Electric power supply system for a traction motor

Abstract

The invention relates to a system (1) for powering an electric traction motor, the system (1) comprising an energy converter (20), an electric battery (50) acting as an electrical energy reservoir, a supercapacitor (60) acting as a temporary electrical energy reservoir and a switch (30) comprising a first and a second on / off power switches (31, 32) connecting the energy converter (20) to the battery (50) and to the supercapacitor (60) respectively, under the control of an electronic control unit (40) configured to ensure gradual connection of the sources (50, 60) to the energy converter (20) by said switch (30), the first and second on / off power switches (31, 32) being operated, during a determined period of time, as current limiters limiting the electric current (Ik) flowing therethrough. Such a system (1) is further arranged to precharge the supercapacitor (60) when the latter is discharged.

Description

[0001] ELECTRICAL POWER SUPPLY SYSTEM FOR A TRACTION MOTOR

[0002] Technical Field

[0003] The present invention relates to an electrical power supply system for a traction motor and in particular for an energy-autonomous transport vehicle.

[0004] Prior art

[0005] Today, two categories of energy-autonomous vehicles use an electric motor as a traction engine. An electric vehicle uses only one or more electric motors for propulsion. A hybrid vehicle uses one or more electric motors in conjunction with a combustion engine used alternately and / or in addition to propel itself. One of the main advantages of an electric traction motor is that it is reversible, which allows the vehicle's potential and kinetic energy to be recovered during deceleration phases.

[0006] In an autonomous vehicle, the energy supplied to the electric motor is stored in a battery that needs to be recharged regularly from the mains or by the combustion engine. The range in electric traction depends mainly on the battery's charging capacity but also on the battery's capacity to recharge through energy recovery.

[0007] The batteries used in electric traction are batteries with a high mass and volume capacity so as not to excessively weigh down vehicles or take up too much space in a vehicle. The most commonly used batteries in vehicles today are lithium batteries and nickel batteries, which have a similar volume capacity and present different advantages and disadvantages.

[0008] Lithium batteries are available in several categories: Lithium-Ion, Lithium-Ion-Polymer, Lithium-Phosphate. The main advantages of lithium batteries are a high mass capacity, low self-discharge, good energy efficiency that can restore up to 90% of the energy required for its charge, and a fast charging capacity when it is discharged below 75% of its capacity. This type of battery can cause overheating problems that can lead to a fire or explosion of the battery when it is overcharged. Although it does not have a "memory" effect, a complete discharge of the battery can damage it. In addition, the use of high charging current reduces its lifespan and it is preferable to perform fast recharges only when the battery is completely discharged to achieve a near-complete recharge.A full battery charge can only be achieved under controlled voltage, current, and temperature conditions to avoid any risk of fire or explosion. To prevent any problems, these batteries must be equipped with a regulation circuit or BMS (Battery Management System) that will regulate the battery current according to various control parameters, in order to prevent the battery from finding itself in a critical situation.

[0009] Nickel batteries mainly include NiMH (Nickel Metal Hydride) and NiCd (Nickel Cadmium) batteries. Although heavier, their main advantage is that they are less expensive than lithium batteries and have a longer lifespan. Nickel batteries can be used with high currents over wide temperature ranges without the risk of overheating. However, the energy efficiency of nickel batteries is lower than that of lithium batteries, and overcharging with high currents can damage the nickel battery. In addition, using high charging currents also reduces the lifespan of these batteries.

[0010] Regardless of the battery type, the battery charging current depends on its own parameters, and it is necessary to avoid overcharging the battery with excessively high currents. These limitations have the effect of limiting the recharging capacity of such batteries by energy recovery. Indeed, since the battery voltage and charging current must be controlled and dependent on the state, it is not possible to recover all the energy that the electric motor could provide. Vehicles must limit the energy recoverable by the electric motor to the energy recoverable by the battery. Such a limitation does not allow the full capacity of an electric motor to be used during deceleration.An electric motor can be used in particular as an electric brake, which on the one hand generates a lot of electricity but also reduces the mechanical braking effort which dissipates the kinetic and potential energy of the vehicle into heat, also releasing fine particles linked to the wear of the brake pads.

[0011] For electric vehicles alternating between strong accelerations and strong decelerations, such as a racing car, it is known to have an auxiliary electric energy reservoir with a capacity lower than that of a battery, but whose charging characteristics are much less restrictive. Such auxiliary reservoirs use supercapacitors, i.e. capacitors with a very high capacity that can reach several hundred Farads.

[0012] Although having a lower mass and volume energy storage capacity than a battery, a supercapacitor can charge and discharge much faster than a battery and withstand a much greater number of charge and discharge cycles with an energy efficiency between charge and discharge much higher than a battery. However, compared to a battery, a capacitor has leakage currents leading to faster self-discharge and above all a very significant voltage variation which is a function of the capacitor's charge.

[0013] To be able to couple a supercapacitor and a battery, it is known to use an energy converter whose effect is to bring the voltage across the terminals of the supercapacitor to a value close to that of the battery in order to be able to connect it in parallel to the battery in order to receive the surplus energy that cannot be supplied to the battery. Such an energy converter is relatively expensive and complex because the current and voltage regulation is carried out to suit the battery while working with very high voltage and current values, i.e. several hundred volts and several hundred amperes.In addition, such a converter needs to operate as a step-up and step-down converter while being bidirectional, which does not optimize its energy efficiency and adds conversion losses of around 20% to 30% to transmit and restore energy between the supercapacitor and the traction motor.

[0014] Although they allow for more energy to be recovered and returned, solutions coupling a supercapacitor and a high-capacity battery for an electric traction vehicle are not optimized. We can cite as an example the architectures disclosed by documents US 2008 / 0290842 A1 and US 2021 / 0150372 A1 which provide for a battery and a supercapacitor connected respectively in parallel with each other or in series. Said document US 2008 / 0290842 A1 discloses more specifically an arrangement of an industrial vehicle according to which a battery can be disconnected in favor of a capacitor during the deceleration or load lowering phases and according to which said capacitor can be disconnected in favor of the battery during the traction or load raising phases.Said document US 2021 / 0150372 A1 provides for at least one pair of power modules each comprising a battery and a supercapacitor connected in series, said power modules being operated alternately to prevent voltage fluctuations at the terminals of the supercapacitor of each of the power modules.

