Charging device and charging method for an electrical energy store

Abstract

The invention discloses a concept for charging an electrical energy store, for example a traction battery in an electric vehicle. For this purpose, superimposing an alternating voltage at a predetermined amplitude and frequency on a direct voltage which is intended for charging the electrical energy store is proposed. The alternating voltage can be adjusted according to the properties of the electrical energy store to be charged with respect to the impedance of the electrical energy store.

Description

[0001] Description

[0002] title

[0003] Charging device and charging method for an electrical energy storage device

[0004] Technical area

[0005] The present invention relates to a charging device for an electrical energy storage device, in particular an electrical energy storage device in an electric vehicle. The present invention further relates to a charging method for such an energy storage device.

[0006] State of the art

[0007] Vehicles that are fully or at least partially electrically powered have what's known as a traction battery. This traction battery serves as an electrical energy storage device and provides the electrical energy required to propel the vehicle.

[0008] For example, a single-phase or multi-phase alternating current can be used to charge the traction battery. The alternating current is typically rectified by a charging circuit provided in the vehicle and adjusted to a voltage level suitable for charging the traction battery. Alternatively, it is also possible to provide a direct current to the vehicle and use this to charge the traction battery. Higher charging capacities are generally available for charging the traction battery using direct current. In addition to the current state of charge or a possible restriction on the maximum charging current, the temperature of the traction battery cells also represents a limiting factor during the direct current charging process.

[0009] The document DE 10 2014 203 859 A1, for example, describes a method for controlling the temperature of a traction battery arranged in a vehicle during a charging process at a charging station in order to bring the battery cells to a temperature that is as suitable as possible for the charging process.

[0010] Disclosure of the invention

[0011] The present invention provides a charging device and a charging method for an electrical energy storage device having the features of the independent patent claims. Further advantageous embodiments are the subject of the dependent patent claims.

[0012] Accordingly, it is provided:

[0013] A charging device for an electrical energy storage device, comprising an input terminal, an output terminal, and a superimposition device. The input terminal is designed to be connected to a DC voltage source. The output terminal is designed to be connected to the electrical energy storage device. The superimposition device is designed to superimpose a predetermined AC voltage onto an electrical DC voltage provided at the input terminal. Furthermore, the superimposition device is designed to provide the DC voltage superimposed on the AC voltage at the output terminal. The predetermined AC voltage superimposed on the DC voltage has a predetermined frequency and a predetermined amplitude.

[0014] Furthermore, it is planned:

[0015] A charging method for an electrical energy storage device, comprising a step of providing a direct current voltage. The method further comprises a step of superimposing a predetermined alternating current voltage on the provided direct current voltage. The predetermined alternating current voltage has a predetermined frequency and a predetermined amplitude. Furthermore, the method comprises a step of providing the direct current voltage with the superimposed alternating current voltage to the electrical energy storage device.

[0016] Advantages of the Invention The present invention is based on the finding that electrical energy storage devices, such as the traction battery of an electric vehicle, can have an electrical internal resistance whose real part of the impedance depends on the frequency of the charging current. For example, the real part of the impedance for the internal resistance of a traction battery can have a maximum at approximately 0.1 Hz and then initially decrease with increasing frequency. Furthermore, a minimum of the real part of the impedance can occur, for example, in the range of approximately 1 kHz, while the real part of the impedance increases again with even further increasing frequencies.

[0017] Furthermore, the present invention is based on the finding that the maximum permissible charging power or maximum permissible charging current of a traction battery can depend on numerous parameters, such as the cell temperature of the battery cells. In particular, the charging power can be limited at relatively low temperatures.

[0018] Based on these findings, one idea of ​​the present invention is to provide a concept for charging an electrical energy storage device, in particular the traction battery of an electric vehicle, which enables improved charging performance of the traction battery. To this end, the invention provides for not providing a pure electrical direct voltage for charging the traction battery, but rather superimposing an alternating voltage component on the direct voltage for charging the battery. Such a charging voltage with a superimposed alternating voltage component varies the impedance of the traction battery. In particular, the real part of the impedance decreases, for example, up to a frequency of approximately 1 kHz. This makes it possible to achieve higher charging currents that can be absorbed by the traction battery.

