Research On High Stability Control Of Aero-engine And Their Application In Acceleration Control

Traditional surge avoidance control belongs to passive methods. The safety of the aero-engine isguaranteed by a conservative surge margin, but the performance of the engine is greatly sacrificed.Meanwhile, higher requirements are put forward on the propulsion system in moden advanced air-crafts, such as higher load, higher efficiency and higher thrust-weight-ratio. And high stability controlhas become one of key technologies in the advanced aero-engine. Therefore, following a review ofdevelopments in this field domestic and abroad, researches on key technologies of high stability con-trol are carried out, such as compression system modeling, compressor surge active control and com-pressor instability prediction. The application of the high stability control in turbofan engine accelera-tion optimization process is also researched.The compression system model of Moore Greitzer has been extended to include the spool dy-namic and higher harmonics of rotating stall. Simulation results test the influences of the spool dy-namic on the compression, which may lead to instability like the system inner disturbances.To explain the mechanism of the surge and rotating stall phenomena, nonlinear dynamic analysishas been done on MG model, based on bifurcation theory. It can be seen from the analysis results thatthe hysteresis loop of rotating stall is caused by a subcritical fork bifurcation at the peak point of thecompressor characteristic map, and the surge is related to a Hopf bifurcation, which will not occur inthe system with a low B-parameter.Four compressor surge active control strategies have been proposed, which are named surge androtating stall output feedback control, surge and rotating stall control via closed coupled valve (CCV)and throttle, surge control based on second order sliding mode and surge active/passive hybrid controlbased on fuzzy logic. A state estimator is employed to estimate the flow coefficient in the output con-troller, the pressure signal, which is easily to collect, is the only feedback parameter to achieve activecontrol. Compared to single actuator scheme, the advantages of using CCV and throttle as actuatorsimultaneously are demonstrated. Benefit from the character of the second order sliding mode, thesurge active controller possesses a better robustness on uncertainties such as un-modeled system dy-namic and disturbances. The active/passive hybrid control system uses a bleed valve as actuator, andcontains a surge active controller as main operating mode to enlarge compressor workingrange, and asurge avoidance controller as back-up mode to guarantee the reliability of the whole system. Thefuzzy logic simplifies the design process and the structure of the hybrid control system. Compressor instability precursor signal simulation methods based on MG model and chaotictime series have been studied. The construction of instability precursor signal is critical to compressorstability management simulation tests. The constructed signal also can be used to verify the effective-ness of compressor instability prediction algorithms with the absence of true experimental signal.Three compressor instability prediction algorithms have been proposed respectively based ontime-frequency analysis, mathematical morphology fractal dimension, and time series modeling.Envelope detection methods such as mathematical morphology filtering are used to detect low fre-quency instability precursors, which are hided in high frequency signals. Mathematical morphologyfractal dimension analysis is one advanced nonlinear signal processing technology, which can extractthe changes of compressor stability through quantization of the signal complexity. Since the variationsof complex system states are usually reflected in output signals, modelling the time series of systemoutput, prection the output by the model, the mean square of prediction error can be used as compres-sor stability index.A new aircraft engine acceleration optimization strategy which combined with SQP algorithmand stability management has been proposed. Based on summarization of the features and restrictivefactors of turbofan engine acceleration process, SQP based acceleration optimization is researched. Tomake full use of the remaining surge margin, the boundary condition of surge margin is minimized,and then, the engine operating point is adjusted realtime according to the output of the engine instabil-ity prediction system.All of the research results in this dissertation lay a solid theoretical reference on high stabilitycontrol technologies, including surge active control and stability seeking control.