Voltage converter arrangement, charging circuit, and method for operating a voltage converter arrangement

Abstract

The invention discloses a voltage converter arrangement for galvanically isolated power transmission between a three-phase alternating voltage connection and a direct voltage connection. The voltage converter arrangement comprises a transformer having three primary windings and one secondary winding. The three primary windings of the transformer are arranged in a delta configuration, with a primary winding and a preferably bipolar switching element being arranged in series in each case.

Description

[0001] R. 415148

[0002] - 1 -

[0003] Description

[0004] title

[0005] Voltage converter arrangement, charging circuit and method for operating a voltage converter arrangement

[0006] Technical field

[0007] The present invention relates to a voltage converter arrangement and a charging circuit for an electrical energy storage device with such a voltage converter arrangement. The present invention further relates to a method for operating a voltage converter arrangement. In particular, the present invention relates to a galvanically isolated voltage converter arrangement for converting electrical energy between a three-phase AC voltage connection and a DC voltage connection.

[0008] background

[0009] Vehicles that are fully or partially electrically powered generally have an electrical energy storage device, such as a traction battery. Such a device can provide a direct current (DC) voltage, which can be converted into a single- or multi-phase alternating current (AC) voltage suitable for powering an electric motor using a suitable circuit (inverter). When the vehicle is stationary, the electrical energy storage device can be recharged from an external energy source. (For charging the electrical R. 415148)

[0010] - 2 -

[0011] For example, the alternating current (AC) voltage of a low-voltage network can be used for energy storage. For this purpose, the single- or multi-phase AC voltage of the low-voltage network must be converted into a direct current (DC) voltage suitable for charging the electrical energy storage device using a suitable charging circuit.

[0012] For example, the publication DE 10 2017 212 834 A1 describes a circuit topology in which such a charging circuit includes components of the electric drive system.

[0013] For charging the electrical energy storage device in an electric vehicle, it is desirable to provide galvanic isolation between the external energy source, in particular the AC mains, and the vehicle's electrical system with the high-voltage battery.

[0014] Disclosure of the invention

[0015] The present invention provides a voltage converter arrangement, a charging circuit for an electrical energy storage device, and a method for operating a voltage converter arrangement with the features of the independent claims. Further advantageous embodiments are the subject of the dependent claims.

[0016] Accordingly, the following is planned:

[0017] A voltage converter arrangement with a DC voltage connection and an AC voltage connection, as well as a transformer and a rectifier circuit. The DC voltage connection is designed to be coupled to a DC electrical network. In R. 415148

[0018] - 3 -

[0019] The DC network can, for example, power an electrical energy storage device such as the traction battery of an electric vehicle. The AC connection is designed to be coupled to a three-phase AC electrical network. This AC network could, for example, be a low-voltage power supply network. The transformer comprises three primary windings and one secondary winding. The primary and secondary windings are all wound around a common leg of the transformer. Furthermore, the three primary windings of the transformer are connected in a delta configuration. At each node, two primary windings are electrically coupled. Between each pair of nodes, a series connection consisting of a primary winding and a switching element is provided.The rectifier circuit is designed to convert an alternating voltage applied to the secondary winding of the transformer into a direct voltage in a first operating mode, and to supply this direct voltage to the DC terminal of the rectifier circuit, for example, in the form of two half-bridges. Furthermore, the rectifier circuit can be designed to convert a direct voltage supplied at the DC terminal into an alternating voltage in a second operating mode, and to supply this alternating voltage to the secondary winding.

[0020] Furthermore, the following is planned:

[0021] A charging circuit for an electrical energy storage device with a voltage converter arrangement according to the invention. The AC voltage connection can be designed to be coupled to a multi-phase electrical energy source, for example, a multi-phase AC network such as a low-voltage power supply network. The DC voltage connection R. 415148

[0022] - 4 - can also be designed to be coupled with the electrical energy storage device.

