High-voltage (HV) system for a vehicle, vehicle with such an HV system, and method for heating an HV battery of the HV system.

Abstract

The invention relates to an HV system (1) for a vehicle (2), comprising an HV battery (3) with two HV battery cell packs (3.1, 3.2) and two bidirectional isolating onboard battery chargers (OBC1, OBC2), wherein a positive potential terminal (DCP1) of a primary side of an isolating DC / DC converter of the first onboard battery charger (OBC1) is connected to a positive terminal (HVP1) of the first HV battery cell pack (3.1), a negative potential terminal (DCN2) of a primary side of an isolating DC / DC converter of the second onboard battery charger (OBC2) is connected to a negative terminal (HVN2) of the second HV battery cell pack (3.2), and a negative potential terminal (DCN1) of the DC / DC converter of the first onboard battery charger (OBC1) and a positive potential terminal (DCP2) of the DC / DC converter of the second onboard battery charger (OBC2) are connected to a central tap (HVM) of the HV battery (3), and wherein - The secondary sides of the isolating DC / DC converters of the two onboard battery chargers (OBC1, OBC2) are electrically connected in parallel to each other and to a DC side of a common AC / DC converter, wherein an AC side of the common AC / DC converter is connected to charging connection lines (LL1, LL2, LL3, LN) of an AC charging port (5), or - The AC sides of the two onboard battery chargers (OBC1, OBC2) are connected electrically in parallel to each other with charging connection lines (LL1, LL2, LL3, LN) of an AC charging port (5).

Description

[0001] The invention relates to an HV system for a vehicle, a vehicle and a method for heating an HV battery.

[0002] A self-heating battery circuit and a vehicle are known from the prior art, as described in WO 2024 / 066325 A1. The self-heating battery circuit comprises two battery packs, two capacitors, multiple phases of bridge arms, and multiple phases of windings that correspond one-to-one to the multiple phases of the bridge arms. Each phase of the winding is connected to the midpoint of a corresponding bridge arm. A negative electrode of the first battery pack is connected to a positive electrode of the second battery pack. The negative electrode of the first battery pack and the positive electrode of the second battery pack are connected to a neutral point of the multiple phases of the windings. A positive electrode of the first battery pack is connected to a first bus terminal of the multiple phases of the bridge arms.A negative electrode of the second battery pack is connected to a second bus terminal of the multi-phase bridge arms. A first end of the second capacitor is connected to a second end of the first capacitor. The first end of the second capacitor and the second end of the first capacitor are connected to the neutral point of the multi-phase windings. A second end of the second capacitor is connected to the negative electrode of the second battery pack. A first end of the first capacitor is connected to the positive electrode of the first battery pack.

[0003] US Patent 10,854,933 B2 describes battery pack voltage switching systems and control logic for electric vehicles with multiple battery packs. A method for controlling the operation of a vehicle includes a vehicle controller that receives a voltage switching signal to modify a voltage output of the vehicle's battery system. The vehicle controller determines whether the rotational speed of a traction motor is below a calibrated base speed. If so, the vehicle controller transmits a pack isolation signal to an inverter to electrically disconnect the traction battery packs from the traction motor. The vehicle controller also determines whether the bus current of a DC bus is below a calibrated bus current threshold.If this is the case, the vehicle controller transmits an opening signal to open one or more package contactors and a closing signal to close one or more package contactors, causing the vehicle battery system to output the second voltage.

[0004] From US patent 2022 / 0102986 A1, an HV system for a vehicle is known, comprising an HV battery with two HV battery cell packs and two bidirectional isolating onboard battery chargers, wherein a positive potential terminal of a primary side of an isolating DC / DC converter of the first onboard battery charger is connected to a positive terminal of the first HV battery cell pack, a negative potential terminal of a primary side of an isolating DC / DC converter of the second onboard battery charger is connected to a negative terminal of the second HV battery cell pack, and wherein AC sides of the two onboard battery chargers are electrically connected in parallel to each other with charging connection leads of an AC charging port.

[0005] The invention is based on the objective of providing an improved HV system for a vehicle compared to the prior art, a vehicle improved compared to the prior art and a method for heating an HV battery improved compared to the prior art.

[0006] The problem is solved according to the invention by an HV system for a vehicle with the features of claim 1, a vehicle with the features of claim 6 and a method for heating an HV battery with the features of claim 7.

[0007] Advantageous embodiments of the invention are the subject of the dependent claims.

