VOLTAGE TRANSFORMER

Abstract

The invention relates to a voltage transformer for converting a primary-side alternating voltage at a first voltage level into a secondary-side alternating voltage at a second voltage level, the voltage transformer having a DC link in which a first direct voltage generated from the primary-side alternating voltage is converted into a second direct voltage by means of a DC-to-DC voltage converter, characterised in that an output circuit for providing a third direct voltage for the connection of at least one load is coupled to the DC link, in particular to the DC-to-DC voltage converter thereof.

Claims

1. A voltage transformer for converting a primary-side alternating voltage (MVAC) at a first voltage level into a secondary-side alternating voltage (LVAC) at a second voltage level, comprising: a direct voltage intermediate circuit in which a first direct voltage from a primary-side alternating voltage is converted into a second direct voltage by a DC-to-DC converter, and a decoupling circuit for providing a third direct voltage, wherein the decoupling circuit is coupled with the direct voltage intermediate circuit, for connecting at least one consumer.

2. The voltage transformer as claimed in claim 1, wherein a first voltage level of the first direct voltage is a voltage level of an AC medium voltage network and wherein a second voltage level of the second direct voltage is a voltage level of an AC low-voltage network.

3. The voltage transformer as claimed in claim 1 wherein the decoupling circuit is integrated into the DC-to-DC converter in an electrical and/or magnetic manner.

4. The voltage transformer as claimed in claim 1 wherein the DC-to-DC converter is constructed in a modular manner from a multiplicity of individual DC-DC converter modules which are connected to one another in parallel on a secondary side.

5. The voltage transformer as claimed in claim 4, wherein the DC-DC converter modules are connected on a primary side either directly in series or via AC-DC converter modules in series.

6. The voltage transformer as claimed in claim 4 further comprising one or more a decoupling modules added to some or all of the DC-DC converter modules on the primary side, wherein the decoupling modules are connected to one another to form the decoupling circuit.

7. The voltage transformer as claimed in claim 6, wherein the one or more decoupling modules are connected to one another in series, in order to provide the third direct voltage.

8. The voltage transformer as claimed in claim 4 further comprising a DC-DC converter module which has a primary-side converter cell and a secondary-side converter cell which are coupled with one another via galvanically isolated windings of a transformer.

9. The voltage transformer as claimed in claim 8, wherein the decoupling module is coupled with a further winding of the transformer, such that the decoupling module is supplied with electrical energy via the transformer in an inductive manner.

10. The voltage transformer as claimed in claim 8 wherein the transformer has a magnetic core on which windings of the transformer are arranged.

11. The voltage transformer as claimed in claim 1 further comprising a charging station for charging electric vehicles is coupled with the third direct voltage.

12. The voltage transformer as claimed in claim 11, wherein the charging station is coupled with the third direct voltage via a DC-DC converter.

13. A method for providing electrical energy for charging electric vehicles with direct current, comprising: converting, using a voltage transformer, a primary-side alternating voltage at a first voltage level into a secondary-side alternating voltage at a second voltage level, wherein the voltage transformer has a direct voltage intermediate circuit in which a first direct voltage generated from a primary-side alternating voltage is converted into a second direct voltage by a DC-to-DC converter, and feeding a third direct voltage is decoupled from the direct voltage intermediate circuit into the electric vehicle for charging the electric vehicle.

14. The method as claimed in claim 13 wherein the third direct voltage is decoupled from the DC-to-DC converter of the direct voltage intermediate circuit and is fed into the electric vehicle for charging the electric vehicle.

15. The voltage transformer as claimed in claim 1 wherein the decoupling circuit is coupled with the direct voltage intermediate circuit by the DC-to-DC converter of the direct voltage intermediate circuit.

Description

[0022] The invention is explained in greater detail hereinafter by means of exemplary embodiments using drawings.

[0023] In the drawings

[0024] FIG. 1shows a voltage transformer in a block diagram representation and

[0025] FIG. 2shows a voltage transformer in the form of a cascaded H-bridge (CHB) and

[0026] FIG. 3shows a DC-DC converter module and

[0027] FIG. 4shows the circuit of one phase of the voltage transformer according to FIG. 2 using DC-DC converter modules according to FIG. 3 and

[0028] FIG. 5shows the topology of the entire voltage transformer using DC-DC converter modules according to FIG. 3 and

[0029] FIG. 6shows the voltage transformer according to FIG. 5 with decoupling circuits connected to one another in parallel and

[0030] FIG. 7shows one alternative embodiment of the circuit of one phase of the voltage transformer and

[0031] FIG. 8shows a voltage transformer with a modular multilevel converter and

[0032] FIG. 9shows the circuit of one phase of the voltage transformer according to FIG. 2 with an alternative form of the decoupling modules and

[0033] FIG. 10shows the circuit of one phase of the voltage transformer with provision of the third direct voltage at a different voltage level.

