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 leads (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 (ULMAX) for charging the traction battery (42), which can be a low voltage value (U1) or a high voltage value (U2), wherein the motor vehicle (40) has: a charging controller (50) for monitoring and controlling the charging process, a vehicle-side charging plug (32), the motor vehicle traction battery (42) which has a technical charging voltage level (UM) with the high voltage value (U2), a charging voltage adjuster (44) by which the charging station voltage (UL) is adapted as required to the technical charging voltage level (UM) of the traction battery (42), a protective relay (60) assigned to the charging lines (L1, L2) between the traction battery (42) and the charging plug (32), and an electrical voltage meter (62) associated with the charging lines (L1, L2) between the protective relay (60) and the charging plug (32), with the procedure steps for connected charging plugs (28,32): Registration of 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 maximum charging voltage (UR), With the vehicle protection relay (60) open: the charging station charging controller (22) controls an insulation test performed by the charging station insulation tester (26) for an insulation test voltage (UI) that corresponds to the requested maximum charging voltage (UR) or the maximum charging station voltage (ULMAX) if the latter is lower than the requested maximum charging voltage (UR). Measurement of the insulation test voltage (UI) by the voltmeter (62), If the measured insulation test voltage (UI) corresponds to a lower voltage value (U1) than that of the technical charging voltage level (UM): The vehicle charging control (50) registers a charging process with the charging station charging control (22) with the low voltage value (U1) as the new requested charging voltage (UR) and adjusts the charging voltage adaptor (44) to a charging station voltage (UL) corresponding to the low voltage value (U1).

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. US Patent 2019 / 0 070 971 A1 discloses a vehicle with a traction battery with a DC charging voltage level of 400 V. In vehicles where high drive power and the shortest possible charging time for the traction battery are desired, traction batteries with a higher technical charging voltage level, such as 800 V, are used.

[0003] Many high-voltage charging stations, however, offer a lower maximum charging voltage, for example, a nominal 400 V, including most charging stations in China. German Patent Application DE 10 2018 000 490 A1 describes the situation where a motor vehicle with a DC charging voltage of 800 V is charged at a charging station with a maximum charging voltage of 400 V.

[0004] 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.

[0005] 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 charging voltage, in this example a high voltage of, for instance, 800 V. If the traction battery charging voltage level exceeds the nominal maximum charging station voltage of, for example, 400 V, the electrical insulation of the charging cables against earth potential is first tested by a charging station insulation tester with the vehicle's protective relay open. This test is performed at the lower of the two voltage values: the traction battery voltage and the maximum charging station voltage.After the charging station's insulation test, the charging station's charging control unit ultimately rejects a charging process according to existing communication protocols, because the vehicle's charging control unit continues to request a high charging voltage of, for example, 800 V. The reason for this is that, according to the existing communication protocols, the vehicle's charging control unit has no information at this point about the maximum charging voltage of the connected charging station.

[0006] DE 10 2019 007 868 A1 discloses a charging station with an insulation monitor. DE 10 2019 111 407 A1 and US 2020 / 0 185 936 A1 each disclose charging voltage adaptors in a motor vehicle with a traction battery.

[0007] As a result, with sufficiently restrictive communication protocols, the vehicle's 800V traction battery can only be charged at charging stations with a maximum charging voltage of the same high value. This means that the network of charging stations suitable for charging a traction battery with a high charging voltage level of, for example, 800V, may be very sparse.

[0008] 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 at its technically adjustable lower charging voltage at charging stations with a lower maximum charging station voltage.

[0009] This problem is solved according to the invention by a method having the features of claim 1.

[0010] The invention is described below using the example of a motor vehicle with a traction battery charging voltage of 800 V (high voltage value) and a charging station with a maximum charging station voltage of either 400 V (low voltage value) or 800 V. These voltage values ​​are, of course, only examples. In any case, the traction battery is a so-called high-voltage traction battery with a charging voltage of well over 60 V. The term "charging voltage" for the traction battery is always understood here to mean the maximum nominal voltage value at which and to which the traction battery can be charged by a charging station in order to keep the charging time as short as possible.The technical charging voltage level can therefore also be the voltage level at which the electric traction motor of the vehicle is preferentially supplied by the traction battery during driving. 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's traction battery, which forms the charging interface to the vehicle.

