DC VOLTAGE CONVERTER ARRANGEMENT, FUEL CELL VEHICLE AND METHOD FOR OPERATING A DC VOLTAGE CONVERTER ARRANGEMENT

Abstract

A DC voltage converter arrangement includes a plurality of full switch bridges and transformers and is for a galvanically separate, at least indirect electrical coupling of a fuel cell unit to a traction network including a high-voltage battery. The plurality of full switch bridges and transformers transform a DC input voltage to an alternating voltage, transform the alternating voltage to a transformed alternating voltage, and transform the transformed alternating voltage to a DC output voltage. At least one of the full switch bridges is included in a resonance circuit including an inductance and a capacitor.

Claims

1. A DC voltage converter arrangement for the galvanically separate, at least indirect electrical coupling of a fuel cell unit to a traction network that includes a high-voltage battery, the DC voltage converter comprising: a first electrical terminal pair at a fuel cell side and configured to receive a DC input voltage; a first full switch bridge including first switches and configured to transform the DC input voltage to a first alternating voltage; a second full switch bridge including second switches and connected in parallel with the first full switch bridge and including second switches configured to transform the DC input voltage into a second alternating voltage; a first transformer having: a primary side configured to receive the first alternating voltage; and a secondary side, wherein the first transformer is configured to transform the first alternating voltage into a first transformed alternating voltage according to a ratio of the primary side and the secondary side of the first transformer, a second transformer having: a primary side configured to receive the first alternating voltage; and a secondary side, wherein the second transformer is configured to transform the second alternating voltage into a second transformed alternating voltage according to a ratio of the primary side and the secondary side of the second transformer; a third full switch bridge electrically connected to the secondary side of the first transformer and including third switches; a fourth full switch bridge switched in series with the third full switch bridge, electrically connected to the secondary side of the second transformer and including fourth switches, wherein the third full switch bridge and the fourth full switch bridge are configured to collectively transform the first and second transformed alternating voltages to a DC output voltage; and a second electrical terminal pair at a battery side and configured to output the DC output voltage, wherein at least one of the first, second, third, and fourth full switch bridges is included in a resonance circuit including an inductance and a capacitor.

2. The DC voltage converter arrangement according to claim 1, wherein at least one of the secondary side of the first transformer and the secondary side of the second transformer is associated with the resonance circuit, wherein the resonance circuit is driven by a stray inductance present at at least one of the secondary side of the first transformer and the secondary side of the second transformer.

3. The DC voltage converter arrangement according to claim 2, wherein at least one of the capacitor and the stray inductance is dimensioned or configured such that a load current flowing through the third switches of the third full switch bridge or through the fourth switches of the fourth full switch bridge is reduced or minimized.

4. The DC voltage converter arrangement according to claim 3, wherein switching times of the third switches and the fourth switches are chosen such that they substantially pass none of the load current through the third switches and the fourth switches, wherein the load current is substantially sinusoidal.

5. The DC voltage converter arrangement according to claim 2, wherein the first transformer is associated with a first resonance circuit including a first capacitor and driven by a stray inductance at the secondary side of the first transformer, wherein the second transformer is associated with a second resonance circuit including a second capacitor and driven by a stray inductance at the secondary side of the second transformer.

6. The DC voltage converter arrangement according to claim 1, wherein the first electrical terminal pair is connected to an output terminal pair of a boost converter electrically connected to the fuel cell unit.

7. The DC voltage converter arrangement according to claim 6, wherein a first DC voltage is present at an input side of the boost converter and a second DC voltage level higher than the first DC voltage level is present at an output side of the boost converter, wherein the second DC voltage level corresponds to the DC input voltage, wherein the DC output voltage is higher than the DC input voltage.

8. The DC voltage converter arrangement according to claim 6, wherein a distributor unit is electrically connected to the output terminal pair of the boost converter and electrically connected at the output side to at least one secondary consumer of a fuel cell system including the fuel cell unit.

9. A fuel cell vehicle having a fuel cell system, comprising: a fuel cell unit; and a DC voltage converter arrangement electrically connected to the fuel cell unit and configured to supply electricity to a traction network having at least one of a high-voltage battery and a traction motor, wherein the DC voltage converter arrangement includes: a first full switch bridge including first switches and configured to transform the DC input voltage to a first alternating voltage; a second full switch bridge including second switches and connected in parallel with the first full switch bridge and including second switches configured to transform the DC input voltage into a second alternating voltage; a first transformer having: a primary side configured to receive the first alternating voltage; and a secondary side, wherein the first transformer is configured to transform the first alternating voltage into a first transformed alternating voltage according to a ratio of the primary side and the secondary side of the first transformer; a second transformer having: a primary side configured to receive the first alternating voltage; and a secondary side, wherein the second transformer is configured to transform the second alternating voltage into a second transformed alternating voltage according to a ratio of the primary side and the secondary side of the second transformer; a third full switch bridge electrically connected to the secondary side of the first transformer and including third switches; a fourth full switch bridge switched in series with the third full switch bridge, electrically connected to the secondary side of the second transformer and including fourth switches, wherein the third full switch bridge and the fourth full switch bridge are configured to collectively transform the first and second transformed alternating voltages to a PC output voltage; and a second electrical terminal pair at a battery side and configured to output the DC output voltage, wherein at least one of the first, second, third, and fourth full switch bridges is included in a resonance circuit including an inductance and a capacitor.

