DE102022207731A1 - Battery management system - Google Patents

Abstract

The present invention relates to a battery management system (1), comprising: a first current path (2), which is connected on a first side to a first charging and discharging contact (3) of the battery management system (1), and is intended for this purpose on a second Side to be connected to a first pole (4a) of a battery (4), a first transistor (5), which is arranged in the first current path (2) in order to switch the first current path (2), a second current path (6 ), which is connected on a first side to a second charging and discharging contact (7) of the battery management system (1), and is intended to be connected on a second side to a second pole (4b) of the battery (4), a third current path (8), which is connected on a first side to the first charging and discharging contact (3) and on a second side to the second charging and discharging contact (7), the third current path (8) being on the The side of the first transistor (5) facing the first charging and discharging contact (3) is connected to the first current path (2), a second transistor (9), which is arranged in the third current path (8), around the third current path (8 ) to switch, and a control logic (10) which is set up to: switch the first transistor (5) into a conducting state and the second transistor (9) into a non-conducting state in order to charge and discharge the battery (4 ) and to switch the first transistor (5) into a non-conducting state and the second transistor (9) into a conducting state in order to prevent the battery (4) from being overcharged.

Description

State of the art

The present invention relates to a battery management system.

Battery management systems (BMS) are generally used in battery modules to enable safe and reliable use of the battery cells or battery modules. The main functionality of the battery management system is often monitoring the battery temperature, battery voltages, state of charge (SOC) and/or a charge/discharge current of the battery. The battery management system also often offers the possibility of discharging currents or charging currents from external devices, e.g. B. from chargers or inverters.

Battery management systems are typically also used in the area of electric bicycles.

Basically, there are two different circuit topologies through which both a charging current and a discharging current of a battery can be switched.

In a first topology, a common interface is used for charging and discharging currents. Typically, both a discharge current and a charging current of the battery are routed via a common pin of a plug. In such a topology, two electrical switches, typically MOSFETs, are usually connected in series to enable a flowing current to be interrupted for both positive and negative currents, i.e. for charging currents and discharging currents. The MOSFETs are typically arranged in such a way that their parasitic diodes are connected in opposite poles to one another. This prevents leakage current from flowing through the parasitic diodes through the series-connected MOSFETs.

In a second topology, two separate interfaces are used, with one interface being used for a charging current and another interface being used for a discharging current. In this case, a plug has, for example, a first pin, which is suitable for discharging the battery, and a second pin, which is suitable for charging the battery. Here too, two electrical switches, typically MOSFETs, are typically used, with one of the interfaces being switched by an associated switch. The parasitic diode of the MOSFET is aligned accordingly in order to prevent a charging current or a discharging current.

However, both of these typical topologies have disadvantages. Using a single interface for charge and discharge currents results in an external current, such as a charge current, having to flow through both of the series-connected MOSFETs, resulting in losses within the MOSFETs. This also causes the battery management system to heat up more than would be the case if the charging current only had to flow through a single MOSFET. Since the cooling capacity of the battery management system is typically limited, this means that comparatively expensive MOSFETs have to be used in order to avoid power losses. Particularly when using the battery management system in electric bicycles, the charging current is significantly lower than a discharging current. However, since the current must flow through both MOSFETs, this means that both MOSFETs must be sufficiently dimensioned.

Using two separate interfaces for charging and discharging currents means that each current only needs to flow through a single MOSFET, reducing losses. For example, when using the same MOSFETs, the losses are halved compared to the topology described above. This makes it possible for a dimension of the battery management system to be made comparatively smaller and for cheaper MOSFETs to be used. For example, MOSFETs with a higher drain-source resistance can be used. However, with the second topology, the flexibility of the battery management system for deployment is reduced. For example, additional cabling is necessary because the separate interfaces have to be wired. This increases the cabling effort. The dimension of the interfaces is also increased because separate interfaces have to be provided for charging and discharging currents.

