Device and method for protection during the discharge of a capacitor

Abstract

The invention relates to a device comprising a power electronics system comprising a capacitor (2), an electrical power source (4), a switch device for connecting or disconnecting the electrical power source. A discharge circuit (7) comprises a switch (9) and a resistor through which the capacitor discharges when the switch is closed. An electronic circuit (6) controls the closing of the switch (9) upon receipt of a discharge request. The device comprises a comparator (10) formed by a discrete electronic component, which compares the temporal evolution of a parameter (P) of the discharge circuit and a predefined reference time function (FR).The comparator comprises an output having a first state (E1) when the value (V1) of said parameter is less than the value (V2) of the reference function, and a second state (E2) when the value (V1) of said parameter is greater than the value (V2) of the reference function. The switch (9) is open when the output of the comparator is in the second state (E2). Application to an automobile powertrain and corresponding method. figure for the abstract: figure 1.

Description

Title of the invention: Device and method for protection during the discharge of a capacitor TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the field of protection of electronic components, in particular power electronic components comprising capacitors. It applies in particular to voltage converters such as inverters. It relates in particular to the discharge of capacitors which is carried out under certain conditions in a controlled manner by an electronic control device.

[0002] By capacitor is meant any capacitive electrical storage device. STATE OF THE ART

[0003] In power electronic components comprising capacitors, in particular inverters, it may be desirable in certain situations to discharge the capacitors.

[0004] The invention is described below with reference to an inverter for controlling an electric traction motor of an electric or hybrid-electric vehicle, but is also applicable to any other electrical consumer comprising capacitors.

[0005] If we consider the inverter of an electric or hybrid-electric vehicle, this is for example the case when the vehicle is stopped, that is to say when the key, the activation button, or other equivalent device of the vehicle is placed in the off position. This is also the case when a vehicle accident is detected or suspected, or when certain types of errors occur on the CAN bus (or similar) of the vehicle. Other life situations may require a discharge of the capacitors controlled by the control electronics of the inverter or the vehicle.

[0006] More generally, this discharge aims to discharge all the capacitors in the network, i.e. all the capacitors of the equipment connected to the same bus or the same circuit, for example the high voltage bus of an electric vehicle.

[0007] This discharge is carried out through a resistor, or a set of resistors, which allows the energy initially present in the capacitors to be dissipated as heat. This discharge being controlled, in this case by an electronic control device, we sometimes speak of an "active" discharge.

[0008] This discharge of the capacitors is carried out when the battery which supplies the system is disconnected from the inverter. More generally, this discharge must not be carried out only when no electrical source is likely to maintain a high voltage in the capacitors even while the discharge is carried out.

[0009] Indeed, if the voltage is maintained in the capacitors during discharge, there is a risk of causing overheating of the discharge resistors, which can lead to deterioration of these resistors, and in extreme cases damage to the environment of the resistors or even a fire.

[0010] Such maintenance of a high voltage while the active discharge is carried out can occur either because the main supply battery has remained connected as indicated above, or because at the time when the discharge is commanded the electric motor controlled by the inverter still has a high speed which induces a voltage in the phases of the motor which are connected to the inverter. The reasons why the battery could remain connected while the discharge of the capacitors is commanded include a failure of the electromagnetic relay generally used to disconnect the battery, as well as the increase in the opening time of this relay due to its wear over time. Another reason can be delays in the opening orders of the electromagnetic relay used to disconnect the battery, or a desynchronization between the opening order of this relay and the command of the discharge of the capacitors.

[0011] Some protection solutions have been developed in this context.

[0012] Document US20230132671 thus proposes to ensure, when a control device emits a signal requesting the activation of an active discharge, that the battery is actually disconnected before authorizing this discharge. For this, at least one criterion which makes it possible to guarantee that the battery is disconnected is observed, and the active discharge is only launched if this criterion is met.

[0013] This solution brings a certain reliability to the system, but it delays the active discharge even in the very majority of situations where it can be carried out without problem. Furthermore, it does not resolve the problem of a voltage induced in an inverter by the rotation of the motor that it controls.

