Method for charging a traction battery of a motor vehicle

Abstract

Method for charging a traction battery (42) of a motor vehicle (40) with an electric traction motor (41) by means of a stationary charging station (20), wherein the charging station (20) comprises: a charging station charging controller (22) for monitoring and controlling the charging process, a charging voltage converter (24) for providing a DC charging station voltage (UL) fed into charging lines (L1,L2), an insulation tester (26) for testing the electrical insulation of the charging lines (L1,L2) against earth potential (G) and a charging station-side charging plug (28), wherein the charging voltage converter (24) provides a fixed maximum charging station voltage (UL) for charging the traction battery (42), which can be a low voltage value (U1) or a high voltage value (U2), and wherein the motor vehicle (40) has: a vehicle charging controller (50) for monitoring and controlling the charging process, an insulation tester (46) for testing the electrical insulation of the charging lines (L1, L2) against earth potential (G), a vehicle-side charging plug (32) and a charging voltage adaptor (44) by which the charging station voltage (UL) is adapted as required to the technical charging voltage level (UM) of the traction battery (42), wherein the traction battery (42) has a technical charging voltage level (UM) with the high voltage value (U2), with the process steps for connected charging plugs (28,32): Registration of a charging process by the vehicle charging controller (50) to the charging station charging controller (22) with the low voltage value (U1) as the requested charging voltage (UR), Control of an insulation test performed by the charging station insulation tester (26) by the charging station charging control unit (22) for the requested charging voltage (UR), Reporting the maximum charging station voltage (UL) by the charging station controller (22) to the vehicle charging controller (50), and If the reported maximum charging station voltage (UL) corresponds to the high voltage value (U2): Continue or register a charging process by the vehicle charging control (50) to the charging station charging control (22) with the high voltage value (U2) as the requested charging voltage (UR) and adjust the charging voltage adjuster (44) to a charging station voltage (UL) corresponding to the high voltage value (U2).

Description

[0001] The invention relates to a method for charging a traction battery of a motor vehicle with an electric traction motor by means of a stationary charging station.

[0002] The high-voltage traction batteries of vehicles powered by either a supplementary or exclusively electric motor have different technical DC charging voltage levels, such as 400 V or 800 V, depending on the manufacturer and model. Vehicles where high drive power and the shortest possible charging time for the traction battery are desired therefore use traction batteries with a high technical charging voltage level, for example, 800 V. Many high-voltage charging stations, however, offer a lower maximum charging voltage, for example, a nominal 400 V, as is the case with charging stations in China. German patent DE 10 2018 000 490 A1 discloses a vehicle with a high technical charging voltage level of 800 V, where the traction battery consists of two 400 V sub-batteries.Through internal vehicle switches, both partial batteries are connected in series at a charging voltage of 800V, or are charged individually and alternately at a charging voltage of 400V.

[0003] From DE 10 2019 007 868 A1, a motor vehicle with an insulation monitor is known which monitors the insulation during a charging process with a higher or lower charging voltage.

[0004] From DE 10 2019 111 407 A1, US 2020 / 0185936 A1 and US 2019 / 0070971 A1, a motor vehicle with a charging voltage adaptor is known.

[0005] Due to the existing communication protocols that define the communication between the charging station charging control and the vehicle charging control, initiating a charging process of a motor vehicle with a high technical traction battery charging voltage level of, for example, 800 V is difficult or impossible at a charging station with a lower maximum charging station voltage of, for example, 400 V.

[0006] After the vehicle's charging plug (which may also be a charging socket) is electrically connected to the charging station's charging plug, the vehicle registers itself with the charging station's control unit via its charging controller, specifying the nominal voltage level of the traction battery's charging voltage. If the traction battery's charging voltage exceeds the nominal maximum charging station voltage, the charging station's control unit categorically rejects a charging process according to existing communication protocols. This can result in a very sparse network of charging stations suitable for charging traction batteries with a high charging voltage level of, for example, 800 V.

[0007] The object of the invention is therefore to create a method for charging a motor vehicle traction battery with a (higher) technical charging voltage level, which also allows charging with its technically adjustable lower charging voltage at charging stations with a lower maximum charging station voltage.

[0008] This problem is solved according to the invention by a method having the features of claim 1.