Disclosure of the invention

The battery management system according to the invention comprises a first current path, which is connected on a first side to a first charging and discharging contact of the battery management system, and is intended to be connected to a first pole of a battery on a second side, a first transistor, which is in the first current path is arranged to switch the first current path, a second current path which is connected on a first side to a second charging and discharging contact of the battery management system, and is intended to be connected to a second pole of the battery on a second side a third current path, which is connected on a first side to the first charging and discharging contact and on a second side to the second charging and discharging contact, the third current path being on the side of the first transistor facing the first charging and discharging contact is connected to the first current path, a second transistor which is arranged in the third current path to switch the third current path, and control logic which is designed to switch the first transistor into a conducting state and the second transistor into a non-conducting state state to enable charging and discharging of the battery, and to switch the first transistor to a non-conducting state and the second transistor to a conducting state to prevent overcharging of the battery.

A charging and discharging contact is a contact through which a battery connected to the battery management system can be either charged or discharged. Both a consumer and a charger can be connected to the charging and discharging contact. The battery management system includes a first charging and discharging contact and a second charging and discharging contact to contact the two poles of the battery. There are two contacts via the two charging and discharging contacts, which are typically a positive and a negative connection contact. The first pole of the battery and the second pole of the battery are in particular a positive and a negative pole of the battery.

The first transistor is arranged in the first current path to switch the first current path. This means that the first current path is interrupted when the first transistor is switched to a non-conducting state. If the first transistor is switched back into a conductive state, the first current path is also conductive. The first transistor thus provides a switch arranged in the first current path.

The second transistor is arranged in the third current path in a corresponding manner. If the second transistor is switched to a conductive state, the third current path is also conductive. If the second transistor is switched to a non-conducting state, the third current path is also non-conductive.

The control logic switches the battery management system into different operating states. In one of these operating states, the battery can be charged and discharged. The first transistor is switched to the conducting state and at the same time the second transistor is switched to the non-conducting state. In a further operating state, overcharging of the battery is prevented. In such an operating state, the first transistor is switched to the non-conducting state and at the same time the second transistor is switched to the conducting state.

If the first transistor is switched to the conductive state, the charging and discharging contacts are supplied with a voltage from the poles of the battery and a charging current can be drawn. Since the second transistor is switched to the non-conducting state at the same time, there is no short circuit between the charging and discharging contacts.

If the first transistor is switched to the non-conducting state, the first charging and discharging contact is separated from the battery and the battery cannot be charged or discharged. Because the second transistor is switched to the conductive state, the two charging and discharging contacts are short-circuited. This is typically detected by a connected charger and a charging process is aborted. This can prevent overcharging of the battery.

The battery management system according to the invention enables power losses via the transistors to be minimal. When charging and discharging the battery, a current path is only routed via a single transistor in the battery management system. The means necessary for cooling the battery management system are therefore reduced and the efficiency of the system is increased. The costs for such a battery management system are also kept low.

A battery management system is created which works with a minimum number of charging and discharging contacts and also has particularly low power losses due to discharging or charging the battery via a switchable current path.

The subclaims show preferred developments of the invention.

Preferably, the control logic is further configured to switch the first transistor into a non-conducting state and the second transistor into a non-conducting state in order to prevent the battery from discharging. In addition to the operating state in which charging and discharging of the battery is possible and the operating state in which overcharging of the battery is prevented, a further operating state is thus created in which discharging of the battery is prevented. For this purpose, the first transistor is switched to the non-conducting state and at the same time the second transistor is switched to the non-conducting state. This operating state can also be referred to as the standby state. A charger that is connected to the battery management system in this state is not immediately short-circuited because the second transistor is not in a conductive state. This makes it possible, for example, to first detect that the charger is connected and then to bring the first transistor into the conductive state, whereby the system switches to the operating state in which charging and discharging of the battery is possible.

Preferably, the first transistor is arranged in the first current path in such a way that a cathode of a parasitic diode of the first transistor is arranged on the side of the battery and an anode of the parasitic diode of the first transistor is arranged on the side of the first charging and discharging contact. In particular, if the first pole is a positive pole of the battery, this ensures that the battery cannot discharge via the first current path if the first transistor is not in a conducting state.

