Field weakening
6.2.10.1 Synchronous motor
The d-current component is normally equal to zero in a synchronous motor.
The "field weakening range" is the speed range, which can only be reached if a
negative Id is set.
This negative magnetizing current (Id), which counteracts the pulse wheel voltage,
is preset by the maximum voltage controller. Thus higher speeds can be reached
with the same torque (but higher total current).
If the inverter is in error state, the magnetising current is = 0 A.
The motor regenerats the full rotor voltage into the inverter.
This voltage must not be higher than the overvoltage threshold, otherwise the in-
verter will be damaged.
The safety distance which should be maintained to the max. speed is preset with
pn70 overspeed factor (EMF). A value of 90% for pn70 means, the error is trig-
gered at 90% of the max. theoretically permissible speed value. The resulting limit
value is displayed in pn72.
The response to the error is defined with pn71 E. overspeed (EMF) st. mode. Since
this speed range should only be reached when the motor "runs away" or the con-
trollers are badly adjusted, the safe response is 0: fault.
If the speed measurement is decelerated (smoothing by Pt1 and scan time) this
deceleration must be considered and pn70 must be selected lower.
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