Method for protecting an on-board charger of an electric vehicle against undervoltage when recharging the traction battery

Abstract

The present invention relates to a method for protecting an on-board electric charger of an electric vehicle, comprising the following consecutive steps of triggering electrical recharging (E2) by the charger, during which an AC charging current is converted into a DC charging current; measuring (E3), continuously during recharging, a DC charging voltage (V1) output by the charger; comparing (E4) said DC charging voltage (V1) with a predetermined threshold of fixed value; and ordering the recharging to stop (E5) if said charging voltage (V1) is detected as being below the threshold for at least a predetermined period of time. The invention applies to electric vehicles and hybrid vehicles when recharging by plugging into an external charging station.

Description

[0001] DESCRIPTION

[0002] Title: METHOD FOR PROTECTION AGAINST UNDERVOLTAGES OF AN ON-BOARD CHARGER OF AN ELECTRIFIED VEHICLE FOR CHARGING

[0003] THE TRACTION BATTERY

[0004] The present invention claims priority from French application No. 2202131 filed on 11.03.2022, the content of which (text, drawings and claims) is incorporated herein by reference.

[0005] The field of the invention relates to a method for protecting an on-board charger of a traction battery for an electrified motor vehicle, and more specifically for recharges operating a conversion of alternating current into direct current.

[0006] Traction batteries are recharged from a charging station external to the vehicle, which delivers an alternating voltage charging current. An on-board charger is then provided to convert this alternating current into a direct current compatible with the battery system.

[0007] High-power electrical charging must be monitored to ensure that it is carried out within the electrical operating ranges appropriate for the battery system to avoid damage and accelerated aging. In addition, it is necessary to ensure the protection of the on-board electrical charger.

[0008] A known type of AC / DC (Alternating / Direct) electrical conversion module for an electric vehicle charger comprises MOSFET transistors (Metal Oxide Semiconductor Field Effect Transistor) arranged and controlled in switching according to an opening and closing state scheduling program so as to smooth the alternating current into a direct current. In addition, the voltage is continuously controlled at a voltage substantially higher than the battery voltage in order to ensure that the charging current flows from the charger to the battery.

[0009] When driving the AC / DC conversion module, there is a phenomenon of transistor "switching jump" which can cause a very short voltage drop. These switching jumps do not affect the battery and are not harmful to the charger circuits, therefore they should not trigger an anomaly removal or a stop of charging. However, in the event of a persistent undervoltage fault in the charger, it may happen that a charging current flows from the battery to the charger and damages its electronic circuits.

[0010] Known from the state of the art is patent document WO2017 / 061188A1 describing an on-board charger for an electrified vehicle and a protection method in which the difference between the battery voltage and the charger output voltage is measured. If it is detected that the difference is greater than a critical threshold, an anomaly is detected.

[0011] However, this solution has drawbacks. A first drawback is that the protection is based on both battery voltage measurement and charger voltage measurement. It is therefore dependent on the proper functioning of both measurement sensors and increases the probability of failure of the anomaly detection function. A second drawback is that it does not prevent anomaly detection for voltage drops of a few milliseconds, which are invisible to the battery and not harmful to the charger circuits.

[0012] There is therefore a need to address the above-mentioned problems. One objective is to improve the reliability of undervoltage anomaly detection and to avoid untimely alerts that could result from "switching jumps" of a MOSFET transistor in the AC / DC conversion module. Another objective is to improve the responsiveness of the charging shutdown procedure in the event of a persistent anomaly.

[0013] More specifically, the invention relates to a method for protecting an on-board electric charger of an electrified vehicle, said charger being capable of carrying out an electrical recharge of a traction battery of the vehicle from a charging current delivered by a power source external to the vehicle, said method comprising the following successive steps: triggering the electrical recharge by the charger during which an alternating charging current is converted into a direct charging current, measuring, continuously during the recharge, a direct charging voltage delivered by the charger.

[0014] According to the invention, the method further comprises the following successive steps during recharging: comparing said DC charging voltage with a predetermined threshold of fixed value, controlling the stopping of recharging in the event of detection that said charging voltage is lower than the threshold for at least a predetermined duration.

