Disturbance Rejection in Hard Disk Drives with Multi-Rate Estimated State Feedback

Abstract Multi-rate control has been proposed as a solution to improve the performance of Hard Disk Drives (HDDs). Some authors report unexpected decrease in performance when using this approach. This paper presents an analytical method to obtain the closed loop sensitivity function of a multi-rate control system, realized through estimated state feedback. By using this tool, it is shown how disturbance rejection in multi-rate control may be worse than in single-rate. The paper reports both simulation and experimental results, which confirm the possible decrease in performance.