A method of controlling the charging of a low-voltage battery of an electric vehicle via a high-voltage battery of the electric vehicle, corresponding power supply system and vehicle

Abstract

A method of controlling the charging of a low-voltage battery (12) of an electric vehicle (V) via a high-voltage battery (14) of the electric vehicle is described. In a first operating state of the vehicle, wherein the vehicle is on, energy is transferred from the high-voltage battery (14) to the low-voltage battery (12) via a DC / DC converter (16) of the vehicle. A request for turn-off of the vehicle is detected, and in response to the turn-off request, the vehicle passes from the first operating state to a second operating state of the vehicle, wherein the electrical apparatuses of the vehicle are off except for the high-voltage battery and the DC / DC converter, and a timer is initialized. In the second operating state of the vehicle, energy is transferred from the high-voltage battery to the low-voltage battery via the DC / DC converter, and the timer is increased at a constant rate. The vehicle passes from the second operating state to a third operating state of the vehicle, wherein all electrical apparatuses of the vehicle including the DC / DC converter are off and the charging of the low-voltage battery is interrupted, in response to at least one of the following conditions: (i) the state of charge (SOCLV) of the low-voltage battery reaches a minimum safe value; (ii) the timer reaches a timeout value; (iii) a fault in the low-voltage battery is detected; (iv) a fault in the DC / DC converter is detected; and (v) the state of charge (SOCHV) of the high-voltage battery decreases below a threshold value. A request for turn-on of the vehicle is detected and, in response to the turn-on request, the vehicle passes from the second or third operating state to the first operating state of the vehicle.

Description

[0001] “A method of controlling the charging of a low-voltage battery of an electric vehicle via a high-voltage battery of the electric vehicle, corresponding power supply system and vehicle” ****

[0002] TEXT OF THE DESCRIPTION

[0003] Field of the invention

[0004] The present invention relates to electric vehicles equipped with a high-voltage battery, for example an 800 V battery, which supplies energy mainly to the electric powertrain (for this reason also called “traction battery”), and a low-voltage battery, for example a conventional 12 V battery, which supplies some basic circuits of the vehicle. Such vehicles may include BEV (Battery Electric Vehicle) or HEV (Hybrid Electric Vehicle) vehicles.

[0005] The invention has been developed with reference to the management of the charge level or state of charge (SOC) of the low-voltage battery, which can be charged by transferring energy to it from the high- voltage battery via a DC / DC converter installed on board the vehicle.

[0006] Prior art

[0007] Some electric vehicles contain both a high-voltage battery (e.g., 800 V - also referred to as an “HV battery” in the present description) primarily devoted to power the powertrain and other relevant electrical loads (e.g., the air conditioning system of the cabin, the battery pack heating and / or cooling system, etc.), and a conventional low-voltage battery (e.g., 12 V - also referred to as an “LV battery” in the present description) devoted to power some basic electrical circuits of the vehicle, such as in traditional internal combustion engine vehicles.

[0008] In such electric vehicles, in the absence of an alternator, a DC / DC converter is usually present that is used to transfer energy from the high- voltage battery to the low-voltage battery, to maintain the charge level of the latter above a level that ensures proper functionality.

[0009] Document US 9428122 B2 is exemplary of such prior art. It discloses an active control system for a low-voltage DC / DC converter (LDC) in a vehicle. The DC / DC converter is disposed between a high-voltage battery and a low-voltage battery, and increases or decreases the voltage in two directions. A Vehicle Control Unit (VCU) is configured to control the DC / DC converter. The VCU is configured to control the converter in an active control mode not to start in order to achieve the minimum charging time of the low-voltage battery if the full-speed charging time is shorter than a first full-speed reference charging time, and to control the converter in accordance with the active control mode when the active control mode starts if the full-speed charging time is longer than the first full-speed reference charging time. In this case, the active mode is configured to charge the low-voltage battery with the output voltage of the DC / DC converter in a voltage table based on driving information.

