DE102020206520A1 - Method for operating a battery system - Google Patents

Abstract

The invention relates to a method for operating a battery system (10) with several strings (20) which can be connected in parallel, each having at least one battery module (12) in which several battery cells (14) are connected in series, with the at least one battery module ( 12) a battery cell monitoring unit (16) is provided, which can be connected to a battery control unit (30), and wherein the individual strings (20) can be switched on and off separately and independently of one another, comprising the following steps: ), whereby all strings (20) are switched off when the need for compensation is determined; - Determination of a target cell voltage which corresponds to the lowest cell voltage of all battery cells (14) of the battery system (10); - Equalization of the battery cells (14) to the level of the target cell voltage, - Monitoring of string voltage differences between the strings (20) and comparing Amounts of the respective phase voltage differences with a first predetermined threshold value SW; - comparison of amounts of the respective phase voltage differences with a value of SW - ε, where ε is a second predetermined threshold value. The invention also relates to a vehicle which comprises at least one battery system (10) which is operated using the method according to the invention.

Description

The invention relates to a method for operating a battery system with several strings that can be connected in parallel, each having at least one battery module in which several battery cells are connected to one another in series, a battery cell monitoring unit being provided for the at least one battery module, which can be connected to a battery control unit, and whereby the individual strands can be switched on and off separately and independently of one another.

The invention also relates to a vehicle which comprises at least one battery system which is operated with the method according to the invention.

State of the art

In today's electrically powered vehicles (Electric Vehicle, EV), several battery cells are not only connected to one another in series, but also in parallel. This achieves a sufficiently high battery capacity and thus a long vehicle range, but the required power can also be made available. Such cells are usually connected in parallel within a module, with several modules connected in series in order to achieve the required battery voltage. Such systems are referred to as single-line systems or 1-line systems. But also a parallel connection on string level, i.e. several battery modules with only serially connected battery cells, are used more and more, especially for autonomously operated EVs, in order to be able to switch off only the defective string in the event of a fault and thus a certain security level (Safe Stop Level, SSL) to be able to achieve. The individual strings are connected to each other in parallel by switches (in each strand). The battery cells of these multi-string systems or multi-string systems also have to be balanced from time to time, i.e. their voltages have to be adjusted. With today's compensation processes, such multi-line systems can also be compensated, but the process sequence of a 1-line system cannot be transferred 1: 1, since further criteria have to be taken into account.

The document US 2019/0103750 A1 describes a power management system for use with battery cells that enables the battery cells and batteries to be converted into variable energy storage sources.

The document DE 10 2015 223 580 A1 relates to a method for regulating or controlling a phase current for an electric drive by means of a battery system with a plurality of battery cells and a central control device.

Disclosure of the invention

According to the invention, a method for operating a battery system is proposed. In this case, the battery system comprises several strings which can be connected in parallel and each have at least one battery module in which several battery cells are connected to one another in series. The battery cells are, for example, rechargeable lithium battery cells.

A battery cell monitoring unit (Cell Supervising Circuit, CSC), which can be connected to a battery control unit (Battery Control Unit, BCU), is provided for the at least one battery module. The battery cell monitoring unit is preferably designed as a module-internal battery cell monitoring unit. The battery cell monitoring unit can, for example, record the individual battery cell voltages and the temperature in the battery module, convert the type of signal from analog to digital and transmit it to the higher-level battery control unit.

The individual lines can be switched on and off separately and independently of one another. Connecting is to be understood, among other things, to establish an electrical connection with a consumer, as a result of which electrical energy can flow from the connected strand to the consumer. Connecting is also to be understood as establishing an electrical connection between individual strings, whereby the connected strings are interconnected in parallel. The strings connected in parallel with one another can then be connected to a consumer. Shutdown is understood to mean, among other things, the disconnection of an electrical connection to a consumer, as a result of which electrical energy can no longer flow from the disconnected strand to the consumer. Switching off is also to be understood as the disconnection of an electrical connection of individual strings, as a result of which the strings that have been switched off are no longer interconnected.

If the strings each have several battery modules, the battery modules are connected to one another in series and the individual battery modules can also be switched on and off separately and independently of one another.

