METHOD AND DEVICE FOR DETECTING FAULTS AND PROTECTION FOR POWER SWITCHING ELECTRONIC DEVICES

Abstract

The method detects a fault in a power switching electronic device (OT.sub.1) by using the thermo-acoustic effect and comprises the steps of: a) detecting an acoustic signal (SA) generated by thermo-acoustic effect in the electronic device when it is in operation; determining (FFT) a frequency spectrum of the detected acoustic signal and obtaining, from the frequency spectrum, a spectral signature (SEP) associated with the detected acoustic signal; comparing (CSG) the spectral signature (SEP) with a plurality of reference spectral signatures (Sgn); and, deciding (CSG) on the presence of at least one fault in the electronic device when at least one coincidence is identified in the comparison step c) between the spectral signature and the plurality of reference spectral signatures.

Claims

1. A method for detecting faults and protection of electronic power switching devices using the thermo-acoustic effect and comprising the steps of: a) detecting an acoustic signal generated by thermo-acoustic effect in the electronic power switching device when the latter is in operation, b) Determining a frequency spectrum for the detected acoustic signal and obtaining, using a frequency spectrum, a spectral signature associated with said detected acoustic signal, c) comparing said spectral signature with a plurality of reference spectral signatures, and d) deciding on the presence of at least one fault in said electronic power switching device when at least one match is identified in said comparison step c) between said spectral signature and said plurality of reference spectral signatures.

2. The method according to claim 1, wherein said determining step b) comprises a calculation by Fourier transform of said frequency spectrum of the detected acoustic signal.

3. A device for detecting faults and protection for the implementation of the method according to claim 1, wherein said device is intended to monitor an electronic power switching device in which a fault is likely to appear, wherein said device comprises at least one acoustic sensor, one input interface comprising amplification means and analog-digital conversion means and a digital signal processing unit; said digital signal processing unit comprising a spectral signal calculation software module capable of calculating a spectral signature of an acoustic signal detected by said acoustic sensor, a storage memory capable of storing a plurality of reference spectral signatures, and a software module for comparison and fault decision capable of detecting the presence of at least one fault in said electronic power switching device using at least one match identified between said spectral signature of said detected acoustic signal and said plurality of reference spectral signatures stored in said storage memory.

4. The device according to claim 3, wherein said device comprises a plurality of acoustic sensors and said input interface and is of the type with several acoustic signal input paths and also comprises sampling means.

5. The device according to claim 3, wherein, when a fault is detected, said digital signal processing unit delivers, as output, a fault signal for said electronic power switching device under surveillance.

6. The device according to claim 3, wherein, when a fault is detected, said digital signal processing unit delivers, as output, a fault alert comprising a light, sound or a display signal on a screen, with or without an indication of the type of fault.

7. The device according to claim 3, wherein said device comprises at least one ultrasonic acoustic sensor.

8. An electronic power switching assembly comprising at least one electronic power switching device and an associated device for detecting faults and protection, characterized in that said associated device for detecting faults and protection is a device according to claim 3.

9. The assembly according to claim 8, wherein, when a fault is detected, said associated device for detecting faults and protection commands a shutdown of said electronic power switching device or operation of the power switching device in a down-graded mode.

10. The assembly according to claim 8, characterized in that wherein said electronic power switching device is presented in the form of a power module, a converter or an inverter and comprises at least one cavity in which an acoustic sensor is housed.

Description

DESCRIPTION OF THE FIGURES

[0027] Other advantages and characteristics of the method and device will become clearer upon reading the detailed description below of the several specific embodiments thereof with reference to the annexed drawings, in which:

[0028] FIG. 1 is a block-diagram of a first embodiment of an electronic power switching assembly comprising a three-phase inverter and a fault detection and protection device that is equipped with a single acoustic sensor;

[0029] FIG. 2 is a block-diagram of a second embodiment of an electronic power switching assembly comprising a three-phase inverter and another fault detection and protection device that is equipped with three acoustic sensors;

[0030] FIG. 3 is a cross-section of a conventional power module comprising an integrated acoustic sensor which is adapted for the electronic power switching assembly of FIG. 2.

