Short-circuit detection and protection for a building element with insulated gate by monitoring and controlling the gate voltage

Description

[0001] The field of the invention is that of power electronics module controls for managing the operation of power electronic components. As is known, power modules are electronic components that handle high power levels and therefore require special attention in their design and monitoring throughout their lifecycle and use.

[0002] More specifically, the invention relates to the protection of insulated gate power components such as IGBT (Insulated Gate Bipolar Transistor) insulated gate power transistors or MOSFET (Metal Oxide Semiconductor Field Effect Transistor) insulated gate power transistors.

[0003] These power components are subject to close monitoring to ensure their operational status is monitored at all times to detect any potential degradation. Generally, the proper functioning of this type of power component is verified by checking the current flowing through its two terminals: the collector and emitter for an IGBT transistor, or the drain and source for a MOS transistor. If an abnormal current or a short-circuit current flows through these two terminals, the transistor's operation, and potentially even the integrity of the component itself, may be compromised.

[0004] Currently, the verification of the current through the two terminals mentioned above is done by monitoring the voltage or current directly between the two terminals mentioned, i.e. at the conduction channel of a transistor.

[0005] Typically, this function of monitoring the integrity of the power component, directly on the current flowing through the two terminals of the three-pole connector, is performed using the following methods: Adding an isolated current sensor to one of the two terminals of the power transistor is one method. For example, a transformer positioned at the collector (or drain) allows for direct measurement of the current flowing through that terminal. However, using a sensor increases the transistor's size. Current can also be measured using a resistor connected in series (i.e., a shunt) across one of the two terminals carrying the current to be measured. However, using a resistor for this purpose results in significant energy consumption due to the resistor's dissipation. The current flowing through the power transistor's collector can also be measured using a current mirror integrated into the power component.A current mirror is an electrical circuit that replicates the current flowing through the collector, thus providing easy access to a portion of the current value. However, this type of circuit is highly specific to certain types of electronic components. This architecture therefore requires a significant investment in adaptation. It is also possible to study the collector voltage using a diode. However, this option increases the overall size of the power transistor and has the disadvantage of being blind to short-circuit detection for the duration of the power transistor's open / close transition.

[0006] Solutions are proposed in documents US 2020 / 212906 A1, US 2021 / 293874 A1, US 10 141 923 B2, US 2012 / 248864 A, CN 108 508 342 A or JP 2015 053749 A without being totally satisfactory.

[0007] The invention aims to overcome all or part of the problems mentioned above by proposing a device for detecting a short-circuit current between the collector (or drain) and the emitter (or source) of the power transistor which is simple, compact and has a relatively low production cost.

[0008] To this end, the invention relates to a power stage as defined in claim 1. The power stage comprises a power transistor controlled via a driver, the power transistor having three terminals, including a collector c, an emitter e, and a gate g connected to the driver, the power stage also includes a device for detecting a short-circuit current DC between the collector C and the emitter E, the detection device including a voltage sensor capable of detecting a voltage Vge at the level of the grid gof the power transistor outside a predefined voltage range.

[0009] According to one aspect of the invention, the detection device includes an energy storage device configured to deliver an additional voltage to the grid g if the equivalent capacity of the grid Cge is unloaded.

[0010] According to one aspect of the invention, the energy storage device is an inductor positioned between the driver and the grid g of the power transistor.

[0011] According to one aspect of the invention, the power stage includes a voltage reducer capable of reducing the voltage Vge à the grid g up to a threshold voltage.

[0012] According to one aspect of the invention, the power stage includes a recorder capable of recording a malfunction of the power transistor.

[0013] The invention also relates to a method for detecting a short-circuit current cc between a collector c and an emitter e of a power transistor comprising a gate g, the power transistor being included in the power stage according to claim 1, the method comprising the following steps: Voltage detection Vge à the grid g of the power transistor outside a predefined voltage range, Gate voltage reduction g of the power transistor to a predefined reduction voltage, Opening of the power transistor.

[0014] The invention has the advantage of allowing the analysis of the current between the collector and emitter of a power transistor by monitoring the gate voltage of the power transistor through a compact and simply designed detection device.

