EP4308403A1

EP4308403A1 - Charging station and method for operating a charging station

Info

Publication number: EP4308403A1
Application number: EP22718609.5A
Authority: EP
Inventors: Johannes Visosky
Original assignee: Keba Energy Automation GmbH
Current assignee: Keba Energy Automation GmbH
Priority date: 2021-03-31
Filing date: 2022-03-24
Publication date: 2024-01-24
Also published as: DE102021108246A1; WO2022207467A1

Abstract

Proposed is a charging station (1) for charging and/or discharging an energy store (2) of an electric vehicle (3) with/of electric energy by means of a polyphase supply system (4) that can be coupled to the charging station (1), the charging station (1) comprising: an AC-to-DC converter (400) which can be coupled to a number of phases (L1, L2, L3) of the polyphase supply system (4); a DC link (500) which is connected downstream of the AC-to-DC converter (400) and includes a number of DC link capacitors (501, 502) which are connected between a positive output conductor (401) and a negative output conductor (402) of the AC-to-DC converter (400); and a DC-to-DC converter (600) which is connected downstream of the DC link (500) and includes a first half bridge (H1) connected to the positive output conductor (401) as well as a second half bridge (H2) connected to the negative output conductor (402), the center tap (M1) of the first half bridge (M2) and the center tap (M2) of the second half bridge (H2) being connected via a choke (605).

Description

CHARGING STATION AND METHOD OF OPERATING A

CHARGING STATION

TECHNICAL AREA

The invention relates to a charging station for charging and/or discharging an energy store of an electric vehicle with electrical energy by means of a multi-phase network that can be coupled to the charging station. The inventions also relate to a method for operating such a charging station.

STATE OF THE ART

The present technical field relates to the charging of an energy store in an electric vehicle. For example, the applicant's European patent EP 2 882 607 B1 describes a charging station for electric vehicles, with at least one input interface for feeding electrical energy from a stationary power supply network into the charging station, with a connection socket for connecting a charging plug of an electric vehicle for the controlled delivery of electrical energy to the electric vehicle, with a plurality of electrotechnical components comprising an electronic control device for switching, measuring or monitoring the recorded and / or emitted electrical energy, and with a housing enclosing the electrotechnical African components.

Different charging methods are known for electric vehicles, for example there are fast charging methods in which the charging station provides the electric vehicle with direct voltage/current (DC), or alternatively alternating current charging - methods in which the electric vehicle has single-phase or multi-phase, in particular two-phase or three-phase, alternating current (AC) is made available, which the charging vehicle uses a built-in AC/DC converter to convert into direct current for the energy store to be charged. When changing charging process, charging logic in the vehicle or the energy storage device controls the charging process.

Consequently, both an AC/DC converter and a DC/DC converter (direct current voltage converter) are used in a charging station suitable for DO charging. For this purpose, the document EP 2 515 424 B1 shows a DC voltage converter for stepping up and/or stepping down voltages, with at least one first connection and at least one second connection and at least one third connection, with an energy flow between the first and second connections on the one hand and the third connection on the other hand is possible, a first half-bridge that can be operated in a clocked manner, which is connected in parallel to the first connection and has a series connection of at least one first switching device and a second switching device, and a second half-bridge that can be operated in a clocked manner and is parallel to is connected to the second connection and has a series connection of at least one third switching device and at least one fourth switching device, where the midpoints of the two half-bridges that can be operated in a clocked manner are connected to one another via at least one choke, with this at least one choke as the flying inductance is operated.

Other conventional solutions are from the documents EP 3 664244 A1,

EP 3 729 593 A1, DE 11 2013 007 137 T5, EP 2 465 176 B1,

DE 10 2016 212 135 A1, DE 10 2017 100 138 A1, WO 2020/167132 A1 and DE 10 2009 060 364 A1 are known.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to create an improved charging station for charging and/or discharging an energy store of an electric vehicle. The task is solved by a charging station with the features of claim 1 and by a method with the features of claim 17.

According to a first aspect, a charging station, in particular a charging station without a transformer, is proposed for charging and/or discharging an energy store of an electric vehicle with electrical energy by means of a multiphase network that can be coupled to the charging station. The charging station includes an AC/DC converter that can be coupled to a number of phases of the multiphase network, an intermediate circuit connected downstream of the AC/DC converter, which has a number of output conductors connected between a positive output conductor and a negative output conductor of the AC/DC converter Intermediate circuit capacitors, and a DC/DO converter connected downstream of the intermediate circuit, which has a first half bridge connected to the positive output conductor and a second half bridge connected to the negative output conductor, with the center tap of the first half bridge and the center tap of the second half bridge being connected via a choke are.

The charging station has, for example, a housing, in particular a waterproof housing, with an interior space in which a plurality of electrical and/or electronic components and a connection socket connected to at least one of the components for connecting a charging plug for the energy store of the electric vehicle are arranged .

The charging station can also be referred to as a charging connection device. The charging station is designed in particular as a wall box. The charging station is suitable for charging or regenerating the energy store of an electric vehicle by electrically connecting the charging station to the energy store or the charging electronics of the electric vehicle via its connection socket and the charging plug of the electric vehicle. The charging station acts as a source of electrical energy for the electric vehicle, with the electrical see energy can be transferred to an energy storage device of the electric vehicle by means of a connection socket and charging plug. The charging station can also be referred to as an intelligent charging station for electric vehicles.

Examples of the electrical and/or electronic components of the charging station include a contactor, universal current-sensitive circuit breaker, direct current, overcurrent and fault current monitoring device, relay, connection terminal, electronic circuits and a control device, for example comprising a printed circuit board on which a plurality of electronic Are arranged components for controlling and / or measuring and / or monitoring the energy states at the charging station or in the connected electric vehicle.

The AC/DC converter can also be referred to as a converter. The AC/DC converter is set up in particular for converting an AC voltage into a DC voltage and/or for converting a DC voltage into an AC voltage. The charging station includes in particular an intermediate circuit downstream of the converter with a number of intermediate circuit capacitors, which are connected to an intermediate circuit center point.

The multiphase network is, for example, a multiphase subscriber network. The multi-phase network can also be a multi-phase power supply network. In particular, the polyphase network has a number of phases, for example LI, L2 and L3, and a neutral conductor (also denoted by N).

It should be noted that the “charging and/or discharging of an energy store” includes both supplying electrical energy and drawing electrical energy. This means that the energy store can act as a consumer or as a producer in the subscriber network.

