METHOD FOR UNLOADING A STACK OF FUEL CELLS TO SUPPLY ELECTRIC TRACTION MACHINE OF A MOTOR VEHICLE

Description

Technical field of the invention

[0001] The present invention relates to the field of hydrogen fuel cells.

[0002] The invention relates more particularly to a method of discharging a fuel cell following an interruption, voluntary or emergency, of the hydrogen supply to the fuel cell. Technical background

[0003] Hydrogen fuel cells are used as a source of electrical power in many applications, particularly in the field of transportation.

[0004] Some so-called "electric" motor vehicles are equipped with a fuel cell used in combination with a high-voltage battery to power, in particular, the electric drive system of the motor vehicle comprising at least one electric traction machine.

[0005] More specifically, fuel cell motor vehicles are powered by electricity resulting from an electrochemical reaction between hydrogen, which is for example stored in a tank, and oxygen from the air.

[0006] In such an architecture, the high-voltage battery constitutes the primary power source, and the hydrogen fuel cell serves as the secondary or auxiliary power source. The fuel cell is therefore part of a so-called "range extender" system, which is designed and engineered to extend the range of the high-voltage battery.

[0007] This architecture constitutes a multi-energy platform and allows for the integration of a compact high-voltage battery. Indeed, the high-voltage battery is sized to ensure normal vehicle use, while the auxiliary energy source is configured to handle exceptional vehicle uses, such as during very long journeys.

[0008] This architecture, called multi-energy, is advantageous for utility-type motor vehicles with at least partial electric propulsion because there is a compromise between vehicle range, transportable mass and available volume.

[0009] There are also motor vehicles whose architecture consists of a high-power hydrogen fuel cell designed to directly power the electric motor vehicle's drivetrain.

[0010] In general, the interruption of the fuel supply to a hydrogen fuel cell, i.e. hydrogen, can be caused by the stopping of the vehicle's ignition, this is referred to as a voluntary or classic stop, or following any malfunction of the vehicle or during an accident, and this is referred to as an emergency stop.

[0011] Following the interruption of the fuel cell supply, constituting a voluntary or emergency shutdown, the hydrogen flow rate decreases and then reaches a zero value, the volume of residual hydrogen contained inside the fuel cell being then very low.

[0012] However, residual hydrogen capable of producing residual energy from the fuel cell is present within the volume of the fuel cell stack, which is formed by a stack of electrochemical cells. This residual energy must be completely consumed to reach zero voltage in the fuel cell and thus ensure the safety of the fuel cell system, and the vehicle in general.

[0013] In the state of the art, there are systems designed to discharge the residual energy of the fuel cell until a zero value of the fuel cell voltage is obtained.

[0014] However, the function of discharging residual energy within the fuel cell is generally performed by one or more mechanical or electronic switches associated with one or more dissipative elements such as resistors or varistors. These additional components dedicated to discharge are typically electrically connected in parallel with the fuel cell.

[0015] For example, US patent 5105142 describes a fuel cell discharge system using multiple switches and resistors electrically connected in parallel. The successive parallel connection of resistors allows the fuel cell's load impedance to be controlled, thus providing a means of controlling the fuel cell discharge based on the mass and pressure of residual hydrogen. The drawback of this solution is the size required by the multiple resistors and electromechanical relays. Furthermore, this principle is primarily suited to stationary applications.

[0016] Each of the documents US2019379070 and WO2020020524 proposes a discharge system composed of electromechanical relays associated with a resistor and electrically connected in parallel with the fuel cell.

[0017] However, these different fuel cell discharge systems have certain drawbacks. First, the components responsible for the discharge function—that is, the combination of switches and dissipative elements—are dedicated solely to this purpose. Any failure of these components can cause a complete failure of the fuel cell system due to their parallel electrical connection to the fuel cell, resulting in high repair costs.

[0018] The invention proposes in particular to remedy the aforementioned drawbacks and to offer a method of discharging residual energy inside the fuel cell ensured by a reduced number of components and a reduced size. Summary of the invention

[0019] The invention proposes a method for discharging the electrical circuit of a motor vehicle comprising at least one electric traction machine of the vehicle equipped: of an electrical supply network comprising: -- a high voltage battery, -- a range extender system comprising a hydrogen fuel cell which is associated with a DC / DC voltage converter itself comprising a filter inductance through which a current flows from the filter inductance, a primary filtering capacitor which is at the voltage of the hydrogen fuel cell, and a secondary filtering capacitor which is at the output voltage of the DC / DC voltage converter, of a high voltage consumption network, supplied by the electrical supply network, comprising at least one electric traction machine of the motor vehicle associated with an inverter and ancillary equipment, and of a control module.

