DE102019216007A1 - Battery system for a motor vehicle, method for operating a battery system and motor vehicle - Google Patents

Abstract

The invention relates to a battery system (10) for a motor vehicle, comprising a negative pole (21), a positive pole (22), a battery module (5) for storing electrical energy, and a control unit (30) which is electrically connected in series with the Battery module (5) is connected so that the control unit (30) can flow through a charging current for charging the battery module (5). The control unit (30) is set up to time-limit the charging current flowing through the control unit (30) to the duration of a predetermined charging interval. The invention also relates to a method for operating a battery system (10) according to the invention, the control unit (30) being controlled in such a way that the charging current flowing through the control unit (30) is limited in time to the duration of a predetermined charging interval. The invention also relates to a motor vehicle which comprises at least one battery system (10) according to the invention, which is operated with the method according to the invention.

Description

The invention relates to a battery system for a motor vehicle, which has a negative pole, a positive pole, a battery module for storing electrical energy and a control unit which is connected electrically in series with the battery module so that a charging current for charging the battery module can flow through the control unit is, includes. The invention also relates to a method for operating a battery system according to the invention. The invention also relates to a motor vehicle which comprises at least one battery system according to the invention that is operated according to the method according to the invention.

State of the art

Conventional motor vehicles have a drive which usually comprises an internal combustion engine. Furthermore, conventional motor vehicles include a battery system for supplying a starter and other consumers of the motor vehicle with electrical energy and a generator for charging the battery system. A generic battery system comprises a battery module with at least one, preferably with a plurality of battery cells, which are connected in series, for example, so that the battery module has a nominal voltage of 12 V, for example. Said battery cells are, for example, lithium-ion battery cells.

A generic battery system also comprises a switching device by means of which the battery module can be switched on, that is to say connected to an on-board network of the motor vehicle, and switched off, that is to say separated from the on-board network. When the battery module is switched on, the said nominal voltage supplied by the battery cells is applied between a positive pole and a negative pole of the battery system.

Due to the chemical properties of lithium ion battery cells, such a battery system must not be charged under certain environmental conditions, such as low temperatures. Otherwise the battery cells could be damaged by lithium plating. When using such a battery system in a vehicle electrical system that is not specifically designed for the use of lithium ion battery cells, the battery must then be disconnected from the electrical system in order to avoid charging the battery system by the generator.

Due to the slow control times of the generator in the vehicle electrical system, rapid load changes in the absence of buffering by a battery system lead to high transient overvoltages. These overvoltages, which are also referred to as load dumps, can lead to malfunctions and even damage to other components in the vehicle electrical system. A load dump is, for example, a voltage of 32 V that is applied for a duration of 300 ms.

From the document DE 10 2013 204 527 A1 a battery cell device with a lithium-ion battery cell is known. The battery cell device has a monitoring device for monitoring the battery cell, which comprises a sensor device and a state determination device. A lithium deposition safety function is provided by means of which a critical battery cell state in which the battery cell can be damaged by lithium deposition on the battery cell electrode can be determined, and the battery cell in a lithium deposition operating mode designed as a safe operating mode, in which the battery cell has no voltage at the output terminals Battery cell device releases, can be transferred.

The document US 2014/0260233 A1 discloses an actuator system for suspension of a vehicle. In this case, an electrical energy store is provided which is designed as a lithium-ion battery, for example. The energy store is provided to absorb regenerative electrical energy that is generated during operation of the actuator system. This allows voltage spikes to be isolated from the vehicle's electrical system.

Disclosure of the invention

A battery system for a motor vehicle is proposed. The battery system comprises a negative pole and a positive pole and a battery module for storing electrical energy. The battery module has, for example, several lithium-ion battery cells which are connected in series. The battery module supplies a nominal voltage of, for example, 12 V.

