Hybrid fuzzy control for the goethite process in zinc production plant combining type-1 and type-2 fuzzy logics

Abstract

The goethite process is a complicated reaction system which holds a significant position in zinc hydrometallurgy process. It exhibits nonlinear behavior and time-delay nature because of the chemical reactions. To achieve the stable and real-time control performance, a hybrid fuzzy control strategy integrating a type-1 and a type-2 fuzzy logic controllers is proposed in this paper. According to the on-line measured pH, the type-1 fuzzy controller (T1 FLC) via the Takagi–Sugeno fuzzy control is employed to control the zinc oxide additive rate. A parameter tuning method that does not require the system model is designed for the T1 FLC. Because the ferrous ion concentration cannot be measured on-line, the interval type-2 fuzzy logic controller (IT2 FLC) is utilized to control the oxygen flow rate. According to the feedback information, gradient descent algorithm is used to update the parameters in the IT2 FLC. Because of the unknown system structure, gradient descent information is estimated by the simultaneous perturbation stochastic approximation. Finally, simulations are conducted using the practical production data. The simulation results show the effectiveness of the proposed strategy. The hybrid fuzzy control strategy improves the control performance of the goethite process, compared with PID controller.