The advantage of higher max. speed is contrary to several disad-
vantages:
➢ the drive has more „speed oscillation“ as in the base speed range
➢ Not all motors are suitable for field weakening operation. That
means, a very high magnetizing current is required to reduce the volt-
age, and thus be able to reach higher speed.
➢ The rotor position information must be very exactly. A system posi-
tion error of a few degrees (e.g. through malfunctions or inaccurate
encoder mounting) can make the drive out of control.
6.2.10.2 Asynchronous motor
The rated flow is reduced according to a 1/x characteristic in the field weakening
range, dependent on the output frequency.
The weak time (n
w
) is calculated from parameters dr05, dr28, dr25 (=> Field weak-
ening / Torque limiting characteristic Chapter 6.2.10.4).
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