# In-the-Loop Simulation Experiment of Aero-Engine Fault-Tolerant Control Technology
## 4 Discussion  
According to the working principle of aeroengine, this paper establishes the component level model and adaptive model of a turbofan engine, then carries out the research on sensor fault diagnosis based on analytical redundancy, carries out the research on fault-tolerant control method based on analytical redundancy and switching control rate, and finally carries out the real-world in the loop simulation verification.  
The work of this subject is as follows:  
(1) According to the principle of component level modeling, the component-level model of turbofan engine is established by using the design point data of a turbofan engine. The simulation results show that the accuracy of the model meets the requirements. Then, the performance degradation of gas circuit components, sensor noise, and fault are set on the basis of the model. By comparing the results of the model with the initial setting, it can be proved that the performance degradation simulation and noise injection of the model meet the requirements.  
(2) The fault-tolerant control verification based on analytical redundancy is carried out. If there is no fault, the sensor value of the real engine is used for PID control. If there is a fault, the analytical redundancy, that is, the estimated value corresponding to the adaptive model, is used to replace the error value of the corresponding sensor as the feedback signal for closed-loop control, so as to isolate the fault sensor and ensure the stability of the system. The low-voltage speed closed-loop control and EPR closed-loop control are designed. When the sensor fails, the control rate participated by the failed sensor can be replaced by the control rate without the participation of the failed sensor, and the  
Figure 9: Using hardware in the loop simulation platform, the simulation results of Nh and Nl of fault-tolerant control under high-pressure rotating speed fault. **(a)** Nl simulation results of fault-tolerant control under high-pressure rotating speed fault. **(b)** Nh simulation results of fault-tolerant control under high-pressure rotating speed fault.  
fault tolerance is carried out by switching the control rate. The simulation results show that the above two fault-tolerant effects are good, and the disadvantages of the fault-tolerant method based on switching control rate compared with the fault-tolerant method based on analytical redundancy are analyzed.  
(3) This paper studies the principle and application method of physical in the loop simulation system, transplants the digital simulation system to the physical in the loop simulation system, and then carries out the research on fault-tolerant control. The experimental results show that the adaptive model tracking effect is good, and can provide accurate analytical redundancy in case of sensor failure, so as to realize fault-tolerant control.  
Summarizing the research work of this paper, in my opinion, it can be improved in the following four aspects in the future:  
(1) The component level model does not include the starting process. If this process is added, the simulation will be more comprehensive.  
(2) The closed-loop control of engine model is relatively simple and has no unique innovation. If more complex and accurate control laws can be designed, the fault diagnosis and fault-tolerant control in this paper will be more meaningful.  
(3) In the aspect of fault-tolerant control, only the fault-tolerant control for sensor fault is studied, and the fault-tolerant control for actuator is not studied.  
(4) The physical in loop simulation is relatively simple. Ethernet and signals used for communication are digital quantities. In the future, analog quantities can be used for more comprehensive semi-physical simulation.