Charging Station with High Frequency Distribution Network

Abstract

A charging station for electric vehicles includes a central part for converting a grid AC voltage from an electrical grid into a high frequency AC voltage; a distribution network for distributing the high frequency AC voltage; and a plurality of coils directly connected to the distribution network, wherein each coil is adapted for transferring energy to an electrical vehicle.

Claims

1. A charging station for electric vehicles, the charging station comprising: a central part configured to convert a grid AC voltage from an electrical grid into a high frequency AC voltage; a distribution network configured to distribute the high frequency AC voltage; and a plurality of coils directly connected to the distribution network, wherein each of the plurality of coils configured to transfer energy to an electrical vehicle.

2. The charging station of claim 1, wherein the central part comprises at least one transformer at an output side, which is connected to the distribution network; and/or wherein the central part comprises at least two transformers having secondary coils connected in parallel and/or in series to the distribution network.

3. The charging station of claim 1, wherein the central part comprises a grid side AC-to-DC converter for receiving the grid AC voltage and at least one network side DC-to-AC converter, which are interconnected via a DC link.

4. The charging station of claim 3, wherein the central part comprises at least two DC-to-AC converters, which are connected to the DC link via a DC distribution network.

5. The charging station of claim 3, wherein the DC-to-AC converter is composed of at least one converter unit which is one of a neutral point clamped type, a T type, a flying cap type, or a modular multi-level converter type.

6. The charging station of claim 3, wherein the DC-to-AC converter is composed of at least two converter units, each of the at least two converter units comprising an input, which are connected in series via the inputs; and/or wherein the at least two converter units, are connected in parallel via the inputs.

7. The charging station of claim 4, wherein each of the DC-to-AC converters comprises two converter units, each of the two converter units comprising an output, which are connected via a transformer of the central part the outputs.

8. The charging station of claim 1, wherein a resonant tank comprising a capacitor and an inductor is connected in the distribution network.

9. The charging station of claim 8, wherein the resonant tank is connected between a transformer of the central part and the plurality of coils.

10. The charging station of claim 1, wherein a resonant tank comprising a capacitor and an inductor is connected between a converter unit of the central part and a transformer of the central part.

11. The charging station of claim 1, wherein the grid voltage is a medium voltage of more than 3 kV; and/or wherein the high frequency AC voltage is a low voltage of less than 3 kV.

12. The charging station of claim 1, wherein the frequency of the grid AC voltage is less than 100 Hz; and/or wherein the frequency of the high frequency AC voltage is more than 400 Hz.

13. The charging station of claim 1, wherein at least some of the plurality of coils are part of a transformer integrated into a charging pole.

14. The charging station of claim 13, wherein the charging pole comprises an AC-to-DC converter configured to receive a voltage from the transformer; wherein the AC-to-DC converter of the charging pole supplies a DC-to-DC converter to generate a charging voltage.

15. The charging station of claim 1, wherein at least some of the plurality of coils are coils configured to wirelessly transfer energy via an air gap.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The subject-matter of the invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings.

[0045] FIG. 1 schematically shows a charging station according to an embodiment of the invention.

[0046] FIG. 2 schematically shows a charging station according to a further embodiment of the invention.

[0047] FIG. 3 schematically shows a charging station according to a further embodiment of the invention.

[0048] FIG. 4 schematically shows a DC-to-AC converter for a charging station according to an embodiment of the invention.

[0049] FIG. 5 schematically shows a further DC-to-AC converter for a charging station according to an embodiment of the invention.

[0050] FIG. 6 schematically shows a further DC-to-AC converter for a charging station according to an embodiment of the invention.

[0051] FIG. 7 schematically shows a converter unit for a charging station according to an embodiment of the invention.

[0052] FIG. 8 schematically shows a further converter unit for a charging station according to an embodiment of the invention.

[0053] FIG. 9 schematically shows a further converter unit for a charging station according to an embodiment of the invention.

[0054] FIG. 10 schematically shows a further converter unit for a charging station according to an embodiment of the invention.

[0055] FIG. 11 schematically shows a further DC-to-AC converter for a charging station according to an embodiment of the invention.

[0056] FIG. 12 schematically shows a further DC-to-AC converter for a charging station according to an embodiment of the invention.

