VOLTAGE CONVERTER ARRANGEMENT, FUEL CELL SYSTEM AND METHOD OF OPERATING A VOLTAGE CONVERTER ARRANGEMENT

Abstract

A voltage converter arrangement for the electrical coupling of a fuel cell unit is provided, which is connected or can be connected on the input side, to a traction network, which is connected or can be connected on the output side, and which comprises a high-voltage battery may comprise a measuring unit for measuring the input voltage supplied by the fuel cell unit, and a comparison unit, which is electrically connected to the measuring unit and is in turn electrically coupled to a controller unit, which is designed to cause the fuel cell unit to be operated at predeterminable operating points, and which is configured to seek time-varying operating points from the fuel cell unit in an impedance operation. A fuel cell system and a method for operating a voltage converter arrangement is also provided.

Claims

1. A voltage converter arrangement for the electrical coupling of a fuel cell unit, which is connected or can be connected on an input side of the voltage converter arrangement, to a traction network which includes a high-voltage battery and is connected or can be connected on an output side of the voltage converter arrangement, comprising: a measuring unit for measuring the input voltage supplied by the fuel cell unit; and a comparison unit, which is electrically connected to the measuring unit and is in turn electrically coupled to a controller unit, which is designed to cause the fuel cell unit to be operated at predeterminable operating points, wherein the controller unit is designed to perform an impedance operation that seeks out periodically varying operating points from the fuel cell unit, and wherein, during the impedance operation, the output side of the voltage converter arrangement outputs a DC voltage.

2. The voltage converter arrangement according to claim 1, wherein the controller unit is designed to specify a resultant AC voltage as a reference variable, in that the measuring unit is designed to detect voltage response of the fuel cell unit applied to a pair of connectors on the input side to the induced time-varying operating points, and in that the comparison unit is designed to compare the measured voltage response with the reference variable.

3. (canceled)

4. The voltage converter arrangement according to claim 1, wherein the alternating operating points are selected around a predeterminable or predetermined reference operating point.

5. A fuel cell system, comprising: a fuel cell unit; a traction network in which a high voltage battery is present; and a voltage converter arrangement for the electrical coupling of the fuel cell unit, which is connected or can be connected on an input side of the voltage converter arrangement, to the traction network, which is connected or can be connected on an output side of the voltage converter arrangement, including: a measuring unit for measuring the input voltage supplied by the fuel cell unit and a comparison unit, which is electrically connected to the measuring unit and is in turn electrically coupled to a controller unit, which is designed to cause the fuel cell unit to be operated at predeterminable operating points, wherein the controller unit is designed to perform an impedance operation that seeks out periodically varying operating points from the fuel cell unit, and wherein, during the impedance operation, the output side of the voltage converter arrangement outputs a DC voltage.

6. A method for operating a voltage converter arrangement which electrically couples a fuel cell unit connected on the input side of the voltage converter arrangement to a traction network comprising a high-voltage battery connected on the output side of the voltage converter arrangement, which voltage converter arrangement comprises a measuring unit for measuring the input voltage supplied by the fuel cell unit and a comparison unit electrically connected to the measuring unit, which comparison unit is in turn electrically coupled to a controller unit which causes the fuel cell unit to be operated at predeterminable operating points, the method comprising: performing an impedance operation that seeks out periodically varying operating points from the fuel cell unit; and during the impedance operation, outputting a DC voltage at the output side of the voltage converter arrangement.

7. The method according to claim 6, wherein the controller unit predetermines a resulting AC voltage as a reference variable, in that the measuring unit detects a voltage response of the fuel cell unit applied to a pair of connectors on the input side to the induced time-varying operating points, and in that the comparison unit compares the measured voltage response with the reference variable.

8. (canceled)

9. The method according to claim 6, wherein the alternating operating points are selected around a predeterminable or predetermined reference operating point.

10. The method of claim 9, wherein the alternating operating points do not deviate more than ten percent from the reference operating point.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0021] Further advantages, features and details will be apparent from the claims, from the following detailed description and from the drawings.

[0022] FIG. 1 shows a schematic representation of a fuel cell system with a voltage converter arrangement which electrically connects the fuel cell unit to a traction network comprising a battery, to which two consumers are connected.

[0023] FIG. 2 shows a characteristic U/I curve of a fuel cell unit, on which two operating points and an intermediate reference operating point are highlighted.

[0024] FIG. 3 shows a voltage curve, over time, of the input voltage supplied by the fuel cell unit in impedance or impedance spectroscopy operation.

DETAILED DESCRIPTION

[0025] FIG. 1 shows a schematic representation of a fuel cell system comprising a fuel cell unit 102. This fuel cell unit 102 is connected to connectors 114, 116 of a pair of connectors on the input side of a voltage converter arrangement 100, which is designed, for example, as a modified DC-to-DC converter. The voltage converter arrangement 100 is electrically connected with its two connectors 118, 120, i.e., with its pair of connectors on the output side, to a traction network 106 (on-board network) in which a high-voltage battery 104 is present. This on-board network is used to supply electrical energy to a first consumer 122 and to a second consumer 124. The traction network 106 can also supply electrical energy to other consumers which are not shown in more detail.