[0015] Let us describe in more detail in connection with figure 1, a system 1 for supplying an electric traction motor of a vehicle in accordance with the state of the art, close to the architecture according to document US 2008 / 0290842 A1, that is to say comprising a battery mounted in parallel with a capacitor.

[0016] For the sake of simplification, the said figure 1 only includes the essential elements used to power the traction motor. The latter can be a permanent magnet synchronous motor with, for example, three phases, or be any other type of synchronous motor. Such a traction motor can be asynchronous or even direct current. It is reversible, that is to say that it can operate both as a generator transforming mechanical energy into electrical energy, and as a motor transforming electrical energy into mechanical energy.

[0017] Such a system 1 comprises an energy converter 20 having a direct current input / output 23 and electrical connections connected to the electric traction motor. Said energy converter 20 bidirectionally transforms the energy supplied to or returned by the traction motor into incoming or outgoing current Ik. The variations in current Ik and voltage Vk at the terminals of the energy converter 20 depend on numerous parameters. For example, the current Ik can vary as a function of the power supplied by the traction motor in the deceleration phase or vice versa as a function of the energy required by the traction motor to accelerate or maintain a rotation speed. The energy converter 20 is adapted to the type of traction motor so that the signals received from or supplied by the phases of said motor can be converted appropriately.

[0018] Said power supply system 1 comprises one or more electric batteries 50 serving as a reservoir of electrical energy. We will hereinafter include under the term “battery”, a single battery or a set of batteries also called in the literature “battery pack”. It further comprises one or more supercapacitors 60 serving alone or mutually as a temporary reservoir of electrical energy. In the same way, we will hereinafter include under the term “supercapacitor”, a single supercapacitor or a set of supercapacitors also called in the literature “pack of supercapacitors”.

[0019] Such a system 1 further comprises a switch 30 connected on the one hand to the battery 50 and to the supercapacitor 60 and on the other hand to said energy converter 20. The role of such a switch 30 consists of providing a function of switching and selecting the source to be used, from among the battery 50 and the supercapacitor 60, to maximize the performance of the battery / supercapacitor hybridization. More precisely, said switch 30 is arranged to direct the electric current Ik coming from the energy converter 20 to the supercapacitor 60 during deceleration phases of the vehicle and vice versa to deliver to said energy converter 30 such an electric current delivered by the battery 50 or by the supercapacitor 60 to satisfy the traction function of said electric motor.Traditionally, said switch 30 is arranged to deliver such a current Ik from the supercapacitor 60 then from the battery 50 when a voltage Vsc across said supercapacitor 60 reaches a minimum voltage threshold.

[0020] Such a switch 30 can be described mainly in the form of a pair of power switches 31 and 32. The power switch 31 electrically connects the battery 50 to the energy converter 20. The power switch 32 electrically connects the supercapacitor 60 to said energy converter 20. The two power switches 31 and 32 are controlled by an electronic control unit 40 comprising one or more microprocessors or microcontrollers, also known by the English acronym ECU (for "Engine Control Unit") to alternatively connect the converter 20 to the battery 50 or to the supercapacitor 60.

[0021] The electronic control unit 40 cooperates, for example via a CAN bus (from the English “Controller Area Network” - not shown in FIG. 1) or by any other equivalent means, with different computers of the vehicle. Thus, the electronic control unit 40 receives information relating to said vehicle, such as, by way of non-limiting examples, the speed of movement of the vehicle, the rotation speed of the wheels, instructions emanating from the human-machine interfaces for controlling the vehicle (braking, acceleration), or even from automatic or semi-automatic piloting entities, etc.

[0022] The two power switches 31 and 32 describe inverse or symmetrical functions: when the power switch 31 is open, the power switch 32 is closed and vice versa. Such complementary power switches 31 and 32 are generally made from MOSFET (Metal-Oxide Semiconductor Field Effect Transistor) type transistors or more generally from insulated-gate bipolar transistors (also known by the acronym IGBT, from the English “insulated-gate bipolar transistor”). Such transistors are voltage-driven, respectively referenced Vc31 and Vc32 for the power switches 31 and 32. Thus, when such a control voltage Vc31 or Vc32 applied between the gates and emitters of said transistors is lower than a first determined voltage (for example, a voltage Vc31 or Vc32 equal to a zero potential difference Vge), the power switch is open.Conversely, when such a potential difference Vge is greater than a second determined voltage (for example of the order of 15 volts), the power switch becomes conductive. The control voltages Vc31 and Vc32 are therefore applied, respectively, to the power switches 31 and 32 under the impulse of the electronic control unit 40 in an appropriate manner respectively to cause the opening or closing of said power switches 31 and 32 in a few milliseconds.

[0023] A battery 50 is a high-capacity battery, for example a lithium or nickel battery or any other technology having comparable advantages in terms of mass and / or volume capacity. A regulation circuit (not shown in FIG. 1) coupled to the battery 50 has the function of regulating said battery 50 by controlling the current Ib and the voltage Vb supplied or received by the battery 50 to ensure homogeneous distribution at the level of the different elements constituting said battery 50. The regulation circuit is advantageously connected to the electronic control unit 40 to provide it with information on the status of said battery 50 (output voltage Vb, output current Ib, state of charge, temperature, maximum current available, etc.). Regularly charging a battery 50 during each deceleration of the vehicle can reduce its lifespan.Also, generally, the energy recovery current Ik from the traction motor is directed solely or mainly to the supercapacitor 60. The energy converter 20 is the member allowing the transformation of the originally continuous electrical power supply (from the battery(ies) 50 or the supercapacitor(s) 60) generally into three-phase to drive the electric traction motor. At the input on the continuous side of the inverter 21 there is a capacitor 22 with a capacity, for example of approximately 1 mF, intended to smooth and filter this current Ik. It is the voltage Vk of this capacitor 22 which is read at the input of the inverter 21.

[0024] The battery 50 is an energy storage device that maintains a relatively stable voltage Vb throughout its state of charge. Conversely, the voltage Vsc of the supercapacitor 60 varies greatly during its use. During a discharge phase of said supercapacitor 60, for example during sudden use of the traction motor, its voltage Vsc will drop. The opposite occurs during a regeneration phase, for example during deceleration of the vehicle.

[0025] If the battery 50 is connected to the inverter 21, the voltage Vk of the inverter 21 (therefore that of the capacitor 22) and that Vb of the battery are in equilibrium. If a change of source must be carried out, the voltage of the capacitance of the inverter 21 must be balanced with the voltage of the new source, in this case the supercapacitor 60. The opposite occurs if the source must be switched from the supercapacitor 60 to the battery 50. This switching mission is ensured by the switch 30.