[0057] FIG. 13 schematically shows a charging station according to a further embodiment of the invention.

[0058] FIG. 14 schematically shows a charging station according to a further embodiment of the invention.

[0059] The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0060] FIG. 1 shows a charging station 10, which comprises a central part 12 and a plurality of charging poles 14, which are interconnected with the central part 12 via a high frequency AC distribution network 16.

[0061] The central part 12 is connected with an electrical grid 18, which may be three-phase, and the AC distribution network 16, which may be single-phase. The central part 12 converts a medium voltage from the grid 18 of for example 3.3 kV to 20 kV into a low voltage of for example 230 V to 690 V, which is supplied to the distribution network 16. The input voltage from the electrical grid 18 may have a frequency of 50 Hz or 60 Hz. The frequency of the voltage in the AC distribution network 16 may be a high frequency of more than 400 Hz, for example more than 10 kHz.

[0062] The central part 12 may be composed of an AC-to-DC converter 20 and a DC-to-AC converter 22, which are interconnected via a DC link 21. Alternatively, the central part 12 may comprise a direct AC-to-AC converter, which may have a single-stage structure, for example by utilizing a matrix-type converter topology.

[0063] For the AC-to-DC converter 20, a medium voltage active or passive rectifier, such as a multi-pulse rectifier with diodes or thyristors may be used. The AC-to-DC converter 20 also may be a multilevel converter and/or a modular multilevel converter.

[0064] The DC-to-AC converter 22 may be a multilevel converter and/or a modular multilevel converter. The DC-to-AC converter 22 may be composed of several converter units as will be described below in more detail.

[0065] A charging pole 14 comprise a transformer 24, which is directly connected with its primary coil 26 with the AC distribution network 16. An AC-to-DC converter 30, such as a passive diode rectifier, is connected to a secondary coil 28 of the transformer 24. It also may be that the AC-to-DC converter is an active rectifier. A charging pole 14 also may comprise a DC-to-DC converter 32, for example a buck/boost-converter, which is supplied by the AC-to-DC converter 30. To the DC-to-DC converter 32 or to the AC-to-DC converter 30, an electric vehicle may be connected for charging.

[0066] In FIG. 1, the components 20, 22 of the central part 12 may be provided in one housing and/or building.

[0067] As shown in FIG. 2, the components 20, 22 of the central part 12 also may be distributed into several housings and/or buildings. It also may be possible that at least two DC-to-AC converters 22, such as the ones as described with respect to FIG. 1, are connected to the DC link provided by the AC-to-DC converter 20.

[0068] The AC-to-DC converter 20 and the at least two DC-to-AC converters 22 may be interconnected with a DC distribution network 34. The DC voltage in the DC distribution network 34 may be medium voltage, for example between 3.3 kV and 20 kV. For example, in a rather large charging station 10, a single low voltage high frequency AC distribution network 16 may lead to large conduction losses in the AC distribution network 16. In order to achieve highly efficient distribution, the intermediate DC distribution network 34 may be included. That is, a medium DC voltage, which is available by rectifying a medium voltage AC voltage with the AC-to-DC converter 20, may be used for distribution to reduce long distance conduction losses. The charging station 10 and its central part 12 may be divided into several sub-charging areas and each sub-charging area may be equipped with a DC-to-AC converter 22, which may convert the medium DC voltage into a low voltage high frequency AC voltage for local distribution.

[0069] FIG. 3 shows a charging station 10, for example as in FIG. 1, where the charging poles 14 have been replaced with coils 36 for wireless power transfer. For example, such coils 36 may be provided in a ground below a parking place of an electric vehicle 38 or in a street.

[0070] Also, a high frequency AC distribution network 16 may be used as a primary side for a wireless power transfer to moving vehicles 38. In this case, by installing the high frequency AC distribution network 16 along a roadway, even moving electric vehicles 38 may be charged.

[0071] A secondary coil 37 of the electric vehicle 38 may couple via a magnetic field with the primary coil 36 (for example via an air gap). The electric vehicle 38 itself then may have an AC-to-DC converter 30 and optionally a DC-to-DC converter 32 as described with respect to FIG. 1 and/or as described below.

