• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 84 subscribers
  • Views 1993 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

InstaSPIN for 3-ph stepper

ChrisClearman
Guru** 118000 points
Other Parts Discussed in Thread: DRV8301-69M-KIT

I've been playing with a 3-ph Stepper (50 poles, 80V+ capable) and DRV8301-69M-KIT @ 50Vbus

I can run at < 1 Hz, with 0 speed command full holding torque, and nearly instantaneous full speed reversals. Full speed (833+ Hz) with no load is about 0.63 A @ 50 V bus (powering entire kit).

Essentially everything in InstaSPIN-FOC and -MOTION work as is with 3-ph steppers except

  1. The Ls that is identified is valid for the low current test we do....but steppers are designed to take much more current, hence they will saturate at high speed and high load, lowering the actual Ls causing a current control instability. 
    1. Simply take the Ls that is identified, and divide by 2 when you store it in user.h
  2. It is possible that the current controllers (which use Ls in the calculation) are now too stiff. I did not notice this in my no-load experimentation, but it could be likely.
    1. If this is an issue simply divide IqIq Kp and Ki by two, and set those in the controller

 

What does using InstaSPIN-FOC on a stepper bring you?

  • Under constant velocity, current usage will be much less
  • Peak torque will be higher
  • Under a blocked rotor the angle will be held much longer
  • If you are able to move from a 2-ph to a 3-ph stepper operation will be more efficient because
    •  2-ph connection between the motor and the converter requires an additional wire or sqrt(2) more cross-section in one of the wires
    • 2-ph converter must be larger.  Either 4-phases with the same current on each phase, or sqrt(2) more Amps for one of the phases or all of the phases

I've also sent this over to LineStream, so I would expect to see something with an Encoder for additional position control at some point.

We are also looking at 2-ph stepper control for release at some later date...

Here are a few videos of the speed reversal....sorry, I haven't captured the single RPM control yet.

 

Curious if anyone is working with these types of motors....

 

  • 0
    Prodigy 130 points

    I am considering using a 3 phase stepper for a project but I have a question first.

    This application requires torque mode but at low/zero speed - so I plan on using an encoder.  To work properly torque ripple must be very low to non-existent (when turned by hand the operation should feel smooth) and I am concerned about the necessary encoder resolution to provide enough information about electrical angle to make this possible.  When using an 8 pole brushless motor a 4000 count encoder seems to ensure proper operation but when you substitute a 50 pole motor...

    So the question is - for a 50 pole motor what encoder resolution would you consider ideal?  

  • 0 in reply to Gary Swindell
    TI__Guru** 118000 points
    I've sent this to Adam, who works with encoders more than I do.
  • 0 in reply to ChrisClearman
    Guru 12800 points
    Gary,

    In order to get really smooth position control you want a fair amount of samples per electrical angle. In your system you will get about 80 samples per electrical angle. In running three phase steppers in sensored control, I've found it difficult to remove the torque ripple with an encoder that imprecise (relative to the number of pole pairs).

    You would probably need a a more accurate encoder I would guess in the neighborhood of 25000 counts or more. That way you can get a very precise angle placement for the FOC.

    If you were to use a PMSM you should be able to get very smooth control with a 4000 count encoder.
  • 0
    Prodigy 120 points
    I am starting 2ph stepper with instaSpin-FOC.
  • 0 in reply to Paul JayHoon Kim
    TI__Guru** 118000 points
    2-ph steppers won't work with InstaSPIN-FOC. Only 3-ph.