[0008] A high-voltage (HV) system for a vehicle comprises an HV battery with two HV battery cell packs. Each HV battery cell pack, in particular, contains a plurality of electrically connected series and / or parallel rechargeable electrochemical battery cells.

[0009] According to the invention, the HV system comprises two bidirectional isolating onboard battery chargers, also referred to as onboard chargers (OBCs). These are, for example, two separate devices or onboard battery charger components of a common bidirectional isolating onboard battery charger.

[0010] The bidirectional isolating onboard battery chargers enable, in a generally known manner, the charging of the high-voltage battery via an AC charging port at an external AC power source, particularly a power grid. The design of the bidirectional isolating onboard battery chargers used for this purpose is generally known. They include, in particular, at least one isolating DC / DC converter and at least one AC / DC converter, especially as a power correction filter or power factor correction filter (PFC).

[0011] In the solution according to the invention, a positive potential terminal of a primary side of an isolating DC / DC converter (DC / DC converter = DC voltage converter) of the first onboard battery charger is connected to a positive terminal of the first HV battery cell pack, a negative potential terminal of a primary side of an isolating DC / DC converter of the second onboard battery charger is connected to a negative terminal of the second HV battery cell pack, and a negative potential terminal of the primary side of the isolating DC / DC converter of the first onboard battery charger and a positive potential terminal of the primary side of the isolating DC / DC converter of the second onboard battery charger are connected to a center tap of the HV battery.

[0012] The HV system also features an AC charging port with charging cables. Specifically, each charging cable can be connected to a corresponding charging contact of the AC charging port via a charging switching element, either by closing the respective charging switching element or while the respective charging switching element is closed.

[0013] In an embodiment according to the invention, the secondary sides of the isolating DC / DC converters of the two onboard battery chargers are connected electrically in parallel to each other and are connected to a DC side of a common AC / DC converter, wherein an AC side of the common AC / DC converter is connected to the charging connection lines of the AC charging port (AC = alternating current, DC = direct current).

[0014] In an alternative embodiment according to the invention, the AC sides of the two onboard battery chargers are electrically connected in parallel to each other and are connected to the charging connection lines of the AC charging port.

[0015] The common bidirectional isolating onboard battery charger and / or the respective bidirectional isolating onboard battery charger shall in particular include at least one AC / DC converter as a power correction filter or power factor correction filter (PFC = Power Factor Correction).

[0016] A vehicle according to the invention comprises the HV system. The vehicle is in particular an electrically powered vehicle, wherein the HV battery is in particular a traction battery of the vehicle and is thus in particular provided for an electrical energy supply of at least one electric drive motor for driving the vehicle.

[0017] In one embodiment, the center tap is formed by a closed series connection between a negative terminal of the first HV battery cell pack and a positive terminal of the second battery cell pack. Particularly in this embodiment, it is advantageously also provided that a first parallel connection is arranged between the positive potential terminal of the primary side of the isolating DC / DC converter of the first onboard battery charger and the positive terminal of the second HV battery cell pack, and a second parallel connection is arranged between the negative potential terminal of the primary side of the isolating DC / DC converter of the second onboard battery charger and the negative terminal of the first HV battery cell pack.

[0018] This makes it possible to connect the two HV battery cell packs electrically in series by closing the series connection element and opening the two parallel connection elements, and conversely, to connect them electrically in parallel by opening the series connection element and closing the two parallel connection elements. For example, each of the two HV battery cell packs has a voltage, specifically a nominal voltage, of 400 V. When the HV battery cell packs are connected in parallel, the HV battery then has a battery voltage, specifically a nominal voltage, of 400 V, and when the HV battery cell packs are connected in series, it has a battery voltage, specifically a nominal voltage, of 800 V.

[0019] In a method according to the invention for heating the HV battery of the HV system, the first HV battery cell pack is alternately recharged into the second HV battery cell pack and the second HV battery cell pack is recharged into the first HV battery cell pack using the two bidirectional insulating onboard battery chargers, in particular by appropriately controlling the two bidirectional insulating onboard battery chargers, especially by means of a control unit. That is to say,It is specifically intended that the two bidirectional isolating onboard battery chargers are controlled, particularly by means of the control unit, in such a way that the first HV battery cell pack is alternately recharged into the second HV battery cell pack by means of the two bidirectional isolating onboard battery chargers and the second HV battery cell pack is recharged into the first HV battery cell pack by means of the two bidirectional isolating onboard battery chargers.