The method according to the invention comprises at least the following steps.

First of all, a compensation requirement of the battery system is determined. this happens for example after driving an electric vehicle. When the need for compensation is determined, all lines are switched off. This is necessary in order to prevent the voltage difference arising in the individual strings when balancing, which would lead to high balancing currents.

A target cell voltage for balancing the battery cells is then determined. The target cell voltage corresponds to the lowest cell voltage of all battery cells in the battery system.

All strands are then balanced at the same time. The equalization takes place according to the known passive standard equalization process, in which the cell voltages are adjusted to the level of the lowest cell voltage. Advantageously, any other compensation method can also be used in the method according to the invention, which does not impair the method sequence described here.

When balancing the battery cells, the phase voltage differences between the phases are monitored and the amounts of the respective phase voltage differences are compared with a first predetermined threshold value SW. The phase voltage differences are preferably continuously monitored.

The amounts of the respective phase voltage differences should not exceed the first predetermined threshold value SW. The first predetermined threshold value SW is preferably at a value less than 5 V, in particular less than 3 V, very particularly approximately 1 V.

Shortly before the first predefined threshold value SW is reached, the amounts of the respective phase voltage differences are compared with a value of SW − ε, where ε is a second predefined threshold value. The second predefined threshold value ε is preferably at a value less than 20%, in particular less than 15%, preferably less than 10% of the value of the first predefined threshold value SW.

If the amounts of the respective string voltage differences are smaller than the value of SW - ε, the balancing of the battery cells or the strings is continued.

It is then checked whether the battery system is switched on or whether all battery cells or all strings have been balanced. Switching on a battery system is understood to mean, among other things, establishing an electrical connection with a consumer, as a result of which electrical energy can flow from the switched-on battery system to the consumer, such as starting an electric vehicle.

The balancing is only ended when the battery system is switched on or all battery cells or all strings have been balanced.

If one or more amounts of the phase voltage differences are greater than or equal to the value of SW - ε, the balancing of the phase or phases with a lower phase voltage is first aborted in order to prevent the phase voltages from drifting further apart.

It is then checked whether the one or more amounts of the phase voltage differences are less than or equal to a value of SW − 2ε.

The balancing of the strand or strings in which the balancing was interrupted is only continued if the one or more amounts of the strand voltage differences are less than or equal to the value of SW - 2ε, by a toggling addition and Advantageously, to avoid switching off the equalization.

It is then checked whether the battery system is switched on or whether all battery cells or all strings have been balanced. The balancing is only ended when the battery system is switched on or all battery cells or all strings have been balanced.

Preferably, the battery cells of a string are first equalized to the level of the lowest cell voltage of this string and only when this string has been equalized, i.e. all battery cells of this string have been equalized to the level of the lowest cell voltage of this string, is the equalization to the level of the target cell voltage.

Alternatively, the target cell voltage can be taken into account from the start and the energy reduction of all battery cells of the battery system is geared equally to the battery cell that has the target cell voltage.

If the battery system is switched on during the equalization, only those strings are advantageously connected in which the amounts of the string voltage differences are less than or equal to the first predetermined threshold value SW in order to prevent equalizing currents that damage the battery.

The battery cell monitoring unit of the at least one battery module preferably has a variable electrical resistance for balancing the battery cells, which is also referred to as a potentiometer and is available inexpensively, precisely and in a small design.

The variable electrical resistance is preferably set in such a way that as soon as the amount of the phase voltage difference reaches the first predetermined threshold value SW, the resistance value changes. This would mean that the equalization would not be interrupted and the voltage would be continuously adjusted with a variable discharge current. This process could be permanently active during the equalization and thus represent a type of resistance / current control.

Furthermore, a vehicle is proposed which comprises at least one battery system which is operated with the method according to the invention.

Advantages of the invention

In an advantageous manner, the solution proposed according to the invention can provide a method for operating a multi-line battery system.

The method according to the invention can be implemented purely in terms of software in the battery control unit or, in the case of several battery systems connected in parallel, in a higher-level control device.

The method can advantageously be implemented cost-effectively using standard hardware. Building on the existing electronic hardware, in particular the battery cell monitoring units, the method according to the invention is implemented in software in the battery management system in the battery control unit.