[0015] According to one variant, said fixed threshold value is between 40% and 60% of the maximum value of the battery voltage.

[0016] According to one variant, said threshold value is between 180 volts and 270 volts, preferably equal to 210 volts.

[0017] According to one variant, the predetermined duration is between 300 milliseconds and 1 second, preferably equal to 500 milliseconds.

[0018] According to a variant, in which the charger comprises a module for converting the alternating charging current into direct charging current comprising electrical switches arranged to operate the conversion of the alternating current into direct current, the command to stop the charging comprises the command to open the switches of the conversion module.

[0019] According to a variant, the method further comprises, when ordering the charging stop, a step of recording a fault code signaling an undervoltage anomaly of the charger, and a step of signaling the fault code via an on-board communication network of the vehicle.

[0020] According to a variant of the method, in which the external power source is a charging terminal intended to deliver a charging current to the vehicle through a cable connected to an on-board charging socket box, the method further comprises, at the time of the command to stop charging, recording the fault code in a first permanent anomaly state, then in the event of detection of the disconnection of the cable from the charging socket box, modifying the fault code in a second furtive anomaly state, the first state informing that the undervoltage anomaly persists and that electrical charging is inhibited, the second state informing that the undervoltage anomaly is restored and that electrical charging is authorized.

[0021] According to the invention, an on-board electric charger for an electrified vehicle is envisaged, said charger comprising a control unit and being capable of carrying out an electrical recharge of a traction battery of the vehicle from a charging current delivered by a power source external to the vehicle. According to the invention, the control unit is configured to implement the method according to any one of the preceding embodiments during an electrical recharge.

[0022] Furthermore, according to the invention, an electrified vehicle is envisaged comprising an electric traction machine, a traction battery intended to electrically supply said electric machine and an on-board electric charger according to the invention.

[0023] The invention makes it possible to improve the reliability of the charger output undervoltage anomaly monitoring function because the undervoltage detection threshold is independent of the battery voltage measurement sensor. Because only the charger output voltage value is measured, the probability of a monitoring function failure is reduced. In addition, the duration threshold is configured to a value that allows the monitoring function to tolerate short voltage drops that result from failed switchings during conversion. This improves the reliability of monitoring against false anomalies. Furthermore, the charging stop procedure is executed by the AC / DC conversion switches of the charger. This improves the responsiveness of the charging stop command.

[0024] Other characteristics and advantages of the present invention will appear more clearly on reading the detailed description which follows, comprising embodiments of the invention given as non-limiting examples and illustrated by the appended drawings, in which:

[0025] [Fig.1] schematically represents an electrical architecture of a rechargeable electrified vehicle comprising an on-board charger designed to implement the method according to the invention.

[0026] [Fig.2] represents a simplified electrical diagram of the battery charging system of an electrified vehicle comprising an AC / DC charger configured to implement the invention.

[0027] [Fig.3] is a diagram representing an embodiment of the method for protecting the on-board charger of an electrified vehicle according to the invention.

[0028] The invention applies to electrified vehicles, in particular rechargeable motor vehicles. This includes electric vehicles with fully electric motors and so-called "Plug-In" hybrid vehicles equipped with a charging box. The invention relates more specifically to a method for protecting against undervoltage anomalies of an on-board charger of an electrified vehicle comprising an AC / DC conversion module designed to deliver the direct charging current to the traction battery.

[0029] In Figure 1, an example of an electrified vehicle 1 intended to implement the invention is schematically represented. The vehicle 1 comprises a powertrain provided with a control unit 2, an electric traction machine (not shown) powered by a traction battery system 3 and an on-board charger 9 for the battery 3.

[0030] The charger 9 cooperates with an electrical charging socket box 7 intended to be connected by means of a charging cable 10 to an external power source 11 connected to an electrical power supply network 8, generally operating at alternating voltage. The term on-board means that the charger 9 is integrated and fixed inside the vehicle. The charger 9 is a permanent system of the vehicle. For example, the charger 9 is positioned under the body of the vehicle 1 near the charging socket box 7, and it is electrically connected between the box 7 and the battery system 3.

