One hall sensor possible in BLDC control?

[Solcar]

I was contemplating brushless motor control and ways to simplify it. There are single phase brushless motors, but those are usually used only for low power because of high torque ripple.

It seems it could be possible to get the benefit of a single hall sensor that a single phase BLDC ought to need, and combine that with a three phase motor. Electronic circuitry would need to extrapolate the position of two of the phases as the rotor goes around.

Or use back emf for two or even all three of the phases and the hall sensor for maintaining absolute position sensing for increased performance compared to totally sensorless controllers.

 

[bowlofsalad]

I was contemplating brushless motor control and ways to simplify it. There are single phase brusless motors, but those are usually used only for low power because of high torque ripple.

It seems it could be possible to get the benefit of a single hall sensor that a single phase BLDC ought to need, and combine that with a three phase motor. Electronic circuitry would need to extrapolate the position of two of the phases as the rotor goes around.

Or use back emf for two or even all three of the phases and the hall sensor for maintaining absolute position sensing for increased performance compared to totally sensorless controllers.

I asked a similar question, https://endless-sphere.com/forums/viewtopic.php?f=30&t=69086 which may interest you. The idea presented is there is nothing more efficient than BEMF at higher speeds. Hall sensors are great for rotor position from a stop or slow speeds, but require compensation algorithms at higher speeds (which isn't super accurate), meaning combining the hall sensor data with BEMF is worthless if you can use BEMF alone. Think of it like this, if something is 100% accurate, and another thing is 90% accurate, if you combine the two what do you come up with? Nothing better than 100%.

Some controllers do hall sensor start only and switch to sensorless shortly afterwards. I know that the phase runner does this and I imagine other controllers do as well. http://www.ebikes.ca/shop/ebike-parts/controllers/c-phaserunner.html

I wish I had a definitive answer to the other half of your question, but I probably don't understand what you are asking well enough. I don't know why you asked this question, but you did ask it in the electric bicycle technical section, implying you might use this motor on an electric bicycle. Something to consider is that to a large degree the need for hall sensors with purely pedal assist likely comes to zero, unless you want to go in reverse or use some form of freewheeling, then hall sensors are probably something to want.