In particular, a control unit is provided which can control individual or all elements and units of the charging station. Furthermore, the choke of the DC/DC converter can preferably be operated as a flying inductance. here the DC/DO converter with the flying inductance can function like a quasi-potential separation. For example, the DC/DO converter has a number of semiconductor switching elements, which are in the form of MOSFETs, for example. In particular, the DC/DC converter works as a voltage inverter, the DC/DC converter preferably being driven in such a way that the diodes of the MOSFETs never become conductive in an undesired manner during undisturbed operation. During operation, the inductance preferably flies back and forth between the input potential and the output potential. This functionally results in the quasi-potential separation. In the event of a ground fault in the energy store (accumulator, rechargeable battery), the potential of the energy store can move freely relative to the potential of the intermediate circuit of the charging station. The regulation of the inductor current of the inductor in the event of a ground fault is preferably not affected. The duty cycle of the DC/DC converter does not have to be changed either.

The proposed DC/DC converter preferably behaves functionally like a DC/DC converter with a transformer. The output potential to ground can be freely shifted within certain limits during operation without affecting the function of the DC/DC converter.

With appropriate dimensioning of the semiconductor switching elements of the DC/DC converter, it is possible for a person to touch one pole of the output of the charging station without a significant direct current flowing through the person's body.

According to one embodiment, the choke of the DC/DC converter can be operated as a flying inductor.

According to a further embodiment, the charging station is a transformerless charging station. According to a further embodiment, the DC/DO converter is designed as a bidirectional DC/DO converter for stepping up and/or stepping down voltages. The DC/DO converter can also be referred to as a DC voltage converter. In particular, the DC/DC converter has a symmetrical design and can buck and boost in both directions.

According to a further embodiment, the respective half-bridge comprises a series connection of two semiconductor switching elements. The center tap of the half-bridge is between the two series-connected semiconductor switching elements.

According to a further embodiment, the respective semiconductor switching element is designed as a MOSFET, preferably as a SiC MOSFET, or as an IGBT or as a SiC cascode.

In particular, the present topology acts as a bidirectional voltage translation device (DC transformer), the voltage translation, which can be adjusted by the control unit, depending on the ratio between the on-time and off-time of the semiconductor switching elements. With a duty cycle of 50%, the voltage transformation ratio is 1.

According to a further embodiment, the charging station comprises a control unit which is set up to control the semiconductor switching elements in such a way that two corresponding semiconductor switching elements of the two half-bridges switch simultaneously, in particular switch with an identical switch-on delay.

In this case, in particular, the two mains-side semiconductor switching elements of the half-bridges can be switched simultaneously, and the two load-side semiconductor switching elements of the two half-bridges can also be switched simultaneously. In particular, the control unit never turns on the semiconductor switching elements of a half bridge at the same time.

According to a further embodiment, an interference suppression circuit is arranged between the intermediate circuit and the DC/DO converter, which circuit has two interference suppression capacitors connected in parallel with the intermediate circuit capacitors. The node connecting the two interference suppression capacitors is connected to earth potential. The ground potential can also be referred to below as ground or earth.

According to a further embodiment, the charging station includes an intermediate output circuit connected downstream of the DC/DC converter with a number of capacitors which are connected between a negative output potential tap and a positive output potential tap of the charging station and can be arranged in parallel with the energy store of the electric vehicle.

According to a further embodiment, an interference suppression circuit on the load side is arranged between the DC/DC converter and the intermediate output circuit. The load-side interference suppression circuit has two interference suppression capacitors connected in parallel with the number of capacitors in the output intermediate circuit, with the node connecting the two interference suppression capacitors being connected to ground potential.

According to a further embodiment, the control unit is set up to activate the semiconductor switching elements in such a way that the line-side semiconductor switching element of the first half-bridge and the load-side semiconductor switching element of the second half-bridge have overlapping switch-on times (switch-on times) and/or that the line-side semiconductor switching element of the second half-bridge and the load-side semiconductor switching element of the first half-bridge have overlapping turn-on times. The ratio of the switch-on times of the network-side semiconductor switching elements corresponds to the switch-on times of the load-side semiconductor switching elements preferably a predetermined quotient.

This activation with the overlapping switch-on times causes a charge shift in the interference suppression capacitors in such a way that the potential of the energy store can be adjusted relative to ground potential. This allows balancing with respect to earth potential (mass).

The control unit can be implemented in terms of hardware and/or software. In the case of a hardware implementation, the control unit can be designed as a device or as part of a device, for example as a computer or as a microprocessor or as a control computer. In the case of a software implementation, the control unit can be designed as a computer program product, as a function, as a routine, as part of a program code, or as an executable object.

According to a further embodiment, the control unit is set up to switch off one of the line-side semiconductor switching elements of the two half-bridges earlier than the other line-side semiconductor switching element of the two half-bridges, so that a line-side primary circuit and a load-side secondary circuit can be coupled via the inductor or is provided.

In accordance with a further embodiment, the control unit is set up to switch off one of the load-side semiconductor switching elements of the two half-bridges earlier than the other load-side semiconductor switching element of the two half-bridges, so that coupling of a mains-side primary circuit and a load-side secondary circuit via the inductor is made possible or is provided.

According to a further embodiment, the semiconductor switching elements are MOSFETs. The control unit is set up to open the gates of the MOS To control FETs of the half-bridges with such phase-shifted control signals that a coupling of a mains-side primary circuit and egg nes load-side secondary circuit via the inductor is made possible or provided.

In this embodiment, the symmetry of the output voltage with respect to ground can be regulated relative to one another by a slight phase shift in the drive signals of the first half-bridge and the second half-bridge. The phase shift periodically results in a short-term coupling of the input circuit and the output circuit. This even if no active power is being transmitted through the charging station.

According to a further embodiment, the control unit has a charging current regulator, a balancing current regulator and a differential voltage regulator. In this case, the charging current controller is set up to set the ratio of the switch-on times of the line-side semiconductor switching elements to the switch-on times of the load-side semiconductor switching elements. The balancing current controller is set up to provide an adjustment signal for balancing the potential at the negative output potential tap and the potential at the positive output potential tap with respect to ground potential. Furthermore, the differential voltage controller is set up to provide a target value for the setting signal as a function of at least one measured voltage in the load-side secondary circuit.

According to a further embodiment, the differential voltage regulator is slower than the balancing current regulator.