[0019] In addition, the battery cells heat up due to the superimposed alternating voltage component. This can cause a further reduction in the internal cell resistance, especially in cold temperatures. Accordingly, the battery cells very quickly reach a cell temperature that allows for higher charging currents. Thus, the inventive concept can accelerate the charging process for the traction battery, allowing a desired target charge level to be reached more quickly or a larger amount of energy to be transferred to the traction battery within a given period of time.

[0020] According to one embodiment, the superimposition device is designed to set the frequency of the alternating voltage, which is superimposed on the direct voltage, in a range between approximately 100 Hz and 1000 Hz. Depending on the application, different limits for the frequency of the alternating voltage are also possible. If necessary, the frequency can also be set in an interval between 10 Hz and 2000 Hz or other suitable limits. The frequency can be selected in such a way that it comes as close as possible to the minimum of a real part of the impedance of the battery cells in the traction battery. It has been shown that superimposing the direct voltage with an alternating voltage in the aforementioned range does not lead to any significant impairment of the service life (state of health, SoH) of the traction battery.Furthermore, AC voltage components in the specified range are not affected, or only very slightly affected, by any DC link capacitors present. In particular, it is possible for the superimposition device to select and adjust the frequency of the AC voltage depending on the battery impedance, the battery's aging behavior, the vehicle electrical system characteristics (including the properties of the DC link capacitor), and, if applicable, the properties of the AC voltage generation.

[0021] According to one embodiment, the superimposition device is designed to adjust the frequency of the alternating voltage and / or the amplitude of the alternating voltage using a battery voltage, a state of charge, a cell temperature, and / or an impedance of the electrical energy storage device connected to the output terminal of the charging device. In this way, the charging voltage or the charging current for charging the electrical energy storage device can be specifically adapted to the respective properties of the electrical energy storage device to be charged. In particular, it is possible, for example, to influence the temperature development in the battery cells by means of the alternating voltage components superimposed on the direct voltage, thus conditioning the battery cells as quickly as possible to an optimal temperature for charging.

[0022] According to one embodiment, the amplitude of the alternating voltage applied to the

[0023] A DC voltage is superimposed, less than or equal to the DC component of the voltage provided at the output terminal. Thus, even with a DC voltage superimposed with an AC voltage, an electrical voltage with the same sign is always present, so the electrical voltage never drops below 0 volts.

[0024] According to one embodiment of the charging device, the input terminal of the charging device is designed to be coupled to a DC charging station for an electric vehicle. A DC voltage with an at least approximately constant voltage level is thus applied to the input terminal of the charging device. An AC voltage can then be superimposed on this DC voltage by means of the superimposition device, thus providing the combination of the DC voltage and the superimposed AC voltage for charging the traction battery in the electric vehicle.

[0025] According to one embodiment, the superimposition device is designed to adjust the voltage level of the direct voltage applied to the input terminal of the charging device and to superimpose the adjusted direct voltage with the alternating voltage. In this way, the direct voltage for charging the traction battery can be adjusted to the respective requirements of the traction battery to be charged. For this purpose, a corresponding direct voltage conversion can take place in the superimposition device, for example. For example, an electrical energy storage device with a higher voltage level, for example, 800 to 1000 volts, can thus also be charged by a direct voltage charging station that is only designed for lower voltage levels, for example, 400 V.

[0026] According to one embodiment, the superposition device comprises an electrical power converter and an electrical machine. A first connection point of the DC voltage connection of the electrical power converter is electrically coupled to a first connection point of the output connection of the charging device. A second connection point of the DC voltage connection is electrically coupled to a second connection point of the output connection of the charging device. Furthermore, a respective phase connection of the electrical machine is electrically coupled to a corresponding phase connection of the power converter. A first connection point of the input connection of the charging device is electrically coupled to a star point of the electrical machine. Finally, a second connection point of the input connection of the charging device is electrically coupled to the second connection point of the output connection of the charging device.In this way, the components, in particular the power converter and the electric motor of an electric drive system already present in an electric vehicle, can be used to superimpose an alternating voltage on the direct voltage and, if necessary, to adjust the voltage level of the direct voltage. Thus, the adjustment of the charging voltage for the charging concept according to the invention can be implemented in a particularly simple manner.

