Fault Diagnosis Research On Power Devices Open-circuit Of Power Converters

Power converters are widely used in industrial applications,electrification transportations,new energies,power systems and domestic appliances.According to the surveys,the failures of power switches include short-circuit fault and open-circuit fault,currently,the short-circuit fault have maturely hardware and software protections,while the open-circuit is still under researches.This dissertation researches on two-level three phase voltage-source rectifier and inverter based on analysis of phase currents,deep study is done on failure mechanie analysis,online fault detection and location,the main contents is as following.Regarding the two level three-phase voltage source rectifier,a novel single and multiple open circuit fault detection and identification method is proposed based on the analysis of primary inductance energy storage.Primary voltage and current during one period is divided into six state interval according to the zero-crossing point of primary voltage,each state interval operates under only two effective line-to-line voltages and three power transistors,the open circuit fault causes inductance energy storage abnormal in some state intervals,different fault types and causes different abnormal state interval.The envelopes consisted the mean current of the adjacent line-to-line currents are compared with peaks and valleys of line-to-line currents,the results are used to measure whether the energy storage is normal or abnormal.and online,fast,accurate diagnosis method is designed.The robustness of the proposed method are verified by the disturbance from the grid and the load side.The performance of the proposed method is compared with the similar methods,which highlights the advantages of the proposed method.Regarding the two level three-phase voltage source inverter,the definition of the allelic points and their functions are given,the design requirement of the function is given,an novel transistor single and multiple open-circuit fault detection and identification method is proposed.Mean function and zero-crossing current samples during a period is designed as allelic point functions.Under fault conditions,center points of legs,as allelic points,will changes.Based on the function value and the residuals among them,an online,fast and accurate diagnosis algorithm is proposed.The robustness of the proposed algorithm is verified under variable speed and load torque changes.Discusses of the tuning efforts is given.The performance of the proposed method is compared with the similar methods,which highlights the advantages of the proposed method.Regarding the periodic signal,an online simplified Fourier series calculation method is proposed,the original signals are pretreated by data reconstruction according to DCcomponent-crossing points.Then the convolution between reconstructed signals and the given signals is used to estimate the Fourier series of the original signal,the experimental results show that the accuracy of proposed simplified Fourier series approximate with the results of Fast Fourier Transform.The proposed online simplified Fourier method is applied to calculate DC and AC components of phase currents of inverter.Meanwhile,a novel normalized algorithm of DC and AC components is proposed,specially,the normalized DC and fundamental components are used to design an online,fast and accurate fault location method.Meanwhile,the effectiveness of the proposed algorithm is verified in different motor speed and different load problems.Discusses of the tuning efforts is given.The performance of the proposed method is compared with the similar methods,which highlights the advantages of the proposed method.Regarding the power converter of symmetrical topologies,such as two level voltage source three-phase rectifier and inverter,a novel fault diagnosis method is proposed based on distance formula to measure the current similarity and to describe characteristics of global symmetry and local symmetry of topological structure.Two diagnostic strategies are presented:(i)the original phase currents are reconstructed by zero-crossing point,then Euclidean distance,correlation coefficient,cosine similarity,dynamic time warping distance are used to quantitatively analyze the similarity among reconstructed phase current,in order to describe the symmetrical characterization of topological structures,finally,combined with the phase current average values,an online,fast and accurate diagnosis algorithm is proposed.(ii)The kernel density estimation and energy estimation of the original phase current are calculated,similarity measurement of density function and energy function based on Euclidean distance is used to describe symmetry characterization of topological structure,and then combined with the current average,an online,fast and accurate diagnosis algorithm is proposed.The robustness of the proposed method are verified by the disturbance from the grid and the load side.The performance of the proposed method is compared with the similar methods,which highlights the advantages of the proposed method.This dissertation deeply studies the single and multiple open-circuit fault diagnosis in two level three phase voltage source rectifier and inverter based on the analysis of phase current,different fault detection and identification methods are proposed.The experimental results show that the proposed algorithm has high accuracy,fast diagnosis,strong robustness,low cost,low tuning efforts.The researches can be used as an online monitoring alarm system in power converter,and provide fault information to the maintenance decision system and fault tolerant control system,as one of the core technology,can greatly improve the reliability of the power converter,as well as great economic benefits.