Battery having a plurality of battery modules arranged in battery strings, and method for operating the battery

A battery includes a plurality of battery modules which are arranged in battery strings and are selectively activated or deactivated by driving. The battery module voltage of a respective battery module contributes to an output voltage of the corresponding battery string of the battery in the activated state. The battery further includes a switching converter topology which is coupled to the battery strings and is configured to selectively generate currents flowing into one or more of the battery strings.

This application claims priority under 35 U.S.C. §119 to patent application no. DE 10 2012 207 671.9, filed on May 9, 2012 in Germany, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

The present disclosure relates to a battery having a plurality of battery modules which are arranged in battery strings and can be selectively activated or deactivated by means of driving, the battery module voltage of a respective battery module contributing to an output voltage of the corresponding battery string of the battery in the activated state. The disclosure also relates to an associated method for operating the battery. In addition, the disclosure relates to a vehicle having the battery.

It is becoming apparent that new batteries, on which very high demands with regard to reliability, safety, performance and service life will be imposed, will be increasingly used in future in stationary applications, for example wind power installations, in vehicles, for example hybrid and electric vehicles, and in the consumer sector, for example in laptops and mobile telephones. Batteries having lithium ion technology, in particular, are suitable for such tasks. They are distinguished, inter alia, by a high energy density and an extremely low self-discharge.

Previous disclosures by the applicant presented methods concerning how a lithium ion battery can be expediently subdivided into modules which are then connected to form individual strings which then directly drive an electric motor. An example of a modular battery is disclosed in the document DE 10 2010 027 864 A1. The corresponding principle is explained in more detail by way of example below usingFIG. 1.

According toFIG. 1, a battery100has a plurality of battery strings101with battery modules102. Each battery module102has one or more battery cells103, only one battery cell103of which is illustrated in the drawing for each battery module102. Each battery module102also respectively has two switches104,105, a respective battery module102being able to be activated or deactivated depending on the switching position of the switches104,105. In the activated state, the battery module voltage of the respective connected or activated battery module102contributes to an output voltage of the corresponding battery string101, which output voltage is then available at a connection106. In contrast, in the deactivated state, the battery module102is decoupled from the battery string101and is bridged in an electrically conductive manner.

An advantage of the arrangement according toFIG. 1is that a battery voltage can thus be set in a variable manner. For example, with sufficiently fine division of the battery strings101into a multiplicity of battery modules102and with appropriate driving, a sinusoidal profile of the battery voltage can be set at the terminals106, which profile has a phase shift. This makes it possible to drive a (three-phase) electric motor107, even without the need for a special interposed inverter.

Previous disclosures by the applicant also presented a battery, in which the individual battery modules are connected to a DC/DC converter.FIG. 2illustrates such an arrangement by way of example, the circuits of the battery modules102shown each being supplemented with a secondary subcircuit207of the DC/DC converter. The DC/DC converter is preferably in the form of a flyback converter. The secondary subcircuits207each have a diode201and a secondary coil202. The primary-side subcircuit206of the battery200has a primary coil204and a switch205. DC-isolation between the battery modules202and the primary-side subcircuit206can also be effected using the coil core203. As an advantage of the circuit topology shown, it is possible, for example, to charge the battery modules202from the 12-V power supply system or, depending on the configuration of the DC/DC converter, from the 220-V domestic power supply system. However, the circuit topology fromFIG. 2results in a high wiring complexity and therefore high costs since each battery module202must be wired to a separate secondary coil202on the DC/DC converter. In addition, although it is possible to carry out active balancing between the battery modules102and individual battery strings101in the battery200during operation by connecting the individual battery modules102for different periods of time depending on their performance during the production of the desired AC output voltages, such a method cannot be used at a standstill or during charging, for example.

SUMMARY

The battery according to the disclosure has a plurality of battery modules which are arranged in battery strings and can be selectively activated or deactivated by means of driving. The battery module voltage of a respective battery module contributes to an output voltage of the corresponding battery string of the battery in the activated state. The battery also comprises a switching converter topology which is coupled to the battery strings and is designed to selectively generate currents flowing into one or more of the battery strings.

The method according to the disclosure in principle comprises steps in which the output voltages of battery strings are set or maintained in a suitable manner by driving the corresponding battery modules in such a manner that a predetermined selection of battery strings, which comprises one or more battery strings, is supplied with current using the switching converter topology.

Another aspect of the disclosure also discloses a motor vehicle having an electric motor and the battery according to the disclosure, the battery being arranged in a drive train of the electric motor.

An advantage of the disclosure is that it is possible to supply the battery strings with current in a flexible manner with simultaneously little wiring complexity, for example in order to charge battery modules of one or more of the battery strings or of all battery strings.

In one preferred development of the disclosure, the switching converter topology is furthermore also designed to draw current from battery strings.

The switching converter topology preferably has a flyback converter.

In one advantageous embodiment of the disclosure, the switching converter topology is integrated in the battery in such a manner that the currents flowing into one or more of the battery strings can be generated in addition to a battery current flowing at a battery terminal. This further increases the flexibility.

