would do it.

There are VFD's that will run brushless servos, but there are a lot more that will not.

[DennisCNC]

I thought that a brushless AC servo is like a 3ph motor

[Al_The_Man]

A AC servo has a permanent magnet rotor, which in a servo should be kept in synchronism with the rotating field, hence the feedback sensors.
A 3ph induction motor induces the magnetic field in the rotor by means of its own magnetic field. The position of which changes as the rotor increases in speed, An ac servo can run in synchronism with the supplied AC, an ordinary squirel cage induction motor can never reach synchronism.
Al.

[interflexo]

A VFD with encoder vector control can perform servo work.

In this mode the user will command torque through the 0-10V analogue VFD's input along with the direction digital input. The user still needs one axis motion control hardware for trajectory planning with a bipolar analogue +/-10V output and an encoder to close the position loop. Some hardware is needed to convert the motion controller's +/-10V analogue output on the 0-10V analogue VFD's input plus the digital direction signal.

The induction motor can deliver 100% full torque at standstill but there are thermal issues when not using external electric fans or water cooling.

[clintonedward]

Will a 3PH VFD run a AC servo?
Will it run all of them or only some?

I'm thinking it will, but making sure.

The new VFDs with vector control can run AC Servo just fine as long as you set the parameters correctly. Otherwise, you can just use the VFDs with V/F method but the performance may not be that great.

[mike_Kilroy]

Try if u really want and have the motor and vfd. But my advice to u is dont spend money on either as u will not make a spindle out of it. Syncronization means just that. U will never keep it in sync due to torque disturbances. U likely will not be able to even accel from 0 to 20rpm b4 if falls out of sync and stalls. But experiment to prove it to urself. I have done this, i have spent 40 yrs as ee in servo field. Just dont spend big more money than u r willing to throw away and u can remain happy afterwards. This only 1/2 applies if it is vector vfd and mfgr has experience making it work.

Sent from my SCH-I545 using Tapatalk

[Al_The_Man]

The new VFDs with vector control can run AC Servo just fine as long as you set the parameters correctly. .

What make(s) of VFD?
I have tried BLDC motors on a VFD with very poor results, I contacted Hitachi when they announced theirs would run a P.M. motor and they replied the VFD would have to be custom tailored to the Motor!!
Max.