[0020] The discharge process comprises the following successive steps: stopping the motor vehicle, electrically disconnecting the high-voltage battery from the high-voltage network, interrupting the hydrogen supply to the hydrogen fuel cell, and discharging the energy from the electrical circuit into the stator winding of the electric traction machine.

[0021] The discharge process is characterized in that the energy discharge step of the electrical circuit is carried out by driving the DC / DC voltage converter by means of the control module.

[0022] According to other features of the invention: The vehicle shutdown stage corresponds to a voluntary stop of the motor vehicle. The electrical circuit energy discharge stage comprises the following successive sub-stages: -- discharge of the energy produced by the consumption of residual hydrogen contained in the hydrogen fuel cell by the DC / DC voltage converter through control of a discharge current by the control module up to a predetermined voltage threshold value of the hydrogen fuel cell, -- electrical disconnection of the range extender system from the high-voltage consumption network, -- discharge of energy from the high-voltage consumption network's capacitors into the stator of the electric traction machine by the inverter. The electrical circuit energy discharge stage comprises a sub-stage, which is carried out in parallel with the two preceding sub-stages.Discharge of energy from the primary and secondary filtering capacitors of the DC / DC voltage converter by controlling the filter inductor current by the control module; the vehicle shutdown step corresponds to an emergency stop of the motor vehicle, prior to the electrical circuit energy discharge step; the electrical circuit discharge process includes an electrical disconnection step of the range extender system from the high-voltage network, carried out simultaneously with the electrical disconnection step of the high-voltage battery from the high-voltage consumption network; the electrical circuit energy discharge step includes the following substeps: -- discharge of energy from the high-voltage consumption network capacitors into the stator of the electric traction machine by the inverter, -- the electrical circuit energy discharge step includes a substep,which is carried out in parallel with the previous sub-step,of discharge of residual hydrogen contained in the hydrogen fuel cell and of discharge of energy from the primary and secondary filtering capacitors of the DC / DC voltage converter by driving the filtering inductor current by the control module; the process of driving the filtering inductor current by the control module is configured to achieve a low value of the hydrogen fuel cell voltage by means of a succession of n self-discharge cycles of the primary and secondary filtering capacitors of the range extender system; each self-discharge cycle of the primary and secondary filtering capacitors of the range extender system includes: -- a step of driving the DC / DC voltage converter of the range extender system by the DC / DC voltage converter control module to obtain a positive value of the filtering inductor current,The positive value of the filter inductor current supplied by the primary filter capacitor to the secondary filter capacitor causes: --- a decrease in the voltage value of the hydrogen fuel cell, and --- an increase in the output voltage value of the DC / DC voltage converter; and -- a driving step of the DC / DC voltage converter of the range extender system by the driving module to obtain a negative value of the filter inductor current, the negative value of the filter inductor current supplied by the secondary filter capacitor to the primary filter capacitor causes: --- a decrease in the output voltage value of the DC / DC voltage converter,and --- the growth in the voltage value of the primary filter capacitor; and the process of driving the filter inductance current by the control module is configured so that the voltage value of the hydrogen fuel cell at the end of an n+1 self-discharge cycle is less than the voltage value of the hydrogen fuel cell at the end of an n self-discharge cycle. Brief description of the figures

[0023] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the attached drawings in which: [ Fig.1 ] - there figure 1 is an electrical diagram of the architecture of an electric motor vehicle comprising a range extender system according to the invention, in normal operation of the fuel cell; [ Fig. 2 ] - there figure 2is an electrical diagram of the architecture of an electric motor vehicle according to the figure 1 , in residual energy discharge mode of the fuel cell following a voluntary shutdown of the fuel cell power supply; [ Fig.3 ] - there figure 3 is a diagram of the steps in the electrical circuit discharge process of an electric motor vehicle following a conventional shutdown of the fuel cell power supply; Fig. 4 ] - there figure 4 is a detailed electrical diagram of the range extender system according to the figure 2 , in residual energy discharge mode of the fuel cell following an emergency shutdown of the fuel cell power supply; [ Fig. 5 ] - there figure 5 is a diagram of the steps in the electrical circuit discharge process of an electric motor vehicle following an emergency shutdown of the fuel cell power supply; Fig. 6 ] - there figure 6is a graphical representation of the self-discharge process of the primary and secondary filtering capacities of the range extender system following an emergency shutdown of the fuel cell supply. Detailed description of the invention

[0024] In the description that follows, identical, similar or analogous elements will be designated by the same alphanumeric references.

