Nonlinear dynamic modeling in low frequency and control system stability domain determination for a LPE

Algorithms have been presented for the low-frequency nonlinear dynamic modeling and stability domain determination of liquid propellant engines. Also, the considerations that can facilitate the modeling process and remove the drawbacks have been presented. The defined algorithms and the stated considerations have been applied for a particular liquid propellant engine. The equations describing the mentioned engine have been classified into 11 subsystems. The simulations have been performed in the MATLAB Simulink software environment. Each simulated subsystem represents one or several physical subsystems whose interactions have been defined in the overall form of engine configuration. The engine modeling results have been validated by the data of cold and warm tests of the subsystems and engine. In the process of determining the stable operation range of the mentioned engine, by linearizing the obtained nonlinear model, which accompanies the correct determination of model input and output, and by applying the Nyquist criterion, the stability analysis of the regulator and engine systems has been performed control system and the stability margin and the cutoff frequencies have been obtained. Finally, the effects of structural and process parameters of the relevant subsystems on the engine’s stable range of performance have been evaluated.