Robust MRAC-based Fault Tolerant Control for Additive and Multiplicative Faults in Nonlinear Systems

In this paper, three different types of faults (abrupt-additive, gradual-additive and multiplicative) are introduced to two new reconfigurable structures for Fault Tolerant Control (FTC) of a Single Input-Single Output (SISO) non-linear process. The first FTC structure, named MRAC-LPV, is based on an MRAC design using an LPV system, while the second FTC structure is based on an MRAC with a H∞ Gain Scheduling Controller (MRAC-H∞GS-LPV) also designed by using an LPV system. Both MRAC controllers were implemented using the Lyapunov theory methodology because it guarantees the stability of the closed-loop system. The proposed schemes were tested using the nonlinear model of the system. To compare the performance of these schemes, a Coupled-Tank system is used as testbed in which the different types of faults with different magnitudes and different operating points were tested. Results showed that the use of an H∞ Gain Scheduling Controller in combination with an MRAC improves the FTC performance because the controller was able to deal in an efficient manner with the faults and the changes in the operating points of the nonlinear model of the system.