DE102018210907A1 - Watercraft with two parallel DC-DC converters and method of operating such a watercraft - Google Patents

Abstract

The present invention relates to a watercraft with a voltage source (BZ), a traction motor (Mo), a system (V) electrical consumers and two DC-DC converters (G.1, G.2) and a method for operating such a watercraft. The voltage source (BZ) is able to provide direct current of a first voltage (U1). The traction motor (Mo) consumes DC of a second voltage (U2). The system (V) of electrical consumers consumes DC of a third voltage (U3). Both DC-DC converters (G.1, G.2) are connected to the voltage source (BZ) and are connected in parallel with each other. The first DC-DC converter (G.1) is electrically connected to the traction motor (Mo), the second DC-DC converter (G.2) to the system (V) electrical consumers. The first DC-DC converter (G.1) is able to convert direct current of the first voltage into direct current of the second voltage (U.2). The second DC-DC converter (G.2) is able to convert direct current of the first voltage (U.1) into direct current of the third voltage (U3).

Description

The invention relates to a watercraft, in particular a manned or unmanned underwater vehicle, with a voltage source, a traction motor, a system of electrical load and two DC-DC converters and a method for operating such a watercraft.

Frequently, at least three different voltages occur on board an electrically driven watercraft. A voltage source supplies DC current of a first voltage. A traction motor, which is powered by a network, drives the vessel and needs from the network DC power of a second voltage. A system of electrical consumers includes, for example, actuators and electronic devices and requires DC a third voltage. Therefore, at least two DC-DC converters are needed on board the vessel in order to be able to provide both the DC voltage of the first voltage and the DC voltage of the third voltage from the supplied DC voltage of the first voltage. One way to realize this requirement is that a DC-DC converter supplies the DC voltage of the second voltage and another DC-DC converter from the supplied DC voltage of the second voltage generates DC current of the third voltage.

The object of the invention is to provide a watercraft having the features of the preamble of claim 1 and a method having the features of the preamble of claim 12, which leads to lower power losses during operation of the two DC-DC converter than in known watercraft.

This object is achieved by a watercraft having the features specified in claim 1 and by a method having the features specified in claim 12. Advantageous developments emerge from the subclaims, the following description and the drawings.

• - eine erste Spannungsquelle,
• - ein Fahrnetz mit einem Fahrmotor,
• - ein System elektrischer Verbraucher,
• - einen ersten Gleichspannungswandler und
• - einen zweiten Gleichspannungswandler.

The watercraft according to the invention comprises

• a first voltage source,
• a driving net with a drive motor,
• - a system of electrical consumers,
• - A first DC-DC converter and
• - A second DC-DC converter.

The first voltage source is capable of providing direct current to a first voltage. The drive network with the traction motor consumes DC of a second voltage. The system of electrical consumers consumes DC of a third voltage. The three voltages are different in pairs.

Both DC-DC converters are connected to the first voltage source and are connected in parallel with each other. The first DC-DC converter is electrically connected to the traction motor, the second DC-DC converter with the system electrical loads.

The first DC-DC converter is capable of converting direct current of the first voltage (supplied from the first voltage source) into direct current of the second voltage (consumed by the driving network). The second DC-DC converter is capable of converting direct current of the first voltage into direct current of the third voltage (consumed by the system of electrical consumers).

According to the solution, the two DC-DC converters are connected in parallel and convert the direct current of the first voltage source directly into that direct current which the driving network or the system requires electrical consumers. This arrangement reduces the power losses compared to an arrangement in which the two DC-DC converters are connected in series and therefore the DC power from the first power source must be converted once or twice depending on the configuration to drive the direct current for the traction motor or the direct current for the DC motor System to provide electrical consumers. Lower power losses also result in less heat loss that must be dissipated. Dissipating heat loss is often a relevant issue, especially on board an underwater vehicle. Lower power losses also have the consequence that the range and / or duration of use of the vessel is increased.

Because the two DC-DC converters are connected in parallel, the load that causes the system electrical load and the driving network with the traction motor as a whole, distributed to two DC-DC converter.