[0010] Document CN 115649092 A is also exemplary of the prior art.

[0011] One can now think of the scenario in which the electric vehicle gets turned off (e.g., because the desired destination has been reached) at a time when the charge level of the low-voltage battery is particularly low. Since the DC / DC converter that charges the low-voltage battery stops working when the vehicle is off, it could happen that the residual energy in the low-voltage battery is so low that it is not possible to subsequently restart the electric vehicle. In fact, the low-voltage battery supplies, among its loads, also the electronic control units that manage the contactors of the high-voltage battery. In the absence of sufficient power from the low-voltage battery, therefore, the contactors cannot be operated and the high-voltage battery remains electrically isolated, and it is not even possible to transfer energy from it to the low-voltage battery via the DC / DC converter. Furthermore, keeping the low-voltage battery at a low charge level for a prolonged period of time also has negative effects of premature aging of the battery itself.

[0012] Therefore, there is a need in the art to develop a method of controlling the charging of the low-voltage battery in an electric vehicle, in order to prevent the charge level of the low-voltage battery from falling so much as to prevent a subsequent restart of the vehicle itself and / or to produce premature aging effects of the battery itself.

[0013] Object of the invention

[0014] The object of the invention is to solve the above-mentioned technical problem. In particular, the object of the invention is to provide a method of controlling the charging of the low-voltage battery in an electric vehicle (i.e. , a vehicle in which the low-voltage battery is kept charged via a DC / DC converter that transfers energy to it from a high-voltage battery, or traction battery) that allows the charge level of the low-voltage battery to always be maintained above a critical level that ensures its correct operation, even in the case in which the electric vehicle is turned off at a time when the charge level of the low-voltage battery is particularly low.

[0015] Summary of the invention

[0016] The object of the invention is achieved by a method having the features that form the subject of the following claims, which form an integral part of the technical teaching provided herein in relation to the invention.

[0017] The method may be implemented by one or more electronic control units of a vehicle, for example a control unit of the battery management system (BMS).

[0018] Furthermore, the object of the invention is achieved by a power system of an electric vehicle and by an electric vehicle having the features that form the subject of the following claims.

[0019] Brief description of the figures

[0020] The invention will now be described with reference to the attached figures, provided purely by way of non-limiting example, in which:

[0021] - Figure 1 is a block diagram exemplary of a system for controlling the charging of a low-voltage battery of an electric vehicle, according to one or more embodiments of the present description;

[0022] - Figure 2 is a state diagram exemplary of the control logic sequence implemented by a method of controlling the charging of a low-voltage battery of an electric vehicle, according to one or more embodiments of the present description;

[0023] - Figures 3 and 4 are block diagrams illustrating some steps of the method of controlling the charging of a low-voltage battery of an electric vehicle, according to one or more embodiments of the present description; and

[0024] - Figure 5 is a diagram exemplifying the time course of the state of charge of a low-voltage battery of an electric vehicle, during the execution of a method according to one or more embodiments of the present disclosure.

[0025] Detailed description

[0026] As anticipated, the invention is applicable to electric vehicles (pure, “BEV”, or hybrid, “HEV”) provided with a high-voltage battery, a low-voltage battery, and a DC / DC converter that transfers energy from the former to the latter to maintain the charge level of the low-voltage battery (here indicated with SOCLV) above a minimum threshold that ensures its correct operation. Also as discussed above, if the state of charge SOCLV of the low-voltage battery is below a certain critical threshold at the time when the vehicle is turned off and consequently the transfer of energy from the high-voltage section to the low-voltage section of the vehicle is interrupted (since the DC / DC converter is deactivated), it could happen that the residual energy in the low-voltage battery is so low that it does not allow the vehicle to be started again later. Therefore, it is preferable that, before interrupting the energy transfer from the HV battery to the LV battery, the state of charge SOCLV of the LV battery is equal to or greater than a minimum safe value that ensures the ability to restart the vehicle and also avoids the degradation or premature aging of the low-voltage battery, which is intensified if the battery is kept for relatively long periods of time at a too low charge level.