According to a further embodiment, the anode of a first diode is coupled to the negative output potential tap and the cathode of the first diode is coupled to the intermediate circuit center point. Furthermore, the anode of a second diode is coupled to the intermediate circuit center and the cathode of the second diode is coupled to the positive output potential tap. According to a further embodiment, the anode of the first diode is connected to the negative output potential tap and the cathode of the first diode is connected to the intermediate circuit center point. Furthermore, the anode of the second diode is connected to the intermediate circuit center and the cathode of the second diode is connected to the positive output potential tap.

According to a further embodiment, an overvoltage protection element is coupled between the intermediate circuit center point and a node to which the cathode of the first diode is connected and to which the anode of the second diode is connected. The overvoltage protection element is in particular a varistor or a bidirectional suppressor diode, such as a bidirectional transildiode.

In accordance with a further embodiment, a series connection made up of a first overvoltage protection element and the first diode is arranged between the intermediate circuit center point and the negative output potential tap. Furthermore, a series connection made up of a second overvoltage protection element and the second diode is arranged between the intermediate circuit center point and the positive output potential tap.

According to a further embodiment, an EMC filter device and an LCL filter device connected downstream of the EMC filter device are coupled between three mains-side connection terminals for the three phases of the multi-phase network and the AC/DC converter. The LCL filter device preferably includes at least three inductors and three capacitors.

According to a further embodiment, the AC/DC converter is designed as a 3-point AC/DC converter.

According to a further embodiment, a resonant capacitor is connected to the center tap of the first half-bridge, which is parallel to the mains side semiconductor switching element of the first half-bridge is connected, with a further resonant capacitor connected to the center tap of the first half-bridge, which is connected in parallel to the load-side semiconductor switching element of the first half-bridge ^¬ th. Furthermore, a ^reversing capacitor is connected to the center tap of the second half bridge, which is connected in parallel to the line-side semiconductor switching element of the second half bridge, with a reversing ^capacitor connected to the center tap of the second half bridge, which is parallel to the load-side semiconductor switching element of the second half ^bridge is switched. The reversing capacitors bring about a ^soft switching and thus a reduction in the switching losses. The ^reversing capacitors can also be referred to as ZVS capacitors of the ^snubber capacitors (ZVS; zero-voltage switching).

According to a further embodiment, the charging station comprises a ^connection socket with a number of coupling points for connecting a charging cable. In particular, the charging cable connects the electric vehicle or the energy store of the electric vehicle to the connection socket and is set up to transmit the charging current.

The connection socket can have further coupling points, for example to connect a protective conductor and/or one or more signal or data ^transmission conductors. The connection socket can be designed in such a way that it is compatible with different specifications, in particular the connection socket can be backwards compatible, which means that it can be coupled, for example, to a ^charging cable for single-phase, two-phase or three-phase ^charging . In embodiments, the charging station can have a number of connection sockets for differently configured charging cables.

According to a further embodiment, the charging station includes a communi ^¬ cation module. The communication module is preferably set up to negotiate a charging plan with charging electronics of the energy store coupled to the charging station. Negotiation takes place, for example, as described in ISO 15118. For example, the charging electronics of the energy store requests a certain charging power via the communication module at the charging station and the charging station, for example a control device of the charging station, determines whether the charging power requested can be provided. In particular, a current state of the subscriber network and/or the power supply network is taken into account. If the requested charging power cannot be provided, the charging station can make a “counterproposal” via the communication module, which can be accepted by the charging electronics of the energy store, or the charging electronics can make its own request again. In this way, the charging station and the charging electronics communicate until the charging plan is negotiated. Negotiating the charging plan can be part of the pairing process when a battery is reconnected to the charging station.

According to a further embodiment, the charging station comprises a power switching device for safely disconnecting the number of output conductors from the multi-phase subscriber network. The power switching device can be designed as an electro-mechanical element, such as a contactor or a four-phase relay. The power switching device can be designed and controlled individually for a respective phase of the multiphase subscriber network and/or for a respective output conductor of the switching matrix, so that individual assignments can be interrupted by means of the power switching device, for example.

According to a further embodiment, a reversing capacitor is connected to the center tap of the first half-bridge, which is connected in parallel to the one input-side semiconductor switching element of the first half-bridge, with a further reversing capacitor connected to the center tap of the first half-bridge, which is connected in parallel to the load-side semiconductor switching element of the first Half bridge is switched. Furthermore, a reversing capacitor is connected to the center tap of the second half-bridge, which is parallel to the one output-side semiconductor switching element of the second half-bridge is connected, with a reversing capacitor connected to the center tap of the second half-bridge, which is connected in parallel to the load-side semiconductor switching element of the second half-bridge. The reversing capacitors cause soft switching and thus a reduction in switching losses. The oscillating capacitors can also be referred to as ZVS capacitors or ^snubber capacitors (ZVS; zero-voltage switching). In this respect, it is possible to connect a ^resonant capacitor in parallel with each semiconductor switching element in order to implement a loss-reducing soft switching behavior, ie a ZVS switching behavior.

According to a second aspect, a method for operating a ^charging station for charging and/or discharging an energy store of an electric ^vehicle with electrical energy using a multi-phase network that can be coupled to the charging station is proposed, the charging station having a ^number of phases of the AC/DC converter that can be coupled to a polyphase network, an intermediate circuit connected downstream of the AC/DC converter, which has a number of intermediate circuit capacitors connected between a positive output conductor and a negative output conductor of the AC/DC converter, and a DC/DO converter connected downstream of the intermediate circuit , which has a first half-bridge connected to the positive output conductor and a second half-bridge connected to the negative output conductor. The procedure includes ^:

Controlling the controllable semiconductor switching elements of the converter in such a way that currents with at least two different current intensities, in particular with at least two different ^effective ^values , result on the phases.

This method has the same advantages as explained for the charging station according to the first aspect. The embodiments described for the proposed ^charging station apply to the proposed method. speaking. Furthermore, the definitions and explanations for the charging station also apply accordingly to the proposed method.

As used herein, "a" is not necessarily to be construed as being limited to exactly one element. Rather, a plurality of elements, such as two, three or more, can also be provided. Any other count word used here should also not be understood to mean that there is a restriction to precisely the stated number of elements. Rather, numerical deviations upwards and downwards are possible, unless otherwise stated.

Further possible implementations of the invention also include combinations of features or embodiments described above or below with regard to the exemplary embodiments that are not explicitly mentioned. The person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

Further advantageous refinements and aspects of the invention are the subject matter of the subclaims and of the exemplary embodiments of the invention described below. The invention is explained in more detail below on the basis of preferred embodiments with reference to the enclosed figures.