[0025] There figure 1 is a diagram of the electrical circuit 10 of the architecture of an electric motor vehicle comprising a high voltage network 12 called consumption which is electrically supplied by an electrical supply network 22.

[0026] The power supply network 22 consists of a main power supply and an auxiliary power supply which are electrically connected to each other in parallel.

[0027] The power supply network 22 consists of a high-voltage battery 24, which serves as the primary power source, and a range extender system 28, which serves as the auxiliary power source. The range extender system 28 comprises a hydrogen fuel cell 30 coupled to a DC / DC voltage converter 32 of the range extender system 28, arranged at the output of the hydrogen fuel cell 30.

[0028] The DC / DC voltage converter 32 of the range extender system 28 constitutes a voltage booster enabling the value of the voltage supplied by the hydrogen fuel cell 30 to be adapted to the high voltage consumption network 12 of the electric motor vehicle.

[0029] The high-voltage battery 24 is the main source of electrical energy and supplies most of the high-voltage consumption network 12. Indeed, the high-voltage battery 24 is sized to ensure the normal use of the "electric" motor vehicle punctuated by regular phases of recharging the high-voltage battery 24.

[0030] The high-voltage battery 24 is equipped with at least one main switch 26 of the high-voltage battery 24 intended to electrically connect or disconnect the high-voltage battery 24 from the high-voltage consumption network 12 between a connection or disconnection position of the main switch 26 of the high-voltage battery 24. The hydrogen fuel cell 30 associated with the DC / DC voltage converter 32 of the range extender system 28 constitutes an additional energy source implemented in the electrical supply network 22 initially composed of the high-voltage battery 24.

[0031] The hydrogen fuel cell 30, which is at a voltage value of 40, provides a current of 42 from the hydrogen fuel cell 30.

[0032] The range extender system 28 commonly called in English "Range extender" is designed to extend the operating time of the high voltage battery 24.

[0033] The high-voltage consumption network 12 supplies an electric traction machine 16 belonging to the vehicle's traction chain as well as electricity-consuming elements such as ancillary equipment 20.

[0034] Conventionally, the electric traction machine 16 comprises a stator associated with a stator winding of the electric traction machine 16.

[0035] The electric vehicle's power supply network 22 is electrically connected to the high-voltage consumption network 12 by means of a distribution box 21.

[0036] An inverter 14 is electrically arranged upstream of the traction electric machine 16, ensuring a voltage regulator role to provide the voltage required to power the traction electric machine 16.

[0037] The auxiliary equipment 20 is electrically connected to the distribution box 21 via a voltage converter 18 from the high-voltage consumption network 12 intended to reduce the voltage and thus supply the auxiliary equipment 20 with low voltage.

[0038] The distribution box 21 redistributes the high voltage 22 on the one hand to the inverter 14 to supply the traction electric machine 16 and on the other hand to the voltage converter 18 of the high voltage consumption network 12 to supply the ancillary equipment 20. Other elements not shown can also be connected to the distribution box 21.

[0039] The architecture presented at the figure 1 relates to a motor vehicle whose high-voltage power supply 12 is mainly powered by the high-voltage battery 24 during normal use of the vehicle.

[0040] When the main switch 26 of the high-voltage battery 24 is in the connected position, the high-voltage battery 24 supplies the vehicle's electrical power supply 22, including the drivetrain. When the high-voltage battery 24 is completely discharged, the auxiliary power source, consisting of the hydrogen fuel cell 30, is started and produces the electrical power necessary to propel the vehicle, under normal operating conditions of the hydrogen fuel cell 30.

[0041] The electrical diagrams of a vehicle's architecture figures 2 And 4 detail the electrical diagram of the range extender system 28.

