Patent ID: 7944159

Claim:
A method of determining the position of a rotor in a brushless DC motor comprising the steps of: applying a sequence of current pulses to the stator phases, such that each stator phase experiences an equal number of current pulses in a first direction; measuring for each pulse the rise time for the stator phase current to exceed a predetermined threshold level; summing the measured rise times for which each stator phase has experienced a current pulse in a first direction to generate respective scalar parameters for each stator phase, the respective scalar parameters being indicative of the inductance of each stator phase; and thereby determining the orientation of the rotor by ranking the scalar parameters in size order and calculating the ratios of the median value scalar parameter to the smallest value and to the largest value of the scalar parameters to determine how close to or far from alignment the rotor orientation is with the axis of the stator phase between the largest and smallest scalar parameters.