[0031] The external power supply source 11 delivers a charging current to the vehicle. The power supply source 11 may be a domestic socket, a fixed domestic station (commonly called a "Wallbox" in English) or a charging terminal of a motorway station provided for this purpose, or even a mobile charging terminal. In the example described below, the external power supply source 11 is a charging terminal capable of delivering an alternating voltage of the single-phase or three-phase type.

[0032] The traction battery system 3 is intended for the electrical power supply of the traction machine of the vehicle. It comprises electrical energy storage means 6. In the context of the invention, the voltage of the traction battery system may be of the 48V type or higher, of the 400 volt type according to the preferred embodiment (between 350 volts and 450 volts), of the 800 volt type (between 700 volts and 900 volts), or even higher. The battery system 3 ensures the supply of electrical energy for the needs of the electric traction machine. The electric battery 6 comprises energy storage elements comprising electrochemical cells, for example of the Lithium-ion type.The battery system 3 also includes a management computer 4 (designated by the acronym BMS for “Battery Management System” or TBCU for “Traction Battery Control Unit”) adapted to monitor the parameters specific to the battery in cooperation with current and voltage sensors, such as the state of charge SOC (“State of Charge”), the open circuit voltage OCV (“Open Circuit Voltage”) expressed in Volts, the charging current expressed in Amperes, the state of health SOH (“State of Health”), the voltage or even the temperature of the battery.

[0033] The protection method according to the invention does not concern the recharging of the 12-volt accessory battery. Consequently, and for the sake of clarity, the 12-volt accessory battery and the 12-volt on-board network are not shown in Figure 1, even though these devices are of course integrated into the motor vehicle.

[0034] In addition, high-voltage contactors 5 of the battery system 3 ensure the disconnection / connection of the battery 6 with the vehicle's power electrical circuit, the charger 9, the socket box 7 and the electric traction machine. The high-voltage contactors 5 are power switches that can be controlled in opening and closing by the computer 4 of the battery system 3 to connect it and isolate it from the other electrical systems of the vehicle.

[0035] The charger 9 has the function of managing the communication between the different charging stations and of monitoring and controlling the electrical charging at the station. The charger 9 also includes an AC / DC alternating / direct type electrical conversion module and another DC / DC direct / direct type module. In charging situations at the station, it converts an alternating voltage to a direct voltage, in particular during charging in mode 2 or mode 3 in which it is necessary to convert an alternating voltage in 220V of single-phase or three-phase type (or 110V according to the electrical standard of the region) to a direct voltage compatible with the battery system. In addition, in the context of so-called fast or mode 4 charging, the charging current is delivered directly by the terminal 11 to the battery, that is to say without voltage conversion.In a driving situation, another function of the charger is the DC / DC conversion between the traction battery and the on-board systems of the vehicle, for example the on-board network and the low-voltage battery in 12V (called the service battery). In addition, the vehicle comprises a control unit 2 acting as a supervisor of the vehicle's computers, designated by the acronym EVCU for "Electronic Vehicle Control Unit". In this example, the control unit 2 supervises in particular the electric traction machine, the traction battery system 3 and the charger 9. The control unit 2 is a computer whose function is to centralize the data collected from the vehicle and to retransmit them to other computers of the vehicle via a data communication bus 12, for example of the CAN type.

[0036] For the purposes of the charger protection method 9, the control unit 2 collects information relating to anomalies detected by the charger 9 and the battery system 3 so as to retransmit them to another centralized control unit 14 designated by the acronym BSI for Intelligent Servitude Box. In this non-limiting example, the box 14 and the control unit 2 communicate via a second communication bus 13, of the CAN type.

[0037] More precisely, the box 14 is responsible for recording a diagnostic and alert log that can be consulted by a vehicle control service 1. An anomaly is recorded in the memory of the box 14 in the form of an anomaly code representative of the level of severity and the state of the anomaly.

