Hierarchical Control for Wastewater Treatment Process Based on FTSMC-LESO

Wastewater treatment processes (WWTPs) is considered as a complex control problem due to the strong nonlinearities, uncertainties, and disturbances. In this paper, a hierarchical control strategy based on Linear Extension Observer (LESO) and Fast Terminal Sliding Mode Control (FTSMC) is studied to achieve the objectives of reducing the energy consumption (EC) and enhancing the effluent quality (EQ) in WWTPs. Firstly, a Fast Terminal Sliding Mode Control based on LESO (FTSMC-LESO) is designed as the lower layer of the control strategy, and the stability is proved by Lyapunov theory. Then, an optimization function for dissolved oxygen (DO) setpoint is investigated as the upper layer to optimize the setpoint in real time. Finally, simulations are conducted to verify the effectiveness of the hierarchical control strategy on the Benchmark Simulation Model No.1 (BSM1). The experimental results show that compared with the default PI control, the designed control strategy can realize stable control of wastewater treatment process and simultaneously improve EC and EQ.