Multirate Output Control for SISO Non-Minimum Phase Systems

Abstract

The application of muhirate output control (MROC) to SISO non-minimum phase (NMP) systems exhibiting inverse response is considered in this paper. It is shown that the MROC improves considerably the control performance of such systems and the reasons for this are clarified. A detailed comparison between the MROC and linear time invariant (LTI) control structures (both continuous and discrete) like the PlO, IMC and observer/state feedback is carried out on a wide range of simple processes. The main advantage in the application of the MROC to NMP systems is that a drastic improvement in disturbance attenuation can be achieved while maintaining similar tracking capabilities. Sufficiently small sampling intervals yield an almost perfect disturbance rejection but degrades the robustness properties. This tradeoff is discussed in the paper and it is shown that an appropriate design of the MROC leads to good robustness properties with excellent performance incomparable to LTI control schemes. For the design of the MROC a tuning algorithm for optimal pole placement, based upon undershoot and settling time, is developed for two poles and one zero systems