Method and control device for determining a maximum current limit of a battery system with at least two batteries

Abstract

This invention relates to a method for determining the maximum current limit (40) of a battery system having at least two batteries, wherein the following steps are performed: detecting corresponding single currents (10⁻¹, 10⁻²) on the at least two batteries; detecting the total current (10⁻²s) of the battery system; determining corresponding current ratios (12⁻¹, 12⁻²) between the detected single currents (10⁻¹, 10⁻²) and the detected total current (10⁻²s); determining a maximum individual current limit (15⁻¹, 15⁻²) of the battery system for each of the at least two batteries based on the determined current ratios (12⁻¹, 12⁻²) and the nominal maximum current limit (30⁻¹, 30⁻²) of the corresponding batteries; selecting the smallest determined maximum individual current limit (15⁻¹, 15⁻²) as the maximum current limit (40) of the battery system; and providing the determined maximum current limit (40) as a maximum current limit signal (41). Alternatively or additionally, resistors (11⁻¹, 11⁻², 11⁻²s) may also be used for this purpose. In addition, the present invention relates to a control device (1).

Description

[0001] This invention relates to a method and a control device for determining the maximum current limit of a battery system having at least two batteries. Furthermore, this invention relates to a method and a battery system control device for controlling a battery system having at least two batteries.

[0002] In a battery system with multiple cells connected in parallel, the individual cells are typically not identical and therefore do not have exactly the same electrical performance. This can be due to differences in manufacturing processes and varying aging behaviors. Consequently, even cells with identical structures connected in parallel may exhibit different current distributions. When operating a battery system, the unique current limits of each individual cell must be observed under all circumstances.

[0003] The technical problem to be solved by the present invention is to realize a method and a control device for determining the maximum current limit of a battery system having at least two batteries, thereby enabling reliable determination of the maximum current limit of the battery system.

[0004] The technical problem described above according to the present invention is solved by a method having the features of claim 1 and a control device having the features of claim 6. Advantageous designs of the invention are derived from the dependent claims.

[0005] In particular, a method is provided for determining the maximum current limit of a battery system having at least two batteries, wherein the following measures are performed:

[0006] Detect the corresponding single current on at least two batteries.

[0007] Detect the total current of the battery system.

[0008] Determine the corresponding current ratio between the detected single current and the detected total current.

[0009] Based on the determined current ratios and the nominal maximum current limits of the corresponding batteries, the maximum individual current limits of the battery system are determined for each of the at least two batteries.

[0010] and / or

[0011] Receive or estimate the individual resistances of the at least two batteries.

[0012] Receive or estimate the total resistance of the battery system.

[0013] Determine the corresponding resistance ratio between the received or estimated single resistance and the received or estimated total resistance.

[0014] Based on the determined resistance ratio and the nominal maximum current limit of the corresponding battery, the maximum individual current limit of the battery system is determined for each of the at least two batteries.

[0015] The minimum definite maximum individual current limit is selected as the maximum current limit of the battery system, and the definite maximum current limit is provided as the maximum current limit signal.

[0016] Furthermore, a control device is specifically provided for determining the maximum current limit of a battery system having at least two batteries, wherein the control device is configured to perform the following measures:

[0017] Receive single currents detected on each of the at least two batteries.

[0018] Receive the detected total current of the battery system.

[0019] Determine the corresponding current ratio between the detected single current and the detected total current.

[0020] Based on the determined current ratios and the nominal maximum current limits of the corresponding batteries, the maximum individual current limits of the battery system are determined for each of the at least two batteries.

[0021] and / or

[0022] Receive or estimate the individual resistances of at least two cells.

[0023] Receive or estimate the total resistance of the battery system.

[0024] Determine the corresponding resistance ratio between the received or estimated single resistance and the received or estimated total resistance.

[0025] Based on the determined resistance ratio and the nominal maximum current limit of the corresponding battery, the maximum individual current limit of the battery system is determined for each of the at least two batteries.

[0026] Select the smallest definite maximum individual current limit as the maximum current limit of the battery system, and provide the definite maximum current limit as the maximum current limit signal.

