Method for heating a battery for an electric vehicle system

Abstract

The invention relates to a method for heating a battery (10) for an electric vehicle system (1), the electric vehicle system (1) comprising the battery (10), an inverter (11) connected to the battery (10), and an electric machine (12) connected to the inverter (11), the inverter (11) being capable of enabling an exchange of electrical energy between the battery (10) and the electric machine (12) so as to heat the battery (10). The invention further relates to the electric vehicle system comprising the battery (10), the inverter (11), and the electric machine (12). The invention also relates to the electric vehicle comprising the electric vehicle system. Figure 1

Description

Title of the invention: Method for heating a battery for an electric vehicle system. Technical field of the invention

[0001] The present invention relates to the technical field of batteries for electric vehicles. More particularly, the present invention relates to a method for heating a battery for an electric vehicle system.

[0002] The invention also relates to the electric vehicle system for which the battery heating process is implemented. State of the art

[0003] Lithium batteries in general, and lithium iron phosphate (LFP) batteries in particular, offer several advantages that explain their increasing use in electric vehicles. For example, LFP batteries offer enhanced safety thanks to improved thermal and chemical stability, thus reducing the risks of overheating and fire. Furthermore, LFP batteries are more durable, withstanding a greater number of charge-discharge cycles, which extends their lifespan. LFP batteries are also more environmentally friendly, as they use less toxic and more abundant materials than other types of lithium-ion batteries. Finally, their production cost is often lower, making them attractive for a wide range of applications, including the manufacture of electric vehicles.

[0004] LFP batteries experience a performance degradation under cold conditions, such as in winter. At low temperatures, the electrochemical reaction inside the battery slows down, which reduces the battery's power output. This results in a decrease in operating time and an increase in charging time. Furthermore, cold temperatures increase the battery's internal resistance, leading to a loss of energy efficiency.

[0005] These combined factors therefore make LFP batteries less efficient in cold climates, which can pose challenges for their use in electric vehicles or energy storage systems in regions where winter temperatures are severe.

[0006] For example, an electric car user equipped with an LFP battery who parks their vehicle outside on a cold winter day will have to wait longer for charging due to the low temperatures which degrade the power of the LFP battery.

[0007] There is therefore a need to warm up the LFP battery, especially in cold weather, in order to compensate for the degradation of the performance of said LFP battery.

[0008] An existing solution is to use auxiliary heating devices such as immersion heaters (TPCs) in the cooling circuit, or a heating mat placed in the bottom of the battery tray.

[0009] However, these solutions have several drawbacks: they are expensive and require an additional and time-consuming manufacturing step during the production of electric vehicles. Furthermore, the addition of auxiliary components increases the risk of electric vehicle failure. Moreover, the auxiliary components heat the entire battery module, including the casing and the water circuit, whereas only the heating of the cell electrochemistry is necessary, resulting in wasted energy.

[0010] Object and invention

[0011] The present invention aims to provide a solution that addresses all or part of the aforementioned problems.

[0012] This objective can be achieved through the implementation of a method for heating a battery for an electric vehicle system, the electric vehicle system comprising: - a battery configured to provide direct current voltage and electrical energy, - an inverter connected to the battery and capable of generating alternating current voltage (ACV) from the direct current voltage, - an electrical machine connected to the inverter and configured to receive alternating voltage, the inverter being configured to present a first configuration in which the inverter ensures a transfer of electrical energy from the battery to the electric machine, and a second configuration in which at least part of the electrical energy is returned from the electric machine to the battery through the inverter,

[0013] the reheating process comprising the following steps: - Commanding the inverter so that said inverter is in the first configuration, - Supplying the alternating voltage generated by the inverter to the electrical machine, - Modifying a stator current in a stator of the electrical machine, - Detecting a switching value relative to the stator current, - upon detection of the switching value, modification of the inverter configuration so that said inverter is in the second configuration so that at least part of the electrical energy is returned from the electrical machine to the battery through the inverter.

[0014] When the inverter is in the second configuration, the return of at least part of the electrical energy to the battery may be intended to heat the battery, and in particular the electrochemistry or active chemistry of the battery by generating joule losses in the battery.