The battery system further comprises a control unit, which is connected electrically in series with the battery module. A charging current for charging the battery module can thus flow through the control unit. When a charging current flows through the control unit, electrical energy is drawn from an on-board network of the motor vehicle. As a result, an overvoltage in the vehicle electrical system can be reduced in a targeted manner.

According to the invention, the control unit is set up to set the value of the charging current flowing through the control unit and to limit it in time to the duration of a predetermined charging interval. Preferably the duration is Charging interval less than or equal to 1 s.The duration of the charging interval is particularly preferably less than or equal to 500 ms.

Surprisingly, it was found that lithium plating can be avoided if the lithium ion battery cells of the battery system are only charged for the duration of relatively short charging intervals, that is, if the charging current is limited in time to the duration of a correspondingly short charging interval.

The control unit of the battery system can be controlled, for example, by a management system. The control unit is preferably activated accordingly only when a temperature of the lithium ion battery cells falls below a predetermined minimum temperature. At a higher temperature, the charging current can flow continuously; there is no need to limit the charging current over time.

Preferably, only the charging current for charging the battery module is limited in time. A discharge current for discharging the battery module and for supplying electrical consumers in the motor vehicle is not limited in time.

According to an advantageous development of the invention, the control unit comprises a series resistor. The series resistor is connected electrically in series with the battery module. The charging current for charging the battery module can thus flow through the series resistor. Electrical energy is converted into heat in the series resistor. Furthermore, the charging current is limited by the series resistor. By quickly switching the charging current on and off through the load resistor, an overvoltage in the on-board network can be reduced in a targeted manner by varying the ratio of switch-on and switch-off times.

According to an advantageous embodiment of the invention, the control unit comprises a buck converter. A step-down converter, which is also referred to as a “buck converter”, allows a desired charging current to be set with a relatively low power loss. By precisely setting the charging current, overvoltage in the vehicle electrical system can be reduced in a targeted manner.

According to a further advantageous embodiment of the invention, the control unit comprises a control switch. The control switch is designed as a field effect transistor, in particular as a MOSFET. The control switch can be opened in the linear range until the desired current / voltage value is reached. The linear control can be implemented, for example, with an active clamping circuit. For this purpose, the control unit also includes a control diode which is electrically connected to a GATE connection and a DRAIN connection of the control switch. The control diode is preferably a Zener diode.

According to a further advantageous embodiment of the invention, the control unit comprises a switching transistor and a series resistor. The switching transistor is designed as a field effect transistor, in particular as a MOSFET. The switching transistor can be permanently switched on or off. When the switch is switched on, a current flows from the positive pole of the battery system via the switching transistor and the series resistor to the positive terminal of the battery module, bypassing the switching unit. By quickly switching the switching transistor on and off, an overvoltage in the vehicle electrical system can be reduced in a targeted manner by varying the ratio of the switch-on and switch-off times.

According to an advantageous development of the invention, the battery system further comprises a chopper unit. The chopper unit has a chopper switch and a chopper resistor. The chopper unit is arranged electrically between the negative pole and the positive pole of the battery system in such a way that when the chopper switch is closed, a chopper current flows through the chopper resistor, bypassing the battery module. In the chopper resistor, electrical energy is converted into heat. By quickly switching the current on and off through the chopper resistor, an overvoltage in the on-board network can be reduced in a targeted manner by varying the ratio of switch-on and switch-off times.

The chopper switch is preferably designed as a field effect transistor, in particular as a MOSFET. The chopper unit preferably comprises a hysteresis controller which is electrically connected to the GATE connection, the DRAIN connection and the SOURCE connection of the chopper switch. In the event of an overvoltage in the vehicle electrical system, the hysteresis controller causes the chopper switch to operate in a clocked manner, which is then switched on and off relatively quickly until a desired mean value of the vehicle electrical system voltage is reached.

