Power converter, charging device for an electric vehicle, and method for operating a power converter

Abstract

The invention relates to an electrical power converter for energy transfer between an AC voltage terminal and a DC voltage terminal. The power converter is characterized by a particularly simple and thus efficient and cost-effective configuration with a minimal number of required switching elements.

Description

[0001] R. 417919

[0002] - 1 -

[0003] Description

[0004] title

[0005] Power converter, charging device for an electric vehicle and method for operating a power converter

[0006] Technical field

[0007] The present invention relates to an electrical power converter and a method for operating such an electrical power converter. The present invention further relates to a charging device for an electric vehicle with such a power converter.

[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 example, the AC voltage from a low-voltage network can be used to recharge the electrical energy storage device. For this purpose, the single- or multi-phase AC voltage of the low-voltage network must be converted into a DC voltage suitable for recharging the electrical energy storage device using a suitable charging circuit. R. 417919

[0010] - 2 -

[0011] For example, the publication DE 10 2017212 834 A1 describes a circuit topology in which such a charging circuit includes components of the electric drive system.

[0012] Disclosure of the invention

[0013] The present invention provides an electrical power converter, a method for operating an electrical power converter, and a charging device for an electric vehicle, comprising the features of the independent claims. Further advantageous embodiments are the subject of the dependent claims.

[0014] Accordingly, the following is planned:

[0015] An electrical power converter comprising an AC input, a DC input, a transformer, a first circuit component, and a second circuit component. The AC input is designed to be electrically coupled to a multiphase AC power supply. The DC input is designed to be electrically coupled to a DC power supply. The transformer comprises a primary and a secondary side. The second circuit component is arranged between the DC input and the secondary side of the transformer. In particular, the second circuit component is designed to rectify an AC voltage supplied at the secondary side of the transformer and supply it at the DC input.Additionally or alternatively, the second circuit component can also be designed to convert a DC voltage supplied at the DC terminal into an AC voltage and supply it to the secondary side of the transformer. The first circuit component comprises four bipolar switching elements arranged in series. A first bipolar switching element is arranged between the first node and a second node. A second bipolar R. 417919.

[0016] - 3 -

[0017] A switching element is arranged between the second node and a third node. A third bipolar switching element is arranged between the third node and a fourth node. A fourth bipolar switching element is arranged between the fourth node and a fifth node. The second node is electrically coupled to a first terminal on the primary side of the transformer. The fourth node is electrically coupled to a second terminal on the primary side of the transformer. One phase terminal of the AC voltage connection is electrically coupled to the third node, the first node, and the fifth node.

[0018] Furthermore, the following is planned:

[0019] A charging device for an electric vehicle comprising a charging port and a power converter according to the invention. The charging port is designed to be electrically coupled to an AC voltage source. The AC voltage port of the power converter is electrically coupled to the charging port. Furthermore, the DC voltage port of the power converter is designed to be electrically coupled to an electrical energy storage device, for example, a traction battery of the electric vehicle.

[0020] Finally, the following is planned:

[0021] A method for operating an electrical power converter, an electrical power converter according to the invention. The method comprises a step for controlling the bipolar switching elements in the first circuit component. The controlling of the switching elements in the first circuit component can be carried out using a previously stored modulation scheme. Preferably, the method comprises a step for controlling the switching elements in the second circuit component. The controlling of the switching elements in the second circuit component can be carried out using a further previously stored modulation scheme. R. 417919

[0022] - 4 -

[0023] Advantages of the invention

[0024] To charge an electric vehicle using electrical energy from an AC grid, it is necessary to rectify the AC voltage from the grid and adjust the output DC voltage to a level suitable for charging the vehicle's electrical energy storage system. Conversely, the electrical energy from the vehicle's energy storage system can also be used to operate an AC load or to feed electrical energy into an AC grid. For this, the DC voltage from the energy storage system must be converted into AC voltage and the voltage level adjusted to a target output voltage.To meet all the requirements, including galvanic isolation between the AC and DC voltage connections, conventional approaches have so far required relatively complex circuit topologies. These require a correspondingly large installation space and are also associated with high costs.