[0011] The charging station features a charging station controller for monitoring and controlling the charging process. To generate a high-voltage direct current (DC) charging voltage, the charging station includes a voltage converter that transforms the supplied alternating current (AC) voltage from the mains supply into the charging station voltage used to charge the vehicle's traction battery. Initially, only the scenario where the voltage converter cannot provide the full voltage of the traction battery's technical charging voltage as the maximum charging station voltage, but rather a lower voltage, for example, 400 V DC, is considered.

[0012] The charging station is equipped with an insulation tester for checking the electrical insulation of the charging cables against ground 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 ground potential. Furthermore, the charging station has a charging plug that can be mechanically and electrically connected to a corresponding 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.

[0013] The vehicle has its own charging control system to monitor and control the charging process. The vehicle's electric traction battery has 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 charging voltage of, for example, 800 V nominally. The traction motor can also be efficiently supplied with electrical energy at this high technical charging voltage. Furthermore, the high technical charging voltage of the vehicle's traction battery 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 cables, a ground potential cable, and usually at least one data cable. Alternatively, or additionally, 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 adapt 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 a process known as "boosting." Alternatively, the charging voltage converter can, for example, connect two 400 V modules of the traction battery 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] The vehicle has a protective relay between the traction battery and the vehicle's charging connector. This protective relay electrically disconnects the charging cables from the traction battery until the actual charging process has physically begun, and particularly during the charging preparation phase. The protective relay is controlled by the vehicle's charging control unit. In this context, "protective relay" refers to any technical design of a contactor, not necessarily a technical relay.

[0017] The vehicle also features an electrical voltmeter connected to the vehicle's charging lines, between the protective relay and the charging plug. This voltmeter can therefore always determine the electrical voltage in the section of the charging lines between the protective relay and the vehicle's charging plug. The voltmeter measures the DC voltage between the two charging lines.

[0018] According to the inventive method, the following process steps are provided for interconnected charging plugs: First, the vehicle's charging control unit requests a charging process, or a charging process request, to the charging station's charging control unit, specifying a high desired charging voltage of, for example, 800 V. The initial registration at a charging station always occurs with this high desired charging voltage of, for example, 800 V, to ensure that the charging request is recognized, accepted, and ultimately executed by a charging station with a high maximum charging voltage of, for example, 800 V. If necessary, the vehicle's charging voltage adaptor is adjusted or switched accordingly to the high maximum charging station voltage of 800 V.

[0019] In this way, the full performance potential of a charging station with a high maximum charging station voltage can be easily utilized.

[0020] A charging station with a low maximum charging voltage, for example 400 V, does not immediately reject a registered charging request according to the applicable communication protocols, but rather accepts it provisionally for the maximum charging voltage of 400 V. During this phase, the vehicle's protective relay is open, so the traction battery is not electrically connected to the charging station via the charging cables.

[0021] The charging station's charging controller then performs an insulation test via the charging station's insulation tester at a test voltage that corresponds to the requested charging voltage or, if the latter is lower, to the maximum charging station voltage. In this case, the lower of the two voltages, corresponding to the maximum charging station voltage, is selected as the insulation test voltage, resulting in an insulation test voltage of approximately 400 V. For the insulation test, any protective relay on the charging station side is also closed, if present, so that the insulation test voltage is applied along the entire length of the charging cables between the vehicle's protective relay and the charging station's voltage converter. However, this is only necessary if the insulation tester is not located between the charging station's protective relay and the charging plug.The vehicle's voltage meter, located in the live section of the vehicle's charging cables, now measures the applied insulation test voltage and transmits this value to the vehicle's charging control unit. Since the applied insulation test voltage corresponds to the maximum charging station voltage, the vehicle's charging control unit already has this voltage value at this early stage.

[0022] Therefore, if the measured insulation test voltage is lower than the initially registered or requested desired charging voltage, the vehicle charging control unit now registers the low measured voltage value from the insulation test or a correspondingly low suitable voltage value as the new requested charging voltage with the charging station charging control unit, and instructs the charging voltage adjuster to adjust itself to a voltage value corresponding to the low voltage value from the voltage measurement or the suitable low voltage value for charging the traction battery.

