Research On Open Circuit Fault Diagnosis Technology For Power Switch Of NPC Three-Level Inverter

With the continuous development of power electronics technology,multi-level inverters have been widely used in high voltage and high-power applications,among which the Neutral Point Clamped(NPC)three-level inverter is the most widely used.The three-level inverter has advantages such as high voltage resistance,low harmonic content of output voltage,and low switching loss.However,due to its complex circuit structure and a large number of power devices,the probability of failure greatly increases.According to industry statistics and analysis,power conversion devices are one of the components with the highest fault rate in three-level inverters,mainly manifested as short circuit faults and open circuit faults.At present,there are relatively mature software protection algorithms and hardware protection circuits for short circuit faults,while open circuit faults are still in the research and experimental stage.This article takes the IGBT power transistor of NPC type three-level inverter as the research object,conducts research on the problem of open circuit fault occurrence,and studies the application of fault diagnosis algorithms for inverter fault detection,as well as the identification and positioning of faulty power switches.Firstly,this thesis describes the research background and significance of the topic,summarizes the current research status in the field of fault diagnosis at home and abroad,introduces the topology,operating principle,and modulation methods of NPC type three-level inverters,analyzes the inverter faults,and summarizes the basic characteristics of the inverter output three-phase current under different fault types.Firstly,this article elaborates on the research background and significance of the topic,summarizes the current research status in the field of fault diagnosis at home and abroad,introduces the topology,working principle,and modulation mode of NPC threelevel inverters,and conducts fault analysis on the inverters.It summarizes the basic characteristics of the inverter’s output three-phase current under different fault types.A fault diagnosis algorithm based on current residual is studied for single transistor faults and double transistor open circuit faults in NPC type three-level inverters.Firstly,the mathematical model of an NPC three-level inverter based on MLD is analyzed,and an observer is built to observe the three-phase current output by the inverter during normal operation.The observed current is residual with the actual system output current,and the residual characteristics of different fault types are analyzed.Based on the residual characteristics,a fault diagnosis algorithm is designed for three-level inverter fault diagnosis.Finally,the feasibility of the algorithm is verified in the MATLAB/Simulink simulation environment.Research a fault diagnosis algorithm based on symmetry by utilizing the symmetry characteristics of inverter topology structure for fault detection.The NPC type threelevel inverter has a high degree of symmetry,and during normal operation,the inverter is structurally symmetrical in three phases.If the inverter malfunctions,the symmetry is disrupted.Based on the characteristics of three-phase output current of inverters under different fault conditions,a fault location algorithm is designed for the localization and identification of inverter fault power transistors.The effectiveness and feasibility of the fault diagnosis algorithm were verified in the MATLAB/Simulink simulation environment.In order to further verify the effectiveness and robustness of the symmetry based algorithm,validation was conducted on the established experimental platform.The experimental results showed that the algorithm can accurately detect faults and locate them in the fault tube,without any false alarms.The effectiveness of the algorithm was verified.