Hi Azalin,
I don't think that is quite what I had in mind. I think that setting modifies the behavior of the Space Vector Modulator which is the drive output mechanism.
It sounds like it might get you a few more rpm but it also sounds a crude way to achieve it, I imagine the electrical noise of the drive would go from
bad (normal for servo drives) to shocking!

May I suggest searching Google for some videos put together by Texas Instruments about (and search by) Field Oriented Control. It a fascinating subject.
The upshot is that to maximize torque of an AC servo the applied field current must be in phase-quadrature with the field of the rotor. The control algorithm
results in controlling two parameters, Iq, the quadrature current and Is the in-phase current.

For a permanent magnet rotor you don't need any in-phase current to maintain the rotor field, so consequently for AC servo the controller tries to maintain
Is at zero. This ensures maximum torque for the least current but also ensures maximum Back EMF and therefore determines the highest
possible speed with a given supply voltage.

Where field weakening comes into play is when the controller tries to maintain Is at a negative value and therefore a fraction of the applied
field current is OPPOSED to the permanent magnet thereby reducing (weakening) the net rotor field. This in turn allow a reduction in Back EMF and therefore allows
a greater top speed with the same supply voltage.


The application of field weakening is progressive and smooth and linear. It does not in any way degrade the performance of the servo or unduly pollute the
power supply. Note that the application of field current to reduce the net rotor field is reversible, ie when the field weakening component of the current is
discontinued the rotor field returns t normal.

This is a very clever idea! I recommend to you those videos, it will give you a true appreciation of how AC servos work and why all electromotive control
engineers are nervous, chain smoking wrecks....like me!

Craig