Fig. 1 shows schematically an arrangement with a first embodiment of a charging station and an electric vehicle;

2 shows a schematic circuit diagram of a second embodiment of a charging station for charging and/or discharging an energy store of an electric vehicle;

3 shows a schematic circuit diagram of a third embodiment of a charging station for charging and/or discharging an energy store of an electric vehicle; Fig. 4 shows a schematic circuit diagram of a fourth embodiment of a charging station for charging and / or discharging an Energiespei chers an electric vehicle!

Fig. 5 shows a schematic circuit diagram of a fifth embodiment of a charging station for charging and / or discharging an energy storage chers an electric vehicle!

Fig. 6 shows a schematic circuit diagram of a sixth embodiment of a charging station for charging and / or discharging an energy storage chers an electric vehicle!

FIG. 7 shows the schematic circuit diagram of FIG. 6 with the mains-side primary circuit drawn in and the load-side secondary circuit drawn in!

FIG. 8 shows the schematic circuit diagram of FIG. 6 with the circuit of the balancing current drawn in!

Fig. 9 shows diagrams to illustrate the inductor current and various signals of the DC/DC converter!

FIG. 10 shows the schematic circuit diagram of FIG. 6 with the balancing control drawn in! and

FIG. 11 shows a schematic flowchart of a method for operating a charging station for charging and/or discharging an energy store of an electric vehicle.

In the figures, elements that are the same or have the same function have been provided with the same reference symbols, unless otherwise stated. Fig. 1 schematically shows an arrangement with a first embodiment of a charging station 1 and an electrical energy store 2 of an electric vehicle 3.

In the example of FIG. 1, a multi-phase subscriber network 4 is connected to a multi-phase power supply network 7 by means of a network connection point 6 . The multi-phase subscriber network 4 has in particular a number of phases, for example LI, L2 and L3, and a neutral conductor. In this example, without loss of generality, it is a matter of three-phase power grids. The electric vehicle 2 is coupled to the charging station 1 by means of a charging cable 5 which is connected to a connection socket (not shown) of the charging station 1 .

The charging station 1 can have a number of electrical and/or electronic components (not shown in FIG. 1, see for example FIG. 2) and is for charging and/or discharging the energy store 2 of the electric vehicle 3 with electrical energy using the the charging station 1 coupled multi-phase subscriber network 4 set up.

In addition, the charging station 1 preferably comprises a communication module (not shown). The communication module is set up to negotiate a charging plan with charging electronics of the energy store 2 coupled to the charging station 1 .

Negotiation takes place, for example, as described in ISO 15118. For example, the charging electronics of the energy storage device 2 requests a certain charging capacity via the communication module at the charging station 1 and the charging station 1 determines whether the requested charging capacity can be provided. A current state of the subscriber network 4 and/or the power supply network 7 is taken into account in particular. If the requested charging power cannot be provided, the charging station 1 can use the communication module make a "counterproposal" which can be accepted by the charging electronics of the energy store 2 ^¬ or the charging electronics again makes its own request. In this way, the charging station 1 and the charging electronics of the energy store 2 communicate until the charging plan has been negotiated. Negotiating the charging plan can be part of the pairing process when an energy storage device 2 is newly connected to the charging station 1 .

Fig. 2 shows a schematic circuit diagram of a second embodiment of a charging station 1 for charging and discharging an energy store 110 of an electric vehicle ^100. The second embodiment of FIG. 2 includes all the features of the first embodiment of FIG.

The charging station 1 of FIG. 2 has three connection terminals 101, 102, 103 for the three phases LI, L2, L3 of the multiphase network 4. In particular, the charging station 1 also has another connection terminal (not shown) for the neutral conductor.

According to FIG. 2, an EMC filter device 200 is connected downstream of the connection terminals 101, 102, 103. Furthermore, the charging station 1 of FIG Output potential ^¬ alabgriff 701 and a positive output potential tap 702 are connected.

In particular, an EMC filter device (not shown) can be connected between the negative output potential ^tap 701 and the positive output ^potential tap 702 .

FIG. 3 shows a schematic circuit diagram of a third embodiment of a charging station 1. The third embodiment of FIG. 3 includes all the features of the second embodiment according to FIG. 2, with FIG. 3 illustrating details of the charging station 1. According to FIG. 3, the intermediate circuit 500 connected downstream of the AC/DC converter 400 has two intermediate circuit capacitors 501, 502, which are connected between a positive output conductor 401 and a negative output conductor 402 of the AC/DC converter 400.

The DC/DO converter 600 connected downstream of the intermediate circuit 500 has a first half-bridge H1 and a second half-bridge H2. The first half-bridge H1 is connected to the positive output conductor 401 of the AC/DC converter 400 and includes a series connection of two semiconductor switching elements 601, 602. The first half-bridge H1 is also connected to the negative output potential tap 701.

The second half-bridge H2 is connected to the negative output conductor 402 of the AC/DC converter 400 and includes a series connection of two semiconductor switching elements 603, 604. The respective semiconductor switching element 601, 602, 603, 604 is in the form of a MOSFET, for example. In addition, the second half-bridge H2 is connected to the positive output potential tap 701.

The center tap Ml of the first half-bridge H1 and the center tap M2 of the second half-bridge H2 are connected via a choke 605.

The inductance of the choke 605 is preferably between 10 mH and 100 mH. The value of the inductance of the inductor 605 is selected from the range between 10 mH and 100 mH, in particular depending on the power of the charging station 1 and the selected switching frequency.

The choke 605 of the DC/DO converter 600 can be operated in particular as a flying inductor.

Furthermore, the charging station 1 of FIG. switching semiconductor switching elements 601, 603 and 602, 604 of the two half-bridges H1, H2 simultaneously, in particular with an identical turn-on delay.

In particular, the two mains-side semiconductor switching elements 601, 603 of the two half-bridges H1, H2 can be switched simultaneously, and the two load-side semiconductor switching elements 602, 604 of the two half-bridges H1, H2 can also be switched simultaneously. The semiconductor switching elements 601 and 603 are therefore corresponding semiconductor switching elements, just as the semiconductor switching elements 602 and 604 are corresponding semiconductor switching elements.

Downstream of the DC/DC converter 600 is an intermediate circuit 700 which has a number of capacitors. In the example in the figure, the intermediate output circuit 700 has—without restricting generality—a capacitor 703, which is connected between the negative output potential tap 701 and the positive output potential tap 702 of the charging station 1 and can be arranged in parallel with the energy store 2 of the electric vehicle 3.

