DE102013007704B4 - Battery protection by means of an active current sensor - Google Patents

Abstract

Battery protection for a battery (2) of a vehicle, comprising: a controller (7) which is designed to detect a state of charge of the battery (2), characterized by an active current sensor (1) for measuring a current (IMess) of the battery ( 2), wherein the active current sensor (1) has a first resistance element (4a) and a second resistance element (4b), at which a voltage for measuring the current (IMess) of the battery (2) flowing through the resistance element (4a) is detected andwhich can be blocked, wherein the first resistive element (4a) and the second resistive element (4b) are connected in parallel to one another and the current (IMess) of the battery (2) when the battery (2) is discharged through the first resistive element (4a) and when Charging the battery (2) flows through the second resistance element (4b), the controller (7) being designed to block the first resistance element (4a) when the state of charge of the battery (2) falls below a deep discharge threshold value, so that a discharge current ( Discharge) of the battery (2) is blocked by the first resistance element (4a), and wherein the controller (7) is designed to block the second resistance element (4b) when the state of charge of the battery (2) exceeds an overcharging threshold value, so that a charging current (Icharge) of the battery (2) is blocked by the second resistance element (4b).

Description

The invention relates to battery protection for a battery in a vehicle and the use of such a battery protection in a battery data module for a battery in a motor vehicle.

In motor vehicles, it is customary to use a battery to supply an on-board electrical system or, in the form of traction batteries, to supply power to an electrical drive. In addition, it is known in the vehicle sector to use batteries in high-voltage vehicle electrical systems with voltages above 14 volts and in low-voltage vehicle electrical systems with voltages below 14 volts. With such low-voltage vehicle electrical system and high-voltage vehicle electrical system batteries or traction batteries, a deep discharge is possible when they are used in vehicles due to possible operating errors. A deep discharge results in significant damage to the battery, combined with a severe functional impairment, which can even lead to inoperability after the battery has been recharged.

Deep discharge protection was already considered in the past, but due to the comparatively low cost of the lead-acid batteries previously used in vehicles, it was hardly ever used or was even discarded.

From the document WO 2011/151124 A1 a power supply is known that includes a controller and a power section. A DC output voltage is applied to a first output of the power unit, to which a load with variable power consumption can be connected. A second output of the power unit is routed via a current measuring device, which can be in the form of a shunt resistor, with a battery being connected to this second output via a battery line. In addition, a charging current or discharging current of the accumulator measured by means of an ammeter device is set by controlling the output DC voltage. As a result, the charging current or discharging current of the accumulator can also be determined without its own uninterruptible power supply. The load is switched to the accumulator by means of a power MOSFET switch. To protect against deep discharge, the accumulator itself can be switched off by means of a further switch, which is arranged in the accumulator line.

From the European patent EP 2 022 155 B1 a protection circuit against overcharging and overdischarging for a secondary lithium-ion battery is known. The circuit has overcharge and overdischarge detection circuitry and a control field effect transistor that turns off when overcharge is detected. In addition, the circuit has a deep discharge control field effect transistor that is turned off when a deep discharge is detected. The two field effect transistors are controlled by a corresponding circuit.

From the German patent specification DE 101 46 556 B4 a battery protection system is known which can disconnect a load from a vehicle battery by appropriately driving a field effect transistor.

The German Offenlegungsschrift DE 10 2011 078 548 A1 discloses a current sensor, comprising at least one resistance element, at which a voltage for measuring the current flowing through the resistance element is detected, the resistance element being designed in such a way that at least within a defined measuring range of the current sensor, the electrical resistance of the resistance element decreases when the current flows through the resistance element increases.

The German translation DE 60 2004 001 216 T2 discloses a power management system with a power generator that provides a supply signal to a load for a floating controllable bidirectional current sensor that is connected to the power generator via a first connection and to the load via a second connection to generate a positive current generated by the Power generator flows to the load, and to detect a negative current from the load to the power generator.

