Sliding-mode controller design with internal model principle for systems subject to periodic signals

This paper proposes a sliding-mode control (SMC) scheme based on the internal model principle (IMP) for robust reference tracking and disturbance rejection. The linear IMP controller is known for the capability of perfect tracking and disturbance rejection with an internal model of exogenous signals, while the SMC controller is robust to system perturbations and exogenous signals with unknown dynamics. In this paper, an SMC design based on IMP is proposed to combine the best feature of these two fundamentally different but effective methods. Furthermore, with the help of the SMC, an initial state of the internal model is determined independently of system perturbations in order that transient performance is greatly improved as compared with that of the linear IMP controller. In addition, by properly assigning the initial state of the internal model, a sliding control law is derived to ensure the existence of a sliding mode during an entire response. This global sliding motion yields excellent robustness of the entire system at the beginning of system response and afterwards. Simulation results show the feasibility of the proposed scheme.