Observer based dual-layer sliding mode fault-tolerant control for dissolved oxygen concentration in wastewater treatment process

Fault-tolerant control (FTC) of dissolved oxygen concentration is the core technology to ensure the robustness of wastewater treatment process (WWTP). However, the dynamic characteristics of microbial community are difficult to be modeled accurately, and external disturbances such as fluctuations in influent water quality and equipment failures further increase the control difficulty. Therefore, how to effectively compensate for the unmodeled dynamics and improve the system robustness is still a key problem to be solved in the field of WWTP control. In order to address this problem, this paper proposes an FTC method for dissolved oxygen concentration that integrates a dual sliding mode observation mechanism and an intelligent optimization strategy. Firstly, a state observer with an adaptive compensation mechanism is constructed based on the sliding mode control (SMC) method to realize the simultaneous estimation of dissolved oxygen concentration and unmodeled dynamics. Secondly, an adaptive robust fault-tolerant controller is designed by combining the Lyapunov stability theory. Then, a double sliding mode surface containing observation error and control error is established. Thirdly, a differential evolutionary algorithm is introduced to perform a global optimization of the robust gain parameters, which transforms the complex robustness problem into an optimal gain solving problem. Simulation experiments are conducted to compare the fault-tolerant control effect of different control methods with the proposed method, and the results verify the superiority of the method proposed in this paper.