Preferably, the first transistor and/or the second transistor is a field effect transistor, in particular a MOSFET.

The first transistor is preferably designed to conduct higher currents in a conductive state than the second transistor. This makes it possible for a more cost-effective component to be used for the second transistor. This is possible because, on average, lower currents flow through the second transistor than through the first transistor. Although short-term high currents can occur through the second transistor if it short-circuits a connected charger, this is quickly detected and prevented with an appropriate charger before the second transistor is damaged. However, high currents must flow through the first transistor during a discharging process, even over a longer period of time. This is therefore preferably designed to be more powerful than the second transistor.

• - einen Stromsensor, welcher in dem ersten Strompfad oder in dem zweiten Strompfad angeordnet ist und mit der Steuerlogik gekoppelt ist,
• - einen Spannungssensor, welcher mit der Steuerlogik gekoppelt ist und dazu eingerichtet ist, eine Batteriespannung zumindest einer Batteriezelle der Batterie zu erfassen und/oder
• - einen Temperatursensor, welcher mit der Steuerlogik gekoppelt ist und dazu eingerichtet ist, eine Temperatur der Batterie oder des Batteriemanagementsystems zu erfassen.

More preferably, the battery management system includes a sensor system which includes one or more of the following sensors:

• - a current sensor, which is arranged in the first current path or in the second current path and is coupled to the control logic,
• - a voltage sensor, which is coupled to the control logic and is set up to detect a battery voltage of at least one battery cell of the battery and/or
• - a temperature sensor, which is coupled to the control logic and is set up to record a temperature of the battery or the battery management system.

With such sensor technology, a state of the battery and the battery management system can be recorded particularly precisely by the control logic and different methods can be used to identify which operating state the battery management system should be brought into. In particular, it is possible by means of the sensor system to recognize whether charging and discharging of the battery should be made possible, overcharging of the battery should be prevented, or discharging of the battery should be prevented. The voltage sensor is preferably provided with information from individual battery cells of the battery. A temperature sensor is arranged in particular in the battery management system and/or in the battery and coupled to the control logic.

The control logic is preferably set up to determine, based on measured values from the sensor system, whether charging and discharging of the battery should be enabled, and in response to this, the first transistor and switch the second transistor accordingly. Thus, in response to enabling charging and discharging of the battery, the first transistor is switched to the conductive state and the second transistor to the non-conductive state. Whether charging and discharging of the battery should be made possible can be determined in different ways by the sensors. For example, it can be determined that the battery should be charged when a predetermined charging voltage is present between the first and second charging and discharging contacts. Charging and discharging of the battery can also be made possible if it is detected that there is no excessive discharge current and/or that there is no excessive charging current.

It is also advantageous if the control logic is set up to determine, based on measured values from the sensor system, whether overcharging of the battery should be prevented and, in response, to switch the first transistor and the second transistor accordingly. Thus, in response to preventing overcharging of the battery, the first transistor is switched to the non-conducting state and the second transistor is switched to the conducting state. The fact that overcharging of the battery should be prevented is recognized, for example, by the fact that an existing charging current is too high or a temperature of the battery rises above a certain limit value or a voltage of the battery rises above a certain limit value.

It is also advantageous if the control logic is set up to determine, based on measured values from the sensor system, whether a discharge current of the battery exceeds a predefined limit value and, in response to the fact that the discharge current of the battery exceeds the predefined limit value, not to switch the first transistor into the conductive state and the second transistor to switch to the non-conductive state in order to prevent the battery from discharging. This is particularly dependent on the current state of charge of the battery.

The measured values of the sensor system can be combined and evaluated in a variety of ways in order to identify which switching state is advantageous for the first transistor and the second transistor.

A battery system which has the battery management system according to the invention is also advantageous and has all the advantages of the battery management system according to the invention. The battery system preferably comprises a charger, which is designed to be connected to the first charging and discharging contact and to the second charging and discharging contact in order to charge the battery. This is preferably done using a plug connector. The charger is preferably set up to detect a short circuit between the first and second charging and discharging contacts and to interrupt a charging process in response to the fact that the short circuit exists. The charger can preferably detect an increase in a charging current or a drop in a charging voltage via the charging and discharging contacts and then conclude that the short circuit has occurred. It is thus achieved that a charging process of the battery by the charger can be interrupted by switching the second transistor into the conductive state. More preferably, the battery system includes the battery.

