Adaptive Robust Controller Design for Nonminimum Phase Systems: Applied to a Dual Stage Hard Disk Drive
Improvement of the head positioning performance in hard disk drives is necessary for increasing storage density, and reducing data access time. The adaptive robust backstepping method has recently proposed for this problem, however, the developed method can be used only for minimum phase systems. Applying this method on hard disk drives, which is naturally modeled by a non-minimum phase system, is possible by considering the nom-minimum phase behavior of the system as uncertainty. However, performing such design procedure may significantly reduce the closed loop performance. In this thesis two methods are proposed to extend previously proposed backstepping method for non-minimum phase systems. In these methods the non-minimum phase model of the system is incorporated in the design scheme rather than considering it as uncertainty, in order to improve control effort and overall performance. In the first proposed method a zero placement routine is added to the design procedure to reclaim the controller. Next, the adaptive part of the controller is replaced by a totally new model reference control structure in order to enable the controller to include non-minimum phase models. Both methods are developed for dual stage hard disk drive systems and by performing some simulations the significance of each method on the performance improvement is studied and compared in detail.