[0027] According to one embodiment, the charging device is integrated into a DC charging station for an electric vehicle. This can, in particular, be a rapid charging station for electric vehicles, which provides a DC voltage for charging the traction battery in an electric vehicle. The output connection of the charging device is designed to be coupled to a DC charging connection for an electric vehicle. In such a configuration, the DC voltage superimposed with an AC voltage can thus be completely generated and provided already in the charging station. If necessary, a wireless or wired communication connection can be provided between the vehicle and the charging station. Data can be exchanged via such a communication connection in order to specify the frequency and / or amplitude of the AC voltage that is to be superimposed on the DC voltage.

[0028] According to one embodiment, the input terminal of the charging device is designed to be coupled to a first electrical energy storage device, and the output terminal of the charging device is designed to be coupled to a second electrical energy storage device. The first electrical energy storage device and the second electrical energy storage device can, for example, each be part of a traction battery for an electric vehicle. In such a configuration, the charging device can be designed to transfer electrical energy from the input terminal and thus from the first electrical energy storage device to the output terminal and thus to the second electrical energy storage device. In this way, for example, a transfer of electrical energy from the first electrical energy storage device to the second electrical energy storage device is possible.By superimposing an alternating voltage on the direct voltage provided by the first electrical energy storage device, it is also possible, for example, to thermally condition the battery cells of the electrical energy storage device and thus prepare them for an upcoming charging process.

[0029] The above embodiments and further developments can be combined with each other as desired, where appropriate. Further embodiments, further developments, and implementations of the invention also include combinations of features of the invention not explicitly mentioned above or described below with regard to the exemplary embodiments. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

[0030] Short description of the drawings

[0031] Further features and advantages of the invention are explained below with reference to the figures. These show:

[0032] Fig. 1: a schematic representation of a block diagram of a charging device according to an embodiment;

[0033] Fig. 2: a schematic representation of a current-time diagram to illustrate the charging voltage of a charging device according to an embodiment;

[0034] Fig. 3: a schematic representation of a block diagram of an arrangement for charging an electrical energy storage device with a charging device according to an embodiment;

[0035] Fig. 4: a schematic representation of a possible circuit concept for a charging device according to an embodiment;

[0036] Fig. 5: a schematic representation of an arrangement for charging an electrical energy storage device with a charging device according to a further embodiment; Fig. 6: a schematic representation of an arrangement for charging an electrical energy storage device with a charging device according to yet another embodiment; and

[0037] Fig. 7: a flowchart underlying a charging method according to an embodiment.

[0038] Description of embodiments

[0039] Figure 1 shows a schematic representation of a block diagram illustrating an arrangement for charging an electrical energy storage device 2 according to one embodiment. The electrical energy storage device 2 can be, for example, the traction battery of a fully or at least partially electrically powered vehicle. To charge the electrical energy storage device 2, electrical energy in the form of a direct voltage can be provided by a direct voltage source 3. Such charging of the electrical energy storage device 2 using direct voltage is used in particular for rapid charging processes. Charging powers of well over 100 kW, in particular more than 200 kW or even more than 250 kW, are currently possible.Limiting factors for the maximum charging power for charging an electrical energy storage device 2 include not only the maximum electrical power available from the DC voltage source 3, but also parameters of the electrical energy storage device 2. For example, the maximum charging power can be limited by the temperature of the battery cells, the impedance of the electrical energy storage device 2, the current state of charge, or possibly other parameters. In particular, it is not possible, for example, to charge the electrical energy storage device 2 with the maximum possible charging power as long as the battery cells of the electrical energy storage device 2 have a temperature that is too low.

[0040] The current parameters of the electrical energy storage device 2 can be recorded, for example, using a battery management system (not shown). The maximum charging power can then be set in the form of a maximum permissible charging current and / or a charging voltage. For this purpose, the corresponding data or specifications can be transmitted to the DC voltage source 3, for example.