[0015] By "through the inverter" it is meant that the inverter ensures the transfer of electrical energy from the battery to the electrical machine and vice versa, without requiring any additional cable or electrical connection external to the inverter.

[0016] Advantageously, the described heating process allows the battery to be heated without additional devices, which reduces costs and the risk of failure.

[0017] The heating process, by producing heat at the core of the active parts of the battery, is less energy-intensive than a process that uses an external heating system whose heat produced warms the chemistry of the battery cells by conduction through various walls whose non-zero specific heat unnecessarily consumes energy.

[0018] Advantageously, the described heating process allows for more efficient fast charging, even in cold weather, by preheating the battery.

[0019] The heating process may also have one or more of the following characteristics, taken alone or in combination.

[0020] The inverter can be configured to switch a periodic and alternating electric current comprising a positive half-cycle in which the value of the electric current is positive, and a negative half-cycle in which the value of the electric current is negative, the control of the inverter being configured so that the transfer of electrical energy from the battery to the electric machine takes place during the positive half-cycle, and that the transfer of at least a part of the electrical energy from the electric machine to the battery takes place during the negative half-cycle to heat the battery by Joule effect.

[0021] Advantageously, the heating process allows the electrochemistry of the battery to be heated directly while minimizing the energy lost by thermal conduction in elements near the battery cells such as an aluminum battery casing or a cooling fluid for example.

[0022] The inverter control can be configured according to a relative position of a rotor of the electric machine with respect to a stator winding of the electric machine so as to obtain a rotational torque of the electric machine lower than a threshold torque.

[0023] The threshold torque may for example be less than 300Nm, in particular less than 100Nm, preferably less than 80 Nm.

[0024] Advantageously, obtaining a rotational torque of the electric machine below a threshold torque makes it possible to minimize a rotor current, at least part of which will be returned to the battery by rectification.

[0025] The heating process may further include a step of adding a modulating electric current of variable amplitude to the stator current, the modulating electric current being intended to modulate an amplitude of the stator current.

[0026] Advantageously, the addition of a modulating electric current allows for a greater battery impedance, and therefore greater heating of the battery as well as a spreading of a spectrum of the DC voltage supplied by the battery and seen by any other component connected to the system.

[0027] The electric machine may be a permanent magnet machine, and the inverter control is configured to drive a rotational torque of the electric machine of less than 300Nm, in particular less than 100Nm, preferably less than 80 Nm.

[0028] Advantageously, a rotational torque of the electric machine less than 300Nm, in particular less than 100Nm, preferably less than 80 Nm, makes it possible to reduce vibrations that may be generated.

[0029] The electric machine can be a wound rotor machine, and the inverter control is configured so as to induce a voltage in the rotor of the electric machine lower than a threshold voltage.

[0030] The threshold voltage may be lower than the voltage supplied by the battery, which may be between 600V and 800V.

[0031] Advantageously, an induced voltage in the rotor of the electric machine below a threshold voltage makes it possible to minimize the rotor current which will be returned to the battery, in particular by rectification using rectifier diodes of an excitation chopper.

[0032] The invention further relates to an electric vehicle system comprising: - a battery configured to supply a direct current voltage and electrical energy, - an inverter connected to the battery and capable of generating an alternating current voltage from the direct current voltage, - an electrical machine connected to the inverter and configured to receive alternating voltage, the inverter being configured to present a first configuration in which the inverter ensures a transfer of electrical energy from the battery to the electric machine, and a second configuration in which at least part of Electrical energy is returned from the electric machine to the battery via the inverter.

[0033] Advantageously, the electric vehicle system allows the battery to be heated, particularly in cold weather, without the need for an external heating component to the electric vehicle system, which is economical and reduces the need for maintenance of the electric vehicle system.

[0034] The stator of the electric machine can be connected, on the one hand, to the inverter, and on the other hand, to a charging socket, in particular via a contactor.

[0035] The invention further relates to an electric vehicle comprising the electric vehicle system described above.

[0036] Brief description of the drawings

[0037] Other aspects, objectives, advantages and features of the invention will become clearer upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0038] [Fig-1] represents the electric vehicle system according to the invention.