Brief description of the drawings

• 1 eine schematische Darstellung eines erfindungsgemäßen Batteriemanagementsystems mit daran angeschlossener Batterie und angeschlossenem Ladegerät,
• 2 eine schematische Darstellung eines Stromflusses durch das Batteriemanagementsystem in einem ersten Betriebszustand,
• 3 eine Darstellung eines Stromflusses durch das Batteriemanagementsystem in einem zweiten Betriebszustand,
• 4 eine Darstellung eines Stromflusses durch das Batteriemanagementsystem in einem dritten Betriebszustand, und
• 5 eine schematische Darstellung eines Batteriesystems, welches das erfindungsgemäße Batteriemanagementsystem umfasst.

Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawing. In the drawing is:

• 1 a schematic representation of a battery management system according to the invention with a battery and charger connected to it,
• 2 a schematic representation of a current flow through the battery management system in a first operating state,
• 3 a representation of a current flow through the battery management system in a second operating state,
• 4 a representation of a current flow through the battery management system in a third operating state, and
• 5 a schematic representation of a battery system which includes the battery management system according to the invention.

Embodiments of the invention

1 shows a battery management system 1 according to the invention, which is coupled to a battery 4 and a charger 21 or a load 22.

The battery 4 includes a number of battery cells, which are connected in series, for example. The battery 4 has a positive connection contact, which is coupled to a first battery connection 4a of the battery management system 1. The battery 4 also has a negative pole, which is coupled to a second battery connection 4b of the battery management system 1.

The battery management system 1 has a first charging and discharging contact 3 and a second charging and discharging contact 7. The first charging and discharging contact 3 together with the second charging and discharging contact 7 are the contacts of a plug connector, which allows the battery management system 1 to be contacted. The battery management system 1 is, for example, a structural unit together with the battery 4. Together, these form, for example, a battery pack of an electric bicycle. This can either be plugged into the charger 21 or can be inserted into a designated slot on an electric bicycle in order to supply the electric bicycle, which in this case includes the load 21, with power via the charging and discharging contacts 3, 7.

The battery management system 1 has a first current path 2, which connects the first charging and discharging contact 3 to the first battery connection 4a. A first transistor 5, which is a MOSFET transistor, is arranged in the first current path 2. In this case, for example, a drain connection of the first transistor 5 is connected to the first battery connection 4a and a source contact of the first transistor 5 is connected to the first charging and discharging contact 3. This means that a parasitic diode of the first transistor 5, here the body diode of the MOSFET, is arranged with its cathode side on the side of the battery 4 and with its anode side on the side of the first charging and discharging contact 3.

The first transistor 5 is thus arranged in the first current path 2 in order to switch the first current path 2. The switching process can be triggered via a gate contact of the first transistor 5, which is connected to a control logic 10 of the battery management system 1.

The battery management system 1 further has a second current path 6, which is connected on a first side to the second charging and discharging contact 7 and is connected on its second side to the second pole 4b of the battery 4. The second current path 6 thus connects the second charging and discharging contact 7 with the second battery connection 4b. Preferably no transistor for switching the current path is arranged in the second current path 6. The second current path 6 is therefore preferably not switchable.

The battery management system 1 further comprises a third current path 8, which is connected to the first charging and discharging contact 3 on a first side and to the second charging and discharging contact 7 on a second side. The third current path 8 thus contacts the first charging and discharging contact 3. The third current path 8 does not run via the first transistor 5. This is achieved in that the third current path 8 is connected to the first current path 2 on the side of the first transistor 5 facing the first charging and discharging contact 3. The first current path 2 can have a common section with the third current path 8. However, this is optional, since the third current path 8 can also begin directly at the first charging and discharging contact 3, whereby it is connected to the first current path 2 via the common charging and discharging contact 3, but does not have a common section.

