A Two Degree of Freedom Approach for Discrete‐Time Sliding Mode Control

This paper proposes a new two degree of freedom (2‐DOF) framework for discrete‐time sliding mode control (DSMC) that decouples the disturbed evolution from its nominal counterpart. The novel nominal/disturbed subsystem separation for DSMC can be used to define multiple closed‐loop specifications. The nominal regulation (or tracking) controller and the DSMC disturbance rejection control law are independently determined to achieve enhanced closed‐loop properties. Reaching phase elimination, control effort reduction, enhanced nominal performance, and extension for dealing with unmatched disturbance with respect to a given output are some of the benefits of the proposed framework. Either reaching‐law‐based DSMC or equivalent‐control‐based DSMC can be used to achieve a given disturbance rejection objective due to the flexibility of the proposed framework. A simulation case study based on a benchmark example is used to illustrate the benefits and flexibility of the proposed approach.