Thanks to the two DC-DC converters connected in parallel, the various electrical consumers in the electrical load system are not supplied by two DC-DC converters connected in series. Rather, each transformation of a voltage is performed directly from the first voltage source into the respectively required second or third voltage. Furthermore, the electrical loads and the driving network no longer all depend on the same DC-DC converter, but on two different DC-DC converters. Thanks to the arrangement according to the solution, it is possible to form several subnetworks which are supplied with electrical power independently of each other. In the event of a failure or a short circuit in one subnet, it remains possible to continue to supply the other subnet with voltage. This increases the redundancy.

In one embodiment, at least one DC-DC converter is bidirectional. Thanks to this configuration, direct current can be transformed both from the higher to the lower and from the lower to the higher voltage. This refinement also increases the reliability: If a voltage source has failed or if a line fault has occurred, an alternative current path can be produced from one subnetwork to the other subnetwork via the two DC voltage converters, preferably at least one bidirectional DC voltage converter in the other direction than usual is operated. It is not necessary to provide an additional redundant connection. Thus, the embodiment with the parallel DC-DC converters, of which at least one is bidirectional, saves a further connection.

In an advantageous embodiment, a third DC-DC converter is connected both parallel to the first DC-DC converter and parallel to the second DC-DC converter. This third DC-DC converter is electrically connected to the first voltage source and to the driving network. Also, the third DC-DC converter is capable of converting direct current of the first voltage (supplied from the first voltage source) into direct current of the second voltage (consumed by the driving network).

The parallel connected third DC-DC converter provides redundancy. If the first DC-DC converter fails, the third DC-DC converter supplies the driving network with the traction motor with direct current of the second voltage. The solution according to arrangement according to this embodiment provides even more subnets that can be supplied with electrical power independently.

The first DC-DC converter and the third DC-DC converter can be operated simultaneously, so that the load required for driving the traction motor is distributed to these two DC-DC converters. The load distribution can be adjusted during operation and changed if necessary, for example, when a DC-DC converter is heated more than the other DC-DC converter.

In a development of this embodiment, two third DC-DC converter are connected in parallel to each other and parallel to the first DC-DC converter and in parallel with the second DC-DC converter. This training further increases the redundancy and allows an even better load distribution, which can be changed dynamically.

In an embodiment with a plurality of third DC-DC converters, a third DC-DC converter is used as a preferred third DC-DC converter. It specifies a maximum electrical power which the preferred third DC-DC converter can pick up and convert in continuous operation. As long as the actually recorded electrical power remains below a predetermined power limit, the or each further third DC-DC converter is not used. The performance barrier is above half of the predetermined maximum power, preferably above 75%, more preferably above 90%. As soon as the actually received electrical power reaches or exceeds the predetermined power limit, the or at least one further third DC-DC converter is driven and converts electrical voltage in addition to the preferred third DC-DC converter. The load is then distributed to two parallel third DC-DC converter.

In a further embodiment, a fourth DC-DC converter can convert direct current of the second voltage (required by the driving network) into direct current of the third voltage (required by the system of electrical consumers). This fourth DC-DC converter is electrically connected to the first DC-DC converter (supplies DC of the second voltage) and to the electrical load system.

The fourth DC-DC converter provides redundancy. If the second DC-DC converter fails, the fourth DC-DC converter supplies the electrical load system with voltage. Because the fourth DC-DC converter is connected in series with the first DC-DC converter, no DC-DC converter need be connected in parallel. It is also possible to distribute the load on the second voltage converter on the one hand and the series-connected first and fourth voltage transformers on the other hand.

In a further development of the embodiment with the fourth DC-DC converter, the watercraft comprises a second voltage source in addition to the first voltage source. This second voltage source supplies DC of the second voltage (consumed by traction motor) and is connected to the driving network.

The fourth DC-DC converter provides additional redundancy. If the first power source fails or is unable to provide enough electrical power or voltage, the electrical load system is powered by the second voltage source (providing DC of the second voltage) and the fourth DC-to-DC converter.