According to a preferred embodiment of the invention, the battery system further comprises a switching unit, which is connected electrically in series with the battery module and electrically in parallel with the control unit. By means of the switching unit, the battery module can be electrically connected to the two poles and also be electrically isolated from at least one of the poles. The switching unit is advantageously designed in such a way that a current for charging the battery module and a current for discharging of the battery module can be enabled or prevented independently of one another.

A method for operating a battery system according to the invention is also proposed. The control unit is controlled in such a way that the charging current flowing through the control unit is limited in time to the duration of a predetermined charging interval. The duration of the charging interval is preferably less than or equal to 1 s.Specifically, the duration of the charging interval is less than or equal to 500 ms. As a result, an overvoltage in the vehicle electrical system can be reduced in a targeted manner and lithium plating in the lithium-ion battery cells can be avoided.

Preferably, only the charging current for charging the battery module is limited in time. A discharge current for discharging the battery module and for supplying electrical consumers in the motor vehicle is not limited in time.

According to a preferred embodiment of the invention, the control unit is controlled in such a way that, immediately after the charging interval, a charging current flowing through the control unit is prevented for the duration of a predetermined rest interval. The rest interval is larger than the loading interval. The duration of the rest interval is preferably greater than or equal to 30 s, and the duration of the rest interval is particularly preferably greater than or equal to 60 s.

According to an advantageous development of the invention, the battery system comprises a chopper unit which has a chopper switch and a chopper resistor. The chopper switch is controlled in such a way that a chopper current flows through the chopper resistor, bypassing the battery module. In the chopper resistor, electrical energy is converted into heat, and an overvoltage in the on-board network is further reduced.

The chopper switch is preferably activated in a clocked manner. In clocked operation, the chopper switch is switched on and off relatively quickly, and a desired mean value of the on-board network voltage is established in the event of an overvoltage in the vehicle electrical system.

The chopper switch is particularly preferably controlled by a hysteresis controller. In the event of an overvoltage in the vehicle electrical system, the hysteresis controller causes the chopper switch to operate in a clocked manner, which is then switched on and off relatively quickly until a desired mean value of the vehicle electrical system voltage is reached.

The charging current is preferably set in such a way that an on-board electrical system voltage present between the positive pole and the negative pole is kept below a predetermined maximum value and / or is reduced to a setpoint value.

A motor vehicle is also proposed. The motor vehicle according to the invention comprises at least one battery system according to the invention which is operated with the method according to the invention.

Advantages of the invention

The battery system according to the invention allows electrical power generated by the generator to be quickly dissipated, as a result of which transient overvoltages in the vehicle electrical system are reduced. As already mentioned, it was found that lithium plating can be avoided if the lithium ion battery cells are only charged for the duration of relatively short charging intervals, which are less than 1 s, preferably less than 500 ms. Lithium plating can be avoided even more safely if the duration of a rest interval between two charging intervals is significantly longer. Active control is used with the control unit, which stabilizes the voltage of the vehicle electrical system without an energy store being permanently connected to the vehicle electrical system. In operating states in which the battery system may not be charged, the battery system nevertheless remains as a stabilizing element in the vehicle electrical system, but is only supplied with the minimum current required. The use of a separate chopper unit with a chopper resistor allows additional dissipation of electrical power that is generated by the generator. An overvoltage in the vehicle electrical system can thus be effectively limited to a maximum value by means of the electronic control unit without charging the battery system. The control unit only draws enough power from the vehicle electrical system to limit the electrical system voltage to a permissible value. Damage to the lithium ion battery cells by lithium plating is thus advantageously prevented, and dangerous overvoltages in the vehicle electrical system are advantageously avoided.

Figure list

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

• 1 eine schematische Darstellung eines Batteriesystems an einem Bordnetz eines Kraftfahrzeugs,
• 2 eine schematische Darstellung einer Regeleinheit gemäß einer ersten Ausführungsform,
• 3 eine schematische Darstellung einer Regeleinheit gemäß einer zweiten Ausführungsform,
• 4 eine schematische Darstellung einer Regeleinheit gemäß einer dritten Ausführungsform und
• 5 eine schematische Darstellung einer Choppereinheit.

