A self-healing controller based on sliding-mode control for sensor fault in wastewater treatment processes

Wastewater treatment processes (WWTPs) include numerous sensor devices, which are prone to failure in the difficult work environment after long-term treatment, resulting in the effluent quality not meeting the requirements. The existing control methods do not consider this issue, to address this issue, we introduce self-healing control into WWTPs. Firstly, due to the difficult of analyzing the mechanistic model of WWTPs, this paper establishes a low-order model by using the Takagi–Sugeno fuzzy method. Secondly, with respect to the sensor additive fault, a generalized system is built to turn the problem of estimating the sensor fault into the problem of estimating the actuator fault, and a generalized sliding-mode observer is designed. Then, the system output is corrected by fault estimation, and a self-healing controller based on sliding-mode control is developed. Finally, the simulation experiments of a dissolved oxygen instrument in case of sudden and slow change faults are conducted. The simulation results demonstrate that the generalized sliding-mode observer can estimate the fault precisely and quickly, and the self-healing controller can make the system follow the setpoint quickly and accurately under fault conditions, which verifies the effectiveness of the proposed methods.