Fuel cell system in a bipolar high-voltage network and method for operating a bipolar high-voltage network

1. A bipolar high-voltage network for an aircraft or spacecraft, comprising:

at least one non-insulating DC-DC converter having two unipolar input connections and two bipolar output connections as well as a reference potential connection;

at least two fuel cell stacks being coupled in series between the two unipolar input connections; and

at least two discharge diodes, each being connected in parallel with the output connections of one of the at least two fuel cell stacks,

the DC-DC converter being operable selectively in a step-up converter mode of operation or a step-down converter mode of operation, as a function of an input voltage between the unipolar input connections, the DC-DC converter comprising a first DC-DC converter module, coupled via a module input connection to a first of the unipolar input connections of the DC-DC converter, via a module reference potential connection to the reference potential connection of the DC-DC converter, and via a module output connection to a first of the bipolar output connections of the DC-DC converter, and wherein the DC-DC converter comprises a second DC-DC converter module, coupled via a module input connection to a second of the unipolar input connections of the DC-DC converter, via a module reference potential connection to the reference potential connection of the DC-DC converter, and via a module output connection to a second of the bipolar output connections of the DC-DC converter.

2. The bipolar high-voltage network according to claim 1 , wherein the DC-DC converter modules each comprise inverting buck-boost converters.

3. The bipolar high-voltage network according to claim 1 , wherein the DC-DC converter modules each comprise cascaded step-down/step-up converters.

4. The bipolar high-voltage network according to claim 1 , wherein the DC-DC converter modules each comprise cascaded two-point step-down/step-up converters.

5. The bipolar high-voltage network according to claim 1 , wherein the DC-DC converter modules each comprise uncontrolled or controlled two-point NPC converters.

6. The bipolar high-voltage network according to claim 1 , wherein the DC-DC converter modules each comprise split-pi converters.

7. The bipolar high-voltage network according to claim 1 , further comprising:

a first DC voltage intermediate circuit, coupled between the unipolar input connections of the DC-DC converter; and

a second DC intermediate circuit, coupled between the bipolar output connections of the DC-DC converter.

8. A bipolar high-voltage network for an aircraft or spacecraft, comprising:

at least one DC-DC converter having two unipolar input connections and two bipolar output connections as well as a reference potential connection;

at least two fuel cell stacks being coupled in series between the two unipolar input connections;

at least two discharge diodes, each being connected in parallel with the output connections of one of the at least two fuel cell stacks;

a controlled three-point NPC rectifier, which is coupled to the two bipolar output connections and to the reference potential connection of the DC-DC converter at the input and which comprises three AC voltage phase connections at the output; and

an LC filter module, which is coupled to the three AC voltage phase connections of the controlled three-point NPC rectifier,

the DC-DC converter being operable selectively in a step-up converter mode of operation or a step-down converter mode of operation, as a function of an input voltage between the unipolar input connections.

9. The bipolar high-voltage network according to claim 8 , further comprising:

a first DC voltage intermediate circuit, coupled between the unipolar input connections of the DC-DC converter; and

a second DC intermediate circuit, coupled between the bipolar output connections of the DC-DC converter.

10. An aircraft or spacecraft comprising at least one bipolar high-voltage network, the bipolar high-voltage network comprising:

at least one DC-DC converter having two unipolar input connections and two bipolar output connections as well as a reference potential connection;

at least two fuel cell stacks being coupled in series between the two unipolar input connections; and

at least two discharge diodes, being each connected in parallel with the output connections of one of the at least two fuel cell stacks,

the DC-DC converter being operable selectively in a step-up converter mode of operation or a step-down converter mode of operation, as a function of an input voltage between the unipolar input connections,

the DC-DC converter comprising a first DC-DC converter module, coupled via a module input connection to a first of the unipolar input connections of the DC-DC converter, via a module reference potential connection to the reference potential connection of the DC-DC converter, and via a module output connection to a first of the bipolar output connections of the DC-DC converter, and wherein the DC-DC converter comprises a second DC-DC converter module, coupled via a module input connection to a second of the unipolar input connections of the DC-DC converter, via a module reference potential connection to the reference potential connection of the DC-DC converter, and via a module output connection to a second of the bipolar output connections of the DC-DC converter.

11. A method for operating a bipolar high-voltage network, the bipolar high-voltage network comprising at least one non-insulating DC-DC converter having two unipolar input connections and two bipolar output connections as well as a reference potential connection, at least two fuel cell stacks being coupled in series between the two unipolar input connections; and at least two discharge diodes, each being connected in parallel with the output connections of one of the at least two fuel cell stacks, the DC-DC converter being operable selectively in a step-up converter mode of operation or a step-down converter mode of operation, as a function of an input voltage between the unipolar input connections, the DC-DC converter comprising a first DC-DC converter module, coupled via a module input connection to a first of the unipolar input connections of the DC-DC converter, via a module reference potential connection to the reference potential connection of the DC-DC converter, and via a module output connection to a first of the bipolar output connections of the DC-DC converter, and wherein the DC-DC converter comprises a second DC-DC converter module, coupled via a module input connection to a second of the unipolar input connections of the DC-DC converter, via a module reference potential connection to the reference potential connection of the DC-DC converter, and via a module output connection to a second of the bipolar output connections of the DC-DC converter, the method comprising:

operating the DC-DC converter in a step-down converter mode of operation to output a bipolar voltage between the bipolar output connections and the reference potential connection of the DC-DC converter when electrical power is being supplied to the unipolar input connections of the DC-DC converter from the at least two fuel cell stacks; and

operating the DC-DC converter in a step-up converter mode of operation to output a bipolar voltage between the bipolar output connections and the reference potential connection of the DC-DC converter, when electrical power is being supplied to the unipolar input connections of the DC-DC converter from fewer than the at least two fuel cell stacks.