Multi-objective integrated optimal control for a wastewater treatment process

Multi-objective optimal control is often used to deal with conflicting objectives of the wastewater treatment process (WWTP) to ensure its operational safety and reliability. However, the existing multi-objective optimal control methods mainly analyze the optimization process and control process independently, which may make the set-points fluctuate largely and hard to track, thereby degrading the control and operation performance of WWTP. To solve this problem, a multi-objective integrated optimal control (MIOC) strategy is proposed for WWTP in this paper. The integrated optimal control structure is established by the multi-objective model predictive control framework to achieve the coordinated optimization and control solution. In the integrated optimal control structure, first, a comprehensive cost function with operation indices and tracking errors designed to deal with the conflicting objectives. Second, a multi-gradient algorithm is employed to evaluate the dynamic set-points and control laws. Third, the stability analysis of MIOC is given to prove the proposed method can stabilize the system. Meanwhile, the proposed MIOC method is tested in the Benchmark Simulation Model No. 1 to demonstrate that it can achieve suitable operation performance with satisfactory control accuracy.