DE102011107269B4 - Method and device for solar-assisted charging of a battery and charging device - Google Patents

Abstract

Device for solar-assisted charging of a battery (2), in particular a battery (2) of an electric or hybrid vehicle, by means of at least one solar module, wherein a solar voltage (Us) can be generated by means of the at least one solar module, the device (1) at least one charging device (4) for transmitting electrical energy from an external electrical network to the battery (2), wherein the charging device (4) comprises at least one intermediate circuit capacitor (6), the intermediate circuit capacitor (6) using the solar voltage (Us) or a transformed solar voltage can be charged, the device (1) additionally comprising at least one DC voltage converter (14), the solar voltage (Us) being transformable to a predetermined intermediate circuit voltage (Uz) by means of the DC voltage converter (14), the intermediate circuit capacitor (6) being transformed by means of the transformed solar voltage is rechargeable, characterized in that the device (1) closes additionally comprises at least one control and evaluation device (15), the level of the intermediate circuit voltage (Uz) being able to be evaluated by means of the control and evaluation device (15), with the transmission of electrical energy from the intermediate circuit capacitor (15) by means of the control and evaluation device (15). 6) can be controlled to the battery (2), the transmission taking place if the intermediate circuit voltage (Uz) is greater than or equal to a first predetermined voltage threshold.

Description

The invention relates to a method and a device for solar-assisted charging of a battery, in particular a battery of an electric or hybrid vehicle, and a charging device, in particular a charging device of an electric or hybrid vehicle.

It is known to use solar energy to generate electrical energy. For example, so-called solar modules or solar roofs can be used to convert solar energy into electrical energy.

It is also known to store the electrical energy generated from solar energy in batteries or accumulators.

Also known are motor vehicles, in particular hybrid or electric vehicles, which have a solar module.

So reveals the DE 10 2009 027 685 A1 a solar-powered battery charger, especially for a hybrid and / or electric vehicle. The battery charger has a control device with a connection device for receiving a charging voltage supplied by a solar module, the control device being adapted to selectively apply the charging voltage supplied by the solar module to one or more of the cell blocks of a high-voltage storage system, in particular with a nominal voltage or charging voltage of more than 100 V to switch through. The high-voltage storage unit is divided into several cell blocks, which have a lower nominal voltage or charging voltage than the entire high-voltage storage unit. The solar-assisted battery charging device also has a measuring device for measuring one or more parameters of the plurality of cell blocks of the high-voltage storage device. Furthermore, the battery charging device has a control device, based on the one or more measured parameters, in accordance with a control logic implemented by the control device, to selectively switch the charging voltage supplied by the solar module through to one or more of the cell blocks in order to thereby connect the one or more cell blocks to the the charging voltage is switched through to charge selectively.

WO 2007/025 096 A1 discloses that solar cells are attached to a vehicle in order to form modular solar elements. The publication also discloses a system for connecting the solar elements for charging a high-voltage battery. The solar elements can support charging of the battery through regenerative braking.

The disadvantage is that known methods for solar-assisted charging of a battery of an electric or hybrid vehicle require a large number of additional electrical components to be arranged in the electric or hybrid vehicle, which reduces the available installation space in the electric or hybrid vehicle, increases weight and the production costs of the electric or hybrid vehicle Hybrid vehicle can be increased.

The DE 29 604 437 U1 discloses a drive arrangement for a watercraft which can be driven alternatively or jointly by an internal combustion engine and an electric machine.

WO 2007/025 096 A1 discloses a system for extending the life of a battery in an electric vehicle.

The EP 0 947 042 B1 discloses a generator device capable of supplying varying loads over time.

The DE 198 37 862 C2 discloses a solar module, in particular a portable solar module, with a DC voltage source comprising a solar cell arrangement and optionally a battery arrangement that can be charged by the solar cell arrangement for providing a source voltage.

The technical problem arises of creating a device and a method for solar-assisted charging of a battery and a charging device which enable solar-assisted charging of the battery in addition to charging the battery from an external electrical network, with solar-assisted charging using as little additional as possible to be arranged electrical components is made possible.

The solution to the technical problem results from the subjects with the features of claims 1, 5 and 6. Further advantageous embodiments of the invention emerge from the subclaims.