[0026] Figure 2 illustrates an example of operation of the switch 30 and represents the voltages Vb and Vsc and the currents Ib and Isc during switching controlled by the electronic control unit 40.

[0027] The left part of Figure 2 corresponds to an acceleration caused at an instant t1. For this purpose, it is considered that the supercapacitor 60 is charged to a voltage Vsc much higher than the battery voltage Vb. The electronic control unit 40 simultaneously causes the closing of the power switch 32 and the opening of the power switch 31. The supercapacitor 60 supplies a current Isc to the energy converter 20 and discharges while the battery current Ib is zero. While discharging, the voltage Vsc across the terminals of the supercapacitor decreases as a function of the current drawn. When the voltage Vsc is close to becoming lower than a minimum value Vscm, acceptable by the inverter 21 or determined by the electronic control unit 40 (t=t2 in Figure 2), the vehicle will recover a cruising speed thanks to the energy delivered by the battery 50.For this, said electronic control unit 40 simultaneously causes the power switch 32 to open and the power switch 31 to close. The current Isc becomes zero and the current Ib is delivered to the energy converter 20. The supercapacitor 60 has finished discharging, traction is again provided by the battery 50.

[0028] The right part of Figure 2 corresponds to braking caused at a time t3. Beforehand, the first power switch 32 is open and the second power switch 31 is on, traction being provided by the battery 50. At time t3, the electronic control unit 40 causes the power switch 32 to close and the power switch 31 to open. The supercapacitor 60 receives a negative current Isc emanating from the energy converter 20 and charges while the battery current Ib is zero. While charging, the voltage Vsc across the terminals of the supercapacitor 60 increases as a function of the current received. When the voltage Vsc of the supercapacitor 60 reaches a maximum value VscM for the energy converter 20, the electronic control unit 40 causes the energy recovery in the supercapacitor 60 to stop by opening the power switch 32 and closing the power switch 31.The current Isc becomes zero and the current Ib is delivered by the battery 50 to the energy converter 20, until a next acceleration, at an instant t4.

[0029] Figure 3 illustrates the same situation through the voltage Vk read by the inverter 21 of the energy converter 20 as sources switch during sudden acceleration phases AP of the vehicle or braking RP of the latter, or even during cruising phases CP of said vehicle. Thus, upstream of time t1, the vehicle describes a cruising speed. The voltage Vk is substantially constant because Vk=Vb, the battery 50 ensuring the supply of electrical energy. At time t1, a strong acceleration is commanded, an acceleration phase AP follows a cruising phase CP. The voltage Vk read by the inverter 21 of the energy converter 20 describes the voltage Vsc delivered by the supercapacitor 60. This drops during the discharge of the supercapacitor 60. At time t2, the battery 50 takes over from the supercapacitor 60 during a new cruising phase CP. At time t3 of braking, a RP regeneration phase is triggered.This results in a recharge of the supercapacitor, Vk=Vsc. This increases until it reaches a maximum value VscM acceptable for the energy converter 20. The electronic control unit 40 then causes the energy recovery phase RP to stop and, at the same time, the power switch 32 to open and the second power switch 31 to close. The voltage Vk at the terminals of the inverter 21 of the energy converter 20 becomes the voltage delivered by the battery Vb.

[0030] It should be noted that when the battery 50 is connected, the voltage Vk is stable. Conversely, when the supercapacitor 60 is connected, the voltage Vk increases sharply during the RP regeneration phases and decreases sharply during the AP acceleration phases. The purpose of the switching operations (illustrated in dotted lines in Figure 3) is to rebalance the voltages between the inverter 21 and the storage device 50 or 60 to be connected.

[0031] To better understand the phenomena involved, let us use a hydraulic analogy. Energy storage can in fact be likened to containers having the stored energy as their volume, and the voltage of the sources as their water depth. A battery 50 can be likened to a simple basin of “infinite” capacity compared to that of a supercapacitor 60. The capacity 22 of the inverter 21 of the energy converter 20, and therefore by analogy its capacity, is still much smaller than that of the supercapacitor 60, but its energy is not negligible. For each change of source (battery 50 to supercapacitor 60 and vice versa), the capacity of the energy converter 20 must be rebalanced with respect to that of the source 50 or 60 to be connected.For this, the battery 50 or the supercapacitor 60 must be connected to the energy converter 20 by pipes (in this case, electric cables) including a valve (in this case, the power switches 31 and 32 of the switch 30) to select the source 50 or 60 to be connected to the energy converter 20. When a change of source must take place, the valve 31 opens / closes and the valve 32 closes / opens. However, if the closure of one of the two valves 31 or 32 were instantaneous, the pressure difference (in this case, the potential difference or voltage) between the battery 50 and the capacity of the energy converter 20, would generate an uncontrolled or excessive flow (in this case, an intensity), which would lead to destruction of the equipment. To control and regulate such a flow rate, it is appropriate to close the valve 31 or 32 concerned gradually until there is a differential pressure sufficiently negligible to completely close said valve.To achieve such a less abrupt transition, the document FR31 12904A1 proposes solutions among which, the switch 30 according to FIG. 1 can be arranged to carry out a progressive switching of the current supplied to the energy converter 20 by the supercapacitor 60 and by the battery 50. For this, said document FR31 12904A1 describes a switch 30 comprising first and second power switches 31 and 32, in this case MOSFET (Metal-Oxide Semiconductor Field Effect Transistor) type transistors which make it possible to switch high currents, while having a very low resistivity. Control voltages of the first and second switches 31 and 32, for example the gates of the MOSFETs, receive, via signal amplifiers, a command from an electronic control unit 40.One of the signal amplifiers inverts said control voltage so that when one of the power switches 31 is open, the other power switch 32 is closed and vice versa. Given the high current and voltage values, said document FR31 12904A1 teaches, instead of operating a single switch 30, the use of a plurality of switches (i.e. a number of switch instances 30 equal to four, or even ten or even twenty) each comprising a first switch 32 connecting the supercapacitor 60 to the converter 20 and a second switch 31 connecting the battery 50 to said converter 20. Each switch instance 30 within said plurality has a control voltage of its own and which is delivered by the electronic control unit 40.The latter thus delivers a sequence of individualized control voltages (instead of a single control voltage) to achieve progressive switching of the supercapacitor 60 or the battery 50 to the energy converter 20. Although functional, such a solution requires a large number of power switches (or switches) and costly and complex control of the latter for the electronic control unit 40.

