Disturbance rejection with zero steady-state error for nonlinear large-scale systems

The disturbance rejection problem for nonlinear large-scale systems with external persistent disturbances is considered. By developing a sensitivity approach and the internal model principle, the problem of disturbance rejection for the original control system is solved by designing an optimal control law for the augmented nonlinear system without disturbances. The control law obtained consists of an accurate linear state feedback term, an internal model compensation term and a nonlinear compensation term which is a series sum of the adjoint vectors. Where the state feedback term can stabilize the system, the internal model compensation term eliminates the influence of the disturbances, and the last one compensates the influence of the nonlinear interconnected term. A simulation example is employed to test the validity of the algorithm.