Multi-loop two-degree-of-freedom PI controllers with adaptive set-point weighting

Abstract

This note describes a simple technique to adapt the set-point weighting of multivariable two-degree-of-freedom proportional–integral (PI) controllers. This controller structure has been extensively used in single-input–single-output (SISO) systems to design disturbance and set-point responses independently. In multivariable systems, the interaction among the different loops can be minimized by making the set-point weighting zero. However, the cancellation of the reference direct path leads to a degradation of set-point tracking performance. The weighting adaptation proposed here aims to conserve the interaction magnitude level corresponding to zero weighting but improving the response of the direct control loop. Variable structure control-related concepts may be used to analyse the methodology, since a switching law is used in order to generate the weighting factor.