[0041] For charging the electrical energy storage device 2 according to the concept illustrated in Figure 1, a charging device 1 is further provided. This charging device 1 comprises an input terminal 11, an output terminal 12, and a superposition device 13. The input terminal 11 can be electrically coupled to the DC voltage source 3. This allows the DC voltage source 3 to provide the electrical energy required to charge the electrical energy storage device 2 in the form of a suitable DC voltage at the input terminal 11. The output terminal 12 can be electrically coupled to the electrical energy storage device 2. Thus, the electrical voltage applied to the output terminal 12 can be provided to the electrical energy storage device 2, thereby charging the electrical energy storage device 2.

[0042] Furthermore, a superimposition device 13 is provided in the charging device 1. This superimposition device 13 can superimpose an alternating voltage onto the electrical direct voltage provided at the input terminal 11. The energy required for the electrical alternating voltage to be superimposed can be taken from the direct voltage present at the input terminal 11. In other words, the superimposition device 11 does not provide any additional energy for charging the electrical energy storage device 2.

[0043] The superimposition device 13 can thus superimpose an alternating voltage with a predetermined frequency and a predetermined amplitude onto the electrical direct voltage provided at the input terminal 11. The amplitude of the superimposed alternating voltage is less than or at most equal to the value of the direct voltage. This ensures that the direct voltage superimposed with the alternating voltage always has a positive value and never becomes negative. The amplitude and frequency of the superimposed alternating voltage can be adjusted according to the properties of the electrical energy storage device 2 connected to the output terminal 12. In particular, for example, the frequency of the superimposed alternating voltage can be adjusted depending on the properties of the electrical energy storage device 2. For example, the impedance of the electrical energy storage device 2 can be taken into account for the respective frequency of the alternating voltage.The frequency can be set such that a real component of the impedance of the electrical energy storage device 2 is as small as possible, preferably minimal. For this purpose, the frequency can be set, for example, in a range between 100 Hz and 1000 Hz. Depending on the application, different limits for the frequency of the alternating voltage are also possible. If necessary, the frequency can also be set in a range between 10 Hz and 2000 Hz or other suitable limits.

[0044] The relationships between the amplitude and frequency of the alternating voltage to be superimposed and the respective properties of the electrical energy storage device 2 can be provided, for example, in the form of a previously calculated table (lookup table) or similar. Alternatively, suitable formulaic relationships are also possible. The respective data as the basis for adjusting the amplitude and frequency can be recorded and provided, for example, using a suitable battery management system or similar.

[0045] By appropriately adjusting the amplitude and / or frequency of the superimposed alternating voltage, it is thus possible, on the one hand, to superimpose an alternating voltage on the direct voltage for charging the electrical energy storage device 2, and thus to minimize the real part of the impedance of the electrical energy storage device 2 through the voltage ripple of the superimposed alternating voltage. Furthermore, by appropriately parameterizing the amplitude or frequency of the alternating voltage, the heat development in the electrical energy storage device 2 can also be influenced. This makes it possible, for example, to influence the temperature behavior of battery cells below an optimal charging temperature through the selected superimposition of the alternating voltage in such a way that the battery cells heat up as quickly as possible.Once the battery cells have reached a suitable temperature, the electrical energy storage device 2 can then be charged with a higher, possibly maximum, charging power. Thus, the electrical energy storage device 2 can be charged to a desired state of charge (SoC) within a shorter period of time. Alternatively, a larger amount of electrical energy can be charged into the electrical energy storage device 2 within a predetermined period of time. Figure 2 shows a current-time diagram of the course of an electrical charging current in a charging device 1 according to one embodiment. The dashed line I_DC represents the direct voltage component of the charging current. As previously described, an alternating voltage component I_AC is superimposed on this charging current.It is important to ensure that, on the one hand, the direct current I_DC superimposed with the alternating current component I_AC does not exceed the maximum permissible charging current I_max. On the other hand, the sum of the direct current component I_DC and the alternating current component I_AC should always be positive and not become negative.

