Method for recharging a traction battery with a voltage source of voltage lower than that of the traction battery and corresponding vehicle

Abstract

The present invention relates to a method for recharging a traction battery (28) of an electric or hybrid vehicle, the battery being connected to a smoothing capacitor (26) and to a traction inverter (24) connected to the stator windings (L1, L2, L3) of an electric motor (20), a neutral point (N) of which is connected to a voltage source (40) delivering a voltage (VDC) lower than that of the battery (28), the inverter (24) having three switching arms each comprising a low switch (1_L, 2_L, 3_L), the battery (28) being recharged by applying a switching duty cycle (a) to the switches (1_L, 2_L, 3_L,1_H, 2_H, 3_H), the recharging method being characterized in that a first low switch (1_L) and a second low switch (2_L) close in phase while a third low switch (3_L) opens and closes in phase opposition.

Description

[0001] DESCRIPTION

[0002] Title of the invention: Method for recharging a traction battery using a voltage source lower than that of the traction battery and corresponding vehicle

[0003] The present invention relates to the fields of automobiles and electrical engineering, and more specifically concerns a method for recharging a traction battery of an electric or hybrid vehicle, and an electric or hybrid vehicle having means for implementing such a method.

[0004] An electric or hybrid vehicle has a high-voltage traction battery, with a maximum no-load voltage generally between 400 and 800V (volts), which is discharged to power the vehicle's electric traction motor. The traction battery must therefore be recharged from a charging station external to the vehicle. When the charging station is capable of providing a voltage higher than the maximum no-load voltage of the traction battery, simply connect the outputs of the charging station to the terminals of the vehicle's traction battery to recharge it.

[0005] However, some charging stations only provide a voltage lower than the maximum no-load voltage of the traction battery. In particular, some charging stations can only provide a maximum of 400V. To recharge a traction battery with a voltage higher than 400V with such a charging station, the outputs of the charging station must therefore be connected to the input of a voltage booster, the output of which, providing a voltage higher than the voltage of the traction battery to be recharged, is connected to the terminals of the latter.

[0006] Such a voltage booster comprises at least one inductor, one capacitor and two switches. Given the power that these components must support, they represent a significant cost. In order to reduce the cost of an electric or hybrid vehicle incorporating such a voltage booster, it is often made by reusing the power components already present in the vehicle, for example the stator windings of the vehicle's electric motor, the switches of the vehicle's traction inverter, and a smoothing capacitor connected to the terminals of the traction battery in the vehicle. When the vehicle's stator windings are used as inductors for the vehicle's voltage booster, the rotor of the electric motor is of course not powered.However, depending on the operation of the traction inverter switches during a traction battery recharge, a very high induced voltage may be present at the rotor terminals and damage it, due to a coupling between the stator inductances and the rotor inductance. Significant iron losses also occur when a strong magnetic field appears in the electric motor during this recharge and reduce the efficiency of the recharge. They also risk damaging the rotor by causing significant heating of the rotor. Finally, due to the coupling between the stator inductances and the rotor, the current ripples vary depending on the position of the rotor and can also reduce the efficiency of the recharge.

[0007] By choosing simultaneous operation of the switches, the resulting stator magnetic field created in the electric motor is almost zero and these disadvantages are very limited, but at the cost of a very strong current ripple at the input and output of the voltage booster, which can end up damaging the traction battery and disrupting the operation of the charging device.

[0008] There is therefore a need to improve the implementation of the voltage boost function in an electric or hybrid vehicle, for recharging its traction battery, which is inexpensive while limiting iron losses, and which does not damage the vehicle's electric traction motor.

[0009] The present invention aims to remedy at least in part the aforementioned drawbacks by providing a method for recharging a traction battery of an electric or hybrid vehicle, as well as an electric or hybrid vehicle, using a voltage booster which reuses a traction inverter and an electric motor of the vehicle for recharging the traction battery, while having a switching scheme for the switches of the traction inverter, which limits both the current ripples at the input of the voltage booster and the iron losses in the electric motor.