[0039] [Fig.2] represents a configuration of the electric vehicle system in which Electrical energy is supplied to the electric machine by the battery.

[0040] [Fig.3] represents a configuration of the electric vehicle system in which Electrical energy is supplied from the electric machine to the battery.

[0041] [Fig.4a] is an array that represents vectors of a vector-based command spatial design of a three-phase propulsion system for an electric vehicle.

[0042] [Fig.4b] shows an example of a switching diagram of a three-arm inverter electrically connected between a battery and a three-phase load with the vectors of the spatial vector control of [Fig.4a].

[0043] [Fig.5a] represents an example of a d, q axis reference frame of a wound rotor.

[0044] [Fig.5b] represents an example of a d, q axis reference frame of a rotor with magnets permanent.

[0045] [Fig.6] shows an evolution of the phase current in the electrical machine and of the Battery current in three different driving scenarios.

[0046] [Fig.7] presents an example of simulation of the control modes of the [Fig.6].

[0047] [Fig.8] represents an example of a misaligned rotor position in the system of vectors of the spatial vector control.

[0048] [Fig.9] presents a modulation strategy where a peak current in one phase of the The electric machine evolves according to a low-frequency modulating pattern.

[0049] In the figures and in the following description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale in order to prioritize the clarity of the figures. Moreover, the Different embodiments and variants are not mutually exclusive and can be combined. Detailed description

[0050] The invention relates first to a method for heating a battery 10 for an electric vehicle system 1, in particular an electric vehicle propulsion system. An example of the electric vehicle system 1 is shown in [Fig. 1].

[0051] The term "battery" refers to the traction battery, that is, the battery powering an inverter and an electric machine within an electric vehicle while the vehicle is in motion, as distinct from a vehicle service battery that powers a low-voltage electrical system (e.g., 14V) to which various consumers, including the vehicle's main control unit, are connected. The traction battery can therefore also be understood as a propulsion battery, depending on the electric motor used. Unless otherwise specified, the battery referred to in the following is the vehicle's traction battery. Similarly, the electric machine and the inverter refer to a traction or propulsion electric motor and a traction or propulsion inverter of the vehicle.The electric machine comprises a stator, which generates a magnetic field, and a rotor, which is movable relative to the stator and magnetically coupled to it to convert electrical energy into mechanical energy or vice versa. Finally, the terms "heating" and "reheating" are considered equivalent.

[0052] As can be seen in [Fig. 1], the electric vehicle system 1 includes the battery 10, which is configured to supply a DC voltage Vdc and electrical energy. The battery 10 can be a lithium iron phosphate (LFP) battery. The DC voltage can, for example, be between 500V and 800V.

[0053] The electric vehicle system 1 also includes an inverter 11 connected to the battery 10, notably by electrical cables. In the example of [Fig. 1], the inverter 11 comprises three bridge arms, each bridge arm comprising two transistors Ti. The inverter 11 may alternatively consist of only two bridge arms or of more than three bridge arms.

[0054] Each transistor can be a MOSFET type transistor acting as an electrical switch and capable of switching between a first ON position in which the transistor is triggered and conducts electric current, and a second OFF position in which the transistor is blocked and does not conduct electric current.

[0055] Each transistor may include silicon carbide. Each transistor may switch at a switching frequency between 1 kHz and 20 kHz.

[0056] The inverter 11 may have a first configuration in which said inverter 11 generates a first alternating current linv. The first alternating current linv is representative of a transfer of electrical energy from the battery 10 to the electric machine 12, in particular to a stator of the electric machine 12.

[0057] The inverter 11 can also have a second configuration in which said inverter 11 supplies the battery 10 with a second alternating current Ib, also called charging current, and which is representative of a restitution of at least part of the electrical energy from the electric machine 12, in particular from the stator of the electric machine 12, to the battery 10.

[0058] The first alternating current linv may for example include one or more current pulses.

[0059] The second alternating current Ib is equivalent to the first alternating current linv filtered by the capacitance Cl and the impedance ZI equivalent to the impedance of the battery 10 and the impedance of the wiring between the battery 10 and the inverter 11.

