DE102018217382A1 - Method for operating a battery system and electric vehicle and battery system for an electric vehicle - Google Patents

Abstract

The invention relates to a method for operating a battery system (10) for an electric vehicle, comprising a plurality of battery strings (7) that can be connected in parallel, each battery string (7) having at least one battery module (5), and each battery module (5) having at least one battery cell The individual battery strings (7) can be connected separately and independently of one another to a collecting line (63), only a selected number of the battery strings (7) being switched on when the battery system (10) is discharged, so that at least one of the battery strings ( 7) remains switched off constantly. The invention also relates to a battery system (10) for an electric vehicle, comprising a plurality of battery strings (7) which can be connected in parallel, each battery string (7) having at least one battery module (5), and each battery module (5) having at least one battery cell, and Each of the battery strings (7) is assigned a separate string switch (61), by means of which the individual battery strings (7) can be connected separately and independently of one another to a collecting line (63), and a management system (20) for monitoring the battery strings (7) and for controlling the string switches (61), the management system (20) being set up to carry out the method according to the invention.

Description

The invention relates to a method for operating a battery system for an electric vehicle, the battery system comprising a plurality of battery strings which can be connected in parallel, each battery strand having at least one battery module and each battery module having at least one battery cell. The invention also relates to a battery system for an electric vehicle, which also has a management system for monitoring the battery strings.

State of the art

It is becoming apparent that electric vehicles will increasingly be used in the future. Rechargeable battery systems are used in electrically powered motor vehicles, such as electric vehicles and hybrid vehicles, but also in stationary applications, primarily to supply electrical drive devices with electrical energy. Battery systems with lithium battery cells are particularly suitable for such applications. Lithium battery cells are characterized, among other things, by high energy densities, thermal stability and extremely low self-discharge. Several lithium battery cells of this type are electrically connected in series and in parallel with one another and connected to form battery modules. Several such battery modules are interconnected, in particular in series, to form a battery string. A battery system of the electric vehicle comprises a plurality of battery strings designed in this way and connected in parallel with one another.

During operation of the electric vehicle, the battery cells of the battery system are used to drive the electric vehicle and to supply other consumers, and are discharged in the process. A charge level of the battery cells, battery modules and battery strings is monitored by a management system. If the battery cells are largely discharged, they must be recharged. If the battery strings are used and loaded approximately evenly, the individual battery cells of the battery modules are also discharged approximately uniformly.

The document DE 10 2012 204 933 A1 discloses a battery system and a method for driving battery modules of the battery system. Individual battery modules and battery cells can be connected to a battery string or separated from the battery string. A specific or selected output voltage of the associated battery string can be set by appropriate clocking of a battery module.

The document DE 10 2013 213 266 A1 discloses an energy storage system with a plurality of energy storage module strings connected in parallel. By pulsed operation of an energy storage module string for a specific pulse operating time, the energy storage module string can deliver a pulse current, while the remaining energy storage module strings deliver a continuous current in continuous operation. As a result, the electrical energy storage system can provide increased electrical power for a short time.

The document DE 10 2014 109 092 A1 discloses a propulsion system for a submarine which has a plurality of battery strings which can be connected to a DC voltage network and can be separated from the DC voltage network. The currents through the individual battery strings are adjustable. By appropriately setting the currents through the individual battery strings, the output voltages of the individual battery strands are set such that compensating currents between the individual battery strings are minimized.

Disclosure of the invention

A method for operating a battery system for an electric vehicle is proposed. The battery system comprises a plurality of battery strings which can be connected in parallel, each battery strand having at least one battery module. Each of said battery strings preferably has a plurality of battery modules which are connected in series with one another. Each battery module has at least one battery cell. Each battery module preferably has a plurality of battery cells, it being possible for the battery cells within the battery module to be connected to one another both in series and in parallel. The individual battery strings can be connected separately and independently of one another to a collecting line and can be switched off from the collecting line.

When the battery system is discharged, only a selected number of battery strings are switched on, so that at least one of the battery strings remains switched off continuously. A battery string which is electrically connected to the collecting line is referred to as being switched on. A battery string that is electrically isolated from the collecting line is referred to as switched off. Each of the battery strings is assigned, for example, a separate string switch, by means of which the relevant battery string can be switched on to the collecting line and can be switched off from the collecting line.

