Method and system for direct current charging of an electric or hybrid vehicle battery, using a pre-charging capacity

Abstract

Method and system for direct current charging of an electric or hybrid vehicle battery, using a precharge capacity The invention relates to a method (100) for charging an electric vehicle battery, by a direct current charging terminal providing a maximum voltage strictly lower than the battery voltage, the vehicle comprising: - a charging socket, - a voltage booster connected to the charging socket and to the battery, and comprising a switching arm of which a high switch is connected between a midpoint of the switching arm and a positive terminal of the battery, and a low switch is connected between the midpoint and a negative terminal of the battery, - a precharge capacity connected between the charging socket and the voltage booster, the charging method (100) comprising a step of precharging (105) the precharge capacity by switching (103) the high switch, the low switch remaining open,with a gradually increasing duty cycle. (Figure 2),

Description

Title of the invention: Method and system for direct current charging of an electric or hybrid vehicle battery, using a pre-charging capacity

[0001] The present invention relates to the fields of automobiles and electrical engineering, and more specifically concerns a method for charging a high-voltage battery of an electric or hybrid vehicle, and an electric or hybrid vehicle having means for implementing such a method.

[0002] An electric or hybrid vehicle has a high-voltage battery, with a maximum no-load voltage generally between 400V (volts) and 800V, which is discharged to power an electric motor enabling the vehicle to move forward. The high-voltage battery must therefore be recharged from a charging terminal external to the vehicle. When the latter is capable of providing a voltage higher than the maximum no-load voltage of the high-voltage battery, it is sufficient to connect the outputs of the charging terminal to the terminals of the vehicle's high-voltage battery to recharge it.

[0003] However, some charging terminals only provide a voltage lower than the maximum no-load voltage of the high-voltage battery. In particular, some charging terminals can only provide a maximum of 400V. To recharge a high-voltage battery with a voltage higher than 400V with such a charging terminal, it is therefore necessary to connect the outputs of the charging terminal to the input of a voltage booster, the output of which, providing a voltage higher than the voltage of the high-voltage battery to be recharged, is connected to the terminals thereof.

[0004] Such a voltage booster comprises at least:

[0005] - a precharge capacity whose two ends are capable of being connected by from the vehicle's contactors to the charging station,

[0006] - an inductance connected on the one hand to a higher potential end of the capacity, and on the other hand at a midpoint of a switching arm,

[0007] - the switching arm, which comprises a first switch called the low switch connected between the midpoint and a negative terminal of the high voltage battery, and a second switch called a high switch connected between the midpoint and a positive terminal of the high voltage battery.

[0008] The precharge capacitor makes it possible to filter voltage variations and stabilize it from the point of view of the charging terminal. This precharge capacitor must be precharged to a set voltage close to the voltage of the charging terminal before closing the vehicle contactors, in order to avoid a high current draw which could lead to these contactors sticking, by melting of material.

[0009] Thus, before starting a charge of the high-voltage battery from the external charging terminal, with a voltage lower than the voltage of the high-voltage battery, and before closing the contactors, the pre-charge capacity is pre-charged to the set voltage. Then the vehicle requests the charging terminal, thanks to communication between the charging terminal and the vehicle, to pre-charge to this set voltage possibly reduced by a margin, for example 9V (Volt), to anticipate a passive discharge of the pre-charge capacity. Only after these pre-charges on either side of the contactors are these commanded to close, then the battery is charged by switching the high and low switches of the voltage booster.

[0010] Furthermore, a smoothing capacitor is generally connected in parallel with the high voltage battery, between the latter and the switching arm, to filter voltage variations from the point of view of the high voltage battery.

[0011] Given the cost of the components of the voltage booster, it is advantageous to reuse for this function, power electronic components already present in the vehicle. An inverter, making it possible to supply alternating current to the electric motor of the vehicle, is in particular connected at the input to the smoothing capacitor and at the output to first ends of stator windings of the electric motor of the vehicle, their second ends, opposite the first ends, being connected to a neutral point of the electric motor. Each of the stator windings is connected by its first end to a switching arm of the inverter.

