Fault-tolerant control in presence of disturbances based on fault estimation

A new formulation of the fault-tolerant control (FTC) problem in presence of disturbances is given, based on fault estimation (FE). Two solutions/controllers to this problem are given. The first one is a new controller that includes a fault estimator, a nominal controller and a fault accommodation block. This controller requires the strict conditions that the nominal controller is stable, and that the transfer matrix of the fault accommodation block is also stable. The second controller does not require these strict conditions, and is obtained by unifying the three blocks of the first controller, in a single controller whose realization is minimal. Therefore, it does not include a fault estimator. A dedicated fault estimator can be added out of the control loop, in order to monitor the performance of the FTC, as defined in the new problem formulation. With respect to the literature, the two controllers can be applied to a larger class of systems, because of the weaker assumptions. An example is presented, which illustrates with comparison, that the controller of the paper has better properties in respect to existing controllers.