The European patent specification EP 0 972 327 B1 discloses a battery protection system having a first terminal, a second terminal, a first battery electrode and a second battery electrode, including: a first switch having a control electrode, a first current conductor electrode coupled to the first terminal of the battery protection system, and a second current conductor electrode, an inductor having a first electrode connected to the second current conductor electrode of the first switch and a second electrode coupled to the first battery electrode of the battery protection system, a resistor whose first electrode is coupled to the second battery electrode of the battery protection system and whose second electrode is connected to the second terminal of the battery protection system, a rectifier whose first electrode is connected to the second electrode of the resistor and whose second electrode is coupled to the first electrode of the inductor, a first comparator whose first input is connected to the first electrode of the resistor is coupled, and its second input with the second electrode of the resistor and the output of which is coupled to the control electrode of the first switch, and a battery monitor circuit including a plurality of inputs and a first output, a first input of the plurality of inputs being connected to the second electrode of the inductor a second input of the plurality of inputs is coupled to the first electrode of the resistor, and the first output is coupled to the control electrode of the first switch.

A disadvantage of the above prior art solutions is that they are complicated and consequently also expensive.

In the future, an increasing use of on-board batteries based on lithium-ion is to be expected, especially in the low-voltage range. This is particularly to be expected against the background of an EU directive to be implemented, according to which the use of lead is also restricted in batteries and accumulators. A deep discharge protection of lithium-ion batteries is therefore desirable. One could think of implementing deep discharge protection using an electronic switch or electromechanical contactor. However, due to the high demands on the current carrying capacity of the electronic switch or electromechanical contactor, this would lead to high costs, since a starting current of around 1000 A and an on-board power supply current of up to 200 A when driving would have to be tolerated.

A control device for battery status detection, which is also called a battery data module (“BDM”), is known for monitoring the battery status. In connection with lead-acid batteries, it is known that the battery data module is used to determine parameters such as the state of charge, the state of health, the internal battery resistance or the electrolyte temperature, taking into account the measured battery voltage and battery terminal temperature as well as the battery current. It is known that the current is measured by a passive measurement shunt. The passive measuring shunt is typically made of a metallic material with a characteristic that allows both the quiescent current in the order of mA and the starting current in the range of approx. 1000 A to be recorded with the required accuracy.

The object of the present invention is to provide improved battery protection for a battery in a vehicle, which at least partially overcomes the disadvantages mentioned above.

This object is achieved by the battery protection according to the invention for a battery of a vehicle according to claim 1 and its use in a battery data module according to claim 10.

Further advantageous refinements of the invention result from the dependent claims and the following description of preferred exemplary embodiments of the present invention.

A battery protection according to the invention for a battery of a vehicle includes a controller that is designed to detect a state of charge of the battery, as is known to those skilled in the art. The battery can be a backup battery, vehicle electrical system battery, traction battery or any other battery that is used in vehicles and can be subject to deep discharge and/or overcharging. The vehicle is in particular a motor vehicle, but can also be another land vehicle or watercraft or aircraft.

In addition, the battery protection includes an active current sensor, also known as an active measurement shunt, which is designed to measure a current in the battery and which, for example, DE 10 2011 078 548 A1 is known in its basic functionality. The active current sensor of the present invention has a resistance element at which a voltage for measuring the current of the battery flowing through the resistance element is detected. The controller can use this voltage, for example, to determine the state of charge of the battery. The controller can determine the state of charge, for example, by measuring or recognizing the battery charging and/or battery discharging current. The active current sensor can be connected directly to the positive or negative pole without there being a load between the battery terminal and the active current sensor.

The resistance element of the active current sensor or the active current sensor is designed in such a way that it can be blocked in one current direction. In addition, the resistance element or the active current sensor is designed such that the electrical resistance of the resistance element decreases at least in a defined measuring range of the active current sensor when the battery current flowing through the resistance element increases. Therefore, the current sensor is also "active" because, in contrast to the passive current sensor, it actively adapts its electrical resistance to the current flowing through it. As a result, with such an active current sensor, a high dynamic range of the current to be measured can be achieved, as is also the case in particular when measuring quiescent and operating currents and/or when measuring the battery power from lithium-ion batteries is required.

