| Based on the 400 Hz centralized aircraft external power supply system,the power supply terminal adopts a three-level cascade converter.Compared with the traditional aircraft external power supply,the new external power supply does not consume fuel during power supply,which can significantly improve the power supply efficiency and quality of the power supply system,and solve the environmental pollution caused by fuel combustion.In this paper,the research on the open-circuit fault of the three-level cascading converter of the corridor bridge of the navigable airliner has important guiding significance for the realization of energy saving and emission reduction of the navigable airliner,the improvement of power supply efficiency,the reduction of noise pollution and the overall improvement of the airport ground operation efficiency.The main research contents of this paper are as follows:(1)The development history,working principle,topological structure,control method and carrier modulation strategy of the three-module cascade converter used in the external power supply system of centralized aircraft are briefly introduced.This paper studies the modulation strategy of CD-SPWM and CPS-SPWM,and compares the harmonic characteristics of the output voltage when the different modulation strategies are adopted.Based on this,the paper analyzes the most suitable carrier modulation strategy for the cascaded converter in the centralized external power supply system.(2)According to the number and location of IGBT faults,all faults are divided into 6categories.The simulation circuit based on three-level cascade converter is built in Matlab/Simulink to simulate the voltage output waveform and FFT harmonic spectrum of different types of faults.The different level characteristics of the voltage output waveform under different fault states can be used as the basis for fault diagnosis.The FFT harmonic spectrum is analyzed by double Fourier analysis,and specific sub-harmonics are selected as the input feature vectors.(3)according to the number of IGBT open-circuit fault location and fault types can be divided into five types,using carrier phase shift modulation strategy,in the Matlab/Simulink to all fault voltage output waveform and harmonic spectrum diagram of the simulation and analysis of characteristics of IGBT open circuit fault,using the fast Fourier transform to extract the fault feature vector,to choose a specific harmonic amplitude or phase as the fault characteristic.(4)The development history and application fields of neural network are briefly introduced.BP neural network is selected as the network structure of fault diagnosis.The fault feature vector extracted in Chapter 3 is encoded and input into the trained neural network to realize the fast fault diagnosis.The results of fault diagnosis are verified under different tuning systems to prove the feasibility of the scheme.(5)By modifying modulation strategy to realize Fault-Tolerant Operation model of the system,the relationship between phase-shifting Angle of carrier phase-shifting modulation strategy and system output characteristics and output level number is analyzed.According to different fault types,different modulation strategies were developed,and simulation circuits were built in Matlab/Simulink to simulate the fault-tolerant operating states of five types of different fault conditions,so as to prove the validity of improving the system Fault-Tolerant Operation theory by modifying the modulation strategies.(6)By designing the circuit and controller parameters,a small power experiment based on three-module cascaded converter was carried out.Realizing the single IGBT open-circuit fault of module 1 bridge arm A and the fault-tolerant state of the system.The experimental results further prove the validity of the control strategy. |
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