Abstract
This paper investigates the control-oriented modeling for turbofan engines. The nonlinear equilibrium manifold expansion (EME) model of the multiple input multiple output (MIMO) turbofan engine is established, which can simulate the variation of high-pressure rotor speed, low-pressure rotor speed and pressure ratio of compressor with fuel flow and throat area of the nozzle. Firstly, the definitions and properties of the equilibrium manifold method are presented. Secondly, the steady-state and dynamic two-step identification method of the MIMO EME model is given, and the effects of scheduling variables and input noise on model accuracy are discussed. By selecting specific path, a small amount of dynamic data is used to identify a complete EME model. Thirdly, modeling and simulation at dynamic off-design conditions show that the EME model has model accuracy close to the nonlinear component-level (NCL) model, but the model structure is simpler and the calculation is faster than that. Finally, the linearization results are obtained based on the properties of the EME model, and the stability of the model is proved through the analysis of the eigenvalues, which all have negative real parts. The EME model constructed in this paper can meet the requirements of real-time simulation and control system design.
Highlights
In recent years, as an ideal power plant for aircraft, turbofan engine has received extensive attention [1,2,3,4,5]
The state variable model solves the application of linear control method in turbofan engines, it only has good fitting effect near the steady-state point used in the model identification
The results show that the path for dynamic parameters fitting will affect the accuracy of the equilibrium manifold expansion (EME) model
Summary
As an ideal power plant for aircraft, turbofan engine has received extensive attention [1,2,3,4,5]. The state variable model solves the application of linear control method in turbofan engines, it only has good fitting effect near the steady-state point used in the model identification. In order to obtain a control-oriented model that guarantees the accuracy and stability in a wide range of working conditions, the equilibrium manifold expansion (EME) model is proposed [25,26,27,28,29]. The EME model contains steady-state and dynamic characteristics of the nonlinear system near the equilibrium manifold, which are beneficial for the modeling of turbofan engines with operating line. The aforementioned EME models are identified from the SISO systems with fuel flow as an input variable, which cannot meet the control requirements of advanced turbofan engines in a wide range of working conditions. The EME model of system (1) is obtained by Taylor expansion, it is still a nonlinear system when the scheduling variable is eliminated
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