[0025] Based on this insight, the idea of ​​the present invention is therefore to create a concept for an electrical power converter between an AC voltage connection and a DC voltage connection, which enables bidirectional voltage conversion in a simple, cost-effective and efficient manner.

[0026] The concept according to the invention makes it possible to realize bidirectional energy transfer with a relatively small number of semiconductor switching elements and a simple transformer for galvanic isolation between the AC voltage side and the DC voltage side.

[0027] Furthermore, the concept according to the invention enables operation with three electrical phases on the AC voltage side. Thus, R. 417919

[0028] - 5 -

[0029] The proposed electrical power converter can be used in a particularly versatile way, without requiring complex and therefore costly circuit topologies.

[0030] According to one embodiment, the four bipolar switching elements of the first circuit component each comprise a series connection of two anti-series connected unidirectional semiconductor switching elements. Such a combination of two unidirectional semiconductor switching elements enables the realization of a circuit arrangement that can block an electrical voltage regardless of the applied polarity.

[0031] According to an alternative embodiment, the four bipolar switching elements of the first circuit component each comprise a monolithic, bidirectionally switching semiconductor switching element. Such semiconductor switching elements are capable of reliably interrupting an electrical voltage regardless of the applied polarity.

[0032] 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, those skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

[0033] Brief description of the drawings

[0034] Further features and advantages of the invention are explained below with reference to the figures. These show:

[0035] Fig. 1: A schematic representation of a basic circuit diagram of a power converter according to one embodiment; R. 417919

[0036] - 6 -

[0037] Fig. 2: a schematic representation of a possible embodiment for a bidirectional switching element according to one embodiment;

[0038] Fig. 3: a schematic representation of a bidirectional switching element according to a further embodiment;

[0039] Fig. 4: a flowchart as it may form the basis of a method for operating an electrical power converter according to one embodiment.

[0040] Description of embodiments

[0041] Figure 1 shows a schematic representation of a basic circuit diagram for an electrical power converter 1 according to one embodiment. The electrical power converter 1 comprises an AC voltage terminal 11 and a DC voltage terminal 12. A multi-phase AC electrical network or a multi-phase electrical load can be connected to the AC voltage terminal 11. A DC voltage network, for example the high-voltage network of an electric vehicle with an electrical energy storage device such as a traction battery, can be connected to the DC voltage terminal 12.

[0042] The electrical converter 1 further comprises a transformer 20 with a primary side 21 and a secondary side 22. The leakage inductance of the transformer 20 is summarized here in the inductance L shown in Figure 1. Alternatively, in an equivalent circuit, the leakage inductance can be arranged as an additional inductance between a third capacitor C1 and the primary side of the transformer 20.

[0043] Furthermore, the power converter 1 comprises a first circuit component 40 and a second circuit component 50. The second circuit component 50R. 417919

[0044] - 7 -

[0045] For example, in the case of electrical power transfer from the AC terminal 11 to the DC terminal 12, the AC voltage supplied by the transformer 20 on the secondary side 22 can be rectified and the rectified voltage supplied to the DC terminal 12. In the reverse direction of power transfer from the DC terminal 12 towards the AC terminal 11, this second circuit component can convert the DC voltage supplied at the DC terminal 12 into an AC voltage and supply it to the secondary side 22 of the transformer 20. For this purpose, the second circuit component 50 can, for example, contain four switching elements S5 to S8 in the form of two half-bridges or one full bridge. The switching elements S5 to S8 can, for example, be unipolar switching semiconductor switching elements.Since the basic operating principle of such a circuit component, preferably an inverter, is considered to be known, it will not be explained in more detail here.