[0020] In this alternating charging process, the first HV battery cell pack is alternately discharged, thereby charging the second HV battery cell pack, and then the second HV battery cell pack is discharged, thereby charging the first HV battery cell pack.

[0021] This alternating charging and recharging results in impedance heating of the HV battery cell packs and thus of the HV battery, because this alternating charging and the resulting alternating current flow, i.e., due to a changing direction of this current flow, across an internal resistance of the respective HV battery cell pack, generates heat loss at the internal resistance, which heats up the respective HV battery cell pack and thus the HV battery.

[0022] The switching between recharging the first HV battery cell pack into the second HV battery cell pack and recharging the second HV battery cell pack into the first HV battery cell pack is carried out in particular at a frequency greater than 1 Hz, for example at a frequency of 100 Hz, and in particular at a frequency of up to 1 kHz.

[0023] This recharging process is carried out particularly when the high-voltage (HV) battery is not being charged via the AC charging port. It is specifically intended that the charging circuits are open or will be opened for the heating of the HV battery during this recharging process, in particular to ensure that there is no voltage at the AC charging port, especially at the AC charging pins of the AC charging port.

[0024] This recharging and thus the heating of the HV battery is carried out, for example, while the vehicle is being driven and / or when the vehicle is parked.

[0025] If the HV system has the series connection element described above, then for the described heating of the HV battery, the series connection element is intended to be closed or will be closed. If the HV system has the two parallel connection elements described above, then for the described heating of the HV battery, the two parallel connection elements are intended to be open or will be opened.

[0026] As described above, both onboard battery chargers are designed as isolating onboard battery chargers. They therefore feature galvanic isolation, which allows them to be connected to different high-voltage potentials on the battery side (utilizing the interruption of the transformer's potential reference from primary to secondary winding).

[0027] The described solution therefore specifically provides that the first bidirectional isolating onboard battery charger is connected to the first HV battery cell pack, and the second bidirectional isolating onboard battery charger is connected to the second HV battery cell pack. Furthermore, the two bidirectional isolating onboard battery chargers are connected in parallel on the secondary side of their isolating DC / DC converters or on the AC side, specifically as described above. The two bidirectional isolating onboard battery chargers allow the first HV battery cell pack to be charged into the second HV battery cell pack and vice versa. The forced AC power through the HV battery cell packs generates heat loss at their internal resistances, which heats the HV battery cell packs and thus the HV battery.

[0028] The described solution makes it possible, in particular, to perform the transfer of charge between the two high-voltage (HV) battery cell packs using the two bidirectional insulating onboard battery chargers, thereby achieving impedance heating of both HV battery cell packs and thus of the HV battery as a whole. This enables, for example, DC fast charging, i.e., direct current fast charging, even at cold temperatures, as this requires raising the HV battery to a required minimum temperature level. For example, during a charging process from a state of charge of 20% at -7°C, the battery temperature should be raised to approximately 0°C (for NMC battery cells) to allow the DC charging process to be carried out with nearly full DC charging power.

[0029] The described solution offers a more cost-effective method of battery heating compared to other options, particularly when compared to battery heating using an inverter. This alternative method incurs additional costs due to the need for a neutral point tap, a required line between the HV battery and the neutral point of the electric machine, a potentially required additional inductance, and a large EMC filter due to the high interference potential generated by the inverter during switching.

[0030] In this alternative method using an inverter and a star point tap, a star point brought out of the electric motor is connected to a switchable center tap of the high-voltage battery. The inverter can set a defined current (positive or negative) by applying pulse patterns to the star point tap. Waste heat is generated at the internal resistance of the battery cells, which immediately warms them. The charging frequency is, for example, 1 Hz to approximately 1 kHz, or 100 Hz. The current waveform can be set via the inverter, for example, sine wave or PWM. Waste heat from the electric motor and the inverter can be used via a cooling system to further heat the battery. To transfer current from the first battery cell pack to the second, semiconductors in the upper row of the inverter are switched on and then off again.To transfer power from the second battery cell pack to the first battery cell pack, semiconductors in the lower row of the inverter switch on and then open again.

[0031] The described solution avoids the additional costs associated with this alternative method, namely the star point tap on the inverter and the connecting cable from the star point tap to the center point of the high-voltage battery. Furthermore, the described solution also eliminates the additional inductance required for the recharging function, which is necessary for the alternative method of battery heating via inverter if the stray inductance of the electric machine is too low.

