Composite robust control of uncertain nonlinear systems with unmatched disturbances using policy iteration

In this paper, the composite robust control problem of uncertain nonlinear systems with unmatched disturbances is investigated. In order to improve the robust control performance, the integral sliding mode control method is considered together with Hoo control for nonlinear systems. By designing a disturbance observer with a new structure, the estimations of disturbances can be obtained with small errors, which are used to construct sliding mode control policy and avoid high gains. On the basis of ensuring the accessibility of specified sliding surface, the guaranteed cost control problem of nonlinear sliding mode dynamics is considered. To overcome the difficulty of robust control design caused by nonlinear characteristics, a modified policy iteration method based on sum of squares is proposed to solve the Hoo control policy of the nonlinear sliding mode dynamics. Finally, the effectiveness of the proposed robust control method is verified by simulation tests.& COPY; 2023 ISA. Published by Elsevier Ltd. All rights reserved.

Automated summary

This paper investigates the composite robust control problem of uncertain nonlinear systems with unmatched disturbances. To improve robust control performance, the integral sliding mode control method is combined with Hoo control for nonlinear systems. A disturbance observer with a new structure is designed to obtain disturbance estimations with small errors, which are then used to construct sliding mode control policy and avoid high gains. The guaranteed cost control problem of nonlinear sliding mode dynamics is considered, and a modified policy iteration method based on sum of squares is proposed to solve the Hoo control policy. Simulation tests verify the effectiveness of the proposed robust control method.