how to soften bldc motor start up

Discussion in 'The Projects Forum' started by etiquoe, Nov 4, 2010.

  1. etiquoe

    Thread Starter New Member

    Jul 11, 2010
    27
    0
    hi..
    i'm still working on my sensored bldc motor driver.
    i need a solution to make my bldc motor start up softer.
    i'm using open loop speed control method.
    and one more problem is at above 50% duty cycle, no start up failure occur, but at below 50% duty cycle, the bldc motor start up often failed.

    anyone help please :confused:

    regards.
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Just by asking to help doesn't help at all.

    U got to show us what u have, tell us what u are doing and want, explain how well u are equipped for power electronics
     
  3. punisher454

    Member

    Jun 29, 2009
    16
    3
    I just got mine working, and one thing I noticed with the sensored setup is deciding how much advance to run.
    Since my motor had no data available I just decoded the right commutation sequence by marking out a degree wheel showing where the hall sensor's were on and off. then I started turning on different combinations of two coils at a time and seeing where the needle I attached to the shaft wanted to go. I filled in a whole table and then chose the UVW commutation sequence that was just a little advanced from the hall sequence. In this mode it sounded very rough and I believe it was cogging while running. the fets got hot quickly even with low pwm's. I figured I needed to advance the timing, so I changed the commutation table to the next position ahead and now it runs smoother, faster, cooler and I believe stronger.
    I also discovered while generating a commutation chart that I could do half stepping by activating all three coils. I dont have a use for that mode, but it was interesting to observe.
    I also got smoother operation by only using PWM on the low sides. I now keep the high side's at 100% during their "on"phase. I had it setup to be able to pwm all channels, but it used two different timers and I suspect that the timers were possibly out of synch.
    Anyhow, try adjusting your commutation table and see if it helps.
     
    etiquoe likes this.
  4. etiquoe

    Thread Starter New Member

    Jul 11, 2010
    27
    0
    actually, my bldc motor, has its dedicated driver. and i want to build my own driver for the motor. i got the commutation table for the motor by observing the hall sensor and the back EMF signal while the motor is being run by its original driver.

    i'm only using PWM on the high side, and keep the lowside 100% during its "on" state.

    i think my bldc runs smooth enough, and there's no problem with the FETs, but it starts up roughly.
     
  5. etiquoe

    Thread Starter New Member

    Jul 11, 2010
    27
    0
    what's the difference of only using PWM on the low side and on the high side?
    which method will give the best performance?
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Hey
    Why are u double posting
     
  7. etiquoe

    Thread Starter New Member

    Jul 11, 2010
    27
    0
    double posting?
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Yes...
    u already have a thread on the same topic.
    Please try to continue from there
     
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