[0032] The described function, in particular the described recharging and the resulting impedance heating, can be implemented using the described solution while the vehicle is in operation without reducing its driving performance. In contrast, with the alternative method of battery heating using an inverter, overmodulation of the inverter is no longer possible when the neutral point is connected to the battery center point.

[0033] Furthermore, compared to the alternative method of battery heating using an inverter, the described solution allows for a smaller dimensioning of the EMC filter, particularly due to a lower current and a lower stray inductance to PA, if the battery recharging function is to be implemented during a DC charging process, i.e. during a direct current charging process.

[0034] Exemplary embodiments of the invention are explained in more detail below with reference to drawings.

[0035] This shows: Fig. 1. Schematic representation of a basic impedance heating of a battery, Fig. 2 schematically a vehicle with an embodiment of an HV system, Fig. 3 schematically an impedance heating of a battery of the embodiment of the HV system according to Fig. 2, Fig. 4 schematically a vehicle with a further embodiment of an HV system, and Fig. 5 schematically an impedance heating of a battery of the embodiment of the HV system according to Fig. 4.

[0036] Corresponding parts are marked with the same reference symbols in all figures.

[0037] Based on the Fig. Sections 1 to 5 below describe an HV system 1 for a vehicle 2, a vehicle 2 with such an HV system 1 and a method for heating, in particular impedance heating, an HV battery 3 of the HV system 1.

[0038] Fig. Figure 1 shows a schematic representation of the basic principles of impedance heating. The high-voltage battery 3 has an internal resistance Ri. The cold high-voltage battery 3 is charged by a transfer current IAC and subsequently discharged. The frequency of this transfer of the high-voltage battery 3 is, in particular, greater than 1 Hz, for example, 100 Hz, so that the transfer processes of the high-voltage battery 3 do not occur within the cell chemistry of the battery cells of the high-voltage battery 3. This prevents this transfer from causing aging of the high-voltage battery 3.

[0039] The alternating current flow of the charging current IAC across the internal resistance Ri, and in particular the changing direction of this current flow due to the charging process, generates heat loss at the internal resistance Ri directly within the respective battery cell. The charging current IAC is advantageously 400 A or more, if possible. The higher the charging current IAC, the greater the heat loss and thus the more effective the impedance heating of the HV battery 3. The heat loss depends on the internal resistance Ri, and therefore, in particular, on the cell geometry of the battery cells. The power loss, and thus the heat loss, is the product of the internal resistance Ri and the square of the charging current IAC.

[0040] The Fig. 2 and Fig. Figures 3, 4, and 5 show the vehicle 2 with two embodiments of the HV system 1. The HV system 1 comprises the HV battery 3 with two HV battery cell packs 3.1 and 3.2. Each HV battery cell pack 3.1 and 3.2 has an internal resistance Ri1 and Ri2, respectively. For example, each HV battery cell pack 3.1 and 3.2 has a voltage of 400 V.

[0041] In the first embodiment according to the Fig. 2 and Fig. 3 is a negative terminal HVN1 of the first HV battery cell pack 3.1 connected to a positive terminal HVP2 of the second HV battery cell pack 3.2, so that the two HV battery cell packs 3.1, 3.2 are electrically connected in series.

[0042] In the second embodiment according to the Fig. 4 and Fig. 5. The negative terminal HVN1 of the first HV battery cell pack 3.1 can be connected to the positive terminal HVP2 of the second HV battery cell pack 3.2 via a series connection element SS. By closing this series connection element SS, the two HV battery cell packs 3.1 and 3.2 are then electrically connected in series. By opening this series connection element SS, the negative terminal HVN1 of the first HV battery cell pack 3.1 and the positive terminal HVP2 of the second HV battery cell pack 3.2 are no longer connected.

[0043] In the examples shown, the HV system has 1 HV loads 4, which can be connected via a first main switching element HS1, i.e., by closing the first main switching element HS1, to a positive terminal HVP1 of the first HV battery cell pack 3.1, and via a second main switching element HS2, i.e., by closing the second main switching element HS2, to a negative terminal HVN2 of the second HV battery cell pack 3.2. The HV loads 4 have a nominal voltage that corresponds to the voltage of the electrically series-connected HV battery cell packs 3.1 and 3.2, for example, 800 V.

[0044] The HV system 1 features two bidirectional isolating onboard battery chargers OBC1 and OBC2. These are, for example, two separate devices or onboard battery charger components of a common bidirectional isolating onboard battery charger.

