BLDC motor control

Thread Starter

MoHo98

Joined Dec 3, 2022
2
Hey there!
We intend to drive a specific BLDC sensorless motor using two different control algorithms . both algorithms are based on BEMF ZC detection.But hardware is different. to clarify, the first hardware detects zero crossing points using analog comparators and interrupts and the second one detects them using ADC (by comparing them to VBus/2)
here's the thing the maximum speed achieved by algorithm one differs from algorithm two's while the applied duty cycle is almost 100% for both algorithms. is it possible? We all know that the max speed is related to the applied voltage so I expected the max speed to be the same no matter which algorithm I used. any idea? thanks!
 

MisterBill2

Joined Jan 23, 2018
13,774
For a comutated BLDC motor the max speed is controlled by the drive frequency, while the torque is affected by the voltage. In all cases the speed is limited by how rapidly the code can advance the drive signal, and that is limited by the sensing scheme.
 

Thread Starter

MoHo98

Joined Dec 3, 2022
2
For a comutated BLDC motor the max speed is controlled by the drive frequency, while the torque is affected by the voltage. In all cases the speed is limited by how rapidly the code can advance the drive signal, and that is limited by the sensing scheme.
Thanks for your reply
Could you please be a little bit more specific?
Should I try changing the switching frequency or something else.
Sorry I'm asking cause I may have misunderstood you
what do you mean by the drive frequency?
Does it include the cpu frequency too?
 

MaxHeadRoom

Joined Jul 18, 2013
26,278
There are a few methods used for BLDC motors that have only two windings energized at any one time.
One is to use feedback from the non powered coil at any given time.
RC ESC (electronic speed controllers use a form of sensorless commutation.
Search the Digikey site for BLDC control, they have a few technical papers from various sources on the subject.
 

MisterBill2

Joined Jan 23, 2018
13,774
By the "drive frequency" I mean the rate of electrical rotation of the magnetic vector generated by the field coils. The torque available to spin the motor is a function of the effectiveness of the drive system, which includes the software. So it is entirely reasonable that different control algorithms will provide different speeds. And at some point there needs to be way to set the desired motor speed.
Beyond that, I am not an expert on BLDC motors, but I have read about how they work.
 
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