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How to best run my Servo Motor sensorless

Ove Lerbrekk72
Prodigy 60 points
Other Parts Discussed in Thread: TMDSHVMTRINSPIN, LVSERVOMTR, DRV8301

Hello,

I hoped to run my 4-pol pair motor sensorless. I normally run the motor at low speed (50-1000 rpm)

I use TMDSHVMTRINSPIN kit and got it running.

Can a sensorless solution accommodate:

  • Go to position from start-up with accuracy within 45 mechanical degrees and hold a constant torque?
  • Give accuracy torque within +-5% @ zero speed

What is the best HW/SW I need to purchase to run this in the best possible way sensorless?

Thanks

  • 0
    TI__Guru** 119560 points
    Can a sensorless solution accommodate:
    •Go to position from start-up with accuracy within 45 mechanical degrees and hold a constant torque?
    No. The FAST sensorless observer requires rotor movement to estimate rotor angle position. It can not be used for position control nor constant holding torque control. There are other software techniques based on injection methodologies that we will be releasing - but they will be for torque and velocity control. We haven't tried them for position and it will probably be limited capability...but we'll see. These current injection techniques require motors to be specially designed as well with very high saliency.

    •Give accuracy torque within +-5% @ zero speed
    Again, no. FAST can not be used to provide accurate torque drive capability at 0 speed. It must be rotating at some minimum speed (depending on motor and HW design). It typically CAN be used to start-up from zero speed with nearly full torque, but it won't be full torque and it won't be perfectly smooth like a sensored application.
  • 0 in reply to ChrisClearman
    Prodigy 60 points
    Ok thanks
    I guessed that when the motor starts turning one could count the number of switching and estimate when it should stop.. or something :-)
    I have loaded the motor and are happy with dynamic performance.

    How should I drive the motor sensorless with TMDSHVMTRINSPIN to get smoothest start with load?

    And how to run for best end stop, if I want motor to hit "the wall" and stop after max reached torque?

    Thanks again
  • 0 in reply to Ove Lerbrekk72
    TI__Guru** 119560 points
    "How should I drive the motor sensorless with TMDSHVMTRINSPIN to get smoothest start with load?"
    Chapter 14 of SPRUHJ1 discusses this...there isn't any right answer. It really depends on the application and the load. I'd say typically that using the ForceAngle feature when starting from 0 will give you the most reliable start-up capability. How much load you can start depends quite a bit on the motor itself. I was just testing on the LVSERVOMTR and I could consistently start up with 6.7A of load (commanding 6.7A of Iq torque from a coupled motor) while this is a 7.1A continuous motor.

    "And how to run for best end stop, if I want motor to hit "the wall" and stop after max reached torque? "
    do you mean if the load > some value, you want the motor to stop?
    If you use the USER_MOTOR_MAX_CURRENT_A you can set the input limit to the Iq_Ref_A, so the speed controller will saturate at this value. If the load > this value the motor will continue to slow down until the load is large enough to stall.

    if you want to turn the motor off at this limit you would have to monitor the Iq_Ref_A signal from the controller and take some action.
  • 0 in reply to ChrisClearman
    Prodigy 60 points

    Hi again Chris,

    I use a 18amp Icont motor that gives 0,45Nm/amp according to datasheet. Ipeak 53amp. Ebus 300Vdc.

    Would TMDSHVMTRINSPIN be able to run this motor at 15Nm? I want  to run the motor with 15Nm load @ 300-450 rpm (500-700W ?) periodically..

    Thanks again for support! 

  • 0 in reply to Ove Lerbrekk72
    TI__Guru** 119560 points
    you will have issues as 15Nm requires 33A. the HVKIT can only handle peak and continuous currents of just under 10A. You should be able to ID and run the motor unloaded, and maybe load it slightly, but I'm afraid your peak currents will trip during start-up under much more load.
  • 0 in reply to ChrisClearman
    Prodigy 60 points
    Thanks again Chris,
    I am new in this game and i don't understand this stuff :-)

    I have loaded the motor with this kit (6-7 Nm according to GUI) manually by hand on the axel-wheel. When i locked my hands quick and hard i got the motor to stand still but it still produced "high" torque like a hammer. (that i understand running sensorless :-) )

    The kit will trip if i overload it right?! No danger? :-)
    I will test some more when i can and then with torque reading on output axel..

    I use Parke motor k500150-5y, could you look this up on web and explain why i manage to load it this much? maybe i read it wrong or they specified it strange?
    It is probably a simple explanation i just don't see it..

    Sorry for the inconvenience..
  • 0 in reply to Ove Lerbrekk72
    TI__Guru** 119560 points
    I'd say the torque value being reported is probably wrong, or the 0.45 Nm/amp value is wrong. The torque value can be wrong at 0 speed when there is no Bemf being generated. The Bemf value is essentially frozen and it may be at a larger value. You can look at the flux value in the Variables to see how it is changing when running at speed vs. stall.
  • 0 in reply to ChrisClearman
    Prodigy 60 points

    Hi again

    I have tested with an external torque transducer and got it up to 7,5-8 Nm (GUI reports about the same). When higher load it slows down and stops (work like a hammer @ 0 rpm). All I did in start-up was changing Max current from 5A to 10A before identify motor. Target was set to 200rpm

    With our own Control System we run this motor frequently up to the 15Nm. I guess we stress motor & system beyond specification but we are monitoring temperature, and both the system & motor has cooling.

    My question is:

    • Could I run this system up to 20A for experiments? What do I need to do?
    • If not, what do I need to use? Should/could I hook up DRV8301-hc-c2-kit to TMDSHVMTRPFCKIT?

    Thanks again!

  • 0 in reply to Ove Lerbrekk72
    TI__Guru** 119560 points
    no, you can't run the HVMTR kit at 20A. There is a fuse (10A usually) and the current scaling and IPM are <20A.

    if running Vbus <= 60V you could use the DRV8301 EVM. You can use the same TMDSCNCD28069MISO controlCARD from the HVKIT to run the DRV8301 EVM. You don't hook up the DRV8301 to the HVKIT though....completely separate.
  • 0 in reply to ChrisClearman
    Prodigy 60 points

    Ok so I need DRV8301-hc-c2-kit and a power supply that can give me max 60Vdc-20A-30A. Then I should be able to run my motor with to 12-15Nm?

  • 0 in reply to Ove Lerbrekk72
    TI__Guru** 119560 points
    what are the ratings on your motor? If it's rated for 300Vdc I don't think you'll create the necessary torque with only 60V will you?
    how much flux was detected (what are you using for USER_MOTOR_FLUX in user.h)

    We don't have an inverter that fits your exact needs. You will need to make your own for full capability.