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.