DE102012211086A1 - Safety electronics unit for battery module of lithium ion battery system of e.g. electric car, has comparator producing alarm signal depending on comparison of voltage threshold value with battery module voltage lying close at module - Google Patents

Abstract

The electronics unit (300) has a comparator (304) and an alarm signal output (306) for an alarm signal (308). A voltage threshold value input (310) is provided for a voltage threshold value (312). The comparator produces the alarm signal depending on a comparison of the voltage threshold value with battery module voltage lying close at a battery module (302). The comparator produces the alarm signal if the comparison results that the battery module voltage is smaller than the voltage threshold value and comprises an input resistor of multiple Kilo ohms or Mega ohms. An independent claim is also included for a battery system.

Description

The present invention relates to a safety electronics for a battery module, a battery cell monitoring unit for monitoring a plurality of battery cells, which form the battery module, and a battery system with the safety electronics. Furthermore, the invention relates to a motor vehicle with the battery system.

State of the art

It is becoming apparent that in the future, both in stationary applications, eg. B. in wind turbines, in vehicles, such. As in hybrid and electric vehicles, and in laptops and mobile phones lithium-ion battery systems will be used, are placed on the very high demands in terms of reliability, safety, performance and service life.

The basic functional structure of a battery system according to the prior art is in the 1 shown. In order to achieve required power and energy data with such a battery system, usually individual battery cells 100 connected in series and sometimes additionally in parallel to a battery. A group of battery cells 100 is in each case to one of several battery cell monitoring units 102 , also called Cell Supervision Circuit or CSC, connected. Another functional unit is the battery management system 104 at which the battery cell monitoring units 102 are connected. The battery management system 104 ensures high safety, performance and service life of the battery system. In addition to battery status detection, it also includes diagnostic and safety functions and communication interfaces for other systems, such as thermal management of the battery system.

A battery disconnect unit 106 between the battery cells 100 and Poland of the battery system is arranged, among other things, a switching on and off of the battery to or from consumers. The battery disconnecting unit 106 is from the battery management system 104 controlled and ensures the protection of the battery system against excessive currents and voltages, and provides safety features such. B. a bipolar separation of the battery cells 100 from the battery poles, such as during maintenance work on the battery system. In conventional battery management systems, standard allowances or safety clearances are usually calculated in order to avoid jeopardizing the safety of the battery system with the highest priority for reasons of providing too high a performance.

The function of a conventional battery cell monitoring unit 102 is in the 2 shown. The battery cell monitoring unit 102 is known to comprise an analog-to-digital converter 200 that has a filter circuit 202 with one of the battery cells 100 connected is. The analog-to-digital converter 200 digitizes a battery cell instantaneous voltage of the battery cell 100 and provides this an evaluation 204 to disposal. The evaluation electronics 204 may then be a control signal for one of the battery cell 100 Parallel connected charge state equalization circuit 206 , engl. also called cell balancing. To ensure safe operation of the battery cell 100 the same is often also an accompanying electronics 208 connected in parallel with a comparator. Since it is known that conventional lithium-ion battery cells 100 an operating voltage of typically 2.8 volts to 4.2 volts, is the accompanying electronics 208 designed so that it is an alarm signal on an alarm signal bus when the lower or upper operating voltage is exceeded or exceeded 210 generated.

The measurement of the battery cell voltage, on the one hand by the battery cell monitoring unit 102 and on the other hand by the accompanying electronics 208 , already ensures a relatively safe monitoring of battery cells today 100 ,

Disclosure of the invention

According to the invention, a safety electronics for a battery module is provided. The safety electronics includes a comparator and an alarm signal output for an alarm signal. The safety electronics further includes a voltage threshold input for a voltage threshold, the comparator generating the alarm signal in response to a comparison of the voltage threshold with a battery module voltage applied to the battery module.

In addition, a battery cell monitoring unit is provided for monitoring a plurality of battery cells. The multiple battery cells form a battery module. The battery cell monitoring unit monitors battery cell voltages of the battery cells. The safety electronics according to the invention is connected to the battery module and provides the battery cell monitoring unit with the alarm signal via an alarm signal bus.

Furthermore, a battery system is provided. The battery system includes a plurality of battery cells that form at least one battery module of a battery. The battery cells each have a battery cell fuse. In addition, the battery system comprises the inventive Battery cell monitoring unit for monitoring the at least one battery module of the battery and the security electronics according to the invention for the at least one battery module of the battery. Furthermore, the battery system comprises a battery disconnection unit for disconnecting the battery from a consumer, a battery management unit and an alarm signal bus, which connects the alarm signal output of the safety electronics with the battery management unit. The battery management unit controls the battery disconnection unit in response to the alarm signal.

