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Is it possible to start any BLDC motor in FOC ...

tnhtn
Intellectual 800 points
Other Parts Discussed in Thread: INSTASPIN-BLDC, TMDSCNCD28035ISO

without tuning parameters?

In the past, we were able to start most  BLDC motors, from small ones to very big ones, by controlling the feeding voltage and the PWMs to the inverter ( with the traditional zero-crossing scheme);  but, of course, we suffered  spikes and therefore we are thinking to switch to FOC.

What should we concentrate on to  build an universal ESC only for  BLDC motors using FOC (without physical tuning for each motor)?

Would it be that by controlling voltage and PWMs it is enough to spin the motors in the FOC scheme?

I'd like to have hear advices to head me in the correct direction.

Many thanks.

  • 0
    TI__Guru** 119500 points

    Tinhtan Nguyen said:

    without tuning parameters?

    Not really.

    I mean, you can do open loop start-up or forced commutation and get many motors "to spin", but they aren't really being controlled.

    To have any automatic current control tuning you really need to know about the time constant of the motor (relies on R and L).

    To use any sort of sensorless rotor observer you can either rely on very rough 6-step style commutation estimations (like Bemf zero crossing or InstaSPIN-BLDC), but to do FOC you have to use an observer, which are almost all motor model based, meaning you need to know parameters of the model: for example FAST requires Rs, Ls, and Flux.

    AND these parameters can change during operation, so you need to be able to track them - which we can do with InstaSPIN-FOC.

    Tinhtan Nguyen said:

    Would it be that by controlling voltage and PWMs it is enough to spin the motors in the FOC scheme?

    Well, in any three phase motor control system you are only controlling voltages through PWM switching of an inverter....the key is in the logic (and feedback for that logic) to do so correctly to keep the motor stable and operating effeciently and with they dynamics required for the application.

     

    InstaSPIN-FOC is clearly the premium solution on the market, with the ability to self identify needed motor model parameters, track them in run-time as they change, and configure automatic tuning of the current controllers.

    InstaSPIN-MOTION adds a premium velocity controller than can be tuned extremely rapidly (thanks to built-in inerital and friction ID) and works over the operation range of the motor (you don't need different tuning gains for different operating points like you do with a PI controller).

     

     

  • 0 in reply to ChrisClearman
    Intellectual 800 points

    Thanks Chris for quick answer.

    A simple speed controller, I think, only cares how to start motors and keeps the speed as stable as possible at a certain (POT) dial position. The dial is calibrated by following  the voltage of the DC voltage suppliers (12V,24V, 36V,...,100V, ...). So users have to know the motor limitations and have to have the DC voltage supplier accordingly.

    With the Bemf zero-crossing scheme, we only need to sense the DC voltage supplier (for the POT), the dial postion, and the zero-crossing interrupts for speed  estimations and therefore we can control/stabilize the desired speed.


    What I have seen and like it with InstaSPIN-FOC that the motor can run at much slower speeds which we can not do that so far with our ESCs. Because of after trials and errors with different voltage levels and PWM freqs, the motors under our ESCs start as a higher speed.

     

     

  • 0 in reply to tnhtn
    TI__Guru** 119500 points

    Tinhtan Nguyen said:
    A simple speed controller, I think, only cares how to start motors and keeps the speed as stable as possible at a certain (POT) dial position

    it's not a true speed controller if it isn't using a measured or estimated speed in a feedback loop to control the speed.  some of the hobby ESCs use the commutation rate as a speed feedback, and some don't use any at all. In an application like a helicopter this can be acceptable if all you care about is keeping a rough speed.

    yes, some ESCs just commutate essentially full out and change the Vbus to change the speed. It is simple and sometimes good enough.

    Most ESCs aren't controlling current. They may shut off the PWMs if they hit a current limit, but they aren't actively controlling the current.

    FOC is always controlling the current (assuming it is getting good measurements) and only creating a magnetic field in the stator to maximum the torque production use of the motor.  The efficiency gain  from our customers in ESC applications now using InstaSPIN-FOC has been stated to us as a 10-25% increase in length of time they can fly on the same battery.

    FOC is certainly more complicated, but it's much higher performnace.

    Tinhtan Nguyen said:
    InstaSPIN-FOC that the motor can run at much slower speeds which we can not do that so far with our ESCs.

    In general this is very true, but with SOME hobby motors it may not be. FOC control relies on good current measurements and our FAST observer also relies on a good Bemf signal.  The REALLY high KV motors often have minute Flux (V / Hz) that produce very small Bemf and if they are high torque they will have ridiculously low Ls that causes a large short circuit current (switching and current ripple) that makes taking low-side current measurements very challenging. 

    There is a thread on here with a customer who sent me their dental motor which is like this...the current ESC uses some pretty interesting techniques to get very good low speed performance and ok (not as good as InstaSPIN-FOC) high speed performance.

     

  • 0 in reply to ChrisClearman
    Intellectual 800 points

    Actually, our ESCs are not for hobby at all. We also make our very high KV motors and almost none of ESCs available in the market at the time were able to start our motors therefore we decided to develop our own ESCs.

    The ESCs were able to start a wide range of motors and they do have a rpm feedback for speed control.

    Thank you again Chris.

    And have a good weekend!

  • 0 in reply to ChrisClearman
    Intellectual 800 points

    To try InstaSPIN-BDLC (I already have the DRV8301-HC-EVM Rev D with the F28069M ControlCard),

    Could I just order the F28035 MCU controlCARD only?

    Thanks.

  • 0 in reply to tnhtn
    TI__Guru** 119500 points

    That's the easeiest way: TMDSCNCD28035ISO

    you can then use the GUI and all the projects.