When driving the electric vehicle, only the battery strings of the battery system that are switched on are discharged. No electricity flows through the switched off battery strings and therefore the switched off battery strings are not discharged. When the electric vehicle is driving, at least one battery string is not discharged.

According to a preferred embodiment of the invention, when one of the connected battery strings is drained when the battery system is discharged, this drained battery string is switched off and another battery string is switched on which is at least partially charged or fully charged.

The battery cells of the battery modules of the individual battery strings each have a state of charge (SOC), which is detected by appropriate sensors. For example, the voltages of the battery cells are measured by voltage sensors, and the charge states are calculated from the measured voltages. The state of charge of the battery cells of a battery string define a state of charge of the battery string. The individual battery cells, and thus also the battery strings, have a maximum charging capacity to which the current state of charge is based.

In this context, a battery string whose current state of charge is less than 20% of its maximum charge capacity is called empty. In this context, a battery string whose current state of charge is between 20% and 85% of its maximum charging capacity is referred to as partially charged. In this context, a battery string whose current state of charge is greater than 85% of its maximum charging capacity is referred to as fully charged. These limit values between the charge states can be seen here as examples and can also be defined differently. However, the limit value proposed here of 20% of the maximum charging capacity for determining whether the battery string is empty should not be undershot too much in order to avoid deep discharge of the battery cells.

According to an advantageous embodiment of the invention, the battery train that is least charged of the at least partially charged or fully charged battery trains is switched on. So if one of the connected battery strings is emptied and switched off, the one of the non-emptied battery strings that has the lowest state of charge is switched on.

According to a preferred development of the invention, when the battery system is discharged, the number of battery strings connected is selected such that the number of battery strings connected can supply a required battery current and that the number of battery strings connected is minimal. Thus, only as many battery strings are always connected as are required to supply the required battery power, for example to drive the electric vehicle.

According to an advantageous further development of the invention, when the battery system is discharged, exactly one specific battery string remains switched on until the specific battery string is empty. This particular battery string is thus discharged first and is the first of the battery strings to be empty. If this battery string is then drained and switched off, a different battery string is determined, which remains switched on when the battery system is discharged.

This operating mode of the electric vehicle and the battery system can be used, for example, when the electric vehicle is operated primarily on short distances and at low speeds. In this case, only a relatively small battery current is required to drive the electric vehicle, which can be supplied by a single battery string.

In this case, in addition to the one particular battery string, a quantity of battery strings is preferably connected, which is calculated in such a way that the number of battery strings connected can supply a required battery current. This is particularly necessary if a higher battery current is required for a short time, for example when accelerating the electric vehicle.

According to another advantageous development of the invention, at least two specific battery strings remain connected when the battery system is discharged until the specific battery strings are empty. These specific battery strings are thus discharged first and are the first of the battery strings to be discharged. If these battery strings are then empty and are switched off, other battery strings are determined which remain switched on when the battery system is discharged.

This operating mode of the electric vehicle and the battery system can be used, for example, when a higher battery current is predominantly required to drive the electric vehicle. This is particularly the case if the electric vehicle is operated predominantly at medium or higher speeds. The battery current required to drive the electric vehicle depends not only on the speed, but also, for example, on acceleration processes and on gradients when driving uphill.

In addition to the at least two specific battery strings, a quantity of battery strings is preferably connected, which is calculated in such a way that the number of connected battery strings can supply a required battery current. This is especially necessary if a higher battery current is required for a short time, for example when the electric vehicle is accelerating strongly.

According to a preferred development of the invention, only a selected number of battery strings is also switched on when the battery system is being charged, so that at least one of the battery strings remains switched off continuously during charging.

Preferably only empty battery strings are switched on when charging the battery system. So only drained battery strings are charged. Partially charged battery strings and fully charged battery strings are therefore not charged.

A battery system for an electric vehicle is also proposed. The battery system comprises a plurality of battery strings which can be connected in parallel, each battery strand having at least one battery module. Each of said battery strings preferably has a plurality of battery modules which are connected in series with one another. Each battery module has at least one battery cell. Each battery module preferably has a plurality of battery cells, it being possible for the battery cells within the battery module to be connected to one another both in series and in parallel.

The battery system also comprises a plurality of string switches, with a separate string switch being assigned to each of the battery strings. By means of the string switches, the individual battery strings can be connected separately and independently of one another to a collecting line and can be switched off from the collecting line.

