Charging device and charging method for electrical energy store

Abstract

A solution for charging an electrical energy store, such as a traction battery in an electric vehicle, is disclosed. To this end, it is proposed that an AC voltage having a predetermined amplitude and frequency is superimposed on a DC voltage provided for charging the electrical energy store. In this case, the AC voltage can be adapted with respect to the impedance of the electrical energy store according to the characteristics of the electrical energy store to be charged.

Description

Technical Field

[0001] This invention relates to a charging device for an energy storage device, particularly for an energy storage device in an electric vehicle. Furthermore, this invention relates to a charging method for such an energy storage device. Background Technology

[0002] Vehicles that are fully or at least partially electrically powered are equipped with a so-called traction battery. The traction battery acts as an energy storage device and provides the electrical energy necessary to propel the vehicle.

[0003] To charge the traction battery, single-phase or multi-phase AC voltage can be used. Typically, the AC voltage is rectified and adapted to a suitable voltage level for charging the traction battery by means of a charging circuit located in the vehicle. Alternatively, a DC voltage can be provided at the vehicle and used to charge the traction battery. Here, a higher charging power is typically provided for charging the traction battery using DC voltage. In addition to the current state of charge or possible limitations on the maximum charging current, the temperature of each individual cell of the traction battery during the DC charging process is also a limiting parameter.

[0004] For example, published document DE 10 2014 203 859 A1 describes a method for temperature regulation of traction batteries arranged in a vehicle during the charging process at a charging station, so as to bring individual battery cells to a temperature that is as suitable as possible for the charging process. Summary of the Invention

[0005] This invention proposes a charging device and a charging method for an energy storage device, having the features of the independent claims. Further advantageous embodiments are the subject of the dependent claims.

[0006] Accordingly, a charging device for an energy storage device is provided, the charging device having an input connector, an output connector, and a superposition device. The input connector is designed for connection to a DC voltage source. The output connector is designed for connection to the energy storage device. The superposition device is designed to superimpose a predetermined AC voltage onto the DC voltage provided at the input connector. Furthermore, the superposition device is designed to provide a DC voltage superimposed with the AC voltage at the output connector. Here, the predetermined AC voltage superimposed on the DC voltage has a predetermined frequency and a predetermined amplitude.

[0007] Furthermore, a charging method for an energy storage device is provided, which includes a step of providing a DC voltage. The method further includes a step of superimposing a predetermined AC voltage onto the provided DC voltage. Here, the predetermined AC voltage has a predetermined frequency and a predetermined amplitude. Additionally, the method includes a step of providing a DC voltage with the superimposed AC voltage at the energy storage device.

[0008] Advantages of the present invention.

[0009] The present invention is based on the understanding that an energy storage device, such as a traction battery in an electric vehicle, can have an internal resistance, the real part of which is related to the frequency of the charging current. For example, the real part of the impedance to the internal resistance of a traction battery can have a maximum value at approximately 0.1 Hz and then decrease as the frequency increases thereafter. Furthermore, for example, the real part of the impedance can be found in the range of approximately 1 kHz, and the real part of the impedance increases further as the frequency increases.

[0010] Furthermore, this invention is based on the understanding that the maximum permissible charging power or maximum permissible charging current of a traction battery can be related to a large number of parameters, such as the temperature of a single battery cell. In particular, charging power is limited at relatively low temperatures.

[0011] Based on these understandings, the present invention is conceived of providing a scheme for charging an energy storage device, particularly a traction battery for an electric vehicle, which enables improved charging power of the traction battery. To this end, according to the invention, instead of using a pure DC voltage, an AC voltage percentage is superimposed on the DC voltage used for charging the battery. This charging voltage with the superimposed AC voltage percentage alters the impedance of the traction battery. Specifically, the real part of the impedance is reduced, for example, to a frequency of approximately 1 kHz. This allows for a higher charging current that can be received by the traction battery.

