Fractional order controllers for throughput and product quality control in a grinding mill circuit

This paper presents the design and application of a multiple-input–multiple-output fractional order proportional-integral (MIMO FOPI) controller to a grinding mill circuit. The MIMO FOPI controller parameters are tuned using an off-line optimization process based on Particle Swarm Optimization (PSO). Its performance is compared to a single-input–single-output fractional order proportional-integral (SISO FOPI) controller designed and tuned using the same procedure based on PSO. The results show that the MIMO FOPI achieves better results compared to the SISO FOPI controller in most of the cases simulated, even in the presence of hardness and composition variations in the processed ore, and also in the presence of process noise.