Stable Peak Filtering Method to Reject High Frequency Disturbance in Hard Disk Drives

In this paper, novel solutions are provided for designing the disturbance filter when there are significant plant dynamics within the bandwidth of the filter. The filter zero is designed appropriately so that the root loci originating from both the filter poles and the lightly damped plant poles go to the stable region under certain low gain condition. By providing compromised departure angles from filter poles and plant poles, the stability margin especially the gain margin is dramatically increased. The resulting closed-loop systems can provide large gain attenuation at the resonance frequency, and thus have more disturbance rejection capability.