Patent ID: 7545113

Claim:
A method to regulate each harmonic of a plurality of harmonics in a system having a periodic disturbance to a commanded value and the system has a rotating load adapted to operate at speeds in a speed range, the method comprising the steps of: for each one of the plurality of harmonics: transforming a feedback signal having at least one harmonic component due to the one of the plurality of harmonics from a source reference frame to a harmonic reference frame of the one of the plurality of harmonics to form a qd feedback signal; subtracting the qd feedback signal from the commanded value to form a qd signal; regulating the qd signal wherein the step of regulating the qd signal comprises the steps of: regulating the qd signal with a proportional integral (PI) regulator at rotational speeds above a predetermined value; and when the rotational speed goes below the predetermined value, bypassing the PI regulator and keeping the qd signal at q and d values at values that were at or above the predetermined speed, transforming the regulated qd signal to a destination reference frame to form a compensation signal; and adding the compensation signal to a control signal to form a qd control signal to drive the one of the plurality of harmonics towards the commanded value.