New insights on the override control problem

This paper considers the override (OR) control strategy, employed for systems possessing limits on the plant variables (states and output). The aim of this work is to analyze the OR control problem on the basis of the well studied anti-windup (AW) control problem in order to facilitate transparency and systemati-zation in the OR control system design. The performance objective related to the OR control problem is first defined and a general structural representation for OR control, comprising potential static and dynamic configurations as special cases, is then presented. The effect of OR control on the closed-loop is evaluated in terms of a general framework, termed conditioning of the plant, which permits the unification and comparison of all OR control schemes. A difference system describing the mismatch between the OR control system and the ideal output constrained system responses is further employed for comparison of OR control schemes and for synthesis of compensators as it readily quantifies the OR control objective. Finally, an optimal LMI-based optimization method for designing static OR controllers is provided and the resulting performance of the design strategy is shown by a simulation example.