[0032] Statement of the invention

[0033] The invention proposes to improve the energy efficiency, reliability and cost of a power supply system for an electric traction motor advantageously using alternately and exclusively a battery and a supercapacitor. This objective is achieved by proposing a progressive switching between battery and supercapacitor, a particularly clever technique and contrary to known switching, taking the opposite view of the teaching drawn from prior techniques and doctrine in the field of power electronics.

[0034] More particularly, the invention proposes a system for supplying an electric traction motor, said system comprising:

[0035] - an energy converter having a direct current input / output for connection to the electric traction motor, said energy converter bidirectionally transforming the energy supplied to or returned by the motor into current entering or leaving through its current input / output;

[0036] - an electric battery serving as a reservoir of electrical energy;

[0037] - a supercapacitor serving as a temporary reservoir of electrical energy;

[0038] - a switch comprising a first terminal connected to the current input / output of the converter, a second terminal connected to the battery and a third terminal connected to the supercapacitor, said switch comprising a first power switch connecting the battery to the energy converter and a second power switch connecting the supercapacitor to said energy converter, said first and second power switches being controlled by respective control voltages for: o delivering an electric current from the energy converter to the supercapacitor or to the battery, or o delivering such an electric current emanating from the supercapacitor or from the battery to said energy converter;

[0039] - an electronic control unit arranged to produce said control voltages of the first and second power switches of the switch, from measurements: o of the intensity of the electric current called or delivered by the energy converter; o of potential differences respectively at the terminals of the battery, the supercapacitor and the energy converter.

[0040] To prevent destruction of the system and to simplify its layout, the electronic control unit is configured to produce a control voltage:

[0041] - less than a first low threshold determined to cause the first or second power switch to open completely, with no electric current passing through the latter;

[0042] - greater than a second high threshold determined to cause the total closing of the first or second power switch, the latter not limiting the intensity of the electric current passing through it;

[0043] - included in the linear zone of the first or second power switch, the latter limiting the intensity of the electric current passing through it. To propose source changes between battery and supercapacitor while the traction motor delivers high power, the electronic control unit can be configured to produce a control voltage in the linear zone of the first or second power switch according to a measurement of the temperature (operating temperature of said first or second power switch, so as to regulate the current limitation of said first or second power switch according to the measured operating temperature of the latter.

[0044] Likewise, to limit any excessive heating of the first and second power switches, the electronic control unit may be configured to produce a control voltage in the linear zone of the first or second power switch for a period of time less than a determined maximum duration.

[0045] When the system's supercapacitor is fully discharged, it may be necessary to precharge it prior to the nominal implementation of said power supply system. For this, the switch may include:

[0046] - upstream of the first terminal of the switch connected to the current input / output of the energy converter, a first switch / relay, called “main relay” for connecting or disconnecting the first and second power switches of the energy converter;

[0047] - a second switch / relay, called a “bypass relay” positioned to connect or disconnect the battery (50) from the energy converter independently of the first power switch and the main relay.

[0048] In this case, to control said main and bypass relays and determine the operation of the system, the electronic control unit can be configured to produce inverted control signals of said main and bypass relays to cause them to open or close, so as to determine: - a first precharge configuration of the supercapacitor of the system according to which said inverted control signals jointly cause the opening of the main relay and the closing of the bypass relay;

[0049] - a second nominal operating configuration of the system according to which said inverted control signals jointly cause the main relay to close and the bypass relay to open.

[0050] According to this advantageous embodiment ensuring possible precharging of the supercapacitor, the electronic control unit can further be arranged to configure the system according to:

[0051] - the first precharge configuration of the supercapacitor as soon as the voltage across the terminals of the latter is lower than a determined minimum value;

[0052] - the second nominal operating configuration of said system as soon as the supercapacitor presents at its terminals a voltage greater than or equal to said determined minimum value (Vscm).

[0053] To obtain sufficient current capacity, the first and second power switches of a system according to the invention may each comprise several power transistors connected in parallel.

[0054] Brief description of the drawings

[0055] The invention will be better understood and other characteristics and advantages thereof will appear on reading the following description of particular embodiments of the invention, given as illustrative and non-limiting examples, and referring to the appended drawings, among which: Figure 1, already described, represents an example of embodiment of a power supply circuit for an electric traction motor according to the state of the art; - Figure 2, already described, illustrates, through an example, the voltages at the terminals of a battery and a supercapacitor of such a system according to Figure 1, as well as the currents delivered by each of its sources, during a switching of sources;

[0056] - figure 3, already described, illustrates, through the same example as that presented by figure 2, the voltage at the terminals of an energy converter of a system according to figure 1, during such switching of sources;

[0057] - figure 4 represents an exemplary embodiment of a power supply circuit for an electric traction motor according to the invention, according to a nominal operating configuration;

[0058] - figure 5 illustrates an exemplary embodiment of a switch of a system according to figure 4;

[0059] - figure 6 illustrates an example of driving a typical power transistor and capable of being used to arrange such a switch according to said figure 5.

[0060] Detailed description

[0061] In order to simplify the description of the different embodiments which will be represented in the remainder of this description, the same references will be used in the different figures to designate the same elements or similar elements which are interchangeable with each other.

[0062] A first example embodiment of a power supply circuit for an electric traction motor according to the invention is shown in Figure 4. Such an arrangement is very similar to that already described in connection with Figure 1. However, the arrangement of the switch 30 and the control method implemented by the electronic control unit 40 are different. Furthermore, according to a preferred embodiment, a system 1 according to the invention may comprise an additional pair of power switches or relays 33 and 34 to advantageously allow the implementation of a particularly innovative and efficient method of precharging the supercapacitor 60.This first example of embodiment presented in connection with figure 4 is particularly interesting for vehicles alternating strong accelerations and strong decelerations, such as electric racing vehicles or heavy vehicles moving in urban areas, for example electric buses.

[0063] For the purposes of simplification, Figure 4, like Figure 1, only includes the essential elements used to power a traction motor of a vehicle. Such a system 1 thus includes an energy converter 20 similar to the energy converter already described in connection with Figure 1. It has a direct current input / output 23 which is electrically connected to the phases of the electric traction motor. The current input / output 23 is intended to receive a direct current Ik. The values ​​of current Ik and voltage Vk can vary within current and voltage amplitudes specific to said energy converter 20.

