Internal Model Control with Improved Butterworth Filter Based on Inverted Decoupling for Multivariable Systems

Multi-input and multi-output (MIMO) systems not only have large time-delay and strong coupling but also have the complexity in the controller design caused by multiple time delays. Especially the existence of the non-minimum phase (RHP zero) in the controlled process model brings more difficulties to the control system. Due to the simplicity of the structure and calculation of the internal model control based on the inverted decoupling (ID-IMC), an improved Butterworth filter is introduced into the ID-IMC system design, so that the performance of the closed-loop control system is improved. Moreover, some realizable conditions are discussed to avoid the adverse effects caused by the pure time-leading and unstable poles (RHP poles). Aiming at the problems of the external disturbance and uncertainty, a sensitivity function and a mu analysis are employed to analyze the robust stability (RS) and robust performance (RP) of the system. Simulations are carried out to demonstrate the effectiveness of the proposed method.