DETAILED DESCRIPTION

[0031] Electronic power switching devices are built from power modules that are associated in order to form full switching bridges such as polyphase inverters, or in order to be connected in parallel in order to conduct the desired current. The power module is typically an arm of a switching bridge.

[0032] The power modules, which are built using a planar architecture for the electronic chips, or using a 3D architecture, all have a structure of stratified layers, made of insulating or conducting materials, between which the electronic chips comprising semiconductor power switches, such as MOSFET or IGBT transistors, are integrated. Power switches typically switch at frequencies between a few hertz and a few hundred kilohertz. The result of this is repetitive heat pulses which lead to the generation of thermo-acoustic waves in the stratified structures of the power modules. The heat pulses are partially converted into mechanical energy of an acoustic nature by thermo-acoustic effect. The acoustic waves propagate, are deflected or reflected in the stratified structure of the power modules and are the bearers of information regarding this structure.

[0033] The invention leverages the above phenomenon to detect faults in electronic power switching devices. The acoustic wave produced by the electronic power switching device being monitored is detected and modifications in a spectral signature deduced from its frequency spectrum are detected by comparisons to previously recorded reference spectral signatures. Using the modifications of the spectral signature of the acoustic wave, the invention provides the detection of faults at an early stage. The invention also provides detection of the type of fault, such as, for example, a detachment or de-stratification of a layer, a crack in the fastening of a chip, a vacuum in a power module, etc.

[0034] Thus, it is possible to monitor and filter, during manufacturing, electronic power switching devices by examining their acoustic responses in relation to pre-defined specifications. During its life span, the health of an electronic power switching device can be monitored, continuously or according to a pre-defined periodicity, by an electronic monitoring unit that analyzes the acoustic waves emitted by the device so as to detect the presence of a fault and to protect the device from a risk of deterioration.

[0035] Embodiments of the invention are described below in the context of the fault detection and protection in a three-phase inverter.

[0036] As shown in FIG. 1, a three-phase inverter OT1 comprises three power modules, PM1.sub.A, PM1.sub.B and PM1.sub.C, and a switch command circuit SWC.

[0037] A schematic diagram of power module PM1.sub.A, with IGBT type transistors, is shown in FIG. 1. The power module comprises an IGBT high-side transistor TI.sub.HS, and an IGBT low-side transistor TI.sub.LS. Diodes ID.sub.HS and ID.sub.LS, called free wheel, are respectively associated with transistors TI.sub.HS and TI.sub.LS. The diodes ID.sub.HS, ID.sub.LS are mounted between the collector electrodes C.sub.HS, C.sub.LS, respectively, and between the emitter electrode E.sub.HS, E.sub.LS of the transistor TI.sub.HS, TI.sub.LS, respectively. The collector electrode C.sub.HS of the transistor TI.sub.HS is connected to continuous positive voltage +DC and the emitter electrode E.sub.LS of the transistor TI.sub.LS is connected to continuous negative voltage DC. The transistors TI.sub.HS and TI.sub.LS are switch controlled through their respective gate electrodes G.sub.HS and G.sub.LS. The output OUT.sub.A of the PM1.sub.A module corresponds to the interconnection point of the emitter electrode E.sub.HS and collector electrode C.sub.LS of the transistors TI.sub.HS and TI.sub.LS and delivers alternating current voltage.

[0038] It should also be noted that power modules PM1.sub.A, PM1.sub.B and PM1.sub.C could also comprise other power switches, such as MOSFET transistors or GTO thyristors, etc.

[0039] The switch command circuit SWC delivers gate control signals SC.sub.HS, SC.sub.LS, which switch control transistors TI.sub.HS, TI.sub.LS of modules PM1.sub.A, PM1.sub.B and PM1.sub.C.

