A novel robust control design is proposed for aircraft engines. The engine is modeled as an uncertain dynamic system (UDS), whose uncertainty may be (possibly fast) time-varying. The possible value of the uncertainty is prescribed to be within fuzzy sets. This distinguishes our modelling from the Takagi-Sugeno inference system. The uncertainty is divided into matched and mismatched portions. While the matched uncertainty lies within the range space of the input matrix, the mismatched uncertainty falls outside, which poses a significant challenge for the control design. The objective is to propose a new robust control design for aircraft engines, which are subject to mismatched uncertainty. A robust control, which is deterministic and is not IF-THEN fuzzy rule-based, is designed. The control design parameter needs to be feasible, i.e., within a prescribed range. Some prescribed deterministic performances of the system are guaranteed. By taking the control cost and the performance threshold into consideration, which is under the influence of both matched and mismatched uncertainty, the unique optimal choice of the design parameter is proposed. As a result, this control design delicately blends optimality with mismatched uncertainty. This design is applied to a turbofan engine. Hardwarein-the-loop (HIL) laboratory testing in the flight envelope demonstrates the superiority of the control design. Index Terms-Aircraft engine, robust control, fuzzy system, mismatched uncertainty, optimal design, hardware-inthe-loop testing
I. INTRODUCTIONA IRCRAFT engines play an important role in both civil and military applications [1]. At present, with increasing improvements in engine performance, such as higher thrustweight ratio, economic efficiency, and security, aircraft engines have become increasingly sophisticated. This sophistication has enhanced the inherent and significant coupling and promoted the development of multivariable control.
This paper proposes a hierarchical multivariable robust control design for a class of uncertain nonlinear dynamic system. The dynamic system is described by an uncertain T-S fuzzy model. The uncertainties in the model are structure matched and norm-bounded. For this fuzzy model, a hierarchical robust control consisting of two level compensators is presented. While the level 1 compensator ensures the basic robust performance, the level 2 compensator restrains the uncertainty. Under this design, the controlled system is uniformly bounded and uniformly ultimately bounded. To illustrate the design approach, the application to a multivariable control of turbofan engines is discussed. The semi-physical simulations of the controlled turbofan show that the resulting control is able to guarantee the prescribed boundedness in a more practical condition.
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