Commutation of BLDC motors with respect to number of poles

Question

I have a BLDC motor with HALL sensors. Datasheet reads the motor is 4 pole technology. Somewhere else it says "Number of pole pairs = 2". I can only assume that they both mean the same thing. It also features 3 HALL sensors at 120°

My question is, what would be fundamentally different in commutation of a BLDC motor with respect to the number of poles, like sequence or number of switching on/off for driver transistors?

For example, If I have a fully working code for a 6 pole or 8 pole motor, what would I need to do to make it work with 4 pole as well?

Answer 1

'Pole pairs' is the number of North and South magnet pole pairs. 'Poles' is the number of individual North and South poles (always an even number).

Unless it has a separate rotation sensor, The controller cannot tell how many poles the motor has or what mechanical speed it is doing. From the controller's point of view all motors have 2 poles and 3 phases, which requires 6 commutation steps per 'electrical' revolution. So you could have a 4 pole motor that needs 12 steps per revolution, and the controller will think it has done a full revolution when the rotor has only gone half way around.

All else being equal, a controller which works with 6 or 8 poles should also work with 4 or 2 poles. Secondary factors might have an effect, eg. 2 pole inrunners often have very low inductance and are designed for high rpm, which might not suit a controller designed for high torque outrunners.