[0012] It is therefore possible to reuse the stator windings of the electric motor and the switching arms of the inverter to raise the voltage at the output of the charging terminal in order to charge the high voltage battery of the vehicle, the switching arms being able to operate simultaneously or out of phase in order to reduce the current ripples at the output of the voltage booster.

[0013] It is then necessary to add a switch called a step-up switch, between the neutral point of the electric motor and the highest potential end of the precharge capacity, in order to be able to disconnect this precharge capacity from the electric motor when the electric motor is used for driving the vehicle.

[0014] Document EP4052952 proposes such a solution for recharging the high-voltage battery of a vehicle, using a direct current charging terminal with a voltage lower than the battery voltage. This document recommends precharging the precharge capacity using the inverter and the stator windings as a voltage step-down device with a duty cycle of 50%.

[0015] Now the inventors have found that using the inverter as a voltage step-down device with such a duty cycle immediately charges the pre-charge capacitor with a current strong enough to stick the step-up switch and the inter inverter breakers, by melting material, when these switches are dimensioned as precisely as possible. In addition, such a precharge makes it difficult to control the precharge voltage at the terminals of the precharge capacity, this voltage rising very quickly, which then requires a passive discharge after the precharge, to reach the set voltage.

[0016] There is therefore a need for a method for charging a high-voltage battery of a vehicle and an associated charging system, using a charging terminal with a voltage lower than the voltage of the battery to be charged, which do not damage the components of the charging system or do not require oversizing of these components.

[0017] The present invention aims to remedy at least in part the aforementioned drawbacks by providing a method for charging a high voltage battery of a vehicle and an associated charging system, which slow down the precharging of the precharging capacity and therefore the intensity of the current flowing through the components of the charging system during precharging of the precharging capacity.

[0018] To this end, the invention proposes a method for charging a battery of an electric or hybrid vehicle, by an external direct current charging terminal providing a maximum charging voltage strictly lower than a battery voltage, the vehicle comprising: - a charging socket connected to the charging station, - a voltage booster connected at the input to the charging socket and at the output to the battery, the voltage booster comprising at least one inductor and at least one switching arm, the switching arm comprising a high switch connected between a midpoint of the switching arm and a positive terminal of the battery, and a low switch connected between the midpoint and a negative terminal of the battery, the midpoint being connected via the inductor to a positive terminal of the charging socket, - a precharge capacity connected between the charging socket and the voltage booster, the charging method comprising a step of precharging the precharging capacity, and being characterized in that the precharging step comprises switching of the high switch, the low switch of the switching arm remaining open, the switching taking place with a duty cycle increasing progressively.

[0019] Of course, when only one switching arm of the vehicle is used during the precharging step of the charging method according to the invention, while the vehicle has several switching arms, the high and low switches of the unused switching arms remain open throughout the precharging step.

[0020] In this application, the vehicle battery is understood to be a high-voltage battery capable of powering the inverter and the electric motor while the vehicle is running. Similarly, the electric motor and inverter in this patent application refer to an electric traction or propulsion motor and a traction or propulsion inverter of the vehicle. The terms "charge" or "recharge" are further considered equivalent in this application.

[0021] Further, in this application, components are "connected" together when only a few conductors or components of zero or near-zero resistance electrically connect them, such as switches. The switches or relays in this application are mechanical or semiconductor-based.

[0022] Finally, in this patent application, unless otherwise stated, an input or output connection of a functional assembly such as the voltage booster is understood to be a connection to the terminals of this input or respectively of this output, with respect to the function mentioned. Thus, the voltage booster making it possible to raise the voltage at the terminals of the charging socket to bring it to the level of the battery voltage, the input of the voltage booster is located at the charging socket and the output of the voltage booster is located at the battery.