[0064] The energy converter 20 bidirectionally transforms the energy supplied to or returned by the motor into current entering or leaving it through its current input / output 23. The energy converter 20 is adapted to the type of traction motor so that the signals received from or supplied by the phases of said motor can be adequately converted.

[0065] Such a system 1 comprises a battery 50 and a supercapacitor 60 connected to the energy converter 20 via a switch 30 which consists of ensuring a function of switching and selecting the source to be used, from among the battery 50 and the supercapacitor 60. The role of said switch consists of maximizing the performance of the battery / supercapacitor hybridization. As in the case of a known power supply system according to FIG. 1, said switch 30, according to FIG. 4, is arranged to direct the electric current Ik coming from the energy converter 20 to the supercapacitor 60, or even to the battery 50, during deceleration phases of the vehicle and vice versa to deliver to said energy converter 30 such an electric current delivered from the battery 50 or the supercapacitor 60 to satisfy the traction function of said electric motor. Such a switch 30 can be symbolized by a pair of power switches 31 and 32.The power switch 31 electrically connects the battery 50 to the energy converter 20 and the power switch 32 electrically connects the supercapacitor 60 to said energy converter 20. The two power switches 31 and 32 are controlled by the electronic control unit 40 which comprises one or more microprocessors or microcontrollers, also known by the English acronym ECU (for "Engine Control Unit") to alternately connect the energy converter 20 to the battery 50 or to the supercapacitor 60. Thus, said switch 30 comprises a first terminal 30k connected to the current input / output 23 of the converter 20, a second terminal 30b ensuring the connection of the battery 50 to the power switch 31 and a third terminal 30sc for connecting the supercapacitor 60 to the power switch 32.The first and second power switches 31, 32 are controlled by respective control voltages Vc31, Vc32 to deliver the electric current Ik coming from the energy converter 20 to the supercapacitor 60 or to the battery 50 during the braking phase of the vehicle, or to deliver such an electric current Ik emanating from the supercapacitor 60 or from the battery 50 to said energy converter 20, during the traction phase by the electric motor.

[0066] The electronic control unit 40 can be connected via a CAN bus (from the English “Controller Area Network” - not shown in FIG. 4), or by any other equivalent means, to the various computers of the vehicle. Thus, the electronic control unit 40 receives information relating to said vehicle, such as, by way of non-limiting examples, the speed of movement of the vehicle, the rotation speed of the wheels, instructions emanating from the human-machine interfaces for controlling the vehicle (braking, acceleration), or even from automatic or semi-automatic piloting entities, etc.Said electronic control unit 40 is thus configured to produce said control voltages Vc31, Vc32 of the power switches 31 and 32 of the switch 30, from different measurements, in particular of the intensity of the electric current Ik called (traction phases) or delivered (braking phases) by the energy converter 20, of potential differences Vb, Vsc, Vk respectively measured at the terminals of the battery 50, of the supercapacitor 60 and of said energy converter 20. Said control voltages produced by the electronic control unit 40 are such that the two power switches 31 and 32 of the switch 30 describe inverse or symmetrical functions: when the power switch 31 is open, the power switch 32 is closed and vice versa.

[0067] The power switches 31 and 32 advantageously comprise one or more power transistors connected in parallel, advantageously of the MOSFET or IGBT type (an English acronym for "insulated-gate bipolar transistor"). Thus, when such a control voltage Vc31 or Vc32 applied between the gate and the emitter of such a transistor is lower than a first determined low threshold Vcl (for example, a voltage Vc31 or Vc32 equal to a potential difference between gate and emitter Vge equal to three volts), the power switch is completely open, no electric current flows through it. Conversely, when such a potential difference Vge is greater than a second determined high threshold Vch (for example, of the order of twelve volts), the power switch becomes completely conductive and does not limit the intensity of the electric current flowing through it.The control voltages Vc31 and Vc32 are therefore applied, respectively, to the power switches 31 and 32 under the impulse of the electronic control unit 40 in an appropriate manner respectively to cause the total opening or closing of said power switches 31 and 32 in a few milliseconds.

[0068] Although having a similar function to that of a known switch 30 and presented in connection with FIG. 1, a switch 30 according to the invention presented in connection with FIG. 4 is structurally different. In addition, the opening and closing control of said power switches 31 and 32 performed by the electronic control unit 40 is also different. In connection with FIG. 4, FIG. 5 presents a non-limiting example of arrangement of a power switch 31 or 32 of the switch 30 according to the invention. Such a power switch 31 or 32 is referenced 300 in FIG. 5.Such a power switch 300 has the mission of controlling the current Ib or Isc flowing from the sources 50, 60 to the energy converter 20, during changes of sources in electrical energy 50 and 60, during cruising phases CP and acceleration AP mentioned previously in connection with FIG. 3, and conversely, has the mission of controlling the current Isc flowing from the energy converter 20 to the supercapacitor 60 or to the battery during regeneration phases RP. Such a power switch 300 must be arranged to alternately block or allow the electric current to pass completely but also to finely control the intensity of said current during the phases of switching of electrical sources 50 and 60. According to the example illustrated by FIG. 5, a power switch 300 comprises power transistors arranged in “common emitter” mode.To illustrate such an exemplary embodiment, Figure 5 shows MOSFET type power transistors. However, the invention would not be limited by this sole choice of electronic components or by such an arrangement in common emitter mode. Any other arrangement of power transistors allowing controllable bidirectional use can be envisaged. Such a power switch 300 has two “arms” 300A and 300B, each of the arms ensuring a direction of passage of the electric current within the switch 300. Thus, the arm 300A ensures a passage of current from a source 50 or 60 to the energy converter 20. Conversely, the arm 300B ensures a current flowing in the opposite direction, i.e. from said energy converter 20 to the source 50 or 60. The arms 300A and 300B are independently controlled by control voltages Vca, Vcb, in this case gate-emitter voltages Vge of the arm making it possible to open and close said arm.Such control voltages Vca and Vcb constitute a plural control voltage Vc produced and delivered by the electronic control unit 40. Each arm 300A, 300B may comprise several power transistors arranged in parallel for each of the arms in order to obtain sufficient current capacity, for example of the order of five hundred amperes. Thus, in FIG. 5, the arm 300A comprises three power transistors 301A, 302A and 303A connected in parallel forming a resulting power transistor 300A, controllable in switching by a gate-emitter voltage Vge=Vca. Similarly, the arm 300B comprises three power transistors 301B, 302B and 303B connected in parallel forming a resulting power transistor 300B, controllable in switching by a gate-emitter voltage Vge=Vcb.The number of transistors forming an arm 300A, 300B of the switch 300 may be less than or greater than three, depending on the amplitude of the electric current intended to pass through said switch 300.