[0034] The reference numbers used in the figures have the following allocation: [0035] 1 Voltage transformer [0036] 2 AC-DC converter [0037] 3 DC-to-DC converter [0038] 4 DC-AC converter [0039] 5 primary-side direct voltage circuit [0040] 6 secondary-side direct voltage circuit [0041] 7 decoupling circuit [0042] 8 coupling network [0043] 9 DC-DC converter [0044] 10 consumer [0045] 11 DC-DC converter [0046] 12 electrical system [0047] 13 primary-side alternating voltage network [0048] 14 secondary-side alternating voltage network [0049] 20 AC-DC converter modules [0050] 30 converter cell [0051] 31 transformer [0052] 32 converter cell [0053] 33 winding [0054] 34 core [0055] 35 winding [0056] 36 decoupling module [0057] 37 DC-DC converter module [0058] 38 diode full bridge [0059] 39 modular multilevel converter [0060] 40 integrated converter module [0061] MVAC primary-side alternating voltage [0062] MVDC first direct voltage [0063] LVAC secondary-side alternating voltage [0064] LVDC second direct voltage [0065] MVDC2, [0066] LVDC2 third direct voltage

[0067] FIG. 1 shows the voltage transformer 1 in an electrical energy supply system in which a primary-side alternating voltage network 13, for example a three-phase AC medium voltage network, is coupled with a secondary-side alternating voltage network 14, for example a four-line AC low-voltage network.

[0068] The primary-side alternating voltage network 13 is connected to a direct voltage intermediate circuit 3, 5, 6 via an AC-DC converter 2. A primary-side alternating voltage MVAC at a first voltage level is converted into a first direct voltage MVDC by the AC-DC converter 2. In the direct voltage intermediate circuit 3, 5, 6, a DC-to-DC converter 3 is present which is coupled with the direct voltage output of the AC-DC converter 2 via a primary-side direct voltage circuit 5 and to which the first direct voltage MVDC is thus supplied. The DC-to-DC converter 3 converts the first direct voltage MVDC into a second direct voltage LVDC. The DC-to-DC converter 3 is coupled with a DC-AC converter 4 via a secondary-side direct voltage circuit 6. The DC-AC converter 4 converts the second direct voltage LVDC supplied to it from the DC-to-DC converter 3 into a secondary-side alternating voltage LVAC of the secondary-side alternating current network 14.

[0069] In the secondary-side direct voltage circuit 6, an electrical system 12 can be connected which is operated with a direct voltage at a low voltage level LVDC, for example a photovoltaic system which, via a DC-DC converter 11, is connected to a coupling network 8 via which the electrical system 12 is connected to the secondary-side direct voltage circuit 6.

[0070] In addition, FIG. 1 shows a consumer 10 which is operated with a third direct voltage MVDC2 at a high voltage level. It can be a charging station for electric vehicles, for example, which is coupled with the third direct voltage MVDC2 via a DC-DC converter 9. According to the invention, the third direct voltage MVDC2 is provided via a decoupling circuit 7 which is coupled with the direct voltage intermediate circuit 3, 5, 6, in particular with the DC-to-DC converter 3. Advantageous ways of coupling the decoupling circuit 7 with the DC-to-DC converter 3 are explained hereinafter.

[0071] The normal (known) structure of a voltage transformer without a decoupling circuit 7 of this type shall firstly be described by means of FIG. 2. FIG. 2 shows a voltage transformer in CHB topology. In this case, the circuit components for one phase (phase C) of the three-phase primary-side alternating voltage network 13 are specified in detail in the right part of FIG. 2. For the other phases A, B, a comparable circuit is included which is only depicted as a block for the purpose of simplification. The circuit in a phase A, B, C firstly has a series connection of primary-side AC-DC converter modules 20 which together (as a series connection) form the AC-DC converter 2 of a phase A, B, C. In this way, the AC-DC converter 2 can also be constructed in a modular manner.

[0072] A DC-DC converter module 37 is connected downstream of a respective AC-DC converter module 20. The entirety of the DC-DC converter modules 37 forms the DC-to-DC converter 3. The DC-DC converter modules 37 can be connected in parallel on the secondary side and are then connected to the direct voltage connection of the DC-AC converter 4. The individual DC-DC converter modules 37 can have a structure with 2 converter cells 30, 32 in each case which are connected via a transformer 31. A DC-DC converter module can in this way be designed as a multiple active bridge, for example.