As mentioned, the resistive element is designed in such a way that it can be blocked so that practically no current flows through it. As a result, the active current sensor is also designed as a switch at the same time. The resistance element is blocked, for example, by applying a blocking voltage, as is known for transistors.

The control of the battery protection is designed to block the resistance element when the state of charge of the battery falls below a deep discharge threshold value or exceeds an overcharging threshold value, so that a discharge current or charging current of the battery is blocked by the resistance element. The deep discharge threshold or overcharge threshold can be permanently stored in the controller, e.g. in a read-only memory, and/or it can be adjustable. By blocking the resistive element, the loads located downstream of the battery protector, viewed from the battery, are disconnected from the battery and consequently from the discharge current. Accordingly, these loads can no longer generate discharge current in the battery and further discharge of the battery due to these loads is prevented or no further charging current flows and the battery is protected from overcharging. The charging current can be generated by an on-board generator, e.g. in conventional vehicles, or by a DC/DC converter, as used in hybrid or electric vehicles. The controller can be in the form of an integrated circuit, for example a microcontroller or the like.

The battery protection can also be configured as deep discharge protection and overcharge protection at the same time. In such exemplary embodiments, the battery protection can have, for example, two resistance elements, one of which carries the charging current and the other the discharging current and is correspondingly blocked by the controller (see also below). It is also possible for there to be only one resistance element, through which the charging current or discharging current optionally flows by controlling a corresponding switching element or switching circuit, and which is correspondingly blocked when an imminent deep discharge or overcharging is detected.

The active current sensor thus fulfills two functions. On the one hand, it provides a voltage that can be used to determine the current flowing from the battery and, on the other hand, it has a switching function that blocks a discharge current (or charge current) and can thus prevent further discharge (or charge) of the battery. In this way, a cost-effective and compact battery protection can be implemented.

In some exemplary embodiments, the current sensor is designed such that the percentage resolution of the current measurement in relation to the current value of the current or the current measurement current through the resistance element remains essentially constant at least over the defined measurement range of the current sensor.

The resistance element can be a transistor, in particular a field effect transistor. The transistor or field effect transistor is blocked, for example, by applying a corresponding gate voltage.

The voltage for measuring the current flowing through the resistance element can be detected as a gate-source voltage or a base-emitter voltage at the transistor element.

In some exemplary embodiments, the active current sensor has two MOS field effect transistors which are connected in parallel and are of complementary design.

In general, the resistance element can be formed by two resistance elements connected in parallel, current from the battery flowing through one resistance element in one current direction and current flowing through the other resistance element in a different current direction. As a result, for example, a discharge current flows through one resistance element and a charging current flows through the other resistance element. The discharging current or the charging current can consequently be blocked by blocking the respective resistance element.

The active current sensor for measuring the current of the battery can, for example, have two parallel-connected field effect transistors (e.g. MOSFET), with the source connection of one field effect transistor being connected to the drain connection of the other field effect transistor, with a discharge current of the battery passing through the first field effect transistor of the two field effect transistors flows. A battery charging current flows through the second field effect transistor of the two field effect transistors. Correspondingly, the controller can also be designed to block the second field effect transistor of the two field effect transistors when the state of charge of the battery exceeds an overcharging threshold value. The overcharge threshold may be permanently stored in the controller, e.g., in a read-only memory, and/or it may be adjustable.

In some exemplary embodiments, the active current sensor has at least one first control loop, in which the resistance element is arranged and with which the voltage across the resistance element is regulated to a defined reference voltage value. If two resistance elements are present, two such control circuits can be implemented, so that for each direction of current the voltage across the resistance element through which the current flows is regulated to a defined reference voltage value. The reference voltage values can be set independently of one another. The first and/or the second control circuit can each have an amplifier element which is designed as an actuator.

