Single and multiple faults in system actuators and sensors for ethanol production

This paper focuses on the study of a fault detection and isolation system strategy applied to an ethanol production bioprocess that involves a two-stage bioreactor with a cell recycling loop to reach high biomass concentrations. The various actuators and sensors of this type of bioprocess, impose to develop a fault detection and isolation strategy. In this work, we study the case where multiple faults (with a small delay between them) or simultaneous faults can occur. We assume that only one type of faults can occur at a time and we will focus on the actuators and sensors 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 on an adaptive observer method, for detection, isolation and identification of actuator and sensor single and multiple 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 in a nonlinear model of a two-stage ethanol bioprocess with a cell recycling loop.