[0042] The 28-volt battery extender system provides a second power source which includes: a pre-charge circuit 34 comprising a pre-charge resistor 36 associated with a pre-charge switch 38 intended to ensure the connection / disconnection of the range extender system 28 to the power supply network 22, and two main switches including a first main switch 44 and a second main switch 46, and a control module 48 of the DC / DC voltage converter 32 which is configured in particular to control the process of discharging the residual energy produced by the hydrogen fuel cell 30 following an interruption of the hydrogen supply to the hydrogen fuel cell 30.

[0043] The control module 48 receives information from the hydrogen fuel cell 30 defining the state 50 of the hydrogen fuel cell 30, such as, for example, the amount of residual hydrogen contained in the hydrogen fuel cell 30 and the output voltage 41 of the DC / DC voltage converter 32, which is also the voltage of the high-voltage battery 24. The control module 48 is configured to send the following information based on the state 50 of the hydrogen fuel cell 30: a setpoint value 52 of current 42 from the hydrogen fuel cell 30 to the DC / DC converter 32, and a setpoint value 54 of discharge current 43 to the inverter 14.

[0044] The DC / DC voltage converter 32 as detailed in the figure 4 consists of a low voltage input stage 66 and a high voltage output stage 64.

[0045] The low voltage input stage 66 includes a primary filtering capacitor 56 which is at the voltage 40 of the hydrogen fuel cell 30 when it delivers current, and a filtering inductor 60 through which a current 61 flows from the filtering inductor 60.

[0046] The high voltage output stage 64 includes a secondary filtering capacitor 58 which is at the output voltage 41 of the DC / DC voltage converter 32.

[0047] Two controllable semiconductors, for example transistors 62, are arranged between the low voltage 66 and high voltage 64 stages and form part of the driver module 48 of the DC / DC voltage converter 32. These components constitute a safety system required to isolate all high voltage power sources.

[0048] The entire electrical circuit 10 of the architecture of a motor vehicle with at least partial electric traction includes capacitors such as those present in the DC / DC voltage converter 32, the inverter 14, and other auxiliary electrical components connected electrically in parallel. Each of these various capacitors has a capacitance that can be relatively large, the capacitance being proportional to the amount of electrical charge that can be stored in the capacitor for a given voltage.

[0049] The primary filter capacitor 56 is designed to suppress noise beyond the DC / DC voltage converter 32 of the range extender system 28. The secondary filter capacitor 58 is designed not to prevent the generation of overvoltages and therefore noise. The precharge circuit 34 is therefore necessary because when the filter capacitors 56 and 58 are discharged, it is dangerous to connect them to the high-voltage battery 24. The precharge resistor 36 and the precharge switch 38 are necessary to create a transient precharge state that limits the current transferred between the high-voltage battery 24 and the capacitors.

[0050] Initially, the second main switch 46 and the pre-charge switch 38 are closed to electrically connect in parallel the capacitors and the high-voltage battery 24 charged to different voltages, by means of the pre-charge resistor 36 thus limiting the current.

[0051] Then, in a second step, when the output voltage 41 of the DC / DC converter 32 equals the voltage of the high-voltage battery 24, the pre-charge switch is opened and the main switch 44 is closed to electrically connect the two main switches 44 and 46 directly in parallel, and the voltages on both sides are then balanced following the pre-charge transient state. The high-voltage battery 24 also includes main switches and a pre-charge circuit (not shown) similar to the main switches 44 and 46 and the pre-charge circuit 34 of the range extender system 28, designed to ensure the connection / disconnection of the high-voltage battery 24 to the power supply network 22.

[0052] THE figures 2 And 4present the electrical diagram of the architecture of a vehicle following the interruption of the hydrogen supply to the hydrogen fuel cell 30 following an E0 stage of stopping the motor vehicle.

[0053] The interruption of the power supply to the hydrogen fuel cell 30 illustrated in the figure 2 is caused by the stopping of the contact of the electric motor vehicle, and this is then referred to as a voluntary stop or classic stop.

