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Sensorless Motor Driver with reliable start from zero RPM

HJWF
Prodigy 50 points
Other Parts Discussed in Thread: DRV11873, DRV8312, DRV8301-69M-KIT

Hello,

I am looking for a motor driver for an unusual application. I want to test the mechanical condition of a small turbine generator with a permanent magnet three-phase coil (thus a three phase PMSM, but used as a generator). For testing it I want to drive it as a motor with a simple test setup, utilising a sensorless motor driver. I was thinking of starting with the evaluation board for the new DRV11873. When the whole assembly is driven this way, I can determine its mechanical condition (mainly degree of friction of the bearings) by looking at the achieved RPM and consumed input current at a certain input voltage.

The challenge is that the turbine generator may have fairly high friction, specially at zero RPM, so it will need all the torque that such a sensorless motor driver can give, right from the start, to begin rotating at all.

To my understanding the typivcal driver configurations start with a controlled ramp until sufficient back EMF is available for the sensorless control mode. In my application such a ramp may need to be fairly slow, to overcome the startup friction.

For the DRV11873 I did not find any information about details of the startup algorithm however.  Therefore my question, if this driver evaluation module would be suitable for my application, would the ramp likely be slow enough?

Thanks in advance.

HJWF

  • 0
    TI__Guru** 114905 points

    Hi HJWF,

    I will have to do a little research, but will get back to you soon with the information.

    Can you tell me more about the PMSM you intend to drive? What is the inductance, resistance, max speed, motor voltage constant Ke? Does it have four terminals or three?

    Thanks.

  • 0 in reply to Rick Duncan
    Prodigy 50 points

    Thanks for the fast response, Rick.

    We have two slightly different (customised) designs. Phase windings connected in star configuration, but only three terminals, thus no access to the star point.

    line inductance : 6.3 mH at the first design, 7 mH at the second design

    line resistance : 4 ohms at the first design, 9.5 ohms at the second design

    voltage constant for both : approx. 0.3 V/rad/sec

    nominal speed 2600 rpm, upper limit up to 10,000 rpm.

    Note :  For the planned friction testing we probably will not need to drive it to nominal or max speed, it may be even sufficient to rotate the assembly at only 500 rpm, so a smaller motor driver may do.

    Thanks.

    HJWF

     

  • 0 in reply to HJWF
    TI__Guru** 114905 points

    Hi HJWF,

    Since you have no access to the motor common, you will have to make one for the board to work.

    Please refer to the post below. This post describes how to make an artificial common that will work for the DRV11873 using a either a wye or delta configured motor.

    0675.DRV11873(10873)Connection for Delta Wiring Motor.pdf 

    The startup procedure begins with an alignment phase, then blindly spins the motor at maximum torque, unless the maximum current is exceeded. If the maximum current is exceeded, the device will stop driving the motor until the current decreases.  Once it is determined that the motor is spinning sufficiently, the loop is closed and the motor is then controlled by the PWM input.

    Finally, the EVM should work for your application. There is always the chance that it may not as the motors you mention have not been validated.

  • 0 in reply to Rick Duncan
    Prodigy 50 points

    Many thanks, I will give it a try.

    HJWF

  • 0 in reply to HJWF
    Intellectual 370 points

    Hi HJWF,

    This driver EVM is also based on the DRV11873 chip. However, it is set for Delta BLDC motor by default (i.e. it has a resistor network installed).

    https://catalog.precisionmicrodrives.com/order-parts/product/m10-400-drivers-and-evaluation-modules

    HTH!

    Cheers,

    -Al

  • 0 in reply to Al Bencomo
    TI__Guru** 118240 points

    is your generator really only 12V 1.5A (the capability of the DRV11873 device)?

    I would suspect it is higher voltage and much higher current.  Please give the voltage/current of the motor and I'll give you some suggestions.

    For the start-up, does it just need to reliably start or must it always start in a single direction (zero reverse operation allowed)?

    Will the motor have a load when you do this testing?  Coupling?

     

  • 0 in reply to Al Bencomo
    Prodigy 50 points

    Hi Al,

    good to know that there is a new EVM available for the  DRV11873, thanks. For this task I meanwhile had to change to another driver however.

     

    Best Regards

    HJWF

  • 0 in reply to ChrisClearman
    Prodigy 50 points

    Hi Chris,

    you are right, the generator needs higher voltage and current. I just wanted to start with a simple solution however, so I was hoping that with this undersized driver the device would at least start rotating and run at a low RPM, so I could see if the rotor is still in good condition with reference to friction. Unfortunately the driver does not try long enough to start the generator (motor). After a quarter or a half rotation it stops trying.  I guess it does not see movement in the expected time and therefore stops trying.

    So I went to the next stronger driver DRV8312 and bought the EVM "595-DRV8312-69-KIT". Some more learning required to operate this one, but after I found suitable identification settings for the motor identification routine, it now works fine.

    The only enhancement I'm reflecting about is perhaps running the device at higher RPM, presently the 24V-supply limits it to about 600 rpm.

    Your questions :

    Regarding nominal supply voltage and current, there are no such parameters available, because it is a self-designed generator device.  The motor parameters are :

    Rs 4.8 Ohm, Ls 4.3 mH, Flux 0.98 V/Hz.

     These data are also being confirmed by the automatic motor parameter identification of "InstaSPIN MOTION"

    So If I want to run the device at about 3000 rpm, I guess I would need a supply voltage above 50 Volts.

    The available current from the EVM (3.5Amps) was enough at the given friction and loads to rotate, some more reserve would however be nice.

    Regarding startup behaviour, it is no problem if the device initially rotates a certain angle in the wrong direction, as long as it reliably starts up also under heavy load still.

     Best Regards

    HJWF

  • 0 in reply to HJWF
    TI__Guru** 118240 points

    Excellent, glad you had success with InstaSPIN-MOTION!

    There is a DRV8301-69M-KIT which support 60V/40A, it may meet your needs better.

    We also have a nice 10A version coming, but unfortunately it's only 24V so it won't meet your high speed requirements.

     

  • 0 in reply to Rick Duncan
    Prodigy 10 points
    Access Denied

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    When clicking this link. Please tell me more about the three wire wye configuration for this driver.