[0009] The invention is described below using the example of a motor vehicle with a traction battery charging voltage of 800 V and a charging station with a maximum charging voltage of either 400 V or 800 V. Naturally, all these voltage values ​​are only examples. In each case, however, the traction battery is a so-called high-voltage traction battery with a charging voltage well above 60 V. The term "charging voltage" for the traction battery is always understood here to mean the maximum voltage at which the traction battery can be charged by a charging station, in order to keep the charging time as short as possible. The charging voltage can also be the voltage used to power the electric traction motor of the motor vehicle.In this context, a charging station is not to be understood as a column in the spatial sense, but rather as a stationary charging terminal for charging the vehicle traction battery, which forms the charging interface to the vehicle.

[0010] The charging station includes a charging station control unit for monitoring and controlling the charging process. To generate a high-voltage direct current (DC) charging voltage, the charging station has a voltage converter that, in the configuration considered for the invention, generates a lower charging station voltage from the supplied alternating current (AC) voltage of a power supply network compared to the technical charging voltage level of the vehicle's traction battery. This lower voltage is, for example, a DC voltage of 400 V.

[0011] The charging station is equipped with an insulation tester for checking the insulation of the charging cables against earth potential. Before initiating a charging process, the charging station's insulation tester checks the electrical insulation or resistance of the two DC charging cables, through which the electrical charging energy flows from the charging station to the vehicle's traction battery, relative to earth potential. Finally, the charging station has a charging plug that can be mechanically and electrically connected to a corresponding or complementary charging plug on the vehicle to electrically connect the respective charging cables. In this context, "charging plug" does not refer to a specific shape, but rather to an assembly that is designed to be mechanically and electrically pluggable with another plug.

[0012] The vehicle has its own charging control unit for monitoring and controlling the charging process. The vehicle also has its own separate insulation tester for testing the electrical insulation of the vehicle's charging cables against ground potential via the charging station's grounding system.

[0013] The vehicle has an electric traction battery with a relatively high technical charging voltage, for example, 800 V. This allows for very fast charging of the traction battery at charging stations with a maximum nominal charging voltage of, for example, 800 V. The traction motor can also be efficiently supplied with electrical energy at this high technical charging voltage. A high technical charging voltage for the vehicle's traction battery also helps to keep heat losses relatively low.

[0014] The vehicle has a charging plug on its side that can be connected to the corresponding charging station charging plug. This involves electrically connecting two charging lines, a ground wire, and usually at least one data line. However, data transmission between the charging station's charging controller and the vehicle's charging controller can also be wireless.

[0015] The vehicle is equipped with a charging voltage converter that, if necessary, can adjust a low charging station voltage of, for example, 400 V to the technical charging voltage level of the traction battery of, for example, 800 V by boosting it. The charging voltage converter can also, for example, allow two 400 V modules of the traction battery to be electrically connected in parallel during charging, while they are connected in series during driving. In this way, the traction battery can be charged with either a charging station voltage of 400 V or 800 V. The charging voltage converter is controlled by the vehicle's charging control unit.

[0016] According to the inventive method, the following process steps are provided for interconnected charging plugs: First, the vehicle's charging control unit registers a charging process, or rather a charging request, with a lower desired charging voltage of, for example, 400 V to the charging station's charging control unit. The registration at a charging station always uses this lower desired charging voltage of, for example, 400 V, to ensure that the charging request is also accepted by a charging station with a lower maximum charging voltage of, for example, 400 V.

[0017] A charging station with a low maximum charging voltage, for example 400 V, does not reject the requested charging request but accepts it. The charging station's charging control system and the vehicle's charging control system then prepare the charging process, ultimately starting and carrying it out at the lower maximum charging voltage of 400 V. This allows even a vehicle with a traction battery capable of handling a relatively high technical charging voltage to be charged at a charging station with a lower maximum charging voltage.

[0018] If a vehicle with a high technical traction battery charging voltage level of, for example, 800 V, registers with a charging station that can provide a higher maximum charging station voltage of, for example, 800 V, using a lower voltage value of, for example, 400 V as the requested charging voltage, the charging station's charging control system first initiates and controls an insulation test by the charging station's insulation tester for the vehicle-requested charging voltage of 400 V, as this is provided for in the existing charging protocols and charging procedures.

[0019] Only after the insulation test for 400 V has been successfully passed does the charging station control unit report the available maximum charging station voltage to the vehicle's charging control unit, in accordance with the applicable communication protocols. Only then, therefore, does the vehicle's charging control unit learn – according to the applicable communication protocols – the maximum charging station voltage that the charging station can actually provide.

