Patent ID: 12255461

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

FIG.1shows a charging station10, which comprises a central part12and a plurality of charging poles14, which are interconnected with the central part12via a high frequency AC distribution network16.

The central part12is connected with an electrical grid18, which may be three-phase, and the AC distribution network16, which may be single-phase. The central part12converts a medium voltage from the grid18of 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 network16. The input voltage from the electrical grid18may have a frequency of 50 Hz or 60 Hz. The frequency of the voltage in the AC distribution network16may be a high frequency of more than 400 Hz, for example more than 10 kHz.

The central part12may be composed of an AC-to-DC converter20and a DC-to-AC converter22, which are interconnected via a DC link21. Alternatively, the central part12may comprise a direct AC-to-AC converter, which may have a single-stage structure, for example by utilizing a matrix-type converter topology.

For the AC-to-DC converter20, a medium voltage active or passive rectifier, such as a multi-pulse rectifier with diodes or thyristors may be used. The AC-to-DC converter20also may be a multilevel converter and/or a modular multilevel converter.

The DC-to-AC converter22may be a multilevel converter and/or a modular multilevel converter. The DC-to-AC converter22may be composed of several converter units as will be described below in more detail.

A charging pole14comprise a transformer24, which is directly connected with its primary coil26with the AC distribution network16. An AC-to-DC converter30, such as a passive diode rectifier, is connected to a secondary coil28of the transformer24. It also may be that the AC-to-DC converter is an active rectifier. A charging pole14also may comprise a DC-to-DC converter32, for example a buck/boost-converter, which is supplied by the AC-to-DC converter30. To the DC-to-DC converter32or to the AC-to-DC converter30, an electric vehicle may be connected for charging.

InFIG.1, the components20,22of the central part12may be provided in one housing and/or building.

As shown inFIG.2, the components20,22of the central part12also may be distributed into several housings and/or buildings. It also may be possible that at least two DC-to-AC converters22, such as the ones as described with respect toFIG.1, are connected to the DC link provided by the AC-to-DC converter20.

The AC-to-DC converter20and the at least two DC-to-AC converters22may be interconnected with a DC distribution network34. The DC voltage in the DC distribution network34may be medium voltage, for example between 3.3 kV and 20 kV. For example, in a rather large charging station10, a single low voltage high frequency AC distribution network16may lead to large conduction losses in the AC distribution network16. In order to achieve highly efficient distribution, the intermediate DC distribution network34may be included. That is, a medium DC voltage, which is available by rectifying a medium voltage AC voltage with the AC-to-DC converter20, may be used for distribution to reduce long distance conduction losses. The charging station10and its central part12may be divided into several sub-charging areas and each sub-charging area may be equipped with a DC-to-AC converter22, which may convert the medium DC voltage into a low voltage high frequency AC voltage for local distribution.

FIG.3shows a charging station10, for example as inFIG.1, where the charging poles14have been replaced with coils36for wireless power transfer. For example, such coils36may be provided in a ground below a parking place of an electric vehicle38or in a street.

Also, a high frequency AC distribution network16may be used as a primary side for a wireless power transfer to moving vehicles38. In this case, by installing the high frequency AC distribution network16along a roadway, even moving electric vehicles38may be charged.

A secondary coil37of the electric vehicle38may couple via a magnetic field with the primary coil36(for example via an air gap). The electric vehicle38itself then may have an AC-to-DC converter30and optionally a DC-to-DC converter32as described with respect toFIG.1and/or as described below.

It has to be noted that wireless power transfer coils36as described with respect toFIG.3may be combined with the charging station10ofFIG.1, where, for example, some of the charging poles14may be replaced with such coils36. It also may be possible that some or all of the charging poles14ofFIG.2connected to one DC-to-AC converter22are replaced with coils36for wireless power transfer.

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 network16and/or the DC distribution network34. The renewable energy source and/or the battery storage may be connected to the high frequency AC distribution network16via an AC-to-DC converter, analogous to the converter22. The renewable energy source and/or the battery storage may be connected to the DC distribution network34via a DC-to-DC converter. This DC-to-DC converter also may be of a modular type.

In the embodiments shown inFIGS.1to3of the charging station10, the power rating of the central part12may be smaller as the sum of the power ratings of the charging poles14and/or the coils36, when it is assumed that only some of the charging poles14and/or coils36are used for charging.

For example, with respect toFIG.1, the charging station10may have three charging poles14and the power rating of an individual charging pole may be 300 kW. Since it is very rare that all the charging poles14are in operation at the same time, the power rating of the central part12may be designed lower than the maximum required power. For example, even though the total power rating of all charging poles14is 900 kW, the central part12may 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 pole14and/or coil36.

FIG.4shows a DC-to-AC converter22that may be used in the charging stations10as shown inFIGS.1to3.