Advantageously, further hardware-technical alternatives can also be used with the aim of optimal compensation under the condition of ensuring that the vehicle can be started at any time. For example, instead of today's fixed resistors, variable electrical resistances can be used in the battery cell monitoring units. Thanks to the variable resistances, continuous compensation with the smallest phase voltage differences can be made possible.

In addition, the method according to the invention can be used not only for low-voltage systems, but also for high-voltage systems of any voltage. Furthermore, the method according to the invention can be used for any passive compensation methods and compensation strategies.

Figure list

Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

• 1 ein erstes einsträngiges Batteriesystem,
• 2 ein zweites einsträngiges Batteriesystem,
• 3 ein dreisträngiges Batteriesystem,
• 4.1 bis 4.4 jeweils ein Balkendiagramm der einzelnen Batteriezellenspannungen zu unterschiedlichen Zeitpunkten während eines Ausgleichens eines ersten Strangs gemäß einer ersten Ausführungsform des erfindungsgemäßen Verfahrens,
• 5.1 bis 5.4 jeweils ein Balkendiagramm der einzelnen Batteriezellenspannungen zu unterschiedlichen Zeitpunkten während eines Ausgleichens des ersten Strangs gemäß einer zweiten Ausführungsform des erfindungsgemäßen Verfahrens,
• 6.1 bis 6.5 jeweils ein Balkendiagramm der einzelnen Batteriezellenspannungen zu unterschiedlichen Zeitpunkten während eines Ausgleichens eines zweiten Strangs und
• 7 eine schematische Darstellung eines Verfahrensablaufs zum Betreiben eines Batteriesystems.

Show it:

• 1 a first single-string battery system,
• 2 a second single-string battery system,
• 3 a three-string battery system,
• 4th .1 to 4.4 each a bar chart of the individual battery cell voltages at different times during a balancing of a first string according to a first embodiment of the method according to the invention,
• 5 .1 to 5.4 each a bar chart of the individual battery cell voltages at different times during a balancing of the first string according to a second embodiment of the method according to the invention,
• 6th .1 to 6.5 each a bar chart of the individual battery cell voltages at different times during a balancing of a second string and
• 7th a schematic representation of a method sequence for operating a battery system.

1 and 2 each show a single-strand battery system 10 .

According to the representations 1 and 2 it can be seen that a strand 20th of the single-string battery system 10 a number of identically constructed battery modules 12th with several battery cells 14th includes. For example, in the strand 20th twelve battery modules 12th be provided interconnected in series with one another, of which in the illustration according to FIG 1 and 2 only three battery modules 12th are shown. The strand 20th is with a first line contactor 22nd or a second line contactor 24 provided, with the help of which the strand 20th can be switched off completely. In addition, the identical battery modules include 12th of the strand 20th a module-internal battery cell monitoring unit each 16 that come with a battery control unit 30th to operate the battery system 10 connected is. The battery cell monitoring unit 16 For example, the individual battery cell voltages and the temperature in the battery module 12th detect the signal type of convert analog to digital and to the higher-level battery control unit 30th transfer.

The individual battery modules 12th of the strand 20th as shown in 1 each include, for example, twelve battery cells 14th that are within the respective battery modules 12th are connected in series. A series connection designed in this way is also referred to as a 12s1p connection.

This in 2 illustrated second single-string battery system 10 differ from the first single-string battery system 10 according to 1 by the fact that the in 2 shown battery modules 12th battery cells connected in parallel 14th exhibit. In the 2 shown battery modules 12th are each in accordance with 12s3p interconnection, ie with twelve battery cells connected in series 14th provided, with three battery cell strings being connected in parallel.

Embodiments of the invention

In the following description of the embodiments of the invention, the same or similar elements are denoted by the same reference numerals, a repeated description of these elements being dispensed with in individual cases. The figures represent the subject matter of the invention only schematically.

According to the representation 3 is a three-strand battery system 10 , which is operated with the method according to the invention.

3 shows the structure of a battery system 10 as shown in 1 but with three strands 20th . The individual strands 20th are in their structure with regard to the battery modules arranged therein 12th arranged in series, identical to the structure of the battery system 10 with one strand 20th according to 1 .

