Abstract
The Proportional-Integral-Derivative (PID) controller structure is very widely used in industrial applications. However, there exist plants that cannot be stabilized by a PID controller. To overcome this problem, Yamada and Hagiwara proposed a design method for modified PID controllers that make the control system for any unstable plant stable, and the method produces admissible sets of P-parameters, I-parameters and D-parameters that are independent of each other. When these modified PID control systems are applied to real plants, the influence of disturbances in the plant must be considered. In many cases, the disturbance in the plant is unknown. It is comparatively easy to attenuate known disturbances, but it is difficult to attenuate unknown disturbances. From a practical viewpoint, it is desirable to design a modified PID control system that can attenuate unknown disturbances. Recently, a design method for modified PID control systems for single-Input/single-output plants to attenuate unknown disturbances was proposed, but there has not been a design method for modified PID control systems for multiple-input/multiple-output plants to attenuate unknown disturbances. In this paper, we propose a design method to solve this problem.