Research On Switch Fault Diagnosis Method Of Flying Capacitor Multilevel Converter

With the fast development of the times,the situation of energy shortage is becoming increasingly severe,among which it is very essential to decrease energy consumption and improve the utilization rate of energy.As the core of energy transformation,the converter plays an important role in the efficient utilization of energy.Among them,the flying capacitor multilevel converter(FCMC)has been widely studied and applied in the fields of rail transit equipment,medium and high voltages transmission system,new energy vehicles and so on.Usually,power switching device is one of the most vulnerable components in power electronic system due to frequent turn-on and turn off,among which open circuit and short circuit are the most common.The short-circuit fault of power switching devices will produce a lot of over-current,which will burn the circuit components.Although there are mature hardware protection measures,the additional hardware circuit will increase the cost.The open circuit fault of power switching devices will affect the output voltage of the converter.The converter with fault-tolerant design is an important way to ameliorate the reliability of the power electronic system.Meanwhile,the fault diagnosis of switching devices provides the necessary technical support for the fault-tolerant design of FCMC.Therefore,the research on fault diagnosis of FCMC power switching devices in this paper is of great significance to ameliorate the reliability of the power electronic system.The research focus and achievements are mainly included in the following three points:(1)Analyze the GaN-based flying capacitor multi-level topology,discuss the causes of switch short-circuit and open-circuit failures,deeply analyze the characteristics of switch failures in FCMC,and summarize the influence of circuit parameters on the short-circuit characteristics of GaN devices and the current collapse effect.(2)The switch fault diagnosis method of flying capacitor multilevel converter based on discrete Fourier transform is proposed.According to the Discrete Fourier Transform(DFT),the inductor voltage harmonics and the inductor DC component of the flying capacitor multilevel DC-DC Buck converter(FCBC)are analyzed.At the same time,the carrier phase sequence is changed,and the switching node voltage harmonics of the flying capacitor multilevel DC-AC inverter(FCMC)are analyzed.Extract fault characteristic information separately,and find out the mapping relationship between different faults and fault characteristic signals.According to the analysis results,a DFT-based switching fault diagnosis method for flying capacitor multilevel converters is designed.For short-circuit and open-circuit faults,the flying capacitor three-level DC-DC Buck circuit and five-level DC-AC circuit simulation platform built by MATLAB,the simulation results preliminarily verify that the proposed fault diagnosis method can quickly identify the type of failure and locate it.(3)The GaN-based three-level FCBC and five-level FCMC experimental platforms are built.The experimental results display that the proposed fault diagnosis method can effectively and quickly identify the type and location of the fault,with fast diagnosis speed(within 20 microseconds),good robustness,and diagnosis algorithm Simple,small amount of calculation,less CPU resources and other advantages.