MULTIRATE OUTPUT CONTROL FOR SISO NONMINIMUM-PHASE SYSTEMS

The application of multirate output control (MROC) to SISO non-minimum phase (NMP) systems exhibiting severe inverse response is considered in this paper. It is shown that the MROC improves considerably the con trol performance of such systems, and the reasons for this are clarifi ed. A detailed comparison between the MROC and linear time-invariant ( LTI) control structures (both continuous and discrete) like the PID, I MC, and observer/state feedback is carried out on a wide range of simp le 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. Sufficie ntly small sampling intervals yield an almost perfect disturbance reje ction but degrades the robustness properties. This trade-off is discus sed in the paper, and it is shown that an appropriate design of the MR OC leads to good robustness properties with excellent performance inco mparable to LTI control schemes. For the design of the MROC, a tuning algorithm for optimal pole placement, based upon undershoot and settli ng time, is developed for two poles and one zero systems.