The DC-to-AC converter22comprises a DC link21with a capacitor39, a converter unit40connected in parallel with its inputs42to the DC link21and a transformer46, which is connected with its primary coil48to an output44of the converter unit40. The secondary coil50of the transformer46is connected to the high frequency AC distribution network16. A DC blocking capacitor52may be interconnected between the output44and the primary coil48.

As shown inFIG.5, in the case of higher voltages, two or more converter units40may be connected in series with their input42. Every one of these converter units40may be connected in parallel to a capacitor39of a split DC link21, which is composed of series-connected capacitors39. In the case ofFIG.5, the outputs44of two converter units40may be connected via the primary coil48of the transformer46with each other.

As shown inFIG.6, in the case of higher currents, two or more converter units40may be connected in parallel with their inputs42and in parallel to the DC link21. As inFIG.5, the outputs44of two converter units40may be connected via the primary coil48of the transformer46with each other.

FIGS.7to8show possible topologies for the converter units40as shown inFIGS.4to6and below.

FIGS.7to9show converter units40, which comprise 4 series-connected semiconductor switches54, which are interconnected between the inputs42. At the middle point, the switches54provide the output44. Every converter unit40may comprise and/or may be interconnected with a DC link56, which may comprise one or more series-connected capacitors58.

FIG.7is a neutral point clamped converter unit40, in which two intermediate middle points between two upper und two lower switches54are connected via diodes60with a middle point of a split DC link56.

FIG.8is a T-type converter unit40, where the middle point between the switches54providing the output44is interconnected via two anti-series-connected switches62with the middle point of the split DC link56.

FIG.9is a flying capacitor type converter unit40, where two intermediate middle points between two upper und two lower switches54are connected via a capacitor64with each other.

FIG.10shows a modular multi-level converter unit40, which comprises a plurality of series-connected converter modules66, which are interconnected between the inputs42. The output44is provided at a middle point between the converter modules66. Every converter module66may comprise a converter bridge68composed of two switches70and a capacitor72connected in parallel to the converter bridge68.

FIG.11andFIG.12show two further examples of a DC-to-AC converter22. A plurality of converter units40(here4) are connected in series with their inputs42. Every one of these converter units40is connected in parallel to a capacitor39of a split DC link21, which is composed of series-connected capacitors39.

InFIG.11, every converter unit22is associated with one transformer46. The output44of every converter unit22is connected via the primary coil of the transformer46with one of its inputs42. All transformers46are connected in parallel with their secondary coils.

InFIG.12, two converter units22are associated with one transformer46. The output44of a first converter unit22is connected via the primary coil of the respective transformer46with the output44of a second converter unit22. Again, the transformers46are connected in parallel with their secondary coils.

FIG.13andFIG.14show further examples of charging stations, where a resonant tank74is provided in the high frequency section. Resonant operation may be used for the high frequency AC distribution network16.

The resonant tank74may comprise a resonant capacitor76and a resonant inductor78and/or may be used to make the current waveform in the distribution network16more of sinusoidal shape. With a resonant operation, a soft switching for the converter units40of the DC-to-AC converter22may be achieved.

As shown inFIG.13, one way to implement the resonant operation is inserting the resonant tank74directly in the distribution network16. The resonant tank74may be connected between the one or more transformers46of the central part12and the transformers24of the charging poles14(and/or the coils36for wireless power transfer).

As shown inFIG.14, one or more resonant tanks74may be connected between the output44of a converter unit40and the transformer46. In this case, a resonant tank74may be provided for every transformer46. In general, the DC blocking capacitor52and a leakage inductance78of the transformer46may be used for the resonant tank74.

FIG.14furthermore shows an exemplary overall circuit diagram of a charging station10. For every phase of the medium voltage from the grid18, the AC-to-DC converter20of the central part12comprises a modular multi-level converter as shown inFIG.10, which is composed of converter modules66as shown inFIG.10. These modular multi-level converters are connected in parallel to the DC link21.

In general, the AC-to-DC converter20of the central part12may be of any type of rectifier stage. Like the DC-to-AC converter22, a modular converter and/or the converter types as shown inFIGS.7to10may be used.

In summary, the high frequency AC distribution network16in particular in combination with a modular DC-to-AC converter22of the central part12of the charging station10may result in a small foot print and high power density for the high frequency transformers46,24. An easy scaling with respect to the medium voltage provided by the grid18is possible due to the modularity of the DC-to-AC converter22. Furthermore, the power rating of the central part12may 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.

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

10charging station12central part14charging pole16high frequency AC distribution network18electrical grid20AC-to-DC converter21DC link22DC-to-AC converter24transformer26primary coil28secondary coil30AC-to-DC converter32DC-to-DC converter34DC distribution network36coil for wireless power transfer37secondary coil of electric vehicle38electric vehicle39DC link capacitor40converter unit42input44output46transformer48primary coil50secondary coil52DC blocking capacitor54semiconductor switch56DC link58capacitor60diode62semiconductor switch64capacitor66converter module68converter bridge70semiconductor switch72capacitor74resonant tank76capacitor78inductor