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All information related to Torque Control using FOC technique consider a current control, so they suppose a correlation between req_Id (Id desired) and requested mechanical torque. PI regulators tunning inside FOC control achieve zero steady state error, transient times, etc, but all based on a req_Iq=req_mechtorque principle. My experimental guess is that for the same req_Iq, when battery is at 84V or at 60V the FOC provides different mechanical torque when it is supposed to provide the same. I am trying to guess why. I know Ud and Uq are control signals for reaching the desired Iq, so Vbatt is considered as battery voltage drop is reflected in Vd and Vq, so why is torque reduced when lower battery voltages?

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Image source: https://www.roboteq.com/applications/all-blogs/13-field-oriented-control-foc-made-ultra-simple

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I think I can answer myself now: No, FOC control does not consider Voltage drop of the battery, so the "Torque control" is indeed a "Current control", so a voltage drop would result in a torque reduction for the same current, that is not considered in the equation.

Torque-Current Reference Generation can result from MTPA (Maximum Torque Per Amper algorithm), or could result from a different algorithm that considers voltage variation to compensate Torque-Current mapping.

There is no clear information about VDC compensation in FOC control for commercially available motor controllers, but it has been included in the newest release of Motor Control Blockset in Matlab:

FOC control with MTPA (voltage independent)

FOC control with custom Current Reference Generator (voltage dependent)

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