The Literature Reviewofe Characteristic Parameters Extraction of Powerin Power Electronic Circuit指导老师：江宁强学生姓名:于杏学生号：115108000887日期：2016.01.11ABSTRACT：Main power device is the core part of power electronic circuits .It’s fault feature extraction is the foundation of fault diagnosis and forecast in power electronic circuits ,which is quiet useful to the reliability .The article introduces the reliability distribution of main power devices,and emphatically analyses Failure Mechanism and declining of MOSFET and IGBT.And also make a classification of parameter fault feature extraction methods:Direct Extraction and Indirect Extraction.What’s more,there are introductions of different extraction methods.In the end ,the article poins out its research difficulties and direction.KEY WORDS:fault feature extraction; reliability; Failure Mechanism; power electronic; power switch device.INTRODUCTION:Because of its advantages of low noise, high efficiency, high power density, morden power electronic circuits is widely used in industry, military, aerospace and other fields[1].Take an important role in the circuit transformation, new energy power generation.With the increasingly complicated power electronic circuits, power level continuously high,Especially when used in some important fields such as aviation, aerospace, Higher request to the reliability of the power electronic circuit.With the further study of the principle of the power device failure, and the continuous development of sensor technology and signal detection technology, it is possible to realize fault diagnosis of power electronic devices, failure prediction and state prison test [2]. What’s more, choosing appropriate fault characteristic parameters and the corresponding fault feature extraction method are the most difficulty points. Therefore, in view of the failure characteristic parameters extraction technology research of power electronics power device is critical to the improvement of power electronic circuits’ reliability.1 The reliability of the power electronic circuit power devices1.1 The reliability of the power device requirementsAlthough with the development of semiconductor technology and material technology, the failurerate of main power device has been decreased.But it is still high the main reason for the failure.Fig. 1 Device failure distribution diagramIt can be seen from figure 1 that the main power switch tube failure rate (including a half conductor device and weld failure) accounted for 34%. According to the degree of change causing by the failure，barrier of power electronic circuits r is divided into catastrophic failure and parametric failure .A catastrophic failure is called hard fault ,which always happens suddenly, and tends to cause a sharp change of the circuit function, easy to cause catastrophic co-nsequences.So the diagnosis to fault diagnosis is a focus of power electronics research [4]. Parametric faults is also called soft barrier, which refers to the electronic device with the decay of performance caused by electronic devices. Soft fault is graded a sudden loss of functional sex, although not cause circuit, but will lead to the change of the performance s-ystem.And if it does not be carrieed on the effective processing, a catastrophic failure can appear. Therefore, the research of the power electronic circuit‘s soft fault monitoring is animportant mean to enhance the reliability of the power electronic circuit segment. At prese-nt, the focus of the study of power electronic circuit soft fault mainly on the reliability of the d evice, such as the service life of power devices.,reliability modeling, condition monit-oring ,etc.1.2 Power device failure mechanism and characteristics of recession1.2.1 Power MOSFET failure mechanism and characteristics of recessionMetal oxide semiconductor field effect transistor, abbreviation for MOSFET, based on grid vol tage to control the power of drain current Tube. Power MOSFET with high input impe-dance, low on resistance, fast switching speed, simple driving circuit , low power loss, etc, widely used in small and medium-sized power electricity transformation. Figure 2 shows t-he N type equivalent circuit of the power MOSFET, 3 A lead pole of the source (S) resp-ectively, the ga te (G) and drain (D).Fig. 2 Equivalent circuit of N-channel MOSFETFigure 2 : Rg, Rbe respectively T1 gate resistance and parasitic transistor base -- the emitt-er resistance; Cgd, Cgs, Cds for parasitic electrode capacitance; D1 for parasitic diodes. T-he main failure reasons of power MOSFET can be divided into chip related failure and fai-lur e related to packaging Two categories. Chip related failure reasons are: 1) electrical lo-ad; 2) electrostatic discharge, 3) the parasitic transistor mistakenly trigger to T1 And the re-verse rec overy parasitic diode D1; 4) with ionizing radiation effect The hot carrier effect; 5) Thermal e xcitation. Failure related to encapsulate the original Fall off due to mainly inc-lude: 1) the lea d; 2) welding layer failure. In practical application ,the failure of power M-OSFET is usually the consequnse of several factors.While, the dominant factors in the pro-cess of recession on ly has one or two.At present, the research for the characteristics of the power MOSFET recession mainly on th e effects of ionizing radiation [5] and hot carrier effect [6]. Due to these two kinds of micro effects can destroy the crystal structure and the distribution of oxidation layer , they can eve ntually lead to macroscopic characteristics change, the main performance are: 1) U-th threshol d voltage drift; 2) the most large linear transconductance Gm decreased; 3) the increase of co nduction resistance Rdson.1.2.2 IGBT failure principle and characteristics of recessionCompared to the power MOSFET , IGBT has advantages : high pressure and load strong .So it is widely used in high power electric energy conversion. The power module of IGBT usuallycontains two kinds semiconductor silicon chips:IGBT and diode chip .The failure of IGBT power module usually caused by internal fatigue limit ,which combinea with external operating environment and other factors . The related failure mode can be divided into the same chip:related failure (internal failure) and packaging related failure (external failure). The internal failure associated with the semiconductor physics characteristics of IGBT device, Forms like insulation breakdown, hot carrier injection and electron mobility and so on. This is mainly caused by high temperature and electrical stress of components inside it .The high temperature from device in the abnormal short circuit current and local encapsulation defects, while the electric stress is derived from the overshoot of collector voltage IGBT’s turn-off and gate electrostatic damage.Generally, the internal failure caused by overvoltage and overcurrent external electric stress is short, so it belongs to the transient failure of IGBT device. In addition, from the perspective of materials science,by the aging of IGBT