Speed Estimation; Characteristics - ABB FSO-21 User Manual

Note: Observe restrictions for use. Perform at least the Standstill Identification run
(preferably the Normal Identification run).
In the encoderless mode,
• the motor must decelerate when the power is switched off – for example, in a
crane application, the hanging load would potentially cause an accelerating
motion, thus the encoderless mode cannot be used for these types of
applications.
• the drive cannot be used in generator mode (torque limit) operation where an
external force is rotating the motor faster than the drive controls the motor.
• depending on the load, the frequency estimation of an encoderless drive may not
be equal to the actual induction motor speed.
WARNING! Do not use the encoderless mode in applications in which the
external load of the application can rotate the motor driven shaft (active load).
In this case, you must use an encoder.


Speed estimation

In the encoderless mode, the FSO module monitors the frequency with which the
drive rotates the magnetic field in the motor. The FSO module has no way of
detecting the actual speed with which the motor shaft rotates.
Note: "Speed" is used in this manual instead of "frequency".
Note: You must take into account in the system design that in the encoderless mode,
the FSO speed estimation and the actual motor speed differ by the motor slip, which
is dependent on the load of the motor among other things.
Note: The motor speed references in the drive refer to the mechanical axle speed but
the monitoring limits set in the FSO safety functions refer to the electrical frequencies
present in modulation. These two differ by the slip, which is dependent on the
operating point of the motor. You must take this into account when you define
monitoring limits for safety functions. Otherwise it is possible that unnecessary
monitoring limit hits occur.
Note: In the encoderless mode, the FSO module and the drive motor control system
calculate a speed estimation independently from each other. This is why the two
estimations can differ slightly.


Characteristics

The allowed speed range depends on the used motor.
Max. speed range =
Safety information and considerations 33
-30000...+30000 rpm
Number of motor pole pairs