4 shows a schematic circuit diagram of a fourth specific embodiment of a charging station 1 for charging and/or discharging an energy store 2 of an electric vehicle 3 . The fourth embodiment of FIG. 4 includes all the features of the third embodiment of FIG.

In addition, the charging station 1 of FIG. 4 has an interference suppression circuit 550 arranged between the intermediate circuit 500 and the DC/DC converter 600. The interference suppression circuit 550 comprises two interference suppression capacitors 551, 552 connected in parallel to the intermediate circuit capacitors 501, 502 Node 553 connecting capacitors 551, 552 is connected to earth potential (ground). Furthermore, the charging station 1 of FIG. 4 has a load-side interference suppression circuit 650 arranged between the DC/DC converter 600 and the output intermediate circuit 700. capacitors 651, ^652. The node 653 connecting the two interference suppression capacitors 651, 652 is connected to ground potential (ground).

5 shows a schematic circuit diagram of a fifth embodiment of a charging station 1 for charging and/or discharging an energy store 2 of an electric vehicle 3. The fifth embodiment of FIG. 5 includes all the features of the fourth ^embodiment of FIG.

The charging station 1 of FIG. 5 also has a first diode 801 and a second diode 802. The anode of the first diode 801 is connected to the negative ^output potential tap 701, and the cathode of the first diode 801 is connected to the intermediate circuit center point 503. The anode of the second diode 802 is connected to the intermediate circuit center point 503, and the cathode of the second diode 802 is connected to the positive output potential tap ⁷⁰² .

According to FIG. 5, an oscillating ^capacitor 606 is connected to the center tap M1 of the first half-bridge H1 and is connected in parallel to the semiconductor switching element 601. Furthermore, a resonant capacitor 607 is connected to the center tap M1 of the first half ^bridge H1, which capacitor is connected in parallel to the semiconductor switching element 602.

Analogously, a ^resonant capacitor 608 is connected to the center tap M2 of the second half-bridge H2 and is connected in parallel to the semiconductor switching element 603 . Correspondingly, a resonant capacitor 609 is connected to the center tap M2 of the second half-bridge H2 and is connected in parallel to the semiconductor switching element 604 .

The reversing capacitors 606, 607, 608, 609 bring about soft switching and thus a reduction in the switching losses. The resonant capacitors can also be referred to as ZVS capacitors or snubber capacitors (ZVS; zero-voltage switching). 6 shows a schematic circuit diagram of a sixth embodiment of a charging station 1 for charging and/or discharging an energy store 2 of an electric vehicle 3 . The sixth embodiment of FIG. 6 includes all features of the fifth embodiment of FIG.

Furthermore, the charging station 1 according to FIG. 6 has an overvoltage protection element 803 which is coupled between the intermediate circuit center point 503 and a node 804 to which the cathode of the first diode 801 is connected and to which the anode of the second diode 802 is connected.

The overvoltage protection element 803 is, for example, a varistor or a bidirectional suppressor diode, such as a bidirectional transildiode.

The functionality of the diodes 801, 802 and the overvoltage protection element 803 is the protection of the semiconductor switching elements 601, 602, 603, 604 against overvoltage from the upstream network 4. The diodes 801, 802 and the overvoltage protection element 803 achieve this in particular by the Po potential of the output potential tap 702 cannot become more negative than the potential of the intermediate circuit center point 503 and the potential at the output potential tap 701 cannot become more positive than the potential of the intermediate circuit center point 503.

As an alternative and not shown, a series connection made up of a first overvoltage protection element and the first diode 801 can be arranged between the intermediate circuit center point 503 and the negative output potential tap 701, and a series connection made up of a second overvoltage protection element and the second Diode 802 may be arranged. The control unit 610 is preferably set up to control the semiconductor switching elements 601, 602, 603, 604 in such a way that the line-side semiconductor switching element 601 of the first half-bridge H1 and the load-side semiconductor switching element 604 of the second half-bridge H2 have overlapping switch-on times and /or that the line-side semiconductor switching element 603 of the second half-bridge H2 and the load-side semiconductor switching element 602 of the first half-bridge Hl have overlapping switch-on times. The ratio of the switch-on times of the line-side semiconductor switching elements 601, 603 to the switch-on times of the load-side semiconductor switching elements 602, 604 is in particular adjustable or constant, ie has a predetermined quotient.

In addition, the control unit 610 is preferably set up to turn off one of the line-side semiconductor switching elements 601, 603 of the two half-bridges Hl, H2 earlier than the other line-side semiconductor switching element 603, 601 of the two half-bridges Hl, H2, so that a coupling of a line-side primary circuit K1 ( see Fig. 7) and a load-side secondary circuit K2 (see Fig. 7) is provided via the choke 605. Such a coupling for the circuit K3 of a balancing current is shown in FIG. Details on this are explained below.

As FIG. 6 shows, the semiconductor switching elements 601, 602, 603, 604 can be in the form of MOSFETs. The control unit 610 can preferably be set up to control the gates of the MOSFETs 601, 602, 603, 604 of the half-bridges Hl, H2 with such phase-shifted control signals G1, G2, G3, G4, so that a coupling of the mains-side primary circuit Kl (See he Fig. 7) and the load-side secondary circuit K2 (see Fig. 7) is provided via the choke 605.

The above, in particular the mode of operation of the choke 605 that can be driven as a flying inductance and the output potential control, is explained in more detail below with reference to the diagrams in FIG. 9 . For this purpose, FIG. 9a shows the current in the inductor 605 and FIG. 9b shows the output voltage as Ul, positive to ground as U2, negative to ground as U3 and the mean output voltage as U4. Furthermore, Fig. 9c shows the reverse voltages of MOSFETs 601, 602, 603 and 604, where VI is the reverse voltage across MOSFET 601, V2 is the reverse voltage across MOSFET 602, V3 is the reverse voltage across MOSFET 603 and V4 is the reverse voltage across MOSFET 604 is. Furthermore, FIG. 9d shows the gate signals of the MOSFETs 601, 602, 603 and 604. Here the gate signal G1 is assigned to the MOSFET 601, the gate signal G2 is assigned to the MOSFET 602, which is the gate signal G3 assigned to the MOSFET 603 and the gate signal 604 is assigned to the MOSFET 604 assigned.