A device is proposed for solar-assisted charging of a battery, in particular a battery of an electric or hybrid vehicle. The battery is preferably a high-voltage battery or traction battery of the electric or hybrid vehicle, with electrical energy from the high-voltage battery being transmitted to an electric motor of the electric or hybrid vehicle in a motor operating mode and electrical energy being transmitted from the electric machine to the high-voltage battery during a generator operating mode. The high-voltage battery can use one or more circuit breakers, for example so-called Contactors are electrically connected to a high-voltage network of the electric or hybrid vehicle, in which so-called high-voltage components such as a converter and the above-described electric machine are arranged. Opening the circuit breaker causes the high-voltage battery to be separated from the high-voltage network. The battery can also be a low-voltage battery or on-board network battery of the electric or hybrid vehicle, which is provided for the electrical supply of low-voltage components, for example control devices, in the electric or hybrid vehicle.

The solar-assisted charging of the battery takes place by means of at least one solar module, whereby a solar voltage can be generated from solar or solar energy by means of the at least one solar module. This can take place, for example, by means of the so-called photoelectric effect.

The device comprises at least one charging device for transmitting electrical energy from an external electrical network to the battery. The electrical network can be an alternating current network or a direct current network. The charging device is therefore used to transfer electrical energy from the external electrical network to the high-voltage or low-voltage battery. In an electric or hybrid vehicle, in particular in a plug-in hybrid vehicle, a charging process can generally only take place when the electric or hybrid vehicle is at a standstill Charging socket, is introduced, whereby an electrical connection of the external electrical network and the vehicle-side battery is established.

The charging device comprises at least one intermediate circuit capacitor. Depending on the type of external electrical network and its properties, the charging device can include, for example, a nominal voltage, an element for inverting and / or an element for rectifying and / or a step-up converter and / or a step-down converter and / or an element for voltage transformation. Here, an inverter denotes an element for generating an alternating voltage from a direct voltage. Inverters can be designed as two-phase inverters, for example. Inverters include electrical or electronic switching elements, e.g. MOSFET or IGBT. An element for rectification refers to an electrical element for generating a direct voltage from an alternating voltage. Such elements for rectification can, for example, comprise a plurality of power diodes. A step-up converter denotes a DC-DC converter, an amount of an output voltage of the step-up converter being greater than an amount of an input voltage of the step-up converter. Analogously, a step-down converter also designates a DC-DC converter, an amount of an output voltage of the step-down converter being smaller than an amount of the input voltage of the step-down converter. An element for voltage transformation denotes an element for alternating voltage conversion, wherein an amount of an amplitude of an input voltage can be different from an amount of an amplitude of an output voltage.

The charging device can be connected on the input side to the external electrical network and can, for example, have a first voltage input for such a connection. On the output side, the charging device can be connected to the battery, it being possible for switches or circuit breakers to be arranged between a voltage output of the charging device and the battery, by means of which the charging device can be electrically connected to or disconnected from the battery.

Furthermore, the intermediate circuit capacitor of the charging device can be charged by means of the solar voltage or a transformed solar voltage. For this purpose, in addition to a first voltage input for connecting the external electrical network, the charging device can have a further voltage input for e.g. the solar voltage or the transformed solar voltage, with a voltage applied to the further voltage input dropping directly across the intermediate circuit capacitor.

In this way, electrical energy generated from solar energy can advantageously be transferred to the battery by means of an existing charging device for charging the battery, whereby a number of electrical components required overall is reduced. For example, electrical elements connected downstream of the intermediate circuit capacitor, i.e. electrical elements arranged between the intermediate circuit capacitor and the battery, can be used both for transmitting electrical energy from the external electrical network to the battery and for transmitting electrical energy generated from solar energy to the battery. This functional integrity results in an advantageous manner in a reduced installation space requirement when realizing solar-assisted charging of a battery and in reduced production costs. The additional solar-assisted charging of the battery advantageously results in an extension of the range of an electric or hybrid vehicle and compensation for self-discharge losses in the battery. If the battery to be charged is a low-voltage battery, there is advantageously support for a low-voltage on-board network during operation of the electric or hybrid vehicle and when the electric or hybrid vehicle is at a standstill.