In order to provide the corresponding reference voltage values, a reference voltage source that is controlled by the controller is provided in some exemplary embodiments. The reference voltage source can supply a first reference voltage for the first control circuit and/or a second reference voltage for the second control circuit.

In general, the controller can block the resistance element or elements via its own blocking voltage line, which is connected to the resistance element, via an OR gate or some other combination with, for example, the control circuit that controls the resistance element.

The active current sensor can be controlled in such a way that the voltage present at the resistance element, in particular the source-drain voltage in the case of the field effect transistor, is independent of the current flowing through the active current sensor. The gate voltage required to achieve this is then proportional to the current flowing through the resistance element, ie independent of the discharge current or charge current.

In addition, a temperature sensor can be integrated into the active current sensor, which outputs a temperature of the resistance element or elements. The controller can use the temperature to calculate the measurement current, which increases accuracy since the electrical resistance of the resistance elements is temperature-dependent.

Some exemplary embodiments relate to the use of battery protection as described above integrated in a battery data module for a motor vehicle battery. As mentioned at the beginning, the battery data module can be designed to determine parameters such as the state of charge, the state of health, the battery internal resistance or the electrolyte temperature, taking into account the measured battery voltage and battery terminal temperature as well as the battery current.

The integration of the battery protection, as described above, in the battery data module allows a particularly favorable realization of the battery protection. The battery protection can be integrated into the housing of the battery data module. In addition, for example, the control commands and/or control lines required for battery protection can be integrated into the controller or the control chip of the battery data module. The battery data module can also be integrated, for example, in a pole terminal of a battery or arranged on a pole terminal. This also ensures that no further electrical load worth mentioning is arranged between the battery protection and the corresponding pole of the battery.

The battery protection described above or the battery data module described above can also be used in a battery management system of a vehicle or be integrated into it.

• 1 schematisch ein Ausführungsbeispiel eines aktiven Messshunts veranschaulicht;
• 2 schematisch ein Batteriedatenmodul mit einem aktiven Messshunt nach 1 zeigt; und
• 3 eine KfZ-Batterie mit dem Batteriedatenmodul von 2 darstellt.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:

• 1 schematically illustrates an embodiment of an active measurement shunt;
• 2 schematically shows a battery data module with an active measurement shunt 1 shows; and
• 3 a car battery with the battery data module from 2 represents.

An exemplary embodiment of a battery data module 10 with an active measurement shunt 1 for a motor vehicle battery 2 is described below with reference to FIG 1 until 3 explained. The active measurement shunt 1 is also referred to below as “active shunt 1”. In the present exemplary embodiment, the motor vehicle battery 2 is a lithium-ion battery for a low-voltage on-board network of a motor vehicle, without the present invention being restricted thereto.

The battery data module 10 ( 2 ) is directly connected to a negative pole 12 of the car battery 2 (see 3 ), without further electrical load between the negative pole 12 and the battery data module 10. There is therefore no electrical load between the battery data module 10 and the negative pole 12. A negative line 14 for supplying the vehicle electrical system leads from the battery data module 10 . A positive line 13 goes from the positive pole 11 of the car battery and is, for example, connected to a vehicle body.

The battery data module 10 has a controller 7 which is connected to a reference voltage source 6 and the active shunt 1 . It is connected to the active shunt 1 via four wires, one wire carrying a temperature signal "T" from a temperature sensor 9 of the active shunt 1, one wire carrying the discharge current I _discharge from the active shunt 1, one wire carrying the charging current I _charge from the active shunt 1 and a line a blocking voltage U _blocking from the controller 7 to the active shunt 1. Between the active shunt 1 and the controller 7, an A / D converter 8 is connected, which converts corresponding analog signals from the active shunt 1 into digital signals and converts digital signals from the controller 7 into analog signals.