[0027] Therefore, the method according to the present invention relates to the management or control of a charging procedure of the low-voltage battery that is performed automatically, without the need for any intervention by the driver, after the vehicle has been turned off. This procedure substantially allows the low-voltage battery charging system to be kept active (i.e. , to keep active the high-voltage battery and the DC / DC converter connected to it) even after the vehicle has been turned off, if at the time of turning off it is detected that the state of charge SOCLV of the low-voltage battery is so low that it cannot ensure the subsequent restart of the vehicle and / or exposes the low-voltage battery to a risk of degradation or premature aging, until the state of charge SOCLV of the LV battery reaches at least the minimum safety value. Furthermore, as further discussed below, the method described herein allows some borderline cases to be taken into account in order to better manage the low-voltage battery charging phase.

[0028] Figure 1 is a block diagram exemplary of a system 1 for controlling the charging of the low-voltage battery, which may be implemented on board an electric vehicle V. The system 1 may comprise one or more electronic control units (ECUs) and one or more actuators, which are involved in managing the low-voltage battery charging. In particular, the system 1 includes a first electronic control unit 11 that detects and provides information relating to the state of the low-voltage battery 12, namely a signal SOCLV indicative of the state of charge (e.g., expressed as a percentage of the total capacity of the battery 12) and / or a fault signal FaultLVBatt that, if asserted, indicates a fault in the low-voltage battery 12. Electronic control unit 11 may also be referred to as an IBS (Intelligent Battery Sensor) electronic control unit. The system 1 also includes a second electronic control unit 13 that detects and provides information regarding the state of the high-voltage battery 14, namely a signal SOCHV indicative of the state of charge (e.g., expressed as a percentage of the total capacity of the battery 14). Electronic control unit 13 may also be referred to as a BMS (Battery Management System) electronic control unit. The system 1 also includes a third electronic control unit 15 that manages one or more functions of the electric powertrain and / or of the energy management system of the vehicle V, and a DC / DC converter 16 that converts the high voltage of the battery 14 to the lower voltage of the battery 12 to transfer energy from the HV battery 14 to the LV battery 12. Electronic control unit 15 may also be referred to as a VDCM (Vehicle Dynamic Control Module) electronic control unit. In particular, electronic control unit 15 receives signals SOCLV and FaultLVBatt from electronic control unit 11 and signal SOCHV from electronic control unit 13, and generates two signals DCDC_Conv_En and Chrg_Tgt that are transmitted to DC / DC converter 16; in turn, DC / DC converter 16 generates two signals FaultDCDC and Chrg_Fbk that are transmitted to electronic control unit 15. Essentially, signal DCDC_Conv_En enables (or activates) DC / DC converter 16 when asserted, while signal Chrg_Tgt is indicative of a target (low) voltage at the output of DC / DC converter 16 (substantially, the VDCM electronic control unit 15 determines, via a control algorithm, the target output voltage of the DC / DC converter 16 to charge the low-voltage battery 12 and achieve a target state of charge). Signal FaultocDc, if asserted, indicates a fault in the DC / DC converter 16 and signal Chrg_Fbk is a feedback signal provided by the DC / DC converter 16 during the charging of the low-voltage battery 12.

[0029] The system 1 implements a method of controlling the charging of the low-voltage battery 12 that can be better understood by referring to the state diagram in Figure 2. Such a method 2 can also be implemented in a distributed form (i.e. , in such a way that the operations of the method are divided among the various electronic control units of system 1 ).

[0030] Substantially, the state diagram of method 2 is traversed starting from an initial state 21 in which the vehicle V is on (e.g., the vehicle is moving from the starting point to the final destination). In state 21 , the low-voltage battery 12 is charged, via the DC / DC converter that takes energy from the high-voltage battery 14, following a “normal” and otherwise conventional charging strategy.

