Methods for closed-loop compensation of ultra-high frequency disturbances in hard disk drives and hard disk drives utilizing same

A method for cancelling high frequency disturbances in a closed-loop servo control system of a hard disk drive, the hard disk drive comprising a disk, an actuator arm comprising a head configured to read and write data to the disk, and a servo controller configured to control the actuator arm, the servo controller using a position error signal to generate a controller output signal, the method comprising:

• using a plant configured to mechanically model the disk drive and to receive a control command to which a disturbance is added and to generate a plant output;
• using a disturbance observer configured to use the control command and the plant output to generate a delayed and estimated version of the disturbance, the disturbance observer comprising a Q filter having a selected center frequency ω0;
• and
• filtering the delayed and estimated version of the disturbance in a perfect phase cancellation filter to reject selected disturbances and to align a desired attenuation frequency with the selected center frequency of the Q filter, an output of the perfect phase cancellation filter being subtracted from the controller output signal to generate the control command.