[0038] Figure 2 shows a diagram of the vehicle's electrical system for recharging the battery system 3. The electrical system includes the charger 9, the external charging station 11 and the electric traction machine 20. Figure 2 is a simplified and non-limiting diagram. Other electrical systems and elements, not shown in Figure 2, may be included, such as, for example, an equipment circuit, switches or even an air conditioning compressor power supply circuit.

[0039] The battery system 3 comprises the electrochemical energy storage cells 6 and high voltage switches, indicated in more detail by the references K1, K2, K3 and K4, making it possible to selectively connect and isolate the battery with the other systems. The traction battery 6 has a voltage Vbat at its terminals. The traction battery 6 can be electrically connected directly to the charging station 11, in direct voltage for charging in mode 4, when the switches K4 and K3 are closed. The switches K1 and K2 make it possible to electrically connect the battery 6 to the output of the charger 9 in direct voltage. More precisely, the charger 9 receives as input an alternating voltage V0 delivering an alternating charging current supplied by the external terminal 11. The input voltage is a single-phase or three-phase voltage.The charger 9 comprises an AC / DC voltage conversion module 91, a means (voltage sensor) for measuring the voltage V1 at the output of the conversion module 91 and a control unit 92.

[0040] In this preferred embodiment, the AC / DC conversion module 91 is a unit comprising several MOSFET transistors controlled by the control unit 92. These transistors are arranged and controlled by an opening and closing state scheduling program to convert the AC input voltage V0 (single-phase or three-phase) into a DC charging voltage V1. The switching frequency of the scheduling program is controlled as a function of the measurement of the frequency of the charging current delivered by the terminal 11. This control ensures optimal AC / DC conversion efficiency. The type of AC / DC conversion module 91 for electrical charging is in no way limiting of the charger protection method.

[0041] The protection method according to the invention aims to ensure that the voltage V1 remains significantly higher than the voltage Vbat during recharging and in electrical operating conditions avoiding damage to the charger circuits.

[0042] For the implementation of the protection method according to the invention, the control unit 92 comprises a means for recording a predetermined threshold SV for detecting an undervoltage and a duration threshold SD for an undervoltage, a means for detecting the connection and disconnection of a charging cable to the vehicle's charging socket box, a means for generating a signal of an undervoltage anomaly in the form of an anomaly code and means for communicating data with the EVCU supervisor. The values ​​of the thresholds SV and SD are fixed and recorded in the memory of the control unit in the design of the vehicle.

[0043] The charger 9 further comprises DC / DC voltage conversion means 93. The charger 9 further comprises means for monitoring one or more alternating voltages V0 at the input of the charger 9, in particular the measurement of the voltage V0 and the measurement of the frequency of the voltage V0.

[0044] As part of the monitoring of undervoltage events of the charger 9, a fault code may be recorded in a first permanent fault state, i.e. the detected undervoltage fault persists. This situation triggers a stoppage of charging. In a second stealth fault state, the fault is considered to have been restored or repaired. The undervoltage event has then disappeared. Charging may be authorized again.

[0045] We will now describe an embodiment of the method for protecting the charger 9 implemented by a computer of the vehicle, in this example the control unit 92 of the charger 9. The control unit 92 is provided with a computer with integrated circuits and electronic memories, the computer and the memories being configured to execute the protection method according to the invention. But this is not obligatory. Indeed, the computer could be external to the control unit 92, while being coupled to the latter 92. In the latter case, it can itself be arranged in the form of a dedicated computer comprising a possible dedicated program, for example. Consequently, the control unit, according to the invention, can be produced in the form of software modules (or computer software), or electronic circuits (or hardware), or a combination of electronic circuits and software modules.

[0046] In Figure 3, an embodiment of the algorithm of the protection method according to the invention is described. In a first step E1, the vehicle is in a situation of electrical recharging of the traction battery. The vehicle is parked at a charging terminal. A charging cable is connected to the vehicle's charging socket box. With reference to Figure 2, the terminal 11 has an alternating charging voltage V0, for example according to the 220V standard. The traction battery 6 of the vehicle is electrically connected to the charging terminal 11.

