Fractional-Order Proportional Derivative Controller Synthesis and Implementation for Hard-Disk-Drive Servo System

In this brief, a fractional-order (FO) proportional derivative (PD) controller is designed in a systematic way based on the frequency responses data model for the hard-disk-drive (HDD) servo system. The open-loop system using the designed FO controller is with a flat-phase feature around the gain crossover frequency, which obtains the robustness to loop-gain variations. Thus, the control performance can be made uniform with more consistency than the optimized traditional integer-order controller when the loop gain changes. The theoretical foundation of the FO controller design is presented first. Thereafter, the implementation details of the designed controller in the real-time HDD servo system are introduced, which are important for the real applications of the FO controllers in practice. From the experimental validation, the presented FO-PD controller and the design synthesis are found to be efficient in improving the track-following control performance for the HDD servo system.