Furthermore, the device additionally comprises at least one DC voltage converter, wherein the solar voltage can be transformed to a predetermined intermediate circuit voltage by means of the DC voltage converter. The intermediate circuit capacitor can then be charged using the transformed solar voltage. Here, the transformed solar voltage drops across the intermediate circuit capacitor. For example, a voltage output of the at least one solar module can be electrically connected to a voltage input of the DC voltage converter, a voltage output of the DC voltage converter being electrically connected to the previously described further voltage input of the charging device or directly to the intermediate circuit capacitor. This advantageously results in the solar voltage generated by the at least one solar module being able to be adapted to a desired intermediate circuit voltage.

According to the invention, the device additionally comprises at least one control and evaluation device, with the level of the intermediate circuit voltage being able to be evaluated by means of the control and evaluation device. A transfer of electrical energy from the intermediate circuit capacitor to the battery can be controlled by means of the control and evaluation device. Electrical energy is transmitted if the intermediate circuit voltage is greater than or equal to a first predetermined voltage threshold. The control and evaluation device can also evaluate a level of the solar voltage and control the DC voltage converter described above in such a way that it sets a desired level of the transformed solar voltage.

Furthermore, the control and evaluation device can close circuit breakers or switches which are arranged between a voltage output of the charging device and the battery if the intermediate circuit voltage is greater than or equal to the first predetermined voltage threshold. As a result, the charging device is electrically connected to the battery.

This advantageously results in a particularly simple and efficient charging of the battery using the electrical energy generated from the solar energy. In particular, the first predetermined voltage threshold ensures that electrical energy currently stored in the intermediate circuit capacitor is large enough to charge the battery. The first predetermined voltage threshold can also be selected such that an intermediate circuit voltage or an intermediate circuit voltage transformed by means of electrical components arranged between the intermediate circuit capacitor and the battery is greater than a current battery voltage. For this purpose, the control and evaluation device can be connected to the battery or a control device of the battery in terms of data technology and the first predetermined voltage threshold as a function of a current battery voltage and / or current properties of the battery, for example a current state of charge of the battery (SOC) and / or a current one Determine the operating status of the battery (SOH).

In a further embodiment, a transfer of electrical energy from the intermediate circuit capacitor to the battery can be ended by means of the control and evaluation device if the intermediate circuit voltage is less than a second predetermined voltage threshold. The second predetermined voltage threshold can be different from the first predetermined voltage threshold, in particular smaller than the first predetermined voltage threshold. The second predetermined voltage threshold can also be equal to the first predetermined voltage threshold. For example, the control and evaluation device can control the opening of the switches or circuit breakers arranged between the voltage output of the charging device and the battery if the intermediate circuit voltage is less than the second predetermined voltage threshold. This ensures that the high-voltage side (electronics and high-voltage battery) is only active when enough solar energy is available to charge the high-voltage battery. The second predetermined voltage threshold can also be determined as a function of a current battery voltage and / or current properties of the battery.

In a further embodiment, the at least one solar module and the at least one DC voltage converter form an overall module, an output voltage of the overall module being the transformed solar voltage, that is to say equal to an output voltage of the DC voltage converter. The overall module can also include the control and evaluation device described above. For example, the at least one solar module and the at least one DC voltage converter can be arranged within a common housing. The control and evaluation device can also be arranged within this housing.

This results in an advantageous manner that all additional electrical and electronic components that are necessary for additional solar-assisted charging of the battery are integrated in an overall module, which can be arranged, for example, in an electric or hybrid vehicle. In this case, only one additional voltage input is required in an existing charging device, for example in an electric or hybrid vehicle be created, which enables a voltage to be applied directly to the intermediate circuit capacitor. Additional further electrical or electronic components do not have to be integrated into the existing charging device.

In an alternative embodiment, the at least one charging device and the at least one DC voltage converter form an overall module, the charging device having at least one further voltage input in addition to the first voltage input, wherein a voltage applied to the at least one further voltage input is an input voltage of the DC voltage converter, wherein a Output voltage of the DC voltage converter drops across the intermediate circuit capacitor. The entire module can also be referred to as an extended charging device. The existing charging device, e.g. of an electric or hybrid vehicle, is expanded by an additional DC voltage converter, which transforms a solar voltage generated by a solar module to a desired voltage level. This advantageously results in the solar module being able to be arranged in the electric or hybrid vehicle independently of the DC voltage converter. As a result, the solar module can be designed with less space requirements.

In addition, the control and evaluation device can also be included in the overall module, which also comprises the charging device and the at least one DC voltage converter.

