Method for controlling a battery system

Abstract

The present invention relates to a method for controlling a battery system (10), in particular a vehicle battery system, having a plurality of battery units (12) connected in series, the method comprising the steps of: (a) measuring output voltages of the battery units (12) and, if the difference between two output voltages of different battery units (12) exceeds a threshold value: (b) carrying out balancing for charge equalisation between the two battery units (12) until the difference between the two output voltages is equalised, (c) repeating steps (a) and (b), and in the process: (d) measuring the time periods between which balancing is carried out, wherein the method is characterised by the steps of: (e) determining a change in the time periods over a plurality of measurements, and (f) controlling the battery system (10) depending on the change detected in step (e).

Description

[0001] Method for controlling a battery system

[0002] The present invention relates to a method for controlling a battery system with a plurality of battery units connected in series as a function of time periods between which balancing is carried out, a battery management system and a computer program product for carrying out such a method and a data carrier signal which transmits such a computer program product.

[0003] The present invention is based on known battery control methods, which are commonly implemented with battery management systems. Battery management systems are used to monitor, control, and protect rechargeable batteries. They can detect the state of charge, provide deep discharge protection, or protect against overcharging. They are used in many mobile devices as well as battery-powered vehicles.

[0004] It is known that when several battery cells are connected in series to form a battery, especially with lithium batteries, the individual battery cells can have different output voltages due to manufacturing tolerances, aging or technical problems during the charging and discharging cycles.

[0005] To maintain or increase the capacity and service life of a battery or battery pack, balancing is performed between battery units. Balancing describes a charge transfer in which the voltages of the individual battery units are equalized. Such balancing is necessary for battery units connected in series. Battery units connected in parallel balance themselves because they are directly connected to each other.

[0006] Such balancing processes require a certain amount of time to complete. Generally speaking, the higher the charge transfer required for balancing, the longer the balancing process takes.

[0007] Battery management systems can, among other things, perform tasks related to diagnosing and troubleshooting a battery system. For this purpose, parameters such as voltage, current, temperature, or state of charge can be monitored. Some of the errors that occur can be corrected directly by the battery management system, while others require more complex repair or replacement of the battery system. For example, a cell imbalance—i.e., unequal voltages or charge levels of individual cells in the battery system—can be compensated for by the battery management system initiating a balancing process through a switching operation.Other types of damage, such as reduced capacity of individual battery cells or other battery units, age-related damage, internal short circuits or contact faults, environmental damage such as moisture, salt, unusual temperatures, or even mechanical damage, often require repair or replacement of the affected battery units or the battery system. Early detection of such damage is helpful for the safe and reliable operation of the battery system.

[0008] One method for detecting damage is to measure the duration of a necessary balancing and compare this period with the periods of previously required balancing. This duration is also referred to as the balancing length.

[0009] The disadvantage of the known solutions is that it is not possible to detect some of the errors sufficiently early and it is also not possible to distinguish between the different causes of the various errors with sufficient certainty.

[0010] Inaccurate fault detection can lead to more frequent failures and increased maintenance effort, which increases operating costs and reduces system availability. Furthermore, undetected or misinterpreted faults can lead to dangerous situations such as thermal runaways, reduced service life, increased operating costs, and damaged components.

[0011] The object of the present invention is to at least partially remedy the disadvantages described above in a cost-effective and simple manner. In particular, the object of the present invention is to provide a method that reduces failures of a battery management system and increases its availability. The above object is achieved by a method having the features of claim 1, a battery management system having the features of claim 6, a computer program product according to claim 9, and a data carrier signal according to claim 10. Further features and details of the invention emerge from the subclaims, the description, and the drawings.Features and details that are described in connection with the method according to the invention naturally also apply in connection with the battery management system according to the invention and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is or can always be made mutually.

[0012] According to the invention, a method is intended to enable the control of a battery system, in particular a vehicle battery system, with several battery units connected in series. Such a method is characterized by the following steps:

[0013] (a) Measuring output voltages of the battery units and, if the difference between two output voltages of different battery units exceeds a threshold value:

[0014] (b) Carrying out a balancing operation to equalise the charge between the two battery units until the difference between the two output voltages is equalised,

[0015] (c) Repeat steps (a) and (b), and:

[0016] (d) measuring the periods between which balancings are carried out, the method being characterized by the steps:

[0017] (e) determining a change in the time periods over several measurements, and

[0018] (f) controlling the battery system depending on the change detected in step (e).

