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Motor Drivers Forum
InstaSpin BLDC DRV8301
Do you have any publications outlining the stall torque obtained with insta-spin versus a sensor-based BLDC Control method? I have the DRV8301 kit and would be happy to conduct that test if you could provide me with the setup conditions to complete this task.
Defining "stall torque" on InstaSPIN-BLDC is somewhat difficult to do since IS-BLDC is a sensorless algorithm that depends on measured back-EMF to function properly. When the motor stalls, the speed goes to zero, as does the back-EMF signal. The commutation process stops in a position where the applied stator field is oriented correctly w.r.t. the rotor, and full torque continues to be generated. As long as you don't commutate again, AND the motor shaft angle does not change, you should be able to generate this torque forever. However, if the motor shaft drifts from this position, it will probably result in such a weak back-EMF signal that the algorithm won't be able to track it properly, and miscommutation will result. But even if the motor shaft is locked, remember that the back-EMF integrator is still running, trying to anticipate when it should commutate again. Theoretically, integrating a value of zero back-EMF should result in no change in the flux signal (which is used to commutate the machine), and you should continue to generate torque. However, the chances are pretty good that the noise in the system will eventually cause the flux signal to wander over the upper or lower flux threshold, again, resulting in miscommutation.
So, the conclusion is that when you stall, you should be able to generate full torque for a while, but after that, the machine will eventually miscommutate unless you immediately prevent the rotor from moving, AND turn off the back-EMF integrator.
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