[0023] Since the charging station's charging control system receives a permissible and technically feasible voltage value for the requested charging voltage at this early stage, the preparation process is not interrupted but continues. This also ensures that the charging station's insulation test is performed at the voltage level at which the subsequent charging process takes place.

[0024] 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 charging station voltage.

[0025] 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.

[0026] 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.

[0027] 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 assigned to the traction battery 42, which increases the charging voltage from, for example, 400 V to 800 V or which can connect the traction battery modules 42', 42'' electrically in parallel or in series, so that the traction battery 42 can alternatively be charged with a charging voltage of 400 V if the voltage adjuster 44 connects the two modules 42', 42'' electrically in parallel, or it can be charged with a charging voltage of 800 V if the charging voltage adjuster 44 connects the two traction battery modules 42', 42'' electrically in series.

[0028] The vehicle 40 has a vehicle charging controller 50 that controls the entire charging process on the vehicle side and communicates with a corresponding charging station-side charging controller 22. The vehicle 40 has an insulation tester 46 that can check the two charging lines L1, L2, which lead 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 vehicle 40 has a protective relay 60 electrically connected to the two charging lines L1, L2 between the traction battery 42 or the charging voltage adapter 44 on the one hand and the vehicle-side charging plug 32 on the other. The protective relay 60 can electrically interrupt the two charging lines L1, L2 between the charging station 20 and the traction battery 42 as needed.The protective relay 60 is controlled by the vehicle-side charging control unit 50.

[0029] Furthermore, the motor vehicle 40 has an electrical voltmeter 62 connected to the charging lines L1, L2 between the protective relay 60 and the charging plug 32. The voltmeter 62 allows the electrical voltage between the two charging lines L1, L2 to be measured, for example during an insulation test on the charging station side.

[0030] 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 maximum charging station voltage ULMAX with a low voltage value U1 of nominally 400 V DC. However, there are also charging stations that provide a maximum charging station voltage with a high voltage value U2, for example, nominally 800 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 both a maximum charging station voltage with a high voltage value U2 of 800 V and a low voltage value U1 of 400 V.Since communication and the charging process with a charging station with a high maximum charging station voltage of U2 (800 V) are unproblematic, this embodiment only considers the case where the maximum charging station voltage ULMAX corresponds to a lower voltage value U1 (e.g., 400 V) than the higher voltage value U2 (800 V) of the technical charging voltage level of the traction battery 44. The charging station 20 has its own separate insulation tester 26, which checks the electrical insulation or electrical resistance of the two charging lines L1 and L2 with respect to earth potential G as soon as this is initiated by the charging station charging controller 22. The charging station 20 has its own protective relay 64, assigned to the internal charging lines L1 and L2, which is controlled by the charging station charging controller 22.

[0031] Charging station 20 is electrically assigned a charging station charging plug 28, which can be electrically connected to the vehicle charging plug 32 to form a charging plug arrangement 30. This electrically connects the two charging lines L1, L2, at least one data line D and a separate grounding line.

[0032] The inventive method is first described using the example of a charging station with a maximum charging station voltage ULMAX and a low voltage value U1 of 400 V, since the special feature of the inventive method becomes effective in this constellation.

[0033] After the two charging plugs 28 and 32 are connected, the vehicle charging controller 50 notifies the charging station charging controller 22 of a charging process with the high, maximum voltage value U2 of 800 V as the requested charging voltage UR, which corresponds to the maximum technical charging voltage level of the traction battery 42. This notification is provisionally accepted by the charging station charging controller 22, whereupon it instructs the charging station insulation tester 26 to perform an insulation test for the maximum charging station voltage ULMAX of U1, which is 400 V, since an insulation test at the high voltage value U2 of 800 V is neither possible nor technically feasible.During the insulation test, the two charging lines L1 and L2 coming from the charging voltage converter 24 are tested for their insulation resistance with respect to earth potential G at an insulation test voltage UI with a voltage value of U1 equal to 400 V, provided the protective relay 64 is closed and the insulation tester is installed on the charging station side upstream of the protective relay. During the insulation test, the maximum charging station voltage ULMAX of approximately 400 V is applied to the charging lines L1 and L2 between the vehicle-side protective relay 60 and the charging voltage converter 24.

