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DRV8711- Relation between sine current wave and PWM frequency and Vm

Hadi Kalani
Prodigy 120 points
Other Parts Discussed in Thread: DRV8711, DRV8825

Dear friends

I put a 8 pin deep micro switch to change tha value of torque in DRV8711. By changing the Torque value, fortunately I succeed to obtain the reasonable the sine cuurent graph. But when I change the Vm or PWM frequency this wave is destroyed. In result I must change the value of torque.

1- Is there any relation between the PWM frequency and Torque?

2-  Is there any relation between the Vm and Torque?

3- I do the same experints on DRV8825 and this deriver has also the same problem.  As you know  we need to change the speed of stepper motor in our devices during time.

Pleses help us kindly to deal with this problems. 

Many Many Thanks.

Hadi

 

  • 0
    TI__Guru** 114905 points

    Hi Hadi,

    Hadi Kalani said:
    1- Is there any relation between the PWM frequency and Torque?

    Yes, there is. Depending on the decay modes and off time, the average current in each winding may be lower.

    Hadi Kalani said:

    2-  Is there any relation between the Vm and Torque?

    Yes, VM affects how fast the current can be injected into the windings during the drive phase. At low VM, the full current may not be reached. The inductance of the motor also affects this.

    Hadi Kalani said:
    3- I do the same experints on DRV8825 and this deriver has also the same problem.  As you know  we need to change the speed of stepper motor in our devices during time.

    What is the VM, motor inductance and resistance, and rated current?

    What speed and microstep rate are you using?

  • 0 in reply to Rick Duncan
    Prodigy 120 points

    Dear Reck

    Do you think, is that right, by changing speed  (PWM frequency) of stepper motor the sine-like current wave is destroyed. Therfore, we must set the DRV register to approch the sine-like current wave for each speed (PWM frequency).

    What sholud be done that the variation of motor speed does not deteriorate the sine-like curent wave? 

    Many many thanks. 

  • 0 in reply to Hadi Kalani
    TI__Guru** 114905 points
    Hi Hadi,

    Can you provide scope captures of the current at slow and fast speed?

    What is the VM, motor inductance and resistance, and rated current?

    What speed and microstep rate are you using?