Fault tolerant control by flatness approach

Martínez Torres, César (2013) Fault tolerant control by flatness approach. Doctorado thesis, Universidad Autónoma de Nuevo León.

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Resumen

The objective of this PhD work is provide a flatness based active fault tolerant control technique. For such systems, it is possible to find a set of variables, named flat outputs such that states and control inputs can be expressed as functions of flat outputs and their time derivatives. The fault detection and isolation block has to provide a fast and accurate fault isolation, this action is carried out by exploiting the non-uniqueness property of the flat outputs, in fact if a second set of flat outputs algebraically independent and differentially coupled of the first are found, the number of residues augments. By consequence this could help to isolate more faults than if only one set is found. Regarding reconfiguration if the flat system counts with the properties listed above we will obtain versions of states and control inputs as much of flat outputs vector are found, because each control input and state is function of the flat output. The proposed approach provides in this manner one measure related to a faulty flat output vector and one or more computed by using and unfaulty one. The redundant state signals could be use as reference of the controller in order to hide the fault effect. This will be helpful to provide an entirely flatnessbased fault tolerant control strategy. The works presented in this manuscript are under the next hypothesis: The flat outputs are always states of the system or a linear combination of them. The control loop is closed with a state feedback controller. The states included in the flat output vector are measured or at least estimated. Faults affecting the actuators are considered rejected by the controller, by consequence reconfiguration is only carried out after sensor faults. Since a flat system could be linear or nonlinear, the proposed approach could be applied in either of two type of systems. Feasibility of this approach is analyzed in two nonlinear plants, an unmanned quadrotor and a three tank system.

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