[0060] The second alternating current Ib is intended to heat the battery 10, and in particular the electrochemistry or active chemistry of the battery 10 by joule effect, in particular in the resistive part of the impedance of the battery 10.

[0061] The electric vehicle system 1 also includes an electric machine 12 connected to the inverter 11. In [Fig. 1], the inductors L1, L2, L3 represent the stator of the electric machine 12. The stator stores the electrical energy supplied by the battery 10 and then returns at least a portion of it to the battery 10. This return of at least a portion of the electrical energy is due, among other things, to losses in the transistors Ti. The second alternating current Ib represents the return of at least a portion of the electrical energy from the electric machine 12 to the battery 10.

[0062] The inductors L1, L2, L3 can be connected on one side to the inverter 11 and on the other side to a charging socket, in particular via a contactor. In other words, the stator of the electric machine 12 can be connected on one side to the inverter 11 and on the other side to a charging socket, in particular via a contactor. Advantageously, this allows for DC charging via an external fast charging station.

[0063] One or more sensor(s) can be arranged on each phase of the electric machine 12 and can be configured to measure parameters relating to the electric machine 12 such as the currents flowing in each phase and an angular position of the rotor.

[0064] The electric vehicle system 1 may include a control unit 13 in communication, on the one hand, with one or more sensor(s) to receive a value of the currents flowing in each phase as well as information relating to the position angular velocity of the rotor, and, on the other hand, to the inverter 11 to control a state of each transistor Ti of the inverter 11, for example by switching a transistor from the conducting state to the blocking state. As an example, referring to [Fig. 6], upon detection of a switching value Imax, the control unit 13 commands the inverter 11 to switch the inverter 11 from the first configuration to the second configuration. Then, upon detection of the switching value Imin, the control unit 13 commands the inverter 11 to switch the inverter 11 from the second configuration to the first configuration.

[0065] The inverter 11 can be bidirectional, that is to say, it allows a transfer of electrical energy on the one hand, from the battery 10 to the electric machine 12, and on the other hand from the electric machine 12 to the battery 10.

[0066] The control unit 13 may include a microcontroller or a processor associated with one or more sensors arranged to measure a characteristic quantity relating to the electric machine 12. For example, the control unit 13 may include a microcontroller associated with a hall effect current sensor capable of measuring the electric current in the stator of the electric machine 12.

[0067] By the control unit 13 controls the inverter 11, it is understood that the control unit 13 can switch the transistors Ti between the ON state and the OFF state by sending a control signal to each of the transistors. The control unit 13 can control the transistors Ti by pulse-width modulation or any other modulation strategy.

[0068] In [Fig.1], an impedance ZI represents an impedance of the battery 10 and the connecting cables, and a capacitor Cl is a DC coupling capacitor intended to ensure a stable power supply to the battery 10 while limiting the overvoltages produced by the switching of the transistors Ti.

[0069] The following describes the battery heating process implemented by the electric vehicle system 1 described above.

[0070] First, the inverter 11 is controlled, notably by the control unit 13, so that said inverter 11 is in the first configuration such that the inverter 11 generates the first alternating current linv, and such that the inverter ensures a transfer of electrical energy from the battery 10 to the electric machine 12. The circulation of the first alternating current linv in the electric machine 12 results in electromagnetic energy accumulating in the stator of the machine. The accumulation of electromagnetic energy takes place during a positive half-cycle of the first alternating current linv during which the first alternating current linv is positive. The inverter 11 is then in the first configuration shown in [Fig. 2].

[0071] The second alternating current Ib generated by the inverter 11 is supplied by the battery 10 after filtering the first alternating current linv by the impedance ZI and the capacitance Cl. In other words, the voltage supplied by the battery 10 is applied, through the inverter 11, in particular through the switching of the transistors Ti of the inverter 11, to a combination of the coils L1, L2, L3 of the stator of the electric machine 12. There is a transfer of electrical energy from the battery 10 to the stator of the electric machine 12.

[0072] By "through the inverter", it is meant that the transfer of electrical energy from the battery 10 to the electrical machine 12 and vice versa, is done by a flow of current in one or more transistors Ti of the inverter 11 without having to use additional electrical connections such as electrical cables.