[0010] To this end, the invention proposes a method for recharging a traction battery of an electric or hybrid vehicle, the vehicle further comprising a smoothing capacitor and a traction inverter, the smoothing capacitor and the input of the traction inverter being connected to the terminals of the traction battery, the outputs of the traction inverter being connected to stator windings of an electric traction motor of the vehicle, and a neutral point of the electric traction motor being connected to a positive terminal of a voltage source delivering a voltage lower than the voltage at the terminals of the traction battery, the traction inverter having three switching arms each comprising a low switch and a high switch, the recharging method comprising a step of recharging the traction battery being carried out by applying a switching duty cycle to the switches,the recharging method being characterized in that during the recharging step, a first and a second of the low switches close in phase while a third of the low switches opens and closes in phase opposition with respect to the first and second low switches.,

[0011] It should be noted that in this application, the traction battery is understood as a battery powering the inverter and the electric motor when the vehicle is running, unlike a possible service battery of the vehicle powering a low-voltage electrical network of the vehicle (for example 14V) to which various consumers are connected, including a main computer of the vehicle. The traction battery can therefore also be understood as a propulsion battery depending on the electric motor used. Unless otherwise stated, the battery referred to in this application is the traction battery of the vehicle. Similarly, the motor and the inverter in this patent application refer to an electric traction or propulsion motor and respectively to a traction or propulsion inverter of the vehicle, unless otherwise stated.Finally, the terms “charge” or “recharge” are considered equivalent in this application.

[0012] Furthermore, in this patent application, unless otherwise stated, an input or output connection of a functional assembly such as the inverter or the voltage booster is understood to be a connection to the terminals of this input or respectively this output, that is to say a parallel connection to this input or respectively this output, the terms input and output being related to the function concerned. Here the inverter is in particular connected at the output (with respect to its inverter function) to the stator windings of the electric motor of the vehicle.

[0013] Each switching arm of the inverter usually comprises two controlled switches, including a high switch, connected to the positive input terminal of the inverter, itself connected to the positive terminal of the traction battery when the relays or switches for connection to the battery are closed, and a low switch, connected to the negative input terminal of the inverter, itself connected to the negative terminal of the traction battery when the relays or switches for connection to the battery are closed. Each switching arm therefore comprises a high switch and a low switch connected in series, a midpoint between the two switches being connected to a stator winding of the electric traction motor.

[0014] In addition, the traction inverter may comprise more than three switching arms depending on the number of phases of the electric traction motor. In this case, the person skilled in the art will be able to adapt the switching scheme proposed by the invention depending on this number of phases, for example for a motor having six phases and an inverter having six switching arms, four low switches of the inverter operate in phase and two other low switches of the inverter operate in phase opposition with the four previous low switches.

[0015] Of course, although the operation of the high switches is not mentioned, each high switch always operates in phase opposition with the low switch of the same arm, so as not to short-circuit the traction battery, that is to say that when the high switch of an arm is closed, then the low switch of this arm is open.

[0016] Thanks to the invention, the recharging of the traction battery by a charging terminal providing a voltage lower than that of the battery, uses a voltage booster of inexpensive additional cost compared to a vehicle without a voltage booster, since the voltage booster reuses many elements of the vehicle's traction chain. In addition, the recharging method according to the invention achieves a compromise between, on the one hand, the amplitude of the current ripples at the input and output of the voltage booster during recharging, and on the other hand the amplitude of the voltage induced in the rotor due to the use of the stator windings. Thus, the recharging method does not damage either the traction battery or the electric motor, and has limited iron losses, therefore a good efficiency of the recharging process of the traction battery.

[0017] According to a preferred and optional characteristic of the recharging method according to the invention, the recharging step is preceded by a step of measuring the angular position of an axis of a rotor winding of the electric traction motor, and a step of choosing the third low switch as the one of the low switches which is capable of charging that of the stator windings with an axis forming the largest angle with the measured angular position of the axis of the rotor winding. This characteristic makes it possible to minimize the direct component of the stator current in a Park frame of the electric motor, and therefore to minimize the voltage induced on the rotor. Of course, the axis of a winding is taken here, when the winding is made up of a set of turns superimposed on each other, as the axis orthogonal to these turns and passing through their middle.When a winding comprises several sets of turns, the axis of the winding corresponds in a similar way to the main direction of the magnetic flux formed by the sets of turns. Therefore, in this characteristic of the invention, the stator winding forming a magnetic flux whose main direction is the furthest from the main direction of the magnetic flux formed by the rotor winding is chosen. The angle considered is therefore in absolute value.

[0018] According to another preferred and optional characteristic of the recharging method according to the invention, the latter comprises a step of pre-positioning the axis of the rotor winding, orthogonally to the axis of one of the stator windings, following the measurement step and preceding the step of choosing the third low switch as being the one which is capable of charging said stator winding with an axis which has thus become orthogonal to the axis of the rotor winding.

[0019] This other feature allows the direct component of the stator current to be completely cancelled during battery recharging, and therefore the voltage induced on the rotor to be cancelled.

[0020] Optionally, the pre-positioning step is conditioned by the fact that one of the stator windings forms an angle with the axis of the rotor winding, less than a threshold value. Thus, if during the step measuring the angular position of the axis of the rotor winding, it is found that this axis is aligned or almost aligned with the axis of one of the stator windings, which implies a strong direct component of the stator current during recharging, therefore a strong voltage induced on the rotor, the rotor winding is pre-positioned so that its axis is perpendicular to that of one of the stator windings, which will be supplied in phase opposition with the other two stator windings. This will avoid this voltage induced on the rotor during recharging.