[0012] Furthermore, the individual battery cells heat up due to the increased proportion of the superimposed AC voltage. This is especially true at lower temperatures, causing a further decrease in the internal resistance of each cell. Consequently, the individual battery cells reach the cell temperature that allows for higher charging currents very quickly. Therefore, the charging process for the traction battery can be accelerated by the solution according to the invention, thereby reaching the desired target state of charge more quickly or transferring a larger total amount of energy to the traction battery within a predetermined time period.

[0013] In one embodiment, the superposition device is designed to set the frequency of the AC voltage superimposed on the DC voltage within a range of approximately 100Hz to 1000Hz. Depending on the application, different threshold values ​​for the AC voltage frequency are also possible. If necessary, the frequency can also be set between 10Hz and 2000Hz or other suitable threshold ranges. Here, the frequency can be selected such that it is as close as possible to the minimum real part of the impedance of a single cell in the traction battery. It has been shown that superimposing AC voltage on DC voltage within the mentioned range does not cause a significant adverse effect on the traction battery's State of Health (SoH). Furthermore, the AC voltage percentage within the mentioned range is not adversely affected, or is only adversely affected to a very small extent, by the presence of intermediate circuit capacitors. Particularly feasible is for the superposition device to select and set the AC voltage frequency based on battery impedance, battery aging characteristics, on-board electrical network characteristics (including the characteristics of intermediate circuit capacitors), and, if necessary, the characteristics generated by the AC voltage.

[0014] In one embodiment, the superposition device is designed to set the frequency and / or amplitude of the AC voltage based on the battery voltage, state of charge, cell temperature, and / or impedance of an energy storage device connected to the output connector of a charging device. In this way, the charging voltage or charging current used to charge the energy storage device can be specifically adapted to the corresponding characteristics of the energy storage device to be charged. For example, it is particularly feasible to influence the temperature generation in a single battery cell by the proportion of AC voltage superimposed on a DC voltage, and thus to adjust the single battery cell to the optimal temperature for charging as quickly as possible.

[0015] In one embodiment, the amplitude of the AC voltage superimposed on the DC voltage is less than or equal to the proportion of the DC voltage to the voltage supplied at the output terminal. Therefore, even when an AC voltage is superimposed on a DC voltage, a voltage of the same sign is always applied, ensuring that the voltage is never less than 0 volts.

[0016] According to one embodiment of the charging device, the input connector of the charging device is designed to be coupled to a DC voltage charging station for electric vehicles. Therefore, a DC voltage having a nearly constant magnitude is applied at the input connector of the charging device. An AC voltage can then be superimposed on the DC voltage by means of a superposition device, thus providing a combination of the DC voltage and the superimposed AC voltage for charging the traction battery in the electric vehicle.

[0017] In one embodiment, the superposition device is designed to adapt the magnitude of the DC voltage applied to the input connector of the charging device and to superimpose an AC voltage onto the adapted DC voltage. In this way, the DC voltage used to charge the traction battery can be adapted in magnitude to the corresponding requirements of the traction battery to be charged. For this purpose, a corresponding DC voltage conversion can be implemented in the superposition device, for example. The energy storage device can thus also be charged by a DC voltage charging station, for example, at a higher voltage of 800 to 1000 volts, which is designed only for lower voltage levels, such as 400V.

[0018] In one embodiment, the superposition device includes an electric converter and a motor. A first connection point of the DC voltage terminal of the electric converter is electrically coupled to a first connection point of the output terminal of the charging device. A second connection point of the DC voltage terminal is electrically coupled to a second connection point of the output terminal of the charging device. Furthermore, the phase terminals of the motor are electrically coupled to their corresponding phase terminals of the converter. A first connection point of the input terminal of the charging device is electrically coupled to a star connection point of the motor. Finally, a second connection point of the input terminal of the charging device is electrically coupled to a second connection point of the output terminal of the charging device. In this way, components of the electric drive system already present in the electric vehicle, particularly the converter and motor, can be used to superimpose AC voltage onto DC voltage and, if necessary, adapt the magnitude of the DC voltage. Therefore, adaptation of the charging voltage for the charging scheme according to the invention can be achieved in a particularly easy manner.