[0069] We can notice that Figure 5 shows a preferred configuration of a power switch 300 comprising a transient voltage suppression diode 300D, an electronic component also known by the English acronym TVS for “transient-voltage-suppression”). Such a diode provides a protection function in the event of an overvoltage and has no impact on the operation of a power switch 300.

[0070] Figure 6 shows typical voltage-current curves for three temperature levels Tvj (25°C, 125°C and 150°C) of a power transistor. This figure is taken from charts of an insulated-gate bipolar transistor (IGBT). These curves illustrate the behavior of a power transistor when it is intended to be used as a power switch. For different operating temperatures T, the curves describe the collector current le for a control voltage Vge between gate and emitter. Thus, for a voltage Vge lower than seven volts, the current le is almost zero. The transistor can be considered as completely open. Conversely, when a control voltage Vge is higher than twelve volts, the current le is no longer limited and can exceed, in this case, one thousand two hundred amperes.The transistor can be considered as fully conducting. Between these two limit values ​​of the voltage Vge (seven volts and twelve volts), the transistor can limit the intensity of the current le. Thus, for example, whatever the temperature Tvj, a control voltage Vge of the order of nine volts, makes it possible to limit the current le to four hundred amperes. If this control voltage Vge remains constant, the transistor transforms into a variable resistor and dissipates a lot of energy in the form of heat. A prolonged duration of a voltage Vge of the order of 9V leads to the destruction of the transistor.

[0071] It is therefore for this reason that the state of the art, as recommended by document US 2021 / 0150372 A1, teaches the operation of such power switches in “all or nothing” mode alternating control voltages Vge lower than a first low threshold (in this case in Figure 6, seven volts) to control an opening of the power switch and a control voltage Vge higher than a second high threshold (in this case in Figure 6, twelve volts) to control a closing of the power switch. A so-called “linear zone” control of the power transistor in which the transistor behaves as an adjustable resistor is prohibited in power electronics. There is therefore no solution in the transport and / or automotive industry exploiting this “linear” operating zone of power transistors.Linear transistor control is used in signal processing for very low current and voltage values ​​in applications far removed from the power supply systems or circuits of electric traction motors, for example to make audio-visual equipment for which variable resistors based on transistors are used.

[0072] The invention goes against the state of the art by exploiting the linear zone of the power transistors, such as those described in Figure 5, forming the power switches 31 and 32 of the switch 30 according to Figure 4. The invention makes it possible to use said transistors punctually as variable resistors, limiting the electric current flowing through them from a certain value of the control voltage Vc applied to them. To use the hydraulic analogy previously mentioned, during a transition of sources between battery and supercapacitor, a valve (a power switch) must be "semi-closed", in order to limit the flow (electric current) to fill the capacity of the inverter 21 of the energy converter 20.When the latter is charged to an acceptable level, that is to say at a level close to the source concerned, the said valve (in this case the power switch) becomes completely open and allows the flow (the electric current) to flow freely.

[0073] It has been found that in more than 95% of the cases of transitions, that is to say, alternations between battery and supercapacitor as electrical power source, transitions that we will call "typical source changes", the switching time of a power switch is less than a few milliseconds. In the preferred application example of a power supply system for an electric traction motor, such as system 1 according to FIG. 4, the current flowing through the power switches 31, 32 is limited to approximately four hundred amperes, when applying a control voltage Vge of the order of nine volts. Experience shows that the power transistors forming a power switch such as the switch 300 according to FIG. 5, absorb the power peak without difficulty.There are source changes that we will call "atypical source changes" which correspond to transitions that occur while the traction motor is developing its maximum power. This situation is much less frequent, less than 5% of cases. The current Ik required by the energy converter 20 at these times is of the order of three hundred amperes. Since the current saturation is determined at four hundred amperes during switching, the capacitor 22 of the inverter 21 of the energy converter 20 is then supplied with a current of only one hundred amperes. The switching time is therefore longer than during a typical source change. During this longer switching, the transistors of the switch 30 are more stressed over time.To overcome this drawback, the intensity of the current passing through the switch 30 can be limited to a higher value than the four hundred amperes previously mentioned in order to reduce the switching time and therefore the stress on the components.

[0074] In connection with Figure 7, to enable such low-cost progressive source switching, the electronic control unit 40 is also adapted to produce and deliver the control voltages Vc31 and Vc32 applied to the power switches 31 and 32. Such control voltages no longer describe a binary signal unlike the prior art, oscillating between a first control voltage value Vcl lower than a first threshold below which the switch is fully open, and a second value Vch higher than a second high threshold, above which the switch is fully on. To ensure typical source change cases, the invention provides such a control voltage Vc31 and Vc32 describing a signal having three “plateaus”

[0075] - two plates respectively describing the two values ​​Vcl and Vch of control voltage Vc mentioned in connection with the state of the art to open (control voltage lower than the low threshold, for example three volts) or close (control voltage higher than the high threshold, for example 12 volts) entirely said power switches 31 and 32,

[0076] - a third “plateau” describing an “intermediate” control voltage value Vci (for example, around nine volts) in the linear zone of the transistors forming said power switches, to limit the intensity of the electric current passing through said switches and thus allow a progressive switching during a period of time during which the power switch 31 or 32 concerned is partially conducting.

[0077] Figure 7 thus illustrates an example of production of the control voltage Vc31 to connect or disconnect the battery 50 to the energy converter 20. According to this example, the power switch 31 is arranged in accordance with Figure 5. To illustrate the fact that a battery 50 can only be recharged via a third-party charging device (from an external source such as, for example, the mains) and not during a regeneration phase dedicated to the charging of the supercapacitor 60, said power switch 31 may comprise only a single arm 300A. Conversely, if said system 1 also provides for recharging the battery 50 during a regeneration phase, the power switch 31 comprises the two arms 300A and 300B. According to Figure 7, the connection of the battery 50 is made while the vehicle is not at full power. The current Ik is therefore moderate.During a period of time dt1, of the order of three milliseconds, the control voltage has a substantially constant intermediate control voltage Vci in the linear zone of the power transistors. The temperature T of the latter rises but said transistors withstand said rise because the duration dt1 remains very short.

