Improvement of Min-Max limit protection in aircraft engine control: An LMI approach

Current aircraft engine control logic employs a Min-Max selector structure. This structure must provide desired thrust and prevent the engine from exceeding any safety or operational limits. Careful analysis shows that there is no assurance for traditional Min-Max algorithm with linear compensators to protect output limits in transient regime, while limit violation can cause serious damages and even lead to loss of engine. In this paper, according to analysis outcomes, a strategy is presented to design linear regulators of Min-Max selector control to improve transient limit protection. For this objective, the isolated limitation loops are designed overshoot/undershoot-free to reduce the possibility of limit violation during activeness of the individual limit regulator. Despite the success of this approach, it is observed that some outputs influenced by engine acceleration or deceleration exceed their limits when other loop regulators are active. To overcome this problem, the limit values of these outputs are considered in controller design process of other loops using state feedback method and a set of linear matrix inequalities (LMIs). Simulation results show that the proposed approach effectively decreases the possibility of transient limit violation and can improve Min-Max limit protection in aircraft engine control.