Battery pack system and method for operating a battery pack system

Abstract

The invention relates to a method for operating a battery system having a plurality of battery pack modules connected in parallel, wherein a rated current is specified for each battery pack module; for each battery pack module, an operating current is calculated based on the specified rated current; the sensor current flowing through each battery pack module is measured respectively by a current sensor assigned to the battery pack module; the measured sensor currents of the plurality of battery pack modules are compared with each other; wherein when the lowest sensor current among the measured sensor currents deviates from at least one of the sensor currents of the other battery pack modules by at least a threshold value, the steps are carried out: comparing the operating current of the battery pack module having the lowest sensor current with the lowest sensor current; when the operating current deviates from the lowest sensor current by at most a limit value, a fault is identified in the battery pack module having the lowest sensor current. The invention also relates to a battery system for an electric vehicle, which is configured to carry out the method according to the invention.

Description

Technical Field

[0001] The invention relates to a method for operating a battery system having a plurality of battery pack modules connected in parallel for an electric vehicle, wherein the sensor current flowing through each battery pack module is measured by a current sensor assigned to the battery pack module. The invention also relates to a battery system for an electric vehicle, in particular for a construction machine such as an excavator, which is configured to carry out the method according to the invention. Background Art

[0002] It is envisaged that in the future, electric motor vehicles, in particular also construction machines such as excavators, will be used more and more frequently. In the case of such electric vehicles, rechargeable battery systems are used, mainly to supply electrical energy to the electric drive unit. A battery system having lithium battery pack cells is particularly suitable for such applications. Lithium battery pack cells are characterized in particular by a high energy density, thermal stability and extremely low self-discharge. A plurality of such lithium battery pack cells are electrically connected in series with each other and in parallel with each other and connected into a battery pack module. The battery system of an electric vehicle includes a plurality of such configured battery pack modules connected in series and in parallel with each other.

[0003] Construction machines, such as excavators, require battery systems that have an increased voltage and an increased capacity for storing a higher amount of electrical energy compared to battery systems for passenger cars. Such a battery system for an electric vehicle includes a plurality of battery pack modules connected in parallel and a plurality of current sensors, wherein each of the battery pack modules is assigned a current sensor. The respectively assigned current sensor is used to measure the charging current and the discharging current of the corresponding battery pack module.

[0004] During the operation of an electric vehicle, the battery pack cells of these battery pack modules discharge to drive the electric vehicle and to supply power to other consumers. During the operation of the electric vehicle over a longer period of time, aging of the battery pack cells occurs, which can be noticed in terms of a reduction in battery capacity. Here, the internal resistance of the battery increases, whereby the battery is heated more strongly at a constant current. Thus, the battery management system gradually adjusts the discharging current and the charging current of the battery pack module backwards. In addition to the temperature increase, the reduction in capacity also results in a reduced power output, which can be noticed in terms of a reduced discharging current, in particular for a longer prediction period. Damage to the battery pack cells in the battery pack module, in particular in the parallel battery branches, can also be noticed in terms of a reduction in the charging current and the discharging current of the battery pack module.

[0005] Battery pack cells that have aged too strongly and battery pack modules with damaged battery pack cells should be replaced. Depending on the degree of aging or damage, the battery pack module should be immediately disconnected in order to prevent further damage to the battery pack system. However, it is conceivable that all battery pack modules can operate while the current sensor is damaged and thus provides incorrect measured values of the charging current and the discharging current of the battery pack module. In the case of a damaged current sensor, the associated battery pack module does not need to be disconnected; rather, the battery pack system can continue to operate and the damaged current sensor can be replaced at a later point in time.

[0006] A device for monitoring a battery pack system is known from document US 2014 / 0152261 A1. The device mentioned includes: a current sensor for measuring the charging current and the discharging current flowing in the battery pack system; and a voltage sensor for measuring the total voltage of the battery pack system.

[0007] Document JP 2013094032 A discloses a monitoring device for a battery pack system and an energy storage device having such a monitoring device. Here, the monitoring device includes a voltage sensor for measuring the voltage of each battery pack cell of the battery pack system. Summary of the Invention

[0008] A method for operating a battery pack system for an electric vehicle, in particular a construction machine such as an excavator, is proposed. The battery pack system includes a plurality of parallel-connected battery pack modules. Each of these battery pack modules includes a battery pack control device. When the electric vehicle is operating, a rated current is specified for each of these battery pack modules. The specification of the rated current is carried out, for example, according to the corresponding requirements of the user of the electric vehicle.