[0046] The first circuit component 40 comprises four bipolar switching elements S1 to S4 connected in series. A first switching element S1 is arranged between a first node K1 and a second node K2. A second switching element S2 is arranged between the second node K2 and the third node K3. A third switching element S3 is arranged between the third node K3 and the fourth node K4. The fourth switching element S4 is arranged between the fourth node K4 and the fifth node K5. The first node K1, the third node K3, and the fifth node K5 are each coupled to a terminal point of the AC voltage connection 11.Preferably, a first connection point for a first phase L1 is connected to the first node K1, a second phase connection for a second phase L2 is connected to the third node K3, and a third connection point for a third phase L3 is connected to the fifth node K5. A parallel connection to the series connection of the first switching element S1 and the second switching element S2 can be made between the first node K1 and the R. 417919.

[0047] - 8 -

[0048] At the third node K3, a capacitor C3, preferably a first capacitor C3, may be provided. Similarly, in parallel to the series connection between the third switching element S3 and the fourth switching element S4, a further capacitor C4, preferably a second capacitor C4, may be arranged between the third node K3 and the fifth node K5. Both capacitors C3 and C4 have a relatively low capacitance and primarily serve to filter high-frequency signals.

[0049] The primary side 21 of the transformer 20 can be electrically coupled to the second node K2 and the fourth node K4. A capacitor C1, preferably a third capacitor C1, can be provided between the second node K2 and a first connection point of the primary side 21 of the transformer 20. Additionally or alternatively, a capacitor (not shown here) can be provided between the fourth node K4 and another connection point of the primary side 21 of the transformer 20. Optionally, another capacitor C2, preferably a fourth capacitor C2, can also be provided between a connection point of the secondary side 22 of the transformer 20 and the second circuit component 50.

[0050] Figure 2 shows a schematic representation of a circuit arrangement for a bipolar switching element, such as can be used for the bipolar switching elements S1 to S4 in the first circuit component 40. As can be seen from Figure 2, such a bipolar switching element can be realized by a series connection of two anti-series arranged unipolar switching semiconductor elements.

[0051] Figure 3 shows a schematic representation of an alternative bipolar switching semiconductor switching element according to an embodiment, which can also be used as switching element S1 to S4 for the first circuit component 40. This is a monolithic bidirectional switching semiconductor switching element which is capable of switching independently of the applied voltage polarity. R. 417919

[0052] - 9 -

[0053] The control signals for the switching elements S1 to S4 of the first circuit component 40 and for the switching elements S5 to S8 of the second circuit component 50 can, for example, be generated by a control device 60 and provided to the switching elements S1 to S8. The control signals for the switching elements S1 to S8 can be generated based on a suitable modulation method. Preferably, during modulation in each half-bridge with the switching elements S1 / S2, S3 / S4, S5 / S6, and S7 / S8, either the high-side switch is turned on while the low-side switch is turned off, or vice versa. Preferably, the duty cycle or the clocking, e.g., of the high-side switch is used as a degree of freedom for each half-bridge. Preferably, this results in four degrees of freedom for the four half-bridges. Preferably, the phase shift between the phases or the clocking of the individual half-bridges is varied, from which, preferably, three further degrees of freedom are obtained, e.g.,in relation to one of the half-bridges as a reference phase. The modulation adjustment can, for example, be performed in advance based on numerical optimization. The resulting data for optimal modulation can, for example, be stored in a suitable storage device 61 of the control unit 60. During the optimization, for example, the three voltages—that is, the two input voltages between the first node K1 and the third node K3, and between the third node K3 and the fifth node K5, as well as the output voltage at the DC terminal 12—can be used as slowly changing values.

[0054] DC voltage values ​​are considered in relation to the switching of the switching elements. For the combination of these three voltages, the available degrees of freedom can then be varied so that, on the one hand, the desired average phase currents on the input side are maintained, and on the other hand, the losses within the converter 1 are minimized. Depending on the modulation, for example, the conduction losses in the switches S1 to S8 and the transformer 20 can be minimized and / or the smoothest possible switching of the switching elements S1 to S8 can be ensured. (R. 417919)

[0055] - 10 -

[0056] Prior numerical optimization of the modulation parameters allows the optimized parameters to be quickly read and applied at runtime.

