A simplified control method for multivariable stable nonsquare systems with multiple time delays

Time delays in multivariable nonsquare systems challenge the control action, firstly by limiting the degree of freedom and secondly because of the interaction that exists between various input-output channels. Different decoupling techniques associated with multivariable Smith Predictors have been proposed for the control of such plants. The design of the primary controller has also been intensively studied. The method proposed in this paper is a straightforward alternative to previously designed control structures for multivariable stable nonsquare time delay processes. The authors show that in this way the task of designing the controller is much simplified, while the overall performance of the closed loop system remains the same. Further, the control design is suitable for a general class of stable multivariable processes, rather than the limited applicability of the original method to processes that can be described by first order time delay transfer functions. Setpoint tracking, disturbance rejection and robustness tests are presented in comparison with the original method to prove the efficiency of the proposed simplified method.