[0023] Finally, the following is planned:

[0024] A method for operating a voltage converter arrangement, in particular a voltage converter arrangement according to the invention. In the first operating mode, for electrical energy transfer from the AC voltage terminal to the DC voltage terminal, exactly two switching elements on the delta configuration of the primary windings of the transformer are closed, and the remaining third switching element is opened.

[0025] Advantages of the invention

[0026] Conventional circuits currently available for charging an electric energy storage device in a motor vehicle typically use so-called unidirectional switching elements. These unidirectional switching elements are semiconductor devices that can block or control an electrical voltage in one direction, but do not exhibit this blocking property when the polarity is reversed. Therefore, special circuit topologies or two complementary unipolar switching elements arranged in series are required for use with alternating currents.

[0027] The present invention is based on the discovery that so-called bipolar semiconductor switching elements have recently become available, which can block and selectively switch an electrical voltage for both polarities. Based on such bipolar semiconductor switching elements, further novel concepts are therefore possible. R. 415148

[0028] - 5 -

[0029] Based on this finding, the present invention provides a voltage converter arrangement, in particular a galvanically isolated voltage converter arrangement, which is suitable for efficiently converting a supplied (three-phase) alternating voltage into a direct voltage for charging an electrical energy storage device, such as the traction battery of an electric vehicle.

[0030] In particular, the use of a special transformer arrangement for galvanic isolation between the AC and DC voltage connections allows for a particularly clever, efficient and space-saving configuration.

[0031] Furthermore, the proposed concept according to the invention makes it possible to selectively control the load on the individual phases of the connected AC power network. This allows, for example, a targeted symmetrical load on the AC power network to be achieved. In addition, the reactive power component can also be adjusted and, in particular, minimized.

[0032] According to one embodiment, the switching elements in the series circuits of switching element and primary winding between each pair of nodes of the delta configuration on the transformer each comprise a bipolar switching semiconductor switching element. Such bipolar switching semiconductor switching elements are capable of blocking and selectively switching electrical voltages regardless of their polarity. This makes it possible to control the electrical current through the corresponding primary winding using only a single bipolar switching semiconductor switching element. R. 415148

[0033] - 6 -

[0034] According to one embodiment, the primary winding and the three secondary windings of the transformer are wound concentrically around a common leg of the transformer. This allows for very good magnetic coupling. Furthermore, such a configuration enables a particularly compact design, requiring minimal installation space. Preferably, the number of turns in the individual secondary windings, and optionally also in the primary winding, can be identical or at least approximately the same.

[0035] According to one embodiment, the transformer can include an E-core. In this configuration, the primary winding and the three secondary windings of the transformer are wound around a common leg, in particular the inner leg of the E-core of the transformer. However, depending on the application, other suitable configurations are also possible.

[0036] According to one embodiment, an inductor is arranged between each connection point of the AC voltage connection and the corresponding node of the triangular configuration of the primary windings of the transformer.

[0037] According to one embodiment, the voltage converter arrangement includes a control device. The control device is designed to control the switching elements in the delta configuration of the transformer as well as the switching elements in the rectifier circuit. In particular, the control device can be designed to close exactly two switching elements in the delta configuration of the primary windings of the transformer at any given time during operation, especially during the first operating mode of the voltage converter arrangement. In this way, an electrical current flow between all three phase terminals of the AC voltage connection can always be ensured. R. 415148

[0038] - 7 -

[0039] According to one embodiment, in the first operating mode, the rectification of the alternating voltage from the transformer is achieved by active rectification, that is, by controlling switching elements in the half-bridges of the rectifier circuit. Here, an individual duty cycle for controlling the rectifier circuit can be provided for each configuration of the possible switching states of the switching elements on the primary windings of the transformer.

[0040] According to one embodiment, the power transmission can be adjusted by controlling the switching times of the switching elements on the primary windings of the transformer. Furthermore, the power transmission can also be adjusted using the duty cycle for active rectification in the rectifier circuit.

