Electronics > Mechanical & Automation Engineering

Can I simply use two (one and a half) DRV8833s to drive a three-phase BLDC?

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CircuitBreaker:

--- Quote ---There is not holding torque like you have in a stepper motor. You sense the position change then react to that.
--- End quote ---

In understand that everybody does it the way described in the latter part of the quote.
What I don't understand is why you wouldn't have a holding torque if you just continuously apply the (3-way sinusoidal PWM) 'static' current as defined for a particular electrical position. Why wouldn't that hold the motor in place to that specific electrical position as defined by the PWM configuration?

langwadt:

--- Quote from: CircuitBreaker on July 15, 2022, 12:59:48 pm ---
--- Quote ---There is not holding torque like you have in a stepper motor. You sense the position change then react to that.
--- End quote ---

In understand that everybody does it the way described in the latter part of the quote.
What I don't understand is why you wouldn't have a holding torque if you just continuously apply the (3-way sinusoidal PWM) 'static' current as defined for a particular electrical position. Why wouldn't that hold the motor in place to that specific electrical position as defined by the PWM configuration?

--- End quote ---

the point of FOC is to keep the electric magnetic position 90  degrees to the mechanical magnetic position for max torque

thm_w:
I suppose you could calculate the holding torque given that static current. I don't know how to do that, but if its anything like a stepper microstepping, you'll have a miniscule amount of torque away from the poles (full steps).

But as langwadt points out, as soon as you sense a specific deviation in position you'd want FOC to take over and move the electric field.
Sort of a hybrid control system. A lot of the high end servo drives have all of this hybrid control for various purposes, not sure how many of them FOC eliminates the need for.


Found these while looking around, not relevant here though (sensorless only for fans):
https://www.allegromicro.com/en/products/motor-drivers/bldc-drivers/a89301
https://www.allegromicro.com/en/products/motor-drivers/bldc-drivers/amt49406

https://electronics.stackexchange.com/questions/509895/how-to-electrically-brake-a-brushless-motor

ConKbot:
Cap your maximum commanded torque and you'll have a "springy" knob. Command it to go to where it was 100ms ago constantly (with capped torque), and you'll have a "draggy" knob, where if the user holds it there for 100ms or longer, it stays put. Seems like FOC control would be pretty much ideal for this.

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