[0020] If the reported maximum charging station voltage exceeds the lower voltage initially reported by the vehicle's charging control unit as the requested charging voltage, the vehicle's charging control unit will then continue or re-register a charging process with the charging station's charging control unit using the higher voltage value, or with the maximum charging station voltage previously reported by the charging station, provided this is technically feasible for charging. If the charging station's charging control unit accepts the registration of the higher requested charging voltage, the charging voltage adjuster is adapted to the charging voltage corresponding to the higher voltage value, for example, by connecting two 400 V modules of the traction battery in series.

[0021] Furthermore, in this case, the vehicle charging control unit prompts the vehicle's insulation tester, in accordance with standards, to perform an insulation test for the now agreed-upon high charging voltage of, for example, 800 V, preferably before the charging process actually begins. This ensures that the required electrical insulation of the charging cables from earth potential is also guaranteed for the higher voltage, even though the charging station's insulation tester initially only performed an insulation test for a lower voltage of, for example, 400 V. This procedure ensures sufficient insulation safety and complies with regulations.

[0022] If the maximum charging station voltage reported by the charging station charging control to the vehicle's charging control corresponds to the low voltage value that the vehicle's charging control had initially requested, the vehicle's charging voltage adjuster is adjusted or switched to the low voltage value of, for example, 400 V, if this was not already the case.

[0023] The method according to the invention makes it possible for a high-voltage traction battery with a nominally higher technical charging voltage level to also be accepted and charged by a charging station with a lower maximum DC charging station voltage.

[0024] An embodiment of the invention will now be explained in more detail with reference to the drawing. The figure schematically shows a vehicle charging arrangement with a vehicle equipped with an electric traction battery, which is charged by a charging station.

[0025] The figure shows a motor vehicle charging arrangement 10, which is essentially formed by a stationary charging station 20 and a motor vehicle 40, which has an electric traction motor 41 and an electric traction battery 42 that supplies the electric traction motor 41 with electric drive energy.

[0026] The traction battery 42 is a high-voltage traction battery with a technical charging voltage level UM of 800 V and consists, for example, of a pair of two identical traction battery modules 42', 42'', each with a charging voltage of 400 V. A charging voltage adjuster 44 is associated with the traction battery 42, which can connect the traction battery modules 42', 42'' electrically in parallel or in series. This allows the traction battery 42 to be charged either with a charging voltage of 400 V when the voltage adjuster 44 connects the two modules 42', 42'' electrically in parallel, or with a charging voltage of 800 V when the charging voltage adjuster 44 connects the two traction battery modules 42', 42'' electrically in series. The charging voltage adjuster can alternatively increase the supplied charging voltage from 400 V to 800 V.

[0027] The vehicle 40 is equipped with an insulation tester 46, which can check the two charging lines L1 and L2, leading from a vehicle-side charging plug 32 to the charging voltage adapter 44, for sufficient electrical insulation from the electrical earth potential G at a test voltage. The test voltage initially corresponds to a charging voltage first requested by the vehicle charging control unit 50, in this case a low voltage value U1 of, for example, 400 V.

[0028] The motor vehicle 40 also has a vehicle charging control unit 50, which controls the entire charging process on the vehicle side and communicates with a corresponding charging station-side charging control unit 22 for this purpose.

[0029] Charging station 22 is supplied with electrical energy from a high-voltage supply network 12, which is fed into a charging voltage converter 24 of charging station 20 in the form of a high-voltage alternating current. The charging voltage converter 24 is electrically connected to earth potential via a corresponding grounding conductor and converts the supplied alternating current into a high charging station voltage UL with a high voltage value U2 of nominally 800 V DC. However, there are also charging stations that convert a low charging station voltage UL with a low voltage value U1 of, for example, nominally 400 V. The vehicle charging control unit 50 contains a charging control program that allows the traction battery 42 to be charged by a charging station with a maximum charging station voltage with a high voltage value U2 of 800 V as well as with a low voltage value U1 of 400 V.

[0030] The charging station 20 has its own separate insulation tester 26, which tests the electrical insulation or electrical resistance of the two charging lines L1, L2 with respect to earth potential G as soon as this is requested by the charging station's charging control unit 22. A charging station charging plug 28 is electrically assigned to the charging station 20, which can be electrically connected to the vehicle's charging plug 32 to form a charging plug assembly 30. This electrically connects the two charging lines L1, L2, at least one data line D, and a separate grounding line.

[0031] The method according to the invention is first described using the example of a charging station with a maximum charging station voltage UL with a high voltage value U2 of 800 V.