[0027] This method and control device allow for reliable determination of the maximum current limit across the entire operating range of the battery system. Two methods can be used: In the first method, a current ratio is determined for each cell based on the individual current detected on the cell and the total current detected across the battery system. Based on the separately determined current ratios and the nominal maximum current limit, the maximum individual current limit of the battery system is determined for each cell. The smallest determined maximum individual current limit is then selected. The underlying concept is that, in terms of maximum current, the “weakest” cell defines the maximum achievable total current of the battery system, as exceeding that cell's maximum current is not permitted. In the second method, the resistance ratio is alternatively or additionally determined in a similar manner and used to determine the maximum individual current limit. The corresponding results can be combined and integrated. The first method is particularly effective under high current conditions, while the second method is advantageous at lower currents, where the error in current detection is larger, resulting in a reduced signal-to-noise ratio.

[0028] The batteries in the battery system are especially connected in parallel. The individual current of each battery can be detected by a current sensor. Furthermore, the total current of the battery system is also detected by a current sensor. Each battery has a predetermined nominal maximum current limit.

[0029] Components of a control device can be constructed individually or in combination as a combination of hardware and software, for example as program code that executes on a microcontroller or microprocessor. Alternatively, components can be specified to be constructed individually or in combination as application-specific integrated circuits (ASICs) or field-programmable gate arrays (FPGAs).

[0030] The two methods are illustrated below by example. For example, consider a battery system with two batteries connected in parallel.

[0031] For example, the following nominal maximum current limit is specified for batteries:

[0032] I 1，max =150A

[0033] I 2，max =150A

[0034] The detected single current and total current are, for example:

[0035] I system =200A

[0036] I1 = 110A

[0037] I2 = 90A

[0038] Therefore, the following current ratio is derived:

[0039] Ratio 1,I =I system / I1=200A / 110A=1.81

[0040] Ratio 2,I =I system / I2=200A / 90A=2.22

[0041] Therefore, the following maximum individual current limits are derived:

[0042] I 1,maxsystem,I =Ratio 1,I ·I 1，max =1.81·150A=271.5A

[0043] I 2,maxsystem,I =Ratio 2,I ·I 2，max =2.22·150A=333A

[0044] The smallest of these determined maximum individual current limits is selected as the maximum current limit of the battery system:

[0045] I max，system，I =min_n(I n,maxsystem,I )=min_n(I 1,maxsystem,I ;I 2,maxsystem,I )=min_n(271.5A; 333A)=271.5A

[0046] In this example, the first battery is the "weaker" battery in terms of maximum current, so the total current of the battery system must be limited to a maximum current of 271.5A to avoid exceeding the battery's nominal maximum current limit. This determined maximum current limit is smaller than the battery system's nominal maximum current limit of 150A + 150A = 300A. If the battery system provides a total current of 271.5A, reaching the determined maximum current limit, then the ("weaker") first battery provides its nominal maximum current limit of 150A, while the second battery only provides 121.5A.

[0047] In the second method, the individual resistances and total resistance of the two batteries are received, for example, with the following values:

[0048] R system =50mΩ

[0049] R1 = 90mΩ

[0050] R2 = 110mΩ

[0051] These values ​​can be estimated by the battery control device using known methods and provided to the control device by the battery control device.

[0052] Therefore, the following resistance ratio is derived:

[0053] Ratio 1,R =R1 / R system =90mΩ / 50mΩ=1.8

[0054] Ratio 2,R =R2 / R system =110mΩ / 50mΩ=2.2

[0055] This results in the following maximum individual current limits:

[0056] I 1,maxsystem,R =Ratio 1,R ·I 1，max =1.8·150A=270A

[0057] I 2,maxsystem,R =Ratio 2,R ·I 2，max =2.2·150A=330A

[0058] The smallest determined maximum individual current limit is selected as the maximum current limit of the battery system:

[0059] I max，system，R =min_n(I n,maxsystem,R ) = min(I 1,maxsystem,R ;I 2,maxsystem,R ) = min(270A; 330A) = 270A

[0060] Therefore, the results of the first and second methods are almost identical. These examples are used to illustrate the invention. In principle, the values ​​may differ. In particular, battery systems can have more than two batteries. However, the basic method remains the same for more than two batteries.

[0061] One design approach specifies that a weighted average is formed from the corresponding current ratio and resistance ratio, and the maximum individual current limit is determined based on this weighted average. In other words, the current ratio and resistance ratio are combined by a weighted average, which can also be designed as an interpolation between the two ratios. This is particularly important for each cell before determining the maximum individual current limit. This significantly reduces the required computational power. The weighting coefficients allow for parameterized averaging or interpolation. For example, weighting coefficients can be determined and retained empirically for different load scenarios.

