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FW version: Stable

Flux weakening

This subsystem uses d-axis current control to deliver adaptive flux weakening (extending the motor speed range under the same DC-side voltage, for the sake of the torque). Using an integrative feedback, the Back-EMF is kept within a specified range (fwm to fwr). The dynamic sensitivity can be adjusted with fwd. The following picture illustrates the typical enhancement achievable with a common SPM machine:

Field weakening

info
  • The following variables are located in the /driver/dac folder.
  • This page is related to the VECTOR algorithm only.

Parameters​

fwc [.iref]​

The flux weakening current limit <0:disable>.

fwm [.uref]​

If the uref parameter is not set, the actual battery voltage is used.

The flux weakening engage margin. If the Q-axis motor voltage rises above the value specified by this parameter, the negative D-axis current reference is increased. Similarly, if the Q-axis motor voltage falls below the value specified by this parameter, the negative D-axis current reference is decreased. The algorithm presumes that, by increasing the negative D-axis current, the Q-axis voltage generated by the motor is decreased and vice versa (by the field weakening effect).

fwr [.uref]​

If the uref parameter is not set, the actual battery voltage is used.

The flux weakening release margin. If the Q-axis motor voltage falls below the value specified by this parameter, the D-axis current reference (related to flux weakening) is reset.

fwr and fwm params operate together in a hysteresis loop. Always have fwr lower than fwm.

Tuning note

If yours motor's back-EMF is not sinusoidal, typically, to improve the behavior, set the fwm lower and increase the difference between the fwr and the fwm.

fwd [-]​

The flux weakening integrator gain.

This parameter defines how much (how fast) does the Q-axis voltage change affect the negative D-axis current reference. The higher this parameter is, the faster the response of the field weakening algorithm. The lower this parameter is, the lower risks of oscillations and smoother operation in the field weakening region can be assumed.

Tuning note

If your motor's back-EMF is not perfectly sinusoidal, lower this parameter.

States (only esc5)​

idref_fw [A]​

The calculated d-axis field weakening current reference.