• State Resolved
  • Locked Locked
  • Replies 8 replies
  • Subscribers 82 subscribers
  • Views 956 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Speed sensor required for Lab 5B?

Chuck Sampson
Genius 3295 points
Other Parts Discussed in Thread: DRV8301

Hello,

I am developing a motor control for a rotary compressor. I am working through the Insta-spin labs and everthing is ok until I get to Lab5B.  We have no speed feedback sensors -encoder or tach. Does the F28027 allow for self-sensored or field oriented control? I thought the InstaSpin chips used an estimate of the motor's backemf to get speed feedback. Is this wrong? Do I need to use a different chip?

Thanks,

Chuck

  • 0
    TI__Guru** 119670 points
    proj_lab05b is fully sensorless. In fact all the instaspin_foc labs are fully sensorless. The speed estimation is being produced by the FAST estimator.

    What language is confusing you?

    In 5b the write-up talks about tuning the speed controller gains. IMO this section - while accurate - is confusing for those who aren't motor control experts and I recommend trying some educated guessing / manual testing as a better starting point.
  • 0 in reply to ChrisClearman
    Genius 3295 points
    Hi Chris,

    Where Lab 5b gets confusing is on page 89. The author references the speed feedback signal from a tach or an encoder and then goes into an explanation about the velocity filter transfer function. In my system I don't have a speed sensor or a filter. So if I am depending on the back emf for speed information do I just ignore this part -assume the velocity filter response equals 1- and carry on?

    Chuck
  • 0 in reply to Chuck Sampson
    TI__Guru** 119670 points
    "Where Lab 5b gets confusing is on page 89. "

    I agree. The write-up is generalized / theoretical and isn't specific to tuning the InstaSPIN-FOC system in proj_lab05b. The example that starts on page 106 is more helpful IMO.

    I've sent this to the author to see if he would like to comment.
  • 0 in reply to ChrisClearman
    Genius 3295 points
    Hi Chris,

    I think I have the answer to my own question. I researched the "Teaching Old Motor New Tricks" slides by Dave Wilson. On slide 6 he presents a schematic of the InstaSpin circuit. The motor voltages Vu, Vv, and Vw are routed through an RC network that acts as a voltage divider and filter and is input to the ADC. I checked the BOOSTXL_DRV8301_SCH pdf and found that same circuit with the actual component values. So if I assume we use the back_emf for the speed sensor, than the RC network in the DRV8301 schematic should work. I still would like to know what the response is from the author of the lab.

    -Chuck
  • 0 in reply to Chuck Sampson
    TI__Guru** 119670 points
    "So if I assume we use the back_emf for the speed sensor, than the RC network in the DRV8301 schematic should work."

    Bemf from the phase voltage as well as the currents are used by the FAST observer to give a rotor flux angle and speed estimate.
  • 0 in reply to ChrisClearman
    Genius 3295 points
    Oh yeah, forgot. Thanks for reminding me. I will start at page 106 as you suggest.
  • 0 in reply to Chuck Sampson
    TI__Expert 4760 points
    Hi Chuck,
    The voltage input filter parameters should not be used to infer anything about the velocity signal filtering. The voltage input filters are corrected for amplitude and phase shift within the FAST observer, so from a control loop perspective, within the frequency range of the motor signals, these voltage filters can essentially be treated as unity gain.
    The velocity filter is a separate filter inside the FAST observer which takes the internal (noisy) velocity signal and filters it before applying it to the FAST output. You set the pole of the velocity filter via the USER_SPEED_POLE_rps variable. rps stands for radians per second. This is a single-pole filter which creates a phase shift of the velocity signal. This MUST be accounted for in the velocity loop tuning process.
    Hopefully this answers your question.Regards,Dave