[0046] Figure 3 shows a schematic representation of a concept for charging an electrical energy storage device 2 with a charging device 1 according to one embodiment. In the embodiment shown here, the electrical direct voltage for charging the electrical energy storage device 2 is provided by an external direct voltage source 3, for example a direct voltage charging station. The charging device 1 and the electrical energy storage device 2 are both arranged within an electric vehicle 4. The direct voltage charging station can be electrically coupled to the vehicle 4 and thus to the input connection 11 via a direct voltage charging connection. The direct voltage charging station provides an at least approximately constant electrical direct voltage. This is superimposed by an alternating voltage component by means of the charging device 1.The combination of electrical direct voltage and superimposed alternating voltage is then provided as charging voltage to the electrical energy storage device 2.

[0047] Figure 4 shows a schematic representation of a basic circuit concept of a superposition device 13 according to one embodiment. In the embodiment shown here, the superposition device 13 can be implemented, for example, from an electrical power converter 13a and an electrical machine 13b. These can, in particular, also be the components of the electric drive system of an electric vehicle. By using the existing components of the electric drive system in this way, no, or at least almost no, additional hardware components are required.

[0048] The electrical power converter 13a can be electrically connected to the terminals of the output terminal 12 via a DC voltage connection. The AC voltage connections of the power converter 13a can be electrically connected to corresponding phase connections of the electrical phases L1, L2, and L3 of the electrical machine 13b. A star point of the electrical machine 13b can be electrically connected to a first connection point of the input terminal 11 via a relay R. A second connection point of the input terminal 11 is electrically connected to a connection point of the DC voltage connection of the power converter 13a and thus to the corresponding connection point of the output terminal 12. Furthermore, an intermediate circuit capacitor C can be provided at the DC voltage connection.

[0049] By appropriately controlling the switching elements VI to V6 of the power converter 13a, it is thus possible, on the one hand, to superimpose an alternating voltage on the electrical direct voltage provided at the input terminal 11. Furthermore, by utilizing the motor inductances LI to L3, the voltage level of the electrical direct voltage at the input terminal 11 can also be adjusted in order to adjust the voltage to a voltage level suitable for charging the electrical energy storage device 2. In particular, in addition to superimposing an alternating voltage component on the charging voltage, the voltage level of the electrical direct voltage provided on the input side can also be increased by suitable boost converter operation in order to charge an electrical energy storage device 2 with a higher voltage level.

[0050] Figure 5 shows a schematic representation of a principle diagram for a concept for charging an electrical energy storage device 2 with a charging device 1 according to a further embodiment. The embodiment according to Figure 5 differs from the embodiment described in connection with Figure 3 in particular in that the superimposition device 1 is provided outside the vehicle 4, for example in the DC charging station with the DC voltage source 2. Thus, the DC voltage can also be superimposed with the desired AC voltage by the power electronics within the DC charging station. For example, wired or wireless communication can take place between the vehicle 4 and the charging station in order to specify the required parameters for setting the amplitude and / or frequency of the AC voltage to be superimposed.Figure 6 shows a schematic representation of a circuit concept for charging or recharging an electrical energy storage device according to a further embodiment. In the embodiment shown in Figure 6, the input terminal 11 is electrically coupled to a first electrical energy storage device 2a. The output terminal 12 of the charging device 1 is electrically coupled to a second electrical energy storage device 2b. This makes it possible, for example, to draw electrical energy from the first electrical energy storage device 2a and transfer it to the second energy storage device 2b. Here, too, the direct voltage provided by the first electrical energy storage device 2a can be superimposed with an alternating voltage. During such a recharging process, it is possible, on the one hand, to transfer electrical energy from the first electrical energy storage device 2a to the second energy storage device 2b.In particular, by superimposing an alternating voltage component on the direct current, thermal conditioning of the second electrical energy storage device 2b to be charged can also be achieved. Thus, even during a trip to a direct current charging station, the electrical energy storage device 2b can be brought to a suitable temperature in order to be able to carry out the charging process with the highest possible charging power. Of course, a suitable circuit design can also alternatively be used to transfer electrical energy from the second electrical energy storage device 2b to the first electrical energy storage device 2a. In this way, both electrical energy storage devices 2a and 2b can be thermally conditioned.

[0051] Finally, Figure 7 shows a flowchart underlying a charging method for an electrical energy storage device 2 according to one embodiment. The method can, in principle, comprise any steps as previously described in connection with the charging devices 1. Similarly, the previously described concepts with the charging devices 1 can also comprise any components that may be required to implement the method described below.