[0054] The interruption of the power supply to the hydrogen fuel cell 30 illustrated in the figure 4is caused, for example, by a vehicle malfunction or following an accident, and this is then referred to as an emergency stop. In both cases, following the interruption of the hydrogen supply to the hydrogen fuel cell 30, the hydrogen flow rate decreases and then reaches zero. However, a very small volume of residual hydrogen remains inside the hydrogen fuel cell 30. The residual energy produced by the hydrogen fuel cell 30 using this residual volume of hydrogen must be completely consumed in order to reach a zero value for the voltage 40 of the hydrogen fuel cell 30. The figure 3 is a diagram of the steps in the electrical circuit discharge process 10 during a voluntary stop according to the invention shown in the figure 2 The successive stages of the discharge process are as follows: E1: electrical disconnection of the high-voltage battery 24 from the high-voltage consumption network 12 by opening the main switches 26 of the high-voltage battery 24, E2: interruption of the hydrogen supply to the hydrogen fuel cell 30 by closing a hydrogen supply valve, E3: discharge of energy from the electrical circuit 10 into the stator of the electric traction machine 16.

[0055] Step E3 above includes the following sub-steps: -- E4: Discharge of residual energy from the hydrogen fuel cell 30 by the DC / DC voltage converter 32, controlled by the DC / DC voltage converter control module 48, which drives the discharge current 43 down to a predetermined threshold value of the hydrogen fuel cell voltage 40, -- E5: Electrical disconnection of the range extender system 28 from the high-voltage power grid 12 by opening the first and second main switches 44, 46 of the range extender system 28, -- E6: Discharge of the energy stored in the high-voltage power grid 12 into the stator of the traction electric machine 16 via the inverter 14, -- E7: A sub-stage, which is carried out in parallel with sub-stages E5 to E6 above,discharge of residual energy from the hydrogen fuel cell 30 and energy stored in the primary filtering capacitors 56 and secondary filtering capacitors 58 of the DC / DC voltage converter 32 controlled by the control module 48 of the DC / DC voltage converter 32 which drives the current 61 of the filtering inductor 60 according to the self-discharge procedure illustrated in the , figure 6 .

[0056] There figure 5 is a diagram of the steps in the electrical circuit discharge process 10 during a emergency stop according to the invention shown in the figure 4 The successive stages of the discharge process are as follows: E1 and E1': These two steps are carried out simultaneously. E1 involves the electrical disconnection of the high-voltage battery 24 from the high-voltage power grid 12 by opening the main switches 26 of the high-voltage battery 24, and E1' involves the electrical disconnection of the range extender system 28 from the high-voltage power grid 12 by opening the first and second switches 44, 46 of the range extender system 28. E2: The hydrogen supply to the hydrogen fuel cell 30 is interrupted by closing a hydrogen supply valve. E3: The energy from the electrical circuit 10 is discharged. Step E3 comprises the following substeps: -- E4': The energy stored in the capacitors of the high-voltage power grid 12 is discharged by the inverter 14 into the stator of the traction electric machine 16. -- E5': A substep, which is carried out in parallel with substep E4',discharge of residual hydrogen contained in the hydrogen fuel cell 30 and discharge of energy stored in the primary filtering capacitors 56 and secondary filtering capacitors 58 of the DC / DC voltage converter 32 controlled by the control module 48 of the DC / DC voltage converter 32 which controls the current 61 of the filtering inductor 60 according to the self-discharge procedure described in the , figure 6 .

[0057] In the discharge procedure following an emergency shutdown described above, steps E1 and E1' constitute a single disconnection step. Indeed, from a safety perspective, it is required to immediately disconnect all energy sources to eliminate any type of hazard (such as sustaining a fire by fueling a short circuit through damaged cable insulation, creating a hot spot). Therefore, the disconnection commands for the hydrogen fuel cell 30 and the high-voltage battery 24 arrive simultaneously.

[0058] There figure 6 is a graphical representation of the self-discharge process of the primary filtering capacities 56 and secondary filtering capacities 58 of the range extender system carried out at steps E7 and E4'.

[0059] The discharge of the residual energy of the hydrogen fuel cell 30 is carried out by energy losses generated by successive round trips of energy between the primary filtering capacitance 56 and secondary filtering capacitance 58 by driving the current 61 of the filtering inductance 60, one round trip constituting a self-discharge cycle 68.

