One approach to cascade framework design within control structure reconfiguration in faulty systems

The paper is concerned with the problem of control structure reconfiguration to retain fault tolerance in control of linear continuous-time systems. Following the concept of fault tolerant control systems the main idea is to use the nominal system model output as a reference to be followed when a fault occurs, while the nominal control loop is kept untouched and the nominal controller remains part of the reconfigured control loop. Since only the estimation error, obtained as a difference between the measured and nominal output, is used for the fault covering, the state control principe is proposed for nominal control and static output control principe for reconfiguration control law. Using an extended form of Lyapunov function, the modified design conditions are introduced and proven in the paper. The approach also unifies optimization in static output control design, which ensures stability and desired performances. The results, offering the sufficient and necessary design conditions, are illustrated with a numerical example to note the effectiveness of the proposed approach.