In addition, a motor vehicle is provided with the battery system according to the invention, wherein the battery system is connected to a drive system of the motor vehicle.

Advantages of the invention

The safety electronics according to the invention makes it possible to advantageously ensure safe operation of a battery module. In this case, the safety electronics do not monitor at the level of battery cells, as does the case with known accompanying electronics, but at the level of battery modules, which each comprise a plurality of battery cells. If a battery system which has a plurality of battery modules is equipped with the security electronics according to the invention, then fewer security electronics are required and thus equipping the battery system is inexpensive.

Although battery cell monitoring units are also known, which monitor a single battery cell or a plurality of battery cells, which form a battery module. However, the safety electronics according to the invention in particular form a redundant, independent or additional measuring or monitoring means to the known battery cell monitoring units, which enables a high safety rating for equipped with the safety electronics battery systems. The safety electronics can advantageously a classification of such a battery system z. B. in ASIL (Automotive Savety Integrity Level) C or D.

When a battery having battery cells with battery cells is shorted, for example because a consumer connected to the battery is defective or because the battery, a battery module or a battery cell itself is damaged, generally battery cell fuses will be triggered to integrate in the battery cells for safety reasons are. In this case, high negative voltages can occur at battery cell monitoring units, which are connected to the battery cells. If the battery cell fuse triggers a particular battery cell, then the entire voltage of the remaining battery cells can be present with a negative sign at this battery cell fuse and thus at a battery cell monitoring unit. The battery cell monitoring unit may be damaged by high negative voltages, eg. B. ignite and burn off.

Triggering a battery cell fuse immediately reduces the battery module voltage of an affected battery module. The comparator preferably generates the alarm signal when the comparison reveals that the battery module voltage is less than the voltage threshold. The comparator thus detects the consumer-side short circuit.

For example, if a battery cell fuse of a battery cell triggers, with the battery cell voltage of these battery cells remaining within a permissible range of typically approximately 2.8 V to approximately 4.2 V, then the safety electronics recognizes that essentially no critical condition exists and generates in this case in particular, no alarm signal.

According to a preferred embodiment, the comparator has an input resistance of several kilohms or megohms. Battery cell monitoring units are usually equipped with low-impedance inputs, for example in order to achieve a high accuracy of measurement for the battery cell voltages. Frequently, components with low-impedance inputs are damaged when high voltages are applied, since an almost equally high current flows. By contrast, the comparator of the safety electronics is characterized in particular by high-impedance inputs, i. H. Input resistances in the range of several kilohms or megohms, robust against applied high voltages.

The battery cell monitoring unit according to the invention has the advantage that it can make safety measures for the battery module by means of the alarm signal provided by the safety electronics. Preferably, the battery cell monitoring unit includes a short circuit path. The battery cell monitoring unit may short-circuit the battery module with the short-circuit path upon receipt of the alarm signal. As a result, an uncontrollably high, in particular negative, voltage can be prevented at the battery cell monitoring unit.

In general, a battery cell monitoring unit includes an analog-to-digital converter, a control unit, and a communication unit. The analog-to-digital converter typically has multiple inputs at which battery cell voltages are applied. To comply with the known sampling theorem, a low-pass filter is connected upstream of the analog-digital converter inputs. Around allow a largely unadulterated measuring the battery cell voltages, the analog-to-digital converter inputs are low impedance. Is in an error case, z. As in a consumer-side short circuit and a triggered battery cell fuse, a high negative voltage to the analog-to-digital converter inputs, so the analog-to-digital converter can be damaged. The safety electronics according to the invention can help prevent such damage by, for example, generating the alarm signal early on. The high-impedance inputs of the comparator can still ensure the functioning of the safety electronics even when the high voltage is already present.

The battery system of the present invention may also receive the alarm signal and use it, for example, to disconnect the entire battery system from a shorted consumer via the battery disconnect unit, thereby establishing a safe battery system condition. Functioning of the comparator, the alarm signal, and the control of the battery disconnect unit is essentially possible without software that may be down or malfunctioning. In particular, the battery disconnection unit still functions even if, for example, the monitoring unit has already failed or is damaged due to high voltages applied thereto. In a further embodiment, the alarm signal directly controls the battery disconnection unit, whereby a faster disconnection and a higher reliability of the battery system can be achieved.

The voltage threshold is preferably a predetermined value. However, the battery management unit can also determine the voltage threshold value depending on the number of battery cells of the battery module, a battery cell idle voltage, a battery cell internal resistance and a battery current. In addition, the battery system of the safety electronics according to the invention can provide the voltage threshold at the voltage threshold input.

If the battery cell idle voltage, the battery cell internal resistance or the battery current changes, the battery management unit can dynamically determine the voltage threshold and in turn provide it to the safety electronics at the voltage threshold input.