[0019] The core idea of ​​a method according to the invention is that, in a battery system that uses a threshold value as a condition for performing a balancing operation, the length between two or more balancing operations can be used as a meaningful parameter to identify the cause of malfunctions. Surprisingly, this parameter is so meaningful that particularly reliable fault detection can be achieved. In particular, faults that are regularly detected false-positively with other methods can be excluded with a high degree of certainty, and control of the battery system can be improved. As a result, battery system failures can be reduced and its availability increased.

[0020] The method may in particular be a computer-implemented method.

[0021] A battery system comprises multiple battery cells, battery modules, and / or battery packs. Vehicle battery systems supply electrical energy to battery-powered vehicles and feature high-voltage batteries. The battery system can also be a stationary battery system. Operating modes and fault causes can differ between vehicle battery systems and stationary battery systems. For example, regenerative operating modes are more frequently used in stationary battery systems than in vehicle battery systems. Fault causes triggered by temperature changes or vibration, on the other hand, are more likely in vehicle battery systems. Battery system control can take these differences into account and can therefore be implemented depending on the type of battery system. Control is carried out primarily with regard to defined optimization goals.These are selected depending on the application of the battery system and personal preferences. Optimization goals can be or include a long battery system service life, a short charging time, a slow discharging time, the ability to test battery parameters, or combinations of such optimization goals. Battery units are understood to be battery cells, battery modules, and / or battery packs. The threshold is preferably predetermined and depends on the battery system and / or the battery units, in particular on the nominal output voltage of the battery system or the battery units. Balancing is initiated by the battery management system through a switching operation. This type of balancing generally takes place between two battery units arranged next to each other. Balancing can be active or passive. Passive balancing equalizes the charge level of the battery units at a specific point.Here, all battery units can reach either a maximum or minimum state of charge (SOC) at the same time. This can be achieved by removing energy from the cells with a higher state of charge. With active balancing, the energy is redistributed from charged battery units to battery units with a lower state of charge. Passive balancing consumes part of the battery system's energy and is therefore less efficient than active balancing. Balancing for charge equalization is carried out up to a point at which the difference in the output voltages of the different battery units is equalized. This means that they are closer to each other than before charge equalization. A threshold value can also be defined for this purpose, at which equalization is assumed. Preferably, it can be provided that the two output voltages are identical after equalization except for a measurement error.Regulating the battery system depending on the change detected in step (e) may, in particular, include reducing the power output of the battery units, more intensive monitoring of various operating parameters of the battery system, interrupting a charging process, activating protective circuits, activating an active or passive cooling system, activating data recording for later analysis, changing the operating parameters such as deactivating a rapid charging process or switching to more conservative and / or slower, battery-friendly charging strategies to ensure a safe operating window and minimize further aging, shutting down individual battery units, or even shutting down the battery system. Regulating may, in particular, also include or be a control and is therefore to be interpreted broadly.The change in the time periods can be either an increase or a decrease. However, many of the errors manifest themselves as a reduction. Repeating steps (a) and (b) is preferably performed until a termination condition is reached. The termination condition can be an interruption of the battery system's operation, for example, due to an external trigger.

[0022] It can be advantageous if, in a method according to the invention, the balancing lengths of the multiple measurements are also determined in step (e) and the battery system is additionally controlled in step (f) depending on the balancing lengths. The balancing lengths are measured from the start of a balancing process until the completion of the balancing process. They are therefore temporal variables. The term "balancing time" is also known for the size of the balancing length. Controlling the battery system depending on the change in the time periods between which balancings are switched and the balancing lengths detected in step (f) further increases the accuracy of fault detection and thus reduces the failure rate of the battery system to an even greater extent.

[0023] There are further advantages if the battery system is controlled in step (f) in such a way that it is switched off.

[0024] Shutdown is one of the most effective safety measures. In particular, shutdown can prevent particularly serious effects such as thermal runaway, which might have occurred if the battery system or the affected battery unit had continued to operate.

[0025] Further advantages are achieved if the method further comprises the step:

[0026] (e2) Calculating a balancing frequency over the time periods measured in step (d) and / or over the change in the time periods determined in step (e), wherein the control of the battery system in step (f) is carried out as a function of the balancing frequency.

[0027] The balancing frequency can be calculated by periodically adjusting the time periods and / or by periodically adjusting the change in the time periods. The balancing frequency allows for further improved data analysis and thus a more accurate analysis of the battery system for potential faults.