10. A method for operating a DC voltage converter arrangement the method comprising: providing a DC input voltage at a first full switch bridge including first switches and at a second full switch bridge switched in parallel with the first full switch bridge and including second switches; transforming the DC input voltage into an alternating voltage with the first full switch bridge and the second full switch bridge; providing the alternating voltage at a primary side of a first transformer; transforming the alternating voltage to a first transformed voltage at a secondary side of the first transformer; providing the alternating voltage at a primary side of a second transformer; transforming the alternating voltage to a second transformed voltage at a secondary side of the second transformer; transforming the first transformed alternating voltage at the secondary side of the first transformer and the second transformed alternating voltage at the secondary side of the second transformer with a third full switch bridge including third switches and a fourth full switch bridge switched in series with the third switch bridge and including fourth switches; and operating an electrical resonance circuit including a capacitor with a stray inductance present on the secondary side of at least one of the first transformer and the second transformer such that substantially none of a substantially sinusoidal load current flows through at least one of the first switches, the third switches, and the fourth switches at a switching time.

Description

[0026] Further benefits, features and details of the invention will emerge from the claims, the following description of preferred embodiments, and the drawings. There are shown:

[0027] FIG. 1 a schematic block circuit diagram of a DC voltage converter arrangement for the galvanically separate electrical coupling of a fuel cell unit to a traction network (onboard network), providing a total of three different DC voltage levels,

[0028] FIG. 2 an equivalent circuit diagram of a DC voltage converter arrangement for the galvanically separate, at least indirect electrical coupling of a fuel cell unit to a traction network comprising a high-voltage battery,

[0029] FIG. 3 the current curve, the voltage curve, and the switching losses during the switch-off process of the switches of a full switch bridge of the DC voltage converter arrangement of FIG. 2,

[0030] FIG. 4 an equivalent circuit diagram of a DC voltage converter arrangement from the prior art, and

[0031] FIG. 5 the current curve, the voltage curve, and the switching losses during the switch-off process of the switches of a full switch bridge of the DC voltage converter arrangement of FIG. 4.

[0032] FIG. 4 shows a DC voltage converter arrangement 100 according to the preamble of claim 1. Similar to the DC voltage converter arrangement 100 of the invention (Fig. 2), it is also designed to electrically couple a fuel cell unit 102 in galvanically separate and at least indirect manner to a traction network 106 comprising a high-voltage battery 104.

[0033] The DC voltage converter arrangements 100 comprise a first electrical terminal pair 108a, 108b at the fuel cell side, where a DC input voltage U.sub.E is present or can be applied. The DC input voltage U.sub.E is transformable into an alternating voltage by means of a first full switch bridge 110 comprising first switches S.sub.11, S.sub.12, S.sub.13, S.sub.14 and by means of a second full switch bridge 112 comprising second switches S.sub.21, S.sub.22, S.sub.23, S.sub.24 connected in parallel with the first full switch bridge 110. The alternating voltage provided by the first full switch bridge 110 is transformable in a given or predeterminable ratio from a first primary side 114 of a first transformer T.sub.1 to a first secondary side 116 of the first transformer T.sub.1. The alternating voltage provided by the second full switch bridge 112 is transformable in a given or predeterminable ratio from a second primary side 118 of a second transformer T.sub.2 to a second secondary side 120 of the second transformer T.sub.2.

[0034] The transformed alternating voltage is transformable into a DC output voltage U.sub.A by means of a third full switch bridge 122 electrically connected to the first secondary side 116 of the first transformer T.sub.1 and comprising third switches S.sub.31, S.sub.32, S.sub.33, S.sub.34 and by means of a fourth full switch bridge 124 switched in series with the third full switch bridge 122, electrically connected to the second secondary side 120 of the second transformer T2 and comprising fourth switches S.sub.41, S.sub.42, S.sub.43, S.sub.44

[0035] The DC output voltage U.sub.A is provided or able to be provided at a second electrical terminal pair 126a, 126b at a battery side and lies preferably at the voltage level of a high-voltage battery 104, especially a voltage level of a 800V architecture.

[0036] FIG. 5 shows an investigation measuring the switch-off process of the third full switch bridge 122 and/or the fourth full switch bridge 124 in the case of the DC voltage converter arrangement 100 of the prior art. It can be seen that, during the course of the switch-off process, the resistance of the semiconductor increases gradually, as can be noticed from the voltage curve 204. Thus, the voltage increases continuously across the switch, and it can be ascertained with the aid of the current curve 202 that the current flow through the particular switch becomes increasingly less. If the particular switch is closed, the voltage value is at the level of the input voltage and the current flow has halted completely. With the help of the power loss curve 206, it can be seen that this has its maximum during half of the switching process, and the large power loss which occurs results in intense heating of the semiconductor switch.