A charging device is also proposed, in particular a charging device of an electric or hybrid vehicle, for transmitting electrical energy from an external electrical network to a battery, for example a high-voltage or low-voltage battery described above. The charging device has a first voltage input for connecting the external electrical network. The charging device further comprises at least one intermediate circuit capacitor.

Furthermore, the charging device has at least one further voltage input for a solar voltage, wherein the intermediate circuit capacitor can be charged by means of a voltage applied to the further voltage input. In this way, a charging device expanded by a further voltage input with respect to existing shop devices is proposed, wherein the at least one further voltage input can be electrically connected directly to the intermediate circuit capacitor. This results in an advantageous manner that by means of the proposed charging device, for example, a solar voltage as described above can be used for additional solar-assisted charging of the battery via part of the charging device.

Furthermore, the charging device additionally comprises at least one DC voltage converter, wherein a voltage applied to the further voltage input can be transformed to a predetermined intermediate circuit voltage by means of the DC voltage converter. A voltage applied to the further voltage input forms an input voltage of the DC voltage converter, an output voltage of the DC voltage converter dropping across the intermediate circuit capacitor. This results in an advantageous manner that a voltage applied to the further voltage input can be transformed in such a way that a desired intermediate circuit voltage can be achieved. In this case, a charging device, which is additionally expanded to include a DC voltage converter, is proposed, which advantageously enables improved additional solar-assisted charging of the battery.

A method is also proposed for solar-assisted charging of a battery, in particular a battery of an electric or hybrid vehicle, for example a high-voltage or low-voltage battery. Solar-assisted charging takes place by means of at least one solar module, the at least one solar module generating solar voltage. A charging device is used to charge the battery from an external electrical network.

Furthermore, the solar voltage or a transformed solar voltage is applied to an intermediate circuit capacitor of the charging device, the electrical energy stored in the intermediate circuit capacitor then being transferred to the battery. This advantageously enables additional solar-assisted charging of the battery, part of an existing charging device being used to transfer electrical energy from the solar module to the battery.

According to the invention, a level of the intermediate circuit voltage is evaluated, with electrical energy being transferred from the intermediate circuit capacitor to the battery if the intermediate circuit voltage is greater than or equal to a first predetermined voltage threshold. Alternatively or cumulatively, a transfer of electrical energy from the intermediate circuit capacitor to the battery is terminated if the intermediate circuit voltage is less than a second predetermined voltage threshold. This advantageously results in efficient additional solar-assisted charging of the battery using an existing charging device.

The proposed device, the proposed method and the proposed charging device enable solar-assisted charging of the battery even when no external electrical network is connected. In particular, the battery can also be charged while an electric or hybrid vehicle is in operation. This advantageously extends the range of the electric or hybrid vehicle.

• 1 ein schematisches Schaltbild einer ersten Ausführungsform einer Vorrichtung zum solargestützten Laden einer Batterie und
• 2 ein schematisches Schaltbild einer weiteren Ausführungsform einer Vorrichtung zum solargestützten Laden einer Batterie.

The invention is explained in more detail using second exemplary embodiments. The figures show:

• 1 a schematic circuit diagram of a first embodiment of a device for solar-assisted charging of a battery and
• 2 a schematic circuit diagram of a further embodiment of a device for solar-assisted charging of a battery.

In the following, the same reference symbols designate elements with the same or similar technical properties.

In 1 Figure 3 is a schematic circuit diagram of a first embodiment of an apparatus 1 for solar-assisted charging of a battery 2 shown with the battery 2 is a high-voltage battery of an electric or hybrid vehicle, not shown. Also shown is a solar roof 3rd formed solar module, by means of the solar roof 3rd a solar voltage Us can be generated. The device 1 comprises a charging device 4th to charge the battery 2 from an external electrical network (not shown). The charging device 4th has a first voltage input 5 to connect the external electrical network. The charging device also includes 4th an intermediate circuit capacitor 6th . Above the intermediate circuit capacitor 6th an intermediate circuit _voltage U z drops. The charging device 4th further has a first rectifier 7th on, by means of the rectifier 7th an alternating voltage of the external electrical network can be rectified. The rectifier 7th downstream is a step-up converter 8th , which converts the rectified voltage to a desired intermediate circuit voltage Uz transforms. The boost converter 8th downstream is the intermediate circuit capacitor 6th . The charging device also includes 4th an inverter 9 , a transformer 10 and another rectifier 11 . By means of the inverter 9 is the intermediate circuit voltage Uz convertible into an alternating voltage with a desired amplitude and a desired frequency. By means of the transformer 10 this converted voltage can be transformed to a desired voltage level, for example a high-voltage voltage of the electric or hybrid vehicle. By means of the further rectifier 11 the transformed voltage can be rectified and sent to a voltage output 12th the loading device can be applied. Between the voltage output 12th the charging device 4th and the battery 2 are still contactors 13th arranged, by means of which an electrical connection between the voltage output 12th the charging device 4th and the battery 2 can be made or separated.

