Research On Modeling And Distributed Control Of Variable Cycle Engine

Variable cycle engine can change its bypass ratio（BPR）to adapt the demands for thrust and specific fuel consumption（SFC）of different flight tasks,which is an important research direction in the field of aero engine.The distributed control architecture can reduce the weight and complexity of the system and offer more computing units,which is the future development trend of aero engine control system.Compared with the conventional turbofan engine,variable cycle engine has more variable geometries resulting in more actuators and sensors in its control system.So it is more necessary to use distributed control architecture.This paper has done the research of the component level modeling and distributed control of the variable cycle engine.The main contents are organized as follows:Firstly,the application of volume method in mixed flow aero engine modeling was improved.The computation process of the simulation model built with volume method did not need guess values and iterative process.The traditional volume selection method needed an approximate computation step to get the states values of the inner stream into the mixer indirectly that reduced the accuracy of the model.An improved method of selecting volume after the low pressure turbine was proposed.The improved volume selection method could get the states values of the inner stream into the mixer directly and improved the accuracy of the model.Using a bench mark model as reference,simulation showed that replacing traditional volume selection method with improved method reduced the modeling error from10^-2 level to 10^-6 level so that the model could be used for both dynamic simulation and steady simulation of the engine.Secondly,a simulation module library named AeroEngineLib was established in the Matlab/Simulink environment for aero engine modeling based on volume method.The compressor module and turbine module were designed based on map scaling technology that enabled the module library to be in common use.The volume selection mothod and the method for simulating the variable area bypass injectors were proposed and then the variable cycle engine component level model was built with AeroEngineLib.Mode conversion from double bypass to single bypass was simulated with this model.Then the engine characteristics of these two modes were calculated with altitude,velocity and throttling.The results of mode conversion at the flight condition with a height of 0 km and a Mach number of 0 showed that the thrust was increased by 16.823%and the specific fuel consumption（SFC）was increased by 15.163%while the bypass ratio was declined from 0.700 to 0.307.Next,a new linear extend state observer（LESO）was added to the linear active disturbance rejection controller（LADRC）.The information of virtual control value and output was used to observe the estimating error of the total disturbance.Two new structures of LADRC were proposed.The transfer function of these three kinds of LADRC was derived.Through frequency domain analysis,it was known that LADRC had a larger stable region.The stability region of the new structure LADRC was larger than that of the traditional LADRC,and the disturbance rejection performance of the new structure LADRC was better than that of the traditional LADRC.The coupling among variable cycle engine control loops was treated as part of the total disturbance.By estimating total disturbance of the loop in real time and compensating it in the control signal by three LADRCs,three closed control loop were decoupled.The traditional structure LADRC and new structure LADRC were used respectively for building the decoupling control systems.The simulation research showed that it was feasible to establish the decoupling control system of variable cycle engine using LADRC.And the decoupling control systems built by new structure LADRC had better decoupling effect and disturbance rejection performance than the systems built by traditional structure LADRC with the same control bandwidth.Subsequently,a fully distributed control architecture was proposed.The calculations of control algorithm were completely distributed to the smart actuators.And the parameter values required for the calculation were sent to the smart actuator by smart sensors through a serial data bus.Decentralized control of variable cycle engine was realized using the above LADRC based decoupling method.And a time triggered bus communication program was designed using the CANaerospace higher layer protocol based on the CAN bus hardware.Thus the fully distributed control system of variable cycle engine was realized.A simulator was built in the Matlab/Simulink environment with TrueTime toolbox.TrueTime Kernel modules were used to simulate computing units of smart actuators and smart sensors.TrueTime Network module was used to simulate CAN bus.The linear ADRC and CANaerospace protocol were written to the computing unit.The simulation results showed that the established system could adapt to a wide range of intake status and changes in healthy status of the engine and had strong robustness.Finally,the time delay of variable cycle engine fully distributed control system was analyzed.The computational delay of variable cycle engine fully distributed control system was less than centralized control system,but the communication delay was greater than the centralized control system so that the total time delay might be greater than centralized control system.And the time delay might exceed a control period when the bus communication was influenced by serious interference.Simulation results of variable cycle engine fully distributed control simulator showed that the LADRC based variable cycle engine fully distributed control system had certain robustness about time delay.With the control parameters used in this paper,the control system could keep better control results when the time delay was not more than two control periods,and when time delay was more than two control periods,the output of control system appearred jitter and tended to be unstable.The Smith predictor based on virtual control value method and the control value postponing observerd method were used to compensate influence of the time delay respectively.Simulation results showed that the two methods could increase the stability of the variable cycle engine fully distributed control system with time delay,and the system using the control value postponing observerd method had better stability.