[0021] The pre-positioning step comprises, for example, a step of supplying power to the rotor winding and two of the stator windings distinct from the stator winding whose axis is made orthogonal to the axis of the rotor winding by the pre-positioning step. The recharging method according to the invention has a low production cost and is simple to implement, because it is carried out partly in software in a control member of the inverter such as a microcontroller and partly in hardware in components already present in the powertrain of the electric or hybrid vehicle.

[0022] The invention also relates to an electric or hybrid vehicle comprising a traction battery, a smoothing capacitor and a traction inverter, the smoothing capacitor and the input of the traction inverter being able to be connected to the terminals of the traction battery, the outputs of the traction inverter being connected to stator windings of an electric traction motor of the vehicle, and a neutral point of the electric traction motor being able to be connected to a positive terminal of a voltage source delivering a voltage lower than the voltage at the terminals of the traction battery, the traction inverter having three switching arms each comprising a low switch and a high switch, the electric or hybrid vehicle comprising means for recharging the traction battery capable of applying a switching duty cycle to the switches,the electric or hybrid vehicle being characterized in that the recharging means are configured to close a first and a second of the low switches in phase and to open and close a third of the low switches in phase opposition with respect to the first and second low switches.,

[0023] The electric or hybrid vehicle according to the invention further comprises a switch comprising a first terminal connected to the neutral point and a second terminal connected to the positive terminal of the voltage source, and a capacitor connected on the one hand to the second terminal of the switch and on the other hand to a negative input terminal of the traction inverter. The capacitor makes it possible to avoid an excessive current draw in the stator inductances when starting the charge, and the switch makes it possible to disconnect this capacitor from the neutral point before a rolling phase of the vehicle.

[0024] The electric or hybrid vehicle according to the invention preferably comprises means for measuring the angular position of an axis of a rotor winding of the electric traction motor, and means for choosing the third low switch as that of the low switches which is capable of loading that of the stator windings with the axis forming the largest angle with the measured angular position of the axis of the rotor winding by the measuring means.

[0025] It also preferably comprises means for pre-positioning the axis of the rotor winding, orthogonally to the axis of one of the stator windings, the third low switch being chosen by the selection means as being the one capable of loading said stator winding with an axis made orthogonal to the axis of the rotor winding by the pre-positioning means.

[0026] The pre-positioning means comprise, for example, means for supplying the rotor winding and two of the stator windings distinct from the stator winding, the axis of which is made orthogonal to the axis of the rotor winding by the pre-positioning means.

[0027] The electric or hybrid vehicle according to the invention has advantages similar to those of the recharging method according to the invention.

[0028] 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:

[0029] [fig 1] represents a vehicle charging system according to the invention implementing the charging method according to the invention, the vehicle being connected to an external charging terminal, in one embodiment of the invention,

[0030] [fig 2] represents a first switching diagram usable in the charging system of figure 1, as well as stator currents in an electric motor of the vehicle, and an input current in the corresponding charging system, this first switching diagram not being proposed by the invention,

[0031] [fig 3] represents a second switching scheme usable in the charging system of figure 1, as well as stator currents in an electric motor of the vehicle and an input current in the charging system corresponding to this second switching scheme not being proposed by the invention,

[0032] [fig 4] represents steps of a recharging method according to the invention, in the embodiment of the invention of figure 1, [fig 5] represents a third switching scheme usable in the recharging system of figure 1, as well as stator currents in an electric motor of the vehicle, and an input current in the recharging system corresponding to this third switching scheme being proposed by the invention,

[0033] [fig 6] represents the electric motor of the vehicle of figure 1, in a case of use of the embodiment of figure 1, and in particular a position of a rotor winding of the motor relative to the stator windings of the motor,

[0034] [fig 7] reproduces, as a function of the phase shift between the switches of a traction inverter of the vehicle of figure 1, a curve representative of the current ripple at the input of the charging system, a curve representative of the ripple of a direct component of stator current in the vehicle electric motor, a curve representative of the absolute value of this direct component and a curve representative of the absolute value of a quadratic component of the stator current, a curve representative of an average of the stator current and a curve representative of an average of the homopolar current in the electric motor, all these curves being derived from simulations carried out for a duty cycle of 0.5 and for a situation in which the axis of the rotor winding of the electric motor is aligned with the axis of one of the stator windings of the electric motor,

[0035] [fig 8] reproduces the same simulation curves as those of figure 7 in a situation where the axis of the rotor winding of the electric motor is orthogonal to the axis of one of the stator windings of the electric motor.

