Field of the Invention

The invention relates to the field of power supplies, particularly for a charging system, e.g. for electric vehicles. The invention further relates to a method and to a use of a power supply.

Background

Charging systems for electric vehicles (EV) require high power levels. For instance, for a range of about 300 to 400 k for the charged vehicle, a charging pole may require about 350 kW. In many cases, EV charging stations have more than one charging pole. This may result in bulky frontends for the system that feeds the charging pole.

Description

It is therefore an objective of the invention to provide an improved charging system for electric vehicles. This objective is achieved by the subject-matter of the independent claims. Further embodiments are evident from the dependent patent claims and the following description.

One aspect relates to a charging system that is configured for delivering a low-voltage (LV) power signal to at least one charging box for charging electric vehicles and/or to other types of power supplies. The charging system comprises a LIT-based rectifier (LIT: Line Interphase Transformer), configured for connecting an input of the LIT-based rectifier to an AC medium-voltage power signal and for outputting a medium-voltage DC-signal; a modular DC/DC converter with large step-down gain, configured for transforming the medium-voltage DC-signal into a medium-voltage HF-AC-signal; and a medium-frequency transformer, MFT, configured for transforming the medium- voltage HF-AC-signal into a low-voltage HF-AC-signal for the at least one charging box (HF: high frequency).

The low-voltage power signal of the EV charging stations may have a voltage, ranging from about 400 V to 1000 V, or about 230 V, or about 110 V. This voltage or the low- voltage range may be the output-voltage of the charging box. The output-voltage of the charging box may be variable, e.g. depending on the charging needs. The input- voltage of the charging box may be a fixed voltage, e.g. ranging from about 400 V to 1000 V. Said input-voltage (and/or the power supply system) may be used for different and/or further types of power supplies with similar power demand, for instance for power data-centres with a plurality of computing servers, and/or for so-called “drives”, i.e. electrical machines connected via converter, e.g. in manufacturing centres. The drives may be implemented as electric motors, for instance as low-voltage motors or, after a transformation, as medium-voltage motors, and/or as other machines.

The power per EV charging station to be delivered may be about 350 kW, particularly for fast charging. EV charging stations may have several charging poles. Not every charging pole in one site may need to deliver this (“full”) power, not all cars may be charged at the same time. As an example, an EV charging station may have a power rating of around 2 MW. The AC medium-voltage power signal, which serves as an input for the LIT-based rectifier, may have a so-called medium-voltage (MV) of about 10 kV - 30 kV. The power signal may be part of a medium-voltage grid. The AC medium- voltage power signal may have, e.g., 3 phases, with AC of low frequency, for example of 50 or 60 Hz. The LIT-based rectifier may comprise a line-side interphase transformer - e.g. designed as a 12-pulse LIT or 18-pulse-LIT - and a multi-pulse diode rectifier. The rectifier is configured to output a medium-voltage DC-signal. There may be no galvanic insulation from the medium-voltage power signal. The DC-signal may provide an uncontrolled MV DC-link. Some schematic examples of LITs are depicted in the figures.

The modular DC/DC converter with large step-down gain may be configured to deliver the MV HF-AC-signal with a frequency of multiple times the mains frequency, for example of about 5 kHz - 20 kHz. One implementation of a modular DC/DC converter with large step-down gain may be a multilevel flying capacitor inverter. The MV HF-AC- signal is fed into the Medium-Frequency Transformer, MFT, configured for transforming the medium-voltage HF-AC-signal into the low-voltage HF-AC-signal, which may be an input for the at least one charging box and/or for the charging pole. The MFT may provide both a galvanic insulation from the medium-voltage power signal and a voltage adaption to the low-voltage HF-AC-signal. In at least some countries, the galvanic insulation from the MV grid may be a legal requirement. In case of more than one charging box, the charging boxes may comprise means for a galvanic insulation between the charging poles.

Accordingly, the charging system a simple system at low manufacturing-cost. Nevertheless, it can provide high power, due to its connection to an AC medium- voltage power signal or a medium-voltage grid. Moreover, the charging system is of small-size and low losses, for instance by avoiding large and expensive 50 Hz transformers.

