Single winding BEMF sensing brushless DC motor

摘要

A method of electronically commutating a permanent magnet rotor brushless DC motor having three phase stator windings for producing rotating magnetic flux that comprises the steps of: (a) Commutating current to successive combinations of two windings to cause flux rotation in the desired direction; (b) Sensing in only one of the windings the periodic back EMF induced by rotation of the permanent magnet rotor; (c) Sensing enabled in two out of six 60 degree intervals of flux rotation when the sensed winding has no current commutated to it; (d) Digitising the sensed back EMF signal in the one winding by detecting the zero-crossings of the signal; (e) Determining a half period time of the signal by obtaining a measure of the time between the pulse edges in the digitised signal which are due to zero-crossings; and (f) From the half period time deriving the 60 degree flux rotation time (commutation period) and causing each commutation to occur at times that are substantially defined by each logic transition in the digitised signal due to zero-crossings and at the derived 60 and 120 degree angles of flux rotation which follows the zero-crossings.