[0040] As shown in FIG. 1, a fault detection device DEP is associated with a three-phase inverter OT1. An acoustic sensor CA is placed close to the inverter OT1 in order to detect an acoustic signal SA.sub.0 emitted by the inverter. The acoustic signal SA.sub.0 is provided to an analog input of the fault detection device DEP.

[0041] The fault detection device DEP is built around a dedicated electronic monitoring unit ECU. In another embodiment, the device DEP can be implanted in a micro-computer equipped with appropriate interface circuits.

[0042] The electronic monitoring unit ECU comprises an acoustic signal input interface IT and a digital signal processing unit SPU.

[0043] The acoustic signal input interface IT comprises an input amplifier AP and an analog-digital converter CAN. The input amplifier AP receives the acoustic signal AP as input, delivered by the acoustic sensor CA. The input amplifier AP performs a bandpass filtering of the acoustic signal SA.sub.0 and adjusts the amplitude level of the acoustic signal for later processing. An amplified acoustic signal SA.sub.1 is delivered as output by the amplifier AP. The amplified acoustic signal SA.sub.1 is digitized by the analog-digital converter CAN in order to then be provided to a data input port of the digital signal processing unit SPU.

[0044] The digital signal processing unit SPU is typically built around a microprocessor P with which is associated a read-only memory ROM and a random-access memory RAM, input/output interface means (not shown) and a storage memory MEM. A micro-program is hosted in memory in the unit SPU so as to provide the functions of signal processing by the sequential provision of series of instructions.

[0045] The functions of processing the signal executed by the unit SPU are shown in FIG. 1, in the form of the FFT and CSG blocks.

[0046] The FFT block is a software module for the calculation of the spectral signature SEP of the acoustic signal SA.sub.1. The spectral signature SEP is deduced from the frequency spectrum of the acoustic signal SA.sub.1 which is obtained by a Fourier transform.

[0047] The CSG block is a software module for comparison and fault decision, The SCG block compares the spectral signature SEP of the acoustic signal SA.sub.1 with the plurality of reference spectral signals previously recorded in the storage memory MEM, so as to detect one or more possible matches between the spectral signature of the acoustic signal SA.sub.1 and the reference spectral signals. The storage memory MEM stores a knowledge base comprising a plurality of reference spectral signatures Sgn representative of different states of functioning and different types of faults that may occur in the inverter OT1. The CSG block decides the presence of a fault and its probable type as a function of the results of the comparison. When a fault in the inverter OT1 is detected by the CSG comparison and decision module, the CSG module delivers, as output, a fault signal DI and can activate a fault alert.

[0048] The fault signal DI is transmitted to the switch command circuit SWC which can then halt the operation of the inverter OT1 by blocking at an inactive level the gate control signals SC.sub.HS, SC.sub.IS to the switch controlling transistors TI.sub.HS TI.sub.LS of the inverter OT1. The switch command circuit SWC can also command the operation of the inverter OT1 in a down-graded mode when the detected fault is less critical.

[0049] The fault alert WA can include, for example, a light or sound signal, or a display on a screen, with or without an indication of the probable type of fault.

[0050] In reference to FIGS. 2 and 3, another embodiment of a three-phase inverter OT2 is disclosed, in which each of the three power modules PM2.sub.A, PM2.sub.B and PM2.sub.C comprises an acoustic sensor CA integrated into its structure. In addition, in this embodiment, the inverter OT2 comprises an electronic control unit ECU2 dedicated to the fault detection and protection device according to the invention, which is integrated into a command unit UC of the inverter OT2.

[0051] As shown in FIG. 2, power modules PM2.sub.A, PM2.sub.B and PM2.sub.C are arranged side by side according to a planar arrangement and comprise integrated acoustic sensors CA.sub.A, CA.sub.B and CA.sub.C, respectively.

