Sliding Mode Control

The fundamental principles of first and second order sliding mode control are presented. It is shown that first order sliding mode control is robust to exogenous disturbances, but involves the use of a discontinuous control signal that may lead to a chattering effect in which the control input rapidly fluctuates. Chattering is generally undesirable, as it can damage actuators, but in some cases it is possible to alleviate it by approximating the discontinuous term with a continuous function. It is shown that the control input generated when using second order sliding mode control is smooth, but still robust to exogenous disturbances and model uncertainty. The use of higher order sliding mode techniques is introduced for the real-time differentiation of signals and the observation of system states and disturbances. Lastly, a multiple input multiple output super twisting controller-observer system suitable for the control of marine vehicles is presented.