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

Description

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

[0002] In a battery system with multiple batteries connected in parallel, the individual batteries are generally not exactly identical and therefore do not have exactly the same electrical properties. This can be due to differences in manufacturing and different aging behavior. Therefore, even when batteries of the same design are connected in parallel, a different current distribution can occur. When operating the battery system, the individual current limits of each battery must always be observed.

[0003] US 2019 / 214837 A1 describes a method for limiting the landing current of a battery of a battery system with two batteries.

[0004] The invention is based on the object of providing a method and a control device for determining a maximum current limit of a battery system with at least two batteries, with which the maximum current limit of the battery system can be reliably determined.

[0005] The object is achieved according to the invention by a method having the features of patent claim 1 and a control device having the features of patent claim 6. Advantageous embodiments of the invention emerge from the subclaims. In particular, a method for determining a maximum current limit of a battery system with at least two batteries is provided, wherein the following measures are carried out: Detecting a respective individual current at the at least two batteries, detecting a total current of the battery system, determining a respective current ratio between the detected individual currents and the detected total current, determining maximum individual current limits of the battery system for each of the at least two batteries based on the respectively determined current ratio and a nominal maximum current limit of the respective battery;and / or receiving or estimating a respective individual resistance of the at least two batteries, receiving or estimating a total resistance of the battery system, determining a respective resistance ratio between the received or estimated individual resistances and the received or estimated total resistance, determining maximum individual current limits of the battery system for each of the at least two batteries based on the respectively determined resistance ratio and a nominal maximum current limit of the respective battery; ; Selecting the smallest determined maximum individual current limit as the maximum current limit of the battery system, providing the determined maximum current limit as the maximum current limit signal.

[0006] Furthermore, in particular, a control device for determining a maximum current limit of a battery system with at least two batteries is provided, wherein the control device is configured to carry out the following measures: Receiving an individual current detected at each of the at least two batteries, receiving a detected total current of the battery system, determining a respective current ratio between the detected individual currents and the detected total current, determining maximum individual current limits of the battery system for each of the at least two batteries based on the respectively determined current ratio and a nominal maximum current limit of the respective battery;and / or receiving or estimating a respective individual resistance of the at least two batteries, receiving or estimating a total resistance of the battery system, determining a respective resistance ratio between the received or estimated individual resistances and the received or estimated total resistance, determining maximum individual current limits of the battery system for each of the at least two batteries based on the respectively determined resistance ratio and a nominal maximum current limit of the respective battery; ; Selecting the smallest determined maximum individual current limit as the maximum current limit of the battery system, providing the determined maximum current limit as the maximum current limit signal.

[0007] The method and the control unit enable a maximum current limit to be reliably determined across the entire operating range of the battery system. Two approaches can be used for this: In the first approach, a current ratio is determined for each battery from the individual currents recorded at the batteries and a total current recorded at the battery system. Based on the respective determined current ratio and a nominal maximum current limit, a maximum individual current limit of the battery system is determined for each battery. From this, the smallest of the determined maximum individual current limits is selected. This is based on the idea that the "weakest" battery in terms of maximum current defines the maximum possible total current of the battery system, since the maximum current of this battery must not be exceeded.In the second approach, resistance ratios are determined alternatively or additionally in a similar manner and used to determine maximum individual current limits. The respective results can also be summarized and combined. The first approach works particularly well for large currents, whereas the second approach is advantageous for smaller currents, where the error in detecting the currents is greater, thus reducing the signal-to-noise ratio.

[0008] The batteries of the battery system are connected in parallel, in particular. An individual current can be detected at each of the batteries using a current sensor. Furthermore, the total current of the battery system is also detected, in particular using a current sensor. Each of the batteries has a predetermined nominal maximum current limit.

[0009] Parts of the control unit can be implemented individually or collectively as a combination of hardware and software, for example, as program code executed on a microcontroller or microprocessor. However, parts can also be implemented individually or collectively as an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA).

[0010] The two approaches are explained below using examples. A battery system with two batteries connected in parallel is considered as an example.

[0011] For example, the following nominal maximum current limits are specified for the batteries: I 1 , max = 150 A I 2 , max = 150 A

[0012] The recorded individual currents and a total current are, for example: I system = 200 A I 1 = 110 A I 2 = 90 A

[0013] This results in the following current ratios: Ratio 1 , I = I system / I 1 = 200 A / 110 A = 1 , 81 Ratio 2 , I = I system / I 2 = 200 A / 90 A = 2 , 22

[0014] This results in the following maximum individual current limits: I 1 , maxsystem , I = Ratio 1 , I ⋅ I 1 , max = 1 , 81 ⋅ 150 A = 271 , 5 A I 2 , maxsystem , I = Ratio 2 , I ⋅ I 2 , max = 2 , 22 ⋅ 150 A = 333 A