[0072] It has to be noted that wireless power transfer coils 36 as described with respect to FIG. 3 may be combined with the charging station 10 of FIG. 1, where, for example, some of the charging poles 14 may be replaced with such coils 36. It also may be possible that some or all of the charging poles 14 of FIG. 2 connected to one DC-to-AC converter 22 are replaced with coils 36 for wireless power transfer.

[0073] In any of the embodiments described herein, a renewable energy source, such as a photo voltaic power generation station, and/or a battery storage system may be directly connected to the high frequency AC distribution network 16 and/or the DC distribution network 34. The renewable energy source and/or the battery storage may be connected to the high frequency AC distribution network 16 via an AC-to-DC converter, analogous to the converter 22. The renewable energy source and/or the battery storage may be connected to the DC distribution network 34 via a DC-to-DC converter. This DC-to-DC converter also may be of a modular type.

[0074] In the embodiments shown in FIGS. 1 to 3 of the charging station 10, the power rating of the central part 12 may be smaller as the sum of the power ratings of the charging poles 14 and/or the coils 36, when it is assumed that only some of the charging poles 14 and/or coils 36 are used for charging.

[0075] For example, with respect to FIG. 1, the charging station 10 may have three charging poles 14 and the power rating of an individual charging pole may be 300 kW. Since it is very rare that all the charging poles 14 are in operation at the same time, the power rating of the central part 12 may be designed lower than the maximum required power. For example, even though the total power rating of all charging poles 14 is 900 kW, the central part 12 may be designed with a power rating of 600 kW or even of 300 kW. The total installed power rating of power electronics may be reduced with the high frequency AC distribution network supplying more than one charging pole 14 and/or coil 36.

[0076] FIG. 4 shows a DC-to-AC converter 22 that may be used in the charging stations 10 as shown in FIGS. 1 to 3.

[0077] The DC-to-AC converter 22 comprises a DC link 21 with a capacitor 39, a converter unit 40 connected in parallel with its inputs 42 to the DC link 21 and a transformer 46, which is connected with its primary coil 48 to an output 44 of the converter unit 40. The secondary coil 50 of the transformer 46 is connected to the high frequency AC distribution network 16. A DC blocking capacitor 52 may be interconnected between the output 44 and the primary coil 48.

[0078] As shown in FIG. 5, in the case of higher voltages, two or more converter units 40 may be connected in series with their input 42. Every one of these converter units 40 may be connected in parallel to a capacitor 39 of a split DC link 21, which is composed of series-connected capacitors 39. In the case of FIG. 5, the outputs 44 of two converter units 40 may be connected via the primary coil 48 of the transformer 46 with each other.

[0079] As shown in FIG. 6, in the case of higher currents, two or more converter units 40 may be connected in parallel with their inputs 42 and in parallel to the DC link 21. As in FIG. 5, the outputs 44 of two converter units 40 may be connected via the primary coil 48 of the transformer 46 with each other.

[0080] FIGS. 7 to 8 show possible topologies for the converter units 40 as shown in FIGS. 4 to 6 and below.

[0081] FIGS. 7 to 9 show converter units 40, which comprise 4 series-connected semiconductor switches 54, which are interconnected between the inputs 42. At the middle point, the switches 54 provide the output 44. Every converter unit 40 may comprise and/or may be interconnected with a DC link 56, which may comprise one or more series-connected capacitors 58.

[0082] FIG. 7 is a neutral point clamped converter unit 40, in which two intermediate middle points between two upper und two lower switches 54 are connected via diodes 60 with a middle point of a split DC link 56.

[0083] FIG. 8 is a T-type converter unit 40, where the middle point between the switches 54 providing the output 44 is interconnected via two anti-series-connected switches 62 with the middle point of the split DC link 56.

[0084] FIG. 9 is a flying capacitor type converter unit 40, where two intermediate middle points between two upper und two lower switches 54 are connected via a capacitor 64 with each other.

[0085] FIG. 10 shows a modular multi-level converter unit 40, which comprises a plurality of series-connected converter modules 66, which are interconnected between the inputs 42. The output 44 is provided at a middle point between the converter modules 66. Every converter module 66 may comprise a converter bridge 68 composed of two switches 70 and a capacitor 72 connected in parallel to the converter bridge 68.