[0045] A positive potential terminal DCP1 of a primary side of an isolating DC / DC converter of the first onboard battery charger OBC1 is connected to the positive terminal HVP1 of the first HV battery cell pack 3.1, a negative potential terminal DCN2 of a primary side of an isolating DC / DC converter of the second onboard battery charger OBC2 is connected to the negative terminal HVN2 of the second HV battery cell pack 3.2, and a negative potential terminal DCN1 of the primary side of the isolating DC / DC converter of the first onboard battery charger OBC1 and a positive potential terminal DCP2 of the primary side of the isolating DC / DC converter of the second onboard battery charger OBC2 are connected to a center tap HVM of the HV battery 3.

[0046] In the second embodiment according to the Fig. 4 and Fig. 5 the center tap HVM is formed by the closed series connection element SS between the negative terminal HVN1 of the first HV battery cell pack 3.1 and the positive terminal HVP2 of the second HV battery cell pack 3.2, i.e. this center tap HVM of the HV battery 3 exists only when the series connection element SS is closed.

[0047] In the example shown, the negative potential terminal DCN1 of the primary side of the isolating DC / DC converter of the first onboard battery charger OBC1 and the positive potential terminal DCP2 of the primary side of the isolating DC / DC converter of the second onboard battery charger OBC2 are directly connected to the positive terminal HVP2 of the second HV battery cell pack 3.2 and thus, by closing the series switching element SS, also to the negative terminal HVN1 of the first HV battery cell pack 3.1. In an alternative embodiment not shown, the negative potential terminal DCN1 of the primary side of the isolating DC / DC converter of the first onboard battery charger OBC1 and the positive potential terminal DCP2 of the primary side of the isolating DC / DC converter of the second onboard battery charger OBC2 are directly connected to the negative terminal HVN1 of the first HV battery cell pack 3.1 and thus, by closing the series switching element SS, also to the positive terminal HVP2 of the second HV battery cell pack 3.2 connected.

[0048] The HV system 1 further features an AC charging port 5 with charging connection lines LL1, LL2, LL3, LN. The charging connection lines LL1, LL2, LL3, LN can each be connected to a respective charging contact L1, L2, L3, N of the AC charging port 5 via a charging switching element LS1 to LS4, either by closing the respective charging switching element LS1 to LS4, or while the respective charging switching element LS1 to LS4 is closed. For single-phase charging, the second charging switching element LS2 and the third charging switching element LS3 can be omitted.

[0049] In the illustrated embodiment, the AC sides of the two onboard battery chargers OBC1 and OBC2 are electrically connected in parallel to each other via the charging connection lines LL1, LL2, LL3, and LN of the AC charging port 5. As shown, common AC connection lines VL1, VL2, VL3, and VN are provided between the first onboard battery charger OBC1 and the second onboard battery charger OBC2, and these are connected to the respective charging connection lines LL1, LL2, LL3, and LN of the AC charging port 5.The respective AC connection lines VL1, VL2, VL3, VN are thus connected to a respective AC connection L11, L21, L31, N1, L12, L22, L32, N2 of the first onboard battery charger OBC1 and the second onboard battery charger OBC2, thereby connecting them to each other, and are also connected to the respective charging connection lines LL1, LL2, LL3, LN of the AC charging port 5, thus connecting the respective AC connection L11, L21, L31, N1, L12, L22, L32, N2 of the first onboard battery charger OBC1 and the second onboard battery charger OBC2 to the respective charging connection lines LL1, LL2, LL3, LN of the AC charging port 5.

[0050] In alternative embodiments not shown, the secondary sides of the isolating DC / DC converters of the two onboard battery chargers OBC1, OBC2 are connected electrically in parallel to each other and are connected to a DC side of a common AC / DC converter, wherein an AC side of the common AC / DC converter is connected to the charging connection lines LL1, LL2, LL3, LN of the AC charging port 5.

[0051] In the second embodiment according to the Fig. 4 and Fig. A first parallel connection element PS1 is arranged between the positive potential terminal DCP1 of the primary side of the isolating DC / DC converter of the first onboard battery charger OBC1 and the positive terminal HVP2 of the second HV battery cell pack 3.2, and a second parallel connection element PS2 is arranged between the negative potential terminal DCN2 of the primary side of the isolating DC / DC converter of the second onboard battery charger OBC2 and the negative terminal HVN1 of the first HV battery cell pack 3.1. This makes it possible to connect the two HV battery cell packs 3.1 and 3.2 electrically in series by closing the series connection element SS and opening the two parallel connection elements PS1 and PS2, and to connect the two HV battery cell packs 3.1 and 3.2 electrically in parallel by opening the series connection element SS and closing the two parallel connection elements PS1 and PS2.

