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Q_D axis resistance and inductance

MARK PESACH
Intellectual 850 points

Hi

I am using the DMC library to control a bldc motor with FOC, i saw Dave Wilsons lecture on how to 

set the PI current controller coefficient (Kp,Ki) with respect to the RL constants of the motor.

if i understand correctly - for FOC we need the L and R in the Q_D reference?

if true i will be very happy if someone can explain or refer me to how calculate this values from the known phase 

to phase values .

thank you very much.

MARK

  • 0
    TI__Guru** 114905 points

    Hi Mark,

    Our experts have been contacted and should reply soon.

  • 0
    TI__Guru** 119380 points
    no, the R and L are not in a different reference. they are the actual Rs (ohm) and Inductance (henry) that can be measured. it depends on your observer if the values should be phase to phase or phase to neutral, and if delta or Y connected.

    If you use InstaSPIN-FOC it includes a Motor ID feature to find these values, load them into the observer (FAST), and set the PI current loop tuning based on these values.
  • 0 in reply to ChrisClearman
    TI__Expert 4760 points
    Hi Mark,

    Yes, you should represent the values as they would appear in the d-q reference frames. For a permanent magnet motor with no saliency, the values for d and q will be the same. If there is saliency, the inductance value will be different for both d and q. If it is an ACIM, the resistance value will be different between d and q.

    The voltages represented at the output of the d-q current regulators are peak values from line-to-neutral. Therefore, to scale the motor impedance properly w.r.t. the current, the load should also be represented as line-to-neutral. If you have the line-to-line values for R and L (delta wound), you can convert them to equivalent line-to-neutral values (Wye wound) by multiplying your values by 3.

    Before these values can be applied in InstaSPIN-FOC, they must be properly scaled. The I term is equal to L/R divided by the sampling frequency that the current PI controller runs at. The division by the sampling frequency accounts for the natural scaling required by any digital integrator. The P term is equal to L times the desired bandwidth (in radians/sec) times fullScaleCurrent divided by fullScaleVoltage. By default, in InstaSPIN-FOC we set the desired bandwidth (in Hz) to the current loop sampling frequency (in Hz) divided by 8*pi.

    If you have any additional questions, please let me know.

    Regards,
    Dave
  • 0 in reply to Dave (Wisconsin) Wilson
    Intellectual 850 points

    Hi
    thank you very much for the reply.
    Dave , i am a big fan of your videos and blogs ,thank you very much for sharing your knowledge! .
    i am not using InstaSPIN, i am implementing the FOC algorithem with the delfino IDDK code example , in sensored approach using absolute encoder .
    can you please explain how to set the fullScaleCurrent and fullScaleVoltage?
    fullScaleCurrent is the max allowed currents on Id and Iq axis?
    fullScaleVoltage is the max allowed voltages Vq,Vd on the id and iq axis in duty cycle percentage (1- is max)  ?

    best regards
    MARK

  • 0 in reply to MARK PESACH
    Intellectual 850 points

    just saw the explanation in the "Teaching your pi controller to behave part 10"

    thanks!