[0015] The invention will be better understood and other advantages will become apparent upon reading the detailed description of an embodiment given by way of example, a description illustrated by the accompanying drawing in which:

[0016] [ Fig.1 ] there figure 1 represents a power stage comprising a power transistor and a short-circuit current detection device according to the invention;

[0017] [ Fig.2 ] there figure 2 represents a method for detecting a short-circuit current between a drain and a source of a power transistor according to the invention.

[0018] [ Fig.3 ] there figure 3 represents the method of detecting a short-circuit current by means of a timing diagram.

[0019] For the sake of clarity, the same elements will carry the same markers in the different figures.

[0020] There figure 1 represents a power stage 2 comprising a power transistor 4 controlled via a driver 6. The power transistor 4 has three terminals: a collector c, an emitter e, and a gate g connected to the driver 6. The power transistor 4 is an insulated-gate bipolar transistor (IGBT). Insulated Gate Bipolar Transistor Alternatively, power transistor 4 is a field-effect transistor (in English, metal oxide semiconductor Field-effect transistor Or MOSFET ) and therefore includes a drain, a source and a gate connected to the driver 6. Therefore, for a field-effect transistor, the drain can be considered as the collector c, the source can be considered as the emitter e.

[0021] In this context, the invention consists of detecting and protecting the insulated-gate power component, namely the power transistor 4, when it is subjected to an abnormal current. This abnormal current, called a "short-circuit current," occurs when a low impedance, called a "short circuit," is present across the terminals of an electrical source and has a current exceeding a predefined current for the "normal" operation of the power transistor 4. This short-circuit current can be of two types: A type 1 short circuit is a short circuit applied during the conduction of the power transistor 4, that is, when the abnormal current is superimposed on a normal current. Therefore, during a type 1 short circuit, a voltage measured between the gate g and the emitter e of the power transistor 4, called the gate voltage Vge, The capacitance of power transistor 4 increases rapidly and in the same proportion as the increase in short-circuit current. A type 2 short circuit is a short circuit established before power transistor 4 turns on. Therefore, when power transistor 4 turns on, the abnormal current, or short-circuit current, immediately flows through power transistor 4. During a type 2 short circuit, the equivalent capacitance Cge view of the grid g the power transistor 4 remains constant and of low value compared to an equivalent capacitance measured at the gate of the power transistor 4 during so-called "normal" operation.

[0022] In other words, both type 1 and type 2 short circuits are related to a circuit external to the power transistor 4, forming a closed electrical loop and including an electrical load, connected to the power transistor 4 via the collector c and the emitter e. Thus, a type 1 short circuit is a short circuit appearing in this external circuit while the power transistor 4 is already conducting, whereas a type 2 short circuit is a short circuit already present in the external circuit before the conduction of the power transistor 4 is established.

[0023] Thus, the power stage 2 includes a short-circuit current detection device 8 cc between the collector c and the emitter e. The detection device 8 includes a voltage sensor 82 capable of detecting and measuring the voltage between the grid g and the transmitter e named Vge at the level of the grid g of power transistor 4. More specifically, the voltage sensor 82 is configured to compare this gate voltage measurement Vge à a defined voltage range, and report if the grid voltage measurement Vge est outside the predefined voltage range. Indeed, the presence of a short circuit in power transistor 4, and particularly between collector c and emitter e, can result in a significant increase in the current intensity between these two terminals of power transistor 4 and induces the degradation of power stage 2. Now, this overvoltage induced by the increase in current flowing through power transistor 4 is expressed by the following formula: ΔVg = Δlds Gm

[0024] Where Δ Vg represents the voltage variation Vge à the grid, Δ Ids represents the variation of the current between the collector c and the emitter e and Gm represents the transconductance of power transistor 4. As an indicative example, the transconductance Gm is equal to 300 Siemens, for example.