[0015] Of these, the smallest determined maximum individual current limit is selected as the maximum current limit of the battery system: I max , system , I = min_n I n , maxsystem , I = min I 1 , maxsystem , I ; I 2 , maxsystem , I = min 271 , 5 A , 333 A = 271 , 5 A

[0016] In the example, the first battery would be the "weaker" battery in terms of maximum current, so the total current of the battery system, depending on this battery, must be limited to a maximum current of 271.5 A so that the nominal maximum current limit of this battery is not exceeded. Compared to a nominal maximum current limit of the battery system of 150 A + 150 A = 300 A, the specified maximum current limit is smaller. If a total current of 271.5 A, i.e., up to the specified maximum current limit, were provided from the battery system, the first ("weaker") battery would provide a current at its nominal maximum current limit of 150 A, while the second battery would only provide 121.5 A.

[0017] In the second approach, individual resistances of the two batteries and a total resistance are received, which have, for example, the following values: R system = 50 mΩ R 1 = 90 mΩ R 2 = 110 mΩ

[0018] The values ​​can, for example, be estimated by a battery controller using methods known per se and provided by this to the control unit.

[0019] This results in the following resistance ratios: Ratio 1 , R = R 1 / R system = 90 mΩ / 50 mΩ = 1 , 8 Ratio 2 , R = R 2 / R system = 110 mΩ / 50 mΩ = 2 , 2

[0020] This results in the following maximum individual current limits: I 1 , maxsystem , R = Ratio 1 , R ⋅ I 1 , max = 1 , 8 ⋅ 150 A = 270 A I 2 , maxsystem , R = Ratio 2 , R ⋅ I 2 , max = 2 , 2 ⋅ 150 A = 330 A

[0021] Of these, the smallest determined maximum individual current limit is selected as the maximum current limit of the battery system: I max , system , R = min _ n I n , maxsystem , R = min I 1 , maxsystem , R ; I 2 , maxsystem , R = min 270 A , 330 A = 270 A

[0022] The results of the first approach and the second approach are therefore almost identical. The examples serve to illustrate the invention. In principle, the values ​​can also be different. In particular, the battery system can also have more than two batteries. However, the basic procedure is the same even with more than two batteries.

[0023] In one embodiment, a weighted average is calculated from the respective current ratio and resistance ratio, with the maximum individual current limits being determined based on the respective weighted average. In other words, the current ratio and the resistance ratio are combined by weighted averaging, which can also be carried out in the form of an interpolation between the two ratios. This is done, in particular, for each battery before the maximum individual current limits are determined. This can, in particular, save the required computing power. The weighting factors allow the averaging or interpolation to be parameterized. The weighting factors can, for example, be determined and maintained empirically for different load scenarios.

[0024] Taking the above example, with a weighting factor w for each battery, we get: Ratio n , gewichtet = w ⋅ Ratio n , I + 1 − w ⋅ Ratio n , R

[0025] In a further embodiment, it is provided that weighting factors are selected as a function of the total current when forming the weighted average. This allows different weighting factors to be selected for different ranges of the total current. It can be provided that the weighting factors are determined as a function of the total current. In particular, it is provided that the weighting factors are selected such that a component of the resistance ratio predominates in a lower range of the total current, whereas a component of the current ratio predominates in the upper range of the total current. This can reduce errors due to a poorer signal-to-noise ratio when detecting currents at low currents. Overall, this improves the determination of the maximum current limit.

[0026] In one embodiment, the current ratios and / or resistance ratios and / or weighted averages are filtered over time using a low-pass filter, with the maximum individual current limits being determined based on the filtered ratios and / or filtered weighted averages. This allows a temporal progression of the current ratios and / or resistance ratios to be smoothed.

[0027] Taking the above example, we then get (for the weighted averages): Ratio n , gewichtet , geglättet = Tiefpass Ratio n , gewichtet , τ

[0028] Here, τ is a smoothing coefficient according to the respective implementation of the low-pass filter.

[0029] Further features of the control unit design are described in the embodiments of the method. The advantages of the control unit are the same as those of the embodiments of the method.

[0030] Furthermore, in particular, a method for controlling a battery system with at least two batteries is also provided, wherein a method according to one of the preceding embodiments is carried out, and wherein a current of the battery system is limited based on the determined maximum current limit. This enables the active limitation of the total current of the battery system according to the determined maximum current limit.

[0031] Furthermore, in particular, a battery system controller is also provided, comprising at least one control unit according to one of the embodiments described above, wherein the battery system controller is configured to limit a current of the battery system based on a maximum current limit determined by means of the control unit.

[0032] The control unit and the battery system controller can be used in particular in a vehicle, in particular in a motor vehicle. Therefore, a vehicle is also proposed, comprising at least one control unit according to one of the described embodiments and / or comprising at least one battery system controller. In principle, however, the method and the battery system controller can also be used in other mobile or stationary battery systems.