The battery system also includes a management system for monitoring the battery strings and for controlling the string switches. The management system is set up to carry out the method according to the invention. For this purpose, the management system has appropriate hardware, for example a processor and memory, and is connected to the string switches and to the battery strings via signal lines.

Advantages of the invention

The method according to the invention for operating a battery system of an electric vehicle allows the battery cells of the battery strings to be fully discharged, at least approximately, before the battery cells are recharged. The battery cells thus experience only, at least approximately, complete charge cycles and discharge cycles. Partial charge cycles, which occur when partially charged battery cells are recharged, are advantageously avoided. Through the use of full charge cycles, the battery cells, and thus also the battery system, have a longer service life than would be the case with the use of partial charge cycles. As a result, the service life of the battery system in the electric vehicle is increased and the costs of the electric vehicle are advantageously reduced, in particular with respect to the service life of the electric vehicle. The method according to the invention is particularly suitable for use in medium-temperature cells with solid electrolyte, since in these battery cells the effects of the charging cycles on the service life of the battery cells are particularly significant. Furthermore, the method according to the invention enables a high degree of flexibility through various embodiments, which are adapted to the use of the battery system and to the behavior of a user of the electric vehicle. In addition to mobile use in an electric vehicle, the method according to the invention is also suitable for stationary use.

Figure list

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

• 1 eine schematische Darstellung eines Batteriesystems mit mehreren Batteriesträngen und
• 2 eine schematische Darstellung eines Batteriemoduls mit mehreren Batteriezellen.

Show it:

• 1 is a schematic representation of a battery system with multiple battery strings and
• 2nd is a schematic representation of a battery module with several battery cells.

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 symbols, and a repeated description of these elements is dispensed with in individual cases. The figures represent the subject matter of the invention only schematically.

1 shows a schematic representation of a battery system 10th for an electric vehicle with several, in the present case five, battery strings 7 . Each of the battery strings 7 of the battery system 10th includes several battery modules 5 which are electrically connected in series. Any battery module 5 comprises at least one battery cell 2nd , preferably several battery cells 2nd . A battery system 10th For an electric vehicle, a larger number of battery strings can also be used 7 include.

The battery strings are on the input side 7 electrically connected to each other. Each of the battery strings 7 is a separate string switch 61 assigned which is electrically serial with the respective battery string 7 connected is. The said string switches 61 are parts of a switching unit 60 of the battery system 10th . The string switches 61 the switching unit 60 can be designed, for example, as a contactor, as an electromechanical relay or as a semiconductor switch.

By closing a string switch 61 the associated battery string 7 on the output side with a manifold 63 electrically connected. One with the manifold 63 electrically connected battery string 7 is called switched on. By opening a string switch 61 the associated battery string 7 on the outlet side of the manifold 63 electrically isolated.

One from the manifold 63 electrically isolated battery string 7 is called switched off.

The battery system 10th also includes a management system 20th for monitoring the battery strings 7 and to control the string switches 61 . The management system 20th is by means of a signal line with the switching unit 60 connected. By transmitting appropriate commands from the management system 20th via the signal line to the switching unit 60 can the string switch 61 can be opened and closed separately. By appropriately controlling the string switches 61 through the management system 20th so can the battery strings 7 switched on and off.

The management system 20th is also by means of signal lines, not shown here, with the battery strings 7 connected. The battery strings transmit via said signal lines 7 Management system data 20th . This data includes, in particular, messages relating to the state of charge (SOC) of the individual battery cells 2nd the battery modules 5 the battery strings 7 . The switching unit also transmits 60 the current positions of the individual string switches 61 via the signal line to the management system 20th .

The battery system 10th supplies in particular electrical energy for driving the electric vehicle and is, among other things, with power electronics 23 connected. The power electronics 23 is designed as an inverter or inverter. By means of the power electronics 23 is a three-phase drive motor 25th controllable of the electric vehicle. The power electronics 23 is a main switch 65 assigned.

With closed string switch 61 and the main switch is closed 65 a partial flow flows IT through the relevant connected battery string 7 to the manifold 63 . From the manifold 63 a battery current flows IB through the power electronics 23 . The said battery power IB corresponds to the sum of the partial flows IT of all connected battery strings 7 .

