Performance enhancement of non-minimum phase feedback systems by fractional-order cancellation of non-minimum phase zero on the Riemann surface: New theoretical and experimental results

Abstract: The non-minimum phase (NMP) zero of a linear process located in the feedback connection cannot be cancelled by the same pole of controller according to the internal instability problem. However, such a zero can partly be cancelled by the same fractional-order pole of a pre-compensator located in series with process without facing internal instability. This paper first presents new theoretical results on the properties of this method of cancellation, and provides design techniques for the pre-compensator. It is especially shown that by appropriate design of pre-compensator this method can simultaneously increase the gain and phase margin of the system under control without a considerable reduction of open-loop bandwidth, and consequently, it can make the control problem easier to solve. Then, a method for realization of such a pre-compensator is proposed and performance of the resulted closed-loop system is studied through an experimental setup.