Patent ID: 7489096

Claim:
A method of determining an angular position of a rotor of a brushless direct current motor having a stator with multi-phase windings, control circuitry providing excitations switched one after another to motor phases such that the excitations produce stator flux vectors lying in different directions in a full 360 electrical degree range, and a measurement circuit that delivers responses for the phase excitations, the method comprising the acts of: selecting a main excitation stator flux vector resulting in a minimal inductivity shown by a measured response; selecting two other stator flux vectors, one of which is in a previous and another of which is in a subsequent direction with respect to a direction of the main excitation stator flux vector; and computing a ratio between differences of measured responses for the selected stator flux vectors in order to estimate an angular position of the rotor of the brushless direct current motor, wherein the selection of the main excitation stator flux vector is done by selecting a vector that corresponds to a maximal value among {i 0 , . . . i 2p-1 }, where if more than one equivalent maximal value is found, then any of their indices are selectable for the index of the main excitation stator flux vector; the ratio between differences of measured responses for the selected stator flux vectors being computed as a fraction, the numerator of which is i n minus i λ , and the denominator of which is i m minus i n , if i λ is greater than i n , else if i m does not equal i λ , then the denominator is i m minus i x , else the denominator is 1, where m denotes the index of the direction of the main excitation, and λ, n denote indices of the directions before and, respectively, after the direction of the main excitation; and wherein the estimated position is obtained as m times π over p plus the calculated ratio between differences of measured responses for the selected stator flux vectors times π over 2p.