It is preferred that the alarm bus forms a separate hardware line. As a result, a redundancy can be produced, which increases the operational reliability and reliability of the battery system.

In a further preferred refinement, the battery system comprises accompanying electronics, which has a comparator. The accompanying electronics is connected to each battery cell and checks by means of the comparator, whether a battery cell voltage of the battery cell exceeds an upper voltage limit or falls below a lower voltage limit. Depending on these tests, the monitoring electronics generates another alarm signal. The safety electronics preferably supplement the accompanying electronics and the battery cell monitoring unit in order to increase the operational safety of the battery system.

The battery system is preferably a lithium-ion battery system.

drawings

Embodiments of the invention will be explained in more detail with reference to the drawings and the description below. Show it:

1 a battery system of the prior art,

2 a battery cell monitoring unit of the prior art,

3 a safety electronics according to an embodiment of the invention, and

4 a battery module in case of damage according to an embodiment of the invention.

Embodiments of the invention

In the 3 is a safety electronics 300 for a battery module 302 shown. The safety electronics 300 includes a comparator 304 and an alarm signal output 306 for an alarm signal 308 , Furthermore, the safety electronics includes 300 a voltage threshold input 310 for a voltage _threshold U _threshold 312 , The comparator 304 compares the voltage _threshold U _threshold 312 with one on the battery module 302 applied battery _{module voltage} U _modul . Depending on the comparison, the comparator generates the alarm signal 308 ,

The battery module 302 in the present embodiment comprises six individual lithium-ion battery cells 314 , In other embodiments, for example, four, twelve or more lithium-ion battery cells 314 be. Every lithium-ion battery cell 314 typically provides a battery _{cell voltage} U _cell between about 2.8V and about 4.2V. The sum of these n equal to six battery _{cell voltages} U _cell forms the battery _{module voltage} U _{modul of} the battery _module 302 , U _modul (t) = n × U _cell (t) where n = 6 (1)

The battery _{module voltage} U _module changes depending on the state of charge and load of the battery module over time.

Several battery modules 302 can form a lithium-ion battery, the term battery generally relates to a secondary storage or accumulator. The battery forms together with a battery management unit, the safety electronics 300 and a battery disconnecting unit, a battery system.

To charge differences between the individual lithium-ion battery cells 314 is any lithium ion battery cell with a charge state equalization circuit 316 connected.

Per battery module 302 is a battery cell monitoring unit 318 provided with each lithium-ion battery cell 314 connected to monitor them. The battery cell monitoring unit 318 includes an analog-to-digital converter and an electronic evaluation system. The analog-to-digital converter has multiple inputs connected to the lithium-ion battery cells 314 are connected and tap there each a battery _cell voltage U _cell . To comply with the Nyquist sampling theorem, each of the analog-to-digital converter inputs is a low-pass filter 320 upstream. In order not to degrade the measurement accuracy of the A / D converter by any voltage drop or the like, input resistances of the A / D converter and resistances in the low-pass filters are 320 chosen low impedance.

In the 4 is the battery module 302 shown in a claim. The battery module 302 is with a consumer 400 connected, for example, due to a defect in the 4 schematically drawn short circuit 402 having. The consumer generally designates an inverter, a pulse inverter, a generator and / or an electric motor.

The lithium-ion battery cells 302 include battery cell fuses in case of damage 404 , One of the battery cell fuses 404 dissolves in the place 406 ie it disconnects the battery circuit at this point 406 ,

The battery cell monitoring unit 318 Also monitors during this event of damage the battery _{cell voltages} U _cell , indicated by arrows 407 in the 4 are shown. The analog-to-digital converter inputs and low-pass filters together form voltage measuring units, of which in the 4 an example of a voltage measuring unit 408 is shown. The circuit of the battery comprises a series connection of a number of n lithium-ion battery cells 314 , so in the case of damage shown, for example, a damage voltage of U _damage to the voltage _{measuring unit} 408 at. U _harm = - (n - 1) · U _cell (2 )

By the short circuit 402 creates a high negative damage voltage at the voltage measuring unit 408 that would lead to their damage. The one with the battery module 302 Connected safety electronics 300 However, the battery _module voltage U _modul (t) continuously compares with the voltage _threshold U _threshold (t). U _mod (t) <U _threshold (t) (3)

The battery management unit of the battery system continuously determines the voltage threshold as a function of the number n of lithium-ion battery cells 314 of the battery module 302 , a battery _{cell idling voltage} U _OCV , a battery _{cell internal resistance} R _i and a battery _current I _batt in the following manner: U _threshold (t) = n · (U _OCV - R _i · I _batt ) (4)

Both the open circuit voltage U _OCV and the internal resistance and in particular the battery current change with time, so that the voltage _threshold U _threshold is generally time-dependent. However, equation (4) assumes that the values across all lithium-ion battery cells 314 of the battery module 302 identical or at least nearly equal. In another embodiment, the battery management unit may generate a more accurate voltage threshold, such as by providing accurate values of the individual lithium-ion battery cells 314 considered.

