The FOC algorithm provides control for
adjusting the rotor flux by changing the flux current component Id. Reducing the
rotor flux enables motor to enter the field weakening zone through which motor speed
can go beyond rated speed.
Note: During flux weakening operation, the motor cannot deliver
the rated torque. The torque limit Iq is automatically adjusted based on the
circular motor current limit defined by ILIMIT = Id2 +
Iq2 .
Steps to enable the flux
weakening:
- Set the FLUX_WEAK_EN bit in
FieldCtrl register as 1b.
- Adjust FLUX_WEAK_CURR_RATIO to
limit the maximum flux component of current to torque component current ratio.
This value limits the flux component current Id and maintain the torque
component current Iq based on the circular limit ILIMIT as Id2 +
Iq2 .
- Maximum modulation index beyond
which the field weakening is enabled can be tuned using FLUX_WEAKE_REF
configuration. This register field values sets the square of modulation index
value above which the Id is regulated to weaken the flux.
Note: Entering field weakening is not efficient below rated
speeds. Field weakening is recommended to be activated only when the modulation
index limit is reached and no longer be able to meet the desired speed requirement
with the sine modulation.