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  • Author Author: dougw
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Make Life Accessible - Motor Suite Test - blog 8

dougw

This entry is a first exploration of the Kinetis Motor Suite capabilities, demonstrating motor reversing and sequencing through several states.

Next time I will try to hook up the Hall effect sensors to see if I can work at lower speeds.

 

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MLA Design Challenge

 

The full set of Clear Walk project blogs can be found here:

Make Life Accessible

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  • How do you think will Hall effect sensors help you at lower speeds? The state of the Hall effect sensors changes every 60 degrees of electrical revolution. This is of little help to FOC algorithm. They may help you if you are using trapezoidal control as back-EMF zero crossing detection is not reliable at low speeds, but FOC algorithm will probably use some other means of sensorless rotor position estimation.

  • in reply to kulky64

    The way I understand it, BLDC motors require sensing to know when to commutate the phases. When the speed is high enough, there is enough back-emf in the un-powered phases to deduce rotor position and figure out commutation timing. When rotation is not fast enough for significant back-emf or perhaps when no computer is available, Hall sensors can be used instead. NXP has an application note that might help explain it better:

    http://www.nxp.com/files/microcontrollers/doc/app_note/AN4058.pdf

    I don't know if it will work better, since I have never done anything tricky with a BLDC motor, but I seem to recall reading somewhere that hooking up the Hall effect sensors would provide better low speed control.

    Doug

  • in reply to dougw

    Hi Doug,

     

    The hall sensors should always allow you to know which phase in the commutation cycle you're at (i.e. even with a stall), whereas with the sensorless method you won't know at very slow speeds/standstill.

     

    Good luck with your project, and super-interested to hear more about the control algorithms. I used a BLDC chip for driving a DC motor a while back, and used the sensor feedback for speed/position determination. However it was an old-school method of control (using analog integration of pulses to determine speed). Modern methods using microcontrollers/DSPs are far more advanced. The FOC method mentions is quite new I think, it may well use things other than back EMF for sensorless control, but it is beyond what little I know about BLDCs. While the hall sensors may not help with that method (I have no idea), if back EMF is being used then at slow speeds there could well be issues.

    I tried to write up some short motor notes a while back, here and here - in case any of that is useful or gives ideas.

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  • in reply to dougw

    Hi Doug,

     

    The hall sensors should always allow you to know which phase in the commutation cycle you're at (i.e. even with a stall), whereas with the sensorless method you won't know at very slow speeds/standstill.

     

    Good luck with your project, and super-interested to hear more about the control algorithms. I used a BLDC chip for driving a DC motor a while back, and used the sensor feedback for speed/position determination. However it was an old-school method of control (using analog integration of pulses to determine speed). Modern methods using microcontrollers/DSPs are far more advanced. The FOC method mentions is quite new I think, it may well use things other than back EMF for sensorless control, but it is beyond what little I know about BLDCs. While the hall sensors may not help with that method (I have no idea), if back EMF is being used then at slow speeds there could well be issues.

    I tried to write up some short motor notes a while back, here and here - in case any of that is useful or gives ideas.

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