Equivalent transfer function based multi-loop PI control for high dimensional multivariable systems

A new equivalent transfer function (ETF) parameterization algorithm to incorporate the loop interaction effect into the design of multi-loop PI controllers for high dimensional multivariable processes is presented in this paper. The design scheme consists of two stages. In the first, by exploiting the relationship between the equivalent closed-loop transfer function and the inverse of open-loop transfer function, the analytical expression of ETF is derived. In the second stage, based on the ETF, controller parameters for each loop are determined by utilizing the existing PI tuning rules and the simple internal model control method. The proposed ETF parameterization algorithm is more accurate and reasonable compared to the conventional ETF model approximation methods. Furthermore, the advantage of the multi-loop PI controller designed by the proposed ETF is more significant when applied to higher dimensional processes with complicated interaction modes. Several typical industrial process examples show the well-balanced and robust response with the minimum integral absolute error.