Design of robust controllers for a milk of lime blending tank

This paper presents the use of an industrial milk of lime blending tank (MLBT) for the design and evaluation of different robust controllers. The plant is a multi-input, multi-output non-linear system with high interaction between loops and large disturbance actions. The IMC, H_∞ and μ methods are used to design controllers which provide robust stability as well as good nominal performance in the control of the density at the output and the level of juice in the tank in the face of uncertainties due to non-linearities within the system and disturbance actions. A non-linear model and operating records of disturbances taken from the real process are used to develop the weighting functions to include the plant uncertainties in the design procedure. Finally, a comparison between the performance of the designed robust controllers and a conventional PID is carried out.