[0014] Document US9209737 also proposes testing whether the battery is disconnected from the inverter when a discharge of the capacitors must be carried out. To do this, for a short predetermined period, the discharge of the capacitors is initiated. Using an electronic circuit comprising a voltage divider and a microcontroller, the voltage of the capacitors is evaluated before and after this short period. This solution thus makes it possible to ensure that at the time of triggering the active discharge, the battery was disconnected. However, the proposed solution is ineffective in the event of untimely reconnection of the battery during the discharge, and it implements complex, and therefore expensive, programmable components that may present software failures. Statement of the invention

[0015] The present invention thus aims to propose a solution for protecting against overheating of resistors or other components used to carry out an active discharge of capacitors, in particular in a voltage converter such as an inverter.

[0016] To this end, the invention relates to a device comprising: • a power electronics system comprising at least one capacitor, • a power source, • a switching device configured to connect or disconnect said electrical power source to the power electronics system, • a discharge circuit comprising a discharge resistor and a switch, said discharge circuit being configured so that when the switch is closed, the at least one capacitor discharges through the resistor, and an electronic circuit configured to control the closing of the switch upon receipt of a discharge request.

[0017] The device further comprises a comparator, in the form of a discrete electronic component, said comparator being configured to compare, upon receipt of said discharge request, the temporal evolution of a parameter of the discharge circuit and a predefined reference temporal function. The comparator comprises an output having a first state when the value of said parameter is less than or equal to the value of the reference function, and a second state when the value of said parameter is greater than the value of the reference function.

[0018] The device is configured to control the opening of the switch when the output of the comparator is in the second state.

[0019] The use of a comparator is a simple, reliable, and inexpensive solution to ensure that a parameter varying during discharge experiences a normal temporal variation, i.e., conforming to an expected discharge law. This indicates an active discharge of the capacitor which takes place under safe conditions for the resistances of the discharge circuit. Otherwise, the device makes it possible to immediately stop the discharge of the capacitor to protect the discharge circuit.

[0020] The parameter of the discharge circuit used may be the voltage across the at least one capacitor or a voltage representative of the voltage across the at least one capacitor.

[0021] The parameter of the discharge circuit used can alternatively be the intensity of the current in the discharge circuit.

[0022] The electronic circuit and the comparator can be carried by the same electronic card.

[0023] The power electronics system may include an inverter.

[0024] The electronic card can then be a control card for the inverter.

[0025] In the device, at any instant of the discharge, the reference function can be a function of the expected value of the parameter in the absence of a voltage source connected to the power electronics system.

[0026] The reference function can thus correspond to the expected value of the parameter to which a threshold is added.

[0027] The threshold may for example be constant or be a function of the expected value.

[0028] The electrical power source may comprise a battery.

[0029] The switching device may comprise an electromechanical relay configured to connect or disconnect said battery to the power electronics system.

[0030] The invention also relates to a powertrain of an electric or hybrid electric motor vehicle comprising a device as defined above, and an electric motor controlled by the power electronics system.

[0031] In such a traction chain the electrical power source may comprise the rotating electric motor.

[0032] The invention finally relates to a method for discharging at least one capacitor of a power electronics system comprising the steps of: • reception by an electronic circuit of a discharge request, • control of the closing of a switch of a discharge circuit, said closure causing the discharge of a capacitor through a resistor, • comparison, using a comparator in the form of a discrete electronic component, of the time evolution of a parameter of the discharge circuit varying during a discharge and a predefined reference time function; • opening of the switch when the value of said parameter is greater than the value of the reference function.

