(143a) Design of Decentralized Pid Controller for Enhanced Robust Stability of Multivariable Control Systems

This paper presents a new design method of the multi-loop PID controller for robust stability of the given multi-input, multi-output (MIMO) process that contains uncertainties in plant description. The initial multi-loop PID controller parameters are obtained by the IMC design methods which included Lee et al. [1], Jung et al. [2], etc. The multiplicative weight for complex uncertainty can be found by considering a set of possible plants, and then the data of multiplicative weight which is still in the presence of complex uncertainty form can be estimated and transferred into the mathematical model by using the Curve Fitting (CF) Method [3]. Finally, the multiplicative weight is specified in case of the first order, second order or third order models. The H_∞ design technique is applied directly to select the optimal PID control parameters by detuning the closed-loop time constant λ. Therefore, the multivariable control systems can not only achieve robust stability but also satisfy robust performance. The effective of the proposed method is demonstrated by some illustrative examples.