[0019] In one embodiment, the charging equipment is integrated into a DC voltage charging station for electric vehicles. This can particularly relate to fast charging stations for electric vehicles, which provide DC voltage for charging the traction battery in the electric vehicle. Here, the output connector of the charging equipment is designed to couple with the DC voltage charging connector for the electric vehicle. Therefore, in such a configuration, a DC voltage superimposed with AC voltage can be fully generated and provided at the charging station. Here, if necessary, a wireless or wired communication connection can be established between the vehicle and the charging station. Through such a communication connection, data can be exchanged to specify the frequency and / or amplitude of the AC voltage superimposed on the DC voltage.

[0020] In one embodiment, the input connector of the charging device is designed to be coupled to a first energy storage device, and the output connector of the charging device is designed to be coupled to a second energy storage device. The first and second energy storage devices can also be, for example, parts 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 connector and thus from the first energy storage device to the output connector and thus to the second energy storage device. In this way, for example, it is possible to transfer electrical energy from the first energy storage device to the second energy storage device. Here, by superimposing an AC voltage onto the DC voltage provided by the first energy storage device, it is also possible to thermally regulate the individual cells of the energy storage device and thus prepare for the upcoming charging process.

[0021] Wherever meaningful, the above design schemes and improvements can be combined arbitrarily with each other. Other design schemes, modifications, and implementations of the present invention also include combinations of features not explicitly mentioned in the preceding or following descriptions of the embodiments. In particular, those skilled in the art will also add various aspects as improvements or supplements to the corresponding basic forms of the present invention. Attached Figure Description

[0022] Further features and advantages of the invention will now be explained with reference to the accompanying drawings. Herein: Figure 1 A block diagram of a charging device according to one embodiment is shown; Figure 2 A schematic diagram of a current-time graph is shown, which is used to illustrate the charging voltage of a charging device according to one embodiment; Figure 3 A block diagram of an arrangement for charging an energy storage device according to one embodiment is shown. Figure 4 A schematic diagram of a feasible circuit scheme for a charging device according to one embodiment is shown; Figure 5 A schematic diagram of an arrangement for charging an energy storage device according to another embodiment is shown. Figure 6 A schematic diagram of an arrangement for charging a power storage device according to yet another embodiment is shown; and Figure 7 A flowchart is shown based on a charging method according to one embodiment. Detailed Implementation

[0023] Figure 1A block diagram is shown, illustrating the arrangement for charging an energy storage device 2 according to one embodiment. The energy storage device 2 can be, for example, the traction battery of a fully or at least partially electrically driven vehicle. To charge the energy storage device 2, electrical energy in the form of a DC voltage source 3 can be provided. This charging scheme using a DC voltage for the energy storage device 2 is particularly useful in fast charging. In this case, charging power far exceeding 100kW, especially 200kW or even 250kW, can currently be achieved. Besides the maximum electrical power that can be utilized by the DC voltage source 3, the parameters of the energy storage device 2 are also limiting factors for the maximum charging power used to charge the energy storage device 2. The maximum charging power can be limited, for example, by the temperature of a single battery cell, the impedance of the energy storage device 2, the current state of charging, or other parameters if necessary. In particular, it is not feasible, for example, to charge the energy storage device 2 at the maximum feasible charging power as long as the temperature of a single battery cell of the energy storage device 2 is too low.

[0024] For example, the current parameters of the energy storage device 2 can be detected by means of a battery management system (not shown). The maximum charging power can then be set in the form of the maximum permissible charging current and / or charging voltage. For this purpose, the corresponding data or preset values ​​can be transmitted to the DC voltage source 3, for example.