[0078] Figure 7 describes the control voltage Vc32 of the power switch 32 whose function is to connect or disconnect the supercapacitor 60 to the energy converter 20. To be able to power the energy converter 20 and thus meet the needs of the electric traction motor in the acceleration phase AP, the power switch 32, for example arranged according to Figure 5, comprises a first arm 300A allowing the through current Isc to flow to the energy converter 20. The power switch 32 further comprises a second arm 300B to allow the recharging of said supercapacitor 60 during the braking or regeneration phases RP by authorizing the current Isc to flow from the energy converter 20 to the supercapacitor 60 or the battery 50. The control voltages Vc32a and Vc32b, respectively of the arms 300A and 300B, correspond to a plural control voltage Vc32.Said control voltages Vc32a and Vc32b are described in Figure 7. In this representation, at each transition or change of source, the electric traction motor is at full power. The time period dt2 or dt3 during which the arm 300A or 300B of the power switch 32 is partially conducting is therefore greater than that dt1 described previously in connection with the curve Vc31 of the control voltage of the power switch 31. The intermediate plateau Vci thus results in a curve likely to increase the saturation value of the electric current flowing through when the temperature T of the electronic components forming said power switch 32 increases. In this way, the invention also responds to the atypical source changes previously mentioned.

[0079] Thus, Figure 7 illustrates an electronic control unit 40 arranged to deliver an intermediate value Vci of control voltage Vc adjusted (constant sensitive by step or variable) according to the amplitude of the current Ik called by the energy converter 20, or even according to the temperature T of said transistors forming the power switches 31 and 32 during progressive transition phases. Said electronic control unit 40 may be a microcontroller or another type of microprocessor circuit better known by the acronym ECU (from the English "Electronic Control Unit") which is commonly used for the various computers present in vehicles. Said unit 40 may further advantageously comprise an analog circuit for producing and delivering the control voltages Vc31 and Vc32.

[0080] Figure 4 shows an advantageous embodiment according to which the switch 30 comprises additional power switches 33 and 34, acting as relays of the fully open or fully closed type. Such an arrangement makes it possible to implement a pre-charging of the supercapacitor 60 via the battery 50, when said supercapacitor is fully discharged or at least has a voltage Vsc lower than a minimum value Vscm, acceptable by the energy converter 20 or determined by the electronic control unit 40, for example at the end of a period of parking of the vehicle. Implementing such a pre-charging of the supercapacitor 60 requires significant energy which must be transferred from the battery 50. A direct connection between said battery 50 and the supercapacitor would be likely to cause the destruction of the system 1.The invention provides, like what it proposes to carry out progressive transitions when changing sources, to control the load current thanks to an exploitation of the relays 33 and 34 as well as a linear zone control of the power switches 31 and 32 previously described by the electronic control unit 40 arranged for this purpose.

[0081] Let us examine such a control of the switch 30 by said unit 40.

[0082] A first switch / relay 33, hereinafter called the “main relay”, is positioned in series, downstream of the power switches 31 and 32 and upstream of the energy converter 20. A second switch / relay 34, hereinafter called the “bypass relay”, is positioned in parallel from upstream of the power switch 31, downstream of the battery 50, and downstream of said switch / relay 33 and upstream of the energy converter 20. Thus, upstream of the first terminal 30k of the switch 30 connected to the current input / output 23 of the energy converter 20, the main relay connects or disconnects the first and second power switches 31, 32 of the energy converter 20.The bypass relay 34 connects the battery 50 to the energy converter 20 or disconnects said battery 50 from said energy converter 20, independently of the respective configurations of the power switch 31 and the main relay 33.

[0083] The electronic control unit 40 is configured to produce inverted control signals Vc33, Vc34 of said main and bypass relays to cause them to open or close, so as to configure the power supply system 1 according to:

[0084] - a first precharge configuration of the supercapacitor 60 for which said inverted control signals Vc33, Vc34 jointly cause the opening of the main relay and the closing of the bypass relay;

[0085] - a second nominal operating configuration of said power supply system 1 for which said inverted control signals Vc33, Vc34 jointly cause the main relay 33 to close and the bypass relay 34 to open.

[0086] The electronic control unit 40 thus controls the opening and closing of each of said relays 33 and 34. The energy to be transferred in the case of a precharge of a supercapacitor 60 is much greater than during a switching of sources. In addition, the time required for such a precharge is longer than the duration of a progressive change of sources. To implement such a precharge, it is therefore essential to prioritize the control of heat dissipation in the transistors of the power switches 31 and 32 to preserve their integrity.

[0087] First of all, in order for a vehicle to be able to operate normally, without the supercapacitor 60 being precharged, by exploiting the electrical energy delivered by the battery 50, the electronic control unit 40 causes the main relay 33 to open and the bypass relay 34 to close. The switch 30 allows the precharging of the supercapacitor 60 while leaving the battery 50 connected directly to the energy converter 20 to supply the traction motor. The power switches 31 and 32 are connected in series between the battery 50 and the supercapacitor 60, while being disconnected from the energy converter 20. The potential difference between the battery 50 and the supercapacitor 60 is then distributed between the two power switches 31 and 32. The invention makes it possible to control the two power switches 31 and 32 in a linear zone with current to precharge the supercapacitor 60 from the battery 50.To ensure heat dissipation that can be tolerated by the transistors of the two power switches 31 and 32 (for example, a maximum power of one thousand watts), said power switches are controlled by means of a control voltage Vc31 and Vc32 (gate-emitter voltage Vge). As an illustrative example, let us assume that the supercapacitor 60 needs to be precharged and that the maximum power that each of the power switches 31 and 32 can dissipate is one thousand watts. The initial voltage Vsc across said supercapacitor 60 is therefore zero while that Vb across the terminals of the battery 50 is four hundred volts. Thus, at the respective terminals of said power switches 31 and 32, there is a potential difference of two hundred volts. The electronic control unit 40 delivers control voltages Vc31 and Vc32 (Vc32b in this case) so that a current of five amperes flows through said power switches 31 and 32.The supercapacitor charges. As Vsc increases, the potential difference across the power switches 31 and 32 decreases. The electronic control unit 40 regulates the control voltages Vc31 and V32 to regularly increase the limit of the current flowing through said power switches 31 and 32 to maintain substantially a constant maximum dissipated power. When the supercapacitor 60 reaches a minimum charge sufficient for the system to operate normally, the precharging of the latter is then interrupted by the electronic control unit 40. The latter delivers control voltages Vc31 and V32 so as to cause the power switch 31 to open and the power switch 32 to close.In order for the supercapacitor to be able to supply the traction motor via the energy converter 20, said electronic processing unit 40 simultaneously causes the bypass relay to open and the main relay 33 to close. The switch 30 thus switches from a first precharging configuration of the supercapacitor 60 to a second nominal operating configuration of the traction motor supply system.

