(Trapezoidal vs FOC) choosing a commutation type for BLDC motor.

Thread Starter

Chethan_Raj

Joined Aug 1, 2022
22
Hello there, I've been planning to build an ESC from scratch for my BLDC motor, for an quadcopter project, and I have trouble figuring out the right commutation methods for design, I did some fair amount of research and found the most methods of control to be sensorless( as there are lower number motors with Inbuit encoders or hall effect sensors i could find on the internet). so i assume back emf is the way to go, I've decided to go with trapezoidal control even with torque ripple, but i see some vendors using FOC control even for drone BLDC's. Aren't the FOC control output sinusoidal, how could they run these motors off sinusoidal signals, those motors aren't PMSM to begin with. So how does this work. Should i go with trapezoidal control with torque ripple?.
 

nsaspook

Joined Aug 27, 2009
13,418
https://forum.allaboutcircuits.com/threads/brushless-motor-esc-bldc-controller.185344/post-1714212
249621-7666c769b721fc6fedffb04821457673.png

Electromagnetically there is little actual difference between BLDC and PMSM motors but there are differences in stator and magnet design to optimize for the type of drive waveform to the Back EMF generated. 6 step Square, trapezoidal or sine with sensor or sensorless rotor position detection.

https://forum.allaboutcircuits.com/threads/pic32mk-mc-qei-example.150351/post-1550621
FOC from the controller pins doesn't need to be a sine wave. What matters is the drive signal internally as it moves.
https://forum.allaboutcircuits.com/threads/pic32mk-mc-qei-example.150351/post-1532387

https://forum.allaboutcircuits.com/threads/pic32mk-mc-qei-example.150351/post-1530400
 
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Thread Starter

Chethan_Raj

Joined Aug 1, 2022
22
I have a BLDC motor which generates trapezoidal back emf when rotated, now it should be supplied trapezoidal signals to make it spin right. I've been trying to follow this pdf from Texas instruments. I know that we can supply sinusoidal signals to the motor, it would work, but the torque production won't be maximum, so I'm trying to implement an Trapezoidal control prototype, just to check its performance. Please explain me, how does FOC come into picture, as my application( Quadcopter ) doesn't necessarily need Low speed motor performance. But still I can see it's application in drone ESC on the internet. I'm still wrapping my head around your links, Thanks for reply.
 

nsaspook

Joined Aug 27, 2009
13,418
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