VSD Autotune

There are several more important factors than just V & Hz in tuning a VFD related to using it in "Vector Control" mode. To have effective Vector Control, the VFD must track motor performance against the command using a closed loop feedback from the motor, both for position and saturation. Position is done either by external encoder feedback or by internal sensors in the VFD looking at very subtle current waveform distortions indicating the rotor bars passing through the magnetic fields in the stator. Those same highly sensitive current sensors along with rotor position then allows the VFD to track the changes in the current in each cycle to determine how much of the current goes to magnetizing the core (Flux Current), leaving the rest as Torque Current. By separating the vectors of those two components, the drive can then manipulate the V/Hz pattern within each cycle to maxize the Torque Current Vector without causing saturation by the Flux Current Vector, effectively getting the highest performance from the motor. All of this requires having a very precise mathematical model of the motor equivalent circuit in the microprocessor of the VFD. The basis of that motor model is created by either manually entering numerous values of data that often times users don't have, or having the VFD discover them empirically by using the Autotune feature.

If you are using it in basic V/Hz mode (also called "Scalar" mode), there is no need to do an autotune, but it does imporove the performance in some brands of drives that adapt the carrier frequency in sub-cycles to help prevent cable capacitive charging current issues and standing wave generation.

RTFM, if it suggests that you perform an Autotune even if using V/Hz control, it's a good idea unless the motor is within maybe less than 10m of the VFD.

Surprisingly, this is no longer clear in a lot of manuals now. When Vector Control first came out 20 years ago, everyone had to make a big deal about explaining it. The trend I see now in manuals is that they just tell you how to implement it, not how it works or why you use it. The same holds true for a lot of the low-end suppliers' "Tech Support" centers, especially those that are free. The people you get on the phone will simply read the manual to you. It's sad really...