Robust fault estimation for a 3-DOF helicopter considering actuator saturation

Abstract

Fault estimation plays an important role in real-time monitoring, diagnosis and active fault tolerant control of helicopter system. This paper presents several robust observer based actuator fault estimation designs for an experimental 3-DOF helicopter system with the consideration of potential actuator saturation. In order to deal with the non-differentiable problem that induced by input saturation theoretically, the saturation function is approximated by a continuous function in the fault estimation design process. Both Luenberger observer and unknown input observer are adopted in the actuator fault estimation design scheme. Furthermore, in order to achieve sensor reduction and also avoid inaccurate measurement, simultaneous state and actuator fault estimation design is developed for the helicopter system. An energy-to-energy strategy is applied to ensure the robust performance of the proposed fault estimation approaches, in which approximation error of the saturation function, model uncertainties and external disturbances are all taking into account. In addition, pole placement technique is utilized to adjust the transient response of the estimation errors. Observer gains of the proposed fault estimation designs are derived by solving linear matrix inequalities. Finally, based on Quanser’s 3-DOF helicopter platform, comparative simulation and experimental tests are all carried out to show the effectiveness as well as performance of the proposed fault estimation approaches.