[0033] The parameter used in this method may in particular be the voltage across the terminals of the at least one capacitor, a voltage representative of the voltage across the terminals of the at least one capacitor, or the intensity of the current in the discharge circuit. BRIEF DESCRIPTION OF THE FIGURES

[0034] Other advantages, aims and particular characteristics of the present invention will emerge from the following non-limiting description of at least one particular embodiment of the devices and methods which are the subject of the present invention, with regard to the attached drawings, in which: • [Fig. 1] represents an electrical circuit comprising an example of a device corresponding to an embodiment of the invention. • [Fig.2] represents a comparison function which can be performed by a comparator within the framework of the present invention; • [Fig. 3] represents, according to a set of graphs, an active discharge sequence of a capacitor in a device according to an embodiment of the present invention when this discharge takes place without anomaly; • [Fig.4] represents, according to the same set of graphs as that of [Fig.3], an active discharge sequence in a device according to an embodiment of the present invention when a voltage source has remained connected to the inverter. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present description is given as a non-limiting example of embodiment.

[0036] [Fig.l] represents an electrical circuit comprising an example of a device corresponding to an embodiment of the invention, and to the preferred application of the present invention.

[0037] The device of [Fig.l] comprises a power electronics system, which comprises an inverter 1. The inverter 1 comprises at least one capacitor 2. For the sake of simplicity, a single capacitor has been shown in [Fig.l], but obviously the inverter generally comprises a set of several capacitors.

[0038] In the description of the present embodiment, the capacitor 2 of the inverter 1 is mentioned. However, in a power electronics system, different electrical equipment connected to the same source of electrical energy on the same bus or more generally in the same circuit, may include capacitors that may have to be discharged. The invention can thus be applied to the discharge of all the capacitors of this equipment, which can be considered schematically and collectively represented by the capacitor 2.

[0039] The capacitors 2 in an inverter 1 serve to smooth and filter voltage ripples in the inverter circuit, to store and supply energy during load variations, and to improve the quality of the AC output waveform.

[0040] In the remainder of the description, the term capacitor is used in the singular, but it is understood that it may be, as indicated above, a set of capacitors.

[0041] Similarly, capacitor 2 is schematically represented here as an element separate from the inverter, but is usually contained within the inverter housing.

[0042] In the example shown, the inverter 1 drives an electric motor 3. The electric motor 3 may be a traction motor of an electric or hybrid electric motor vehicle. By hybrid electric motor vehicle, it is meant a vehicle implementing at least two systems in series or in parallel to ensure the movement of the vehicle, these two systems operating with different energy sources, one of which is an electrical energy source. The other system may for example be a combustion engine.

[0043] The inverter is powered with direct current by an electrical energy source 4. The direct current electrical energy source 4 typically comprises a battery. Depending on the type and technology of the vehicle equipped, this battery may have a nominal voltage of between 60V and 800V, by way of non-limiting example.

[0044] An electromechanical relay 5, or any equivalent device, makes it possible to connect or disconnect the direct current power supply of the inverter 1.

[0045] In the closed state, the electromechanical relay 5 allows the flow of current, while in the open state the electromechanical relay does not allow the flow of current. The opening of the electromechanical relay 5 is controlled in various situations, for example when the power supply of the inverter is useless, or for safety reasons, for example in the event of a collision of the equipped vehicle.

[0046] The device also comprises a discharge circuit 7, intended to allow the discharge of the capacitor 2. The discharge circuit 7 connects the two poles of the capacitor 2 and comprises a resistor 8 making it possible to dissipate the energy contained in the capacitor into heat when it is useful or desirable to discharge it. Such a discharge is notably carried out, as indicated above, in particular when the vehicle is stopped ("ignition off") or when an accident of the vehicle is detected or suspected, or even when certain types of error occur. In order to allow or prevent the passage of current in the discharge circuit 7, the discharge circuit 7 comprises a switch 9. When the switch 9 is open, it cannot be crossed by a current, and the capacitor 2 is not discharged via the resistor 8.When switch 9 is closed, it allows a discharge current to flow into the discharge circuit, and capacitor 2 is then discharged via resistor 8.

[0047] Obviously, the discharge circuit 7 can be physically integrated into the inverter, but it can alternatively be located in other places in the circuit. As a non-limiting example, the discharge circuit can be installed at the converter level allowing the battery charge to be managed.