Show it:

• 1 a schematic representation of a battery system on an on-board network of a motor vehicle,
• 2 a schematic representation of a control unit according to a first embodiment,
• 3 a schematic representation of a control unit according to a second embodiment,
• 4th a schematic representation of a control unit according to a third embodiment and
• 5 a schematic representation of a chopper unit.

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

1 shows a schematic representation of a battery system 10 on an on-board network of a motor vehicle. The battery system 10 includes a negative pole 21 and a positive pole 22nd . By means of the poles 21 , 22nd is the battery system 10 electrically connected to the electrical system of the motor vehicle.

The battery system 10 includes a battery module 5 for storing electrical energy. The battery module 5 comprises several lithium ion battery cells that are connected to one another in series and in parallel. The battery module 5 is electrical between a positive terminal 12th and a negative terminal 11 arranged and supplies a module voltage VM of, for example, 12 V. The battery module 5 also has an internal battery resistance RIB.

The negative terminal 11 is with the negative pole 21 electrically connected. The negative terminal 11 and the negative pole 21 are electrically connected to a ground of the vehicle electrical system.

The battery system 10 has a switching unit 60 on that electrically between the positive terminal 12th and the positive pole 22nd is switched. The switching unit 60 includes a charging transistor 61 and a discharge transistor 62 . The two transistors 61 , 62 are electrically connected in antiseries. The two transistors 61 , 62 can be controlled by a management system not shown here.

The charging transistor 61 designed as a MOSFET and has a body diode or inverse diode, not shown here. The charging transistor 61 is arranged such that the body diode is conductive for a discharge current and blocks a charging current. When the charging transistor 61 is activated by appropriate control, so is the charging transistor 61 conductive for a charging current and for a discharging current.

The discharge transistor 62 is designed as a MOSFET and has a body diode or inverse diode (not shown here). The discharge transistor 62 is arranged such that the body diode is conductive for a charging current and blocks a discharge current. When the discharge transistor 62 is activated by appropriate control, so is the discharge transistor 62 conductive for a charging current and for a discharging current.

The switching unit 60 also includes a first clamp diode 63 and a second clamp diode 64 . The two clamping diodes 63 , 64 are electrically antiserial and parallel to the transistors 61 , 62 switched. The clamping diodes 63 , 64 are designed as Zener diodes.

The battery system 10 also includes a control unit 30th which are electrical between the positive terminal 12th and the positive pole 22nd is switched. The control unit 30th is thus electrically parallel to the switching unit 60 and in series with the battery module 5 switched.

The control unit 30th can therefore use a charging current to charge the battery module 5 are flowed through. The control unit 30th is set up in particular by the control unit 30th to limit the charging current flowing in time to the duration of a given charging interval.

The battery system 10 also includes a chopper unit 50 . The chopper unit 50 is electrical between the negative pole 21 and the positive pole 22nd arranged. Through the chopper unit 50 can generate a chopper current bypassing the battery module 5 from the positive pole 22nd to the negative pole 21 through the battery system 10 flow.

The electrical system of the motor vehicle includes a generator G for charging the battery module 5 of the battery system 10 and for supplying other consumers of the motor vehicle with electrical energy. The generator G supplies a generator voltage VG and has an internal generator resistance RIG. The generator G also has a generator inductance LG. The generator G also has a generator rectifier DG which, for example, comprises several diodes. A generator current IG flows through the generator G.

The on-board network of the motor vehicle includes further consumers, which are shown here by way of example in the form of a load capacitor CL and a load resistor RL. Said consumers can be switched on and off by means of a load switch SL. There is also a line inductance LL, which is formed in particular by electrical lines in the motor vehicle. A load current IL flows through the consumers of the motor vehicle.