[0052] The two onboard battery chargers OBC1 and OBC2 are, as described above, each designed as an isolating onboard battery charger. They therefore feature galvanic isolation, which allows connection to different high-voltage potentials on the battery side (utilizing the interruption of the transformer's potential reference from primary to secondary winding).

[0053] In the process for heating the HV battery 3 of the HV system 1, the two bidirectional insulating onboard battery chargers OBC1 and OBC2 are used to alternately charge the first HV battery cell pack 3.1 into the second HV battery cell pack 3.2 and vice versa. During this alternating charging process, the first HV battery cell pack 3.1 is alternately discharged, thereby charging the second HV battery cell pack 3.2, and then the second HV battery cell pack 3.2 is discharged, thereby charging the first HV battery cell pack 3.1.

[0054] This alternating charging and recharging process achieves impedance heating of the HV battery cell packs 3.1, 3.2 and thus of the HV battery 3, because this alternating charging and the resulting alternating current flow, i.e., due to a changing direction of this current flow, across the internal resistance Ri1, Ri2 of the respective HV battery cell pack 3.1, 3.2, generates heat loss at the internal resistance Ri1, Ri2, which heats up the respective HV battery cell pack 3.1, 3.2 and thus the HV battery 3.

[0055] The switching between recharging the first HV battery cell pack 3.1 into the second HV battery cell pack 3.2 and recharging the second HV battery cell pack 3.2 into the first HV battery cell pack 3.1 is carried out in particular at a frequency greater than 1 Hz, for example at a frequency of 100 Hz.

[0056] This recharging process is carried out in particular when the HV battery 3 is not being charged via the AC charging port 5. It is specifically intended that, for the heating of the HV battery 3 through this recharging process, the charging switching elements LS1 to LS4 are open or will be opened, in particular to ensure that the AC charging port 5 is de-energized, especially at the AC charging pins, i.e., at the charging port contacts L1, L2, L3, N, of the AC charging port 5.

[0057] This recharging and thus the heating of the HV battery 3 is carried out, for example, during driving operation of vehicle 2 and / or when vehicle 2 is parked.

[0058] In the second embodiment according to the Fig. 4 and Fig. 5 is intended for the described heating of the HV battery 3, that the series switching element SS is closed or is closed and the two parallel switching elements PS1, PS2 are open or are opened.

[0059] In Fig. 3 is for the first embodiment according to Fig. 2. The transfer of the first HV battery cell pack 3.1 to the second HV battery cell pack 3.2 is shown by the first arrow P1, i.e., the first HV battery cell pack 3.1 is discharged and the second HV battery cell pack 3.2 is charged. For this purpose, the charging switching elements LS1 to LS4 are specifically designed to be open to ensure that the charging terminal contacts L1, L2, L3, and N are de-energized. The first onboard battery charger OBC1 transfers power from its DC input voltage source, i.e., from the first HV battery cell pack 3.1, to the common AC connection of both onboard battery chargers OBC1 and OBC2. The second onboard battery charger OBC2 transfers power from the common AC connection to the second HV battery cell pack 3.2 in the same amount.

[0060] The second arrow, P2, illustrates the transfer of power from the second HV battery cell pack 3.2 to the first HV battery cell pack 3.1; that is, the second HV battery cell pack 3.2 is discharged and the first HV battery cell pack 3.1 is charged. For this to occur, the two onboard battery chargers, OBC1 and OBC2, reverse their power flow. The charging circuits LS1 to LS4 remain open. The second onboard battery charger, OBC2, transfers power from its DC input voltage source, i.e., from the second HV battery cell pack 3.2, to the common AC connection of both onboard battery chargers, OBC1 and OBC2. The first onboard battery charger, OBC1, transfers power from the common AC connection to the first HV battery cell pack 3.1 in the same amount.

[0061] Any desired current waveform can be applied to the charging current by the onboard battery chargers OBC1 and OBC2, for example, a square wave or a sine wave. As mentioned above, the switching between these two states occurs primarily at a frequency greater than 1 Hz, for example, at a frequency of 100 Hz. The heating at the respective internal resistances Ri1 and Ri2 of the first HV battery cell pack 3.1 and the second HV battery cell pack 3.2 is at its maximum when the onboard battery chargers OBC1 and OBC2 are charging the HV battery cell packs 3.1 and 3.2 at their maximum current. A rough estimate of the heat loss in the HV battery 3, with a charging current of approximately 40 A for the onboard battery chargers OBC1 and OBC2 and a sum of the internal resistances Ri1 and Ri2 of the two HV battery cell packs 3.1 and 3.2 of 500 mΩ, yields a heat loss of 800 W.

