traction power grid

Abstract

The invention relates to a traction network (1) for an electric or hybrid vehicle, comprising at least one high-voltage battery (2), an inverter (4), at least one intermediate circuit capacitor (3) and at least one DC / DC converter (6), wherein the at least one DC / DC converter (6) is arranged between the high-voltage battery (2) and the inverter (4) and has at least one transformer (21), wherein a positive connection (12) of the high-voltage battery (2) is connected to a positive input (13) of the DC / DC converter (6) on the primary side (14) and a negative connection (15) of the high-voltage battery (2) is connected to a negative input (16) of the DC / DC converter (6) on the primary side (14), wherein the positive connection (12) of the high-voltage battery (2) is connected via a connection line (20) to a negative connection (19) of the DC / DC converter (6) on the secondary side (18).

Description

Technical Field

[0001] This invention relates to a traction power grid for electric or hybrid vehicles. Background Technology

[0002] This traction grid for electric or hybrid vehicles includes a high-voltage battery, at least one intermediate-loop capacitor, and an inverter connected to the motor. The inverter is typically designed as a pulse inverter, but can be designed as a 2-level or 3-level inverter. It has also been proposed to place a DC / DC converter between the high-voltage battery and the inverter, which increases the voltage of the high-voltage battery. This has several advantages. On the one hand, the high-voltage battery can have a lower nominal voltage; on the other hand, voltage fluctuations in the high-voltage battery due to state of charge (SOC) fluctuations can be compensated. The disadvantage is increased component cost. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to create a traction power grid for electric or hybrid vehicles with DC / DC converters, wherein the requirements for components are reduced.

[0004] The solution to this technical problem originates from a traction power grid having the features of claim 1. Further advantageous embodiments of the invention arise from the dependent claims.

[0005] A traction grid for electric or hybrid vehicles includes at least one high-voltage battery, an inverter, at least one intermediate circuit capacitor, and at least one DC / DC converter. The DC / DC converter is positioned between the high-voltage battery and the inverter and includes at least one transformer. Here, the positive terminal of the high-voltage battery is connected to the positive input terminal on the primary side of the DC / DC converter, and the negative terminal of the high-voltage battery is connected to the negative input terminal on the primary side of the DC / DC converter. Furthermore, the positive terminal of the high-voltage battery is connected via a connecting wire to the negative output terminal of the DC / DC converter on the secondary side. This connection means that during traction operation, the DC / DC converter does not need to supply the full voltage to the inverter on the secondary side, but only the voltage difference from the high-voltage battery voltage, which is applied to the negative output terminal. A portion of the current from the high-voltage battery also flows through the primary side of the DC / DC converter. The advantage is that the power semiconductors on the secondary side can be designed for lower voltages, thereby reducing component workload and saving costs. Even during regenerative operation, a portion of the charging current from the high-voltage battery flows directly to the high-voltage battery.

[0006] In one embodiment, the on-board traction grid includes a charger, with the DC / DC converter being part of the charger. This type of charger is also known as an on-board charger (OBC). It can be used to charge a high-voltage battery from a single-phase or multi-phase external AC voltage source. This means the DC / DC converter functions as a boost DC / DC converter during traction operation and as a DC / DC converter during AC charging operation to regulate the AC voltage rectified by the PFC stage (Power Form Corrector), further reducing component consumption.

[0007] In another embodiment, at least one switching element is arranged in the connecting line, and the traction grid is preferably designed to disconnect at least one switching element during the charging operation of the charger. This means that the charger is currently isolated, and therefore the traction grid and the charger are currently decoupled, thereby reducing insulation requirements. In charging mode, all power is transmitted through the currently isolated DC / DC converter. However, since the power during charging operation is significantly lower than that during traction operation, this is not a problem for the power semiconductors on the secondary side of the DC / DC converter.

[0008] In another embodiment, at least two DC / DC converters are connected in parallel. Although this increases the number of components, they can be constructed more simply. Another advantage is that interleaved operation can be achieved, thereby improving efficiency. The two DC / DC converters can have identical structures.

[0009] In another embodiment, the positive terminal of the high-voltage battery is connected to the positive terminal of the DC / DC converter on the secondary side via a bypass line with switching elements. This allows the DC / DC converter to be bridged under certain operating conditions during traction operation, thereby saving converter losses.

[0010] In another embodiment, at least one additional secondary winding of the low-voltage vehicle electrical network (e.g., 12V or 48V) is arranged on the secondary side of the transformer. Alternatively or additionally, another primary winding may be provided, through which the low-voltage vehicle electrical network is charged.

[0011] In another embodiment, at least one DC / DC converter is designed as a resonant converter.

[0012] In another embodiment, the traction power grid is designed to operate the resonant converter at a fixed frequency and a fixed duty cycle during traction operation. This simplifies control and provides high efficiency.

