Computation delay compensation for real time implementation of robust model predictive control

The implementation of Model Predictive Control (MPC) requires to solve an optimization problem online. The computation time, often not negligible especially for Nonlinear MPC (NMPC), introduces a delay in the feedback loop. Moreover, it impedes fast sampling rate setting for the controller to react to uncertainties quickly. In this paper, a dual time scale control scheme is proposed for linear/nonlinear systems with external disturbances. A pre-compensator works at fast sampling rate to suppress uncertainty, while the outer MPC controller updates the open loop input sequence at a slower rate. The computation delay is explicitly considered and compensated in the MPC design. Four Robust MPC algorithms for linear/nonlinear systems in the literature are tailored for the proposed control scheme. The recursive feasibility and stability are rigorously analyzed. Simulation examples validate the proposed approaches.