The active shunt 1 is provided for measuring the discharging and charging current I _mess of the motor vehicle battery 2 . The active shunt 1 has a first and a second control loop. The first control loop is formed by a left-hand field-effect transistor 4a, a left-hand amplifier 5a and a preset reference voltage value +Ref associated therewith, which originates from the reference voltage source 6, which in turn is controlled by the controller 7. The second control loop is formed by a right-hand field-effect transistor 4b, a right-hand amplifier 5b and a corresponding preset reference voltage value -Ref, which also originates from the reference voltage source 6.

The two field effect transistors 4a and 4b of the two control loops are traversed by the current I _mess of the motor vehicle battery 2 to be measured. The discharging current of the motor vehicle battery 2 flows during discharging through the left-hand field effect transistor 4a of the first control circuit and the charging current of the motor vehicle battery 2 flows during charging through the right-hand field effect transistor 4b of the second control circuit. Depending on the current flow direction of the current I _Mess either the left field effect transistor 4a or the right field effect transistor 4b is traversed since the field effect transistors 4a and 4b are blocked for the other current flow direction.

The two field effect transistors 4a and 4b of the first and second control loops are in the form of two MOSFETs which are designed to be complementary to one another and are connected in parallel to one another. The source of the left field effect transistor 4a is mutually connected to the drain of the right field effect transistor 4b and vice versa. The two field effect transistors 4a and 4b form a common switching element 3. In some exemplary embodiments, the two MOSFETs 4a and 4b are designed as an integrated semiconductor element.

The drain-source voltage U _DS of the two connected field effect transistors 4a and 4b is regulated to a defined reference voltage value by the gate voltage of the respective field effect transistor 4a or 4b being regulated by the controller 7 to a corresponding value. As a result of this circuit, the resistance value of the two field effect transistors 4a and 4b depends essentially on 1 divided by the value of the current I _mess . The resistance of the field effect transistor 4a or 4b through which the current flows decreases with increasing current I _mess and with a decreasing current I _mess the resistance value of the respective field effect transistor 4a or 4b through which flows increases.

In order to measure the current I _Mess , the gate-source voltage of the corresponding field-effect transistor 4a or 4b through which the current flows is detected, which is the manipulated variable of the first and second control circuit and is supplied to the A/D converter 8 .

In order to improve the measuring accuracy of the current I _Mess , the current sensor 1 has the temperature sensor 9 which outputs a temperature of the field effect transistors 4a and 4b to the controller 7 as temperature T. The controller 7 then takes the temperature value T into account when calculating the measured current I _meas by knowing the temperature dependency of the transistor characteristics of the field effect transistors 4a and 4b and adapting the measured raw current data accordingly.

The controller 7 has stored a deep-discharge threshold value in a read-only memory and analyzes the state of charge of the vehicle battery 2. As soon as the currently determined state-of-charge value falls below the deep-discharge threshold value, the controller 7 applies a corresponding blocking voltage U _blocking to the left-hand field-effect transistor 4a, so that it blocks. As a result of the fact that the field effect transistor 4a blocks, no more discharge current can flow through it. In general, no discharge current flows through the right-hand field-effect transistor 4b, since this is designed in such a way that current only flows through it in the charging direction. Since no electrical load is arranged between the negative pole 12 of the motor vehicle battery 2 and the battery data module 10, further discharging of the motor vehicle battery 2 is consequently prevented by blocking the left-hand field effect transistor 4a, and effective deep discharge protection is thus implemented.

In the present example, the controller 7 is connected to the gate of the left-hand field effect transistor 4a via a line. The controller 7 can also be connected to the gate of the left-hand field effect transistor 4a via an OR gate or via another link with the left control loop to apply the blocking voltage to the gate of the left field effect transistor 4a and block it.

By integrating the active shunt 1 into the battery data module 10 and by simultaneously using the active shunt 1 as a switch for switching off the loads connected to the motor vehicle battery 2, effective and extremely cost-effective deep discharge protection can be implemented.