In various embodiments, the charging system further comprises an inductor, configured for a filtering connection between each phase of the AC medium-voltage power signal and each input of the LIT-based rectifier. Thus, the inductor, which connects MV grid and LIT-based rectifier, is designed to reduce the current harmonics. In at least some countries, this may be a legal and/or a standard requirement, e.g. to comply with relevant MV grid standards, e.g. with IEEE 519 or I EC 61000-3-6. Advantageously, said requirements may be fulfilled without complex and expensive active frontends to the MV grid, thus leading to a simpler design, lower manufacturing-cost, and/or reducing maintenance efforts.

In various embodiments, the LIT-based rectifier comprises a multi-pulse LIT with a pulse number of 12, of 18, of 24, or of higher than 24. This advantageously leads to a reduction of the harmonics, thus reducing the need for an inductor as described above and/or below and/or reducing its impedance. This further contributes to an efficient power supply system, with quite low complexity in design and manufacturing.

In various embodiments, the LIT-based rectifier comprises a line-side interphase transformer, LIT, and a multi-pulse diode rectifier. This combination of components leads to a modular subsystem of a clear design and/or improved maintenance. The multi-pulse diode rectifier may be realized as a parallel-connected diode rectifier (see, e.g., the figures below). Alternatively, the multi-pulse diode rectifier may be realized as a series-connected diode rectifier, where the “DC-ends“ of the diode rectifier bridges are connected in series.

In some embodiments, each one of the diodes of the multi-pulse diode rectifier is realized as a thyristor. This advantageously provides a fast and simple breaking capability, e.g. in case of an overcurrent.

In various embodiments, the charging system further comprises a plurality of charging boxes, wherein each one of the plurality of charging boxes comprises a low-voltage MFT, a low-voltage AC/DC-converter, and a charging pole for charging electric vehicles. The plurality of charging boxes may comprise, e.g., two, four, six, a dozen and/or more charging boxes. This design of ensures each one of the plurality of charging boxes ensures a galvanic separation or insulation between the charging poles, which may be a legal and/or standard requirement in at least some countries.

Additionally or as an alternative, the charging system or power supply system may be connected to other types of power supplies and/or bridges or control modules. Said power supplies, bridges, and/or control modules may be used for supplying a plurality of servers or other computer in a data-centre, a site for server-clouds, other computing applications, and/or for a plurality of electric motors.

An aspect relates to a method for transforming an AC medium-voltage power signal into a low-voltage power signal for at least one charging box for charging electric vehicles. The method comprising the steps of: providing the AC medium-voltage power signal; transforming, by means of a LIT-based rectifier, the AC medium-voltage power signal into a medium-voltage DC-signal; transforming the medium-voltage DC-signal into a HF-AC medium-voltage signal; and transforming, by means of a medium-frequency transformer, MFT, the HF AC medium- voltage signal into the low-voltage power signal, wherein the low-voltage power signal is a HF-AC signal and is configured to serve as a low-voltage power signal for at least one charging box. This method advantageously provides an easy-to-handle process to deliver high power to a plurality of charging boxes and/or charging poles for charging electric vehicles. Moreover, this concept contributes to a highly scalable design of charging poles, particularly for fast charging.

In various embodiments, the method further comprises the step of filtering, by means of an inductor, each phase of the AC medium-voltage power signal from each input of the LIT-based rectifier. This leads to an easy concept, while complying with high electrical standards, including towards MV grids.

An aspect relates to a charging system described above and/or below for delivering energy to a charging box and/or to a charging pole for charging electric vehicles.

In various embodiments, the low-voltage HF-AC-signal (59) is connected to a DC voltage bus for low-voltage power distribution. In some embodiments, the low-voltage HF-AC-signal is connected to a AC/DC transformer that outputs the LV DC signal to the DC voltage bus. The AC/DC transformer may be a rectifier, an AC/DC, and/or a similar component. The DC voltage bus advantageously provides a kind of multi purpose interface, which may serve as a basis for a plurality of use-cases and/or devices to connect to the DC voltage bus.

An aspect relates to a use of a charging system described above and/or below for delivering energy to a charging box, to a charging pole for charging electric vehicles, to a data-centre, and/or to low-voltage drives. The charging system or power supply system may be used in a data-centre to power, e.g., a plurality of servers, for instance a server cluster or a server cloud. The charging system or power supply system may be used in a manufacturing site to power a plurality of electric motors. The electric motors may have or comprise a bridge or control module with a function similar to the function of a charging box for EVs, in order to power electric motors of different voltages, frequencies, and/or power requirements.