[0060] The self-discharge process of the primary filtering capacities 56 and secondary filtering capacities 58 of the range extender system 28 is represented by the diagram of the figure 6 includes the following steps: First self-discharge cycle 68: State of the electrical circuit 10 at t = 0: current 61 of the filter inductance 60: I self = 0 voltage 40 of the hydrogen fuel cell 30: V pac = V max cycle 1. Output voltage 41 of the DC / DC voltage converter 32: V dcdc = V min cycle 1

[0061] E8: control of the DC / DC voltage converter 32 of the battery extender system 28 by the control module 48 of the DC / DC voltage converter 32 to obtain a positive value of the current 61 of the filter inductance 60,

[0062] E9: current 61 from the filter inductance 60 positive supplied by the primary filter capacitor 56 and the fuel cell 30 which are at the same voltage 40 to the secondary filter capacitor 58 which is at the output voltage 41 of the DC / DC voltage converter 32: decrease in the value of the voltage 40 of the hydrogen fuel cell 30 increase in the value of the output voltage 41 of the DC / DC voltage converter 32 because the value of the current 61 of the filter inductance 60 is positive.

[0063] State at t = 1 / 2 self-discharge cycle 68: current 61 of the filter inductance 60: I self =0 voltage 40 of the hydrogen fuel cell 30: V pac = V pac min 1 output voltage 41 of the DC / DC voltage converter 32: V dcdc = V dccc max 1

[0064] E10: control of the DC / DC voltage converter 32 of the battery extender system 28 via the control module 48 of the DC / DC voltage converter 32 to obtain a negative value of the current 61 of the filter inductance 60,

[0065] E11: negative current 61 from the filter inductance 60 supplied by the secondary filter capacitor 58 to the primary filter capacitor 56: decrease in the value of the output voltage 41 of the DC / DC voltage converter 32, increase in the value of the voltage 40 of the primary capacitance 56 because the value of the current 61 of the filter inductance 60 is negative.

[0066] State at t = 1 self-discharge cycle 68: current 61 of the filter inductance 60: I myself = 0 voltage 40 of the hydrogen fuel cell 30: V pac = V pac max 2. Output voltage 41 of the DC / DC voltage converter 32: V dcdc = V dcdc min 2 with V pac max 2 < V pac max 1, V dcdc min 2 < V dcdc min 1 V pac max 1 - V pac max 2 = Δ V pac And V dcdc min 1 - V dcdc min 2 = Δ V dcdc

[0067] At each self-discharge cycle 68, the voltage 40 of the hydrogen fuel cell 30 decreases, and after several self-discharge cycles 68 lasting on the order of a few milliseconds, the hydrogen fuel cell 30 is completely discharged. The total discharge time of the hydrogen fuel cell 30 is less than one second. Each self-discharge cycle 68 generates energy losses at stage E11 with a voltage value ΔV of 40 in the hydrogen fuel cell 30. pac equal to the voltage difference 40 of the hydrogen fuel cell 30 V pac max 1 at the beginning and at the end V pac max2 of the same self-discharge cycle 68. Several self-discharge cycles 68 will follow one another until a low voltage value 40 of the fuel cell 30 is reached. According to one embodiment of the invention, the DC / DC voltage converter 32 is configured to obtain a voltage value of the primary filtering capacitors 56 and secondary filtering capacitors 58 of less than 60 volts, i.e. a safety voltage value.

[0068] The two transistors 62 of the driver module 48 of the DC / DC voltage converter 32 are configured to control the current 61 of the filter inductance 60 between the low voltage input stage 66 and the high voltage output stage 64 of the DC / DC voltage converter 32 in a positive or negative direction and to a setpoint value of the current 61 of the filter inductance 60 as a function of the voltage values ​​40, 41 of the primary 56 and secondary 58 filter capacitors.

[0069] The control module 48 of the DC / DC voltage converter 32 is configured to control the successive round trips of energy between the primary filtering capacitance 56 and secondary filtering capacitance 58 by imposing the setpoint value of the current 61 of the filtering inductance 60.

[0070] Therefore, it is the DC / DC voltage converter 32 that accumulates the generated energy losses and drives the energy back and forth between the low voltage input stage 66 and the high voltage output stage 64 of the DC / DC voltage converter 32.

[0071] This self-discharge procedure of the primary 56 and secondary 58 filtering capacities is also used during a voluntary shutdown of the supply of the hydrogen fuel cell 30 corresponding to step E7.

[0072] Furthermore, during a voluntary shutdown of the hydrogen fuel cell 30 supply, this self-discharge procedure is also adapted at stage E4 to control the discharge current 43 of the residual energy as a function of the hydrogen pressure loss inside the hydrogen fuel cell 30, and thus to ensure an optimal electrochemical reaction despite the decreasing amount of hydrogen present inside the hydrogen fuel cell 30.