[0031] When vehicle V is turned off (e.g., because the driver has reached his / her final destination), condition C1 is fulfilled (e.g., a signal VehicleOffReq is asserted or set to a logical true value, VehicleOffReq = TRUE), a timer is initialized (e.g., TimerAfterRun = 0), and the method moves to the next state 22. In state 22, a charging strategy of the low- voltage battery 12 is activated, again via the DC / DC converter taking energy from the high-voltage battery 14, which has the purpose of ensuring that the state of charge SOCLV is higher than the minimum safe value before turning off the charging system (i.e., substantially the DC / DC converter 16).

[0032] As long as there are no changes in the state of vehicle V, and in particular as long as the state of charge SOCLV does not reach the minimum safe value, the method remains in state 22 and the timer TimerAfterRun is increased at constant intervals (e.g., TimerAfterRun = TimerAfterRun+TimeStep), as exemplified by the arrow C2 in the diagram in Figure 2.

[0033] If vehicle V is turned on again, condition C3 occurs (e.g., signal VehicleOffReq is de-asserted or set to a false logic value, VehicleOffReq = FALSE) and the method 2 returns from state 22 to state 21 , in which the low-voltage battery 12 is charged following the conventional charging strategy.

[0034] Alternatively, the method 2 passes from state 22 to state 23 (in which the DC / DC converter 16 is deactivated, the charging of the low-voltage battery 12 is interrupted and the timer TimerAfterRun is reset to its initial value, 0) when any of the following conditions occurs, generally indicated by arrow C4 in the diagram of Figure 2, and listed here in an order of increasing “seventy” (although not limitative in this sense): i) the state of charge SOCLV of the low-voltage battery 12 reaches the minimum safe value (possibly considering a certain margin) that allows a subsequent restart of vehicle V; this condition may be signaled by a signal SafeLV_SOC that is asserted or set to a true logic value, SafeLV_SOC = TRUE; ii) the timer TimerAfterRun reaches a maximum value TimerAfterRunLim (timeout value), beyond which the charging of the low- voltage battery 12 is interrupted in any case; this condition may be signaled by the condition TimerAfterRun = TimerAfterRunLim', iii) a fault is detected in the low-voltage battery 12, which does not allow the low-voltage battery to be charged; this condition may be signaled by signal FauftLVBatt being asserted or set to a logic true value, FauftLVBatt = TRUE; iv) a fault is detected in the DC / DC converter 16, which does not allow the low-voltage battery to be charged; this condition may be signaled by signal FaultDCDc being asserted or set to a logic true value, FaultDCDc = TRUE; and v) the state of charge SOCHV of the high-voltage battery 14 is too low (below a certain threshold value) to allow the DC / DC converter 16 to transfer energy to the low-voltage battery 12; this condition may be signaled by a signal HV_SOC_TooLow that is asserted or set to a logical true value, HV_SOC_TooLow = TRUE.

[0035] When the method 2 passes to state 23, therefore, the DC / DC converter 16 is deactivated and the charging of the low-voltage battery 12 is interrupted, and the vehicle remains substantially off and inactive. If vehicle V is turned on again, condition C5 occurs (e.g., signal VehicleOffReq is de-asserted or set to a logical false value, VehicleOffReq = FALSE) and the method 2 passes from state 23 to state 21 , in which the low-voltage battery 12 is charged following the conventional charging strategy.

