Sensorless drive for interior permanent magnet brushless DC motors

This paper describes a position drive for the interior permanent magnet (IPM) brushless DC motors. A new indirect sensing method is proposed which can be applicable for the IPM machines of which the winding inductances vary according to the rotor position. Experimental results form a prototype brushless DC motor built in a compressor of an air conditioner confirm the validity of the sensorless drive from 500 to 7500 rpm.