[0041] The above embodiments and further developments can be combined with one another as appropriate. Further embodiments, further developments, and implementations of the invention also include combinations of features of the invention described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

[0042] Brief description of the drawings

[0043] Further features and advantages of the invention are explained below with reference to the figures. These show:

[0044] Fig. 1: A schematic representation of a basic circuit diagram of a charging circuit for an electrical energy storage device with a voltage converter arrangement according to one embodiment; R. 415148

[0045] - 8 -

[0046] Fig. 2: a schematic representation of a cross-section through a top view of a transformer, as it may form the basis of a voltage transformer arrangement according to a further embodiment; and

[0047] Fig. 3: a flowchart as it may form the basis of a method for operating a voltage converter arrangement according to one embodiment.

[0048] Description of embodiments

[0049] Figure 1 shows a schematic diagram of a charging circuit for an electrical energy storage device 3 according to one embodiment. The charging circuit comprises a voltage converter arrangement 1 with an AC voltage connection 11 and a DC voltage connection 12. An AC voltage network, in particular a three-phase AC voltage network 2, such as a low-voltage power supply network, can be connected to the AC voltage connection 11. Each connection point of the AC voltage connection 11 can be connected to one phase of the AC voltage network 2. A DC voltage network, for example the electrical system of an electric vehicle with an electrical energy storage device 3 such as a traction battery, can be connected to the DC voltage connection 12.

[0050] Furthermore, the voltage converter arrangement 1 includes a transformer 20 and a rectifier circuit 50.

[0051] The transformer 20 comprises several primary windings 21, 22, 23 and one secondary winding 24. The primary windings 21, 22, 23 of the transformer 20 R. 415148

[0052] - 9 - are arranged in a triangular configuration. In particular, a primary winding 21, 22, 23 is arranged between each pair of nodes K1, K2, K3. A series circuit consisting of a primary winding 21-23 and a semiconductor switching element 31-33, in particular a bipolar switching semiconductor switching element, is arranged between each pair of nodes K1, K2, K3. In the embodiment shown in Figure 1, for example, a first primary winding 21 and a first switching element 31 are arranged between the first node K1 and the second node K2. Furthermore, a second primary winding 22 and a second switching element 32 are arranged between the second node K2 and the third node K3. Finally, a third primary winding 23 and a third switching element 33 are arranged between the third node K3 and the first node K1.Each node K1, K2, K3 is connected to a corresponding connection point of the AC voltage terminal 11. An inductor 41, 42, 43 can be provided between the AC voltage connection point and the corresponding node K1, K2, K3.

[0053] The rectifier circuit 50 is arranged between the secondary winding 24 of the transformer 20 and the DC voltage terminal 12. The rectifier circuit 50 can be an active rectifier circuit with two half-bridges. Such an active rectifier circuit 50 can, for example, be formed using four semiconductor switching elements 51, 52, 53, 54. However, since the basic operating principle of such an active rectifier circuit is considered well known, it will not be explained in detail here.

[0054] The rectifier circuit 50 can rectify the AC voltage supplied at the secondary winding 24 of the transformer 20 and supply it at the DC voltage terminal 12 during energy transfer from the AC voltage terminal 11 to the DC voltage terminal 12. Optionally, for inverse energy transfer from the DC voltage terminal 12 to the AC voltage terminal 11, a rectifier circuit can be connected to the R. 415148.

[0055] - 10 -

[0056] DC voltage connection 12: The DC voltage supplied is used to generate an AC voltage by appropriately controlling the switching elements 51 to 54 of the rectifier circuit 50 and is supplied to the secondary winding 24 of the transformer 20.

[0057] The control of the switching elements 31 to 33 in the delta configuration of the transformer 20 and the switching elements 51 to 54 of the rectifier circuit 50 can be carried out, for example, by means of a control device 90.