[0033] The invention will be explained in more detail below using preferred embodiments with reference to the figures. Fig. 1 is a schematic representation of an embodiment of the control unit for determining a maximum current limit of a battery system with at least two batteries; Fig. 2 is a schematic representation of a further embodiment of the control unit; Fig. 3 is a schematic representation of a further embodiment of the control unit.

[0034] In the Fig. 1 A schematic representation of an embodiment of the control unit 1 for determining a maximum current limit 40 of a battery system with two batteries is shown. The control unit 1, in particular, executes the method described in this disclosure, which is explained with reference to the control unit 1.

[0035] The control unit 1 comprises the modules 100 to 103. The modules 100 to 103 can be designed as a combination of hardware and software, for example as program code that is executed on a microcontroller or microprocessor.

[0036] Individual currents 10-1, 10-2, measured at batteries of the battery system, and a total current 10-s of the battery system are fed to the control unit 1. The currents 10-x are measured by current sensors 20, 21, 22 and provided, for example, as current signals.

[0037] In the module 100, the control unit 1 determines a respective current ratio 12-1, 12-2 between the detected individual currents 10-1, 10-2 and the detected total current 10-s.

[0038] In modules 101 and 102, control unit 1 determines maximum individual current limits 15-1, 15-2 of the battery system for each of the two batteries based on the respectively determined current ratio 12-1, 12-2 and a nominal maximum current limit 30-1, 30-2 of the respective battery.

[0039] In module 103, control unit 1 selects the smallest determined maximum individual current limit as maximum current limit 40 of the battery system and provides it as maximum current limit signal 41.

[0040] Alternatively or additionally, it can be provided that the control unit 1 comprises the modules 104-107.

[0041] Alternatively or additionally, the respective (current) individual resistances 11-1, 11-2 of the two batteries of the battery system and a (current) total resistance 11-s of the battery system are then supplied to the control unit 1. The resistances 11-1, 11-2, 11-s can, for example, be provided and transmitted by a battery controller 50 or estimated in some other way.

[0042] In the module 104, the control unit 1 determines a respective resistance ratio 13-1, 13-2 between the received or estimated individual resistances 11-1, 11-2 and the received or estimated total resistance 11-s.

[0043] In modules 105 and 106, control unit 1 determines maximum individual current limits 15-1, 15-2 of the battery system for each of the two batteries based on the respectively determined resistance ratio 13-1, 13-2 and the nominal maximum current limit 30-1, 30-2 of the respective battery.

[0044] In module 107, control unit 1 selects the smallest determined maximum individual current limit as maximum current limit 40 of the battery system and provides it as maximum current limit signal 41.

[0045] The results provided by modules 103 and 107 can also be summarized.

[0046] The control unit 1 can be part of a battery system controller 60, wherein the battery system controller 60 is configured to limit a total current 10-s of the battery system based on the maximum current limit 40 determined by the control unit 1. For this purpose, the maximum current limit signal 41 is evaluated and used in the battery system controller 60.

[0047] In Fig. 2 A further embodiment of the control unit 1 is shown. The embodiment is basically like the one in the Fig. 1 shown embodiment. The same reference numerals denote the same features and terms.

[0048] Additionally, it is provided that a weighted average 14-1, 14-2 is formed from the respective current ratio 12-1, 12-2 and resistance ratio 13-1, 13-2, wherein the maximum individual current limits 15-1, 15-2 are determined based on the respective weighted average 14-1, 14-2. For this purpose, the control unit 1 additionally has modules 108 and 109, which perform the weighted averaging by interpolation between the respective current ratio 12-1, 12-2 and the respective resistance ratio 13-1, 13-2.

[0049] It can be provided that weighting factors when forming the weighted mean value 14-1, 14-2 in the modules 108 and 109 are selected as a function of the total current 10-s, in particular as a function of the total current 10-s.

[0050] In Fig. 3 A further embodiment of the control unit 1 is shown. The embodiment is basically like the one in the Fig. 2shown embodiment. The same reference numerals denote the same features and terms.

[0051] Additionally, it is provided that the weighted averages 14-1, 14-2 in modules 110 and 111 are temporally filtered using a low-pass filter, whereby the maximum individual current limits 15-1, 15-2 are determined based on the filtered weighted averages 16-1, 16-2. Modules 110 and 111 form, in particular, a filter device 2.