[0023] Thanks to the invention, the precharge capacity is charged progressively, so as to limit the current passing through the components of the vehicle's charging system, and not to stick the switches it passes through. This progressive precharge is inexpensive because it uses the control means of the voltage booster switches, these control means already existing because they are used during a step of actual charging of the vehicle's battery. It therefore does not require intermediate damping components.

[0024] During this precharging step, the charging socket is not electrically connected to the charging terminal, the contactor(s) at the input of the vehicle charging system not being closed during this precharging. After this precharging step, once the precharging capacity is precharged, this or these contactor(s) are closed and the actual charging of the battery is carried out, by alternating switching of the high and low switches of at least one of the switching arms.

[0025] During the precharging step, however, only one or more high switches of the vehicle switch. When several high switches switch, they switch in phase, i.e. they close and open at the same time. In addition, the corresponding low switches of the vehicle remain open throughout the precharging step.

[0026] During this precharge, the duty cycle is defined as a value between zero and one, and corresponding to the closing time of the high switch(es) used over a switching period (also called a switching period). A duty cycle of 0.5 (or 50%) means that the high switch(es) are closed for half of this switching period. In the invention, this ratio cyclical is not fixed, it varies in such a way as to adjust the dynamics of the rise in voltage across the precharge capacitor. It starts at a value low enough to allow control of this rise in voltage, and increases progressively at least at the start of precharge.

[0027] According to an optional and advantageous characteristic of the charging method according to the invention, during switching in the precharging step, a switching frequency of the high switch is lower than a high cut-off frequency of a bandwidth of a voltage sensor connected in parallel with the precharging capacitor. This makes it possible to monitor the voltage across the terminals of the precharging capacitor so as to stop this precharging as soon as a set voltage is reached. The switching frequency is for example between 100Hz and 1kHz.

[0028] Alternatively, the duration of the precharge step is determined as a function of a given set of parameters (for example the battery voltage, the progression of the duty cycle and a precharge setpoint voltage). In this case, the choice of the switching frequency is not conditioned by the bandwidth of the voltage sensor.

[0029] In one embodiment of the invention, during the precharging step, the duty cycle evolves according to a slope ramp capable of maintaining a charging current of the precharging capacity below a predetermined maximum current threshold. This predetermined maximum current threshold is for example set according to the sizing of the components of the charging system. For example, if the high and low switches can only support 20A (amperes), the predetermined maximum current threshold is for example set at 20A. The progression of the duty cycle is for example linear. Alternatively, the progression of the duty cycle is not linear, but makes it possible to maintain a charging current of the precharging capacity at an acceptable level, in particular below a predetermined maximum current threshold.

[0030] Furthermore, in this embodiment of the invention, the slope is capable of allowing a set voltage to be reached at the terminals of the precharge capacitor in less than three seconds. Preferably, the set voltage is reached at the terminals of the precharge capacitor in less than two seconds. This makes it possible to comply with the total duration of the checks as recommended by the international standard on the charging of electric vehicles, during an initialization phase before the transfer of energy between the terminal and the vehicle. In addition, this makes it possible to limit the total duration of the battery charging process.

[0031] For information purposes, to precharge the precharge capacity to 400V to within 9V, using a switching frequency of 100kHz, the duty cycle preferably evolves according to a ramp representing an increase of between 1% and 2% per second.

[0032] In the precharging step of the charging method according to the invention, the duty cycle increases from a minimum value corresponding to a closing time over a switching period, for example between 10qs (microseconds) and 200qs, and preferably between 10qs and 100qs. These ranges of values ​​are adapted to start the switching, so as to control the rise in voltage of the precharging capacity, for values ​​of capacities and battery voltages generally used in electric or hybrid vehicles. It should be noted that the minimum value of the duty cycle cannot be zero due to a dead time delay existing between each opening then closing of the switch(es) controlled with this duty cycle.