[0058] Figure 2 shows a schematic cross-section of a transformer 20, such as can form the basis of an embodiment of the voltage transformer arrangement 1. As can be seen in Figure 2, all primary windings 21, 22, 23 and the secondary winding 24 of the transformer 20 can be wound around a common leg 25 of a transformer core. In the embodiment shown in Figure 2, the primary windings 21, 22, 23 and the secondary winding 24 are arranged concentrically from the inside out. The transformer core can, for example, be an E-core made of ferrite. Such an E-core can, for example, have two outer legs 26a, 26b and at least one inner leg 25. The windings 21 to 24 of the transformer 20 can be wound around the inner leg 25 of the E-core.

[0059] The operation of the voltage transformer arrangement 1, and in particular the power transfer between AC terminal 11 and DC terminal 12, can be controlled by selectively switching the switching elements 31 to 33 in the delta configuration of the transformer 20 and by controlling the switching elements 51 to 54 of the rectifier circuit 50. To ensure that an electric current flow is always present in all three phases at the AC terminal 11 during operational use, R. 415148

[0060] - 11 - of the three switching elements 31 to 33 in the delta configuration of the transformer 20, exactly two of the three switching elements 31 , 32, 33 must always be closed during an energy transfer from AC voltage terminal 11 to the DC voltage terminal 12.This results in three possible switching states: either the first switching element 31 and the second switching element 32 are closed and the third switching element 33 is open; or the second switching element 32 and the third switching element 33 are closed and the first switching element 31 is open; or the first switching element 31 and the third switching element 33 are closed and the second switching element 32 is open. By varying the times for switching between these three states with respect to the AC voltage applied to the AC voltage terminal 11, three degrees of freedom are obtained, each specifying how long the voltage converter arrangement 1 remains in each of the three switching states per period. Furthermore, a fourth degree of freedom results from the duty cycle for controlling the switching elements 51 to 54 in the rectifier circuit 50.Here, an individual duty cycle for the rectifier circuit 50 can be specified for each switching state of the switching elements 31 to 33.

[0061] In particular, the duty cycle of the rectifier circuit 50 during active power transfer from the AC voltage terminal 11 to the DC voltage terminal 12 can be controlled in such a way that, on the one hand, the duty cycle for each switching state is as large as possible, while on the other hand minimizing the proportion of circulating reactive power within the system.

[0062] Finally, Figure 3 shows a schematic representation of a flowchart for a method for operating a voltage transformer arrangement, in particular a voltage transformer arrangement 1 according to the invention as described above. Accordingly, the method can, in principle, comprise any steps suitable for realizing the voltage transformer arrangement 1 described above. Similarly, the voltage transformer arrangement 1 described above can also comprise any R. 415148

[0063] - 12 -

[0064] Include components or units suitable for implementing the procedure described below.

[0065] In a first operating mode S1, electrical energy can be transferred from the AC voltage terminal 11 to the DC voltage terminal 12. Optionally, in a further operating mode S2, electrical energy can be transferred in the reverse direction from the DC voltage terminal 12 to the AC voltage terminal 11.

[0066] In the first operating mode S1 for power transmission from the AC terminal 11 to the DC terminal 12, three switching states can be cyclically assumed by the switching elements 31, 32, 33, as previously described. Specifically, in each of these three switching states S1a, S1b, and S1c, two switching elements are closed and the third is open. For example, in the first switching state S1a, the first and second switching elements 31, 32 can be closed and the third switching element 33 open. In the second switching state S1b, the second and third switching elements 32, 33 can be open and the first switching element 31 can be open. In the third switching state S1c, the first and third switching elements 31, 33 can be closed and the second switching element 32 can be open.

[0067] For each of the three switching states S1a, S1b and S1c, individual duty cycles may be provided for controlling the switching elements 51 to 54 of the rectifier circuit 50.

[0068] Optionally, a further operating mode S2 can be provided, in which the power transfer takes place from the DC voltage terminal 12 towards the AC voltage terminal 11. In this mode, the switching elements 51 to 54 of the rectifier circuit 50 are controlled such that, using the DC voltage provided at the DC voltage terminal 12, the rectifier circuit 50 is switched on. 415148

[0069] - 13 -

[0070] An alternating voltage is supplied to the secondary winding 24 of the transformer 20. The power transfer can further be controlled by appropriately controlling the switching elements 31-33 at the primary winding in 21-23.

