Hybrid sensorless control of axial flux permanent magnet motor drives, including zero speed

Sensorless control of an axial flux permanent magnet motor drive is proposed and tested. The motor is not purposely designed for sensorless control and shows a very small inherent saliency. This significantly affects the saliency-based position estimation in the low speed region. Other non-idealities, such as the non-sinusoidal back-EMF waveforms and possible misalignment between stator and rotor make the control more challenging. A robust sensorless control scheme is proposed, able to deal with these non-idealities with a rather simple implementation. The position estimation is based on a closed loop hybrid observer of the permanent magnet flux linkage. Experimental results report torque and speed sensorless control.