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TMS320F28054M: How to maximize torque at startup using sensorless InstaSPIN FOC+MOTION

Jørgen Haaland
Prodigy 50 points
Part Number: TMS320F28054M

Hi,

I need some tips on how to maximize the start torque when using InstaSPIN FOC+MOTION together with a low-inductance sensorless motor. I have read through chapter 14 in the instaspin user guide, and have enabled all recommended features (rs recalibration, rs online, forced angle). However, I want to know how to tune it even more. I have a use-case where I have very high static friction I need to overcome. Here are some questions I have:

  • Is there any recommended way to tune the force angle open loop control for a particular motor (by setting zero_speed_limit and forced_angle_frequency)?
  • The MOTION software is tuned with only one variable (system bandwidth). Would it be possible to get better performance by switching to using the PI controller that comes with FOC? 
  • How important is the SW limit for max current (USER_MOTOR_MAX_CURRENT)? I know this is only a SW limit and is not really limiting the motor from drawing more current. However, would an increase in this variable typically lead to higher start torque?

Also, if you have any other tips or relevant questions I would love to hear them!

Best regards,

Jørgen

  • 0
    TI__Guru** 111460 points
    Jørgen Haaland said:
    Is there any recommended way to tune the force angle open loop control for a particular motor (by setting zero_speed_limit and forced_angle_frequency)?

    Yes. You can refer to Chapter 14 and tune the variables as you mentioned above. If you want to start and run the motor with full load at low speed, you may have to use the sensored based InstaSPIN-Motion if possible.

    Jørgen Haaland said:
    The MOTION software is tuned with only one variable (system bandwidth). Would it be possible to get better performance by switching to using the PI controller that comes with FOC? 

    No if you mean the startup performance.

    Jørgen Haaland said:
    How important is the SW limit for max current (USER_MOTOR_MAX_CURRENT)? I know this is only a SW limit and is not really limiting the motor from drawing more current. However, would an increase in this variable typically lead to higher start torque?

    Yes, it's used to limit the torque current, not for over current protection.

  • 0 in reply to Yanming Luo
    Prodigy 50 points
    Yanming Luo said:
    Yes. You can refer to Chapter 14 and tune the variables as you mentioned above. If you want to start and run the motor with full load at low speed, you may have to use the sensored based InstaSPIN-Motion if possible.

    How should I tune USER_ZEROSPEEDLIMIT and USER_FORCE_ANGLE_FREQ_Hz? I have not found any guidelines on tuning this for a particular motor.

    Yanming Luo said:
    Yes, it's used to limit the torque current, not for over current protection.

    I understand that it is not recommended, but an increasing this value above the rated motor current could possibly help get a little more start torque from the motor?

  • +1 in reply to Jørgen Haaland
    TI__Guru** 111460 points
    Jørgen Haaland said:
    How should I tune USER_ZEROSPEEDLIMIT and USER_FORCE_ANGLE_FREQ_Hz? I have not found any guidelines on tuning this for a particular motor.

    In most cases, you don't need to change these two variables. If you want, just try to tune USER_ZEROSPEEDLIMIT to make the USER_FORCE_ANGLE_FREQ_Hz between 0 and 5Hz.

    Jørgen Haaland said:
    , but an increasing this value above the rated motor current could possibly help get a little more start torque from the motor?

    You can set the USER_MOTOR_MAX_CURRENT according to the maximum torque current of your motor and the maximum peak current of the hardware. Yes, the higher value will enable the motor to output a higher torque if the motor can.