A nonzero threshold value proportional to input voltage (or reference speed) is used for overcoming the problem due to quantization and sampling for digital implementation. The method is fault tolerant and accurate even in the case of noise in measurement (or estimation) of phase back EMFs. The method needs no additional delay circuit as used for calculation of commutation point from back EMF ZCP and involves less calculation burden. The proposed sensorless scheme has the excellent performance from zero to the extra high speed. The simulation study has been carried out for the proposed sensorless scheme. Commutation point is achieved exactly at the same instant when the difference of back EMFs of any two phases becomes zero. This technique is based on the comparison of back EMFs and detection of the points in the back EMF waveforms where they cross each other or in other words they are equal. In this paper a novel position sensorless scheme named Back EMF Zero Difference Point (ZDP) detection has been proposed for six-switch VSI converter fed permanent magnet BLDC motor.