As explained above, to provide overcharging protection, the right-hand field effect transistor 4b can be blocked by the controller 7 in a similar way if the controller of the battery data module detects a charge state of the motor vehicle battery that is above a threshold value. For this purpose, the controller 7 is then connected directly or via an OR gate or the like, as explained above, to the gate of the right-hand field-effect transistor 4b, through which the charging current flows.

Reference List

1

Active measurement shunt

2

car battery

3

Parallel connection of the MOSFET

4a, 4b

MOSFET

5a, 5b

amplifier

6

reference voltage source

7

steering

8th

AD converter

9

temperature sensor

10

battery data module

11

positive pole of the battery

12

negative pole of the battery

13

Positive on-board power supply line

14

Negative on-board power supply line

Idischarge

discharge current

Iload

charging current

IMess

measured current

-Ref

negative reference voltage

+ref

positive reference voltage

T

temperature

USD

drain-source voltage

USblock

blocking voltage

Claims (10)

Battery protection for a battery (2) of a vehicle, comprising: a controller (7) which is designed to detect a state of charge of the battery (2), characterized by an active current sensor (1) for measuring a current (I _Mess ) of Battery (2), wherein the active current sensor (1) has a first resistance element (4a) and a second resistance element (4b), to which a voltage for measuring the current (I _meas ) flowing through the resistance element (4a) of the battery (2 ) is detected and which can be blocked, the first resistance element (4a) and the second resistance element (4b) being connected in parallel with one another and the current (I _Mess ) of the battery (2) when the battery (2) is discharged through the first resistance element (4a) and when charging the battery (2) through the second resistance element (4b), the controller (7) being designed to block the first resistance element (4a) when the state of charge of the battery (2) falls below a deep discharge threshold value , so that a discharge current (I _Discharge ) of the battery (2) is blocked by the first resistance element (4a), and wherein the controller (7) is designed to block the second resistance element (4b) when the state of charge of the battery (2 ) exceeds an overcharging threshold value, so that a charging current (I _charge ) of the battery (2) is blocked by the second resistance element (4b). battery protection after claim 1 , The first and second resistance element (4a, 4b) each being a transistor, in particular a field effect transistor. battery protection after claim 2 , wherein the voltage for measuring the current (I _Mess ) flowing through the first or second resistance element (4a, 4b) is detected as a gate-source voltage or base-emitter voltage at the corresponding transistor. Battery protection according to one of the preceding claims, in which the active current sensor (1) is formed from two parallel-connected and complementarily designed MOS field-effect transistors (4a, 4b). Battery protection according to one of the preceding claims, wherein the active current sensor (1) for measuring a current (I _Mess ) of the battery (2) has two parallel-connected field effect transistors (4a, 4b), the source connection of one field effect transistor (4a) having connected to the drain terminal of the other field effect transistor (4b), with a discharge current (I _discharge ) of the battery (2) through the first field effect transistor (4a) of the two field effect transistors (4a, 4b). battery protection after claim 5 , wherein a charging current (I _charge ) of the battery (2) through the second field effect transistor (4b) of the two field effect transistors (4a, 4b) flows. Battery protection according to one of the preceding claims, wherein the active current sensor (1) has at least one first control circuit in which the first resistance element (4a) is arranged and with which the voltage (U _DS ) across the first resistance element (4a) is set to a defined reference voltage value is regulated. battery protection after claim 7 , Further comprising a reference voltage source (6) which is controlled by the controller (7) and supplies a first reference voltage (-Ref) for the first control circuit. Battery protection according to one of the preceding claims, wherein the active current sensor (1) is controlled in such a way that the voltage (U _DS ) present at the first resistance element (4a, 4b) is independent of the current (I _Mess ) is. Use of the battery protection according to one of the preceding claims, wherein the battery protection is integrated in a battery data module (10) for a battery (2) of a motor vehicle.

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