Sliding mode compensation to preserve dynamic decoupling of stable systems

Dynamic decoupling of linear multiple-input and multiple-output systems involves both static and transient decoupling between inputs and outputs of the system. Different control techniques exist in order to achieve this specification when ideal actuators are considered. However, input saturation changes the direction of the plant input with respect to the controller output and, as a consequence, decoupling is lost. This paper presents a method that allows, by means of a sliding mode (SM) auxiliary loop, maintaining dynamic decoupling even in the presence of actuator saturation. Since the SM compensation is confined to the low-power side of the control system, the discontinuous signal can be implemented with fast switching devices or, in the case of digital controllers, within a microprocessor algorithm. Furthermore, due to the robustness properties of SM, the compensation loop dynamics may be assigned independently of the main control loop. (C) 2007 Elsevier Ltd. All rights reserved.