[0052] Alternatively, the ratios 12-1, 12-2, 13-1, 13-2 can also be filtered by means of the low-pass filter (not shown), wherein the filtering of the weighted average values ​​14-1, 14-2 is advantageous with regard to the required hardware and / or the required computing power. List of reference symbols

[0053] 1 Control unit 2 Filter device 10-1 Individual current 10-2 Individual current 10-s Total current 11-1 Individual resistance 11-2 Individual resistance 11-s Total resistance 12-1 Current ratio 12-2 Current ratio 13-1 Resistance ratio 13-2 Resistance ratio 14-1 Weighted average 14-2 Weighted average 15-1 Maximum individual current limit 15-2 Maximum individual current limit 16-1 Filtered weighted average 16-2 Filtered weighted average 20 Current sensor 21 Current sensor 22 Current sensor 30-1 Nominal maximum current limit 30-2 Nominal maximum current limit 40 Maximum current limit 41 Maximum current limit signal 50 Battery control 60 Battery system control 100-111 Control unit modules

Claims

1. Method for determining a maximum current limit (40) of a battery system comprising at least two batteries, wherein the following actions are carried out: recording a relevant individual current (10-1,10-2) at the at least two batteries, recording a total current (10-s) of the battery system, determining a relevant current ratio (12-1,12-2) between the recorded individual currents (10-1,10-2) and the recorded total current (10-s), determining maximum individual current limits (15-1,15-2) of the battery system for each of the at least two batteries based on the respectively determined current ratio (12-1,12-2) and a nominal maximum current limit (30-1,30-2) of the relevant battery; and / or receiving or estimating a relevant individual resistance (11-1,11-2) of the at least two batteries, receiving or estimating a total resistance (11-s) of the battery system, determining a relevant resistance ratio (13-1,13-2) between the received or estimated individual resistances (11-1,11-2) and the received or estimated total resistance (11-s), determining maximum individual current limits (15-1,15-2) of the battery system for each of the at least two batteries based on the respectively determined resistance ratio (13-1,13-2) and a nominal maximum current limit (30-1,30-2) of the relevant battery; selecting the smallest determined maximum individual current limit (15-1,15-2) as the maximum current limit (40) of the battery system, providing the determined maximum current limit (40) as a maximum current limit signal (41).

2. Method according to claim 1, characterized in that a weighted mean value (14-1,14-2) is formed from the relevant current ratio (12-1,12-2) and resistance ratio (13-1,13-2), the maximum individual current limits (15-1,15-2) being determined based on the relevant weighted mean value (14-1,14-2).

3. Method according to claim 2, characterized in that weighting factors are selected depending on the total current (11-s), when forming the weighted mean value (14-1,14-2).

4. Method according to any 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 mean values (14-1,14-2) are temporally filtered by means of a low-pass filter, the maximum individual current limits (15-1,15-2) being determined based on the filtered ratios and / or filtered weighted mean values (16-1,16-2).

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

6. Control unit (1) for determining a maximum current limit (40) of a battery system comprising at least two batteries, wherein the control unit (1) is configured to carry out the following actions: receiving an individual current (10-1, 10-2) recorded at each of the at least two batteries, receiving a recorded total current (11-s) of the battery system, determining a relevant current ratio (12-1,12-2) between the recorded individual currents (10-1,10-2) and the recorded total current (10-s), determining maximum individual current limits (15-1,15-2) of the battery system for each of the at least two batteries based on the respectively determined current ratio (12-1,12-2) and a nominal maximum current limit (30-1,30-2) of the relevant battery; and / or receiving or estimating a relevant individual resistance (11-1,11-2) of the at least two batteries, receiving or estimating a total resistance (11-s) of the battery system, determining a relevant resistance ratio (13-1,13-2) between the received or estimated individual resistances (11-1,11-2) and the received or estimated total resistance (11-s), determining maximum individual current limits (15-1,15-2) of the battery system for each of the at least two batteries based on the respectively determined resistance ratio (13-1,13-2) and a nominal maximum current limit (30-1,30-2) of the relevant battery; selecting the smallest determined maximum individual current limit (15-1,15-2) as the maximum current limit (40) of the battery system, providing the determined maximum current limit (40) as a maximum current limit signal (41).

7. Control unit (1) according to claim 6, characterized in that the control unit (1) is further configured to form a weighted mean value (14-1,14-2) from the relevant current ratio (12-1,12-2) and resistance ratio (13-1,13-2) and to determine the maximum individual current limits (15-1,15-2) based on the relevant weighted mean value (14-1,14-2).

8. Control unit (1) according to claim 7, characterized in that the control unit (1) is further configured to select weighting factors depending on the total current (10-s), when forming the weighted mean value (14-1,14-2).

9. Control unit (1) according to any of claims 6 to 8, characterized in that the control unit (1) comprises a filter device (2) which is configured to temporally filter the current ratios (12-1, 12-2) and / or resistance ratios (13-1, 13-2) and / or weighted mean values (14-1, 14-2) by means of a low-pass filter, the control unit (1) being further configured to determine the maximum individual current limits (15-1, 15-2) based on the filtered ratios and / or filtered weighted mean values (16-1, 16-2).

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