Research On Fault Diagnosis Technology And Fault Tolerant Control Strategy Of The Three-Level Inverter

As the core technology for high-voltage and high-power applications,Milti-level power converter technology has become a research hotspot in the industrial fields of medium and high voltage and high power such as petrochemical,electric power,metallurgy,mining and so on.To date,multi-level inverters have been developed for more than 30 years,resulting in a large number of topologies.Based on Neutral Point Clamped(NPC)three-level inverter which with simple structure,stable performance and easy control.In this thesis,the fault diagnosis and fault-tolerant control of inverter are studied.After some faults occur,fault-tolerant operation can be used to ensure the stability and reliability of the system.In this thesis,the fault feature information extraction technique based on Empirical Mode Decomposition and fractal geometry theory and the fault diagnosis technology based on Support Vector Machine are studied.Firstly the thesis has introduced the topology,working principle and switching state of the NPC three-level inverter,and analyzed and classified the single-double open-circuit faults of the switching devices.Then the simulation model of NPC three-level inverter is built by MATLAB/Simulink platform,and various types of faults are simulated to obtain the waveforms of the three-phase output line voltage and phase current of the inverter under different fault conditions.The feature vector corresponding to each fault is extracted from the obtained waveform by the combination of Empirical Mode Decomposition and fractal geometry theory.The feature vectors are put into the Support Vector Machine based on Particle Swarm Optimization algorithm for fault training and classification.Finally,the fault diagnosis is completed.Fault-tolerant control methods based on voltage space vector redundancy and topology reconstruction are adopted for different types of faults occurring in the main circuit of NPC three-level inverter.Due to different characteristics of the voltage space vector after faults occur,faults have been divided into type I and type II.When a type I fault occurs,the vector synthesis method and the corresponding Space Vector Pulse Width Modulation(SVPWM)algorithm are obtained by analyzing the voltage space vector.Fault-tolerant control based on voltage space vector redundancy is used for fault-tolerant control.When a Type II fault occurs,the fault-tolerant control method based on topology reconstruction is used to reconstruct the three-level inverter topology into a three-phase eight-switch fault-tolerant inverter.The voltagespace vector of the three-phase eight-switch inverter is analyzed,and the space vector synthesis method and SVPWM modulation algorithm are obtained.The simulation verification in the MATLAB/Simulink toolbox shows that the two fault-tolerant control methods can make the inverter work continuously after the fault occurs,and the reliability is high and the cost is low.Finally,we built a three-level inverter fault-tolerant operation experimental platform,and fault-tolerant analysis based on voltage space vector redundancy and topology-based reconstruction are performed on the experimental platform.