In the same way, the second current path 6 can have a common section with the third current path 8, but this is not necessarily the case.

A second transistor 9, which is also a MOSFET, is arranged in the third current path 8. A drain contact of the second transistor 9 is connected to the first charging and discharging contact 3. A source contact of the second transistor 9 is connected to the second charging and discharging contact 7. The third current path 8 can be switched by the second transistor 9. For this purpose, the second transistor 9 has a gate contact which is coupled to the control logic 10. The second transistor 9 is not in the first current path 2 between the first charging and discharging contact 3 and the first battery connection 4a arranged. This means that a charging current provided by the charger 21 at the charging and discharging contacts 3, 7 does not have to flow through the second transistor 9 in order to charge the battery 4.

The battery management system 1 can be operated in three different operating states. The different operating states are controlled by the control logic 10 by switching the transistors 5, 9.

In a first operating state, the battery management system 1 enables charging and discharging of the battery 4. In a second operating state, the battery management system 1 prevents the battery 4 from being overcharged. In a third operating state, the battery management system 1 prevents the battery 4 from discharging.

The first operating state is an operating state that exists when the battery 4 is used as a power source or is being charged via the charger 21. In the first operating state, the first transistor 5 is switched to a conducting state and the second transistor 9 is switched to a non-conducting state. This makes it possible for the battery 4 to provide an output voltage and a load current at the charging and discharging contacts 3, 7 when the load 22 is connected there.

The first operating state is in 2 shown. Since the first transistor 5 is in a conductive state, a conductive path results from the first charging and discharging contact 3 via the first current path 2, via the battery 4 and via the second current path 6 to the second charging and discharging contact 7. Depending on whether a charger 21 or a load 22 is connected to the charging and discharging contacts 3, 7, the battery 4 is charged or discharged. The second transistor 9 is in a non-conducting state. By providing appropriate control signals, the control logic 10 is suitable for switching the first transistor 5 into the conducting state and the second transistor 9 into the non-conducting state, thus enabling the charging and discharging of the battery 4.

The second operating state is in 3 shown. In the second operating state, the first transistor 5 is switched to the non-conducting state by the control logic 10 and the second transistor 9 is also switched to the non-conducting state in order to prevent the battery 4 from discharging. It is 3 It can be seen that a current path starting from the first charging and discharging contact 3 of the battery management system 1 is in any case interrupted by one of the two transistors 5, 9. Unintentional discharging of the battery 4 can thus be prevented.

It is assumed by way of example that the load 22 is connected to the charging and discharging contacts 3, 7 of the battery management system 1. Since the first transistor 5 is in a non-conducting state, no conductive connection is made between the positive pole 4a of the battery 4 and the first charging and discharging contact 3. This means that no energy can be drawn from the battery 4 by the load 22. It should be noted that no current flows through the parasitic diode of the first transistor 5 either, since the first pole of the battery 4, which is connected to the first battery connection 4a, is the positive pole of the battery 4. With the resulting voltage drop across the first current path 2, no current is conducted through the parasitic diode of the first transistor 5. This effectively prevents the battery 4 from discharging.

The third operating state is in 4 shown. In the third operating state, the first transistor 5 is switched to the non-conducting state by the control logic 10 and the second transistor 9 is switched to the conductive state by the control logic 10. This can prevent overcharging of the battery 4. It is assumed below that the charger 21 is connected to the charging and discharging contacts 3, 7 of the battery management system 1. Because the first transistor 5 is in the non-conducting state, no current is conducted from the charger 21 to the battery 4 via the first current path 2. At the same time, the first charging and discharging contact 3 and the second charging and discharging contact 7 are short-circuited via the second transistor 9. Optionally, this is done via an additional resistor.

Due to the short circuit between the two charging and discharging contacts 3, 7, current flows within the battery management system 1 almost exclusively via the second transistor 9. In this case, too, no current is generated, regardless of the orientation of the parasitic diode of the first transistor 5 Battery 4 conducted. This means that no charging current can flow from the charger 21 to the battery 4 and overcharging of the battery 4 can therefore be prevented.