The battery system 10 furthermore optionally comprises a backup capacitor CS. The back-up capacitor CS is with the positive pole 22nd and the negative pole 21 of the battery system 10 electrically connected. A vehicle electrical system voltage VB is applied to the backup capacitor CS. The said vehicle electrical system voltage VB is thus also between the positive pole 22nd and the negative pole 21 of the battery system 10 at.

2 shows a schematic representation of a control unit 30th according to a first embodiment. The control unit 30th according to the first embodiment comprises a buck converter. The buck converter has a blocking diode 31 , a freewheeling diode 32 , an input capacitor 33 , a switching transistor 34 and a storage inductor 35 on. The storage inductance 35 has a DC resistance 36 , which here in a series circuit with the storage inductance 35 is shown.

The switching transistor 34 is designed as a field effect transistor, in particular as a MOSFET. The switching transistor 34 can be controlled by a management system not shown here. The buck converter causes that from the positive pole 22nd an adjustable current to the positive terminal 12th can flow if between the positive terminal 12th and the ground of the vehicle electrical system has a lower voltage than between the positive pole 22nd and the crowd.

3 shows a schematic representation of a control unit 30th according to a second embodiment. The control unit 30th according to the second embodiment comprises a switching transistor 44 , which is designed as a field effect transistor, in particular as a MOSFET. The control unit 30th according to the second embodiment further comprises an input capacitor 33 and a series resistor 40 . The series resistor 40 is switched in such a way that a charging current for charging the battery module 5 which from the positive pole 22nd through the control unit 30th to the positive terminal 12th flows, also through the series resistor 40 flows. The input capacitor 33 is connected in such a way that it is connected to the positive pole 22nd and the negative pole 21 of the battery system 10 connected is. A GATE connection of the switching transistor 44 is with a control unit 45 connected.

4th shows a schematic representation of a control unit 30th according to a third embodiment. The control unit 30th according to the third embodiment comprises a control switch 41 , which is designed as a field effect transistor, in particular as a MOSFET. The control unit 30th according to the third embodiment further comprises a control diode 42 and an input resistor 43 .

One DRAIN connection of the control switch 41 is with the positive pole 22nd electrically connected. The input resistance 43 the control unit 30th is connected to a GATE connection of the control switch 41 electrically connected. The control switch 41 is about the said input resistance 43 controllable by a management system not shown here.

The control diode 42 is designed as a zener diode. The control diode 42 is with the DRAIN connection and the GATE connection of the control switch 41 electrically connected. On the control diode 42 a control voltage UR drops, which is also between the DRAIN connection and the GATE connection of the control switch 41 is applied. The control voltage UR is, for example, 2.5 V. Between the GATE connection and a SOURCE connection of the control switch 41 a GATE SOURCE voltage UGS drops. The GATE SOURCE voltage UGS is, for example, 2.5 V.

The control unit 30th according to the third embodiment further comprises a series resistor 40 . The series resistor 40 is with the SOURCE connector of the control switch 41 and with the positive terminal 12th electrically connected. The series resistor 40 is thus switched in such a way that a charging current for charging the battery module 5 which from the positive pole 22nd through the control unit 30th to the positive terminal 12th flows, also through the series resistor 40 flows.

5 shows a schematic representation of a chopper unit 50 . The chopper unit 50 has a chopper switch 51 and a chopper resistor 52 on. The chopper switch 51 is designed as a field effect transistor, in particular as a MOSFET.

The DRAIN connection of the chopper switch 51 is with the positive pole 22nd electrically connected. The chopper resistance 52 is with the SOURCE connection of the chopper switch 51 and with the negative pole 21 electrically connected.

The chopper unit 50 is thus connected in such a way that when the chopper switch is closed 51 a chopper current from the positive pole 22nd through the chopper resistance 52 to the negative pole 21 , and thus to the mass of the electrical system, flows. In particular, the chopper current does not flow through the battery module 5 .