[0073] Figure 2 shows the first configuration of the inverter 11 in which transistors T1, T4, and T6 are conducting while transistors T2, T3, and T5 are blocked. In this configuration, the electric current flows along the arrows 11, and the current in the inductors L1, L2, and L3 increases until it reaches the switching value Imax, the switching value Imax being representative of the maximum electrical energy that one wishes to transfer to the stator of the electric machine 12. According to one possibility, the current may only flow in two phases of the electric machine 12. The current sensor transmits the information to the microcontroller or the processor included in the control unit 13. In other words, during the phase shown in Figure 2, the current is transmitted to the microcontroller or processor included in the control unit 13.[2] The electric current in the stator of the electric machine 12 integrates until it reaches an electrical energy in the stator previously fixed by a maximum current value, in other words the switching value Imax. There is a transfer of energy from the battery 10 to the stator of the electric machine 12.

[0074] The maximum current can be determined as a function of one or more parameters, for example, chosen from the following parameters:

[0075] - a need to warm up the battery 10 and a time required to reach a desired battery temperature

[0076] - a maximum current value that the stator of the electrical machine can withstand 12 or a maximum current value permitted to allow the vehicle to restart without performance limitations,

[0077] - a maximum value of the induced current allowed at the rotor when the machine Electric motor 12 has a wound rotor (with the rotor short-circuited). Indeed, in the case of a wound-rotor synchronous machine, sending current to the stator generates, by induction, a current in the rotor when the latter is short-circuited. The current depends on the position of the rotor relative to the stator phases through which current flows.

[0078] - motor parameters, for example the rotor winding can be left open, and in this case, it is the induced voltage that will impose a maximum value on the amplitude and frequency of the stator current.

[0079] The control unit 13 then detects the switching current value Imax relative to the current in one of the phases of the electric machine 12. Upon detection of the switching current value Imax, the control unit 13 modifies the configuration of the inverter 11 so that said inverter 11 is in the second configuration, allowing said inverter 11 to return, at least partially, the electromagnetic energy stored in the stator to the battery 10. In other words, the control unit 13 can command the inverter 11 to allow the transfer of electrical energy from the electric machine 12 to the battery 10.

[0080] The second alternating current Ib can be determined as a function of the first alternating current linv. For example, the second alternating current Ib can have an amplitude and an RMS value that depend respectively on the amplitude and RMS value of the first alternating current linv.

[0081] Figure 3 shows the second configuration of the inverter 11 in which transistors T1, T4, and T6 are blocked while transistors T2, T3, and T5 are conducting. In this configuration, the electric current flows along the arrows Ij. After increasing to the switching value Imax, the current in the inductors L1, L2, and L3 of the stator of the electric machine 12 decreases until it reaches a low switching threshold Imin. The current sensor transmits the information to the microcontroller or processor included in the control unit 13, which controls the switching of the inverter 11 to modify the configuration of said inverter 11 upon detection of the low switching threshold Imin. In other words, during the phase shown in Figure 3, the electric current reverses to ensure the negative part of a current pulse in the battery 10.During this phase, the electrical energy accumulated in the stator of the electric machine 12 is returned to the battery 10.

[0082] Fig. 6 shows the theoretical evolution of the phase current of the motor Im and the battery current which corresponds to the second alternating current Ib in three different control scenarios M1, M2, M3.

[0083] During the rise of the current Im in the electric machine 12 from 0 to Imax, the phase current Im follows an upward slope, showing an accumulation of electromagnetic energy in the electric machine 12. Then, during the transition from Imax to 0, the current Im in the electric machine 12 decreases, showing a restitution, at least partial, of electromagnetic energy to the battery 10.

[0084] The second alternating current Ib follows a similar pattern. During the rise of the motor current up to Imax, the battery 10 supplies the necessary second alternating current Ib, which is visible by the equivalent rise in the curve of battery 10. When the current Im decreases from Imax to 0, a change of sign is observed in the second alternating current Ib, showing that the magnetic flux has changed direction.