[0025] Therefore, it is possible to observe a proportional relationship, for the same transconductance of the power transistor 4, between the voltage Vge à the grid and the current between the collector c and the emitter e. More precisely, during a significant increase in the current intensity between the collector c and the emitter e, synonymous with a short-circuit current cc, tension Vge à The grid also experiences an increase in voltage measurement taken by means of a voltage sensor 82. The voltage sensor 82, which is directly connected to the grid g, therefore allows us to measure the voltage Vge à the grid g so as to be able to detect a short-circuit current cc between the collector c and the emitter e of the power transistor 4.

[0026] As an example, the predefined voltage range in which the voltage Vge The gate voltage range is between 0 volts and +20 volts. Alternatively, this predefined voltage range is between 2 volts and 20 volts when using an insulated-gate MOSFET. In another alternative, when using an insulated-gate IGBT power transistor, the predefined voltage range is between 5 volts and 20 volts.

[0027] In addition, the short circuit may also be present before the power transistor 4 turns on in the case of a type 2 short circuit.

[0028] When the power transistor turns on, an abnormal current, or in other words a short-circuit current, immediately flows through the power transistor. And, the measurable gate voltage does not increase as rapidly and is not as significant as for a type 1 short circuit. Therefore, simply measuring the gate voltage Vge is no longer sufficient since this measurement can be taken late. However, during a short circuit, the equivalent capacitance seen from the grid g The capacitance of the power transistor remains constant and low, approximately ten times lower than when a "normal" current flows through the power transistor. Conversely, in normal operation, that is, when the power transistor is saturated, the capacitance value, as seen from the gate, g, is increased, notably due to the Miller effect, when the voltage measured at the collector cis low. This equivalent capacity measured at the grid g is of high value, and generally greater than one microfarad, at switching instants. And, in a short circuit, the switching instant does not affect the value of the equivalent gate capacitance. The value of the equivalent gate capacitance remains constant and low, that is, less than one hundred nanofarads. This evolution can be understood as the evolution of the charges at the gate.

[0029] Therefore, the variation of the voltage Δ Vg at the level of the grid g is not significant enough to indicate a short-circuit current cc present during this transition phase. In order to highlight this type of short circuit, the detection device 8 includes a capacitance measuring sensor 83 capable of detecting and measuring an equivalent capacitance value Cge of the grid gat the level of the grid g of power transistor 4. More specifically, the capacitance sensor 83 is configured to compare this equivalent gate capacitance measurement Cge to a predefined capacity value, and signal if the equivalent grid capacity measurement Cge is less than the predefined capacity value. In other words, when the equivalent capacity of the grid Cge, between the grid g and the conduction channel is discharged; the capacitance measuring sensor 83 is capable of detecting this equivalent capacitance value. Cge, measure this equivalent capacity value Cge, compare this equivalent capacity value Cge with the normally measurable predefined capacitance value and signal the malfunction. Indeed, in nominal operation of the power transistor 4, that is, at switching instants, the equivalent capacitance of the gate Cge is transiently high, for example greater than 1 µF. Conversely, when the conduction of power transistor 4 is established, the equivalent capacitance of the gate Cge is of a low value, for example, approximately 100 nF. Therefore, when measuring the equivalent capacitance Cge at the level of the grid g If the power transistor's resistance is less than this low equivalent capacitance value for conducting operation of power transistor 4, a type 2 short circuit is detected. As an example, the preset capacitance value could be 100 nF.

[0030] As an indicative example, the capacitance measurement sensor 83 can be a Wheatstone bridge.

[0031] Alternatively, it may also be possible to measure this equivalent grid capacity value. Cge according to the following formula: C ge = Q ge V ge Or Q ge represents the grid load and V ge represents the voltage between the grid and the emitter. The charge Qge can be defined by integrating, with respect to time, the current flowing through the grid g. Furthermore, the gate voltage value Vge is already known via the voltage sensor 82. Thus, the capacitance measuring sensor 83 can also be a device for measuring the gate current intensity. g configured to determine, according to the previous formula, the equivalent grid capacity value Cge.