[0013] In another embodiment, the traction grid is designed to operate the resonant converter as a CLLC or a resonant DAB (dual active bridge) during the charging operation of the charger. Attached Figure Description

[0014] The invention will now be explained in more detail using preferred exemplary embodiments. The accompanying drawings illustrate:

[0015] Figure 1 A schematic block diagram of the traction power grid in the first embodiment is shown.

[0016] Figure 2 A schematic block diagram of a portion of the traction power grid in a second embodiment with two DC / DC converters is shown.

[0017] Figure 3 The diagram shows a circuit layout for a portion of a traction power grid with a low-voltage onboard electrical network.

[0018] Figure 4 A schematic diagram of a portion of the traction power grid in another embodiment is shown.

[0019] Figure 5 A schematic diagram of a portion of a traction power grid in another embodiment is shown, which has two DC / DC converters and

[0020] Figure 6 This illustrates an alternative circuit layout for a portion of the traction power grid. Detailed Implementation

[0021] Figure 1 The traction grid 1 in the first embodiment is shown. The traction grid 1 has a high-voltage battery 2, an intermediate circuit capacitor 3, and an inverter 4 connected to a motor 5. Furthermore, an isolated DC / DC converter 6 with a transformer is arranged between the high-voltage battery 2 and the intermediate circuit capacitor 3. A bypass circuit 7 with a switching element 8, bridging the DC / DC converter 6, is also shown. The traction grid 1 also includes a charger 9 having an AC charging connector 10, a PFC stage 11, and the DC / DC converter 6. The positive terminal 12 of the high-voltage battery 2 is connected to the positive input terminal 13 of the DC / DC converter 6 on the primary side 14. The negative terminal 15 of the high-voltage battery 2 is connected to the negative input terminal 16 of the DC / DC converter 6 on the primary side 14. The positive terminal 17 of the DC / DC converter 6 on the secondary side 18 is connected to the positive terminal of the intermediate circuit capacitor 3. The positive terminal 12 of the high-voltage battery 2 is also connected via a connecting line 20 to the negative terminal 19 of the DC / DC converter 6 on the secondary side 18. This means that the positive potential of the high-voltage battery 2 exists at terminal 19.

[0022] During traction operation, the voltage U of high-voltage battery 2... B Under defined operating conditions, the voltage should be increased. According to the present invention, this increased voltage is now not entirely regulated by the DC / DC converter 6, but only by regulating the desired voltage U. C With the voltage U of high-voltage battery 2 B The voltage difference ΔU between them, where: UC =U B +ΔU. If U B For example, 600V, and the desired voltage U on intermediate circuit capacitor 3 or on the input terminal of inverter 4. C The voltage should be 800V, so the DC / DC converter 6 is controlled to produce 200V ΔU. Only a small portion of the battery current from the high-voltage battery 2 flows through the primary side 14 of the DC / DC converter 6. The main portion of the current flows through the primary side 14 via the connection line 20 and directly into the semiconductor components on the secondary side 18. Because the voltage on the secondary side 18 of the DC / DC converter 6 is lower, they can be designed more cost-effectively. The DC / DC converter 6 can be used to compensate for voltage fluctuations in the high-voltage battery 2 and set any desired operating point in the inverter 4. At the voltage U of the high-voltage battery 2... B Under sufficient operating conditions, DC / DC converter 6 can be deactivated and switch 8 can be closed, thereby bridging DC / DC converter 6 and preventing converter losses.

[0023] During AC charging operation, most of the current also flows directly from the PFC stage 11 to the semiconductor element on the primary side 14 via the connection line 20, and from there to the high-voltage battery 2, while another portion flows through the DC / DC converter 6 (from the secondary side to the primary side). Typically, the DC / DC converter 6 is used as a buck converter in AC charging mode.

[0024] Figure 2 A portion of the traction power grid 1 is shown, which has two DC / DC converters 6 connected in parallel. This allows the required power ΔU to be allocated, or, in the case of a small ΔU, to be supplied solely by the DC / DC converters 6, thus saving converter losses.

[0025] Figure 3 A possible circuit implementation is shown, in which the PFC stage 11 is also integrated into the inverter 4. The DC / DC converter 6 is designed as a resonant converter and has two half-bridges on both the primary side 14 and the secondary side 18. The DC / DC converter 6 has a transformer 21 with a primary winding 22 and a secondary winding 23, the primary and secondary windings sharing a common core 24. The switching element 8 is shown closed, such that the DC / DC converter 6 is bridged in the shown switching position. Another secondary winding 25 with two downstream half-bridges is shown here, via which power is supplied to the low-voltage on-board power grid 26. Various EMC filters 27 are also schematically shown. The main contactor for disconnecting the high-voltage battery 2 and the switching element for closing the AC charging connector 10 during traction operation are not shown.

[0026] In previous variants, charger 9 was not electrically isolated, but this is generally expected for various reasons.