[0036] According to one embodiment of the invention, a vehicle according to the invention comprises a charging system shown in Figure 1, incorporating elements of the vehicle's powertrain.

[0037] In this embodiment of the invention, the vehicle comprises a traction battery 28 with a nominal no-load voltage of 800V. The traction 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 charging terminal 40, capable of supplying 400V at most.

[0038] The charging terminal 40 comprises internal contactors closing before the start of a recharge of the traction battery 28. During this charge, it behaves as a voltage source, with a VDC voltage at its terminals equal to 400V. The vehicle's charging system, connected to the charging terminal 40, comprises a switch 38, a first terminal of which is connected to the negative terminal of the charging terminal 40, and a second terminal of which is connected to a negative terminal of a capacitor 22. The capacitor 22 has a positive terminal connected to the positive terminal of the charging terminal 40 and is therefore connected in parallel to the charging terminal 40 via the switch 38. The capacitor 22 and the switch 38 form a pre-charging system at the input of the charging system. The capacitor 22 also makes it possible to filter voltage variations and to stabilize the latter from the point of view of the terminal.

[0039] The charging system further comprises a switch 36 connected on the one hand to the positive terminal of the 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. A negative terminal of the voltage booster is connected to the negative terminal of the capacitor 22. The voltage booster is therefore connected at the input to the capacitor 22 via the switch 36, and is connected at the output to the traction battery 28.

[0040] The voltage booster consists of stator windings L1, L2, L3 of a three-phase electric motor 20 (referenced figure 6) for traction of the vehicle, a traction inverter 24 and a smoothing capacitor 26 at the output of the voltage booster, the smoothing capacitor 26 being connected to the terminals of the traction battery 28 via relays or switches 32 and 34.

[0041] The stator windings L1, L2, L3 are connected in star and therefore connected together at the neutral point N.

[0042] A first switching arm of the inverter 24 comprises a high switch 1_H, a first terminal of which is connected to a positive output terminal of the voltage booster, and a second terminal of which is connected to a free end of the stator winding L1, that is to say to the end of the stator winding opposite the neutral point N. The first switching arm also comprises a low switch 1_L, a first terminal of which is connected to the free end of the stator winding L1 and a second terminal of which is connected to a negative output terminal of the voltage booster.

[0043] The positive output terminal of the voltage booster is connected to a terminal of the switch 32 and to a positive terminal of the smoothing capacitor 26, while the negative output terminal of the voltage booster is connected to a terminal of the switch 34 and to a negative terminal of the smoothing capacitor 26.

[0044] Similarly, the traction inverter 24 comprises a second switching arm comprising a high switch 2_H, a first terminal of which is connected to the positive output terminal of the voltage booster, and a second terminal of which is connected to a free end of the stator winding L2. The second switching arm also comprises a low switch 2_L, a first terminal of which is connected to the free end of the stator winding L2 and a second terminal of which is connected to the negative output terminal of the voltage booster.

[0045] Finally, the traction inverter 24 comprises a third switching arm comprising a high switch 3_H, a first terminal of which is connected to the positive output terminal of the voltage booster, and a second terminal of which is connected to a free end of the stator winding L3. The third switching arm also comprises a low switch 3_L, a first terminal of which is connected to the free end of the stator winding L3 and a second terminal of which is connected to the negative output terminal of the voltage booster.

[0046] 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 therefore comprises a control circuit (not shown) capable of controlling these switches so as to make them switch according to a duty cycle a. This control circuit is part of the vehicle's charging means.

[0047] In order to better understand the advantages of the recharging method according to the invention, we will now describe in relation to Figures 2 and 3, switching diagrams not proposed by the invention but which can be envisaged for recharging the traction battery 28, and the associated disadvantages.

[0048] In these figures, as well as in figure 5 described later, the duty cycle a corresponds to the ratio between the closing time of the low switches 1_L, 2_L and 3_L and the switching period Tpwm, which is the inverse of the frequency f of this switching. In other words, over a switching period Tpwm, the low switches are closed a *Tpwm microseconds and open (1- a) *Tpwm microseconds, these opening and closing times being able to be distributed over the switching period. For a switching frequency of 20kHz (kiloHertz), the switching period Tpwm is 50ps (microseconds).

[0049] Furthermore, in these figures, the curves V1_L, V2_L and V3_L represent the control voltages of the low switches 1_L, 2_L and 3_L respectively in volts although the units are not shown. In the case of Figure 2, these control voltages are non-zero over a closing time interval of duration a *Tpwm, this time interval being identical for the three low switches 1_L, 2_L and 3_L, that is to say that they are closed at the same time over a switching period, while the high switches 1_H, 2_H and 3_H are open over this time interval. This is therefore a so-called pulsed control.

