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DRV8305: Direction changing with 1pwm mode

vasanth kumar78
Intellectual 955 points
Part Number: DRV8305
Other Parts Discussed in Thread: TMS320F28379D

Hello,

I am working on BLDC motor to control the speed with TMS320f28379D launchxl.

with 1pwm mode, i am able to control the motor in both direction ,but ...in one of the direction i am getting half of the speed than the other i.e. with 50% duty cycle motor is supposed to rotate 5000rpm in both the direction ,but in Clockwise direction getting only 2500rpm only.

What settings should be done for this?

  • 0
    TI__Mastermind 26046 points

    Hi Vasanth,

    Let me understand more about your implementation. 

    Are you using the "DWELL" pin on INHC for your commutation? Are you using active freewheeling or diode freewheeling? Active freewheeling is usually more robust than diode freewheeling in 6-step commutation. 

    When you switch the direction, regardless of whichever mode you are using, are you going in reverse order of the states shown in the 1 PWM truth tables? Are your PWM state inputs (INLA, INHB, INLB, INHC) being controlled by an external MCU and not directly the Hall sensor outputs themselves?

    Thanks,
    Aaron

  • 0 in reply to Aaron Barrera
    Intellectual 955 points

    Thank you for your reply.

    Q:Are you using the "DWELL" pin on INHC for your commutation?

    No, if it is required your suggestion for how to implement 'Dwell mode' would be helpful.

    Q:Are you using active freewheeling or diode freewheeling? 

    Active freewheeling with 1pwm mode.

    Q:When you switch the direction, regardless of whichever mode you are using, are you going in reverse order of the states shown in the 1 PWM truth tables?

    We implemented  this way also but one direction only motor is rotating other one not rotating at all.

    Q:Are your PWM state inputs (INLA, INHB, INLB, INHC) being controlled by an external MCU and not directly the Hall sensor outputs themselves?

     PWM state controlled by MCU.

            Earlier  i implement directly the Hall sensor outputs to INLA, INHB, INLB (as INHC for dwell,didn't implement) but there rotation for other direction not working.

    current logic is to apply the next logic of hall state output as mentioned in guidance video for 1pwm mode.

  • 0 in reply to vasanth kumar78
    TI__Mastermind 26046 points

    Hi Vasanth,

    DWELL pin could be helpful, implementation of the DWELL state is shown by the INHC pin in the table above. DWELL reduces acoustic noise and smoothens out the current overlap during state transitions. 

    What type of motor load are you using? Does the motor resistance change or torque requirement change when going in one direction versus another? For instance, think of a fan blade....if the blades are angled, then going in the opposite direction requires twice as much torque, which will reduce the speed by half when using the same voltage. 

    Thanks,
    Aaron

  • 0 in reply to Aaron Barrera
    Intellectual 955 points

    Thank you for your support.

    My problem resolved by giving proper sequence of hall sensor as you mentioned in TABLE 3.