Patent ID: 7429841

Claim:
A method for detecting the position of a movable element for use in an electrically commutated machine driven by a pulse width modulated voltage, the method comprising the steps of: a. determining an applied voltage across at least one phase of an electrically commutated machine driven by a pulse width modulated voltage, and determining a current in the at least one phase; b. generating a first analog signal indicating the applied voltage; c. generating a second analog signal indicating the current; d. filtering the first analog signal to remove switching harmonics and produce applied voltage information corresponding to a filtered first analog signal; e. filtering the second analog signal to remove switching harmonics and produce phase current information corresponding to a filtered second analog signal; f. scaling and delaying the phase current information in proportion to a resistance and an inductance of the at least one phase, to produce modified phase current information corresponding to scaled and delayed current information; g. using the applied voltage information and the modified phase current information in conjunction with said resistance and said inductance to produce back EMF information corresponding to the at least one phase; h. modifying the back EMF information to correct for a phase lag due to the filtering of the first and second analog signals, to generate modified back EMF information corresponding to the at least one phase; and i. determining a rotor position of the electrically commutated machine, based on the modified back EMF information of the at least one phase.