[0033] The invention also relates to a system for charging a battery of an electric or hybrid vehicle, capable of using an external direct current charging terminal providing a maximum charging voltage strictly lower than a battery voltage, the charging system comprising: - a charging socket capable of being connected to the charging terminal, - a voltage booster capable of being connected at the input to the charging socket and at the output to the battery, the voltage booster comprising at least one inductor and at least one switching arm, the switching arm comprising a high switch connected between a midpoint of the switching arm and a positive terminal of the battery, and a low switch connected between the midpoint and a negative terminal of the battery, the midpoint being connected via the inductor to a positive terminal of the charging socket, - a pre-charge capacity capable of being connected between the charging socket and the voltage booster, the charging system comprising means for precharging the precharging capacity, and being characterized in that the precharging means comprise means for switching the high switch, leaving the low switch of the switching arm open, with a duty cycle increasing progressively. The precharging means comprise in particular the battery, the high switch(es) that the switching means are capable of controlling during a precharging of the precharging capacity, and the inductance(s) connected to this or these high switch(es). The switching means are for example means for controlling the voltage booster.

[0034] In one embodiment of the invention, the voltage booster comprises several inductances formed by stator windings of an electric motor of the vehicle, and several switching arms belonging to an inverter of the vehicle, the inverter being connected at the output to the stator windings and being capable of being connected at the input to the battery. This embodiment makes it possible to reduce the cost and the size of the vehicle's charging system.

[0035] In this embodiment of the invention, the stator windings are for example connected in a star configuration to a neutral point of the electric motor, and the charging system comprises a switch connected on the one hand to the neutral point and on the other hand to the precharging capacity. This switch makes it possible to disconnect the precharging capacity of the electric motor before a driving phase of the vehicle. In alternative embodiments in which the stator windings are not connected in a star configuration, a switch is arranged between the precharging capacity and at least one stator winding of the electric motor, used during the charging method according to the invention.

[0036] The switching means are preferably configured to maintain a charging current of the precharge capacitor below a predetermined maximum current threshold. This predetermined threshold may depend on the number of high switches used to precharge the precharge capacitor. If it is desired to use several high switches without modifying the predetermined maximum current threshold seen by the step-up switch, it is possible to shift the control of the high switches in time within a switching period. This makes it possible to charge the precharge capacitor more quickly for the same duty cycle. However, the voltage rise is so sensitive to the duty cycle, including for very low values, that it is preferable to use a more dynamic ramp on the duty cycle while only controlling a single high switch.

[0037] Furthermore, the switching means are for example configured to increase the duty cycle from a minimum value corresponding to a closing time over a switching period, between 10qs and 200qs and preferably between 10qs and 100qs.

[0038] The charging system according to the invention has advantages similar to those of the charging method according to the invention.

[0039] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which:

[0040] [Fig.l] represents a charging system according to the invention, making it possible to recharge a battery of an electric or hybrid vehicle, in one embodiment of the invention, the charging system being connected to an external direct current charging terminal,

[0041] [Fig.2] represents steps of a charging method according to the invention, implemented by the charging system of [Fig.l], in one embodiment of the invention,

[0042] [Fig.3] represents the evolution of a duty cycle used to switch a switch of the charging system of [Fig.l], expressed in percentages as a function of the time in seconds, during a precharging step of a precharging capacity of this charging system, according to the embodiment of the charging method of [Fig.2],

[0043] [Fig.4] represents the evolution of the voltage at the terminals of the precharging capacity, expressed in volts per second, during the precharging step of the charging method of [Fig.2], and

[0044] [Fig.5] represents the evolution of the charging current of the precharge capacity, expressed in amperes per second, during the precharge stage of the charging process of [Fig.2].

[0045] According to one embodiment of the invention, a vehicle comprises a charging system 2 according to the invention represented in [Fig.l], incorporating elements of the vehicle's powertrain.

[0046] In this embodiment of the invention, the vehicle comprises a battery 28 with a nominal no-load voltage of 800V. It is therefore a high-voltage battery. The battery 28, in this example of use of the invention, is sufficiently discharged to require recharging and therefore has a voltage Vbatt at its terminals of, for example, between 500 and 600V. The vehicle is connected to an external direct current charging terminal 40, capable of supplying 400V at most.