[0071] In summary, the present invention relates to a voltage converter arrangement for galvanically isolated power transmission between a three-phase AC voltage connection and a DC voltage connection. The voltage converter arrangement comprises a transformer with three

[0072] Primary windings and a secondary winding. The three primary windings of the transformer are arranged in a triangular configuration, with each primary winding and a preferably unipolar switching element arranged in series.

Claims

R. 415148 - 14 - Claims 1. Voltage transformer arrangement (1), comprising: a DC voltage connection (12) designed to be coupled to a DC electrical network; an AC voltage connection (11) designed to be coupled to a three-phase AC electrical network (2); a transformer (20) with three primary windings (21-23) and one secondary winding (24);a rectifier circuit (50) designed to convert an alternating voltage applied to the secondary winding (24) of the transformer (20) into a direct voltage and provide it at the DC terminal (12) in a first operating mode and / or to convert a direct voltage provided at the DC terminal (12) into an alternating voltage and provide the alternating voltage at the secondary winding (24) of the transformer (20) in a second operating mode, wherein the three primary windings (21-23) and the secondary winding are all wound around a common leg (25) of a transformer (20), and wherein the three primary windings (21-23) of the transformer (20) are interconnected in a delta configuration, with each node (K1-K3) having two primary windings (21-23) electrically coupled to each other, and between each node (K1-K3) having one primary winding (21-23) electrically coupled to each other; R. 415148 - 15 - A series circuit consisting of a primary winding (21-23) and a switching element (31-33) is provided.

2. Voltage converter arrangement (1) according to claim 1, wherein the switching elements (31-33) in the series circuits of switching element (31-33) and primary winding (21-23) each comprise a bipolar switching semiconductor switching element.

3. Voltage converter arrangement (1) according to claim 1 or 2, wherein the primary windings (21-23) and the secondary winding (24) are wound concentrically around a common leg (25) of the transformer (20).

4. Voltage converter arrangement (1) according to one of claims 1 to 3, wherein the primary windings (21-23) and the secondary winding (24) are wound around a common inner leg (25) of an E-core of the transformer (20).

5. Voltage converter arrangement (1) according to one of claims 1 to 4, wherein an inductor (41-43) is arranged between a connection point of the AC voltage connection (11) and a corresponding node (K1-K3) of the primary windings (21-23) of the transformer (20).

6. Voltage converter arrangement (1) according to one of claims 1 to 5, with a control device (90) designed to close exactly two switching elements (31-33) in the delta configuration of the transformer (20) during the operational operation of the voltage converter arrangement (1).

7. Voltage converter arrangement (1) according to claim 6, wherein the rectification of the alternating voltage from the transformer (20) in the first operating mode comprises active rectification and for each configuration of the possible switching states of the switching elements (31-33) on the primary windings (21-23) of the transformer (20) an individual duty cycle for controlling the rectifier circuit (50) is assigned. R. 415148 - 16 - 8. Charging circuit for an electrical energy storage device (3), comprising: a voltage converter arrangement (1) according to one of claims 1 to 7, wherein the AC voltage connection (11) is designed to be connected to a multi-phase electrical energy source, and wherein the DC voltage connection (12) is designed to be coupled to the electrical energy storage device (2).

9. Method for operating a voltage converter arrangement (1) according to one of claims 1 to 7, wherein in the first operating mode for electrical energy transmission from the AC voltage terminal to the DC voltage terminal two of the switching elements (31-33) are closed and one switching element (31-33) is open.

10. Method according to claim 9, wherein the power transmission is set using a control of the switching times for the switching elements (31-33) on the primary windings (21-23) of the transformer (20) and a duty cycle for active rectification in the rectifier circuit (50).

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