[0009] For each of these battery pack modules, a working current is calculated based on the specified rated current. Here, the calculated working current of the battery pack module can be less than the specified rated current. For example, when the state of charge of the battery pack module is low and an excessive working current would cause too rapid a discharge of the battery pack module, the working current of the battery pack module can be less than the rated current.

[0010] The current flowing through each battery pack module is measured separately by a current sensor assigned to the battery pack module. Hereinafter, the current measured by the current sensor is referred to as the sensor current. The sensor current can be a charging current for charging the corresponding battery pack module and a discharging current for discharging the corresponding battery pack module.

[0011] Perform a comparison of the measured sensor currents of multiple battery pack modules with each other. This means that the individual sensor currents measured by the respective current sensors are compared with each other in terms of value and direction. Herein, in particular, it is determined which of the mentioned current sensors measures the lowest sensor current.

[0012] If the lowest sensor current among the measured sensor currents deviates from at least one sensor current of other battery pack modules by at least a threshold value, then perform the steps mentioned subsequently. By means of this threshold value, in particular, the system-inherent measurement errors of the current sensors used are taken into account. If the lowest sensor current among the measured sensor currents deviates from all other sensor currents by at most this threshold value, then all sensor currents are considered to be approximately equal, and it is assumed that there is no fault in this battery pack system.

[0013] First, compare the pre-calculated operating current of the battery pack module with the lowest sensor current, where the lowest sensor current is measured by the current sensor assigned to this battery pack module.

[0014] If the operating current deviates from the mentioned lowest sensor current by at most a limit value, then a fault is identified in the battery pack module with the lowest sensor current. By means of this limit value, in particular, the system-inherent measurement errors of the current sensors used are taken into account. If the operating current deviates from the lowest sensor current by at most this limit value, then the two currents are considered to be approximately equal, and it is assumed that there is a fault in this battery pack module.

[0015] According to an advantageous design of the present invention, if the operating current of the battery pack module with the lowest sensor current deviates from the mentioned lowest sensor current by at least this limit value, then compare the operating current of the battery pack module with the lowest sensor current with the sensor currents of other battery pack modules.

[0016] Herein, if the operating current deviates from the sensor currents of other battery pack modules by at most this limit value, then a fault is identified in the current sensor assigned to the battery pack module with the lowest sensor current.

[0017] Furthermore, if the operating current deviates from the sensor currents of at least one other battery pack module by at least this limit value, then a fault is identified in the battery pack module with the lowest sensor current.

[0018] According to another advantageous design of the present invention, if the operating current of the battery pack module with the lowest sensor current deviates from the mentioned lowest sensor current by at least this limit value, the operating current of the battery pack module with the lowest sensor current is compared with the operating currents of the other battery pack modules.

[0019] Herein, if the operating current deviates from the operating currents of the other battery pack modules by at most this limit value, a fault is identified in the current sensor assigned to the battery pack module with the lowest sensor current.

[0020] Furthermore, if the operating current deviates from the operating current of at least one other battery pack module by at least this limit value, a fault is identified in the battery pack module with the lowest sensor current.

[0021] Preferably, the central control unit prescribes the same rated current for each of the battery pack modules in the battery pack system. For example, the mentioned rated current corresponds to the total current required by the user of the electric vehicle divided by the number of parallel-connected battery pack modules. Herein, the mentioned rated current is calculated by the central control unit and transmitted to the battery pack control devices of these battery pack modules.

[0022] According to a preferred expansion of the present invention, each of these battery pack modules has a battery pack control device, and this battery pack control device has a management system, which calculates the operating current based on the prescribed rated current and at least one other parameter. This other parameter is, for example, the state of charge of the battery pack module.

[0023] A battery pack system for an electric vehicle, in particular a construction machine such as an excavator, is proposed. This battery pack system includes a plurality of parallel-connected battery pack modules. Herein, each battery pack module has a plurality of battery pack cells. These battery pack cells are connected in series and / or in parallel with each other within the battery pack module. These battery pack modules respectively have a system voltage of, for example, 800V.

