Practical and efficient method for fractional-order unstable pole-zero   cancellation in linear feedback systems
  As a very well-known classical fact, non-minimum phase zeros of the process put some limitations on the performance of the feedback system. The source of these limitations is that such non-minimum phase zeros cannot be cancelled by unstable poles of the controller since such a cancellation leads to internal instability. The aim of this paper is to propose a method for fractional-order cancellation of nonminimum phase zeros of the process and studying its properties. It is specially shown that the proposed cancellation strategy increases the phase and the gain margin without leading to internal instability. Since the systems with higher gain and phase margin are easier to control, the proposed method can be used to arrive at more effective controls. 
Farshad Merrikh-Bayat
math.OC