[0062] In Fig. 5 is for the second embodiment according to Fig.Figure 4 shows the transfer of power from the first HV battery cell pack 3.1 to the second HV battery cell pack 3.2, indicated by the first arrow P1. This means that the first HV battery cell pack 3.1 is discharged and the second HV battery cell pack 3.2 is charged. For this purpose, the charging circuit elements LS1 to LS4 are open to ensure that the charging terminal contacts L1, L2, L3, and N are de-energized. Furthermore, the series circuit element SS is closed and the two parallel circuit elements PS1 and PS2 are open. The first onboard battery charger OBC1 transfers power from its DC input voltage source, i.e., from the first HV battery cell pack 3.1, to the common AC connection of both onboard battery chargers OBC1 and OBC2. The second onboard battery charger OBC2 transfers power from the common AC connection to the second HV battery cell pack 3.2.

[0063] The second arrow, P2, illustrates the transfer of power from the second HV battery cell pack 3.2 to the first HV battery cell pack 3.1; that is, the second HV battery cell pack 3.2 is discharged and the first HV battery cell pack 3.1 is charged. For this to occur, the two onboard battery chargers, OBC1 and OBC2, reverse their power flow. The charging circuits LS1 to LS4 and the two parallel circuits PS1 and PS2 remain open, while the series circuit SS remains closed. The second onboard battery charger, OBC2, transfers power from its DC input voltage source, i.e., from the second HV battery cell pack 3.2, to the common AC connection of both onboard battery chargers, OBC1 and OBC2. The first onboard battery charger, OBC1, transfers power from the common AC connection to the first HV battery cell pack 3.1 in the same amount.

[0064] Any desired current waveform can be applied to the charging current by the onboard battery chargers OBC1 and OBC2, for example, a square wave or a sine wave. As mentioned above, the switching between these two states occurs primarily at a frequency greater than 1 Hz, for example, at a frequency of 100 Hz. The heating at the respective internal resistances Ri1 and Ri2 of the first HV battery cell pack 3.1 and the second HV battery cell pack 3.2 is at its maximum when the onboard battery chargers OBC1 and OBC2 are charging the HV battery cell packs 3.1 and 3.2 at their maximum current. A rough estimate of the heat loss in the HV battery 3, with a charging current of approximately 40 A for the onboard battery chargers OBC1 and OBC2 and a sum of the internal resistances Ri1 and Ri2 of the two HV battery cell packs 3.1 and 3.2 of 500 mΩ, yields a heat loss of 800 W.

[0065] The described solution makes it possible, in particular, to perform the transfer of charge between the two HV battery cell packs 3.1 and 3.2 using the two bidirectional insulating onboard battery chargers OBC1 and OBC2, thereby enabling impedance heating of the two HV battery cell packs 3.1 and 3.2 and thus of the HV battery 3. This allows, for example, DC fast charging even at cold temperatures, as it is necessary to raise the HV battery 3 to a required minimum temperature level. For example, during a charging process from a state of charge of 20% at -7°C, the battery temperature should be raised to approximately 0°C (for NMC battery cells) in order to perform the DC charging process with nearly full DC charging power. Reference symbol list 1 HV system 2 vehicles 3 HV batteries 3.1 First HV battery cell pack 3.2 second HV battery cell pack 4 HV consumers 5 AC charging ports DCN1 negative potential terminal primary side DC / DC converter first onboard battery charger DCN2 negative potential connection primary side DC / DC converter second onboard battery charger DCP1 positive potential connection primary side DC / DC converter first onboard battery charger DCP2 positive potential connection primary side DC / DC converter second onboard battery charger HS1 first main switching element HS2 second main switching element HVM center tap HVN1 negative terminal of the first HV battery cell pack HVN2 negative terminal of the second HV battery cell pack HVP1 positive terminal of the first HV battery cell pack HVP2 positive terminal of the second HV battery cell pack IAC charging current L1 charging port contact L2 charging port contact L3 charging port contact N Charging port contact L11 AC connector first onboard battery charger L21 AC connector first onboard battery charger L31 AC connector first onboard battery charger N1 AC connector first onboard battery charger L12 AC connector second onboard battery charger L22 AC connection second onboard battery charger L32 AC connection second onboard battery charger N2 AC connection second onboard battery charger LL1 charging connection cable LL2 charging connection cable LL3 charging connection cable LN charging connection cable LS1 first charging switching element LS2 second charging switching element LS3 third charging switching element LS4 fourth charging switch element OBC1 first onboard battery charger OBC2 second onboard battery charger P1 first arrow P2 second arrow PS1 first parallel circuit element PS2 second parallel element Ri internal resistance Ri1 Internal resistance of the first HV battery cell pack Ri2 internal resistance of the second HV battery cell pack SS serial switching element VL1 AC connection cable VL2 AC connection cable VL3 AC connection cable VN AC connection cable