[0062] Using the example above, for each battery, with a weighting factor w:

[0063] Ratio n,gewichtet =w·Ratio n,I +(1-w)·Ratio n,R

[0064] The improved design specifies that weighting coefficients are selected based on the total current when forming the weighted average. This allows for the selection of different weighting coefficients for different regions of the total current. The weighting coefficients can be defined as a function of the total current. Specifically, the weighting coefficients are selected such that a portion of the resistance ratio dominates in the lower range of the total current, while a portion of the current ratio dominates in the higher range of the total current. This reduces errors caused by poor signal-to-noise ratios when detecting current at lower current levels. In summary, this improves the determination of the maximum current limit.

[0065] One design approach specifies that the current ratio and / or resistance ratio and / or weighted average are filtered over time using a low-pass filter, wherein the maximum individual current limit is determined based on the filtered ratio and / or the weighted average. This smooths the time curves of the current ratio and / or resistance ratio.

[0066] Using the example above, the result is (for the weighted average):

[0067] Ratio n,加权,平滑 =Tiefpass(Ratio n,加权,平滑 ,τ)

[0068] Here, τ is the smoothing coefficient based on the corresponding implementation of the low-pass filter.

[0069] Other features of the control device design are derived from the description of the method design. The advantages of the control device are the same as those of the method design.

[0070] Furthermore, a method for controlling a battery system having at least two batteries is also provided, wherein the method according to one of the foregoing embodiments is performed, and wherein the current of the battery system is limited based on a determined maximum current limit. This allows for active limiting of the total current of the battery system according to the determined maximum current limit.

[0071] In addition, a battery system control device is provided, which includes at least one control device according to one of the foregoing embodiments, wherein the battery system control device is configured to limit the current of the battery system from a maximum current limit determined by means of the control device.

[0072] The control device and battery system control unit are particularly suitable for vehicles, especially motor vehicles. Therefore, a vehicle having at least one control device according to one of the foregoing embodiments and / or having at least one battery system control unit is also proposed. In principle, the method and battery system control unit can also be used for other mobile or stationary battery systems.

[0073] The invention will now be described in more detail with reference to the accompanying drawings and preferred embodiments. Herein:

[0074] Figure 1 A schematic diagram illustrating an embodiment of a control device for determining the maximum current limit of a battery system having at least two batteries;

[0075] Figure 2 A schematic diagram illustrating another embodiment of the control device;

[0076] Figure 3 A schematic diagram illustrating another embodiment of the control device is shown.

[0077] exist Figure 1 A schematic diagram of an embodiment of a control device 1 for determining the maximum current limit 40 of a battery system having two batteries is shown. The control device 1 specifically performs the method described herein, which is illustrated with respect to the control device 1.

[0078] The control device 1 includes modules 100 to 103. Modules 100 to 103 can be configured as a combination of hardware and software, for example as program code that executes on a microcontroller or microprocessor.

[0079] The individual currents 10⁻¹ and 10⁻² detected on the batteries of the battery system and the total current 10⁻s of the battery system are provided to the control device 1. The current 10⁻x is detected by current sensors 20, 21, and 22 and provided, for example, as a current signal.

[0080] In module 100, control device 1 determines the corresponding current ratios 12-1 and 12-2 between the detected single currents 10-1 and 10-2 and the detected total current 10-s.

[0081] In modules 101 and 102, control device 1 determines the maximum individual current limit 15-1 and 15-2 of the battery system for each of the two batteries, based on the determined current ratios 12-1 and 12-2 and the nominal maximum current limits 30-1 and 30-2 of the corresponding batteries.

[0082] In module 103, control device 1 selects the smallest determined maximum individual current limit as the maximum current limit 40 of the battery system and provides it as the maximum current limit signal 41.

[0083] Alternatively or additionally, control device 1 may be specified to include modules 104-107.

[0084] Then, alternatively or additionally, the corresponding (current) single resistors 11-1, 11-2 of the two batteries in the battery system and the (current) total resistance 11-s of the battery system are provided to the control device 1. The resistors 11-1, 11-2, 11-s can be provided and transmitted, for example, by the battery control device 50, or estimated in other ways.

