Multiple sliding modes with override logic: Limit management in aircraft engine controls

A new control scheme is proposed for turbofan engines, where the objective is to transfer a regulated output between two setpoints, with the additional requirement that a set of limited outputs remains within prescribed bounds. The strategy is based on the traditional max-min selector system, replacing linear regulators with sliding mode controllers where the sliding variable for the limited outputs is defined as the difference between the output and its limit. The motivation for the replacement lies in several recently noted shortcomings associated with the use of linear regulators in the traditional scheme. The proposed technique effectively removes the weaknesses of the traditional scheme. The paper points out these deficiencies and describes the proposed method, establishing overall system stability. The invariance properties leading to limit protection are also elaborated. A design methodology involving a mixed H∞=H2 multi-objective feedback gain synthesis is proposed and demonstrated through a design example. Practical applicability is further demonstrated by simulation using a high-fidelity nonlinear engine simulator (Commercial Modular Aeropropulsion System Simulation, known as C-MAPSS). Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc.