Chao Bi
Quan Jiang, Chao Bi: Method to detect the true zero-crossing points of the phase back EMF for sensorless control of brushless DC motors. April 12, 2005: US06879124 (14 worldwide citation)

In the present system and method, ZCP level signals of each phase voltage are first obtained. Among the detected ZCP level signals, some ZCPs are generated by phase back EMF, which are true ZCPs and other ZCPs by commutations, which are false ZCPs. The duration of the false ZCP level outputs varies ...