Claims

[1] HV system (1) for a vehicle (2), comprising an HV battery (3) with two HV battery cell packs (3.1, 3.2), and two bidirectional isolating onboard battery chargers (OBC1, OBC2), wherein a positive potential terminal (DCP1) of a primary side of an isolating DC / DC converter of the first onboard battery charger (OBC1) is connected to a positive terminal (HVP1) of the first HV battery cell pack (3.1), a negative potential terminal (DCN2) of a primary side of an isolating DC / DC converter of the second onboard battery charger (OBC2) is connected to a negative terminal (HVN2) of the second HV battery cell pack (3.2), and a negative potential terminal (DCN1) of the primary side of the isolating DC / DC converter of the first onboard battery charger (OBC1) and a The positive potential terminal (DCP2) of the primary side of the isolating DC / DC converter of the second onboard battery charger (OBC2) is connected to a center tap (HVM) of the HV battery (3), and wherein - The secondary sides of the isolating DC / DC converters of the two onboard battery chargers (OBC1, OBC2) are electrically connected in parallel to each other and to a DC side of a common AC / DC converter, wherein an AC side of the common AC / DC converter is connected to charging connection lines (LL1, LL2, LL3, LN) of an AC charging port (5), or - The AC sides of the two onboard battery chargers (OBC1, OBC2) are connected electrically in parallel to each other with charging connection lines (LL1, LL2, LL3, LN) of an AC charging port (5). [2] HV system (1) according to claim 1, characterized by , that the center tap (HVM) is formed by a closed series switching element (SS) between a negative terminal (HVN1) of the first HV battery cell pack (3.1) and a positive terminal (HVP2) of the second HV battery cell pack (3.2). [3] HV system (1) according to claim 2, characterized by, that a first parallel connection element (PS1) is arranged between the positive potential terminal (DCP1) of the primary side of the isolating DC / DC converter of the first onboard battery charger (OBC1) and the positive terminal (HVP2) of the second HV battery cell pack (3.2) and a second parallel connection element (PS2) is arranged between the negative potential terminal (DCN2) of the primary side of the isolating DC / DC converter of the second onboard battery charger (OBC2) and the negative terminal (HVN1) of the first HV battery cell pack (3.1). [4] HV system (1) according to any one of the preceding claims, characterized by , that the two bidirectional isolating onboard battery chargers (OBC1, OBC2) are onboard battery charger components of a common bidirectional isolating onboard total battery charger. [5] HV system (1) according to any one of the preceding claims, characterized by, that the charging connection lines (LL1, LL2, LL3, LN) are each connectable or connected via a charging switching element (LS1 to LS4) to a respective charging connection contact (L1, L2, L3, N) of the AC charging connection (5). [6] Vehicle (2) comprising an HV system (1) according to any of the preceding claims. [7] Method for heating an HV battery (3) of an HV system (1) according to one of claims 1 to 5, wherein the two bidirectional insulating onboard battery chargers (OBC1, OBC2) are used alternately to recharge the first HV battery cell pack (3.1) into the second HV battery cell pack (3.2) and to recharge the second HV battery cell pack (3.2) into the first HV battery cell pack (3.1). [8] Method according to claim 7, characterized by , that for heating the HV battery (3) the series switching element (SS) is or will be closed and the two parallel switching elements (PS1, PS2) are or will be open. [9] Method according to claim 7 or 8, characterized by , that the switching between the recharging of the first HV battery cell pack (3.1) into the second HV battery cell pack (3.2) and the recharging of the second HV battery cell pack (3.2) into the first HV battery cell pack (3.1) is carried out at a frequency greater than 1 Hz, in particular 100 Hz. [10] Method according to any one of claims 7 to 9, characterized by , that for heating the HV battery (3) the charging switching elements (LS1 to LS4) are or will be opened.

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