[0088] According to this second advantageous embodiment, the arrangement of the electronic control unit 40 allows precharging of the supercapacitor 60 and switching of sources between battery 50 and supercapacitor 60 by regulating the control voltages Vc31 and Vc32 in particular. Such regulation can advantageously be implemented in an analog manner in order to simplify the integration of the system 1 in a host vehicle. The invention calls upon the exploitation of the linear zone of the power transistors forming the power switches 31 and 32. However, the control of the latter is different between source switching and precharging of the supercapacitor. In the case of switching, the current control allows the fastest possible source change, while respecting the current tolerances to limit heating of the transistors forming said power switches 31 and 32.In the case of precharging of the supercapacitor 60, the current control is carried out in order to guarantee constant heating of the transistors within the dissipation limits permitted by the components.

[0089] Figure 4 shows a system 1 comprising a battery 50, a supercapacitor 60 and two power switches 31, 32 of the switch 30. However, a person skilled in the art can adapt the number of batteries 50 and supercapacitors 60 according to the power supply requirements of the traction motor and the characteristics of the electronic components. In the same way, the number of power switches can be different for connecting battery(ies) 50 and supercapacitor(s) 60, each of said power switches jointly forming the elements 31 and 32 according to Figure 4, which can be controlled by the electronic control unit 40 individually or in solidarity.

[0090] As indicated above, the various embodiments are given as non-limiting examples and many variations are possible. In particular, it is possible to combine the various embodiments or to use a number of power switches, batteries or supercapacitors different from those expressed as an illustrative example.

Claims

CLAIMS 1. System (1) for supplying an electric traction motor, said system (1) comprising: - an energy converter (20) having a direct current input / output (23) for connection to the electric traction motor, said energy converter (20) bidirectionally transforming the energy supplied to or returned by the motor into current (Ik) entering or leaving through its current input / output (23); - an electric battery (50) serving as a reservoir of electrical energy; - a supercapacitor (60) serving as a temporary reservoir of electrical energy; - a switch (30) comprising a first terminal (30k) connected to the current input / output (23) of the converter (20), a second terminal (30b) connected to the battery (50) and a third terminal (30sc) connected to the supercapacitor (60), said switch comprising a first power switch (31) connecting the battery (50) to the energy converter (20) and a second power switch (32) connecting the supercapacitor (60) to said energy converter (20), said first and second power switches (31, 32) being controlled by respective control voltages (Vc31, Vc32) for: o delivering the electric current (Ik) coming from the energy converter (20) to the supercapacitor (60) or to the battery (50), or o delivering such an electric current (Ik) emanating from the supercapacitor (60) or from the battery (50) to said converter of energy (20); - an electronic control unit (40) arranged to produce said control voltages (Vc31, Vc32) of the first (31) and second (32) power switches of the switch (30), from measurements: o of the intensity of the electric current (Ik) called or delivered by the energy converter (20); o of potential differences (Vb, Vsc, Vk) respectively at the terminals of the battery (50), of the supercapacitor (60) and of the energy converter (20); characterized in that said electronic control unit (40) is configured to produce a control voltage (Vc31, Vc32): - less than a first low threshold (Vcl) determined to cause the total opening of the first or second power switch (31, 32), no electric current passing through the latter; - greater than a second high threshold (Vch) determined to cause the total closing of the first or second power switch, said first (31) or second (32) power switch not limiting the intensity of the electric current passing through it; - included (Vci) in the linear zone of the first (31) or second (32) power switch, said first or second power switch (31, 32) limiting the intensity of the electric current passing through it.

2. System (1) according to the preceding claim, wherein the electronic control unit (40) is configured to produce a control voltage (Vc31, Vc32) in the linear zone of the first or second power switch (31, 32) according to a measurement of the operating temperature (T) of said first or second power switch (31, 32), so as to regulate the current limitation according to the operating temperature (T) of said first or second power switch (31, 32).

3. System (1) according to claim 1 or 2, wherein the electronic control unit (40) is configured to produce a control voltage (Vc31, Vc32) in the linear zone of the first or second power switch (31, 32) for a period of time (dt1, dt2, dt3) less than a determined maximum duration.

4. System (1) according to any one of the preceding claims, in which: - the switch (30) comprises: o upstream of the first terminal (30k) of the switch (30) connected to the current input / output (23) of the energy converter (20), a first switch / relay (33), called the “main relay” for connecting to or disconnecting from the energy converter (20), the first and second power switches (31, 32); o a second switch / relay (33), called the “bypass relay” positioned for connecting to or disconnecting from the energy converter (20), the battery (50), independently of the first power switch (31) and the main relay (33); - the electronic control unit (40) is configured to produce inverted control signals (Vc33, Vc34) of said main and bypass relays to cause them to open or close, so as to configure the system (1) according to: o a first precharge configuration of the supercapacitor (60) for which said inverted control signals (Vc33, Vc34) jointly cause the main relay to open and the bypass relay to close; o a second nominal operating configuration of the system (1) for which said inverted control signals (Vc33, Vc34) jointly cause the main relay (33) to close and the bypass relay (34) to open.

5. System (1) according to the preceding claim, for which the electronic control unit (40) is arranged to configure the system (1) according to: - the first precharge configuration of the supercapacitor if the voltage (Vsc) across the terminals of the latter is lower than a determined minimum value (Vscm); - the second nominal operating configuration of said system as soon as the supercapacitor has a voltage (Vsc) at its terminals greater than or equal to said determined minimum value (Vscm).

6. System (1) according to any one of the preceding claims, for which the first and second power switches (31, 32) each comprise several power transistors (301 A, 302A, 303A, 301 B, 302B, 303B) connected in parallel.

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