device is made composed of IGBT device of the material do not match the expansion coefficient and junction temperature volatility, thereby resulting in the device package aluminum bonding wire falls off and solder layer cracking.Similar to those, in power MOSFET ,the most obvious features of IGBT recession in the circuit are also a threshold voltage rise, as well on resistance Rdson increases, moreover IGBT turn-on saturated pressure drop increases .And extend the cut-off time is also an important feature.By conduction, the power switch tube usually have a current in the recession resistance increases,an increasing of the threshold voltage , a reducing of the cut-off time ,and a characteristic signal increasing of the gate current, etc. These characteristic signals directly reflect the changing of power off closed tube parameters.Therefore it can be called first fault features.2 Power switch tube direct extraction of characteristic parameters2.1 Based on the power switch tube on resistance change of fault feature parameters Several extractionThe increasing of conduction resistance in Power MOSFET and IGBT device is one of the important features of the performance decline. At the beginning of the parameter extraction research in the power switch tube failure sign, researchers have proposed using the changes of conduction resistance to achieve the power switch tube performance monitoring.2.2 Based on the power switch tube conduction the fault characteristics of change of pressure drop parametersLiterature [7] proposed the performance test of IGBT can be realized by change of IGBT turn-on saturated pressure drop . In order to get full IGBT module pressure drop and conduction as the change of components aging recession trend, the tested IGBT module can be put in power cycle, and then fix a duty ratio signal to the IGBT gate, at the same time, the change of the saturated pressure drop of the IGBT turn-on can be recorded.2.3 Based on the power switch tube gate current dynamic characteristics change Barrier characteristic parameters extractionIn general, caused by aging fatigue IGBT monomer The bonding line loss for the whole parasitic inductance and IGBT module Resistance effect is relatively weak. In comparison, when the IGBT module A single malfunctioning of the device as a whole (e.g., a single IGBT chip) Parasitic parameters of IGBT module will produce more obvious changes, thereby Can cause the corresponding gate drive current waveform significantly change. Due to the The literature [8] using IGBT gate current dynamic is put forward Characteristics as the fault characteristic parameter in order to realize the fault Monitoring, and provide the corresponding early warning for IGBT module complete failure.3 The power switch tube indirectly extraction of characteristic parameters3.1 Based on characteristic parameter extraction of signal processing3.1.1 Frequency analysis methodSignal processing is a process of a general designation of signal extraction, transformation,ana lysis and synthesize.Methods based on the letter date processing includes the Walsh transform [9][10], basis function, FFT transform, wavelet transform, higher order spectral analysis, etc. Due to the fault information is contained in the power electronic circuit, the key signal usuall y be cyclical, therefore, FFT transformcan can be used to analysize the periodi-c signal from time domain to frequency domain.and extract the fault feature.3.1.2 Wavelet extraction methodBased on the wavelet transform have local features of signal representation in both time and frequency domain ,which can make the characteristic vector dimension reduction ability. Marr wavelet was choosed by literature [11] for the 4 layer wavelet decomposition, and ultimately to each bigest wavelet packet decomposition coefficient as a characteristic to form the reason feature vector. Not only in the wavelet transform coefficients of wavelet decomposition can be the selection of characteristic signal, but also calculated band signal Energy characteristics can be the fault characteristic signal.The study shows that through the establishment of power electronic circuit system accurately System model, and combining with the related parameter identification algorithm to obtain the main circuits Components parameters of the scheme is feasible. Among them, the application in the electric power Subcircuits the domain of fault diagnosis and forecast, accurate system model is An important prerequisite for obtain believable identification parameters. Because of a malfunction,scale is very small, responses of the parameters in the change in the input and output port Electric quantity, drift and may well be the identification parameters Measurement error to drown. Therefore, the power electronic circuit parameter identification In power electronic circuit of precise modeling research and testing technology.3.1.3 Higher order spectral analysis methodHigh order spectrum is also called higher order accumulation or multispectral , the points Ana lysis and processing technology are powerful and fanaticism tool to blind signal and n-onlinea r signal , it has the following advantages: restrain gaussian noise and improve esti-mated per formance of the signal. detect the signal nonlinear; effectively detect amplitude and phase inf ormation. For the higher order spectral analysis, with a double spectrum and in practical appli cation.For the higher order spectral analysis, with a double spectrum and in practical application Thr ee spectrum is most commonly used.3.2 Feature parameter extraction based on systemSystem identification is based on the system’s input and output time function to determine the mathematical model which can be used to describ the behavior of the system,.It is one of the important branches in the modern control theory[12]. The purpose of the mathematical model set up by the identification is to estimate the characterization system behavior.It has been widely used in the prediction of the output system and the design of controller . At present, applications also can be found in the field of power electronic circuit fault diagnosis and forecasting . Carry on the system identification, the system model you must be first obtained by prior knowledge. Then bythe use of input and output datas and solving algorithm ,the unknown parameters in the mode can be got, and then effective model system. Therefore, the system model, the input and output data structure and algorithm is department the three elements of system identification.4 ConclusionWith the reliability problem of power electronic system is outstanding, fault diagnosis and pr ediction technology of power electricity have become research focus.At the present stage,the main problems in practical application conclude too many checkpoi-nts and too complex . Too many checkpoints not only increase the cost of the circuit, at t-he same time, influnce the improvement of the system reliability. 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