Discrete Variable Structure Control Design and Its Application to a Ship Autopilot Servo System

This paper presents a new approach to the discrete-time variable structure control design. Firstly, a new discrete reaching law, which is stable at the origin and can eliminate the chattering caused by conventional discrete reaching law parameters, is proposed. Subsequently, an algorithm for uncertainty estimation is developed. It can be shown that the estimation error dynamics can be decoupled from sliding surface dynamics using the proposed scheme. Robust stability of the closed-loop system can be ensured in the presence of uncertainties with bounded changing rate. No chattering occurs. The proposed algorithm is applied to the control of a ship autopilot servo system. Simulation results show that the proposed controller can track a desired course well whether uncertainties are present or not.