Each of the strands 20th is within the battery system 10 via a first line contactor 22nd or a second line contactor 24 from the battery system 10 separable or connectable with these.

The same applies to the entire battery system 10 , which has a first system contactor 26th or via a second system contactor 28 can be separated from a consumer, for example from an electric drive of a vehicle.

In the following description, the method according to the invention is based on 4th .1 to 4.4, 5 .1 to 5.4 and 6th .1 to 6.5 explained.

The method according to the invention is simplified here using a battery system 10 with a first strand 20th and a second strand 20th described. The first and second strands include 20th one battery module each 12th , the five serially connected battery cells 14th as well as a module-internal battery cell monitoring unit 16 having. The battery cell monitoring unit 16 can record the individual battery cell voltages and transmit them to the higher-level battery control unit 30th transfer.

4th .1 to 4.4 each show a bar chart 40 of the individual battery cell voltages at different times during a balancing of a first string 20th according to a first embodiment of the method according to the invention.

5 .1 to 5.4 each show a bar chart 40 of the individual battery cell voltages at different times during a balancing of the first string 20th according to a second embodiment of the method according to the invention.

6th .1 to 6.5 each show a bar chart 40 of the individual battery cell voltages at different points in time during a balancing of a second string 20th .

For more than two strands 20th is the process flow 100 (please refer 7th ) analogue. The same applies to any number of battery cells 14th .

In the 4th .1 to 4.4, 5 .1 to 5.4 and 6th .1 to 6.5 shown bar graphs 40 each have a first axis 41 and one perpendicular to the first axis 41 standing second axis 42 . This is on the first axis 41 the designation of the individual battery cells 14th plotted while on the second axis 42 the voltage is plotted. The bars 50 in the respective bar charts 40 set the voltage level of the individual battery cells 14th at different times.

After a consumption, such as a trip in an electric vehicle, the strands show 20th (almost) the same line voltage. Present in 4th .1, 5 .1 and 6th .1 shows the line voltage of the respective lines 20th a value of 20.2 V, which is the sum of the battery cell voltages of the five battery cells 14th is equivalent to.

If there is a need for compensation from a battery management system of the battery control unit 30th determined, the first and the second strand 20th switched off. This is required to get the when balancing in the individual strands 20th to prevent the resulting phase voltage difference, which would lead to high equalizing currents.

Then the balancing starts in the two strands 20th contemporaneous. The method is the well-known passive standard compensation method, in which the cell voltages are brought to the level of the lowest cell voltage of all battery cells 14th of the battery system 10 , which is also referred to as the target cell voltage, can be adjusted. As here in 4th .1, 5 .1 and 6th .1, the target cell voltage is the lowest cell voltage of all battery cells 14th of the battery system 10 corresponds to, 3.8 V.

Advantageously, any other compensation method can also be used in the method according to the invention, which is the method sequence described here 100 not affected.

Using the example of the first strand 20th two possible embodiments of the method according to the invention are shown. On the second strand 20th it is irrelevant which embodiment is used, since the smallest cell voltage of the second strand 20th the lowest cell voltage of all battery cells 14th of the battery system 10 , namely the target cell voltage.

In the first embodiment shown in 4th .1 to 4.4 through bar graphs 40 are shown at different times, the battery cells 14th of the first strand 20th to the level of the lowest cell voltage of the first strand 20th balanced and only when the first strand 20th has been balanced, ie all battery cells 14th of the first strand 20th were at the level of the lowest cell voltage of the first strand 20th balanced, the balancing takes place at the level of the lowest cell voltage of all battery cells 14th of the battery system 10 , i.e. the target cell voltage.

In the second embodiment, which is shown in 5 .1 to 5.4 using bar graphs 40 are shown at different times, the target cell voltage is taken into account from the beginning of the equalization and the energy reduction is equal to the battery cell 14th aligned that has the target cell voltage.

Which embodiment is used is not relevant for this method according to the invention; both embodiments are possible.

At the start time t0 in 4th .1, 5 .1 and 6th .1 the equalization is started. The battery cells 14th which are already at the level of the target cell voltage for the corresponding time step are not compensated.

