Novel Centralized IMC-PID Controller Design for Multivariable Processes with Multiple Time Delays

In this paper, a novel centralized IMC (internalmodel-control)-PID (proportion -integration-differentiation) controller is designed for multivariable processes with multiple time delays. To reduce the influence of time delays, the process model is divided into the minimum common time delay part and the remaining part. The IMC-PID controller, consisting of a full-matrix filter and a diagonal PID controller, is obtained based on the IMC principle. The full-matrix filter described as the inverse of the remaining part is too complex to compute. Hence, the Nyquist set is employed to describe the dynamics of the filter. The approximate transfer function matrix of the filter is calculated by complex curve fitting. Besides, to reduce the approximation error and obtain stable filter elements, a compensator is introduced. 'The rules of selecting-compensator parameters are proposed for stable filter elements. Finally, the IMC-PID controller parameters are-determined after comprehensively considering the performance and the robustness. The limitation of the proposed method is dig-cussed. Simulations demonstrate the effectiveness of the proposed method.