A novel sensorless control method for brushless DC motor

The authors present the theory and implementation of a novel sensorless control method for the interior permanent magnet (IPM) brushless DC motor (BLDCM). The proposed new sensorless technique can accurately detect the zero-cross point (ZCP) of back electromotive force (BEMF), which is based on a comparison of the terminal voltage of the un conducting phase during the first and second part of a pulse width modulation (PWM) cycle. Compared with the conventional BEMF sensorless approach, the proposed new sensorless method solves the problem of the sensorless BLDCM drives at very low speeds. Experimental results confirm the validity of the new method.