[0025] In addition, a charging device 1 is provided for charging according to... Figure 1 The energy storage device 2 shown in the diagram is charged. The charging device 1 includes an input connector 11, an output connector 12, and a superposition device 13. The input connector 11 can be electrically coupled to a DC voltage source 3. The DC voltage source 3 can thus provide electrical energy in the form of a suitable DC voltage at the input connector 11, which is configured to charge the energy storage device 2. The output connector 12 can be electrically coupled to the energy storage device 2. Therefore, a voltage applied to the output connector 12 can be provided at the energy storage device 2, thereby charging the energy storage device 2.

[0026] Furthermore, a superposition device 13 is provided in the charging device 1. The superposition device 13 is capable of superimposing an AC voltage onto the DC voltage supplied at the input connector 11. For this purpose, the energy necessary for superimposing the AC voltage can be derived from the DC voltage applied at the input connector 11. In other words, the superposition device 11 does not provide additional energy for charging the energy storage device 2.

[0027] Therefore, the superposition device 13 can superimpose an AC voltage with a predetermined frequency and a predetermined amplitude onto the DC voltage supplied at the input connector 11. Here, the amplitude of the superimposed AC voltage is less than or at most equal to the value of the DC voltage. This ensures that the DC voltage with the superimposed AC voltage is always positive and never negative. Here, the amplitude and frequency of the superimposed AC voltage can be set according to the characteristics of the energy storage device 2 connected to the output connector 12. In particular, for example, the frequency of the superimposed AC voltage can be adapted according to the characteristics of the energy storage device 2. For example, the impedance of the energy storage device 2 can be taken into account for the corresponding frequency of the AC voltage. Here, the frequency can be set such that the real part of the impedance of the energy storage device 2 is as small as possible, preferably minimized. For this purpose, the frequency can be set, for example, in the range between 100Hz and 1000Hz. Different critical values ​​for the frequency of the AC voltage can also be implemented depending on the application. If necessary, the frequency can also be set in the range between 10Hz and 2000Hz or other suitable critical values.

[0028] The relationship between the amplitude and frequency of the AC voltage to be superimposed and the corresponding characteristics of the energy storage device 2 can be provided, for example, in a pre-calculated table (lookup table) or similar form. Alternatively, a suitable formulaic relationship is also possible. For example, the corresponding data can be detected and provided as a basis for setting the amplitude and frequency by means of a suitable battery management system or similar device.

[0029] Therefore, by appropriately setting the amplitude and / or frequency of the superimposed AC voltage, an AC voltage can be superimposed on the DC voltage used to charge the energy storage device 2, and thus the real part of the impedance of the energy storage device 2 is minimized by the ripple voltage of the superimposed AC voltage. Furthermore, by appropriately parameterizing the amplitude or frequency of the AC voltage, heat generation in the energy storage device 2 can also be affected. For example, it is possible to influence the temperature characteristics by selecting the superposition of the AC voltage when the individual battery cell is below its optimal charging temperature, so that the individual battery cell heats up as quickly as possible. Thus, after the individual battery cell has reached a suitable temperature, the energy storage device 2 can be charged with a higher, and if necessary, maximum charging power. Therefore, the energy storage device 2 can be charged to the desired state of charge (SoC) in a shorter time period. Alternatively, a larger total amount of electrical energy can be charged into the energy storage device 2 within a predetermined time period.

[0030] Figure 2A current-time diagram showing the change in charging current in a charging device 1 according to one embodiment is shown. Here, the dashed line I_DC represents the DC voltage percentage of the charging current. As previously described, the charging current is superimposed with the AC percentage I_AC. It should be noted that, on the one hand, the DC current I_DC with the superimposed AC current percentage I_AC does not exceed the maximum permissible charging current I_max. On the other hand, the sum formed by the DC current percentage I_DC and the AC current percentage I_AC should always be positive and not negative.