[0047] In a second step E2, the on-board charger 9 of the vehicle triggers an electrical recharge during which an alternating charging current is converted into a compatible direct charging current of the battery by the AC / DC conversion module 91. The recharge operation is in progress.

[0048] In a third step E3, the charger 9 measures the DC charging voltage V1 delivered by the charger during recharging. This is a monitoring step which is carried out continuously at each instant of recharging. The measurement is carried out from a voltage sensor at the output of the AC / DC conversion module 91. In a fourth step E4, the charger 9 compares the DC charging voltage V1 with respect to a predetermined threshold of fixed value SV. This step aims to check whether or not there is a voltage drop. In this preferred embodiment, the value of the threshold SV is between 40% and 60% of the maximum value of the nominal voltage of the battery 6. For example, for a battery having a nominal voltage varying between 350 volts for a low state of charge (0% of SOC), and 450 volts for a full state of charge (100% of SOC), the value of the predetermined threshold SV is set between 180 volts and 270 volts, preferably the value is equal to approximately 210 volts.The selected value allows the detection of a voltage drop that could pose a risk to the charger circuits if it persists. The SV threshold value remains fixed throughout the charging operation. As long as V1 is higher than the SV threshold, the protection process returns to step E3 of charging voltage monitoring.

[0049] In this step E4, the charger further checks, in the event of detection of a voltage drop below the threshold SV, whether or not this voltage drop persists for at least a predetermined duration SD. For example, a counter CT can be triggered as soon as the load 9 detects a voltage V1 below SV and can be reset as soon as the voltage returns above the threshold SV. The method checks the duration of this counter CT with respect to the threshold SD.

[0050] In this preferred embodiment, the predetermined duration SD is equal to approximately 500 milliseconds. This duration is chosen so as to avoid the detection of untimely anomalies resulting from “switching jumps” of the MOSFET transistor of the AC / DC conversion module. These are events which may appear and cause micro-drops of a few milliseconds which are not harmful to the circuits of the charger 9. The value of the predetermined duration SD is dependent on the robustness of the electronic circuits and the impedance of the traction battery. Higher values ​​are possible. The value of the duration threshold SD remains fixed throughout the recharging operation.

[0051] In this preferred mode, if the charger 9 detects that the charging voltage V1 at the output of the charger 9 is lower than the threshold SV, of 210 volts, continuously for at least the duration of the threshold SD, set at 500 milliseconds, then at a fifth step E5, the charger 9 commands the stopping of the charging. On the contrary, if the voltage drop lasts less than 500 milliseconds, the charger continues the charging. The protection method returns to step E3 of monitoring the charging voltage. This avoids untimely stopping of the charging.

[0052] More specifically, stopping the charging E5 involves the command to open the switches of the AC / DC conversion module 91. The charging is stopped by pausing the AC / DC conversion and by immediately opening the MOSFET transistors. No current flows through the charger. The charger is paused and is isolated from the high voltage circuit and the traction battery 6 to prevent the current from the battery 6 from damaging the electrical circuits of the charger 9.

[0053] Then, when the charging stop is triggered, the method comprises a sixth step E6 of recording a fault code signaling an undervoltage anomaly of the charger 9, and of reporting the fault code through the on-board communication network of the vehicle. With reference to FIG. 1, in this preferred embodiment, the control unit of the charger 9 transmits the fault code to its supervisor 2 through the CAN communication bus 12, then the supervisor 2 redirects the code to the fault diagnosis log recorded by the BSI control unit 14 through the communication bus 13. Other variants of reporting the anomaly are possible, for example to a remote server.

[0054] When the E6 charging stop command is triggered, the fault code is recorded in a first permanent fault state. The first state informs that the undervoltage fault persists and that electrical charging is inhibited.

[0055] According to a preferred variant, at a step E7, if the user disconnects the charging cable, then the charger modifies at a step E8 the fault code in a second stealth anomaly state and authorizes electric charging again. This second state informs that the undervoltage anomaly is restored and that electric charging is authorized. The second state is signaled via the on-board communication bus to the supervisor for recording in the diagnostic log kept by the BSI control unit. In the event of a vehicle overhaul, a technical service is informed of the undervoltage anomaly. This method of managing the diagnosis and the states of the fault codes makes it possible to inform the driver that an anomaly has occurred at the terminal and not at the level of his on-board charger.Furthermore, this method has the advantage of allowing the user to reset the charging by unplugging and plugging the charging cable.