[0032] The detection device 8 also includes an energy storage device 84 configured to deliver an additional voltage to the grid g when the equivalent capacitance value measured at the grid Cge The capacitance measurement sensor reading 83 is less than the predefined capacitance value at the grid. g.In other words, when the capacitance measurement sensor 83 detects that the equivalent capacitance value measured at the grid Cge is less than the predefined capacity value for the grid g, The capacitance measuring sensor 83 drives the energy storage device 84 so that the energy storage device 84 releases an additional voltage to the grid g. However, the release of this additional tension at the grid g This allows for the generation of an overvoltage at the grid level g. From then on, the tension Vge between the grid g and the emitter e increases proportionally to the additional voltage delivered by the storage device 84 until it exceeds the predefined voltage range. At this point, the voltage sensor 82 detects that the voltage Vge at the level of the grid gThe voltage of power transistor 4 is outside the predefined range, thus signaling a short circuit in power transistor 4, allowing it to be opened before its components are damaged. The energy storage device 84 is positioned between the driver 6 and the gate. g of power transistor 4 so as to be able to deliver the additional voltage to the gate g. As an indicative example, this additional voltage is the voltage required for the sum of the voltage measured at the grid g and the additional voltage is greater than the maximum voltage value of the predefined voltage range.

[0033] As an indicative example, the energy storage device 84 is an inductor, with an inductance value of approximately 100 nH, positioned between the driver 6 and the grid gof the power transistor 4. The inductor has the advantage of being a passive component allowing to respond directly to a square wave signal supplied by the driver 6 and to allow the storage and release of enough energy to induce an overvoltage, when the equivalent capacitance seen from the gate of the power transistor 4 is low and discharged.

[0034] Alternatively, the storage device 84 is an active generator that generates an additional voltage to the grid and is controlled by information from the driver 6.

[0035] In the following description, the storage device 84 is considered to be an inductor 84. Thus, as mentioned previously, the inductor 84 is positioned in series between the driver 6 and the gate g so as to create a resonant RLC circuit between driver 6, via a resistor within driver 6, inductor 84 and the gate capacitance gand therefore determine the damping of the system. The following relationship highlights an underdamping of the RLC resonant circuit, allowing inductor 84 to inject the additional voltage into the gate g according to the condition: Rg 2 Cge _ cc L < 1

[0036] Or Rg represents the resistance of driver 6 in the RLC resonant circuit, Cge_cc represents the equivalent capacity of the grid g when power transistor 4 experiences a short circuit and L represents the inductance value of inductance 84.

[0037] Therefore, inductance 84 has the advantage of allowing an additional voltage input at the grid level. g of the power transistor so as to highlight the fact that the voltage value Vge of the grid gis not included in the voltage range and therefore the presence of a DC short-circuit current during this transition phase of power transistor 4.

[0038] Furthermore, power stage 2 includes a voltage reducer 86 capable of reducing the voltage Vge à the grid g up to a threshold voltage, when a short-circuit current DC is detected between the collector C and the emitter E via the voltage sensor 82. More precisely, when the voltage Vge à the grid g If the voltage detected by the voltage sensor 82 is not within the predefined voltage range, the voltage reducer 86 reduces this voltage. Vge à the grid gin order to be within the voltage range. For example, the threshold voltage can be less than 20 volts and / or greater than the voltage at which the power transistor turns on, denoted Vgsth, and is preferably 10 volts. The voltage reducer 86 has the advantage of being able to reduce the short-circuit current according to the relation Δ Vg = Δ Ids Gm , before opening power transistor 4.

[0039] The power stage 2 also includes a recorder 88 capable of recording the short circuit of the power transistor 4. As an example, the recorder 88 is a capacitor which discharges as a result of the short circuit in order to highlight a malfunction of the power transistor 4.

[0040] A detection method 100 is also proposed, represented in figure 2 , of a short-circuit current cc between a collector c and an emitter e of a power transistor 4, comprising a gate g. The 100 detection process includes the following steps: Voltage detection (step 120) Vge at the grid g of the power transistor 4 outside the predefined voltage range. As an example, the predefined voltage range in which the voltage Vge of the grid g is included in a voltage range between 0 Volts and +20 Volts. The 120 voltage detection Vge is performed via the voltage sensor 82. Voltage reduction (step 130) to the grid g of power transistor 4 to a predefined voltage. As a preferred example, the predefined reduction voltage can be 10 Volts. Turn-on (step 140) of power transistor 4.