[0031] Figure 3 A schematic diagram is shown of a scheme for charging an energy storage device 2 using a charging device 1 according to one embodiment. In the embodiment shown here, the DC voltage for charging the energy storage device 2 is provided by an external DC voltage source 3, such as a DC voltage charging station. Here, both the charging device 1 and the energy storage device 2 are arranged inside an electric vehicle 4. The DC voltage charging station is electrically coupled to the vehicle 4 and therefore to the input connector 11 via a DC voltage charging connector. Here, the DC voltage charging station provides at least a nearly constant DC voltage. The DC voltage is superimposed by the charging device 1 through an AC voltage ratio. The combination formed by the DC voltage and the superimposed AC voltage is then provided to the energy storage device 2 as the charging voltage.

[0032] Figure 4 A schematic diagram of the circuit scheme of the superposition device 13 according to one embodiment is shown. In the embodiment shown here, the superposition device 13 can be implemented, for example, by an electric converter 13a and a motor 13b. In this case, it is also possible to involve components of the electric drive system of an electric vehicle. Therefore, by using the existing components of the electric drive system in this way, no additional hardware components are required or at least almost no additional hardware components are required.

[0033] The converter 13a can be electrically connected to the output terminal 12 at its DC voltage terminal. The AC voltage terminal of the converter 13a can be electrically connected to the corresponding phase terminals of the electrical phases L1, L2, and L3 of the motor 13b. The star contact of the motor 13b can be electrically connected to the first connection point of the input terminal 11 via the relay R. The second connection point of the input terminal 11 is electrically connected to the connection point of the DC voltage terminal of the converter 13a and therefore to the corresponding connection point of the output terminal 12. Furthermore, an intermediate circuit capacitor C can be provided at the DC voltage terminal.

[0034] Therefore, by appropriately controlling the switching elements V1 to V6 of the converter 13a, an AC voltage can be superimposed on the DC voltage supplied at the input terminal 11. Furthermore, when using motor inductors L1 to L3, the magnitude of the DC voltage at the input terminal 11 can be adapted to a voltage suitable for charging the energy storage device 2. Thus, in addition to superimposing an AC voltage ratio on the charging voltage, the voltage level of the DC voltage supplied on the input side can be increased by operating a suitable boost chopper, thereby charging the energy storage device 2 at a higher voltage level.

[0035] Figure 5 A schematic diagram of a scheme for charging an energy storage device 2 using a charging device 1 according to another embodiment is shown. According to... Figure 5 Implementation methods and combinations Figure 3 The difference in the described implementation lies particularly in that the superposition device 1 is located outside the vehicle 4, for example, in a DC voltage charging station with a DC voltage source 2. Therefore, it is also possible to superimpose the desired AC voltage onto the DC voltage using power electronics within the DC voltage charging station. Here, for example, wired or wireless communication between the vehicle 4 and the charging station can be implemented to specify the necessary parameters for setting the amplitude and / or frequency of the AC voltage to be superimposed.

[0036] Figure 6 A schematic diagram of a circuit scheme for charging or transferring charge to an energy storage device according to another embodiment is shown. Figure 6 In the embodiment shown, the input connector 11 is electrically coupled to the first energy storage device 2a. The output connector 12 of the charging device 1 is electrically coupled to the second energy storage device 2b. Thus, for example, electrical energy can be obtained from the first energy storage device 2a and transferred to the second energy storage device 2b. It is also possible to superimpose an AC voltage onto the DC voltage provided by the first energy storage device 2a. During this transfer charging process, electrical energy can be transferred from the first energy storage device 2a to the second energy storage device 2b. Here, thermal regulation of the second energy storage device 2b to be charged can also be achieved, particularly by superimposing an AC voltage ratio onto the DC voltage. Therefore, the energy storage device 2b can reach a suitable temperature en route to the DC voltage charging station, allowing the charging process to be carried out with the highest possible charging power. Of course, alternatively, the transfer of electrical energy from the second energy storage device 2b to the first energy storage device 2a can be achieved using a suitable circuit scheme. In this way, thermal regulation of both energy storage devices 2a and 2b is possible.

