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TMS320F28027F: Very Low Speed Constant Torque control using FAST and FOC methods in general

David Doerschuk
Prodigy 20 points
Part Number: TMS320F28027F
Other Parts Discussed in Thread: LAUNCHXL-F28027F, LAUNCHXL-F28069M, BOOSTXL-DRV8305EVM

I'm investigating a constant torque motor controller that can can maintain torque to within +/- 0.75% of setpoint over a speed range of (-20 RPM) to (300 RPM).  I have three questions if I may:

  1. Control at low speeds from 0 RPM to ??? using FOC are augmented by the Forced Angle concept described in TI's literature.  Forced Angle seems to be primarily for initial starting of a motor whose target RPM is much higher. Is it also useful for control and, if not, where is the low-end speed cutoff for using FOC with a 2-pole-pair BLDC motor?
  2. I cannot find anything in the literature or the LAUNCHXL-F28027F lab project software source that supports the FOC maintaining constant torque control when motor speeds become negative.  The mechanical linkage on the motor's output will, in certain unusual process conditions, allow the motor to be driven "backwards".  Ideally, the motor would maintain constant torque control during these episodes, will FOC accomplish that?
  3. If either the low-speed or the negative speed issues disqualify FOC for constant torque control, then is there an alternative technology TI offers to make this possible without going to a rotation sensor solution?

Thank you very much!

David

  • 0
    TI__Guru** 114440 points
    1. For sensorless-FOC, it's difficult to maintain a vey stability running with a very low speed, it's better to use sensored-FOC. As you know, force angle is only for startup which is a current close loop without rotor position feedback control. And you can set the force angle speed by USER_FORCE_ANGLE_FREQ_Hz in user.h.
    2. Lab05a is a torque control mode, you can set the q-axis current reference to implement torque control, the torque current value will control the speed direction and value.
    3. Constant torque control can be used for any speed and run direction, the motor speed will depend on both torque current and load on motor shaft. As item 1, for very low speed, SPM and ACI motor is better to use sensor-FOC like instaSPIN-motion if possible.
  • 0 in reply to Yanming Luo
    Prodigy 20 points
    Thank you for the help, Yanming! I ordered a LaunchXL-F28069M and a new BOOSTXL-DRV8305EVM to go with it. They've arrived, I've got CCS 6.2.0 connected, and I'm reading about InstaSPIN-Motion. I very much appreciate your pointing me in the correct direction!
    Best regards,
    David