[0032] After the two charging plugs 28 and 32 are connected, the vehicle charging controller 50 reports a charging process to the charging station charging controller 22 with a low voltage value U1 of, for example, 400 V as the requested charging voltage UR. This report is accepted by the charging station charging controller 22, whereupon it requests the charging station insulation tester 26 to perform an insulation test for the requested charging voltage of 400 V. In this test, the insulation resistance of the two charging lines L1 and L2 coming from the charging voltage converter 24 is checked against earth potential G. If the insulation resistance is sufficient, i.e., the insulation test is successful, the charging station charging controller 22 reports the maximum charging station voltage UL, corresponding to the high voltage value U2 of 800 V, to the vehicle charging controller 50.Since the traction battery 42 has a technical charging voltage level UM with a high voltage value of 800 V, the vehicle charging control 50 subsequently reports a requested charging voltage UR again at the level of the high voltage value U2 of 800 V.

[0033] Once the charging station charging controller 22 has finally accepted the requested charging voltage UR of the high voltage value U2 of 800 V, the vehicle charging controller 50 instructs the charging voltage adaptor 44 to adjust to or switch to a charging voltage UL corresponding to the high voltage value U2 of 800 V. The charging voltage adaptor 44 therefore simply switches off, allowing the vehicle battery to be charged directly, or it connects, for example, the two traction battery cells 42', 42'' electrically in series for this purpose. Simultaneously, the vehicle charging controller 50 instructs the vehicle's insulation tester 46 to perform an insulation test at the high voltage value U2 of 800 V and to repeat this test continuously throughout the entire subsequent charging process. This ensures compliance with legal regulations regarding safety, and in particular, insulation safety.

[0034] When the vehicle charging controller 50 registers at a charging station 20 with a maximum charging voltage UL with a low voltage value U1 of, for example, 400 V, the charging voltage adjuster 44 is set to a charging voltage UL corresponding to the low voltage value U1 shortly before the start of the actual charging operation, for example by connecting the two traction battery modules 42' 42'' electrically in parallel during the charging operation.

Claims

[1] Method for charging a traction battery (42) of a motor vehicle (40) with an electric traction motor (41) by means of a stationary charging station (20), wherein the charging station (20) comprises: a charging station charging controller (22) for monitoring and controlling the charging process, a charging voltage converter (24) for providing a DC charging station voltage (UL) fed into charging lines (L1,L2), an insulation tester (26) for testing the electrical insulation of the charging lines (L1,L2) against earth potential (G) and a charging station-side charging plug (28), wherein the charging voltage converter (24) provides a fixed maximum charging station voltage (UL) for charging the traction battery (42), which can be a low voltage value (U1) or a high voltage value (U2), and wherein the motor vehicle (40) has: a vehicle charging controller (50) for monitoring and controlling the charging process, an insulation tester (46) for testing the electrical insulation of the charging lines (L1, L2) against earth potential (G), a vehicle-side charging plug (32) and a charging voltage adaptor (44) by which the charging station voltage (UL) is adapted as required to the technical charging voltage level (UM) of the traction battery (42), wherein the traction battery (42) has a technical charging voltage level (UM) with the high voltage value (U2), with the process steps for connected charging plugs (28,32): Registration of a charging process by the vehicle charging controller (50) to the charging station charging controller (22) with the low voltage value (U1) as the requested charging voltage (UR), Control of an insulation test performed by the charging station insulation tester (26) by the charging station charging control unit (22) for the requested charging voltage (UR), Reporting the maximum charging station voltage (UL) by the charging station controller (22) to the vehicle charging controller (50), and If the reported maximum charging station voltage (UL) corresponds to the high voltage value (U2): Continue or register a charging process by the vehicle charging control (50) to the charging station charging control (22) with the high voltage value (U2) as the requested charging voltage (UR) and adjust the charging voltage adjuster (44) to a charging station voltage (UL) corresponding to the high voltage value (U2). [2] Method for charging a traction battery (42) of a motor vehicle (40) according to claim 1, comprising the method step after reporting the maximum charging station voltage (UL) to the vehicle charging control (50): If the reported maximum charging station voltage (UL) corresponds to the low voltage value (U1): Adjust the charging voltage adjuster (44) to a charging station voltage (UL) corresponding to the low voltage value (U1). [3] Method for charging a traction battery (42) of a motor vehicle (40) according to one of the preceding claims, comprising the method step: If the charging voltage adjuster (44) has been set to a charging station voltage (UL) corresponding to the high voltage value (U2): Control of an insulation test performed by the vehicle-side insulation tester (46) by the vehicle-side charging control (50) with the high voltage value (U2).

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