[0085] In module 104, control device 1 determines the corresponding resistance ratios 13-1, 13-2 between the received or estimated single resistors 11-1, 11-2 and the received or estimated total resistance 11-s.

[0086] In modules 105 and 106, control device 1 determines the maximum individual current limit 15-1 and 15-2 of the battery system for each of the two batteries, based on the determined resistance ratios 13-1 and 13-2 and the nominal maximum current limits 30-1 and 30-2 of the corresponding batteries.

[0087] In module 107, control device 1 selects the smallest determined maximum individual current limit as the maximum current limit 40 of the battery system and provides it as the maximum current limit signal 41.

[0088] The results provided by modules 103 and 107 can also be combined.

[0089] The control device 1 may be part of the battery system control unit 60, wherein the battery system control unit 60 is configured to limit the total current of the battery system by 10⁻⁶ based on a maximum current limit 40 determined by means of the control device 1. For this purpose, the maximum current limit signal 41 is evaluated and used in particular in the battery system control unit 60.

[0090] exist Figure 2 Another embodiment of the control device 1 is shown. This embodiment is essentially the same as... Figure 1 The embodiments shown are identical. The same reference numerals denote the same features and terms.

[0091] Furthermore, it is stipulated that weighted averages 14-1 and 14-2 are formed by the corresponding current ratios 12-1 and 12-2 and the resistance ratios 13-1 and 13-2, and the maximum individual current limits 15-1 and 15-2 are determined based on the corresponding weighted averages 14-1 and 14-2. For this purpose, control device 1 also has modules 108 and 109, which perform weighted averaging by interpolation between the corresponding current ratios 12-1 and 12-2 and the corresponding resistance ratios 13-1 and 13-2.

[0092] It can be stipulated that when forming weighted average values ​​14-1 and 14-2 in modules 108 and 109, the weighting coefficients are selected based on the total current 10-s, especially as a function of the total current 10-s.

[0093] exist Figure 3 Another embodiment of the control device 1 is shown. This embodiment is essentially the same as... Figure 2 The embodiments shown are identical. The same reference numerals denote the same features and terms.

[0094] Additional provisions are made that in modules 110 and 111, weighted average values ​​14-1 and 14-2 are filtered in time by low-pass filters, wherein maximum individual current limits 15-1 and 15-2 are determined based on the filtered weighted average values ​​16-1 and 16-2. Modules 110 and 111 specifically constitute filter device 2.

[0095] Alternatively, proportions 12-1, 12-2, 13-1, and 13-2 can be filtered by a low-pass filter (not shown), where the weighted averages 14-1 and 14-2 are advantageous relative to the required hardware and / or computing power.