[0047] The charging terminal 40 comprises internal contactors which close before the start of recharging of the battery 28. Before this charging, the internal contactors are not closed.

[0048] The charging system 2 of the vehicle comprises a charging socket, to which the charging terminal 40 is connected, and at least one mechanical contactor or relay 38 connecting the charging socket to a precharging capacity 22 of the charging system 2. Here the relay 38 comprises a first terminal connected to a negative terminal of the charging socket, and a second terminal connected to a negative terminal of the precharging capacity 22. Alternatively, another relay is additionally or instead arranged between the positive terminals of the charging socket and the precharging capacity 22.

[0049] The precharge capacitor 22 is connected in parallel to the charging socket via the relay 38. The precharge capacitor 22 makes it possible to limit the current draws when the relay 38 closes, and also to filter the voltage variations and stabilize the latter from the point of view of the terminal, when charging the battery 28. A voltage sensor, not shown, is furthermore connected in parallel with the precharge capacitor 22, and is part of the precharge means of the charging system 2.

[0050] The charging system 2 further comprises a first switch 36 connected on the one hand to the positive terminal of the precharging capacitor 22 and on the other hand to a neutral point N forming a positive input terminal of a voltage booster of the charging system 2. The voltage booster is formed from stator windings L1, L2, L3 of a motor of the vehicle, and an inverter 24 of the vehicle, used while driving to provide torque to the wheels of the vehicle. A negative input terminal of the voltage booster is connected to the negative terminal of the precharge capacitor 22. The voltage booster is therefore connected at the input to the precharge capacitor 22 via the first switch 36, and is connected at the output to the battery 28 via relays 32 and 34 called battery relays. The negative input terminal of the voltage booster is a negative terminal common to the inverter 24 and to the precharge capacitor 22. It is connected to the negative terminal of the battery 28 via the battery relay 34 and therefore also corresponds to a negative output terminal of the voltage booster. A positive output terminal of the voltage booster is connected to the positive terminal of the battery 28 via the battery relay 32.

[0051] A second switch 30 is connected on the one hand to the positive terminal of the precharge capacitor 22, and on the other hand to a positive terminal of the battery 28 via the battery relay 32. This second switch 30 makes it possible to directly connect the battery 28 to the charging terminal 40, without an intermediate voltage booster, when the charging terminal 40 delivers a voltage higher than the voltage of the battery 28.

[0052] The voltage booster also comprises a smoothing capacitor 26 at the output of the voltage booster, the smoothing capacitor 26 being connected to the terminals of the battery 28 via the battery relays 32 and 34. This smoothing capacitor 26 is alternatively replaced by mechanisms for smoothing the voltage Vbatt arranged in the battery 28.

[0053] The relays or switches, in this application, are mechanical relays or based on semiconductors.

[0054] The stator windings L1, L2, L3 are mounted in star and therefore connected together at the neutral point N.

[0055] The inverter 24 comprises three switching arms, each comprising: - a midpoint respectively Ml, M2, M3, - a low switch respectively 1_L, 2_L, 3_L connected on the one hand to the respective midpoint Ml, M2, M3 and on the other hand to the negative terminal of the battery 28 via the battery relay 34, and - a high switch respectively 1_H, 2_H, 3_H connected on the one hand to the respective midpoint Ml, M2, M3 and on the other hand to the positive terminal of the battery 28 via the battery relay 32.

[0056] The midpoints Ml, M2, M3 are connected to the ends of the stator windings Ll, ​​L2, L3 respectively, opposite the neutral point N.

[0057] The high switches 1_H, 2_H, 3_H and low switches 1_L, 2_L, 3_L are controlled switches, for example transistors. The charging system 2 comprises a circuit control circuit (not shown) capable of controlling these switches. This control circuit is part of the precharging means of the charging system 2. These precharging means comprise, in addition to the control circuit and the voltage sensor, the precharging capacitor 22, the voltage booster and the battery 28.