[0052] The command unit UC comprises a switch command circuit SWC2 and the electronic control unit ECU2. The command unit UC thus provides the switching control function of power modules PM2.sub.A, PM2.sub.B and PM2.sub.C, by producing gate control signals SC.sub.HS, SC.sub.Ls, and the function of fault detection and protection of the inverter OT2 in association with the acoustic sensors CA.sub.A, CA.sub.B and CA.sub.C.

[0053] The switch command circuit SWC2 is analogous to the switch command circuit SWC of the inverter OT1 of FIG. 1 and will not be disclosed here.

[0054] The electronic control unit ECU2 is distinguished from the electronic control unit ECU of FIG. 1 in that the interface IT2 for the electronic control unit ECU2 comprises three input paths, contrary to interface IT of the electronic control unit ECU which comprises only a single path for the signal SA.sub.0. The three acoustic signals, globally designated SA.sub.ABC, which are delivered by acoustic sensors CA.sub.A, CA.sub.B and CA.sub.C, are provided a three-path input at interface IT2, respectively. The SA.sub.ABC signals are filtered and amplified, then are sampled and time-multiplexed in order to be digitized by an analog-digital converter (not shown) which is analogous to the converter CAN of interface IT (FIG. 1). A digital signal processing unit SPU2 of the electronic control unit ECU2, conducts a processing analogous to that conducted by the digital signal processing unit SPU (FIG. 1) for each of the acoustic signals SA.sub.ABC. In the case of detection of a fault, the signal processing unit SPU2 is signaled to the switch command circuit SWC2 which halts the operation of the inverter OT2, or commands operation in a down-graded mode, depending on the seriousness of the detected fault. In this embodiment, due to the fact that each of the power modules is equipped with its own acoustic sensor, the detection of a fault at a power module is facilitated with respect to the form of the embodiment in FIG. 1.

[0055] It should be noted that the method is suitable for a spatial localization of the fault in the electronic power switching device. Thus, this functionality of spatial localization can be implanted using, for example, three acoustic sensors which are arranged respectively according to three different directional axes (X, Y, Z) defining a spatial identification. The spatial localization of the fault is deduced using the acoustic signals provided by the three sensors.

[0056] An example of a power module PM2.sub.A comprising an acoustic sensor CA.sub.A, and capable of being integrated into the inverter OT2 is shown in FIG. 3.

[0057] Power module PM2.sub.A here has a conventional, planar configuration and comprises electronic chips P1, P2, which are fixed on a DBC (Double Bond Copper) type substrate SUB. The housing CAS of the module PM2.sub.A is made by an overmolding in resin. It should be noted that, in other embodiments, the power module PM2.sub.A will comprise a housing containing chips and filled with an insulating gel.

[0058] Chips P1 and P2, visible in the cross-section view of FIG. 3, are respectively a transistor TI and its associated diode DI (cf. FIG. 1) of the switching arm. Chips P1 and P2 are brazed on an upper, copper face of the substrate SUB. Copper conductors CU and bonding wires BO provide electrical connections to the inside of power module PM2.sub.A and the outside connection terminals BC. An inner copper face of the substrate SUB is brazed on a metallic base plate SEM. The base plate SEM is in close thermal contact with a heat sink DIS. The heat sink DIS here is of the type which relies on circulation of a heat exchanger fluid CAL.

[0059] As shown in FIG. 3, the acoustic sensor CA.sub.A is placed in the center of a cavity HO arranged in the overmolded housing CAS of power module PM2.sub.A. The acoustic sensor CA.sub.A is typically a piezoelectric type ultrasonic sensor for which the resonance frequency corresponds substantially to the switching frequency of the power module, for example, on the order of 40 kHz. The shape and dimensions of the cavity HO are chosen so as to improve the reception of the acoustic wave signal by the sensor CA.sub.A. Optionally, a plate of porous material PP can be arranged in the cavity HO in order to filter noise from the acoustic wave.

[0060] The invention is not limited to the specific forms of embodiment that have been disclosed here as examples. The person skilled in the art, according to the applications of the invention, will be able to provide various modifications and variations which will fall within the scope of the annexed claims.