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Load to heavy, motor is shaking

Toriusss
Prodigy 40 points

Other Parts Discussed in Thread: MOTORWARE, CONTROLSUITE

Dear TI,

I'm running in torque mode for an application, FAST works fine and learning the motor etc. works ok. For this application the max phase current is clipped with 25A and a motor with gearbox

When the load is getting to heavy  the motor is offcourse reducing speed untill it stops. When the it stopped it's trying to startup (forceangle on) really shaky and uncomfortable, because it cannot overwin the load and its trying to restart very fast it seems. Also the sine wave is getting bad. When reducing load it's starting up nicely.

The difference with for example a hallsensor based FOC control application is that the algorithm stay's stable and is "pushing" without shokking.

How can I improve this behavior. I hope it's clear what i'm describing.

Please let me know

Torius

  • 0
    TI__Guru** 119680 points

    yes, it's clear.

    First I would say to disable ForceAngle.

    If you are just pausing it is better to let FAST work as your rotor sensor.

    However, if you stay too long at zero speed then of course the FAST software sensor will lose the angle.  Now you are in a situation with heavy load and no known angle.

    ForceAngle enabled will create a continuously rotating feedback signal in an effort to generate a stator flux output that can get the motor moving. This can cause shaking, reverse rotation, pulses etc. because the rotor and stator flux are not aligned. The forced feeback is telling the system that the rotor is moving, when really it is not.

    If you disable and just use FAST you are essentially getting feedback that the rotor is fixed at a position (which is initially true), but the angle estimate is just the last known value so it isn't accurate and you are unlikely to generate enough torque due to misaligned flux.

    Some things you can do to help the situation is to inject some Id current into the motor to help try to align the rotor and stator flux initially.  But it will have to be large enough to actually move the rotor, so it can be challenging in high load applications.

    this is discussed in SPRUHJ1 chapter 14.

    In both of the above scenarios you can generate enough torque to overcome some amount of load, but never really 100% load CONSISTENTLY.  So, in heavy load, low speed applications like an e-Bike the existing solution isn't really acceptable.  In a washing machine however our solution can work.

    The only real solution to this is to be able to sense the rotor position at zero speed and during initial movement until FAST can take over.  For sensorless we call this Initial (and slow speed) Position Detection (IPD).  We are working diligently on this topic and hope to start rolling out a portion of our solution in the next MotorWare update. There are several different techniques for different motor types and the roll-out will continue into 2015.

    Of course, you can also use hall sensors in some applications (at least as a first step).

  • 0 in reply to ChrisClearman
    Prodigy 40 points

    Chris,


    Thanks for your very clear reply, I understand it. I will look into chapter 14.
    IPD sounds very interesting. Do you have any time schedule for the new Motorware update?

    Torius

  • 0 in reply to Toriusss
    TI__Guru** 119680 points

    MotorWare _14 should release toward end of October or into November. The date is tied to some new HW we are releasing so the date isn't completely fixed due to manufacturing.

    Just a reminder, the first IPD solutions we share are NOT appropriate for all motor types.  We are first releasing something in MotorWare similar to what we have released in controlSUITE - a technique using high frequency injection for highly salient motors.  But in '15 we will release a solution that works on more motors.  We are spending our time on the "how to tune" and "how to transition FAST" portions...trying to make it as "Insta" as possible.