[0058] A charging method 100 according to the invention is now described in relation to [Fig. 2], implemented by the charging system 2 and in particular by a computer of the vehicle, used by the charging system 2 and comprising means for controlling the various switches or relays of the charging system 2.

[0059] A first step 105 of the charging method 100 is the precharging of the precharging capacity 22, implemented by the precharging means of the charging system 2. These precharging means use for example the vehicle computer, capable of communicating with the control circuit of the inverter 24.

[0060] This first precharging step 105 comprises a first sub-step 101 of closing the first switch 36 and the battery relays 32, 34, the second switch 30 and the relay 38 (between the charging socket and the precharging capacity 22) remaining open.

[0061] The first precharge step 105 then comprises a second sub-step 102 of selecting a duty cycle ramp to be applied to the high switch 1_H. This duty cycle a (referenced [Fig.3]) corresponds to the closing time of the high switch 1_H over a switching period. Here, the voltage sensor used at the terminals of the precharge capacitor 22 having a bandwidth of a few kHz, a switching frequency of 100Hz is chosen. It is thus possible to measure the voltage Vc at the terminals of the precharge capacitor 22 during a third subsequent sub-step 103 of switching this first precharge step 105, this third sub-step 103 following the second sub-step 102. Of course, as a variant, a different switching frequency is chosen but lower than the high cut-off frequency of the voltage sensor, for example 1kHz. In this second sub-step 102, a very slow rising ramp of variation of the switching duty cycle a of the high switch 1_H is chosen, starting from a low initial duty cycle. Indeed, the lower this initial duty cycle, the slower and therefore “controllable” the precharging of the precharging capacitor 22 is. This makes it possible to adjust the dynamics of the voltage rise across the terminals of the precharging capacitor 22.

[0062] The choice of the duty cycle ramp, and therefore of its slope, is carried out for example by reading from a data table resulting from prior tests or simulations, the table giving for example a slope value for a given switching frequency value and a given setpoint voltage value, the initial value of the duty cycle being for example fixed. The slope values ​​in this table result from a compromise. In fact, the value of the slope chosen (or read in the table) must correspond to a rising ramp of sufficiently slow duty cycle so that: - the voltage Vc at the terminals of the precharge capacitor 22 rises slowly and allows the switching sub-step 103 of the high switch 1_H to stop as soon as a set voltage Vc*, set for example at 420V, is reached at the terminals of the precharge capacitor 22. If, on the contrary, the ramp is too steep, the voltage Vc at the terminals of the precharge capacitor 22 will instantly reach the value of the voltage Vbatt at the terminals of the battery 28, and it will then be necessary to supervise a passive discharge of the precharge capacitor 22 until the set voltage Vc* is reached.

[0063] - that the charging current I of the pre-charging capacitor 22 does not reach values too high, which could in particular lead to the relay 38 sticking. Indeed, this current I is equal to C x dVc / dt, where C is the value of the precharge capacitor 22 and dVc / dt the variation over time of the voltage Vc across the precharge capacitor 22. The current I is therefore all the greater as the voltage Vc across the precharge capacitor 22 has a rapid dynamic. It should be noted that in this embodiment of the invention, the charging current I is equal to the current II flowing through the stator winding L1 since only the high switch 1_H switches.

[0064] Nevertheless, the value of the chosen slope must correspond to a rising ramp of cyclic ratio sufficiently fast to comply with specifications linked to the preload, which here is not to exceed 3 seconds for the entire first preload step 105.