[0036] As regards condition (i) that determines the passage from state 22 to state 23, the assertion of signal SafeLV_SOC to indicate that the state of charge SOCLV of the low-voltage battery 12 has reached a minimum safety value that allows a subsequent restart of the vehicle V can be carried out with hysteresis, as exemplified in Figure 3. Signal SafeLV_SOC is generated at the output of a set-reset (SR) flip-flop 31 . Basically, flip-flop 31 is set (by asserting the signal at the set input S of the flip-flop, generated by a comparator 32) when the state of charge SOCLV of the low-voltage battery 12 (e.g., sensed by the electronic control unit 11 ) is greater than or equal to a certain upper threshold SafeLV_SOC_Hi, and is reset (by asserting the signal at the reset input R of the flip-flop, generated by a comparator 33) when the state of charge SOCLV is less than or equal to a certain lower threshold SafeLV_SOC_Lo. Thus, substantially, comparators 32 and 33 together with the set-reset flip-flop 31 behave overall as a comparator with hysteresis, which asserts signal SafeLV_SOC when the state of charge SOCLV rises above the upper threshold SafeLV_SOC_Hi and de-asserts signal SafeLV_SOC when the state of charge SOCLV falls below the lower threshold SafeLV_SOC_Lo. The upper threshold SafeLV_SOC_Hi and the lower threshold SafeLV_SOC_Lo can be stored in an electronic control unit of the vehicle, and thus represent two input constants for the control algorithm. The use of two thresholds SafeLV_SOC_Hi and SafeLV_SOC_Lo allows to maintain a safety margin for the state of charge SOCLV of the low-voltage battery 12 and at the same time avoid toggling effects of signal SafeLV_SOC.

[0037] As regards condition (v) that determines the passage from state 22 to state 23, the assertion of signal HV_SOC_TooLow to indicate that the state of charge SOCHV of the high-voltage battery 14 is too low to allow the DC / DC converter 16 to transfer energy to the low-voltage battery 12 can be carried out with hysteresis, as exemplified in Figure 4. Signal HV_SOC_TooLow is generated at the output of a set-reset (SR) flip-flop 41 . Basically, the flip-flop 41 is set (by asserting the signal at the set input S of the flip-flop, generated by a comparator 42) when the state of charge SOCHV of the high-voltage battery 14 (e.g., sensed by the electronic control unit 13) is less than or equal to a certain lower threshold HV_SOC_TooLow_Lo, and is reset (by asserting the signal at the reset input R of the flip-flop, generated by a comparator 43) when the state of charge SOCHV is greater than or equal to a certain upper threshold HV_SOC_TooLow_Hi. Thus, substantially, comparators 42 and 43 together with the set-reset flip-flop 41 behave overall as a comparator with hysteresis, which asserts signal HV_SOC_TooLow when the state of charge SOCHV decreases below the lower threshold HV_SOC_TooLow_Lo and de-asserts signal HV_SOC_TooLow when the state of charge SOCHV rises above the upper threshold HV_SOC_TooLow_Hi. The lower threshold HV_SOC_TooLow_Lo and the upper threshold HV_SOC_TooLow_Hi can be stored in a vehicle electronic control unit, and therefore represent two input constants for the control algorithm. The use of two thresholds HV_SOC_TooLow_Lo and HV_SOC_TooLow_Hi allows to maintain a safety margin for the state of charge SOCHV of the high-voltage battery 14 (e.g., to avoid damaging the high-voltage battery by lowering its state of charge too much) and at the same time to avoid toggling effects of signal HV_SOC_TooLow.

[0038] Figure 5 is a diagram that exemplifies the time course of the state of charge SOCLV of the low-voltage battery 12 in a possible use case, corresponding to a “normal” scenario where the charging of the low-voltage battery 12 is interrupted when the minimum safety level is reached (i.e., when condition (i) of the list of conditions that determine the passage from state 22 to state 23 is met). Substantially, in a first period of time T1 the vehicle V is in state 21 , i.e. the vehicle is on and the low-voltage battery 12 is charged following a conventional charging strategy: the state of charge SOCLV increases over time. At the instant toFF the vehicle V is turned off, when the state of charge SOCLV is still below the minimum safety value (represented in Figure 5 by its upper threshold SafeLV_SOC_Hi). Therefore, in an early part of the subsequent time period T2 in which the vehicle V is off, the vehicle passes to the operating state 22, in which the DC / DC converter 16 is kept active and the low-voltage battery 12 continues to be charged. In Figure 5, the charging rate in state 22 is equal to the charging rate in state 21 (same slope of the SOCLV line), but in various embodiments the two charging rates may be different (e.g., the charging rate in state 22 may be lower or higher than the charging rate in state 21 ). The charging of the low-voltage battery 12 continues until the time tsAFE in which the state of charge SOCLV reaches the safe level (in particular, the upper hysteresis threshold SafeLV_SOC_Hi). At that time, condition (i) is met, which determines the passage from state 22 to state 23, the vehicle V remains turned off and the charging of the low-voltage battery 12 is interrupted. The method of managing and controlling the charging of the low- voltage battery described herein thus allows to reduce the probability that the vehicle V cannot be started due to a charge level that is too low in the low-voltage battery, and also ensures a longer life of the low-voltage battery, as it reduces the effects of aging which are also due to the maintenance of an insufficient charge level for prolonged periods.