[0034] Since the voltmeter 62 is located in the live part of the charging lines L1, L2, it can determine the maximum charging station voltage ULMAX under the given circumstances. The vehicle's charging control unit 50 therefore learns at a relatively early stage that the maximum charging station voltage ULMAX is below the technical charging voltage level of the traction battery.

[0035] In this case, the vehicle charging controller 50 (again) reports a charging process or charging voltage to the charging station charging controller 22 with the voltage value of the insulation test voltage UI determined by the voltmeter 62, or the identical maximum charging station voltage ULMAX, which in this case is U1 = 400V, or a suitable voltage value that is technically reasonable and lower than ULMAX. This prevents the charging station charging controller 22 from terminating the charging process at a later stage of the charging preparation due to an insufficient maximum charging station voltage.

[0036] The entire charging preparation process continues based on the newly requested charging voltage UR of, for example, 400 V, which is now no longer above the maximum charging station voltage ULMAX of 400 V. Once the charging station charging controller 22 has finally accepted the now requested charging voltage UR of the low voltage value U1 of 400 V, the vehicle charging controller 50 instructs the voltage adjuster 44 to adjust to or switch to a charging voltage UL corresponding to the low voltage value U1 of 400 V. The voltage adjuster 44 connects, for example, the two traction battery cells 42', 42'' in parallel or increases the voltage. Simultaneously, the vehicle charging controller 50 instructs the vehicle's insulation tester 46 to perform an insulation test at the low voltage value U1 of 400 V and to repeat this test continuously throughout the entire subsequent charging process.

[0037] When the vehicle charging controller 50 registers at a charging station 20 with a maximum charging voltage ULMAX with a high voltage value U2 of 800 V, the charging voltage adjuster 44 is set to a charging voltage UL corresponding to the high voltage value U2 at the latest shortly before the start of the actual charging operation, for example by electrically connecting the two traction battery modules 42' 42'' in series or by switching it off completely.

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 leads (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 (ULMAX) for charging the traction battery (42), which can be a low voltage value (U1) or a high voltage value (U2), wherein the motor vehicle (40) has: a charging controller (50) for monitoring and controlling the charging process, a vehicle-side charging plug (32), the motor vehicle traction battery (42) which has a technical charging voltage level (UM) with the high voltage value (U2), a charging voltage adjuster (44) by which the charging station voltage (UL) is adapted as required to the technical charging voltage level (UM) of the traction battery (42), a protective relay (60) assigned to the charging lines (L1, L2) between the traction battery (42) and the charging plug (32), and an electrical voltage meter (62) associated with the charging lines (L1, L2) between the protective relay (60) and the charging plug (32), with the procedure steps for connected charging plugs (28,32): Registration of 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 maximum charging voltage (UR), With the vehicle protection relay (60) open: the charging station charging controller (22) controls an insulation test performed by the charging station insulation tester (26) for an insulation test voltage (UI) that corresponds to the requested maximum charging voltage (UR) or the maximum charging station voltage (ULMAX) if the latter is lower than the requested maximum charging voltage (UR). Measurement of the insulation test voltage (UI) by the voltmeter (62), If the measured insulation test voltage (UI) corresponds to a lower voltage value (U1) than that of the technical charging voltage level (UM): The vehicle charging control (50) registers a charging process with the charging station charging control (22) with the low voltage value (U1) as the new requested charging voltage (UR) and adjusts the charging voltage adaptor (44) to a charging station voltage (UL) corresponding to the low voltage value (U1). [2] Method for charging a traction battery (42) of a motor vehicle (40) according to claim 1, comprising the method step after measuring the insulation test voltage (UI): If the measured insulation test voltage (UI) corresponds to the high voltage value (U2): Adjust the charging voltage adjuster (44) to a charging station voltage (UL) corresponding to the high voltage value (U2).

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