[0073] As one aspect of the present invention, FIG. 3 shows the extension of a DC-DC converter module 37 to include a decoupling module 36. It is recognizable that the converter cells 30, 32 are coupled with one another in an inductive manner via windings 33 of the transformer 31. The decoupling module 36 can be connected to the converter cells 30, 32 in an inductive manner, for example, by extending the transformer 31 to include an additional winding 35. The transformer 31 can have a magnetic core 34 on which the windings 33, 35 are arranged, in order to increase the degree of coupling between the windings 33, 35. The decoupling module 36 can be designed as a DC-DC converter cell, for example, which has a similar functionality and a similar structure to the converter cells 30, 32.

[0074] By means of a cut-out of the voltage transformer from FIG. 2 which only shows the structure of phase C, FIG. 4 shows the integration of DC-DC converter modules 37 of the type described in FIG. 3. In particular, it is recognizable that the individual decoupling modules 36 are connected in series. The desired third direct voltage MVDC2 can be tapped via the series connection of the decoupling modules 36, which thus represent the decoupling circuit 7.

[0075] FIG. 5 shows the integration of the DC-DC converter modules 37 into the complete voltage transformer according to FIG. 2 in a strongly schematized manner. In this case, a DC-DC converter module m1 is fully represented only by means of phase C, the remaining modules m2 to mn are constructed in a comparable manner.

[0076] As can be recognized, a third direct voltage MVDC2 in each case decoupled from other third direct voltages MVDC2 can be obtained from each phase A, B, C in the circuit arrangement represented. Three separate consumers 10 can be supplied with the third direct voltage MVDC2 accordingly, for example. It is also possible to connect two or all three of the branches carrying the third direct voltage MVDC2 in parallel or in series. In a parallel connection, the available current can be increased, in a series connection, the available direct voltage can be increased.

[0077] FIG. 6 shows a parallel connection of this type of all three branches carrying the third direct voltage MVDC2.

[0078] As can be recognized, the invention thus also allows for scalability of the third direct voltage MVDC2 provided via the decoupling circuit both in terms of the voltage level and in terms of the available current. The different third direct voltages MVDC2 provided via the individual phases A, B, C are galvanically decoupled from one another, which opens up a multiplicity of application possibilities and interconnection options. A multiplicity of control and error response scenarios can be realized by appropriately controlling the DC-DC converter modules 37 and the decoupling modules 37, for example by way of software-controlled regulation. In particular, realizing the voltage transformer in a CHB topology can be implemented advantageously, since the CHB topology is already established and well received in energy supply technology.

[0079] FIG. 7 shows an embodiment of the voltage transformer in which the AC-DC converter modules 20 described previously as individual components by means of FIG. 4, for example, and the respective converter cells 30 of a DC-DC converter module 37 can be combined, for example as an integrated converter module 40. Moreover, the decoupling circuit can remain identical. In the embodiment according to FIG. 7, direct input-side processing of an alternating voltage from the primary-side alternating voltage network 13 is thus possible.

[0080] FIG. 8 shows an embodiment of the voltage transformer, specifically by means of one phase, as represented in FIG. 4, wherein the primary-side alternating voltage network 13 is connected to the direct voltage input side of the DC-DC converter modules 37 via a modular multilevel converter 39. The modular multilevel converter 37 therefore replaces the individual AC-DC converters 20 in this case.

[0081] In the exemplary embodiments described previously, the decoupling circuit has a fundamentally bidirectional functionality as a result of the bidirectional mode of operation of the decoupling modules 36 used. In applications in which the bidirectionality is not required, this decoupling circuit can also be designed in a unidirectional manner. For this purpose, instead of the decoupling modules 36, unidirectional modules 38 can be used which can be designed in terms of circuitry, for example, as diode full bridges, as represented in FIG. 9. In this case, the power flow can still be controlled independently.

[0082] In the exemplary embodiments described previously, the decoupling module 36 was used in each case in such a way that the third direct voltage is provided at a comparatively high direct voltage level. As represented in FIG. 10, the decoupling module 36 can be connected and configured in such an alternative manner that a voltage LVDC2 at a low voltage level is provided as a third direct voltage, which is advantageous, for example, if separate loads are to be supplied at the voltage level LVDC2. In this way, an additional electrical energy supply can be provided for charging electric vehicles. This topology is in particular advantageous with an input-side cascaded H-bridge (CHB) topology. The additional LVDC intermediate circuit (LVDC2) makes it possible to compensate for the asymmetries in the CHB in the event of different loads. The outputs of the decoupling circuits 7 can be connected in parallel.

[0083] It is also possible to realize the DC-DC converter module 37 with decoupling modules 36 on both sides in such a way that, on the one hand, a third direct voltage MVDC2 is provided at a high voltage level and, on the other hand, a third direct voltage LVDC2 is provided at a low voltage level.