[0026] The consumer 122 comprises a drive unit 128, which is in the form of an electric machine. This electric machine is typically operable by means of a three-phase alternating current and may be formed as a traction motor for a motor vehicle. Since a high DC voltage and a DC current are present in the traction network 106, an inverter 126 is additionally associated with the consumer 122, which converts the DC current into a three-phase AC current. In a further embodiment of the consumer 122, the drive unit 128 can also be used as a generator so that, for example, energy generated by the drive unit 128 during the braking process can once again be fed back to the high-voltage battery 104 via the inverter 126.

[0027] The second consumer 124 may also be connected to the traction network, wherein this network may be formed, for example, as one of the auxiliary units of the fuel cell system, such as a compressor, a recirculation fan, a jet pump or the like. It is also possible that the consumer 124 is formed as a charger, a twelve-volt DC-to-DC converter, a high-voltage heater, an electric air-conditioning compressor, or the like.

[0028] The construction of the voltage converter arrangement 100 is discussed in more detail below. The voltage converter arrangement 100 includes a measuring unit 108 that measures or records the input voltage supplied by the fuel cell unit 102, as illustrated by the dashed arrow. The measuring unit 108 is electrically connected to a comparison unit 110, which in turn is electrically coupled to a controller unit 112. The controller unit 112 is adapted to cause the fuel cell unit 102 to be driven at predeterminable operating points 200, 202, as illustrated by the dashed arrow, in the direction of the fuel cell unit 102.

[0029] In order to be able to perform an impedance measurement on the fuel cell unit 102, the controller unit 112 is designed in impedance operation to seek out in a time-varying or periodically alternating manner operating points 200, 202 from the fuel cell unit 102. This corresponds in essence to a time-varying or periodically alternating load demand from the fuel cell unit 102. The alternation between the operating points 200, 202 may be sinusoidal.

[0030] FIG. 2 shows a typical characteristic U/I curve of a fuel cell unit 102, wherein an operating point 200 with a low load demand and an operating point 202 with a high load demand have been marked on the characteristic U/I curve. The two operating points 200, 202 are located in the linear range of the characteristic curve of the fuel cell unit 102. The controller unit 112 may be designed to query different load requirements in impedance or impedance spectroscopy operation of the voltage converter arrangement 100, which load demands lie in the range starting from the operating point 200 with a low load demand up to the operating point 202 with a high load requirement.

[0031] In so doing, the operating points lying in this range are continuously or on a step-by-step basis “specified” or “run through” by controller unit 112. This querying of the individual operating points takes place periodically in ascending and descending order, in particular between the operating point 200 and the operating point 202; in particular including these two operating points.

[0032] It should be recognized that at operating point 202 there is a low voltage U.sub.1, and that at operating point 200 there is a voltage U.sub.2 that is higher than U.sub.1. When the operating points between the operating point 200 and the operating point 202 are continuously or incrementally cycled through, all voltages that lie between the two voltages U.sub.2 and U.sub.1 are sought out or supplied by the fuel cell unit 102.

[0033] It is, however, alternatively also possible to directly switch or “jump” between the two operating points 200, 202 or alternatively directly between the two voltages U.sub.1, U.sub.2 during the demand, since in some cases the “sluggishness” of the fuel cell unit 102 in response to the demand itself leads to a temporally undulating or sinusoidal voltage curve.

[0034] If the controller unit 112 now causes a periodic switch or “running alongside” of the linear range between the operating points 200, 202, the result is the voltage U shown in FIG. 3, in particular a sinusoidal voltage, plotted over time t. The voltage signal generated by the controller unit 112 is then an AC voltage 250, which is composed of a DC voltage component, in this case a voltage corresponding to a reference operating point 204, and a sinusoidal voltage component. This mode of operation results in an AC voltage 250 being notionally present at the fuel cell unit 102, even without an external measuring device or without external circuit arrangements, which voltage is used for the impedance measurement or for the impedance spectroscopy.

[0035] The controller unit 112 may be designed to specify the resulting AC voltage 250 as a reference variable, wherein the measuring unit 108 is designed to detect a current and/or a voltage response of the fuel cell unit 102 which response is applied to the pair of connectors on the input side to the time-varying operating points 200, 202 induced by the controller unit 112, wherein the comparison unit 110 is designed to compare the measured current and/or voltage response with the reference variable. If necessary, the reference variable is accordingly adjusted so that the current and/or voltage response corresponds to a desired value or to a desired curve.

[0036] During impedance measurement, it has proven to be advantageous if the alternating operating points 200, 202 do not deviate from the reference operating point 204 by more than ten percent, such as not more than five percent. This ensures that the operating points 200, 202 around the reference operating point 204 still lie within the linear range of the characteristic U/I curve of the fuel cell unit 102.

[0037] As a result, an impedance measurement is also possible without the use of external measuring devices, wherein the hardware that is in any case already available can be used for the measurement. This reduces costs and leads to a more compact and simplified design of the fuel cell system or of a motor vehicle which uses this fuel cell system.

[0038] In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.