[0085] The second negative alternating current Ib indicates a discharge of electromagnetic energy stored in the inductances of the electrical machine 12.

[0086] Fig. 7 represents an example of simulation of the control modes of Fig. 6 for current pulses in battery 10 having a value of 500A peak.

[0087] The first alternating current linv can be generated in different ways. For example, there are six possible transistor control combinations (the vectors shown in Figures 4a and 4b) allowing control of the current in the battery 10. Figures 4a and 4b show the six combinations which correspond to six vectors of a spatial vector control in which energy transfer takes place between the electric machine 12 and the battery 10.

[0088] The choice of a combination among the combinations presented in [Fig.4a], i.e. the configuration of the inverter 11, can be defined by the electric machine 12. Indeed, the electric machine 12 must generate the lowest possible rotational torque, preferably zero torque, during the heating of the battery 10. In other words, the orientation of the stator flux can be determined so that the rotational torque of the electric machine 12 is less than or equal to a threshold torque value which can preferably be zero.

[0089] Depending on the type of electrical machine, different ways of selecting the configuration of the inverter 11 can be considered. [Fig. 5a] shows a d, q axis reference frame for a wound rotor and [Fig. 5b] shows the same d, q axis reference frame for a permanent magnet rotor.

[0090] If the electric machine 12 is a separately excited electric machine, in other words, if the rotor is wound, a zero excitation current results in a very low, almost zero, potential torque, except for the salient pole effect. The configuration of the inverter 11 is then chosen so that a magnetic flux in the electric machine 12 is aligned, as closely as possible, with the quadratic axis q of the electric machine 12. This minimizes the induced voltage in the rotor winding. In other words, the configuration of the inverter 11 is selected from the first and second configurations such that an induced voltage in the rotor of the electric machine 12 is less than a threshold voltage value, ideally less than the battery voltage 10, so that there is no current in the rotor by keeping the diodes of a rotor chopper blocked.

[0091] Depending on the voltage induced in the rotor winding of the electric machine 12, the rotor winding can either be left open or short-circuited. Generally, the winding can be short-circuited. However, the permissible short-circuit current depends on the thermal capacitance of the rotor winding and the initial temperature of the electric machine 12. If a maximum acceptable temperature is reached, the electric current in the stator can be adjusted accordingly. modifying the stator voltage to keep the rotor temperature below an acceptable limit.

[0092] In order to control the current and voltage induced in the rotor, the configuration of the inverter 11, in other words, the way in which the inverter's bridge arms are powered, can be chosen according to the relative position of the rotor with respect to the stator winding when the electric machine 12 or the electric vehicle is at rest. Indeed, at rest, the position of the rotor poles with respect to the stator winding is random. The power supply to the electric machine 12 can be adjusted so as to align the magnetic field in the electric machine 12 with the quadratic axis q in Figures 5a and 5b. This makes it possible to reduce the magnetic coupling between the stator and the rotor of the electric machine 12.

[0093] If the rotor stops in an intermediate position where precise power selection is impossible, it is possible to alternate between two arms of the inverter 11 while the other two arms are regularly supplied with power. This creates an oscillation of the stator's magnetic field between two positions. The frequency of this oscillation can be adjusted so that the electrical machine 12 best filters out noise and vibrations due to electromagnetic forces created by the oscillation of the magnetic field in the stator.

[0094] If the electric machine has permanent magnets, the configuration of the inverter 11 can be chosen so that the magnetic flux produced in the electric machine 12 is as close as possible to the axis d, thus resulting in minimal or zero rotational torque. The configuration of the inverter 11 can then be selected from the first and second configurations such that the rotational torque of the shaft of the electric machine 12 is less than a threshold torque value, which may be zero.

[0095] In the case of a synchronous-reluctant magnet machine, i.e., an electrical machine operating on the basis of a combination of a reluctant torque and a synchronous torque, the electrical machine 12 can be aligned so that the angle of the magnetic flux minimizes the rotational torque. The angle of the magnetic flux can vary according to the level of salience.

[0096] The amplitude of the current pulses in the battery 10 can be adjusted so that the reverse magnetic field generated by the magnets of the electric machine 12 does not cause the demagnetization of said magnets.