[0057] Finally, Figure 4 shows a flowchart illustrating how a method for operating an electrical converter, specifically an electrical converter 1 as previously described in one embodiment, can be based. The method can, in principle, comprise any steps that may be necessary for implementing the electrical converter 1 according to one of the previously described embodiments. Similarly, the previously described embodiments of the electrical converter 1 can also comprise any components suitable for implementing the method described below.

[0058] The process begins with step 110. In step 120, the switching elements in the power converter 1, the bipolar switching elements S1 to S4 in the first circuit component 40, and preferably the switching elements S5 to S8 in the second circuit component 50 are controlled. The control can be performed using a previously stored modulation scheme. The process ends with step 130.

[0059] In summary, the present invention relates to an electrical power converter for energy transfer between an AC voltage connection and a DC voltage connection. The power converter is characterized by a particularly simple and therefore efficient and cost-effective configuration with a minimal number of required switching elements.

Claims

R. 417919 - 11 - Claims 1. Electrical power converter (1), with: an AC voltage connection (11) designed to be electrically coupled to a multi-phase AC voltage network; a DC connection (12) designed to be electrically coupled to a DC network; a transformer (20) with a primary side (21) and a secondary side (22); a first circuit component (40); wherein the first circuit component (40) comprises four bipolar switching elements (S1, S2, S3, S4) arranged in series, wherein a first bipolar switching element (S1) is arranged between a first node (K1) and a second node (K2), a second bipolar switching element (S2) is arranged between the second node (K2) and a third node (K3), a third bipolar switching element (S3) is arranged between the third node (K3) and a fourth node (K4), and a fourth bipolar switching element (S4) is arranged between the fourth node (K4) and a fifth node (K5), and wherein the second node (K2) is electrically coupled to a first connection point of the primary side (21) of the transformer (20), and the fourth node (K4) is electrically coupled to a second connection point of the primary side (21) of the transformer (20), and R. 417919 - 12 - a second circuit component (50) arranged between the DC terminal (12) and the secondary side (22) of the transformer (20), and designed to rectify an alternating electrical voltage supplied at the secondary side (22) of the transformer (20) and to supply it at the DC terminal (12) and / or to convert a DC voltage supplied at the DC terminal (12) into an alternating voltage and to supply it at the secondary side (22) of the transformer (20); wherein each phase connection (L1, L2, L3) of the AC voltage connection (11) is electrically coupled to the first node (K1), the third node (K3) and the fifth node (K5).

2. Power converter (1) according to claim 1, wherein the four bipolar switching elements (S1, S2, S3, S4) of the first circuit component (40) each comprise a series connection of two anti-series connected unidirectional semiconductor switching elements.

3. Power converter (1) according to claim 1, wherein the four bipolar switching elements (S1, S2, S3, S4) of the first circuit component (40) each comprise a monolithic bidirectional switching semiconductor switching element.

4. Power converter (1) according to one of claims 1 to 3, a control device (60) designed to control the four bipolar switching elements (S1, S2, S3, S4) of the first circuit component (40) according to a previously stored modulation scheme, wherein the control device (60) comprises a storage device (61) designed to provide previously stored data for one or more modulation schemes.

5. Charging device for an electric vehicle, with: R. 417919 - 13 - a charging port designed to be electrically coupled to an alternating current source; a power converter (1) according to one of claims 1 to 4, wherein the AC voltage connection (11) is electrically coupled to the charging connection, and wherein the DC voltage connection (12) is designed to be electrically coupled to an electrical energy storage device of the electric vehicle.

6. Method for operating an electrical power converter (1) according to any one of claims 1 to 4, comprising the step Controlling (120) the bipolar switching elements (S1, S2, S3, S4) in the first circuit component (40) using a previously stored modulation scheme.

Images