Research On Multi-loop Switching Protection Control And Coordinated Protection Control For Turbofan Engines

With the improvement of the performance of modern aircraft, more and more maneuverability requirements of aero-engines have been asked. However, aero-engines are very complicated nonlinear multivariable time-variant aerothermodynamic systems. In the flight envelope, the aerodynamic and thermodynamic process of the aero-engines will vary greatly with the changes of working environment and the working conditions (such as speed, accelerating, decelerating, etc) of the aero-engine propulsion systems, and different control requirements correspond to different working conditions. This paper researches multi-loop safety protection control via switching and coordinated strategies for the aero-engine to balance contradiction between the rapid response performance and the security.First of all, the control tasks and the safety boundaries during the working procedure are introduced in this paper. Aiming at the disturbances, this paper introduces the theory of the H∞mixed sensitivity, preparing for the following design of the multi-loop safety protection controller. A brief introduction of the equilibrium manifold expansion model of aero-engine is also included in this part.Secondly, aiming at the feature of multiple tasks and multiple objectives of aero-engines, a multi-loop switching protection strategy is adopted to deal with the contradiction between the rapid response performance and the security. After a brief review of the stability theory of the switched systems, the frame of the multi-loop switching protection control is proposed. Multi-loop switching control is a strategy whose design is a complex procedure including the design of corresponding control loops according to the response performances and the security boundaries and the determination of that which loop works according to certain designed switching signal. The normal controller works to ensure the performances of the aero-engine when it is working with a sufficient large security margin, and the corresponding protection control loop will be switched on instead of the normal one to guarantee the security performance once any protected output approaches to the safety boundaries. Not only a compromise between the rapid response performance and the security of the aero-engine but also the reduction of the complexity and the conservation of the controller design comparing to the single controller could be obtained through the switching among several simple controllers. Controllers of the sub-loops are designed using the H∞mixed sensitivity method. The switching law is analyzed in this paper. A switching rule which is easy to design and calculate is proposed where the distance between the protected output and its corresponding safety boundary is considered as the index to judge which control loop should be switched on. It is demonstrated through the simulation that the improvement in both security and the dynamical response performance of the turbofan engine could be obtained due to the proposed multi-loop switching protection control strategy.Thirdly, to get better performance comparing to the multi-loop switching protection control strategy, the multi-loop coordinated of protection control strategy is presented for the aero-engine. Based on the controllers of the sun-loop designed by the H∞mixed sensitivity method, in accordance with a coordinated strategy to weight for each controller, a total global controller is generated. The improvement to the performances due to the proposed strategy is verified through simulation, the comparing with multi-loop switching protection control and some analyses are also implemented in this part.Finally, the conclusion is given and some open problems are also discussed.