Estimation of commutation instances using back emf mapping for sensorless control of brushless permanent magnet motors

This study presents a novel sensorless scheme to control brushless permanent magnet motors using back emf mapping with six-step control. All commutation instances, corresponding to 30 electrical degrees, at various speeds can precisely be calculated using a single known reference slope and a back emf point considered at the same speed. Zero crossing detection point (ZCP), phase shifters, delay managers, integration and third harmonics, hard switching techniques and/or look-up table are eliminated. This increases the signal to noise ratio and overcomes some cases where ZCP could be undetected. Simulation and experimental work on six-step controlled permanent magnet synchronous motors validate the proposed approach.