Depending on the current driving situation of the electric vehicle, the drive motor must 25th deliver a certain torque, which requires a certain electrical power. For example, the drive motor 25th deliver a relatively low torque when driving slowly at low speed, which requires a relatively low electrical power. In the case of strong acceleration, the drive motor must 25th For example, deliver a relatively high torque, which requires a relatively high electrical power.

Depending on the electrical power required by the power electronics 23 the drive motor 25th provides a certain battery current IB from power electronics 23 needed. The required battery power IB the greater the electrical power required, the greater. Every battery string 7 can only have a maximum permissible partial flow IT deliver. If the required battery power IB is greater than the maximum permissible partial flow IT of a battery string 7 , so multiple battery strings 7 be switched on. The number of battery strings 7 that must be switched on depends on the size of the battery current IB required.

2nd shows a schematic representation of a battery module 5 of in 1 shown battery system 10th . The battery module 5 of the battery system 10th has multiple battery cells 2nd on. The battery cells 2nd are inside the battery module 5 in the present case electrically connected in series. The battery cells 2nd can inside the battery module 5 for example, can also be connected in parallel. Every battery cell 2nd of the battery module 5 comprises an electrode unit, each having an anode and a cathode. The anode of the electrode unit is with a negative terminal of the battery cell 2nd connected. The cathode of the electrode unit is with a positive terminal of the battery cell 2nd connected. For the serial connection of the battery cells 2nd inside the battery module 5 is the negative terminal of a battery cell 2nd with the positive terminal of the neighboring battery cell 2nd electrically connected. All battery cells are present 2nd the battery modules 5 identically trained.

The invention is not based on the exemplary embodiments described here and those therein highlighted aspects limited. Rather, a large number of modifications are possible within the scope specified by the claims, which lie within the framework of professional action.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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

• DE 102012204933 A1 [0004]
• DE 102013213266 A1 [0005]
• DE 102014109092 A1 [0006]

Claims (11)

Claims 1. A method for operating a battery system (10) for an electric vehicle, comprising a plurality of battery strings (7) which can be connected in parallel, each battery strand (7) having at least one battery module (5), and each battery module (5) having at least one battery cell (2), and wherein the individual battery strings (7) can be connected separately and independently of one another to a collecting line (63), wherein when discharging the battery system (10) only a selected number of battery strings (7) is switched on, so that at least one of the battery strings (7) remains switched off continuously. Procedure according to Claim 1 , When one of the connected battery strings (7) is empty when the battery system (10) is discharged, the empty battery branch (7) is switched off, and another battery branch (7) is connected, which is at least partially charged. Procedure according to Claim 2 , The battery train (7) which is least charged of the at least partially charged battery trains (7) is switched on. Method according to one of the preceding claims, wherein when discharging the battery system (10) the number of connected battery strings (7) is selected such that the number of connected battery strings (7) can supply a required battery current (IB), and that the number of connected battery strings (7) is minimal. Method according to one of the preceding claims, wherein when discharging the battery system (10) exactly one specific battery string (7) remains switched on until the certain battery string (7) is empty. Procedure according to Claim 5 , In addition to the determined battery string (7), a quantity of battery strings (7) is switched on, which is calculated in such a way that the number of battery strings (7) connected can supply a required battery current (IB). Procedure according to one of the Claims 1 to 4th , At least two specific battery strings (7) remain switched on when the battery system (10) is discharged until the specific battery strings (7) are empty. Procedure according to Claim 7 , In addition to the at least two specific battery strings (7), a quantity of battery strings (7) is connected, which is calculated in such a way that the number of connected battery strings (7) can supply a required battery current (IB). Method according to one of the preceding claims, wherein when charging the battery system (10) only a selected number of battery strings (7) is switched on, so that at least one of the battery strings (7) remains switched off continuously. Procedure according to Claim 9 , wherein only empty battery strings (7) are switched on when charging the battery system (10). A battery system (10) for an electric vehicle, comprising a plurality of battery strings (7) which can be connected in parallel, each battery strand (7) having at least one battery module (5), and each battery module (5) having at least one battery cell (2), and wherein each of the battery strings (7) is assigned a separate string switch (61), by means of which the individual battery strings (7) can be connected separately and independently of one another to a collecting line (63), and a management system (20) for monitoring the battery strings (7) and for controlling the string switches (61), the management system (20) being set up to carry out the method according to one of the preceding claims.

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