Fractional-Order Control for TITO Systems

In this chapter, the tuning rules detailed and exemplified in Chap. 4 are extended for the case of multivariable systems, specifically for the case of the two-inputs-two-outputs systems. First of all, a short review of classical control techniques for multivariable processes is presented followed by a brief introduction of interaction analysis and optimal input–output signals pairing. Some examples of tuning fractional-order controllers for multivariable systems are also presented. In most of the cases, the tuning is based on decoupling of the process followed by an single-input-single-output approach for the design of the fractional-order controllers. The chapter presents a technique for designing a multivariable fractional-order controller for a two-input-two-output (TITO) process. The design is based on specifying and meeting frequency domain performance criteria, such as phase and gain margins, since these serve as important measures for stability and robustness in control loops. The approach is based on the modification of a method for tuning multivariable classical PID controllers.