[0097] If the rotor of the electric machine 12 is in a misaligned position, that is, a position that is not aligned with one of the vectors VI to V6 shown in [Fig. 4b], alternative switching of the inverter 11 between two configurations of the inverter 11, each corresponding to a vector framing the rotor position, is possible. An example of a misaligned rotor position is shown in the [Fig. 8]. In [Fig. 8], the vectors VI to V6 represent the different possible switching combinations of the transistors Ti to generate current pulses in the battery 10, while the vector Va corresponds to a misaligned rotor position. In the case of [Fig. 8], alternative switching of the inverter 11 based on the vectors that bracket the rotor position can be controlled.

[0098] A first possibility may be a switching of the inverter 11 from the combination corresponding to the vector V6 which corresponds to a transfer of electrical energy from the battery 10 to the stator, to the combination corresponding to the vector VI which corresponds to a transfer of electrical energy from the stator to the battery, or vice versa.

[0099] A second possibility is to switch the inverter 11 from the combination corresponding to vector V4, which corresponds to a transfer of electrical energy from the battery 10 to the stator, to the combination corresponding to vector V3, which corresponds to a transfer of electrical energy from the stator to the battery 10, or vice versa. In the case of any position of the stator that imposes a voltage that is not aligned with one of the six vectors shown in [Fig. 4b], it is possible to switch alternately from one vector to another, in particular according to a sequence V0 - VI - V6 - V7, and vice versa for vector Va of [Fig. 8], at a frequency similar to that of inverter operation, for example 10 kHz.

[0100] The heating of the battery 10 can be achieved by regulating the current in the stator of the closed-loop electric machine 12.

[0101] The closed-loop control makes it possible to produce a zero, oscillating or below a threshold torque torque without generating noise, regardless of the position of the rotor.

[0102] The closed-loop control can have as a setpoint a current waveform, for example a harmonic content and / or a current amplitude, in the battery 10. This makes it possible to improve the heating efficiency while minimizing the aging of the battery 10.

[0103] In the case of a wound-rotor electric machine, measuring the rotor current allows for better control of edge effects and therefore better current regulation efficiency in the rotor.

[0104] The heating process may further include a step of adding a modulating electric current of variable amplitude to the stator current. Figure 9 shows a modulation strategy where the trigger value Imax, which is also the maximum current, varies according to a low-frequency modulator, for example between 5 Hz and 60 Hz. The addition of a low-frequency harmonic allows for a higher battery impedance and therefore greater heating. Indeed, the heating of battery 10 is calculated according to the formula R.I², where R is the battery resistance 10 at a given frequency, and I is the RMS value of the low-frequency current harmonic.

[0105] Advantageously, the heating process allows the battery 10 to be heated without the addition of an additional heating device, which reduces costs and the risk of failure.

[0106] Advantageously, the heating process allows the electrochemistry of the battery 10 to be heated directly while minimizing losses by thermal dissipation in a battery 10 casing, for example.

[0107] The heating process allows the battery 10 to be heated by means of the control unit 13 and the inverter 11 already present in the electric vehicle system 1 without the need to use an additional and external battery heating component 10 to the electric vehicle system 1.

[0108] Advantageously, the heating process allows for more efficient fast charging, particularly in cold weather, by preheating the battery 10.

[0109] Advantageously, the heating process allows for a reduction in costs by eliminating the need to use auxiliary heating devices, external to the electric vehicle system 1, thus reducing the production and maintenance costs of the electric vehicle system 1.

[0110] Advantageously, the heating process allows for significant time savings during rapid charging when the battery 10 is cold.

[0111] Advantageously, the heating process makes it possible to exploit the advantage of the wound-rotor synchronous machine in order to control the torque generated in the electric machine 12, rotor heating and the noise that can potentially be generated.

[0112] Advantageously, the process, by generating heat at the heart of the battery chemistry, makes it possible to heat mainly the active part of the battery 10 with a significant energy saving compared to external heating systems where heat is produced outside the battery and then transferred by thermal conduction to the chemistry of the battery cells, heating in the process a large mass of inactive material.

