A global scheme for multiple and simultaneous faults in system actuators and sensors

In this paper, we study the case of more than one faults can occur in the system with a small delay between them or in the same time. We assume that only one type of fault can occur and we will focus on the actuator and sensor faults. The sensor fault problem will be reformulated to an actuator fault one by introducing a state variable transformation, so that an augmented system is constructed. Thus we will design a nonlinear model based adaptive observer method, for detection, isolation and identification of actuator and sensor multiple and simultaneous faults. These approaches use the system model and the outputs of the adaptive observers to generate residuals. Residuals are defined in such way to isolate the faulty instrument after detecting the fault. The validity of the method will be tested in simulation of a nonlinear waste water treatment process.