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Issue in running BLDC motor with microcontroller

Discussion in 'Microcontrollers, Programming and IoT' started by pica, Jul 8, 2017.

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  1. pica

    pica

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    Jul 7, 2017
    Hello guys,

    I am in big trouble with sensorless BLDC motor project. I am trying to achieve the control of sensorless BLDC motor using microcontroller.

    I am using renesas microcontroller. I am able to run the motor but not getting first start.

    I am trying by sequence changing with particular delay but its not working.

    Once I rotate motor with hand, the motor is starting and then control is through back EMF.

    At back EMF stages the motor is working properly. I am worried about my project just because of start up issue.

    Please guys help me with the code to start the initial rotations.

    Seriously I am worried about my project.

    Requesting you all to reply me.
     
  2. kellys_eye

    kellys_eye

    4,275
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    Jun 25, 2010
    Can your motor power supply deliver sufficient start-up current? This can be many times larger than the steady-state value.
     
  3. pica

    pica

    36
    0
    Jul 7, 2017
    Yes. My power supply deliver sufficient start-up current. Please let me know the exact way for first time commutation softwarely. Awaiting for your reply.
     
  4. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Vary the control pulse such that the first few (start-up) cycles are longer than the 'free-running' cycles.
     
  5. pica

    pica

    36
    0
    Jul 7, 2017
    Yes You are right. Can you please show me the same softwarely. Do not write whole code. Just give me idea so that I can implement it. Please show me sftwarely. My project is at last stage.
     
  6. kellys_eye

    kellys_eye

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    Jun 25, 2010
    That's for you to implement - basically a loop that decrements a time interval over whatever the motor start up period/requirements are (see the motor data sheet).
     
  7. pica

    pica

    36
    0
    Jul 7, 2017
    Kellys,

    Thanks. After your suggestion and support, I am able to drive the motor and drive the motor initially.

    Now , What I am facing is, I am not getting torque for the motor. With sensor, my motor reaching upto 20A. But without sensor, it is reaching upto 7A only.

    Please suggest the same.

    Awaiting your help.
     
  8. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Keep using the sensor!

    The torque will be a function of the PWM (drive signal) period and should vary according to the load - in other words you NEED to sense the rotational speed in order to feedback to the PWM circuit (or software) to compensate for motor load and output more current to the motor to maintain its speed.

    If you remove the sensor the software thinks the motor is running at a steady speed/load and won't react to any changes.
     
  9. pica

    pica

    36
    0
    Jul 7, 2017
    Hello Kelly,

    Absolutely you are right. My application is based on sensorless motor.

    I can not use sensors.

    I have one driver which contains dedicated IC for sensorless which is not programable.

    My application is to replace that IC with microcontroller.

    With that driver I am getting 20A current. Also the performance is also quite good with respect to sensored driver.

    I have stucked on the 7A. At 7A motors stops.

    Please suggest.
     
  10. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Can you post a schematic of the arrangement you're trying to use?
     
  11. pica

    pica

    36
    0
    Jul 7, 2017
    Thanks for being online and your prompt replies.

    Which schematic you need. Just tell me.

    Please be online.
     
  12. kellys_eye

    kellys_eye

    4,275
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    Jun 25, 2010
    Post the schematic of the circuit you are using to drive the motor - the microprocessor version.
     
  13. pica

    pica

    36
    0
    Jul 7, 2017
    Please find the basic diagram of my application. Awaiting for your reply.
     

    Attached Files:

  14. kellys_eye

    kellys_eye

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    Jun 25, 2010
    The ULN2003 is your limiting factor. Try replacing them with discrete MOSFETS with low 'on' resistance.
     
  15. pica

    pica

    36
    0
    Jul 7, 2017
    Hello ULN2003 is not a driver IC. It is a simply separator of 5V and 12/24V as I am using microcontroller.

    The ULN is not the issue. The torque should be dependable on something that I don't know?

    Please let me know the same.
     
  16. kellys_eye

    kellys_eye

    4,275
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    Jun 25, 2010
    Torque will be a function of the voltage/current supplied to, and the inductance of, the driven load.

    The issues of LACK of torque parallel those when driving stepper motors and usually require a modified drive waveform - multi-level steps instead of straight 'square waves' that a PWM signal delivers.

    Phase timing is also critical.

    Have you checked the data sheet of the dedicated motor drive device? It will show the generated waveform(s) and you will need to emulate those to get full current at high speed.

    This is AFTER you've checked for areas where limitations could (may) be found in your own driver circuitry i.e. poor driver switching response, not reaching device saturation etc.

    Try 'scoping the drive waveform to see the signal - identify overshoot, undershoot, back EMF etc etc. Compare with the waveforms delivered by the integrated solution. In situations like this you need to 'see' what's happening - theorising is one thing but seeing it happening gives a great understanding.
     
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