[0113] Advantageously, the heating process allows regulation of the current waveform supplied by the battery 10, in particular the harmonic content and the amplitude of the current while minimizing the torque generated by the electric machine 12.

[0114] The invention further relates to the electric vehicle system 1 comprising: - the battery 10 configured to supply the direct current voltage Vdc and electrical energy, - the inverter 11 connected to the battery 10 and capable of generating the alternating current voltage Vac from the direct current voltage Vdc, - the electric machine 12 connected to the inverter 11 and configured to receive the alternating voltage Vac. The inverter 11 is configured to present a first configuration in which the inverter 11 ensures a transfer of electrical energy from the battery 10 to the electric machine 12, and a second configuration in which at least part of the electrical energy is returned from the electric machine 12 to the battery 10 through the inverter 11.

[0115] Advantageously, the electric vehicle system 1 makes it possible to heat the battery 10, particularly in cold weather, without having to use a heating component external to the electric vehicle system 1, which is economical and reduces the need for maintenance of the electric vehicle system 1.

[0116] The invention also relates to an electric vehicle comprising the electric vehicle system 1 described above.

[0117] Although the invention has been described in connection with an electric vehicle battery, other applications can be envisaged. For example, the described heating method and system can be used with any system comprising a battery connected to an inverter or rectifier, in particular a stationary battery storage system (ESS) connected to the home grid where it is desired to maintain the battery at an optimal temperature, and therefore at its rated power, regardless of the battery usage profile and the ambient temperature.

Claims

Demands

1. A method for heating a battery (10) for an electric vehicle system (1), the electric vehicle system (1) comprising: - the battery (10) configured to supply a direct current voltage (Vdc) and electrical energy, - an inverter (11) connected to the battery (10) and capable of generating an alternating current voltage (Vac) from the direct current voltage (Vdc), - an electric machine (12) connected to the inverter (11) and configured to receive the alternating current voltage (Vac), the inverter (11) being configured to have a first configuration in which the inverter (11) ensures a transfer of electrical energy from the battery (10) to the electric machine (12), and a second configuration in which at least part of the electrical energy is returned from the electric machine (12) to the battery (10) through the inverter (11),The heating process comprises the following steps: - controlling the inverter (11) so that said inverter (11) is in the first configuration, - supplying the alternating voltage (Vac) generated by the inverter (11) to the electrical machine (12), - modifying a stator current in a stator of the electrical machine (12), - detecting a switching value (Imax) relative to the stator current, - upon detection of the switching value (Imax), modifying the configuration of the inverter (11) so that said inverter (11) is in the second configuration such that at least a portion of the electrical energy is returned from the electrical machine (12) to the battery (10) through the inverter (11).

2. A heating method according to claim 1 in which the inverter (11) is configured to switch a periodic alternating electric current and comprising a positive half-cycle in which the value of the electric current is positive, and a negative half-cycle in which the value of the electric current is negative, the control of the inverter (11) being configured so that the transfer of electrical energy from the battery (10) to the electric machine (12) takes place during the positive half-cycle, and that the transfer of at least part of the electrical energy from the electric machine (12) to the battery (10) takes place during the negative half-cycle to heat the battery (10) by Joule effect.

3. A heating method according to any one of claims 1 or 2 wherein the control of the inverter (11) is configured as a function of a relative position of a rotor of the electric machine (12) with respect to a stator winding of the electric machine (12) so as to obtain a rotational torque of the electric machine (12) less than a threshold torque.

4. A heating method according to any one of the preceding claims further comprising a step of adding a modulating electric current of variable amplitude to the stator current, the modulating electric current being intended to modulate an amplitude of the stator current.

5. A heating method according to any one of the preceding claims wherein the electric machine (12) is a permanent magnet machine, and the inverter control (11) is configured to drive a rotational torque of the electric machine (12) of less than 300Nm, in particular less than 100Nm, preferably less than 80 Nm.

6. A heating method according to any one of claims 1 to 4 wherein the electric machine (12) is a wound-rotor machine, and the inverter control (11) is configured to induce a voltage in the rotor of the electric machine (12) lower than a threshold voltage.

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