The first transistor 5 is designed to permanently conduct a higher current than the second transistor 9 without suffering damage. This enables a high current from the battery 4 to the load 22, particularly when operating in the first operating state with the load 22 connected. At the same time, the second transistor 9 can efficiently prevent excessive charging current by short-circuiting the charging and discharging contacts 3, 7. With such a short circuit, high currents typically only occur for a very short time, as these are quickly stopped by the charger 21. The high charging current that occurs more frequently in regular operation is not passed through the second transistor 9.

Whether the battery management system 1 is operated in the first operating state, the second operating state or the third operating state is decided by the control logic 10 or alternatively by an external control signal. If the decision is made by the control logic 10, it is advantageous if the battery management system 1 includes a sensor system through which the control logic 10 is provided with decision parameters. For example, the battery management system 1 includes a current sensor 11, which is arranged in the second current path 6 and delivers measurement signals to the control logic 10. Furthermore, the battery management system 1 preferably includes a voltage sensor 12, through which a battery voltage of the battery 4 is detected. A cell voltage of the individual battery cells of the battery 4 is preferred, which can be added up to form a battery voltage, for example. This is therefore advantageous because the control logic 10 typically also takes on other tasks, for example cell balancing. Furthermore, the battery management system 1 preferably includes one or more temperature sensors 13, 13 ', through which, for example, a temperature of the battery management system 1 and a temperature of the battery 4 are detected.

Based on the information provided by the sensors of the control logic 10, a decision can be made as to which operating state should be triggered.

For example, if the current, voltage and/or temperature limit values are exceeded, it can be recognized that the battery 4 is about to be overcharged. If this is recognized by the control logic 10, the third operating state is triggered in order to prevent the battery 4 from being overcharged. This triggers an overload protection.

Furthermore, the control logic 10 can determine, based on the measured values of the sensor system, whether a discharge current flowing through the second current path 6 exceeds a predefined limit value. This is the case, for example, if too high a current is drawn from a connected load 22. If this is the case, the second operating state can be triggered in response to the detection of the discharge current that is too high. Switching the transistors 5, 9 into the open state prevents any further current from being drawn from the battery 4. This prevents the battery 4 from discharging. In the remaining cases, the first operating state can be triggered. This is always the case in particular when the second operating state and the third operating state are not triggered.

5 shows an advantageous battery system 20. This includes the previously described battery management system 1, to which the battery 4 is connected. The charger 21 is part of the battery system 20, which can be connected to the first charging and discharging contact 3 and the second charging and discharging contact 7 of the battery management system 1 via a plug connector with its charging contacts. A charging voltage is provided via the charger 21 in order to charge the battery 4. The charger 21 detects a voltage between its charging contacts and measures a flowing charging current. Based on these values, a short circuit between the charging contacts can be detected. Such a short circuit is always detected when the battery management system 1 is in the third operating state, since in this the charging and discharging contacts 3, 7 of the battery management system 1 are short-circuited via the second transistor 9. In this case, it can be assumed that the battery 4 must be protected from a charging current that is too high. Therefore, charging of the battery 4 is interrupted by the charger 21 in response to the presence of a short circuit.

The battery management system 1 according to the invention uses a common interface or a common contact for charging and discharging the battery 4. However, a separate current path, here the third current path 8, is provided in order to interrupt a charging current. Furthermore, the first current path 2 is provided with the first transistor 5 in order to interrupt discharge currents.

In order to provide overload protection for the battery 4 during a charging process, a current path is created not by interrupting the voltage provided by the charger or the current provided by the charger 21, but by providing a defined current path between the charging and discharging contacts 3, 7 interrupted. Therefore, only one of the transistors 5, 9 is a current-carrying transistor. At the same time, both a charging and a discharging current can be conducted via the same charging and discharging contact 3.

Since a voltage between the charging and discharging contacts 3, 7 of the battery management system 1 will be close to 0 volts when the second transistor 9 is switched to conductive current, which is typically the case when the charging current is too high, the charger 21 is included able to detect this error and stop the charging process. This is typically done via overcurrent or undervoltage detection. In the battery system according to the invention, the second transistor 9 will only be live for a short time.

