Disturbance cancellation techniques for finite reaching time continuous sliding mode control

Sliding mode controllers are characterized, ideally, by infinite frequency switching. While this provides very robust convergence to desired plant dynamics, the implementation of this variable structure control is not generally realizable due to requirement for high frequency switching. As a result, continuous approximations are used that are realizable and do not require high frequency switching. However, they do not provide finite reaching time convergence to the desired plant dynamics and are not robust to unmodeled noise and disturbances. An advancement in sliding mode controllers is the finite reaching time continuous sliding mode controller (FRTC SMC). The FRTC SMC is a true (not approximated) sliding mode control design with finite time convergence to the sliding surface and is more robust to unmodeled disturbances and plant dynamics than continuous approximations. However, the FRTC SMC is not as robust as the traditional SMC. In this paper, we investigate two methods of improving the robustness of the FRTC SMC to unmodeled disturbances and plant dynamics. The first method uses a Sliding Mode Estimator. The second method uses a technique called integral sliding mode control, which is a Lyapunov function based technique. We also demonstrate these disturbance cancellation techniques using a numerical example.