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BLDC Motor Stall

Abhishek kumar3
Prodigy 40 points

Hi all,

This Abhishek from pune India working as an application engineer in semiconductor industries. I am working on BLDC motor project and seeking help from all my dear friends.

I want to stall the motor...I mean to say motor should not move if we try to rotate forcefully.

I am driving the motor by Multipulse generator (MPG) or u can say its a type of PWM.

i have tried to do that but not succeeded yet.

So please  can anyone give me an idea that what exactly we can to do to stall the motor..

Please note its BLDC motor.

Thanks;

Abhishek.

  • 0
    TI__Expert 8885 points

    Hello Abhishek,

    BLDC motors can be stalled by applying DC voltage or more precisely DC current to its stator terminal. DC current produces stationary magnetic field to which rotor gets aligned and does not move as long as current is applied.

    DC current can be applied either by exciting 3-phase or 2-phase simultaneously. The easier way is to excite the 2-phases and leave the 3-phase open.

    Please note that with two phase excitation method at stall condition phase-phase resistance of stator decide the amount of average current based on applied DC voltage. You mush control the current so that it does not exceed winding rating. This can be done by controlling the duty cycle of PWM pulses if DC bus is constant or if possible you can reduce the DC voltage itself keeping 100% duty cycle.

    I hope this clarifies your query, please let me know if you need any further detail.

    Best Regards

    Milan

  • 0 in reply to Milan Rajne
    Prodigy 40 points

    Hello Milan,

    Thanks a lot for your reply !!!!!!!

    Your reply clears my concept but still one query is there..

    I am using H-bridge to control the BLDC motor and i am giving PWM to upper mosfets gate and inverted PWM to corresponding lower mosfet gate.

    According to you i must supply PWM to any two phase simultaneously keeping in mind the duty cycle as i can't reduce the DC bus volage.

    Thanks;

    Abhishek

  • 0 in reply to Abhishek kumar3
    TI__Expert 8885 points

    Hello Abhishek,

    As I mentioned in my previous reply that motor can be stalled by excitation of two or three phase. For easier implementation, I suggested to use 2-phase excitation as used in trapezoidal control (120 degree commutation) of BLDC motor. Here is what you should do:

    1. If choosing 2-phase excitation:

    Inverter leg A:  Apply duty control PWM signal to upper MOSFET and inverted PWM to corresponding lower mosfet with proper dead-time to avoid DC-link shoot through.

    Inverter leg B: Continuously turn on Bottom MOSFET and turn off upper MOSFET.

    Inverter leg C: Turn-off both the switches.

    Effective resistance in this case would be double of per phase resistance and input DC average current will equal to Vdc*Duty_Cycle/(2*Rph_value).

        2.  If choosing 3-phase excitation:

              Only difference is for Inverter leg C: Make it similar to leg B i.e. Continuously turn on Bottom MOSFET and turn off upper MOSFET.

    Effective resistance in this case would be 1.5 times per phase resistance and input DC average current will equal to Vdc*Duty_Cycle/(1.5*Rph_value). So for same duty cycle, current will be higher in this case.

    Best Regards

    Milan