[0028] In this latter process, additional advantages can be achieved if the process further comprises the step of:

[0029] (e3) Calculating a change in the balancing frequency, whereby the control of the battery system in step (f) is dependent on the change in the balancing frequency. The change in the balancing frequency can be calculated using the derivative of the balancing frequency. This also allows for a further increase in the accuracy of the fault analysis. In particular, some of the potential faults occurring in the battery system can be detected particularly early.

[0030] Further advantages are achieved when the battery system is controlled depending on a usage profile.

[0031] Battery system usage profiles are essential for managing and optimizing battery lifetime and efficiency. These profiles vary greatly depending on the application and battery type. The type of usage depends heavily on the application. For example, batteries in electric vehicles have a different usage profile than those in renewable energy storage systems or portable electronic devices. The frequency and intensity of charge and discharge cycles influence battery lifetime. Deep discharges and frequent full recharges can shorten battery lifetime. Furthermore, the operating temperature is crucial for battery performance and lifetime. Extreme temperatures, both high and low, can negatively affect battery performance.A change in the balancing intervals detected in step (f) can therefore be strongly influenced by the respective usage profile. Incorporating the usage profile into the battery system's control can therefore further improve the control accuracy and thus further enhance the previously discussed benefits.

[0032] Further advantages are achieved if the battery system is a vehicle battery system of a vehicle and the method further comprises the steps of: (d4) measuring a distance traveled by the vehicle, between which balancings are switched, (e4) determining a change in the distance over several measurements, and (f4) controlling the battery system depending on the change detected in step (e4).

[0033] With steps (d4), (e4), and (f4), not only the operating time but also the vehicle's operating mode can be used to control the battery system. This can further improve control.

[0034] Further advantages are achieved if the method further comprises the steps of: determining the charge quantities and / or energy quantities converted between the balancings in the battery system, determining a change in the converted charge quantities and / or a change in the converted energy quantities over several measurements, and controlling the battery system depending on the change in the converted charge quantities and / or the change in the converted energy quantities.

[0035] Battery systems can be monitored by linking changes in the time intervals between balancing cycles and / or the balancing frequency with the respective charge quantities implemented in the battery system and measured in ampere hours (Ah) and / or the energy quantities (Wh) of the battery system measured in Wh, or any changes therein. Both charging and discharging processes are summed. Typically, a decrease due to aging or damage is expected. In combination with changes in the balancing length, changes in the charge quantity and / or the energy quantity are particularly meaningful parameters for further optimization. Battery control can thus be further optimized by taking the charge quantities and / or energy quantities into account, thereby contributing to a longer battery service life.

[0036] A further subject of the present invention is a battery management system which is designed to carry out the method according to one of claims 1 to 7.

[0037] A further subject of the present invention is a computer program product comprising instructions which, when the program is executed by a battery management system, cause the latter to carry out the steps of the method according to one of claims 1 to 7.

[0038] Finally, the invention provides a data carrier signal that transmits the computer program product according to claim 9.

[0039] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. They show schematically:

[0040] Fig. 1 is a circuit diagram of a battery system for the application of a battery management system according to a particular embodiment of the invention, and Fig. 2 is an exemplary measured value acquisition in a battery system to explain the method according to the invention.

[0041] Figure 1 shows a schematic circuit diagram of a battery system 10 comprising a plurality of battery units 12 connected in series to form a battery pack 14. The battery pack 14 has an input terminal 16 and an output terminal 18, across which a battery pack voltage is applied. The output voltage applied to each of the battery units 12 is measured by means of a voltage measuring device 20. The measured voltage values ​​are combined and evaluated in a battery management system 22. The battery management system 22 can thereby determine that one of the battery units 12 is a battery unit with a different state of charge 24. The different state of charge is detected when the difference between two output voltages of different battery units arranged next to one another exceeds a threshold value.The battery management system is further configured to control and / or regulate the batteries. In particular, the battery management system 22 is configured to perform balancing between the battery units 12. Balancing, i.e., the balancing process, is generally performed until the charge states of the batteries are equalized again. Other switching devices designed to perform balancing are known from the prior art and are not shown in detail here for reasons of clarity.