[0065] In this second sub-step 102, the switching frequency chosen being 100kHz, the value of the initial duty cycle chosen being for example 30qs, the value of the set voltage Vc* being for example 420V (to take into account the passive discharge phenomenon so as to reach approximately 400V upon connection to the charging terminal 40), and a predetermined maximum current threshold to be respected for the charging current I being for example 22A, the vehicle computer chooses a duty cycle ramp a with a slope of 1.1% per second, that is to say that the closing time of the high switch 1_H starts at 30qs over the switching period of 10ms (milliseconds), and increases by 110 qs with each new switching period of 10ms.

[0066] Once this rising ramp of duty cycle a has been chosen, the third sub-step 103 of the first pre-charging step 105 is the switching of the high switch 1_H, all the other switches of the inverter 24 remaining open. This switching 103 is done with the duty cycle a varying according to the ramp chosen during the second sub-step 102.

[0067] Figures 3 to 5 show curves simulating this third switching sub-step 103, uninterrupted until a voltage Vc is reached across the terminals of the 22 precharge capacity of 420V.

[0068] [Fig.3] shows the evolution of the duty cycle over 1.47s of switching. After these 1.47s, it reaches 1.6% which is very low.

[0069] [Fig.4] shows the evolution of the voltage Vc at the terminals of the precharge capacitor 22, this reaching the set voltage Vc* of 420V after 1.47s of switching. This voltage is therefore reached before the 3 s of maximum duration for the precharge as recommended in the specifications, the switching frequency making it possible to stop the switching at 1.47 s to stop the precharge as soon as the set voltage Vc* is reached.

[0070] [Fig.5] shows the evolution of the charging current I of the precharging capacitor 22 during the switching sub-step 103. It can be seen that it does not exceed the predetermined maximum current threshold of 22A.

[0071] Returning to [Fig.2], the voltage Vc at the terminals of the precharge capacitor 22 being supervised 104 by the computer during the third switching sub-step 103, this continues as long as the set voltage Vc* is not reached (branch N). Otherwise (branch Y), the computer immediately stops the switching 103, and the first precharge step 105 ends, leaving all the switches of the inverter 24 open.

[0072] In an alternative embodiment, in this first precharging step 105, all the high switches 1_H to 3_H are switched in phase with the duty cycle a which evolves according to the ramp chosen during the sub-step 102 of selecting a ramp, or only two of these three switches are switched in phase with this duty cycle a. In all cases, the low switches 1_L to 3_L remain open during this first precharging step 105.

[0073] In parallel with the first precharging step 105, the vehicle requests the charging terminal 40 to also precharge to the set voltage Vc*.

[0074] The charging method 100 comprises, following the first precharging step 105, a second step 110 of connecting the charging socket to the charging terminal 40, by closing the relay 38, as soon as the charging terminal 40 and the precharging capacitor 22 are at a close voltage (within a difference of less than 9V). Otherwise, in particular if the voltage Vc at the terminals of the precharging capacitor 22 has decreased too much by passive discharge, a new switching sub-step 103 is applied until the set voltage Vc* is reached again.

[0075] Then the third step 115 of the charging method 100 is the charging of the battery 28, by switching the switches of the inverter 24 so as to charge the stator windings L1 to L3 with current then to discharge them with current into the battery 28. In other words the stator windings L1 to L3 and the inverter 24 operate, in this charging step 115, as a voltage booster.

[0076] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention. In particular, in a variant, the voltage booster does not reuse the elements of the vehicle's powertrain. In another variant, the inverter used comprises more or less than three switching arms. Finally, the characteristics of the different variant embodiments of the invention envisaged in this application can be combined to achieve the invention, insofar as these variants are not incompatible with each other.