[0048] It is also conceivable that the circuit comprises several discharge circuits 7, located at several points in the circuit. In this case, the present invention can be applied to each discharge circuit.

[0049] The switch 9 is controlled, in order to be opened or closed, by an electronic circuit 6. The electronic circuit 6 may, in certain embodiments, be the same electronic card as the control card of the inverter, that is to say the card which controls the electronic switches (for example the IGBTs) of the inverter to convert the direct current into alternating current having the desired properties. The control of the electronic switches is generally controlled using a microprocessor.

[0050] It is noted that in the example shown here, the electronic circuit 6 also controls the opening or closing of the electromechanical relay 5.

[0051] As explained above, it is necessary to ensure during a discharge of the capacitor 2 using the discharge circuit 7 that no electrical source capable of maintaining the voltage of the capacitor 2 during its discharge is connected to the inverter 1 during the discharge of the capacitor 2. Thus, the electromechanical relay 5 must actually be open. This is not guaranteed by simply knowing the setpoint applied to it.

[0052] Furthermore, the motor 3 must not induce too high a voltage which could prevent or excessively slow down the drop in the capacitor voltage. The concept of electrical energy source thus also includes the electrical machine(s) whose rotation can induce a voltage in the phases of the electrical machine. This thus refers in particular to the electric motor 3, when it is rotating. It is possible to ensure a disconnection between the motor 3 and the inverter 1 to avoid maintaining the voltage in the inverter (in particular at the level of the capacitors of the inverter) by adequately controlling the electronic switches of the power modules of the inverter, for example by short-circuiting the phases of the motor, according to a mode generally designated by the English expression “active short circuit”.

[0053] Generally speaking, it is thus possible to disconnect the electrical energy source from the inverter (or other power electronics device) by controlling the opening of a switch device, which may in particular be the electromechanical relay 5 for the battery, and all of the electronic switches of the inverter for the motor 3 (or other electrical machine).

[0054] A device according to the present invention comprises a comparator 10 used for this purpose. The comparator 10 is an electronic component which makes it possible to compare two values ​​with each other, and to present a different state at the output depending on which value is greater than the other. A comparator is a discrete electronic component which is simple, inexpensive, and reliable.

[0055] A “discrete” electronic component is understood to mean an electrical component which has a single type of electrical or electronic functionality. This concept therefore includes in this document the basic elements of electronic construction as well as simple integrated circuits configured to perform a single function, such as the comparator used in the invention. A discrete electronic component is in the form of an individual component and can be soldered onto a printed circuit board.

[0056] The comparator 10 is here carried by the electronic circuit board 6.

[0057] In practice, the comparator performs the function described with reference to [Fig.2].

[0058] This function uses two inputs, namely in the invention: - the value VI of a parameter of the discharge circuit measured or determined throughout the discharge; - the value V2 of a reference time function.

[0059] Comparator 10 compares the value of the two inputs at any time, and, - if the value of the discharge circuit parameter V1 is less than or equal to the value of the reference time function V2, then the comparator has a first state El at its output (typically, it has a value equal to zero at its output); and - if the value of the discharge circuit parameter V1 is greater than the value of the reference time function V2, then the comparator presents a second state E2 at its output (typically, it presents a value equal to one at its output).

[0060] The parameter is chosen to be variable during the discharge, and to be representative of the progress of this discharge.

[0061] Thus, the parameter used can be the voltage across the capacitor (or a voltage representative of this voltage across the capacitor), or the intensity of the current in the discharge circuit.

[0062] Indeed, the voltage across the capacitor and the corresponding current decrease during the discharge of the capacitor. In particular, this decrease follows an exponential decay law.

[0063] For a given device, this exponential decay law can be determined, and serve as a basis for the formation of a reference function. The reference function is thus a time function which translates, with a certain margin where appropriate, the expected decrease for the parameter observed during a discharge of the capacitor. This margin makes it possible to take into account any inaccuracies in the measurement or determination of the parameter, and / or any dispersions in the conditions of the discharge.

