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How is motor torque calculated on the ATV320 series drives?

Published date: 23 April 2019

Issue:
Customer needs to know the formula by which motor torque is calculated in order to program some custom function blocks for their application.

Product Line:
ATV320 series drives.

Environment:
All models, all serial numbers.

Cause:
Information this detailed is not available in the programming or installation manuals.

Resolution:
 


OTR and SOTR represent the motor torque. 

OTR is filtered value and SOTR is unfiltered value.
The scaling is also different between OTR and SOTR.

This difference, one value with filter and the other one without filter explain the big difference between the maximum value of OTR and SOTR. 

SOTR will represent the instantaneous torque, compare to OTR that will add filter before display.
SOTR represent the real motor torque and OTR is more here to show the value on a display.

Concerning the range, OTR is expressed in % of nominal motor torque with 100% = Nominal motor torque. OTR value is signed with minimum value -300% and maximum value 300%

OTR and SOTR (the torque) are estimated based on motor current measured.
The torque of motor is not measured by the drive. It is calculated from the measurement of motor
current.
OTR = (Iq / Iqn) * (PhirdRef / Phirn) in %
With: Iq : Current torque provide by the command to drive motor
 PhirdRef : Flux provide by the command to drive motor
 Iqn : Nominal Current torque compute with the motor name plate
 Phirn : Nominal flux of the motor

This is for OTR. SOTR use the same data, but concerning the range, SOTR is expressed without unit and scaled on 12bits. SOTR value is signed with minimum value -32767 and maximum value 32767

Like there is no unit on SOTR compare to OTR, the both value will be different.

Example within Red OTR and in Blue SOTR
User-added image
OTR show 32.3% and SOTR show 130.5%

The relation is: SOTR = OTR x 4,096
In this example: SOTR = 32,3 * 4,096 = 132,3 (close to the 130.5 if we take into account the oscillation on the SOTR because of no filter).

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