[0086] FIG. 11 and FIG. 12 show two further examples of a DC-to-AC converter 22. A plurality of converter units 40 (here 4) are connected in series with their inputs 42. Every one of these converter units 40 is connected in parallel to a capacitor 39 of a split DC link 21, which is composed of series-connected capacitors 39.

[0087] In FIG. 11, every converter unit 22 is associated with one transformer 46. The output 44 of every converter unit 22 is connected via the primary coil of the transformer 46 with one of its inputs 42. All transformers 46 are connected in parallel with their secondary coils.

[0088] In FIG. 12, two converter units 22 are associated with one transformer 46. The output 44 of a first converter unit 22 is connected via the primary coil of the respective transformer 46 with the output 44 of a second converter unit 22. Again, the transformers 46 are connected in parallel with their secondary coils.

[0089] FIG. 13 and FIG. 14 show further examples of charging stations, where a resonant tank 74 is provided in the high frequency section. Resonant operation may be used for the high frequency AC distribution network 16.

[0090] The resonant tank 74 may comprise a resonant capacitor 76 and a resonant inductor 78 and/or may be used to make the current waveform in the distribution network 16 more of sinusoidal shape. With a resonant operation, a soft switching for the converter units 40 of the DC-to-AC converter 22 may be achieved.

[0091] As shown in FIG. 13, one way to implement the resonant operation is inserting the resonant tank 74 directly in the distribution network 16. The resonant tank 74 may be connected between the one or more transformers 46 of the central part 12 and the transformers 24 of the charging poles 14 (and/or the coils 36 for wireless power transfer).

[0092] As shown in FIG. 14, one or more resonant tanks 74 may be connected between the output 44 of a converter unit 40 and the transformer 46. In this case, a resonant tank 74 may be provided for every transformer 46. In general, the DC blocking capacitor 52 and a leakage inductance 78 of the transformer 46 may be used for the resonant tank 74.

[0093] FIG. 14 furthermore shows an exemplary overall circuit diagram of a charging station 10. For every phase of the medium voltage from the grid 18, the AC-to-DC converter 20 of the central part 12 comprises a modular multi-level converter as shown in FIG. 10, which is composed of converter modules 66 as shown in FIG. 10. These modular multi-level converters are connected in parallel to the DC link 21.

[0094] In general, the AC-to-DC converter 20 of the central part 12 may be of any type of rectifier stage. Like the DC-to-AC converter 22, a modular converter and/or the converter types as shown in FIGS. 7 to 10 may be used.

[0095] In summary, the high frequency AC distribution network 16 in particular in combination with a modular DC-to-AC converter 22 of the central part 12 of the charging station 10 may result in a small foot print and high power density for the high frequency transformers 46, 24. An easy scaling with respect to the medium voltage provided by the grid 18 is possible due to the modularity of the DC-to-AC converter 22. Furthermore, the power rating of the central part 12 may be reduced and the solution is compatible with the interconnection of renewable energy source and an energy storage for grid support and micro-grid functionalities.

[0096] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art and practising the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or controller or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

LIST OF REFERENCE SYMBOLS

[0097] 10 charging station [0098] 12 central part [0099] 14 charging pole [0100] 16 high frequency AC distribution network [0101] 18 electrical grid [0102] 20 AC-to-DC converter [0103] 21 DC link [0104] 22 DC-to-AC converter [0105] 24 transformer [0106] 26 primary coil [0107] 28 secondary coil [0108] 30 AC-to-DC converter [0109] 32 DC-to-DC converter [0110] 34 DC distribution network [0111] 36 coil for wireless power transfer [0112] 37 secondary coil of electric vehicle [0113] 38 electric vehicle [0114] 39 DC link capacitor [0115] 40 converter unit [0116] 42 input [0117] 44 output [0118] 46 transformer [0119] 48 primary coil [0120] 50 secondary coil [0121] 52 DC blocking capacitor [0122] 54 semiconductor switch [0123] 56 DC link [0124] 58 capacitor [0125] 60 diode [0126] 62 semiconductor switch [0127] 64 capacitor [0128] 66 converter module [0129] 68 converter bridge [0130] 70 semiconductor switch [0131] 72 capacitor [0132] 74 resonant tank [0133] 76 capacitor [0134] 78 inductor