For further clarification, the invention is described by means of embodiments shown in the figures. These embodiments are to be considered as examples only, but not as limiting. Brief Description of the Drawings

The figures depict:

Fig. 1a, 1b, 1c schematically various designs of a charging system according to embodiments;

Fig. 2a, 2b schematically various designs of a charging system according further embodiments;

Fig. 3a, 3b schematically a charging system and a method according to an embodiment; Fig. 4a, 4b, 4c schematically subsystems of a charging system according to embodiments;

Fig. 5a, 5b schematically further subsystems of a charging system according to embodiments;

Fig. 6a, 6b, 6c schematically simulations of an MV grid behaviour of a charging system according to an embodiment;

Detailed Description of Embodiments

Fig. 1a shows a charging system 10 with a 50 Hz MV/LV-transformer 12 for an insulation to an MV grid or AC medium-voltage power signal 11. The 50 Hz low-voltage signal is transformed by a 50 Hz LV/LV-transformer 14. The LV/LV-transformers 14 separate galvanically the plurality of charging poles 19 from each other. The two conversion stages of low-frequency transformers may result in a large system w.r.t. footprint and size. Between each one of the LV/LV-transformers 14 and the respective charging poles 19, an AC/DC-transformer and a DC/DC-transformer is arranged.

Fig. 1b shows a charging system 10 with a multi-winding 50 Hz transformer 13. This is a system with one conversion stage, thus both transforming MV to LV and providing of the plurality of charging poles 19 from each other. Fig. 1c shows a charging system 10 with a first conversion stage of a 50 Hz MV/LV-transformer 12. As a second conversion stage, the system 10 has a low voltage Medium-Frequency Transformer, LV/LV-MFT 17, whose higher frequency is provided by a DC/AC-transformer. Fig. 2a shows a charging system 10 with MV-MFTs 14 for a galvanic separation to the MV grid 11. Furthermore, it has LV/LV-MFTs 17 for a galvanic separation of the charging poles 19 from each other.

Fig. 2b shows a charging system 10 with a first conversion stage, an MV/LV-MFT 15, which is supplied by an MV-DC/AC converter for a high frequency, HF-AC. The second conversion stage are LV/LV-MFTs 17 for a galvanic separation of the charging poles 19 from each other.

Fig. 3a shows a schematic overview over a charging system 10. The charging system 10 is connected to an MV grid or AC medium-voltage power signal 11. The MV grid 11 is connected to inductor 20. The inductor 20 contributes to reduce the current harmonics. The inductor 20 is connected to an input 31 of a LIT-based rectifier 30. The LIT-based rectifier 30 outputs a MV DC-signal 39, which is fed to a modular DC/DC converter with large step-down gain 40, which delivers an MV HF-AC-signal 49, whose frequency is multiple times the mains frequency, e.g. in a frequency-range of about 5 kHz - 20 kHz. The MV HF-AC-signal 49 is fed to a Medium-Frequency Transformer, MFT 50, which transforms it into a low-voltage HF-AC-signal 59. The low-voltage power signal 59 may, additionally or as an alternative, be connected to an AC/DC rectifier 65 that outputs the LV DC signal to the DC voltage bus. The low-voltage HF- AC-signal 59 is then fed into a plurality of charging boxes 60. In an embodiment, the charging boxes 60 may be connected to the DC voltage bus. Each charging box 60 comprises a charging pole 19. Additionally or as an alternative, the low-voltage HF-AC- signal 59 may be fed into supply modules for computing machines, e.g. servers, for electric motors, and/or further types of power supply boxes.

Fig. 3b shows a flow diagram 70 of a method according to an embodiment. In a step 71 , an AC medium-voltage power signal 11 (see Fig. 3a) of low frequency - e.g. 50 Hz or 60 Hz - is provided. The medium-voltage power signal 11 may be part of a MV grid. In a step 72, each phase 11a, 11b, 11c of the AC medium-voltage power signal 11 is filtered from each input 31a, 31b, 31c of the LIT-based rectifier 30 by means of an inductor 20a, 20b, 20c. In a step 73, the AC MV power signal 11 is transformed into a medium-voltage DC-signal 39, by means of a LIT-based rectifier 30. In a step 74, the medium-voltage DC-signal 39 is transformed into a HF-AC medium-voltage signal 49.