[0064] Thus, with respect to the expected parameter decay law, the reference function can be shifted by a fixed threshold, or can be determined according to a function given (for example, the reference function is greater by a given percentage than the expected decay law).

[0065] [Fig. 3] represents, according to a set of graphs, a sequence of active discharge of a capacitor in a device according to an embodiment of the present invention when this discharge takes place without anomaly. The first graph G1 represents the state of the discharge request as a function of time. Thus, when a discharge is necessary, the discharge request goes to the “active request” state, that is to say that a request is issued requesting the discharge of the capacitor. In the example shown, a request to discharge the capacitor is issued at time t=0, the discharge request is then active and is kept active for the duration of the discharge.

[0066] The second graph G2 represents the temporal evolution of the value VI of the parameter P considered to follow the evolution of the discharge of the capacitor (typically the voltage at the terminals of the capacitor or the intensity of the current flowing in the discharge circuit). The graph G2 also represents the value V2 of the reference function FR based on the expected decrease of the parameter P.

[0067] In the example of [Fig.3], the parameter P decreases normally, from the instant t=0, which reflects the fact that the discharge of the capacitor is carried out without an electrical source maintaining the voltage of said capacitor. Thus, at any instant the value VI of the parameter P remains lower than the value V2 of the reference function FR.

[0068] The third graph G3 represents the state of the output of the comparator implemented in the invention, as a function of time. The output of the comparator remains in the first state El (typically “0”) to the extent that the value of the parameter P remains lower than the value of the reference function FR throughout the discharge of the capacitor.

[0069] Graph G4 represents the state of the discharge switch as a function of time. Upon receipt of the discharge request, at time t=0, the switch changes from the open state to the closed state. It can then be crossed by an electric current, so that an electric discharge current is established in the discharge circuit. The energy is dissipated by the resistance of the discharge circuit, and the capacitor gradually discharges.

[0070] Thus, in a case of discharge without anomaly, the discharge of the capacitor is carried out without the protection device developed within the framework of the invention intervening, so that this discharge is carried out normally, as it would be in the absence of the present invention.

[0071] [Fig.4] represents, according to the same set of graphs as that of [Fig.3], an active discharge sequence in a device according to an embodiment of the present invention when a voltage source has remained connected to the inverter.

[0072] In the first graph G1 of [Fig.4], just as in [Fig.3], a request to discharge the capacitor is issued, the request is therefore active from this instant t=0.

[0073] In the second graph G2 of [Fig.4], we see that the parameter P does not decrease as expected according to the reference function FR. In this case, the value VI of the parameter P remains invariant in this example, which may correspond for example to the fact that the battery supplying the inverter is always connected. Consequently, at time t=tl the value VI of the parameter becomes greater than the value V2 of the reference function FR.

[0074] As can be seen in the third graph G3 of [Fig.4], at time tl, the output of the comparator goes to the second state E2 (typically the comparator then returns a value “1” at output).

[0075] The transition to the second state E2 of the comparator then causes the switch of the discharge circuit to open, as shown in the fourth graph G4. Thus, the discharge is immediately stopped as soon as the output of the comparator transitions to the second state E2, although the discharge request is still active, which protects the resistance of the discharge circuit against overheating, and which more generally protects the device.

[0076] In other words, for the discharge switch to be closed, the following two conditions must be cumulatively met in the invention: the discharge request is active, and the output of the comparator is in the first state El.

[0077] In the case shown in [Fig.4] where the discharge is stopped because the evolution of the parameter considered in the discharge circuit does not correspond to the expected evolution, it is possible to make one or more new discharge attempts after the lapse of a time delay. This makes it possible in particular to complete the discharge in the case where the electromechanical relay for connecting or disconnecting the battery is functional but simply takes a little longer than expected to open.

[0078] The invention thus developed makes it possible to protect a power electronic device against deterioration in situations where a discharge of the capacitor is desired. This protection is obtained with a very simple and reliable discrete electronic component. This makes it possible, for example, to use only a single microprocessor for the control and protection of the inverter, while two microprocessors are commonly used to respectively ensure the control and protection of the inverter.

