A Design Method for Modified PID Controllers for Multiple-Input/Multiple-Output Time-Delay Plants

In this paper, we examine a design method for modified Proportional-Integral-Derivative (PID) controllers for multiple-input/rultiplo-output time-delay plants. The PID controller structure is the most widely used one in industrial applications. However, there exist plants those cannot be stabilized using PID controllers. In order to overcome this problem, the modified PID controller, which can stabilize any plant, was proposed by Yamada et al. Yamada, Hagiwara and Shimizu expanded the result by Yamada et al. and proposed a design method for modified PID controllers for time-delay plants. However, no method that guarantees the stability of a PID control system for any multiple-input/multiple-output time-delay plant has been published. In this paper, we propose a design method for modified PID controllers such that the modified PID controller makes the feedback control system for any multiple-input/multiple-output time-delay plant stable, admissible sets of P-parameter, I-parameter and D-parameter are independent from each other and the transfer function from the reference input to the output has a finite number of poles in order to specify the input-output characteristic easily.