As long as the first voltage source provides sufficient voltage, the system electrical load is optionally supplied via the second DC-DC converter or via the first DC-DC converter and the fourth DC-DC converter, which are connected in series. It is possible to divide the electrical load that causes the system electrical loads on the first voltage source and the second voltage source. Furthermore, it is possible to dynamically change the load distribution during operation.

In a preferred embodiment, the first voltage source is a fuel cell system, preferably a fuel cell system with PEM fuel cells (PEM = Proton Exchange Membrane). Other embodiments of a fuel cell system are also possible.

In one embodiment, the watercraft comprises a second voltage source. This second voltage source provides DC of the second voltage (consumed by the car network). For example, the second voltage source is a system with multiple rechargeable batteries. The first DC-DC converter is electrically connected to the driving network and additionally to the second voltage source. The first DC-DC converter is preferably designed as a bidirectional DC-DC converter, i. it can convert both direct current of the first voltage into direct current of the second voltage and direct current of the second voltage into direct current of the first voltage. A further DC-DC converter can also be designed as a bidirectional voltage converter.

This refinement allows the following operating mode: The driving network with the traction motor is supplied exclusively or at least predominantly by the first voltage source. The system of electrical consumers is powered by the second voltage source. The reverse mode is also possible.

In one embodiment, the second voltage source (preferably a battery system) can provide the maximum electrical power required by the driving network and at the same time also prefers the electrical power required by the system of electrical consumers. By contrast, the first voltage source is only able to convert and deliver so much electric power that it is able to supply the transport network with a portion of the maximum required electrical power. This part is sufficient, for example, to operate the traction motor at a reduced speed and preferably at the same time to supply the system electrical consumers, but not sufficient to let the traction motor operate at full speed. In this embodiment, a DC-DC converter, which is electrically connected only to the first voltage source, but not to the second voltage source, only needs to be designed so that it can absorb and convert the maximum electrical power provided by the first voltage source.

The embodiment with the second voltage source provides redundancy without having to provide an additional DC-DC converter. If the first voltage source is not supplying enough voltage or has failed or is highly heated, the second voltage source may supply the system of electrical loads via the first DC-DC converter and the second DC-DC converter connected in series with this supply. In reverse operation, the first DC-DC converter converts DC current of the second voltage into DC current of the first voltage, which is then applied to the electrical connection between the first voltage source and the first DC-DC converter. The second DC-DC converter further converts DC of the first voltage to DC of the third voltage. It is also possible for the system of electrical consumers to be supplied with voltage both from the first voltage source and from the second voltage source. It is also possible to dynamically change the load distribution between the two voltage sources during operation.

In one embodiment, the second voltage source is configured to store electrical energy. The second DC-DC converter is additionally connected to the rechargeable second voltage source and is designed as a bidirectional DC-DC converter. Thanks to this configuration, it is possible that current that is generated in the electrical load system, converted and fed back into the second voltage source.

In particular, the watercraft according to the invention is an underwater vehicle and may be a manned or an unmanned watercraft and may be used for military and / or civilian purposes.

• 1 einen schematischen Schaltplan für ein elektrisches Netz, in welchem die Erfindung nicht angewendet wird;
• 2, auf welche Weise die Brennstoffzellenanlage in dem Netz gemäß 1 die Batterie versorgt;
• 3, auf welche Weise die Batterie in dem Netz gemäß 1 die Verbraucher versorgt;
• 4, auf welche Weise die Brennstoffzellenanlage in dem Netz gemäß 1 die Verbraucher versorgt;
• 5 einen schematischen Schaltplan für ein elektrisches Netz, in welchem eine erste Ausführungsform der Erfindung angewendet wird;
• 6, auf welche Weise die Brennstoffzellenanlage in dem Netz gemäß 5 die Batterie versorgt;
• 7, auf welche Weise die Brennstoffzellenanlage in dem Netz gemäß 5 den Fahrmotor versorgt;
• 8, auf welche Weise die Brennstoffzellenanlage in dem Netz gemäß 5 die Verbraucher versorgt;
• 9, auf welche Weise die Batterie in dem Netz gemäß 5 die Verbraucher versorgt;
• 10 einen schematischen Schaltplan für ein elektrisches Netz, in welchem eine zweite Ausführungsform der Erfindung angewendet wird;
• 11, auf welche Weise die Batterie in dem Netz gemäß 10 die Verbraucher versorgt.

