Functions 09.2008
6SE7087-6QX70 (Version AK) Siemens AG
7-70 Compendium Motion Control SIMOVERT MASTERDRIVES
The maximum current limit of the motor and the converter restricts even
brief periods of operation in the field weakening range. If the sum of
squares Iq and Id exceeds the maximum permissible current, the motor
cannot operate according to the calculated characteristic.
The magnetization of the permanent magnets can vary as a result of
manufacturing tolerances and temperature fluctuations. In order to
improve the absolute torque accuracy in the control of synchronous
motors, it is essential to use the "kT estimator" (function diagram 393).
However, the kT estimator can be used meaningfully only in
conjunction with the friction characteristic (function diagram 399) as it is
capable of correctly only the inner torque of the machine. Friction
losses must be compensated via an additional torque from the friction
characteristic.
NOTE
Torque accuracy
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