[0073] In the present invention, the function of discharging the so-called "residual" energy of the hydrogen fuel cell 30 is ensured by the DC / DC voltage converter 32 constituting an internal discharge means.

[0074] Discharging the residual hydrogen contained within the hydrogen fuel cell 30 through a structural element of the range extender system 28 preserves the initial architecture of the range extender system 28. The DC / DC voltage converter 32 thus fulfills the discharge function of the hydrogen fuel cell 30 on its own and eliminates the need for additional components dedicated to the discharge function, such as switches and additional dissipative elements.

[0075] Such an architecture also ensures precise control of the discharge current 43 by allowing the residual energy of the hydrogen fuel cell 30 to be discharged directly according to the amount of residual energy remaining (mass and pressure). Consequently, the current is controlled according to the remaining partial pressures of hydrogen inside the hydrogen fuel cell 30 in order to obtain the best stoichiometry and thus promote the lifespan of the hydrogen fuel cell 30. LEGEND

[0076] 10: Electrical circuit 12: High-voltage power grid 14: Inverter 16: Electric traction machine 18: High-voltage power grid voltage converter 20: Ancillary equipment 21: Distribution box 22: Power supply network 24: High-voltage battery 26: High-voltage battery main switch 28: Range extender system 30: Hydrogen fuel cell 32: Range extender system DC / DC converter 34: Precharge circuit 36: Precharge resistor 38: Precharge switch 40: Fuel cell voltage 41: DC / DC converter output voltage 42: Fuel cell current 43: Discharge current 44: First main switch 46: Second main switch 48: DC / DC converter driver module 50: Fuel cell status 52 Fuel cell current setpoint 54: Current setpoint56: discharge; 58: primary filtering capacitor; 60: secondary filtering capacitor; 61: filtering inductor current; 62: transistor; 64: high-voltage output stage; 66: low-voltage input stage; 68: self-discharge cycle

Claims

1. Method for discharging the electrical circuit (10) of a motor vehicle comprising at least one electric traction machine (16) of the vehicle equipped with: - an electrical power supply network (22) comprising: -- a high-voltage battery (24), -- a range extender system (28) comprising a hydrogen fuel cell (30) that is associated with a DC-DC voltage converter (32) itself comprising a filtering inductor (60) traversed by a current (61) of the filtering inductor (60), a primary filtering capacitor (56) that is at the voltage (40) of the hydrogen fuel cell (30), and a secondary filtering capacitor (58) that is at the output voltage (41) of the DC-DC voltage converter (32), - a high-voltage consumption network (12), powered by the electrical power supply network (22), comprising the at least one electric traction machine (16) of the motor vehicle associated with an inverter (14) and ancillary equipment (20), - and a control module (48), the discharging method comprising the successive steps of: - (E0) stopping the motor vehicle, - (E1) electrically disconnecting the high-voltage battery (24) from the high-voltage consumption network (12), - (E2) interrupting the hydrogen supply of the hydrogen fuel cell (30), and - (E3) discharging the energy of the electrical circuit (10) into the stator winding of the electric traction machine (16), wherein the step (E3) of discharging the energy of the electrical circuit (10) is carried out by controlling the DC-DC voltage converter (32) by means of the control module (48), characterized in that the step (E0) of stopping the vehicle corresponds to the voluntary stopping of the motor vehicle, in that the step (E3) of discharging the energy of the electrical circuit (10) comprises the following successive sub-steps: - (E4) discharging the energy produced by consuming the residual hydrogen contained in the hydrogen fuel cell (30) by means of the DC-DC voltage converter (32) by controlling a discharging current (43) by means of the control module (48) until a predetermined voltage threshold value (40) of the hydrogen fuel cell (30) is reached, - (E5) electrically disconnecting the range extender system (28) from the high-voltage consumption network (12), - (E6) discharging the energy from the capacitors of the high-voltage consumption network (12) into the stator of the electric traction machine (16) by means of the inverter (14), and in that the step (E3) of discharging the energy of the electrical circuit (10) comprises a sub-step (E7), which is carried out at the same time as the sub-steps (E5) to (E6), of discharging the energy of the primary (56) and secondary (58) filtering capacitors of the DC-DC voltage converter (32) by controlling the current (61) of the filtering inductor (60) by means of the control module (48).