The device further comprises 1 a DC / DC converter 14th and a control and evaluation device 15th . Here form the solar roof 3rd , the DC / DC converter 14th and the control and evaluation device 15th a complete module 16 out. The DC / DC converter 14th has a voltage input 17th on which the solar voltage Us is created. The DC voltage converter 14th a voltage output 18th on that electrically with a voltage output 19th of the entire module 16 connected is. The control and evaluation device 15th evaluates a level or a temporal course of a level of solar voltage Us out. The overall module 16 has further control outputs 20th on which the control and evaluation device 15th data-related control commands to the charging device 4th and other control devices, not shown, of the electric or hybrid vehicle, for example via a CAN bus 21 , can transfer. The control and evaluation device 15th an opening or closing of the circuit breakers 13th Taxes.

The charging device 4th has another voltage input 22nd on, the electrical one with the voltage output 19th of the first overall module 16 connected is. The one at the other voltage input 22nd applied voltage drops directly across the intermediate circuit capacitor 6th and is used to charge the intermediate circuit capacitor 6th . Here is the one at the other voltage input 22nd applied voltage by means of the DC voltage converter 14th transformed solar voltage. It should be noted that the DC-DC converter 14th can be designed as a galvanically isolated DC voltage converter to the solar roof 3rd galvanically from the intermediate circuit capacitor 6th to decouple.

Using the in 1 device shown 1 is an additional charging of the battery in an advantageous manner 2 besides the familiar charging of the battery 2 from the external electrical network possible, with already existing electrical elements of the charging device in an advantageous manner 4th , namely the inverter 9 , the transformer 10 and the further rectifier 11 both for transferring electrical energy from the external electrical network to the battery 2 as well as for transferring electrical energy generated from solar energy to the battery 2 can be used. The control and evaluation device 15th is by means of the control outputs 20th with control inputs 23 the charging device 4th connected and can be a level of the intermediate circuit voltage Uz evaluate. By means of the control and evaluation device 15th is a transfer of electrical energy from the intermediate circuit capacitor 6th into the battery 2 controllable, with a transfer taking place if the intermediate circuit voltage Uz is greater than or equal to a first predetermined voltage threshold. In this case, the control and evaluation device 15th the circuit breakers 13th shut down. Next is by means of the control and evaluation device 15th a transfer of electrical energy into the battery 2 terminable if the intermediate circuit voltage Uz is less than a second predetermined voltage threshold. In this case, the control and evaluation device 15th an opening of the circuit breaker 13th Taxes.

In 2 Figure 3 is a schematic circuit diagram of another embodiment of an apparatus 1 for solar-assisted charging of a battery 2 of an electric or hybrid vehicle. Here is the device 1 analogous to the in 1 device shown 1 built up. With regard to an explanation of the illustrated electronic and electrical components, reference is therefore made to the explanations 1 referenced. In contrast to the in 1 illustrated embodiment of the device 1 now form the charging device 4th , the DC / DC converter 14th and the control and evaluation device 15th a complete module 24 out. The overall module 24 can also be referred to as an extended charging device. The extended charging device, analogous to that in 1 shown charging device 4th a first voltage input 5 and another voltage input 22nd on. Here there is an output voltage of the solar roof 3rd , namely the solar voltage Us , directly at the other voltage input 22nd at. The further voltage input 22nd is electrical with a voltage input 17th of the DC / DC converter 14th connected. One at a voltage output 18th of the DC / DC converter 14th applied voltage drops directly across the intermediate circuit capacitor 6th and thus serves to charge the intermediate circuit capacitor 6th .

