Integrated fault estimation and fault tolerant control for systems with generalized sector input nonlinearity

Abstract

This paper presents a Fault Tolerant Control (FTC) scheme for systems with L2-bounded disturbances and generalized sector nonlinearity at the input. An adaptive observer-based fault estimation (FE) scheme is used to estimate the fault. The nonlinearity causes the control input (the measurable controller output, which is injected into the FE scheme) to differ from the actuator output (which enters the plant); this mismatch (together with the disturbances) causes interactions between the FE and FTC schemes, violating the separation principle and hence they cannot be designed separately. We introduce a method that integrates both FE and FTC schemes, and design them simultaneously (thus overcoming the violation of the separation principle), guaranteeing bounded stability. To obtain the sufficient conditions for stability and minimum L2-gain performance for disturbance rejection, we use the Sector Condition (SC) and successfully re-casted the design as Linear Matrix Inequalities (LMIs) which can be performed in a single step and yield tractable solutions. Through a numerical example, we demonstrate the effectiveness of the proposed method.