[0039] Of course, the details of construction and the embodiments may be widely varied with respect to what is described and illustrated without departing from the scope of the invention as defined by the attached claims.

Claims

CLAIMS1. A method (2) of controlling the charging of a low-voltage battery (12) of an electric vehicle (V) via a high-voltage battery (14) of the electric vehicle (V), the method comprising:- in a first operating state (21 ) of the vehicle (V), wherein the vehicle (V) is on, transferring energy from said high-voltage battery (14) to said low- voltage battery (12) via a DC / DC converter (16) of the vehicle (V);- detecting a request for turn-off of the vehicle (V) and, in response to said turn-off request, moving (C1 ) from said first operating state (21 ) to a second operating state (22) of the vehicle (V), wherein the electrical apparatuses of the vehicle (V) are off except for said high-voltage battery (14) and said DC / DC converter (16), and initializing a timer;- in said second operating state (22) of the vehicle (V), transferring energy from said high-voltage battery (14) to said low-voltage battery (12) via said DC / DC converter (16) of the vehicle (V) and increasing said timer at a constant rate (C2);- moving (C4) from said second operating state (22) to a third operating state (23) of the vehicle (V), wherein all electrical apparatuses of the vehicle (V) including said DC / DC converter (16) are off and the charging of said low-voltage battery (12) is interrupted, in response to the occurrence of at least one of the following conditions:(i) the state of charge (SOCLV) of said low-voltage battery (12) reaches a minimum safe value (SafeLV_SOC_Hi)',(ii) said timer reaches a timeout value;(iii) a fault in said low-voltage battery (12) is detected;(iv) a fault in said DC / DC converter (16) is detected; and(v) the state of charge (SOCHV) of said high-voltage battery (14) decreases below a threshold value (HV_SOC_TooLow_Lo)', and- detecting a request for turn-on of the vehicle (V) and, in response to said turn-on request, moving (C3, C5) from said second operating state (22) or from said third operating state (23) to said first operating state (21 ) of the vehicle (V).

2. The method (2) of claim 1 , comprising comparing the state of charge (SOCLV) of said low-voltage battery (12) to said minimum safetyvalue (SafeLV_SOC_Hi) using a comparator with hysteresis (31 , 32, 33).

3. The method (2) of claim 1 or claim 2, comprising comparing the state of charge (SOCHV) of said high-voltage battery (14) to said threshold value (HV_SOC_TooLow_Lo) using a comparator with hysteresis (41 , 42, 43).

4. A system (1 ) for electrical power supply for an electric vehicle (V), the system comprising:- a low-voltage battery (12), and a first electronic control unit (11 ) configured to sense the state of charge (SOCLV) of the low-voltage battery(12) and detect possible failures (FaultLVBatt) of the low-voltage battery (12);- a high-voltage battery (14), and a second electronic control unit(13) configured to sense the state of charge (SOCHV) of the high-voltage battery (14);- a DC / DC converter (16) configured to transfer energy from said high-voltage battery (14) to said low-voltage battery (12); and- a third electronic control unit (15) connected to the first electronic control unit (11 ), to the second electronic control unit (13) and to the DC / DC converter (16) and configured to carry out the operations of the method according to any of the previous claims.

5. An electric vehicle (V) comprising a power supply system (1 ) according to claim 4.

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