At time t1 in 4th .2 and 6th .2 is the first strand 20th with the first embodiment at the same strand tension level as the second strand 20th while the first strand 20th with the second embodiment at time t1 in 5 .2 at a different strand tension level than the second strand 20th is located.

At time t2 in 4th .3 and 6th .3 is also the strand tension level of the first strand 20th with the first embodiment different from the strand tension level of the second strand 20th .

This shows that regardless of the embodiment selected, phase voltage differences arise during the equalization in the phases 20th can adjust. Even if these are only very small, in the present case with five battery cells 14th If the string voltage difference is 100 mV, this means for strings 20th of approx. 100 battery cells 14th a twenty-fold increase, i.e. a line voltage difference of 2 V. If the driver starts his vehicle while balancing, only the lines will 20th switched on, in which the amounts of the phase voltage differences are less than or equal to a first predetermined threshold value SW in order to prevent battery-damaging equalizing currents. The first predefined threshold value SW is preferably at a value less than 5 V, in particular less than 3 V, very particularly approximately 1 V. In the example, an interconnection would consequently still just be possible.

The method according to the invention should, however, function robustly, that is to say for the driver a start with maximum power, that is to say with all phases, even with larger phase voltage differences 20th , enable. It should also be taken into account that aged battery cells 14th larger string voltage differences will be set. So it must be prevented that the battery system 10 comes into such a situation in which the first predetermined threshold value SW is exceeded.

For this purpose, the phase stresses are determined continuously during the equalization and not only at fixed times, as in 4th .1 to 4.4, 5 .1 to 5.4 and 6th .1 to 6.5 shown in simplified form. Shortly before the first predefined threshold value SW is reached, that is to say when a value of SW − ε is reached, where ε is a second predefined threshold value, the balancing of the strand is aborted 20th with the lower phase voltage in order to prevent the phase voltages from drifting further apart.

As soon as the strand tension of the strand 20th , which is still being balanced, dips back into the voltage range of the threshold value SW, the aborted balancing of the other strand is carried out 20th continued.

This advantageously only takes place when the amount of the phase voltage difference is less than or equal to a value of SW − 2ε, in order to avoid toggling switching on and off of the equalization. The software implementation takes place by means of a hysteresis function. The process continues until the driver starts his electric vehicle or the balancing is ended as soon as all of the battery cells are used 14th have the same voltage level.

7th shows a schematic representation of a process sequence 100 for operating a battery system 10 . After consumption, such as driving an electric vehicle, in a start step 101 the method according to the invention started.

First of all, it is done in one step 102 determining a compensation requirement of the battery system 10 . When determining the need for compensation, all strands 20th switched off. This is needed to help balance out the individual strands 20th to prevent the resulting phase voltage difference, which would lead to high equalizing currents.

This is done in one step 103 determining a target cell voltage for balancing the battery cells 14th . The target cell voltage corresponds to the lowest cell voltage of all battery cells 14th of the battery system 10 .

This is then done in one step 104 balancing in all strands 20th contemporaneous. The equalization takes place according to the known passive standard equalization process, in which the cell voltages are adjusted to the level of the lowest cell voltage. Advantageously, any other compensation method can also be used in the method according to the invention, which is the method sequence described here 100 not affected.

When balancing the battery cells 14th take place in one step 105 a monitoring of string voltage differences of the strings 20th with one another and a comparison of the amounts of the respective phase voltage differences with a first predetermined threshold value SW. The phase voltage differences are preferably continuously monitored.

Shortly before the first predetermined threshold value SW is reached, it takes place in one step 106 comparing the amounts of the respective phase voltage differences with a value of SW - ε, where ε is a second predetermined threshold value.

If an amount or several amounts of the phase voltage differences are greater than or equal to the value of SW - ε, then in one step 107 balancing the strand 20th or the strands 20th terminated with a lower phase voltage in order to prevent the phase voltages from drifting further apart.

