Semi-explicit Distributed NMPC

Abstract

In this chapter, a suboptimal approach to distributed NMPC for systems consisting of nonlinear subsystems with linearly coupled dynamics, subject to both state and input constraints, is considered. The approach applies the dynamic dual decomposition method and reformulates the original centralized NMPC problem into a distributed quasi-NMPC problem by linearization of the nonlinear system dynamics. The approach is based on distributed on-line optimization (by gradient iterations) and can be applied to large-scale nonlinear systems. Further, a semi-explicit NMPC approach to efficiently solve the distributed NMPC problem for small- and medium-scale systems is described. It combines the explicit approximate solution with the on-line optimization and the result is a decrease of the on-line computational complexity. Both the on-line optimization based distributed NMPC and the semi-explicit distributed NMPC are illustrated in a problem to solve a NMPC problem for a nonlinear system consisting of two subsystems.