Sensorless Control for Four-Switch Three-Phase Brushless DC Motor Drives

This paper develops a new method of sensorless control for four-switch three-phase (FSTP) brushless dc (BLDC) motor drives to achieve the lowest manufacturing cost. The novel sensorless control includes the advantages of four-switch three-phase inverter (FSTPI) and sensorless control scheme in the same time. Formerly, it was impossible to achieve sensorless control for FSTPI using the traditional four-space-vectors PWM scheme, because there was no floating phase to detect back EMF. So, this paper proposes a novel asymmetric PWM scheme for FSTP BLDC motor drives to make six commutations and produce four floating phases to detect back-EMF. The operational principle of the sensorless control for FSTP BLDC motor drives is demonstrated by experimental results