Below, the watercraft according to the invention is explained in more detail with reference to an embodiment shown in the drawings. Hereby show:

• 1 a schematic circuit diagram for an electrical network, in which the invention is not applied;
• 2 in what way does the fuel cell plant in the network according to 1 the battery is powered;
• 3 in what way the battery in the network according to 1 supplies the consumers;
• 4 in what way does the fuel cell plant in the network according to 1 supplies the consumers;
• 5 a schematic circuit diagram for an electrical network, in which a first embodiment of the invention is applied;
• 6 in what way does the fuel cell plant in the network according to 5 the battery is powered;
• 7 in what way does the fuel cell plant in the network according to 5 supplies the traction motor;
• 8th in what way does the fuel cell plant in the network according to 5 supplies the consumers;
• 9 in what way the battery in the network according to 5 supplies the consumers;
• 10 a schematic circuit diagram for an electrical network, in which a second embodiment of the invention is applied;
• 11 in what way the battery in the network according to 10 supplies the consumers.

In 1 A schematic circuit diagram for an electrical network is shown in which the invention is not applied. This network is arranged on board a watercraft in the form of a manned or unmanned underwater vehicle. The underwater vehicle should be able to operate in a longer period of time, at least temporarily under water, without having to be connected to an external voltage source.

• - eine Brennstoffzellenanlage BZ, die als eine erste Spannungsquelle fungiert und Gleichstrom einer ersten Spannung U1 liefert,
• - ein System Ba mit einer Menge von wiederaufladbaren Batterien, das als eine zweite Spannungsquelle fungiert und Gleichstrom einer zweiten Spannung U2 liefert,
• - einen Generator G, der von einem nicht gezeigten Dieselmotor angetrieben wird und Gleichstrom der zweiten Spannung U2 liefert,
• - einen elektrischer Fahrmotor Mo, der mindestens eine nicht gezeigte Welle für einen ebenfalls nicht gezeigten Propeller dreht, dadurch das Unterwasserfahrzeug antreibt und Gleichstrom der zweiten Spannung U2 aufnimmt,
• - ein System V elektrischer Verbraucher, welches Gleichstrom einer dritten Spannung U3 aufnimmt und beispielsweise Stellantriebe für Ruder, Sehrohre und Klappen sowie Kühleinrichtungen und elektronische Schaltschränke umfasst,
• - einen ersten Gleichspannungswandler G.1, der Gleichstrom der ersten Spannung U1 in Gleichstrom der zweiten Spannung U2 umwandelt,
• - einen weiteren Gleichspannungswandler G.x, der Gleichstrom der zweiten Spannung U2 in Gleichstrom der dritten Spannung U3 umwandelt, und
• - einen ersten Leistungsschalter LS.1, welcher den ersten Gleichspannungswandler G.1 wahlweise mit der Brennstoffzellenanlage BZ verbindet oder von ihr trennt.

1 shows the following components of this electrical network:

• - a fuel cell system BZ acting as a first voltage source and DC of a first voltage U1 supplies,
• - a system Ba with a quantity of rechargeable batteries acting as a second voltage source and DC of a second voltage U2 supplies,
• - a generator G which is driven by a diesel engine, not shown, and DC of the second voltage U2 supplies,
• - An electric traction motor Mo which rotates at least one shaft, not shown, for a propeller, also not shown, thereby driving the underwater vehicle and direct current of the second voltage U2 receives
• - a system V electrical load, which DC a third voltage U3 includes, for example, actuators for rudders, periscopes and flaps and cooling devices and electronic control cabinets,
• - a first DC-DC converter G.1 , the DC of the first voltage U1 in DC of the second voltage U2 converts,
• - Another DC-DC converter Gx , the DC of the second voltage U2 in DC of the third voltage U3 converts, and
• - a first circuit breaker LS.1 , which is the first DC-DC converter G.1 optionally with the fuel cell system BZ connects or separates from it.