The following table shows an overview of the different operating states: Operating condition First transistor (5) Second transistor (9) Normal loading/unloading "AT" "OUT OF" High discharge current "OUT OF" "OUT OF" High charging current / overcharging "OUT OF" "AT"

In addition to the above written revelation, explicit reference is made to the revelation of 1 until 5 referred.

Claims (10)

Battery management system (1), comprising: - a first current path (2), which is connected on a first side to a first charging and discharging contact (3) of the battery management system (1), and is intended to be connected on a second side to a first pole (4a) of a battery ( 4) to be connected, - a first transistor (5), which is arranged in the first current path (2) in order to switch the first current path (2), - a second current path (6), which is connected on a first side to a second charging and discharging contact (7) of the battery management system (1), and is intended to be connected on a second side to a second pole (4b) of the battery ( 4) to be connected, - a third current path (8), which is connected on a first side to the first charging and discharging contact (3) and on a second side to the second charging and discharging contact (7), the third current path (8) being on the the side of the first transistor (5) facing the first charging and discharging contact (3) is connected to the first current path (2), - a second transistor (9), which is arranged in the third current path (8) to switch the third current path (8), and - a control logic (10) which is set up to: - switching the first transistor (5) into a conducting state and the second transistor (9) into a non-conducting state in order to enable charging and discharging of the battery (4), and - to switch the first transistor (5) into a non-conducting state and the second transistor (9) into a conducting state in order to prevent the battery (4) from being overcharged. Battery management system (1) according to Claim 1 , wherein the control logic (10) is further set up to: - switch the first transistor (5) into a non-conducting state and the second transistor (9) into a non-conducting state in order to prevent the battery (4) from discharging. Battery management system (1) according to one of the preceding claims, wherein the first transistor (5) is arranged in the first current path (2) such that a cathode of a parasitic diode of the first transistor (5) is arranged on the side of the battery (4). and an anode of the parasitic diode of the first transistor (5) is arranged on the side of the first charging and discharging contact (3). Battery management system according to one of the preceding claims, wherein the first transistor (5) and/or the second transistor (9) is a field effect transistor. Battery management system according to one of the preceding claims, wherein the first transistor (5) is designed to conduct higher currents in a conductive state than the second transistor (9). Battery management system according to one of the preceding claims, further comprising a sensor system which includes one or more of the following sensors: - a current sensor (11), which is arranged in the first current path or the second current path and is coupled to the control logic (10), - a voltage sensor (12), which is coupled to the control logic (10) and is set up to detect a battery voltage of at least one battery cell of the battery, and / or - A temperature sensor (13), which is coupled to the control logic (10) and is set up to detect a temperature of the battery or the battery management system. Battery management system according to Claim 6 , wherein the control logic (10) is set up to determine, based on measured values from the sensor system, whether charging and discharging of the battery (4) should be enabled, and in response to this to switch the first transistor and the second transistor accordingly. Battery management system according to one of the Claims 6 and 7 , wherein the control logic (10) is set up to determine, based on measured values from the sensor system, whether overcharging of the battery (4) should be prevented, and in response to this to switch the first transistor and the second transistor accordingly. Battery management system according to one of the Claims 6 until 7 , wherein the control logic (10) is set up to: - determine based on measured values from the sensor system whether a discharge current of the battery (4) exceeds a predefined limit value, and - in response to the fact that the discharge current of the battery (4) exceeds the predefined limit value exceeds to switch the first transistor (5) to the non-conducting state and the second transistor (9) to the non-conducting state in order to prevent the battery (4) from discharging. Battery system (20), comprising a battery management system according to one of the preceding claims, further comprising: - a charger (21), which is designed to be connected to the first charging and discharging contact (3) and to the second charging and discharging contact (7) in order to charge the battery (4), the charger ( 21) is designed to detect a short circuit between the first and second charging and discharging contacts (3, 7) and to interrupt a charging process in response to the fact that the short circuit exists.

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