[0050] The stator currents II, 12, 13 flowing respectively in the stator windings L1, L2, L3 increase during the charging of the inductances constituted by these windings, that is to say during the closing of the low switches 1_L, 2_L and 3_L, and decrease during the charging of the smoothing capacitor 26, that is to say during the opening of the low switches 1_L, 2_L and 3_L corresponding to a period of closing of the high switches 1_H, 2_H and 3_H.

[0051] The current lin at the input of the voltage booster is equal to the sum of the stator currents II, 12, 13 and therefore presents a strong variation over a switching period.

[0052] As a result, this pulsed command causes a strong current ripple in the load terminal 40 because the sum of the stator currents II, 12, 13 have their maxima positioned at the same time. On the other hand, this pulsed command produces a weak stator field, therefore a weak induced voltage at the rotor of the electric motor 20, and consequently low iron losses in the electric motor 20.

[0053] In fact the induced voltage Vf at the rotor is expressed as:

[0054] Vf = Rf*If + di f / dt, where * is the multiplication operator, d. / dt the derivative with respect to time t, Rf is the rotor resistance, If the rotor supply current, and if is the rotor flux, which is: if = (3 / 2) * Maf * Id + Lf * If where Maf is the mutual inductance between the rotor and the stator of the electric motor 20, and Id is the direct component of the stator current of the electric motor 20, expressed in the Park frame.

[0055] The rotor power supply being zero, we have: Vf = dlpf / dt and if = (3 / 2) * Maf * Id

[0056] However, during pulsed control, the stator windings being supplied at the same time each with a quasi-identical current (the stator inductances being configured to be equal but not generally being completely identical), they produce magnetic fields which almost cancel each other out, given the configuration of the stator windings, regularly distributed around the rotor. Thus the rotor flux if produced at the rotor is very low and the voltage Vf induced at the rotor also.

[0057] In the case of Figure 3, the low switches 1_L, 2_L and 3_L close for the same duration but in a staggered manner relative to each other. Indeed, the switching period being divided into sixths, the low switch 1_L is closed for the first three sixths of the switching period, and open for the last three sixths of the switching period, while the low switch 2_L is closed from the third to the fifth sixth inclusive of the switching period and the low switch 3_L is closed for the first sixth of the switching period and the last two sixths of the switching period. This control of the switches is said to be interleaved.

[0058] The stator currents II, 12, 13 flowing respectively in the stator windings L1, L2, L3 therefore increase and decrease out of phase with respect to each other, which is similar to a phase shift. By equating the switching period to 180°, the stator currents II, 12, 13 are therefore 120° out of phase with each other. The current lin at the input of the voltage booster being the sum of these stator currents II, 12, 13, therefore has a low current ripple.

[0059] However, this interlaced control produces a very high induced voltage Vf on the rotor.

[0060] Indeed, since the stator currents II, 12, 13 are out of phase with each other, the stator current vector Is resulting from the vector sum of the stator currents II, 12, 13 vectorized in directions angularly offset by 120°, is a vector rotating at the speed corresponding to the switching frequency. For example, for a switching frequency of 20kHz, with a machine with two pairs of poles per phase, the vector Is will make a complete mechanical revolution in 2 / 20000 = 100ps. The direct component Id of the stator current will therefore present strong variations during the switching period (it should be noted that the rotor does not rotate, therefore the Park reference frame is fixed relative to the stator), which implies a very high induced voltage Vf at the rotor. Similarly, the magnetic fields created by the stator windings are out of phase with each other; the resulting magnetic flux is very significant and generates high iron losses.

[0061] The invention makes it possible to overcome these drawbacks thanks to the recharging method 100 shown in Figure 4 and implemented in the recharging system of Figure 1. The recharging method 100 is for example implemented in software in a microcomputer controlling the traction inverter 24 and in hardware by the traction inverter 24, its control circuit and the measuring means to which the traction inverter is connected, such as a resolver.

[0062] The recharging method therefore comprises a recharging step 140, implementing a switching diagram shown in Figure 5.

[0063] During the recharging step 140, the first and second low switches 1_L and 2_L respectively of the first and second switching arms are closed at the same time over a time interval of duration a *Tpwm over the switching period, and open over the remainder of the switching period, while the third low switch 3_L of the third switching arm is open over the time interval corresponding to the closing of the first and second low switches 1_L and 2_L, and closed over a time interval of duration a *Tpwm over the remainder of the switching period.

