Multirate sliding mode disturbance compensation for model predictive control

In this paper, a novel hierarchical multirate control scheme for nonlinear discrete-time systems is presented,consisting of a robust nonlinear model predictive controller (NMPC) and a multirate sliding mode distur-bance compensator (MSMDC). The proposed MSMDC acts at a faster rate than the NMPC in order to keepthe system as close as possible to the nominal trajectory predicted by NMPC despite model uncertainties andexternal disturbances. The aprioridisturbance compensation turns out to be very useful in order to improvethe robustness of the NMPC controller. A dynamic input allocation between MSMDC and NMPC allowsto maximize the benefits of the proposed scheme that unites the advantages of sliding mode control (strongreduction of matched disturbances, low computational burden) to those of NMPC (optimality, constraintshandling). Sufficient conditions required to guarantee input-to-state stability and constraints satisfaction bythe overall scheme are also provided.