[0041] Voltage reduction (step 130) at the gridg The opening of power transistor 4 can induce an automatic opening (step 140) of power transistor 4. Alternatively, this opening (step 140) can be controlled. However, the control of the opening of power transistor 4 must be prompt.

[0042] The detection process 100 may also include a restoration step (step 110) of additional energy upstream of the detection step 120 if the equivalent capacity of the grid Cge is discharged and less than the predefined capacity, i.e. for example a capacity of about 100 nF.

[0043] Step 110 of the energy stored at the grid is released. g allows the additional energy to be supplied, highlighting a short circuit when switching power transistor 4.

[0044] The detection process 100 may also include, following the detection step 120, a fault recording step (step 128) of the power transistor 4.

[0045] The detection process 100 can also be interpreted according to the timing diagram shown in figure 3 Indeed, a short-circuit current at power transistor 4 can be interpreted as a sharp increase in the current Ip flowing through power transistor 4. However, in the case of a type 1 short circuit, this increase in current is accompanied by an increase in voltage. Vge à the grid g of power transistor 4. Therefore, detection 120 occurs when the voltage Vge is greater than 20 Volts, for example. Then, in order to avoid damaging the power transistor 4, the voltage is reduced Vge (step 130) to the grid gof power transistor 4 at the predefined voltage, such as 10 Volts, and the opening 140 of power transistor 4. In the case of a type 2 short circuit, the output 110 provides sufficient energy to induce the overvoltage, if the equivalent capacitance of the gate Cge If the discharged voltage is below the predefined capacitance (for example, approximately 100 nF), the gate overvoltage detection (120) is triggered. Furthermore, the fault recording step (128) allows the fault to be stored in real time as soon as the power transistor malfunction (4) is detected (120).

[0046] The invention therefore proposes to integrate a voltage sensor at the gate of the power transistor in order to detect an abnormal voltage, that is to say a voltage outside a predefined voltage range for the gate gand to integrate a means of storing and releasing sufficient energy to induce the detection of an abnormal voltage, when the capacity Cge The equivalent view of the gate of the power transistor 4 is discharged in the case of a type 2 short circuit. The invention therefore presents the ability to detect a short circuit in the power transistor from the measurement of the voltage at the gate of the power transistor.

Claims

1. Power stage (2) comprising a power transistor (4) controlled via a driver (6), the power transistor (4) comprising three terminals including a collector c, an emitter e and a gate g linked to the driver (6), the power stage (2) comprising a detection device (8) for detecting a short-circuit current cc between the collector c and the emitter e, the detection device (8) comprising a voltage sensor (82) capable of detecting a voltage Vge at the gate g of the power transistor (4) outside of a predefined voltage range, the detection device (8) comprising a capacitance measurement sensor (83) configured to measure an equivalent capacitance value Cge at the gate g of the power transistor (4) and compare the gate equivalent capacitance value Cge to a predefined capacitance value, the power stage (2) being characterized in that the detection device (8) comprises an energy storage device (84) configured to deliver an additional voltage to the gate g if the capacitance measurement sensor (83) detects that the value of the gate equivalent capacitance Cge is lower than the predefined capacitance value.

2. Power stage (2) according to claim 1, wherein the energy storage device (84) is an inductor positioned between the driver (6) and the gate g of the power transistor (4).

3. Power stage (2) according to any one of claims 1 to 2, comprising a voltage reducer (86) capable of reducing the voltage Vge at the gate g to a threshold voltage.

4. Power stage (2) according to any one of claims 1 to 3, comprising a recorder (88) capable of recording an operating fault in the power transistor (4).

5. Detection method (100) for detecting a short-circuit current cc between a collector c and an emitter e of a power transistor (4) comprising a gate g, the power transistor (4) being included in the power stage (2) according to claim 1, the method (100) comprising the following steps: - detecting (120) a voltage Vge at the gate g of the power transistor (4) outside of a predefined voltage range, - reducing (130) the voltage at the gate g of the power transistor (4) to a predefined reduction voltage, - switching off (140) the power transistor (4).