The chopper unit 50 also includes a hysteresis regulator 55 . The hysteresis regulator 55 is with the GATE connection, the DRAIN connection and the SOU RCE connection of the chopper switch 51 as well as with the negative pole 21 and the negative terminal 11 electrically connected. On the hysteresis regulator 55 , and thus between the DRAIN connection of the chopper switch 51 and the negative pole 21 the vehicle electrical system voltage VB is present.

If the vehicle electrical system voltage VB exceeds a maximum value of 16 V, for example, the hysteresis controller closes 55 the chopper switch 51 . The chopper current then flows through the chopper switch 51 and the chopper resistance 52 . If the vehicle electrical system voltage VB falls below a minimum value of 14 V, for example, the hysteresis regulator opens 55 the chopper switch 51 . The chopper current is then cut off.

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 action.

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

• DE 102013204527 A1 [0006]
• US 2014/0260233 A1 [0007]

Claims (14)

Battery system (10) for a motor vehicle, comprising a negative pole (21), a positive pole (22), a battery module (5) for storing electrical energy, and a control unit (30) which is electrically connected in series with the battery module (5) is switched so that a charging current for charging the battery module (5) can flow through the control unit (30), characterized in that the control unit (30) is set up to time the charging current flowing through the control unit (30) for the duration of a to limit the specified charging interval. Battery system (10) Claim 1 , characterized in that the control unit (30) comprises a series resistor (40) which is connected in series to the battery module (5), so that the series resistor (40) can be flowed through by the charging current for charging the battery module (5). Battery system (10) according to one of the preceding claims, characterized in that the control unit (30) comprises a buck converter. Battery system (10) according to one of the Claims 1 to 2 , characterized in that the control unit (30) comprises a control switch (41) which is designed as a field effect transistor, and that the control unit (30) comprises a control diode (42) which is connected to a GATE connection and a DRAIN connection of the control switch (41) is electrically connected. The battery system (10) according to any one of the preceding claims, further comprising a chopper unit (50) which has a chopper switch (51) and a chopper resistor (52), and which is electrically connected in this way between the negative pole (21) and the positive pole (22) is arranged that when the chopper switch (51) is closed, a chopper current flows through the chopper resistor (52) bypassing the battery module (5). Battery system (10) Claim 5 , characterized in that the chopper switch (51) is designed as a field effect transistor, and that the chopper unit (50) comprises a hysteresis controller (55) which is electrically connected to a GATE connection and a DRAIN connection of the chopper switch (51). Battery system (10) according to one of the preceding claims, further comprising a switching unit (60) which is connected electrically in series with the battery module (5) and electrically in parallel with the control unit (30). Method for operating a battery system (10) according to one of the preceding claims, wherein the control unit (30) is controlled in such a way that the charging current flowing through the control unit (30) is limited in time to the duration of a predetermined charging interval. Procedure according to Claim 8 , the control unit (30) being controlled in such a way that immediately after the charging interval, a charging current flowing through the control unit (30) is prevented for the duration of a predetermined idle interval, the idle interval being greater than the charging interval. Method according to one of the Claims 8 to 9 , wherein the battery system (10) comprises a chopper unit (50) which has a chopper switch (51) and a chopper resistor (52), and wherein the chopper switch (51) is controlled in such a way that a chopper current by bypassing the battery module (5) the chopper resistor (52) flows. Procedure according to Claim 10 , the chopper switch (51) being controlled in a clocked manner. Method according to one of the Claims 10 to 11 , the chopper switch (51) being controlled by a hysteresis controller (55). Method according to one of the Claims 8 to 12th , the charging current being set in such a way that an on-board electrical system voltage (VB) applied between the positive pole (22) and the negative pole (21) is kept below a predetermined maximum value and / or is reduced to a setpoint value. Motor vehicle, comprising at least one battery system (10) according to one of the Claims 1 to 7th , which with a method according to one of the Claims 8 to 12th is operated.

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