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In a 2 pole BLDC motor i can see the net direction of the field flux (coming from north pole and going towards south pole). But in 4 pole BLDC motor what will be the direction of the net field flux? I can only see the 4 pole rotate simultaneously (when motor spins) but what will be the direction of net field flux created by adding the magnetic field of the 4 pole together?

I am asking this question because in FOC we need to know the direction of the field flux. Most people uses encoders but encoders give the position of the rotor with respect to the fixed stator axis. How they uses encoders to know the field flux position with respect to the fixed stator axis??

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They use the encoder to determine the rotor angle (flux) with respect to stator frame. The stator flux is measured with current probes, then transformed to alpha/beta and further to d/q coordinate system by use of Park and Clarke transforms.

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  • \$\begingroup\$ I want to know what is rotor angle? Is this is an angle of some random point (at the circumference of the rotor) with respect to some fixed axis of stator frame or it is an angle of the net flux vector created by rotor field with respect to some fixed axis of stator frame? \$\endgroup\$ – Shashank More Sep 23 at 13:12
  • \$\begingroup\$ @ShashankMore Both of them, moreover there is a mechanical and electrical angle. The encoder is usually mounted such that is oriented with rotor flux, but if it is not, then the offset has to input as software parameter. \$\endgroup\$ – Marko Buršič Sep 23 at 17:52

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