[0064] The principle of this switching scheme used throughout the recharging step 140 is to not create a rotating vector while not having a pulsed command. One of the low switches therefore closes in phase opposition with the other two low switches, which close in phase.

[0065] Of course, the low switch that switches in phase opposition with the other two low switches is not necessarily that of the third switching arm. The choice of this low switch is made during a previous step 130 which will be detailed later.

[0066] Furthermore, in the example of Figure 5 the duty cycle a is 0.5 but it can of course be smaller or larger. The duty cycle a is determined as a function of the state of charge of the traction battery 28. For example, if this state of charge corresponds to a voltage Vbatt of 700V at the terminals of the traction battery 28, to have an average voltage of 400V seen from the charging terminal 40, we choose: a = 1- VDC / Vbatt = 1- 400 / 700 = 0.43.

[0067] In this case the low switches will all be open for a duration equal to 0.14 times the switching period.

[0068] Thanks to the switching scheme in Figure 5, the current lin at the input of the voltage booster has a low current ripple, because the sum of the stator currents II, I2 and I3 varies as one of the stator currents is in phase with another of the stator currents. The current ripple is therefore three times lower than with pulsed control.

[0069] Furthermore, thanks to the invention, the stator current vector Is is always directed along the axis of the stator winding corresponding to the low switch which is in phase opposition with the other two. The resulting magnetic field created by the stator windings is therefore also directed along this direction, as illustrated in Figure 6.

[0070] In this figure 6 are represented the axes a, b, c of the respective stator windings L1, L2, L3 of the three-phase motor 20, offset from each other by an angle of 120°.

[0071] The stator winding L1 powered by the stator current II creates the magnetic field 4>1, the stator winding L2 powered by the stator current 12 creates the magnetic field 2 and the stator winding L3 powered by the stator current 13 creates the magnetic field CD. We see that with the commutation diagram of figure 5, the vector sum 01 + 02 of the magnetic fields created by the stator windings L1 and L2 is directed along the c axis since the magnetic fields 01 and 02 have the same value and are offset on either side of the c axis by the same acute angle of 60°.

[0072] Furthermore, the direct component Id of the stator current in the Park frame being the projection of the stator current vector Is on the axis d of the rotor (or more precisely of the rotor winding R), we see that this current Id is a priori not zero, and neither is its variation. The induced voltage Vf at the rotor is therefore non-zero except when the current Id is zero, that is to say when the axis d is orthogonal to the axis c or more generally to the axis of the stator winding corresponding to the low switch closing in phase opposition with the other two low switches.

[0073] In order to minimize the induced voltage Vf at the rotor and therefore the iron losses in the electric motor 20, the current Id is minimized and for this purpose the low switch closing in phase opposition with the other two low switches is chosen, the one whose corresponding stator winding has an axis forming the largest acute angle (in absolute value) with the axis d of the rotor winding R, not powered.

[0074] For this, the recharging method 100 comprises, prior to the recharging step 140, a step 110 of measuring the angular position P of the axis d of the rotor relative to a reference axis z, here identical to the axis a of the stator winding L1. This angular measurement P makes it possible to determine the acute angle yl (equal to P here given the choice of the reference axis z) that the axis d of the rotor makes with the axis a of the stator winding L1, the acute angle y2 that the axis d of the rotor makes with the axis b of the stator winding L2, and the acute angle y3 that the axis d of the rotor makes with the axis c of the stator winding L3, and to determine in particular what is the largest acute angle in absolute value between these three angles yl, y2 and y3.

[0075] The acute angle y3 being, in this case of use of the invention, greater in absolute value than the acute angles yl and y2, it is judicious to choose the third low switch 3_L as the one closing in phase opposition with the first and second low switches 1_L and 2_L.

[0076] However, in order to completely or almost completely cancel the direct component Id of the stator current, the measurement step 110 is followed by a step 120 of prepositioning the axis d of the rotor winding R, so as to make it orthogonal to one of the axes a, b or c of the stator windings L1, L2 or L3. In this example of use of the invention, the axis d of the rotor winding R is made orthogonal to the axis c of the stator winding L3, which makes it possible to slightly modify the position of the axis d of the rotor winding R.

[0077] For this, for example, the rotor winding R is temporarily supplied with a direct current of 5A (amperes), the stator winding L1 with a direct current of 70A and the stator winding L2 with a direct current of -70A. Alternatively, the prepositioning uses mechanical means. Optionally, this prepositioning step 120 of the recharging method 100 does not take place if the axis d of the rotor winding R has an angular deviation close to 90° with one of the axes a, b or c of the stator windings L1, L2 or L3, for example close to 90° to within 5°.