[0037] This is where the present invention comes in. It is apparent from FIG. 2 that at least one of the full switch bridges 110, 112, 122, 124 is included in a resonance circuit 128, 130 comprising an inductance L.sub.S1, L.sub.S2 and a capacitor C.sub.R1, C.sub.R2.

[0038] In the present case, the first transformer T.sub.1 is associated with a first resonance circuit 128, which is formed by means of a stray inductance L.sub.S1 of the first transformer T.sub.1 and a first capacitor C.sub.R1 present on the secondary side. The second transformer T.sub.2 is associated with a second resonance circuit 130, which is formed by means of a stray inductance L.sub.S1 of the second transformer T.sub.2 and a second capacitor C.sub.R2 present on the secondary side.

[0039] The capacitors C.sub.R1, C.sub.R2 and the stray inductances L.sub.S1, L.sub.S2 are dimensioned or configured such that a load current flowing through the third switches S.sub.31, S.sub.32, S.sub.33, S.sub.34 of the third full switch bridge 122 and a load current flowing through the fourth switches S.sub.41, S.sub.42, S.sub.43, S.sub.44 of the fourth full switch bridge 124 is reduced, in particular, minimized. The switching times of the switches S.sub.31 S.sub.32 S.sub.33 S.sub.34; S.sub.41 S.sub.42 S.sub.43 S.sub.44 are chosen such that they basically correspond to the passing through zero of the sinusoidal load current through the switches S.sub.31, S.sub.32, S.sub.33, S.sub.34; S.sub.41, S.sub.42, S.sub.43, S.sub.44.

[0040] This can be seen from the measurement investigation of a switch-off process in FIG. 3, where the current curve 202 in the switch-off process corresponds almost to zero Amperes and thus the power losses 206 are also much smaller. This results in a thermal relief for the full switch bridges 110, 112, 122, 124.

[0041] With the aid of FIG. 1 it can be seen that a total of three different voltage levels can be provided by means of the DC voltage converter arrangement 100 when using a boost converter 134. The first voltage level is created by the fuel cell unit 102 and lies in the range of 200V to 300 V.

[0042] This first DC voltage level is provided at the input side at the boost converter 134 and it raises the voltage to a second DC voltage level, corresponding to the DC input voltage U.sub.E. The DC input voltage U.sub.E can then be utilized to supply electricity to secondary consumers 138 of a fuel cell system comprising the fuel cell unit 102, there being present here in particular a voltage level lying in the range of 350V to 450V. FIG. 1 furthermore shows the possibility of employing fuses 140.

[0043] The DC input voltage UE may also be utilized for the connection of the traction network 106 comprising the high-voltage battery 104, where a galvanic separation is present in order to meet the requirements on the insulation resistance according to ISO 6496-3. This traction network 106 is operated, for example, at a voltage level of 800V, so that the third voltage level is thus realized.

LIST OF REFERENCE NUMBERS

[0044] 100 DC voltage converter arrangement

[0045] 102 Fuel cell unit

[0046] 104 High-voltage battery

[0047] 106 Traction network

[0048] 108a Terminal (first terminal pair)

[0049] 108b Terminal (first terminal pair)

[0050] 110 First full switch bridge

[0051] S.sub.11 First switch

[0052] S.sub.12 First switch

[0053] S.sub.13 First switch

[0054] S.sub.14 First switch

[0055] 112 Second full switch bridge

[0056] S.sub.21 Second switch

[0057] S.sub.22 Second switch

[0058] S.sub.23 Second switch

[0059] S.sub.24 Second switch

[0060] 114 First primary side (T.sub.1)

[0061] 116 First secondary side (T.sub.1)

[0062] T.sub.1 First transformer

[0063] 118 Second primary side (T.sub.2)

[0064] 120 Second secondary side (T.sub.2)

[0065] T.sub.2 Second transformer

[0066] 122 Third full switch bridge

[0067] S.sub.31 Third switch

[0068] S.sub.32 Third switch

[0069] S.sub.33 Third switch

[0070] S.sub.34 Third switch

[0071] 124 Fourth full switch bridge

[0072] S.sub.41 Fourth switch

[0073] S.sub.42 Fourth switch

[0074] S.sub.43 Fourth switch

[0075] S.sub.44 Fourth switch

[0076] 126a Terminal (second terminal pair)

[0077] 126b Terminal (second terminal pair)

[0078] 128 First resonance circuit

[0079] 130 Second resonance circuit

[0080] C.sub.R1 First capacitor (first resonance circuit)

[0081] C.sub.R2 Second capacitor (second resonance circuit)

[0082] 132a Terminal (output boost converter)

[0083] 132b Terminal (output boost converter)

[0084] 134 Boost converter

[0085] 136 Distributor unit

[0086] 138 Secondary consumer

[0087] 140 Fuse

[0088] C.sub.1 Input capacitor

[0089] C.sub.2 Output capacitor

[0090] 202 Current curve

[0091] 204 Voltage curve

[0092] 206 Power loss curve