Static decouplers for control of multivariable processes

Abstract

AbstractDecouplers can be used to improve performances of multiloop control systems by compensating for process interactions, but they are sensitive to process changes and require fairly detailed process models, which are hard to obtain. These disadvantages of decouplers hinder their successful applications in industry. On the other hand, static decouplers can be designed from process steady‐state gains, which are easier to obtain and can be tuned in the field. However, static decouplers can introduce undesirable effects on loop interactions at high frequencies for some processes. Here it is shown that static decouplers are better applied to the integral control modes for such processes. Because the integral mode is dominant at low frequencies and its magnitude decreases as frequency increases, the static decoupler implemented only on the integral mode will not disturb the frequency response of a control system at high frequencies. A simple antireset windup scheme, guaranteeing given control performances under process input saturations or failures, is provided. For online tuning of the proposed control system, a closed‐loop identification method to find process steady‐state gains is also presented. © 2005 American Institute of Chemical Engineers AIChE J, 2005