[0078] Alternatively, this step 120 of pre-positioning the recharging method 100 only takes place if the axis d of the rotor winding R is almost aligned with one of the axes a, b or c of the stator windings LI, L2 or L3, for example has an acute angle of 5° in absolute value with one of these axes a, b or c.

[0079] The next step of the recharging method 100 is a step 130 of choosing the low switch as the one closing in phase opposition with the other low switches. In the example of use developed here, this is the third switch 3_L, the axis of the stator winding L3 having been made orthogonal to the axis d of the rotor winding R. More generally in this step 130, the low switch closing in phase opposition with the other two low switches is chosen, the one whose corresponding stator winding has an axis forming the largest acute angle (in absolute value) with the axis d of the rotor winding R, not powered.

[0080] The next step of the recharging method 100 is the recharging step 140 using the switching scheme described above in relation to FIG. 5.

[0081] Figure 7 is now described, showing different simulation curves which are a function of the switching phase shift between the low switches 1_L, 2_L and 3_L during the recharging step 140.

[0082] Indeed, in this figure 7, the X axes of the abscissas expressed in degrees correspond to the phase shift between the application of successive commands of two switching arms. For example, a phase shift of 100° means that the low switch 2_L is closed with a phase shift of 100° compared to the closing of the low switch 1_L, and that the low switch 3_L is closed with a phase shift of 100° compared to the closing of the low switch 2_L. This phase shift of 100° corresponds to a time interval of 100 / 180 times the switching period.

[0083] Additionally in Figure 7, the Y axes of the abscissas are expressed in amperes.

[0084] The simulation curves in Figure 7 correspond to a duty cycle of 0.5, a battery voltage of 800V, a maximum current delivered by the terminal of 360A, and a position of the d axis of the rotor winding R aligned with the position of the a axis of the stator winding Ll. The stator inductances LI, L2 and L3 are equal to 200pH (microHenry) in these simulations, and the switching frequency is 15kHz.

[0085] A first Alin curve shows the current ripple as a function of the phase shift chosen on the abscissa, i.e. the difference between the maximum value of the lin current at the input of the voltage booster, and the minimum value of the lin current at the input of the voltage booster.

[0086] Points B on this first Alin curve correspond to the switching pattern of Figure 2, points E on this first Alin curve correspond to the switching pattern of Figure 3, and point C on this first Alin curve corresponds to the switching pattern of Figure 5.

[0087] This first Alin curve shows that the switching scheme proposed by the invention has a current ripple at the input of the voltage booster that is much lower than with pulsed control.

[0088] A second curve Aid shows the ripple of the direct component Id of the stator current as a function of the phase shift chosen on the abscissa, i.e. the difference between the maximum value and the minimum value of this direct component Id.

[0089] This second Aid curve shows that the switching scheme proposed by the invention allows a variation of this direct component Id much lower than in the case of an interlaced control, and therefore much less iron losses, although the position of the rotor is not favorable to obtaining a low direct component Id of stator current.

[0090] The invention therefore allows a very good compromise between pulsed control and interlaced control.

[0091] A third curve Max | Id | shows the variation of the absolute value of the direct component Id of stator current as a function of the phase shift chosen on the abscissa, and a fourth curve Max | Iq | shows the variation of the absolute value of the quadratic component Iq of stator current in the Park frame, as a function of the phase shift chosen on the abscissa.

[0092] A fifth curve <is>shows the variation of the average of the stator currents II, 12, 13 as a function of the phase shift chosen on the abscissa, and a sixth curve <10> shows the variation of the average of the homopolar component of stator current in the Park frame, as a function of the phase shift chosen on the abscissa.

[0093] Figure 8 shows simulation curves corresponding to those in Figure 7, with the units on the abscissa and ordinate being identical and all simulation parameters being identical except for the position of the d-axis of the rotor winding R, which is 90° with the position of the axis of the stator winding connected to the bottom switch switching in phase opposition with the other two bottom switches.

[0094] For this best case of rotor position, we see that the ripple Afin of the current lin at the input of the voltage booster is identical to that of figure 7, but that the ripple Aid of the direct component Id of stator current corresponding to the commutation scheme proposed by the invention, is almost zero. The induced voltage Vf at the rotor is therefore almost zero and the iron losses are very low, by prepositioning the rotor and using the commutation scheme proposed by the invention.