It is also preferred for the individual battery strings to be connected to one another by means of an arrangement having diodes. This advantageous embodiment makes it possible, for example, in a particularly simple manner to deliver the energy stored in a core of the switching converter topology, which is in the form of a flyback converter for example, only to that battery string which has the lowest voltage.

In one particularly favorable embodiment, at least one diode is respectively arranged, for each battery string, between a secondary coil of the switching converter topology and a connection of the respective battery string.

In one development of the method according to the disclosure, the battery string which is intended to be charged is deliberately selected. The other battery strings, that is to say the two other battery strings in the case of a total of three battery strings, are set to a higher output voltage in this case by activating all battery modules in the other battery strings. At the same time, one or more of the battery modules are deactivated or decoupled or bridged in the battery string to be charged.

It is also preferred for at least one diode to be respectively arranged, for each battery string, between a primary coil of the switching converter topology and a connection of the respective battery string. This advantageously makes it possible, in a simple manner, to draw energy from one battery string and to transmit it to another battery string.

In one particularly favorable embodiment of the disclosure, the switching converter topology, for each battery string of the battery, is respectively connected to the same connection of the respective battery string on the primary side and on the secondary side.

The method according to the disclosure can advantageously have steps in which the predetermined battery strings are charged using the switching converter topology, and/or the output voltages of battery strings are set or maintained in such a manner that the battery modules are balanced using the switching converter topology, the primary side of the switching converter topology being supplied using one or more such battery strings which are currently not supplied with current.

The disclosure can therefore be configured in such a manner that energy can be drawn from one battery string and can be transmitted to another battery string. In order to make this possible, the three battery strings, for example, are connected to one another via the abovementioned diode arrangement, with the result that the voltage associated with the battery string with the highest output voltage is always applied to the primary side of the switching converter topology. Since the secondary side can likewise be connected to the battery strings via diodes, it is thus possible to always transmit energy stored in the core to the battery string with the lowest output voltage during conversion. It can therefore be ensured that the energy can be transmitted from the battery string with the highest output voltage to the battery string with the lowest output voltage.

According to the disclosure, the output voltage of the battery strings can therefore be selected by deliberately switching on and bridging individual battery modules in such a manner that energy flows in the desired direction.

The switching converter topology preferably has DC-isolation. DC-isolation between the primary side and the secondary side of the switching converter topology can therefore be favorably achieved. In particular, the battery modules can be electrically decoupled from the primary side in this manner.

In one embodiment, the primary side may also be coupled to a power factor correction stage.

The disclosure can be used, in particular, in such battery modules comprising two switches which are each arranged in such a manner that a respective battery module is activated in a first switching position of the switches and the respective battery module is deactivated in a second switching position of the switches.

The battery is preferably a lithium ion battery.

Advantageous developments of the disclosure are stated in the subclaims and are described in the description.

DETAILED DESCRIPTION

FIG. 3illustrates a battery300with an integrated switching converter topology305according to a first embodiment of the disclosure. As shown inFIG. 3, a principle of supplying battery modules103using a switching converter topology305is applied to the individual battery strings101, rather than to each individual module of the battery modules102. The positive outputs of the battery strings101are each connected to a secondary side304of the switching converter topology. The switching converter topology305is preferably in the form of a flyback converter and, to state it clearly, is also subdivided into three on the secondary side according to the three battery strings101, even though the secondary coil303is present only once. However, a diode301is respectively present for each battery string101, which diode is used as the output diode of the switching converter topology305and is forward-biased in the direction of the respective battery string101. The outputs of the battery strings101, which are each coupled to the switching converter topology305, are also each connected to one of the three terminal connections106of the battery300. The primary side206of the switching converter topology305has a primary coil204and a switch205and can be supplied with energy from the outside by means of connections, which energy is transmitted to the secondary side303via the DC-isolation302. On account of the arrangement of the diodes301, this energy is delivered only to that battery string101which has the lowest voltage. In one particularly advantageous variant of this embodiment, the battery string101which is currently intended to be charged is deliberately selected by setting the two other battery strings101to a comparatively higher output voltage. This can be effected by switching on all battery modules102of the other battery strings101, the battery string101to be charged being set to a lower output voltage, for example by deactivating a battery module102.

FIG. 4illustrates a battery400according to a second embodiment of the disclosure which comprises a switching converter topology305. According to the arrangement shown inFIG. 4, the switching converter topology305or a DC/DC converter is used in such a manner that it can draw energy from one battery string101and can transmit it to another battery string101. In order to make this possible, the three battery strings101are connected to one another via a circuit arrangement having diodes401, with the result that the voltage associated with the battery string with the highest output voltage is always applied to the primary side206of the switching converter topology305. Furthermore, the secondary side304is likewise connected to the three battery strings101via diodes301, the energy stored in the core of the switching converter topology305always being transmitted to the battery string101with the lowest output voltage during conversion. This advantageously makes it possible to ensure that the energy is transmitted from the battery string101with the highest output voltage to the battery string101with the lowest output voltage.

In an advantageous method for operating the battery400, the output voltage of the battery strings101is selected by deliberately switching on and bridging individual battery modules102in such a manner that the energy flows in the desired direction.