In the embodiment, the first voltage U1 less than the third voltage U3 , and the third tension U3 is smaller than the second voltage U2 , In one embodiment, the second voltage U2 by the factor M greater than the first voltage U1 , The third tension U3 is about the factor N greater than the first voltage U1 where N <M. Thus, the second voltage U2 by the factor O = M / N greater than the third voltage U3 ,

1 further shows the electrical connections between these components of the electrical network as solid lines. Nodes are marked with solid circles.

2 shows how the fuel cell system BZ in the network according to 1 the battery system Ba charging, being the first circuit breaker LS.1 closed is. The current path is shown by solid lines. The first DC-DC converter G.1 converts the direct current of the first voltage U1 in DC of the second voltage U2 around. The relationship between the first voltage U1 and the second voltage U2 is close to one M what's by the name 1 : M is indicated. Also shows 2 like the fuel cell plant BZ also the drive motor Mo provided.

3 shows how the battery system works Ba in the network according to 1 the system V electrically powered electrical consumer, especially if the circuit breaker LS.1 is open. The further DC-DC converter Gx converts the DC of the second voltage U2 in DC of the third voltage U3 around. The ratio between the second voltage U2 and the third voltage U3 is at N to one, which by the name N : 1 is indicated.

4 shows how the fuel cell system BZ the system V supplied electrical consumer. First, the first DC-DC converter converts G.1 DC of the first voltage U1 in DC of the second voltage U2 around. Subsequently, the other DC-DC converter converts Gx the DC of the second voltage U2 in DC of the third voltage U3 around.

Thus, the direct current is converted twice, first with the ratio one to M and then with the ratio N to one. This series connection of two DC-DC converters causes relevant power losses. The invention reduces these power losses while providing the system V electrical consumer.

5 and 10 show two embodiments of the network in which the invention is applied. Same components of the network have the same terms as in 1 , The further DC-DC converter Gx as well as the first circuit breaker LS.1 from 1 be in the embodiments according to 5 and 10 not used. The electrical connection between the fuel cell system BZ on the one hand and the two DC-DC converters G.1 and G.2 on the other hand, Vb is designated.

5 shows three DC-DC converter, which are connected in parallel, namely the two DC-DC converter G.1 and G.2 that also in the circuit according to 1 can be used, as well as a third DC-DC converter G.3 , the same as the first DC-DC converter G.1 DC of the first voltage U1 in DC of the second voltage U2 converts, so in the ratio one to M , The second DC-DC converter G.2 Converts electricity in the ratio 1: O.

Also shows 5 a second circuit breaker LS.2 , a third circuit breaker LS.3 and an optional fourth power switch LS.4 , The second circuit breaker LS.2 can the two parallel DC-DC converter G.1 and G.2 and with it the system V electrical load from the fuel cell system BZ to separate. The third circuit breaker LS.3 capable of the third DC-DC converter G.3 and with it the battery system Ba , the generator G and the traction motor Mo from the fuel cell system BZ to separate. The optional fourth circuit breaker LS.4 is capable of the first DC-DC converter G.1 from the parallel components Ba . G and Mo to separate.

6 shows how the fuel cell system BZ in the network according to 5 the battery system Ba electrically supplied. 7 shows how the traction motor Mo in the network according to 5 is supplied. These two ways are the same as the one in 1 , In one mode, the circuit breaker LS.4 opened, and the traction motor Mo is exclusively from the fuel cell BZ provided.