[0027] Figure 4 The traction grid 1 is schematically shown, thereby enabling current isolation from the high-voltage battery 2 during charging operation. For this purpose, a switching element 28 is arranged in the connecting line 20, by which the connection can be broken and the negative terminal 19 can be connected to the negative terminal of the intermediate circuit capacitor 3. The negative terminal 15 of the high-voltage battery 2 is disconnected from the intermediate circuit capacitor 3 by another switching element 29. As a result, charging from the PFC stage 11 is carried out only via the DC / DC converter 6, where current isolation is achieved by a transformer.

[0028] Figure 5 It shows that according to Figure 4 An extension of the principle, it features two DC / DC converters 6. In the shown switching position, the two DC / DC converters 6 are connected in series to charge from the PFC stage 11, which is advantageous in terms of adjusting the turns ratio. For traction operation, all switching elements 30, 31 are switched, causing the two DC / DC converters 6 to be connected in parallel.

[0029] at last, Figure 6 It shows that according to Figure 4 The circuit implementation of the traction power grid 1 is also shown, and a low-voltage on-board power grid 26 is also shown, which is coupled to the core 24 via another primary winding 32, so that the high-voltage battery 2 and the low-voltage on-board power grid 26 can be charged in parallel during charging. The DC / DC converter 6 is designed as a resonant converter, which is preferably controlled at a fixed frequency and a fixed duty cycle during traction operation.

[0030] List of reference numerals

[0031] 1 Traction power grid

[0032] 2. High-voltage battery

[0033] 3. Intermediate circuit capacitor

[0034] 4 Inverter

[0035] 5 motors

[0036] 6 DC / DC converters

[0037] 7. Bypass routes

[0038] 8 Switching elements

[0039] 9. Charger

[0040] 10 AC charging connectors

[0041] 11 PFC level

[0042] 12 Positive terminal connector

[0043] 13 Positive Input Terminal

[0044] 14 Primary Side

[0045] 15 Negative terminal

[0046] 16 Negative Input Terminal

[0047] 17 Positive terminal connector

[0048] 18 secondary sides

[0049] 19 Negative terminal

[0050] 20 connecting cables

[0051] 21 Transformer

[0052] 22 Primary winding

[0053] 23 Secondary winding

[0054] 24 Common Core

[0055] 25 secondary winding

[0056] 26 Low-voltage vehicle-mounted power grid

[0057] 27 EMC Filter

[0058] 28 Switching elements

[0059] 29 Switching elements

[0060] 30 Switching elements

[0061] 31 Switching elements

[0062] 32 Primary winding

[0063] U B High voltage battery voltage

[0064] U C Voltage on intermediate circuit capacitor

[0065] ΔU voltage difference

Claims

1. A traction power grid (1) for an electric or hybrid vehicle, comprising at least one high-voltage battery (2), an inverter (4), at least one intermediate circuit capacitor (3), and at least one DC / DC converter (6), wherein, The at least one DC / DC converter (6) is arranged between the high-voltage battery (2) and the inverter (4) and has at least one transformer (21), wherein the positive terminal (12) of the high-voltage battery (2) is connected to the positive input terminal (13) of the DC / DC converter (6) on the primary side (14), and the negative terminal (15) of the high-voltage battery (2) is connected to the negative input terminal (16) of the DC / DC converter (6) on the primary side (14), wherein the positive terminal (12) of the high-voltage battery (2) is connected to the negative terminal (19) of the DC / DC converter (6) on the secondary side (18) via a connecting line (20).

2. Traction power network (1) according to claim 1, characterized in that The traction power grid (1) includes a charger (9), and the DC / DC converter (6) is part of the charger (9).

3. Traction power network (1) according to claim 1 or 2, characterized in that At least one switching element (28) is arranged in the connecting line (20).

4. Traction power network (1) according to claim 3, characterized in that The traction power grid (1) is designed to open at least one switching element (28) during the charging operation of the charger (9).

5. Traction network (1) according to any of the preceding claims, characterized in that There are at least two DC / DC converters (6) that are connected in parallel during traction operation.

6. Traction network (1) according to any of the preceding claims, characterized in that The positive terminal (12) of the high-voltage battery (2) is connected to the positive terminal (17) of the DC / DC converter (6) on the secondary side (18) via a bypass line (7) having a switching element (8).

7. Traction network (1) according to any of the preceding claims, characterized in that Another secondary inductor (25) of the low-voltage vehicle-mounted power grid (26) is located on the secondary side (18) of the transformer (21), or another primary inductor (32) of the low-voltage vehicle-mounted power grid (26) is located on the primary side (14) of the transformer (21).

8. Traction network (1) according to any of the preceding claims, characterized in that The at least one DC / DC converter (6) is designed as a resonant converter.

9. Traction network (1) according to claim 8, characterized in that The traction power grid (1) is designed to operate the resonant converter at a fixed frequency and a fixed duty cycle during traction operation.

10. The traction power grid (1) according to claim 8 or 9, characterized in that, The traction power grid (1) is designed to operate the resonant converter as a CLLC or resonant DAB during the charging operation of the charger (9).

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