[0037] at last Figure 7A flowchart is shown based on a charging method for an energy storage device 2 according to one embodiment. The method can, in principle, include any of the steps previously described in conjunction with the charging device 1. Similarly, the previously described scheme with the charging device 1 can also include any components necessary to implement the method described below.

[0038] First, a DC voltage is provided in step S1. Then, in step S2, a predetermined AC voltage is superimposed on the DC voltage. The predetermined AC voltage can have a predetermined frequency and a predetermined amplitude. Finally, in step S3, a DC voltage with the superimposed AC voltage is provided at the energy storage device 2 to be charged.

[0039] In summary, the present invention relates to a scheme for charging an energy storage device, such as a traction battery in an electric vehicle. To this end, it is proposed to superimpose an AC voltage with a predetermined amplitude and frequency onto a DC voltage used for charging the energy storage device. Here, the AC voltage can be adapted to the impedance of the energy storage device according to its characteristics.

Claims

1. Charging device (1) for an electrical energy store (2), the charging device having an input connection (11) designed for connection to a direct voltage source (3), an output connection (12) designed for connection to the electrical energy store (2), a superimposition device (13) designed for superimposing a predetermined alternating voltage on a direct voltage provided at the input connection (11) and for providing a direct voltage superimposed with the alternating voltage at the output connection (12), the predetermined alternating voltage having a predefined frequency and a predefined amplitude, the superimposition device (13) being designed for setting the frequency of the alternating voltage within an interval between 100 and 1000 Hz, the superimposition device (13) being designed for setting 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 an electrical energy store (2) connected to the output connection (12) of the charging device (1), the amplitude of the alternating voltage being smaller than a direct voltage proportion of a voltage provided at the output connection, the input connection (11) of the charging device (1) being designed for coupling to a direct voltage charging station for an electric vehicle, the superimposition device (13) being designed for adapting a voltage size of a direct voltage provided at the input connection and for superimposing an alternating voltage on the adapted direct voltage, the superimposition device (13) comprising an electrical converter (13a) and an electrical machine (13b), wherein a first connection point of a direct voltage connection of the electrical converter (13a) is electrically coupled to a first connection point of the output connection (12) of the charging device (1) and a second connection point of the direct voltage connection is electrically coupled to a second connection point of the output connection (12) of the charging device (1), wherein phase connections of the electrical machine (13b) are electrically coupled to corresponding phase connections of the converter (13a), and wherein a first connection point of the input connection (11) of the charging device (1) is electrically coupled to a star connection 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), the input connection (11) of the charging device (1) being designed for coupling to a first electrical energy store (2a) and the output connection (12) of the charging device (1) being designed for coupling to a second electrical energy store (2b), and wherein the charging device (1) is designed for transferring electrical energy from the input connection (11) to the output connection (12), the charging device (1) being integrated in a direct voltage charging station for an electric vehicle, and the output connection (12) of the charging device (1) being designed for coupling to a direct voltage charging connection for an electric vehicle.

10. Charging method for an electrical energy store (2) having the following steps: providing (S1) a direct voltage, ​ ​ wherein ​ 2. The charging device (1) according to claim 1, wherein ​ 3. The charging device (1) according to claim 1 or 2, wherein ​ 4. The charging device (1) according to any one of claims 1 to 3, wherein ​ 5. The charging device (1) according to any one of claims 1 to 4, wherein, ​ 6. The charging device (1) according to any one of claims 1 to 5, wherein ​ 7. The charging device (1) according to any one of claims 1 to 6, wherein ​ ​ ​ ​ 8. The charging device (1) according to any one of claims 1 to 4, wherein ​ 9. The charging device (1) according to any one of claims 1 to 4, wherein ​ ​ ​ ​ A predetermined alternating voltage is superimposed (S2) on the provided direct voltage, wherein The predetermined alternating voltage has a predetermined frequency and a predetermined amplitude; and The direct voltage with the superimposed alternating voltage is provided (S3) at the electrical energy store (2).

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