Claims

Claims

1. Method for charging (100) a battery (28) of an electric or hybrid vehicle, by an external direct current charging terminal (40) providing a maximum charging voltage strictly lower than a battery voltage (Vbatt), the vehicle comprising: - a charging socket connected to the charging terminal (40), - a voltage booster connected at the input to the charging socket and at the output to the battery (28), the voltage booster comprising at least one inductor (Ll, L2, L3) and at least one switching arm, the switching arm comprising a high switch (1_H, 2_H, 3_H) connected between a midpoint (Ml, M2, M3) of the switching arm and a positive terminal of the battery (28), and a low switch (1_L, 2_L, 3_L) connected between the midpoint (Ml, M2, M3) and a negative terminal of the battery (28), the midpoint (Ml, M2, M3) being connected via the inductance (Ll, L2, L3) to a positive terminal of the load socket,- a precharge capacitor (22) connected between the charging socket and the voltage booster, the charging method (100) comprising a step of precharging (105) the precharge capacitor (22), and being characterized in that the precharge step (105) comprises a switching (103) of the high switch (1_H), the low switch (1_L) of the switching arm remaining open, the switching (103) being carried out with a duty cycle (a) increasing progressively.,

2. A method of charging (100) a battery (28) of an electric or hybrid vehicle according to claim 1, wherein during switching (103), a switching frequency of the high switch (1_H) is lower than a high cut-off frequency of a bandwidth of a voltage sensor connected in parallel with the precharge capacitor (22).

3. Method for charging (100) a battery (28) of an electric or hybrid vehicle according to claim 1 or 2, in which the duty cycle evolves (a) as a function of a slope ramp capable of maintaining a charging current (I) of the precharging capacity (22) below a predetermined maximum current threshold.

4. Method for charging (100) a battery (28) of an electric or hybrid vehicle according to claim 3 in which the slope is capable of allowing reaching a set voltage (Vc*) at the terminals of the precharge capacitor (22) in less than three seconds.

5. Method for charging (100) a battery (28) of an electric or hybrid vehicle according to any one of claims 1 to 4, in which the duty cycle (a) increases from a minimum value corresponding to a closing time over a switching period, between 10qs and 200qs.

6. Charging system (2) for a battery (28) of an electric or hybrid vehicle, capable of using an external direct current charging terminal (40) providing a maximum charging voltage strictly lower than a battery voltage (Vbatt), the charging system (2) comprising: - a charging socket capable of being connected to the charging terminal (40), - a voltage booster capable of being connected at the input to the charging socket and at the output to the battery (28), the voltage booster comprising at least one inductor (L1, L2, L3) and at least one switching arm, the switching arm comprising a high switch (1_H, 2_H, 3_H) connected between a midpoint (M1, M2, M3) of the switching arm and a positive terminal of the battery (28), and a low switch (1_L, 2_L, 3_L) connected between the midpoint (M1, M2, M3) and a negative terminal of the battery (28), the midpoint (Ml, M2, M3) being connected via the inductance (Ll, L2,L3) to a positive terminal of the charging socket, - a pre-charging capacity (22) capable of being connected between the charging socket and the voltage booster, the charging system (2) comprising means for pre-charging the pre-charging capacity (22), and being characterized in that the pre-charging means comprise means for switching the high switch (1_H), leaving the low switch (1_L) of the switching arm open, with a duty cycle (a) increasing progressively.,

7. Charging system (2) for a battery of an electric or hybrid vehicle according to claim 6, in which the voltage booster comprises several inductances (L1, L2, L3) formed by stator windings of an electric motor of the vehicle, and several switching arms belonging to an inverter (24) of the vehicle, the inverter (24) being connected at the output to the stator windings and being capable of being connected at the input to the battery (28).

8. Charging system (2) of a battery of an electric or hybrid vehicle according to claim 7, in which the stator windings are connected in star to a neutral point (N) of the electric motor, and in which a switch (36) is connected on the one hand to the neutral point (N) and on the other hand to the precharge capacitor (22).

9. Charging system (2) for a battery of an electric or hybrid vehicle according to any one of claims 6 to 8, in which the switching means are configured to maintain a charging current (I) of the precharging capacity (22) below a predetermined maximum current threshold.

10. Charging system (2) for a battery of an electric or hybrid vehicle according to any one of claims 6 to 9, in which the switching means are configured to increase the duty cycle (a) from a minimum value corresponding to a closing time over a switching period, between 10qs and 200qs.

Images