2. Method for discharging the electrical circuit (10) of a motor vehicle comprising at least one electric traction machine (16) of the vehicle equipped with: - an electrical power supply network (22) comprising: -- a high-voltage battery (24), -- a range extender system (28) comprising a hydrogen fuel cell (30) that is associated with a DC-DC voltage converter (32) itself comprising a filtering inductor (60) traversed by a current (61) of the filtering inductor (60), a primary filtering capacitor (56) that is at the voltage (40) of the hydrogen fuel cell (30), and a secondary filtering capacitor (58) that is at the output voltage (41) of the DC-DC voltage converter (32), - a high-voltage consumption network (12), powered by the electrical power supply network (22), comprising the at least one electric traction machine (16) of the motor vehicle associated with an inverter (14) and ancillary equipment (20), - and a control module (48), the discharging method comprising the successive steps of: - (E0) stopping the motor vehicle, - (E1) electrically disconnecting the high-voltage battery (24) from the high-voltage consumption network (12), - (E2) interrupting the hydrogen supply of the hydrogen fuel cell (30), and - (E3) discharging the energy of the electrical circuit (10) into the stator winding of the electric traction machine (16), wherein the step (E3) of discharging the energy of the electrical circuit (10) is carried out by controlling the DC-DC voltage converter (32) by means of the control module (48), characterized in that the step (E0) of stopping the vehicle corresponds to an emergency stop of the motor vehicle, in that the method for discharging the electrical circuit (10) comprises a step (E1') of electrically disconnecting the range extender system (28) from the high-voltage network (12) that is carried out simultaneously with the step (E1) of electrically disconnecting the high-voltage battery (24) from the high-voltage consumption network (12), in that step (E3) of discharging the energy of the electrical circuit (10) comprises the following sub-steps: - (E4') discharging the energy of the capacitors of the high-voltage consumption network (12) into the stator of the electric traction machine (16) by means of the inverter (14), - and in that the step (E3) of discharging the energy of the electrical circuit (10) comprises a sub-step (E5'), which is carried out at the same time as the sub-step (E4'), of discharging the residual hydrogen contained in the hydrogen fuel cell (30) and of discharging the energy of the primary (56) and secondary (58) filtering capacitors of the DC-DC voltage converter (32) by controlling the current (61) of the filtering inductor (60) by means of the control module (48).

3. Method for discharging the electrical circuit (10) of a motor vehicle according to one of Claims 1 and 2, characterized in that the process for controlling the current (61) of the filtering inductor (60) by means of the control module (48) is configured to reach a low value of the voltage (40) of the hydrogen fuel cell (30) by means of a series of n self-discharging cycles (68) of the primary (56) and secondary (58) filtering capacitors of the range extender system (28).

4. Method for discharging the electrical circuit (10) of a motor vehicle according to Claim 3, characterized in that each self-discharging cycle (68) of the primary (56) and secondary (58) filtering capacitors of the range extender system (28) comprises: - a step (E8) of controlling the DC-DC voltage converter (32) of the range extender system (28) by means of the control module (48) of the DC-DC voltage converter (32) in order to obtain a positive value of the current (61) of the filtering inductor (60), with the positive value of the current (61) of the filtering inductor (60) supplied by the primary filtering capacitor (56) to the secondary filtering capacitor (58) causing (E9): -- a reduction of the value of the voltage (40) of the hydrogen fuel cell (30), and -- an increase of the value of the output voltage (41) of the DC-DC voltage converter (32); and - a step (E10) of controlling the DC-DC voltage converter (32) of the range extender system (28) by means of the control module (48) in order to obtain a negative value of the current (61) of the filtering inductor (60), with the negative value of the current (61) of the filtering inductor (60) supplied by the secondary filtering capacitor (58) to the primary filtering capacitor (56) causing (E11): -- a reduction of the value of the output voltage (41) of the DC-DC voltage converter (32), and -- an increase of the value of the voltage (40) of the primary filtering capacitor (56).

5. Method for discharging the electrical circuit (10) of a motor vehicle according to Claim 4, characterized in that the process for controlling the current (61) of the filtering inductor (60) by means of the control module (48) is configured so that the value of the voltage (40) of the hydrogen fuel cell (30) at the end of a cycle of n+1 self-discharging cycles (68) is less than the value of the voltage (40) of the hydrogen fuel cell (30) at the end of the cycle of n self-discharging cycles (68).