Modeling And Switching Control Design For Two-spool Turbofan Aero-engines

Aero-engine technology is the important manifestation of science,industry,and defense capabilities for a country.An aero-engine has highly nonlinear dynamics and operates in an uncertain environment of limitations,which makes the modeling and control for the aero-engine extremely complex.In addition,there is no accurate model to describe the operating characteristics of the aero-engine in a wide range,and meanwhile,no unified and effective method to measure the accuracy of the model until now,which brings great difficulties and challenges to the design of an aero-engine control system.Theories and methods of switched control systems have distinctive superiority to analyse and design complex control systems with multiple mode features.Often,a complex problem is decomposed into several simple problems which can be solved with the help of design of an appropriate switching law.Therefore,it is an effective method to model and control an aero-engine based on the theory of switched systems.This dissertation studies the problems of switched system modeling,speed regulation switching control,temperature protection switching control and bumpless transfer control for two-spool turbofan aero-engines.The main results are as follows.1.In order to improve the accuracy of an equilibrium manifold expansion(EME)model,a switched EME model is established and an event-driven speed regulation switching controller is designed.Firstly,multiple EME models are obtained by choosing different mappings.Then,the deviation between the state derivative of the EME model and that of the NCL model is taken as an index to measure the accuracy of the EME model.The switching law is obtained by minimizing the index,and then the switched EME model is established.It can be seen that the switching law is designed based on the constructed index,which is different from traditional switching law design.In addition,a state feedback sub-controller is designed by using the input-output linearization technique.Moreover,a sufficient condition for asymptotic stability of the closed-loop switched system under arbitrary switching is given.Furthermore,in order to improve the speed regulation performance of the closed-loop system,an event-driven speed regulation switching controller is designed.2.To improve the applicability of the switched EME model,a multi-switching EME model is established,and a speed regulation switching EME controller is designed based on a modified LQR method.Firstly,considering the difference of aero-engine dynamics in different operating modes,we establish a switched EME model corresponding to each operating mode.Then,a supervisor is designed to determine the operating mode of an aero-engine.This makes the multi-switching EME model a two-layer switched model.The upper layer is the switching between different operation modes,and the lower layer is the switching between different EME models within a single operation mode.Furthermore,in order to improve the robustness of the control system,a speed regulation switching EME controller is designed based on a modified LQR method.Meanwhile,a sufficient condition for asymptotic stability of the closed-loop switched system under arbitrary switching is given.3.In view of the safety of operation,a temperature protection switching controller is designed.Firstly,in order to make the output temperature run along the safe boundary,a common sliding mode surface is designed for all subsystems,and a condition that the parameters of the sub-controllers need to meet is given.Furthermore,the temperature protection switching controller based on sliding mode control method is obtained.Besides,a sufficient condition for asymptotic stability of the sliding mode dynamics is given.Then,considering that chattering may occur in the practical operation for sliding mode control,a temperature protection switching controller based on reference dynamics is designed in order to make the output temperature move away from the safe boundary following ideal dynamics and remain within the safe boundary.Meanwhile,a sufficient condition which guarantees that the controller makes the system state approach the target equilibrium point is given,which reduces the complexity of designing a temperature protection controller to switch to the speed regulation controller,and avoids the danger of the system output over-temperature caused by the temperature protection controller switching off at an inappropriate state.4.A bumpless transfer controller is designed for a switched system and applied to the aero-engine control system.Firstly,considering that the jump of control input in a switched system may cause a serious impact on the system performance,a control structure which can smooth the switching control input signal and a compensator used to compensate the deviation from the original control input signal are proposed.Furthermore,a bumpless transfer controller is obtained.Then,sufficient conditions for asymptotic stability of a switched linear system and a switched nonlinear system with bumpless transfer performance guaranteed are given respectively.Moreover,the recoverability and the effectiveness of the proposed bumpless transfer control strategy are verified respectively,that is,when no switching for the system,the bumpless transfer controller is exactly the same as the original controller;and when switchings occur for the system,the control input signal is still continuous,and meanwhile there is no steady-state error from the original switching control input signal.The conclusions and perspectives are presented in the end of the dissertation.