As shown in Fig. 9a, the mean value of the inductor current through the choke 605 is 60 A. This is the sum of the mean input current of the primary circuit Kl (see Fig. 7) and the mean output current of the secondary circuit K2 (see Fig .7). With reference to FIG. 9d, times A are provided in the gate signals G1, G2, G3, G4 of the MOSFETs 601, 602, 603, 604 for the charge reversal of the resonant capacitors 606, 607, 608 and 609. The charge reversal can be seen at edge B of the MOSFET blocking voltages according to FIG. 9c. The maximum current of + 150 A according to FIG. 9a in the inductor 605 causes a fast charge reversal, the minimum current of -30 A according to FIG in figure 9c. The switching on of the MOSFETs, see A in FIG. 9d, always takes place when the blocking voltage of the MOSFETs is zero in order to reduce or avoid switching-on losses. When the MOSFETs switch off (see A in Fig. 9d), the MOSFET blocking voltage across them increases so slowly during charge reversal that the blocking voltage remains low during turn-off, i.e. there is a dU/dt-limited turn-off. Compared to hard turn-off, this results in far fewer turn-off losses.

At time C in FIG. 9d, MOSFET 603 is switched off earlier than MOSFET 601. This results in the above-mentioned coupling (see Circuit K3 in Fig. 8) of the circuits. The symmetry of the output voltage to ground shifts with each switching process (cf. FIG. 9b at time point C). A symmetry control can thus take place.

As already explained above, there are two possibilities for symmetry control: firstly, a slightly earlier turn-off of one or more MOSFETs and secondly, a slight phase shift of the gate signals G1, G2, G3, G4 of the two half-bridges H1, H2 relative to one another.

As shown in FIGS. 6, 7, 8 and 10, the control unit 610 can have two current regulators which are, in particular, independent of one another. In particular, control unit 610 includes a charging current controller 611 and a balancing current controller 612. In addition, control unit 610 includes a differential voltage controller 613.

The charging current controller 611 is set up in particular to set the ratio of the switch-on times of the network-side MOSFETs 601, 603 to the switch-on times of the load-side MOSFETs 602, 604. The balancing current regulator 612 provides a balancing current (see circuit K3 in Fig. 8 and SY in Fig.

10) to balance the potential at the negative output potential tap 701 and to set the potential at the positive output potential tap 702 to ground potential.

The differential voltage controller 613 is set up in particular to set a target value SWS (see FIG. 10) for a setting signal SY as a function of at least one measured voltage U2, U3 (see FIG. 10) in the load-side secondary Provide circuit K2. The differential voltage controller 613 is slower than the balancing current controller 612.

As explained above, the rapid charging current regulator 611 influences the ratio of the switch-on times (switch-on durations) of the network-side MOSFETs 601, 603 to the switch-on times of the load-side MOSFETs 602, 604. If the ratio is less than 1, the input voltage is reduced, if the ratio is greater than 1, it is increased, if the ratio is 1, the input voltage is merely inverted.

The differential current controller influences the switch-off time of individual MOSFETs 601, 602, 603, 604 or the phase shift. As explained above, the balancing current regulator 612 can set a balancing current according to FIGS. 8 and 10. The differential voltage controller 613 provides the target value SWS for the setting signal SY. For example, this can ensure that an earth leakage current caused by unequal soiling of the output potential taps 701 and 702 to earth is compensated for by the balancing current controller 612 and the output voltage thus remains earth-symmetrical. In addition, it is preferably suitable for compensating for the tendency towards asymmetry caused by timing tolerances in the gate signals G1, G2, G3, G4. Details on this are explained with reference to FIG. 10 .

Here, FIG. 10 shows the schematic circuit diagram of FIG. 6 with drawn-in symmetry control, with some of the reference symbols drawn in FIG. 6 being omitted in FIG. 10 for reasons of clarity.

The control unit 610 shown in FIG. 10 can also be referred to as a control unit or control device and is set up for balancing control. The control unit 610 of FIG. 10 includes a charging current controller 611, a balancing current controller 612 and a differential voltage controller 613. Furthermore, the charging station 1 of FIG. 10 includes a first current measuring device 614, a second current measuring device 615, a first voltage measuring device 616, a second voltage measuring device 617, a first subtraction unit 618, a summing unit 619, a second subtraction unit 620, a halving unit 621 and a PWM generator 622 (PWM; pulse width modulation). The first current measuring device 614 is set up to measure the current I3 flowing from the first half-bridge H1 to the negative output potential tap 701. Correspondingly, the second current measuring device 615 is set up to measure the current I2 flowing from the second half-bridge H2 to the positive output potential tap 702 .

The first subtraction unit 618 is suitable for providing a first difference signal DS1 from a difference between the stream I2 and the stream I3 on the output side. The summing unit 619, on the other hand, sums the streams I2 and I3 and, depending on this, provides a sum signal SSI on the output side.

The halving unit 621 halves the first sum signal SSI, provided by the summing unit 619, and provides a second sum signal SS2 on the output side (SS2=0.5*SS1).

The first voltage measuring device 616 is set up to measure a voltage drop between the negative output potential tap 701 and ground and to provide a first voltage value U3 (negative to ground) on the output side as a function of this measurement.

Furthermore, the second voltage measuring device 617 is set up to measure a voltage drop between the positive output potential tap 702 and ground and to provide a second voltage signal U2 (plus to ground) on the output side depending on the measurement. The second subtraction unit 620 forms a second difference signal DS2 from the difference between U2 and U3 and makes this available on the output side.

The differential voltage regulator 613 receives on the input side the second differential signal DS2 from the second subtraction unit 620 and a differential voltage setpoint DSS and, depending on this, provides the balancing current setpoint SWS on the output side and feeds this to the balancing current Controller 612 closed. The balancing current controller 612 receives the balancing current setpoint SWS on the input side and the first difference signal DSl from the first subtraction unit 618. Depending on these received signals DSl, SWS, the balancing current controller 612 provides the setting signal SY on the output side and feeds it to the PWM generator 622 .

On the input side, the charging current controller 611 receives the halved sum signal SS2 and a nominal charging current value LSS and, depending on this, provides a setting signal for setting the switch-on times of the MOSFETs 601, 602, 603, 604 on the output side.

The PWM generator generates the gate signals G1, G2, G3, G4 for the MOSFETs 601, 602, 603, 604 depending on the received adjustment signal ES and the received adjustment signal SY.

In particular, the differential voltage controller 613 is so slow that it initially cannot change the balancing current in the event of a fault current suddenly occurring. The charge reversal of the capacitors 651 and 652 is preferably not disturbed. As a result, the system behaves like a system that is galvanically isolated from the network 4. Before the differential voltage controller 613 balancing current controller 612 can react in such a case, the DC/DC converter 600 is preferably switched off. If desired, the system could continue to operate with a ground fault if required without driving a current into the ground fault.