[0096] List of reference numerals

[0097] 1. Control equipment

[0098] 2. Filtering device

[0099] 10-1 Single Current

[0100] 10-2 Single Current

[0101] 10-s total current

[0102] 11-1 Single Resistor

[0103] 11-2 Single Resistor

[0104] 11-s total resistance

[0105] 12-1 Current Ratio

[0106] 12-2 Current Ratio

[0107] 13-1 Resistance Ratio

[0108] 13-2 Resistance Ratio

[0109] 14-1 Weighted Average

[0110] 14-2 Weighted Average

[0111] 15-1 Maximum Individual Current Limit

[0112] 15-2 Maximum Individual Current Limit

[0113] 16-1 Filtered Weighted Average

[0114] 16-2 Filtered Weighted Average

[0115] 20 Current Sensor

[0116] 21 Current Sensor

[0117] 22 Current Sensor

[0118] 30-1 Nominal maximum current limit

[0119] 30-2 Nominal maximum current limit

[0120] 40 Maximum Current Limit

[0121] 41 Maximum Current Limit Signal

[0122] 50 Battery control device

[0123] 60 Battery System Control Device

[0124] 100-111 Control Equipment Module

Claims

1. A method for determining the maximum current limit (40) of a battery system having at least two cells, The following measures will be implemented: Detect the corresponding single current (10⁻¹, 10⁻²) on at least two of the batteries. Detect the total current of the battery system (10⁻⁶ s). Determine the corresponding current ratios (12-1, 12-2) between the detected single currents (10⁻¹, 10⁻²) and the detected total current (10⁻²s). Based on the determined current ratios (12-1, 12-2) and the nominal maximum current limits (30-1, 30-2) of the corresponding batteries, the maximum individual current limits (15-1, 15-2) of the battery system are determined for each of the at least two batteries. and / or Receive or estimate the corresponding single resistances (11-1, 11-2) of the at least two batteries. Receive or estimate the total resistance (11-s) of the battery system. Determine the corresponding resistance ratios (13-1, 13-2) between the received or estimated single resistances (11-1, 11-2) and the received or estimated total resistance (11-s). Based on the determined resistance ratios (13-1, 13-2) and the nominal maximum current limits (30-1, 30-2) of the corresponding batteries, the maximum individual current limits (15-1, 15-2) of the battery system are determined for each of the at least two batteries. Select the smallest definite maximum individual current limit (15-1, 15-2) as the maximum current limit of the battery system (40), and provide the definite maximum current limit (40) as the maximum current limit signal (41).

2. The method according to claim 1, characterized in that, A weighted average (14-1, 14-2) is formed from the corresponding current ratios (12-1, 12-2) and resistance ratios (13-1, 13-2), wherein the maximum individual current limit (15-1, 15-2) is determined based on the corresponding weighted average (14-1, 14-2).

3. The method according to claim 2, characterized in that, When forming the weighted average (14-1, 14-2), the weighting coefficients are selected based on the total current (11-s).

4. The method according to any one of claims 1 to 3, characterized in that, The current ratios (12-1, 12-2) and / or resistance ratios (13-1, 13-2) and / or weighted averages (14-1, 14-2) are filtered by low-pass filters over time, wherein the maximum individual current limits (15-1, 15-2) are determined based on the filtering ratios and / or the weighted averages (16-1, 16-2) of the filters.

5. A method for controlling a battery system having at least two batteries, wherein the method according to any one of claims 1 to 4 is performed, and wherein, The total current (60) of the battery system is limited based on the determined maximum current limit (40).

6. A control device (1) for determining the maximum current limit (40) of a battery system having at least two batteries, wherein, The control device (1) is configured to perform the following measures: Receive single currents (10⁻¹, 10⁻²) detected on each of the at least two batteries. Receive the detected total current of the battery system (10-s), Determine the corresponding current ratios (12-1, 12-2) between the detected single currents (10⁻¹, 10⁻²) and the detected total current (10⁻²s). Based on the determined current ratios (12-1, 12-2) and the nominal maximum current limits (30-1, 30-2) of the corresponding batteries, the maximum individual current limits (15-1, 15-2) of the battery system are determined for each of the at least two batteries. and / or Receive or estimate the corresponding single resistances (11-1, 11-2) of the at least two batteries. Receive or estimate the total resistance (11-s) of the battery system. Determine the corresponding resistance ratios (13-1, 13-2) between the received or estimated single resistances (11-1, 11-2) and the received or estimated total resistance (11-s). Based on the determined resistance ratios (13-1, 13-2) and the nominal maximum current limits (30-1, 30-2) of the corresponding batteries, the maximum individual current limits (15-1, 15-2) of the battery system are determined for each of the at least two batteries. Select the smallest definite maximum individual current limit (15-1, 15-2) as the maximum current limit of the battery system (40), and provide the definite maximum current limit (40) as the maximum current limit signal (41).

7. The control device (1) according to claim 6, characterized in that, The control device (1) is further configured to form a weighted average (14-1, 14-2) of the corresponding current ratios (12-1, 12-2) and resistance ratios (13-1, 13-2), and to determine the maximum individual current limit (15-1, 15-2) based on the corresponding weighted average (14-1, 14-2).

8. The control device (1) according to claim 7, characterized in that, The control device (1) is further configured to select the weighting coefficients based on the total current (10-s) when forming the weighted average values ​​(14-1, 14-2).

9. The control device (1) according to any one of claims 6 to 8, characterized in that, The control device (1) has a filtering device (2) configured to filter current ratios (12-1, 12-2) and / or resistance ratios (13-1, 13-2) and / or weighted average values ​​(14-1, 14-2) over time by a low-pass filter, wherein the control device (1) is further configured to determine a maximum individual current limit (15-1, 15-2) based on the filtering ratios and / or the weighted average values ​​(16-1, 16-2) of the filtering.

10. A battery system control device (60) comprising at least one control device (1) according to any one of claims 6 to 9, wherein, The battery system control device (60) is configured to limit the total current (10-s) of the battery system based on the maximum current limit (40) determined by the control device (1).

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