Then in one step 108 checked whether the one amount or the several amounts of the phase voltage differences are less than or equal to a value of SW - 2ε. If the one or more amounts of the phase voltage differences are greater than the value of SW − 2ε, then the steps 105 until 108 repeated as described above. Balancing the strand 20th or the strands 20th whose clearing was previously canceled is only then used in the step 109 continued if the one or more amounts of the phase voltage differences are less than or equal to the value of SW − 2ε, in order to advantageously avoid toggling switching on and off of the compensation.

If the amounts of the respective phase voltage differences are smaller than the value of SW - ε, then in step 109 balancing the battery cells 14th continued.

Then in one step 110 checked whether the battery system 10 is switched on or whether all battery cells 14th or all strands 20th were balanced. When the battery system 10 does not turn on and when the battery cells 14th or the strands 20th The steps have not yet been fully balanced 105 until 110 repeated as described above.

The balancing is only then done in one step 111 terminated when the battery system 10 is switched on or all battery cells 14th or all strands 20th were balanced.

The invention is not restricted to the exemplary embodiments described here and the aspects emphasized therein. Rather, a large number of modifications are possible within the range specified by the claims, which are within the scope of expert knowledge.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 2019/0103750 A1 [0004]
• DE 102015223580 A1 [0005]

Claims (10)

A method for operating a battery system (10) with a plurality of strings (20) which can be connected in parallel, each having at least one battery module (12) in which a plurality of battery cells (14) are connected to one another in series, wherein for the at least one battery module (12) a battery cell monitoring unit (16) is provided which can be connected to a battery control unit (30), and wherein the individual strings (20) can be switched on and off separately and independently of one another, including the following steps: - Determining a compensation requirement of the battery system (10), with all strings (20) being switched off when the compensation requirement is determined; - Determining a target cell voltage which corresponds to the lowest cell voltage of all battery cells (14) of the battery system (10); - Equalizing the battery cells (14) to the level of the target cell voltage, - Monitoring phase voltage differences between the phases (20) and comparing the amounts of the phase voltage differences with a first predetermined threshold value SW; - Comparing the amounts of the respective phase voltage differences with a value of SW - ε, where ε is a second predetermined threshold value. Procedure according to Claim 1 If the amounts of the respective phase voltage differences are smaller than the value of SW - ε, the following steps are carried out: Continuing the equalization; - Check whether the battery system (10) is switched on or whether all battery cells (14) have been balanced; - Ending the equalization when the battery system (10) is switched on or all battery cells (14) have been equalized. Procedure according to Claim 1 , wherein if one or more amounts of the phase voltage differences are greater than or equal to the value of SW - ε, the following steps are carried out: - Aborting the balancing of the strand (20) or the strands (20) with a lower strand voltage; - Check whether the one or more amounts of the phase voltage differences are less than or equal to a value of SW - 2ε; - Continuing the balancing of the strand (20) or the strands (20) whose balancing was interrupted when the strand voltage differences are less than or equal to the value of SW - 2ε; - Check whether the battery system (10) is switched on or whether all battery cells (14) have been balanced; - Ending the equalization when the battery system (10) is switched on or whether all battery cells (14) have been equalized. Method according to one of the Claims 1 until 3 , characterized in that the battery cells (14) of a string (20) are initially balanced to the level of a lowest cell voltage of this string (20) and only when all battery cells (14) of this string (20) are at the level of the lowest cell voltage of this Strand (20) have been balanced, the balancing takes place on the target cell voltage. Method according to one of the Claims 1 until 4th , characterized in that if the battery system (10) is switched on during the equalization, only those strings (20) in which the amounts of the string voltage differences are less than or equal to the first predetermined threshold value SW are switched on. Method according to one of the Claims 1 until 5 , characterized in that the first threshold value SW is less than 5V. Method according to one of the Claims 1 until 6th , characterized in that the second threshold value ε is less than 20% of the value of the first predetermined threshold value SW Method according to one of the Claims 1 until 6th , characterized in that the battery cell monitoring unit (16) of the at least one battery module (12) comprises a variable electrical resistor for balancing the battery cells (14). Procedure according to Claim 7 , characterized in that the variable electrical resistance is set so that as soon as the phase voltage difference reaches the threshold value SW, the resistance value changes. Vehicle comprising at least one battery system (10) which is operated with a method according to one of the preceding claims.

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