List of reference symbols

1

contraption

2

battery

3

Solar roof

4th

Charging device

5

first voltage input of the charging device

6th

DC link capacitor

7th

Rectifier

8th

Boost converter

9

Inverter

10

transformer

11

further rectifier

12th

Voltage output of the charging device

13th

Circuit breaker

14th

DC voltage converter

15th

Control and evaluation device

16

Total module

17th

Voltage input of the DC / DC converter

18th

Voltage output of the DC / DC converter

19th

Voltage output of the entire module

20th

Control outputs of the entire module

21

CAN bus

22nd

further voltage input of the charging device

23

Control inputs of the charging device

24

Total module

Us

Solar voltage

Uz

Intermediate circuit voltage

Claims (6)

Device for solar-assisted charging of a battery (2), in particular a battery (2) of an electric or hybrid vehicle, by means of at least one solar module, wherein a solar voltage (Us) can be generated by means of the at least one solar module, the device (1) at least one charging device (4) for transmitting electrical energy from an external electrical network to the battery (2), wherein the charging device (4) comprises at least one intermediate circuit capacitor (6), the intermediate circuit capacitor (6) using the solar voltage (Us) or a transformed solar voltage can be charged, the device (1) additionally comprising at least one DC voltage converter (14), the solar voltage (Us) being transformable to a predetermined intermediate circuit voltage (Uz) by means of the DC voltage converter (14), the intermediate circuit capacitor (6) being transformed by means of the transformed solar voltage is chargeable, characterized in that the device (1 ) additionally comprises at least one control and evaluation device (15), the level of the intermediate circuit voltage (Uz) being able to be evaluated by means of the control and evaluation device (15), with the transmission of electrical energy from the intermediate circuit capacitor by means of the control and evaluation device (15) (6) can be controlled to the battery (2), the transmission taking place, if the intermediate circuit voltage (Uz) is greater than or equal to a first predetermined voltage threshold. Device according to Claim 1 , characterized in that a transmission can be terminated by means of the control and evaluation device (15) if the intermediate circuit voltage (Uz) is less than a second predetermined voltage threshold. Device according to one of the Claims 1 to 2 , characterized in that the at least one solar module and the at least one DC voltage converter (14) form an overall module (16), an output voltage of the overall module (16) being the transformed solar voltage. Device according to one of the Claims 1 to 2 , characterized in that the at least one charging device (4) and the at least one DC voltage converter (14) form an overall module (24), the charging device (4) having at least one further voltage input (22) in addition to the first voltage input (5), wherein a voltage applied to the at least one further voltage input (22) is an input voltage of the DC voltage converter (14), an output voltage of the DC voltage converter (14) falling across the intermediate circuit capacitor (6). Charging device, in particular charging device (4) of an electric or hybrid vehicle, for transmitting electrical energy from an external electrical network to a battery (2), the charging device (2) having a first voltage input (5) for connecting the external electrical network, wherein the charging device (4) comprises at least one intermediate circuit capacitor (6), the charging device (4) having at least one further voltage input (22) for a solar voltage (Us) or transformed solar voltage, with the voltage applied to the further voltage input (22) being the Intermediate circuit capacitor (6) can be charged, the charging device comprising at least one DC voltage converter (14), wherein a voltage applied to the further voltage input (22) can be transformed to an intermediate circuit voltage (Uz) by means of the DC voltage converter (14), characterized in that the device (1) In addition, at least one tax and A. evaluation device (15), wherein the level of the intermediate circuit voltage (Uz) can be evaluated by means of the control and evaluation device (15), with the transmission of electrical energy from the intermediate circuit capacitor (6) to the battery (6) by means of the control and evaluation device (15). 2) is controllable, the transmission taking place if the intermediate circuit voltage (Uz) is greater than or equal to a first predetermined voltage threshold. A method for solar-assisted charging of a battery (2), in particular a battery (2) of an electric or hybrid vehicle, by means of at least one solar module, the at least one solar module generating a solar voltage (Us), with a charging device (4) for transmitting electrical energy from an external electrical network to the battery (2), a solar voltage transformed by a DC voltage converter (14) being applied to an intermediate circuit capacitor (6) of the charging device (4), characterized in that the level of the intermediate circuit voltage (Uz) is evaluated, electrical energy being transferred from the intermediate circuit capacitor (6) to the battery (2) if the intermediate circuit voltage (Uz) is greater than or equal to a first predetermined voltage threshold and / or electrical energy is transferred from the intermediate circuit capacitor (6) to the battery (2) is ended if the intermediate circuit voltage (Uz) is less than one second predetermined voltage threshold.

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