Multi-rate digital design for sliding-mode-observer-based feedback control

Implementation of sliding-mode-observer-based feedback control is treated as a multi-rate digital signal processing problem. The over sampled delta-sigma modulation techniques is used to design a decimation filter that integrates high-frequency switching output of the sliding mode observer into the feedback control, which operates at much lower predetermined control update rate. Application of a multi-rate sliding mode observer in the function of a nonlinear uncertain system estimator in the terminal guidance loop is demonstrated. It\´s shown in this application that the correctly designed decimation filter for a multi-rate system delivers close-loop system performance superior to that of traditionally proposed low-pass filters of autoregressive type, which estimate "equivalent control" component in the digital sliding mode observer in the manner equivalent to their continuous-time analog implementations.