[0024] The battery pack system also includes a central control unit for prescribing the rated current for the battery pack control devices of these battery pack modules. The control unit calculates the rated current, for example, according to the corresponding requirements of the user of the electric vehicle. Then, the mentioned rated current corresponds, for example, to the total current required by the user of the electric vehicle divided by the number of parallel-connected battery pack modules. Herein, the central control unit transmits the calculated rated current to the battery pack control devices of these battery pack modules.

[0025] The battery pack system also includes a plurality of current sensors for measuring sensor current. Here, each battery pack module among these battery pack modules is respectively assigned a current sensor that measures the sensor current flowing through the battery pack module. The sensor current can be a charging current for charging the battery pack module and a discharging current for discharging the battery pack module.

[0026] Each battery pack module in the battery pack modules of the battery pack system has a battery pack control device, and the battery pack control device has a management system for calculating the operating current according to a specified rated current. The management system is also used to control and monitor the battery pack batteries of the battery pack module.

[0027] The battery pack system is configured to implement the method according to the present invention. For this purpose, the central control unit of the battery pack system and the battery pack control devices of these battery pack modules having management systems have corresponding hardware in the form of a microprocessor and a memory, respectively, and corresponding program codes.

[0028] Advantages of the present invention

[0029] In the case where the sensor currents measured in different battery pack modules are significantly different, the method according to the present invention allows identifying whether a battery pack module among these battery pack modules or the current sensor assigned to the battery pack module is faulty. Thus, the method according to the present invention enables clear fault correlation in the mentioned fault cases, which is very important for the continued operation of an electric vehicle. Especially when a fault is identified in a battery pack module, the battery pack module can be immediately disconnected to prevent further damage to the battery pack system. In this case, one battery pack module is missing and thus the reduced electric power is available for the electric vehicle. However, if a fault is identified in one of the current sensors, the electric vehicle can continue to operate with all the battery pack modules of the battery pack system, and the damaged current sensor can be replaced at a later time point. In this case, all battery pack modules and thus the complete electric power continue to be available for the electric vehicle. Therefore, the method according to the present invention allows for fast and reliable fault correlation in the case of using known and existing standard hardware but with a new intelligent diagnostic strategy. Advantageously, the battery pack system according to the present invention with known standard components has a low construction cost. Description of the drawings

[0030] Embodiments of the present invention are further illustrated based on the drawings and the subsequent description.

[0031] Wherein:

[0032] Figure 1 shows a schematic diagram of a battery pack system in an electric vehicle; and

[0033] Figure 2 A schematic diagram showing a method for operating a battery pack system is shown. Detailed implementation

[0034] In the following description of the embodiments of the present invention, the same or similar elements are denoted by the same reference numerals, and in some cases, the repeated description of these elements is omitted. These drawings only schematically present the subject matter of the present invention.

[0035] Figure 1 A schematic diagram of a battery pack system 10 in an electric vehicle is shown. The electric vehicle is, for example, a construction machine, especially an excavator. The electric vehicle includes an electric motor 31 and a power electronics device 35. In the present case, the power electronics device 35 is designed as an inverter or as a converter. By means of the power electronics device 35, the three-phase electric motor 31 can be controlled in the present case.

[0036] The battery pack system 10 is used to supply electrical energy to the power electronics device 35 and includes three battery pack modules 5 in the present case. These battery pack modules 5 are connected in parallel and electrically connected to the power electronics device 35. Here, each battery pack module 5 has a plurality of battery pack cells. These battery pack cells are connected in series and / or in parallel within the battery pack module 5. These battery pack modules 5 each have a system voltage of, for example, 800 V.

[0037] In the present case, the battery pack system 10 includes three current sensors 15. Here, each of these battery pack modules 5 is respectively assigned a current sensor 15 that measures the current flowing through the battery pack module 5. Here, the current measured by one of the current sensors 15 is referred to as the sensor current. The sensor current can be a charging current for charging the battery pack module 5 and a discharging current for discharging the battery pack module 5.

[0038] The battery pack system 10 further includes a central control unit 20. The control unit 20 especially calculates the rated current for the battery pack module 5 and transmits the calculated rated current to the battery pack control device of the battery pack module 5 via a communication connection, such as a bus system. Each of the battery pack control devices of the battery pack module 5 has a management system 25. The management system 25 is used to calculate the working current according to the rated current specified by the control unit 20. The management system 25 is also used to control and monitor the battery pack cells of the battery pack module 5.