[0079] Nomenclature: 1: Inverter 2: Capacitor 3: Electric motor 4: Source of electrical energy 5: Electromechanical relay 6: Electronic circuit 7: Discharge circuit 8: Resistance 9: Switch 10: Comparator VI: Value of a parameter of the discharge circuit V2: Value of a reference time function El: First output state of the comparator E2: Second output state of the comparator G1: First graph (Status of the discharge request as a function of time) G2: Second graph (Time evolution of parameter P and reference function) G3: Third graph (State of the comparator output as a function of time) G4: Fourth graph (State of the discharge switch as a function of time) P: Parameter (considered to monitor the evolution of the capacitor discharge) FR: Reference function (used to compare with parameter P)

Claims

Claims

1. Device comprising: • a power electronics system comprising at least one capacitor (2), • an electrical power source (4), • a switch device configured to connect or disconnect said electrical power source to the power electronics system, • a discharge circuit (7) comprising a discharge resistor (8) and a switch (9), said discharge circuit being configured so that when the switch is closed, the at least one capacitor discharges through the resistor, and • an electronic circuit (6) configured to control the closing of the switch (9) upon receipt of a discharge request, characterized in that the device further comprises a comparator (10), in the form of a discrete electronic component, said comparator being configured to compare, upon receipt of said discharge request,the temporal evolution of a parameter (P) of the discharge circuit and a predefined reference time function (FR), the comparator comprising an output having a first state (El) when the value (VI) of said parameter is less than or equal to the value (V2) of the reference function, and a second state (E2) when the value (VI) of said parameter is greater than the value (V2) of the reference function; the device being configured to control the opening of the switch (9) when the output of the comparator is in the second state (E2).,

2. Device according to claim 1, wherein said parameter is the voltage across the at least one capacitor (2) or a voltage representative of the voltage across the at least one capacitor (2).

3. Device according to claim 1, wherein said parameter is the intensity of the current in the discharge circuit (7).

4. Device according to one of the preceding claims, in which the electronic circuit (6) and the comparator (10) are carried by the same electronic card.

5. Device according to any one of claims 1 to 4, in which the power electronics system comprises an inverter (1).

6. Device according to claims 4 and 5, in which the electronic card is a control card of the inverter (1).

7. Device according to one of the preceding claims, in which at any instant of the discharge, the reference function (FR) is a function of the expected value of the parameter (P) in the absence of a voltage source connected to the power electronics system.

8. Device according to claim 7, in which the reference function (FR) corresponds to the expected value of the parameter (P) to which a threshold is added.

9. A device according to claim 8, wherein the threshold is constant or is a function of the expected value.

10. Device according to one of the preceding claims, in which the electrical power source (4) comprises a battery.

11. Device according to claim 10, wherein the switching device comprises an electromechanical relay (5) configured to connect or disconnect said battery to the power electronics system.

12. Powertrain of an electric or hybrid electric motor vehicle comprising a device according to one of the preceding claims and an electric motor (3) controlled by the power electronics system.

13. Powertrain of an electric or hybrid electric motor vehicle according to claim 12, in which the electrical power source (4) comprises the rotating electric motor (3).

14. Method for discharging at least one capacitor (2) of a power electronics system (1) comprising the steps of: - receiving by an electronic circuit (6) a discharge request, - controlling the closing of a switch (9) of a discharge circuit (7), said closing causing the discharge of a capacitor (2) through a resistor (5), - comparing, using a comparator (10) in the form of a discrete electronic component, the temporal evolution of a parameter (P) of the discharge circuit (7) varying during a discharge and of a predefined reference time function (RTF); - opening of the switch (9) when the value of said parameter (P) is greater than the value of the reference function (FR).

15. Method according to claim 14, wherein said parameter (P) is the voltage across the at least one capacitor (2), a voltage representative of the voltage across the at least one capacitor (2), or the intensity of the current in the discharge circuit.

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