Multivariable control design of grinding in Vuonos by inverse Nyquist Array method

The object of this study was the development of the control for the primary grinding in the concentrator in Vuonos and, more particularly, the achievement of a controlled particle size at the cyclone overflow and a controlled cyclone feed density. Step tests were carried out in the plant and the data obtained were used for the derivation of a dynamic model. A multivariable controller was designed for the plant using an interactive software package which included the use of the inverse Nyquist array method. Matrices compensating for the interactions were designed by this technique. The controllers were tuned after compensation as single-input single-output systems using standard PI-algorithms. The controllers were successfully applied to the plant by a process computer and there was good agreement between the simulated results and the full scale tests in Vuonos: Changes of the setpoint of either one controlled output variable produced satisfactory responses, while the other controlled output simultaneously remained close to the desired constant value. The multivariable controller designed has been taken into continuous use in Vuonos.