Multirate digital control system design and its application to computer disk drives

A computationally efficient fixed order multirate digital control system is presented. Introducing a periodically time-varying gain, a multirate digital controller is designed, that works without using intersample states and delivers a stable ripple-free closed-loop with discrete-time state matching at each control update instant. Increasing the control update rate thereby tends to improve intersample behavior of the closed-loop system. The multirate controller outputs control at each control update instant, while the multirate control scheme is computed in the background during output measurement sampling period thereby reducing the computational burden for implementation. The proposed multirate scheme is applied to disk drive actuator control. Application results demonstrate the utility of the proposed multirate digital control scheme for improved disk drive actuator control.