[0056] If the fault is resolved, charging can continue. If the fault is more serious and persistent, a further persistent voltage drop may occur and charging is stopped again, which protects the circuits and encourages the user to check the condition of their vehicle.

[0057] Step E8 is not mandatory. Alternatively, the permanent fault code may persist even after the cable is disconnected. This is a more stringent strategy to make vehicle inspection mandatory before recharging.

[0058] If no anomalies are detected during charging, it is stopped as soon as the target state of charge is reached. This value is generally set at a state of charge level between 80% and 100% charge.

[0059] The invention applies to electric vehicles and hybrid vehicles when recharging the traction battery by connecting it to an external charging terminal. More generally, the method applies to any type of recharging by connecting it to an electrical power source external to the vehicle which is designed to deliver an alternating charging current to the vehicle's on-board charger.

Claims

DEMANDS 1. A method for protecting an on-board electric charger (9) of an electrified vehicle (1), said charger (9) being capable of electrically recharging a traction battery (3) of the vehicle (1) from a charging current supplied by an external power source (11) to the vehicle (1), said method comprises the following successive steps: - the triggering of the electrical charging (E2) by the charger (9) during which an alternating charging current is converted into a direct charging current, - the measurement (E3), continuously during charging, of a continuous charging voltage (V1) delivered by the charger (9), - said process being characterized in that it further comprises the following successive steps during recharging: - the comparison (E4) of said DC charging voltage (V1) with respect to a predetermined threshold of fixed value (SV), - the command to stop charging (E5) in case of detection that said charging voltage (V1) is below the threshold for at least a predetermined duration (SD).

2. Protection method according to claim 1, characterized in that said fixed value (SV) of the threshold is between 40% and 60% of the maximum value of the traction battery voltage (3).

3. A protection method according to claim 2, characterized in that said threshold value (SV) is between 180 volts and 270 volts, preferably equal to 210 volts.

4. A protection method according to any one of claims 1 to 3, characterized in that the predetermined duration (SD) is between 300 milliseconds and 1 second, preferably equal to 500 milliseconds.

5. A protection method according to any one of claims 1 to 4, wherein the charger (9) comprises a current conversion module (91) alternating current charging with direct current charging comprising electrical switches, characterized in that the charging stop control (E5) includes the opening control of the switches of the conversion module (91).

6. A protection method according to any one of claims 1 to 5, characterized in that it further comprises, when the charging stop command is activated (E5), a recording step (E6) of a fault code indicating an undervoltage anomaly of the charger (9), and a step of reporting the fault code through an on-board communication network of the vehicle.

7. A protection method according to claim 6, wherein the external power supply (11) is a charging station intended to deliver a charging current to the vehicle (1) through a cable (10) connected to an on-board charging socket box (7), characterized in that it further comprises, at the moment of the command to stop charging (E5), the recording (E6) of the fault code in a first state of permanent anomaly, then in the event of detection (E7) of the disconnection of the cable from the charging socket box, the modification (E8) of the fault code in a second state of transient anomaly, the first state indicating that the undervoltage anomaly persists and that electric charging is inhibited, the second state indicating that the undervoltage anomaly is restored and that electric charging is authorized.

8. On-board electric charger (9) of an electrified vehicle (1), said charger (9) comprising a control unit (92) and being capable of carrying out an electrical recharge of a traction battery (3) of the vehicle (1) from a charging current delivered by an external power source (11) to the vehicle (1), the control unit (92) being characterized in that it is configured to implement the method according to any one of claims 1 to 7 during an electrical recharge.

9. Electrified vehicle (1) comprising an electric traction machine, a traction battery (3) for electrically powering said electric machine and an on-board electric charger (9) for said battery (3) according to claim 8.

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