[0039] Figure 2The figure shows a schematic diagram of a method for operating a battery pack system 10. In an initial step 100, an electric vehicle is started and thereby the battery pack system 10 is also started. The central control unit 20 calculates the total current to be provided by the battery pack system 10 according to the requirements of the user of the electric vehicle. The central control unit 20 also calculates the rated current to be provided by each of the battery pack modules 5 based on this total current.

[0040] The management system 25 of the battery pack control device of the battery pack module 5 calculates the operating current that the corresponding battery pack module 5 can provide respectively according to the specified rated current.

[0041] In the next step 101, the current sensor 15 assigned to the battery pack module 5 measures the sensor current flowing through the battery pack module 5. In the next step 102, the sensor currents measured by the respective current sensors 15 are compared with each other.

[0042] If the lowest sensor current among the measured sensor currents deviates from all other sensor currents by at most a threshold value, all the sensor currents are considered to be approximately equal, and it is assumed that there is no fault in the battery pack system 10. In this case, step 101 is repeated.

[0043] If the lowest sensor current among the measured sensor currents deviates from at least one sensor current of other battery pack modules 5 by at least a threshold value, then in step 103 it is determined which of the mentioned current sensors 15 measures this lowest sensor current. Here, the battery pack module 5 assigned with the current sensor 15 that measures the lowest sensor current is detected as possibly faulty.

[0044] In the next step 104, the previously calculated operating current of the battery pack module 5 detected as possibly faulty is compared with the lowest sensor current measured by the current sensor 15 assigned to the mentioned battery pack module 5.

[0045] If the operating current deviates from the mentioned lowest sensor current by at most a limit value, then in the next step 105 a fault is identified in the battery pack module 5 detected as possibly faulty. In this case, the mentioned faulty battery pack module 5 is disconnected. Then, the battery pack system 10 continues to operate with one less battery pack module 5 and thus with a reduced electric power. Step 101 is repeated.

[0046] If the operating current deviates from the mentioned lowest sensor current by more than the limit value, then in the next step 106, it is first assumed that there is no fault in the battery pack module 5 detected as possibly faulty.

[0047] In this case, in the next step 107, the operating current of the battery pack module 5 detected as possibly faulty is compared with the sensor current of the other battery pack modules 5 and / or with the operating current of the other battery pack modules 5.

[0048] If the operating current deviates from the sensor current of the other battery pack modules 5 and / or the operating current of the other battery pack modules 5 by at most the limit value, then in the next step 108 a fault is identified in the current sensor 15 assigned to the battery pack module 5 detected as possibly faulty. In this case, the battery pack module 5 is not disconnected. Then, the battery pack system 10 continues to operate with a faulty current sensor 15. Step 101 is repeated.

[0049] If the operating current deviates from the sensor current of at least one other battery pack module 5 and / or the operating current of at least one other battery pack module 5 by at least the limit value, then in the next step 109 a fault is identified in the battery pack module 5 detected as possibly faulty. In this case, the mentioned faulty battery pack module 5 is disconnected. Then, the battery pack system 10 continues to operate with one less battery pack module 5 and thus with a reduced electrical power. Step 101 is repeated.

[0050] The operation of the battery pack system 10 and of the electric vehicle is ended at a later point in time by ending step 110.

[0051] Subsequently, the method is illustrated on the basis of some data examples. The central control unit 20 calculates, for example, that the total current to be provided by the battery pack system 10 is 360 A and the rated current to be provided by each of these battery pack modules 5 is 120 A. Two of the current sensors 15 assigned to these battery pack modules 5 measure sensor currents of 100 A each. The operating currents of these battery pack modules 5 are 100 A each. Exactly one of these current sensors 15 measures the lowest sensor current of 80 A. In the present case, the threshold is equal to the limit value and is 5 A respectively.

[0052] The lowest sensor current among the measured sensor currents deviates from the other sensor currents by more than the threshold. Therefore, in step 103 it is determined which of the mentioned current sensors 15 measures the lowest sensor current, and the battery pack module 5 assigned to the current sensor 15 that measures the lowest sensor current is detected as possibly faulty. In step 104, the operating current of the battery pack module 5 detected as possibly faulty is compared with the lowest sensor current.