[0095] 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.< / is>

Claims

CLAIMS 1- Method for recharging (100) a traction battery (28) of an electric or hybrid vehicle, the vehicle further comprising a smoothing capacitor (26) and a traction inverter (24), the smoothing capacitor (26) and the input of the traction inverter (24) being connected to the terminals of the traction battery, the outputs of the traction inverter (24) being connected to stator windings (L1, L2, L3) of an electric traction motor (20) of the vehicle, and a neutral point (N) of the electric traction motor (20) being connected to a positive terminal of a voltage source (40) delivering a voltage (VDC) lower than the voltage (Vbatt) at the terminals of the traction battery, the traction inverter (24) having three switching arms each comprising a low switch (1_L, 2_L, 3_L) and a high switch (1_H, 2_H, 3_H),the recharging method (100) comprising a step of recharging (140) the traction battery (28) carried out by applying a switching duty cycle (a) to the switches (1_L, 2_L, 3_L, 1_H, 2_H, 3_H), the recharging method (100) being characterized in that during the recharging step (140), a first (1_L) and a second (2_L) of the low switches close in phase while a third (3_L) of the low switches opens and closes in phase opposition with respect to the first (1_L) and second (2_L) low switches., 2- Recharging method (100) according to claim 1, characterized in that the recharging step (140) is preceded by a step of measuring (110) the angular position of an axis (d) of a rotor winding (R) of the electric traction motor (20), and a step of choosing (130) the third low switch (3_L) as the one of the low switches which is capable of charging that of the stator windings (L3) of axis (c) forming the largest angle (y3) with the measured angular position (P) of the axis (d) of the rotor winding (R). 3- Recharging method (100) according to claim 2, comprising a step of pre-positioning (120) the axis (d) of the rotor winding, orthogonally to the axis (c) of one of the stator windings (L3), following the measuring step (110) and preceding the step of choosing (130) the third low switch (3_L) as being the one which is capable of charging said stator winding (L3) of axis (c) thus becoming orthogonal to the axis (d) of the rotor winding (R). 4- Recharging method (100) according to claim 3, in which the prepositioning step (120) is conditioned on the fact that one of the stator windings (LI, L2, L3) forms an angle (yl, y2, y3) with the axis (d) of the rotor winding (R), less than a threshold value. 5- Recharging method (100) according to claim 3 or 4, in which the pre-positioning step (120) comprises a step of supplying the rotor winding (R) and two of the stator windings (LI, L2) distinct from the stator coil (L3) whose axis (c) is made orthogonal to the axis (d) of the rotor winding (R) by the pre-positioning step (120). 6- Electric or hybrid vehicle comprising a traction battery (28), a smoothing capacitor (26) and a traction inverter (24), the smoothing capacitor (26) and the input of the traction inverter (24) being able to be connected to the terminals of the traction battery (28), the outputs of the traction inverter (24) being connected to stator windings (L1, L2, L3) of an electric traction motor (20) of the vehicle, and a neutral point (N) of the electric traction motor (20) being able to be connected to a positive terminal of a voltage source (40) delivering a voltage (VDC) lower than the voltage (Vbatt) at the terminals of the traction battery, the traction inverter (24) having three switching arms each comprising a low switch (1_L, 2_L, 3_L) and a high switch (1_H, 2_H, 3_H),the electric or hybrid vehicle comprising means for recharging the traction battery (28) capable of applying a switching duty cycle (a) to the switches (1_L, 2_L, 3_L, 1_H, 2_H, 3_H), the electric or hybrid vehicle being characterized in that the recharging means are configured to close a first (1_L) and a second (2_L) of the low switches in phase and to open and close a third (3_L) of the low switches in phase opposition with respect to the first (1_L) and second (2_L) low switches., 7- Electric or hybrid vehicle according to claim 6, further comprising a switch (36) comprising a first terminal connected to the neutral point (N) and a second terminal connected to the positive terminal of the voltage source (40), and a capacitor (22) connected on the one hand to the second terminal of the switch and on the other hand to a negative input terminal of the traction inverter (24). 8- Electric or hybrid vehicle according to claim 6 or 7, further comprising means for measuring the angular position of an axis (d) of a winding rotor (R) of the electric traction motor (20), and means for choosing the third low switch (3_L) as that of the low switches which is capable of loading that (L3) of the stator windings of axis forming the largest angle (y3) with the measured angular position (P) of the axis (d) of the rotor winding (R) by the measuring means. 9- Electric or hybrid vehicle according to claim 8, comprising means for pre-positioning the axis (d) of the rotor winding (R), orthogonally to the axis (c) of one of the stator windings (L3), the third low switch (3_L) being chosen by the selection means as being the one capable of charging said stator winding (L3) of axis (c) made orthogonal to the axis (d) of the rotor winding (R) by the pre-positioning means. 10- Electric or hybrid vehicle according to claim 9, in which the pre-positioning means comprise means for supplying the rotor winding (R) and two of the stator windings (LI, L2) distinct from the stator winding (L3) whose axis (c) is made orthogonal to the axis (d) of the rotor winding (R) by the pre-positioning means.

Images