In a step 75, the HF AC medium-voltage signal 39 is transformed into low-voltage power signal 59, by means of a medium-frequency transformer, MFT 50. The low- voltage power signal 59 is a HF-AC signal and is configured to serve as a low voltage power signal 61 for at least one charging box 60.

Fig. 4a schematically shows a subsystem of a charging system 10 as drawn in Fig. 3a. The subsystem comprises an AC medium-voltage power signal 11 with phases 11a, 11b, 11c. Each phase 11a, 11b, 11c is connected via an inductor 20a, 20b, 20c, respectively, to phase inputs 31a, 31b, 31c of a LIT-based rectifier 30. The LIT-based rectifier’s first component is a 12-pulse LIT (Line Interphase Transformer) 32, whose outputs 35 are fed to a multi-pulse diode rectifier 37. The LIT shown in Fig. 4a (and, analogously, in Fig. 5a) depicts the magnetic cores, which couple the inductive components of the LIT, as lines coupled by a magnetic reluctance (a small rectangular box as equivalent circuit diagram). The multi-pulse diode rectifier 37 outputs a medium- voltage DC-signal 39. The MV DC-signal 39 may be fed into a modular DC/DC converter with large step-down gain 40. Examples of a modular DC/DC converter with large step-down gain 40 are shown in Fig. 4b and 4c. Fig. 4b and 4c show the output stages and the flying capacitors of the modular DC/DC converter with large step-down gain 40, possibly implemented as a multilevel flying capacitor inverter. Each one of its outputs 49 are fed to a medium-frequency transformer, MFT (50), thus delivering a low- voltage HF-AC-signal 59. Fig. 5a is similar to Fig. 4a, depicting a LIT with an 18-pulse line-side interphase 32 and a respective multi-pulse diode rectifier 37. As an alternative, each of the diodes of the multi-pulse diode rectifiers 37 of Fig. 4a or Fig. 5a may be substituted by a thyristor, thus being able to break or to interrupt the power.

Fig. 5b shows, as an example, a subsystem of an EV charging system, which comprises six charging boxes 60. The charging boxes 60 may be connected to a DC voltage bus 65 for low-voltage power distribution. Each charging box 60 comprises a low-voltage AC/DC-converter and a charging pole 19, and each charging box 60, except one (the second from the top-most one), comprises a low-voltage MFT 17. The charging poles 19 are configured to charge electric vehicles, particularly for fast charging.

Fig. 6a shows results of a simulation of an MV grid 11, connected to a charging system 10 with a 12-pulse LIT 30 (see Fig. 4a). The charging system has an inductor 20a, 20b, 20c of L = 34 mH. The charging system has an output-voltage of 11.7 kV as medium- voltage DC-signal 39, with a power of 2 MW. In Fig. 6a, the current-harmonics of the MV grid 11 are depicted. The first harmonic has a current of 163 A, the 11 ^th harmonic has a current of 5.7 A, the 11 ^th harmonic has a current of 3.4 A, and other current- harmonics are not visible. Fig. 6b shows a voltage of each phase and its sum of a complete sine-curve. Fig. 6c shows the currents of each phase of a complete sine- curve. The simulations show the excellent distortion factor of this embodiment, which further provides a cost-efficient solution. Increasing the inductors 20a, 20b, 20c would further improve this result. List of Reference Symbols

10 charging system

11 medium-voltage signal

11a, 11b, 11c phases of a medium-voltage signal 17 low-voltage M FT

19 charging pole

20 inductor

20a, 20b, 20c inductors of the phases

30 Line Interphase Transformer, LIT

31 input of a LIT

31a, 31b, 31c inputs of each phase of the LIT

32 line-side interphase transformer

37 multi-pulse diode rectifier

39 medium-voltage DC-signal

40 modular DC/DC converter with large step-down gain

49 medium-voltage HF-AC-signal

50 Medium-Frequency Transformer, MFT

59 low-voltage HF-AC-signal

60 charging box

61 power signal

65 DC voltage bus for LV power distribution

70 flow diagram

71 - 75 steps