Open Circuit Fault Diagnosis Research On Power Devices Of Three-phase Four-wire T-type Rectifier

Power converter is the core equipment to achieve efficient use of electric energy,widely used in electric vehicles,aerospace,new energy,CNC machine tools,chemical industry,smelting and other fields.With the continuous progress of science and technology and the continuous exploration of living environment,the increasingly harsh and complex working conditions require higher and higher reliability of power converter.Fault diagnosis technology is an important way to improve the reliability of power converter.By detecting and locating fault devices,it provides basis for maintenance decision and fault-tolerant control,and ensures the safety,reliability,economy and unmanned operation ability of equipment.In this thesis,a series of studies are carried out on the open-circuit fault diagnosis method of power transistor in the three-phase four-wire T-type rectifier system.In this thesis,the double closed-loop control and SVPWM modulation principle of the three-phase four-wire T-type rectifier system are introduced.The distortion characteristics of capacitance voltages and phase currents under the fault of power transistors of upper arm,lower arm and neutral arm are analyzed.A neutral arm power transistor fault diagnosis method based on capacitor voltage symmetry is proposed by taking the capacitance voltage as the fault characteristic.According to the property of three times fluctuation and the symmetry of capacitor voltages and the phase information obtained from the grid phaselocked loop,the method can diagnose the faults of six kinds of power transistor in the threephase neutral arms.In order to improve the robustness of the diagnostic method,adaptive diagnostic thresholds are put forward by using the peak values within the period.In this thesis,a zero-current based fault diagnosis method for power transistors of upper arm,lower arm and neutral arm is designed with phase currents as the fault characteristic.The concept of zero current is used to realize the fault detection at first.A hierarchical judgment strategy is proposed to locate the fault transistor.The first stage fault is judged by combining the polarity information of the corresponding grid voltage at the time of fault detection.Then the overlap zero current range is calculated,and reasonable adaptive threshold is designed to make the second stage fault judgement to distinguish between the neutral arm and the upper and lower arm power transistor fault similarity.All twelve single power transistor fault types can be diagnosed by the method.In this thesis,the proposed methods are simulated and verified by building a threephase four-wire T-type rectifier Matlab/Simulink fault simulation platform.Participated in the construction of the physical experiment platform and carried out the physical experiment verification.Simulation and experimental results show that the fault diagnosis methods proposed in this paper can diagnose the open circuit fault power transistor quickly and accurately,and have strong robustness to variable voltage and variable load,power grid harmonic,etc.,which have important engineering application value.