11 also shows a schematic flowchart of a method for operating a charging station 1 for charging and/or discharging an energy store 2 of an electric vehicle 3 with electrical energy by means of a multiphase network 4 that can be coupled to the charging station 1. The charging station 1 is, for example, as explained in the preceding figures. In step S1, the charging station 1 is coupled to the multi-phase network 4 and to the energy store 2 of the electric vehicle 3.

In step S2, the inductor 605 of the DC/DO converter 600 connecting the center tap M1 of the first half-bridge H1 and the center tap M2 of the second half-bridge H2 is operated as a flying inductance.

Although the present invention has been described on the basis of embodiments, it can be modified in many ways.

REFERENCE LIST

1 charging station

2 energy storage

3 electric vehicle

4 multi-phase subscriber network

5 charging cables

6 grid connection point 7 multi-phase power supply grid

101 terminal block

102 terminal block

103 terminal block

200 EMC filter device

300 LCL filter device

400 AC/DC converter

401 positive output conductor

402 negative output conductor

500 intermediate circuit

501 intermediate circuit capacitor

502 intermediate circuit capacitor

503 DC link center

550 suppression circuit

551 anti-interference capacitor

552 anti-interference capacitor

553 node 600 DC/DC converter 601 semiconductor switching element 602 semiconductor switching element

603 semiconductor switching element

604 semiconductor switching element

605 Thrush

606 reversing capacitor 607 reversing capacitor

608 reversing capacitor

609 reversing capacitor

610 control unit 611 charging current controller 612 balancing current controller

613 differential voltage regulator

614 first current measuring device

615 second current measuring device

616 first voltage measuring device

617 second voltage measuring device

618 first subtraction unit

619 summation unit

620 second subtraction unit 621 halving unit 622 PWM generator

650 suppression circuit

651 anti-interference capacitor

652 anti-interference capacitor

653 knots

700 output intermediate circuit

701 Starting potential pick-up

702 Starting potential pick-up

703 capacitor 801 diode 802 diode

803 overvoltage protection element

804 knots

A, B, C times

E setting signal

Gl gate signal for semiconductor switching element 601 G2 gate signal for semiconductor switching element 602

G3 gate signal for semiconductor switching element 603

G4 gate signal for semiconductor switching element 604

Hl first half bridge

H2 second half bridge

current

12 electricity

13 electricity

Kl circuit

K2 circuit

K3 circuit

LI phase

L2 phase

L3 phase

Ml center tap of the first half bridge

M2 center tap of the second half bridge s Time in seconds

Sl, S2 V experienced steps

SY setting signal

Ul Aus gan gssp annun g

U2 plus to earth

U3 negative to earth

U4 Average output voltage

VI Voltage at the semiconductor switching element 601

V2 voltage at the semiconductor switching element 602

V3 voltage at the semiconductor switching element 603

V4 Voltage at the semiconductor switching element 604

Claims

CLAIMS l. Charging station (l) for charging and/or discharging an energy store (2) of an electric vehicle (3) with electrical energy by means of a multi-phase network (4) that can be coupled to the ^charging station (l), having: one with a number of phases (LI , L2, L3) of the multiphase network (4) that can be coupled AC/DC converter (400), an intermediate circuit (500) connected downstream of the AC/DC converter (400), which has a number of between a positive output conductor (401) and ei ^¬ NEM negative output conductor (402) of the AC / DC converter (400) connected ^intermediate circuit capacitors (501, 502), and the intermediate circuit (500) downstream DC / DC converter (600), which one with the positive output conductor (401) connected first half bridge ^¬ cke (Hl) and with the negative output conductor (402) connected second half bridge (H2), wherein the center tap (Ml) of the first half bridge (Hl) and the center tap (M2) of the second half bridge ( H2) via a throttle (605) are connected, each the other half-bridge (H1, H2) has a series connection of two semiconductor switching elements (601, 602, 603, 604), the charging station (1) having a control unit (610) which is set up to switch the semiconductor switching elements (601, 602, 603, ⁶⁰⁴ ) to be controlled in such a way that two corresponding semiconductor switching elements (601, 603,

602, 604) of the two half-bridges (H1, H2) switch simultaneously, in particular switch with an identical switch-on delay, the semiconductor switching elements (601, 602, 603, 604) being MOSFETs and the control unit (610) being set up to switch the gates of the MOSFETs (601, 602,

603, 604) of the half-bridges (Hl, H2) with such phase-shifted control ^signals (Gl, G2, G3, G4) so that a coupling of a ^mains -side primary circuit (Kl) and a load-side secondary circuit (K2 ) is provided via the inductor (605), the control unit (610) having a charging current regulator (611), a balancing current regulator (612) and a differential voltage regulator (613), wherein the charging current controller (611) is set up to set the ratio of the switch-on times of the line-side semiconductor switching elements (601, 603) to the switch-on times of the load-side semiconductor switching elements (602, 604), the balancing current controller (612) being set up for this purpose , a setting signal (SY) for balancing the potential at the negative output potential tap (701) and the potential at the positive output potential tap (702) with respect to ground potential, and wherein the differential voltage controller (613) is set up to set a target value (SWS) for the setting signal (SY) as a function of at least one measured voltage (U2, U3) in the load-side secondary circuit (K2), the charging station (l) having an intermediate output circuit connected downstream of the DC/DC converter (600). (700) with a number of capacitors (703) which are connected between a negative output potential tap (701) and a positive output potential tialabgriff (702) of the charging station (l) are connected and parallel to the energy store (2) of the electric vehicle (3) can be arranged, the anode of a first diode (801) being coupled to the negative exit potential tap (701) and the cathode of first diode (801) is coupled to the intermediate circuit center point (503) and the anode of a second diode (802) is coupled to the intermediate circuit center point (503) and the cathode of the second diode (802) is coupled to the positive output potential tap (702).

2. Charging station according to claim 1, characterized in that the choke (605) of the DC/DC converter (600) can be driven as a flying inductance.

3. Charging station according to claim 1 or 2, characterized in that the charging station (l) is a transformerless charging station.

4. Charging station according to one of claims 1 to 3 characterized in that the DC/DO converter (600) is designed as a bidirectional DC/DO converter for stepping up and/or stepping down voltages.

5. Charging station according to claim 1, characterized in that the respective semiconductor switching element (601, 602, 603, 604) is designed as a MOSFET, preferably as a SiC MOSFET, or as an IGBT or as a SiO cascode.