The comparator 304 on the basis of the inequality (3) compares the battery _module voltage U _modul and the voltage _{threshold value} U _threshold with one another, whereby the inequality (3) is satisfied due to the damage case. The comparator 304 then generates the alarm signal 308 He is the battery cell monitoring unit 318 and the battery management unit via an independent alarm bus provides. The battery management unit in turn controls a battery disconnection unit 410 to the consumer 400 , and thereby the short circuit 402 , from the battery or the battery module 302 bipolar separates. The battery disconnecting unit 410 thus interrupts the battery circuit, and at the voltage measuring unit 408 There is no high negative voltage. The battery cell monitoring unit 318 This way, before damage, as in the 4 shown to be protected.

The alarm signal can also directly the battery disconnection unit 410 Taxes. By this embodiment, the security electronics is independent of any software and disconnecting the battery from the consumer 400 happens faster.

Furthermore, a voltage difference can additionally be provided for the comparison in inequality (3), so that the comparator 304 only then generates an alarm signal when the voltage _threshold U _threshold significantly, ie by the voltage _{gap, falls} below.

The safety electronics can additionally be used in an existing battery system with accompanying electronics and, in particular, increase the operational reliability of motor vehicles equipped with the battery system.

Claims (10)

Safety electronics ( 300 ) for a battery module ( 302 ), with: a comparator ( 304 ) and an alarm signal output ( 306 ) for an alarm signal ( 308 ), characterized in that the safety electronics ( 300 ) a voltage threshold input ( 310 ) for a voltage threshold ( 312 ), wherein the comparator ( 304 ) as a function of a comparison of the voltage threshold ( 312 ) with one on the battery module ( 302 ) battery module voltage the alarm signal ( 308 ) generated. Safety electronics ( 300 ) according to claim 1, wherein the comparator ( 304 ) the alarm signal ( 308 ), if the comparison reveals that the battery module voltage is less than the voltage threshold ( 312 ). Safety electronics ( 300 ) according to claim 1 or 2, wherein the comparator ( 304 ) has an input resistance of several kilo ohms or megohms. Battery cell monitoring unit ( 318 ) for monitoring several battery cells ( 314 ), which is a battery module ( 302 ), wherein the battery cell monitoring unit ( 318 ) Battery cell voltages of the battery cells ( 314 ) and wherein a safety electronics ( 300 ) according to one of the preceding claims with the battery module ( 302 ) and the battery cell monitoring unit ( 318 ) the alarm signal ( 308 ) via an alarm signal bus. Battery cell monitoring unit ( 318 ) according to claim 4, with a short circuit path, wherein the battery cell monitoring unit ( 318 ) upon receipt of the alarm signal ( 308 ) the battery module ( 302 ) short circuits to the short circuit path. Battery system with: several battery cells ( 314 ), the at least one battery module ( 302 ) form a battery and each a battery cell fuse ( 404 ) exhibit; a battery cell monitoring unit ( 318 ) according to claim 4 or 5 for monitoring the at least one battery module ( 302 ) of the battery; a safety electronics ( 300 ) according to one of claims 1 to 3 for the at least one battery module ( 302 ) of the battery, a battery disconnecting unit ( 410 ) for disconnecting the battery from a consumer ( 400 ); a battery management unit and an alarm signal bus which receives the alarm signal output ( 306 ) of the safety electronics ( 300 ) connects to the battery management unit, wherein the battery management unit the battery disconnection unit ( 410 ) depending on the alarm signal ( 308 ) controls. Battery system according to claim 6, wherein the battery management unit the voltage threshold ( 312 ) depending on the number of battery cells ( 314 ) of the battery module ( 302 ), a battery cell idle voltage, a battery cell internal resistance and a battery current and the safety electronics ( 300 ) the voltage threshold at the voltage threshold input ( 310 ). A battery system according to claim 6 or 7, wherein the alarm bus forms a separate hardware line. Battery system according to one of claims 6 to 8, with an accompanying electronics having a comparator, wherein the accompanying electronics to each battery cell ( 314 ) is connected and by means of the comparator checks whether a battery cell voltage of the battery cell ( 314 ) exceeds an upper voltage limit or falls below a lower voltage limit and generates a further alarm signal in response thereto. Motor vehicle with a battery system according to one of claims 6 to 9, wherein the battery system is connected to a drive system of the motor vehicle.

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