[0052] In step S1, a direct current voltage is first provided. This direct current voltage can then be superimposed with a predetermined alternating current voltage in step S2. This predetermined alternating current voltage can have a predetermined frequency and a predetermined amplitude. Finally, in step S3, the direct current voltage with the superimposed alternating current voltage is provided to the electrical energy storage device 2 to be charged.

[0053] In summary, the present invention relates to a concept for charging an electrical energy storage device, for example a traction battery in a

[0054] Electric vehicle. For this purpose, it is proposed to superimpose an alternating voltage of a predetermined amplitude and frequency on a direct current intended for charging the electrical energy storage device. The alternating voltage can be adjusted according to the properties of the electrical energy storage device to be charged, with respect to the impedance of the electrical energy storage device.

Claims

Claims 1. Charging device (1) for an electrical energy storage device (2), comprising: an input terminal (11) designed to be connected to a direct voltage source (3); an output terminal (12) designed to be connected to the electrical energy storage device (2); a superimposing device (13) designed to superimpose a direct voltage provided at the input terminal (11) with a predetermined alternating voltage and to provide the direct voltage superimposed with the alternating voltage at the output terminal (12), wherein the predetermined alternating voltage has a predetermined frequency and a predetermined amplitude.

2. Charging device (1) according to claim 1, wherein the superposition device (13) is designed to adjust the frequency of the alternating voltage within an interval between 100 and 1000 Hz.

3. Charging device (1) according to claim 1 or 2, wherein the superimposing device (13) is designed to adjust the frequency and / or the amplitude of the alternating voltage using a battery voltage, a state of charge, a cell temperature and / or an impedance of the electrical energy storage device (2) connected to the output terminal (12) of the charging device (1).

4. Charging device (1) according to one of claims 1 to 3, wherein the amplitude of the alternating voltage is smaller than a direct voltage component of the electrical voltage provided at the output terminal.

5. Charging device (1) according to one of claims 1 to 4, wherein the input terminal (11) of the charging device (1) is designed to be coupled to a DC charging station for an electric vehicle.

6. Charging device (1) according to one of claims 1 to 5, wherein the superimposing device (13) is designed to adapt a voltage level of the DC voltage provided at the input terminal and to superimpose the adapted DC voltage with the AC voltage.

7. Charging device (1) according to one of claims 1 to 6, wherein the superposition device (13) comprises an electrical power converter (13a) and an electrical machine (13b), wherein a first connection point of a DC voltage connection of the electrical power converter (13a) is electrically coupled to a first connection point of the output connection (12) of the charging device (1), a second connection point of the DC voltage connection is electrically coupled to a second connection point of the output connection (12) of the charging device (1), wherein in each case a phase connection of the electrical machine (13b) is electrically coupled to a corresponding phase connection of the power converter (13a), and wherein a first connection point of the input connection (11) of the charging device (1) is electrically coupled to a star point of the electrical machine (13b),and a second connection point of the input connection (11) of the charging device (1) is electrically coupled to the second connection point of the output connection (12) of the charging device (1).

8. Charging device (1) according to one of claims 1 to 4, wherein the input terminal (11) of the charging device (1) is designed to be coupled to a first electrical energy storage device (2a), and the output terminal (12) of the charging device (1) is designed to be coupled to a second electrical energy storage device (2b), and wherein the charging device (1) is designed to transmit electrical energy from the input terminal (11) to the output terminal (12).

9. Charging device (1) according to one of claims 1 to 4, wherein the charging device (1) is integrated in a DC charging station for an electric vehicle, and the output terminal (12) of the charging device (1) is designed to be coupled to a DC charging terminal for an electric vehicle.

10. Charging method for an electrical energy storage device (2), comprising the steps: Providing (Sl) an electrical direct voltage; Superimposing (S2) the provided electrical direct voltage with a predetermined alternating voltage, wherein the predetermined alternating voltage has a predetermined frequency and a predetermined amplitude; and Providing (S3) the electrical direct voltage with the superimposed alternating voltage to the electrical energy storage device (2).

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