Elimination of Intersample Ripple in Control Systems with Dual-Rate Regulators through Frequency Domain Compensation

It has been observed that the inclusion of Dual-Rate regulators in a sampled-data control loop occasionally  introduces the phenomenon of intersample ripple in the output of the process being controlled. Several authors have offered explanations for this phenomenon which does not appear to derive from the control method. The aim of this brief report is to demonstrate that, by compensating in frequency through the addition of a digital filter in the control loop, it is possible to eliminate the undesired ripple between samples. The usefulness of a novel tool developed to compute the frequency response of a sampled-data multirate system will be showed. An application example is presented below for illustration.