Patent ID: 8456117
Filing Date: 2013-06-04
Classification: H02P

Abstract:
1. A method of sensing the position of a rotor of an electric motor, said motor having a plurality of phase windings, the method comprising the steps of: driving each phase winding with a stored waveform, said stored waveform profile being set to zero for a predetermined interval at the start and at the end of each driving phase, said stored waveform profile further comprising a torque flattening waveform profile combined with a trapezoidal driving waveform; and monitoring the back EMF in each phase winding during a time period when the stored waveform profile is zero over the predetermined interval at the start and end of each driving phase to determine the zero crossing point of the back EMF for each phase winding by: using a monitoring means having an analogue to digital converter to obtain two samples of the back EMF during the time period when the stored waveform profile is zero over the predetermined interval; using a switching means for connecting the output of the particular phase winding with a zero driving input at any given time to the monitoring means; and using processing means to calculate the zero crossing point by interpolation and thereby determining the position of the rotor.