Considering the nonlinear system with bounded disturbance, a robust model predictive control(MPC) method
based on approximated reachable sets is designed. A robust control invariant set is taken as the terminal constraint set. A
kind of cubic polynomial with simple structure is adopted to approximate the controller to be optimized. Then, the coefficients
of cubic polynomial are computed through online optimization. It is proved in theory that the system is input-to-state stable
by using the proposed robust MPC controller. Finally, simulation results show the feasibility and effectiveness of the method.