6. Charging station according to one of claims 1 to 5, characterized in that an interference suppression circuit (550) is arranged between the intermediate circuit (500) and the DC/DO converter (600), which has two parallel circuit capacitors (501, 502). switched interference suppression capacitors (551, 552), the node (553) connecting the two interference suppression capacitors (551, 552) being connected to ground potential.

7. The charging station as claimed in claim 1, characterized in that a load-side interference suppression circuit (650) is arranged between the DODO converter (600) and the output intermediate circuit (700), which circuit has two interference suppression capacitors connected in parallel with the number of capacitors (703) in the output intermediate circuit (700). (651, 652), the node (653) connecting the two interference suppression capacitors (651, 652) being connected to ground potential.

8. Charging station according to one of claims 1 to 7, characterized in that the control unit (610) is set up to control the semiconductor switching elements (601, 602, 603, 604) in such a way that the line-side semiconductor switching element (601) of the first half-bridge ( Hl) and the load-side semiconductor switching element (604) of the second half-bridge (H2) have overlapping switch-on times and/or that the line-side semiconductor switching element (603) of the second half-bridge (H2) and the load-side semiconductor switching element (602) of the first half-bridge (H1) have overlapping switch-on times, the ratio of the switch-on times of the line-side semiconductor switching elements (601, 603) increasing the switch-on times of the load-side semiconductor switching elements (602, 604) preferably has a predetermined quotient.

9. Charging station according to one of Claims 1 to 8, characterized in that the control unit (610) is set up to switch off one of the line-side semiconductor switching elements (601, 603) of the two half-bridges (H1, H2) earlier than the other line-side semiconductor switching element (601, 603) of the two half-bridges (Hl, H2), so that a coupling of a mains-side primary circuit (Kl) and a load-side secondary circuit (K2) via the inductor (605) is provided.

10. Charging station according to claim 1, characterized in that the differential voltage controller (613) is slower than the balancing current controller (612).

11. Charging station according to claim 1, characterized in that the anode of the first diode (801) is connected to the negative output potential tap (701) and the cathode of the first diode (801) is connected to the intermediate circuit center (503) and the anode the second diode (802) is connected to the intermediate circuit center point (503) and the cathode of the second diode (802) is connected to the positive output potential tap (702).

12. Charging station according to claim 1, characterized in that that an overvoltage protection element (803) between the intermediate ^{circuit center ¬} point (503) and a node (804) is coupled to which the cathode of the first diode (801) is connected and to which the anode of the second diode (802) is connected.

13. Charging station according to Claim 1, characterized in that a series connection of a first overvoltage ^protection element and the first diode (801) is arranged between the intermediate circuit center point (503) and the negative ^output potential tap (701) and between the intermediate circuit center point (503) and the positive ^{Ausgangspotentialab ¬ grip} (702) is arranged a series circuit of a second Überspannungsschutzele ^¬ ment and the second diode (802).

14. Charging station according to one of claims 1 to 13, characterized in that an EMC filter device (200) and an LCL filter device (300) connected downstream of the EMC filter device (200) between three mains-side ^connection terminals (101, 102, 103 ) for the three phases (LI, L2, L3) of the multiphasi ^¬ gene network (4) and the AC / DC converter (400) are coupled.

15. Charging station according to one of claims 1 to 14, characterized in that the AC / DC converter (400) is designed as a 3-point AC / DC converter.

16. Charging station according to one of claims 1 to 15, characterized in that parallel to each semiconductor switching element (601, 602, 603, 604) a To ^¬ oscillating capacitor (606, 607, 608, 609) is connected to implement a ZVS switching behavior.

17. A method for operating a charging station (l) for charging and/or discharging an energy store (2) of an electric vehicle (3) with electrical energy using a multi-phase network (4) that can be coupled to the charging station (l), the charging station ( l) with a number of phases (LI, L2, L3) of the multi-phase network (4) coupled AC / DC converter (400), the AC / DC converter (400) downstream intermediate circuit (500), which a number has intermediate circuit capacitors (501, 502) connected between a positive output conductor (401) and a negative output conductor (402) of the AC/DC converter (400), and a DC/DC converter (600) connected downstream of the intermediate circuit (500) comprises a first half-bridge (H1) connected to the positive output conductor (401) and a second half-bridge (H2) connected to the negative output conductor (402), with:

Operating a choke (605) of the DC/DC converter (600) connecting the center tap (Ml) of the first half-bridge (Hl) and the center tap (M2) of the second half-bridge (H2) as a flying inductor, with the respective half-bridge (Hl, H2) has a series connection of two semiconductor switching elements (601, 602, 603, 604), the charging station (l) having a control unit (610) which controls the semiconductor switching elements (601, 602, 603, 604) in such a way that two corresponding Switch semiconductor switching elements (601, 603, 602, 604) of the two half-bridges (Hl, H2) simultaneously, in particular with an identical switch-on delay, the semiconductor switching elements (601, 602, 603, 604) being MOSFETs and the control unit (610) being the gates of the MOSFETs (601, 602, 603, 604) of the half-bridges (Hl, H2) with such phase-shifted control signals (Gl, G2, G3, G4) that a coupling of a mains-side primary circuit (Kl) and a load-side S secondary circuit (K2) is provided via the inductor (605), wherein the control unit (610) has a charging current controller (611), a balancing current controller (612) and a differential voltage controller (613), wherein the Charging current regulator (611) the ratio of the switch-on times of the line-side term semiconductor switching elements (601, 603) to the switch-on times of the load-side semiconductor switching elements (602, 604), the balancing current controller (612) providing a setting signal (SY) for balancing the potential at the negative output potential tap (701) and the potential at the positive output potential tap (702) with respect to ground potential, and wherein the Differential voltage controller (613) provides a target value (SWS) for the setting signal (SY) as a function of at least one measured voltage (U2, U3) in the load-side secondary circuit (K2), the charging station ( l) an intermediate output circuit (700) connected downstream of the DC/DC converter (600) with a number of capacitors (703) which is connected between a negative output potential tap (701) and a positive output potential tap (702) of the charging station (l) are connected and can be arranged in parallel with the energy store (2) of the electric vehicle (3), the anode of a first diode (801) being coupled to the negative output potential tap (701). t and the cathode of the first diode (801) is coupled to the intermediate circuit center point (503) and the anode of a second diode (802) is coupled to the intermediate circuit center point (503) and the cathode of the second diode (802) to the positive output potential tap (702 ) is paired.