Tuning of a multivariable PI-like fuzzy logic controller

A systematic tuning method for multivariable PI-like fuzzy logic controller is proposed. The system is assumed to be unknown but stable. It can include time delays. In order to keep the structure of the controller simple, the number of the system inputs and outputs are restricted to two. The controller has separate proportional and integral parts which are tuned independently. This means that both parts have their own rule bases. The controller decouples the system not only at low frequencies but also at high frequencies. The tuning of the proportional part is based on the initial derivatives of the system step responses and the tuning of the integral part is based on the static gain of the system. These are measured experimentally. The controller eliminates the steady-state error and keeps the interactions between the system outputs small. A simulation example is presented to illustrate the method