[0042] Figure 2 shows an example of measured value acquisition during operation of a battery system 10. The battery system 10 is operated over a time t with several battery units 12 connected in series. Charging and discharging processes take place here. The output voltages of the battery units 12 are measured continuously or at regular intervals. During operation, a series of balancing units are connected to a battery unit 12. The upper plot shows measured values ​​26 of balancing units, where the measured values ​​26 include the balancing length T and the time t i of the respective balancing. The balancing length T indicates the duration from the start of the charge transfer to the completion of the charge transfer, i.e. the time period until the charge of the corresponding battery unit 12 is equalized again. The plot shows that the balancing lengths T of the balancing units are constant in this example.At the start of the measurement, the time period between two balancings is a value Zi. After a time ti, the balancings must be carried out more frequently, each with a shorter interval Z2. In the lower plot, a jump in the balancing frequency f can therefore be seen. This increase and / or the frequency jump can be used to identify a fault and to regulate the battery system 10. Alternatively or additionally, the size of the change can also be used. Furthermore, the balancing length T, which is required to perform the balancing on the battery unit 12, can be included in the identification. From the measurement of the two parameters time period between balancings and balancing length T, it can be seen in this example that the balancing length T before and after the event is the same, i.e. the balancing length T is not affected by the fault.The individual jump in the time periods suggests that a single event caused a fault. In context, this information may indicate that the fault is not due to the battery chemistry itself, but rather a circuit-related error leading to the more frequent discharge of the battery unit 12. Depending on the application and battery type, the battery management system 22 can disconnect the battery unit 12 deemed faulty from operation, possibly after a discharge, and / or issue a warning prompting a battery inspection at a workshop.

[0043] If, on the other hand, the time periods between which balancing cycles are switched decrease slowly and continuously over several balancing cycles, this may indicate a normal aging process. If there is also an increase in the balancing length T, this can be a further indication of the aging process. Increasing time periods between which balancing cycles are switched, on the other hand, would be an indication that the capacities and states of the cells are equalizing again, which can generally be a sign of cell regeneration. As in other analyses, the battery type, the type of battery system and / or the magnitude of the change can also be taken into account in each case. The above explanations of the embodiments describe the present invention exclusively within the framework of examples.

[0044] List of reference symbols

[0045] 10 Battery system

[0046] 12 Battery unit

[0047] 14 Battery pack

[0048] 16 Input pole

[0049] 18 Output pole

[0050] 20 voltage measuring device

[0051] 22 Battery management system

[0052] 24 Battery unit with different charge level

[0053] 26 measured value

[0054] T Balancing length

Claims

Patent claims 1. A method for controlling a battery system (10), in particular a vehicle battery system, with a plurality of battery units (12) connected in series, comprising the steps: (a) measuring output voltages of the battery units (12) and, if the difference between two output voltages of different battery units (12) exceeds a threshold value: (b) performing a balancing operation to equalise the charge between the two battery units (12) until the difference between the two output voltages is equalised, (c) Repeat steps (a) and (b), and: (d) measuring the periods between which balancings are carried out, the method being characterized by the steps: (e) determining a change in the time periods over several measurements, and (f) controlling the battery system (10) depending on the change detected in step (e).

2. The method according to claim 1, wherein in step (e) the balancing lengths (T) of the plurality of measurements are further determined and in step (f) the battery system (10) is additionally controlled as a function of the balancing lengths (T).

3. Method according to one of the preceding claims, wherein the battery system (10) is controlled in step (f) such that it is switched off.

4. Method according to one of the preceding claims, further comprising the step: (e2) Calculating a balancing frequency over the time periods measured in step (d) and / or over the change in the time periods determined in step (e), wherein the control of the battery system (10) in step (f) is carried out as a function of the balancing frequency.

5. The method of claim 4, further comprising the step: (e3) calculating a change in the balancing frequency, wherein the control of the battery system (10) in step (f) is carried out as a function of the change in the balancing frequency.

6. The method according to any one of the preceding claims, wherein the battery system (10) is a vehicle battery system of a vehicle and the method further comprises the steps of: (d4) measuring a distance travelled by the vehicle between which balancing is carried out, (e4) Determining a change in distance over several measurements, and (f4) Controlling the battery system (10) depending on the change detected in step (e4).

7. Method according to one of the preceding claims, further comprising the steps: Determining the charge quantities and / or energy quantities converted between the balancings in the battery system, Determining a change in the converted charge quantities and / or a change in the converted energy quantities over several measurements, and Control of the battery system depending on the change in the amount of charge converted and / or the change in the amount of energy converted.

8. Battery management system (22) which is configured to carry out the method according to one of the preceding claims.

9. A computer program product comprising instructions which, when executed by a battery management system, cause the system to carry out the steps of the method according to any one of claims 1 to 7.

10. A data carrier signal that transmits the computer program product according to claim 9.

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