[0053] In case A, the operating current of the battery pack module 5 detected as potentially faulty is, for example, 82 A. Thus, this operating current deviates from the lowest sensor current by less than the limit value. Consequently, in step 105, a fault is identified in the battery pack module 5 detected as potentially faulty, and the mentioned faulty battery pack module 5 is disconnected.

[0054] In case B, the operating current of the battery pack module 5 detected as potentially faulty is, for example, 100 A. Thus, this operating current deviates from the lowest sensor current by more than the limit value. However, this operating current deviates from the sensor current of the other battery pack modules 5 and / or the operating current of the other battery pack modules 5 by less than the limit value. Consequently, in step 108, a fault is identified in the current sensor 15 assigned to the battery pack module 5 detected as potentially faulty. The battery pack module 5 is not disconnected, and the battery pack system 10 continues to operate with the current sensor 15 faulty.

[0055] In case C, the operating current of the battery pack module 5 detected as potentially faulty is, for example, 90 A. Thus, this operating current deviates from the lowest sensor current by more than the limit value. This operating current also deviates from the sensor current and / or the operating current of the other battery pack modules 5 by more than the limit value. Consequently, in step 109, a fault is identified in the battery pack module 5 detected as potentially faulty, and the mentioned faulty battery pack module 5 is disconnected.

[0056] The present invention is not limited to the embodiments described herein and the aspects emphasized therein. Rather, within the scope defined by the claims, multiple variants are possible, and such variants are within the scope of the skilled person.

Claims

1. A method for operating a battery pack system (10) for an electric vehicle, wherein the battery pack system has a plurality of battery pack modules (5) connected in parallel, and a rated current is specified for each of the battery pack modules (5); for each of the battery pack modules (5), an operating current is calculated based on the specified rated current; the sensor current flowing through each battery pack module (5) is measured by a current sensor (15) assigned to the battery pack module (5); and a comparison is performed between the measured sensor currents of the plurality of battery pack modules (5); wherein if the lowest sensor current among the measured sensor currents deviates from at least one sensor current of other battery pack modules (5) by at least a threshold value, the following steps are implemented: - comparing the operating current of the battery pack module (5) having the lowest sensor current with the mentioned lowest sensor current; - if the operating current deviates from the mentioned lowest sensor current by at most a limit value, a fault is identified in the battery pack module (5) having the lowest sensor current; wherein if the operating current of the battery pack module (5) having the lowest sensor current deviates from the mentioned lowest sensor current by at least the limit value, then the operating current of the battery pack module (5) having the lowest sensor current is compared with the sensor currents of the other battery pack modules (5); wherein if the operating current deviates from the sensor currents of the other battery pack modules (5) by at most the limit value, a fault is identified in the current sensor (15) assigned to the battery pack module (5) having the lowest sensor current; or, wherein if the operating current of the battery pack module (5) having the lowest sensor current deviates from the mentioned lowest sensor current by at least the limit value, the operating current of the battery pack module (5) having the lowest sensor current is compared with the operating currents of the other battery pack modules (5); wherein if the operating current deviates from the operating currents of the other battery pack modules (5) by at most the limit value, a fault is identified in the current sensor (15) assigned to the battery pack module (5) having the lowest sensor current.

2. The method according to claim 1, wherein if the operating current deviates from the sensor current of at least one other battery pack module (5) by at least the limit value, then a fault is identified in the battery pack module (5) having the lowest sensor current.

3. The method according to claim 1, wherein if the operating current deviates from the operating current of at least one other battery pack module (5) by at least the limit value, a fault is identified in the battery pack module (5) having the lowest sensor current.

4. The method according to any one of claims 1 to 3, wherein the same rated current is specified for each of the battery pack modules (5) by a central control unit (20).

5. The method according to any one of claims 1 to 3, wherein each battery pack module in the battery pack module (5) has a battery pack control device having a management system (25), and the management system calculates the operating current based on the specified rated current and at least one other parameter.

6. A battery pack system (10) for an electric vehicle, the battery pack system comprising: a plurality of battery pack modules (5) connected in parallel; a central control unit (20) for specifying a rated current for the battery pack module (5); and a plurality of current sensors (15) for measuring sensor currents, wherein each battery pack module in the battery pack module (5) is respectively assigned a current sensor (15), and each battery pack module in the battery pack module (5) has a battery pack control device having a management system (25) for calculating an operating current based on the specified rated current, and wherein the battery pack system (10) is configured to implement the method according to any one of claims 1 to 5.

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