8th shows, as in the network according to 5 the fuel cell BZ the system V electrical consumer powered, the second circuit breaker LS.2 closed is. The second DC-DC converter G.2 converts the DC of the voltage U1 the fuel cell plant BZ supplies, in DC, the third voltage U3 around. This will cause the direct current from the fuel cell system BZ through a single conversion into the direct current that the system V electrical consumer receives transformed. Compared to the arrangement of 1 Thus, the power losses are reduced, because only a DC-DC converter G.2 instead of two series-connected DC-DC converters G.1 and Gx be used.

9 shows, as in the network according to 5 the battery system Ba the system V supplied electrical consumer, especially when the circuit breaker LS.2 is open. The circuit breaker LS.4 is closed. This path is different from the way in 3 will be shown. First, as seen in the flow direction, the bidirectional first DC-DC converter converts G.1 the DC with the second voltage U2 the battery Ba supplies, in DC, the first voltage U1 around. Subsequently, the second DC-DC converter converts G.2 DC of the first voltage U1 in DC of the third voltage U3 around.

So if the system V electrical load from the battery system Ba is supplied electrically, then the supplied direct current in the embodiment of 5 and 5 converted twice, namely from the two series-connected DC-DC converters G.1 and G.2 , This results in power losses. One way to reduce these power losses is to use the optional circuit breaker LS.4 provide and leave this open as long as the fuel cell system BZ the system V to supply electrical consumers.

10 shows an alternative embodiment in which the fourth power switch LS.4 is not needed and in which the power losses compared to 5 are lower when the battery system Ba the system V supplied electrical consumer. The advantage of the arrangement of 5 remains intact, namely that between the fuel cell system BZ and the system V electrical load only a single DC-DC converter G.2 is arranged.

In 10 is a fourth DC-DC converter G.4 provided, which direct current of the second voltage U2 in DC of the third voltage U3 converted, so with a tension of N to one like the other DC-DC converter Gx from 1 , The input of this fourth DC-DC converter G.4 is with the electrical connection between the first DC-DC converter G.1 and the traction motor Mo connected, the output with the electrical connection between the second DC-DC converter G.2 and the system V electrical consumer. 11 shows, in which way in the arrangement of 10 the system V electrical load from the battery system Ba is supplied.

In one embodiment, at least one DC-DC converter is designed as a bidirectional DC-DC converter. This is the example of the fourth DC-DC converter G.4 from 10 explained. It is possible that the system V electrical consumers temporarily consumed no electrical energy, but inversely supplies electrical energy. The fourth DC-DC converter G.4 converts the DC of the third voltage U3 which the system V electrical load supplies, in DC the second voltage U2 around, with which the battery system Ba is charged. This embodiment further extends the service life of the underwater vehicle.

LIST OF REFERENCE NUMBERS

Ba

System of rechargeable batteries, is powered by DC of the second voltage U2 charged and gives DC the second voltage U2 ab, acts as the second voltage source

BZ

Fuel cell system, supplying DC of the first voltage U1 , acts as the first voltage source

G

Generator, generates DC of the second voltage U2

G.1

first DC-DC converter, converts DC to the first voltage U1 in DC of the second voltage U2 around

G.2

second DC-DC converter, converts DC of the first voltage U1 in DC of the third voltage U3 around, parallel to the first DC-DC converter G.1 switched

G.3

third DC-DC converter, converts DC of the first voltage U1 in DC of the second voltage U2 around, parallel to the first DC-DC converter G.1 switched

G.4

fourth DC-DC converter, converts DC of the second voltage U2 in DC of the third voltage U3 around

G.x

another DC-DC converter, converts DC to the second voltage U2 in DC of the third voltage U3 around

LS.1

first circuit breaker, which the first DC-DC converter G.1 optionally with the fuel cell system BZ connects or separates from it

LS.2

second power switch, which the first DC-DC converter G.1 and the second DC-DC converter G.2 optionally with the fuel cell system BZ connects or separates from it

LS.3

third power switch, which the third DC-DC converter G.3 optionally with the fuel cell system BZ connects or separates from it

LS.4

fourth power switch, which the first DC-DC converter G.1 optionally with the components BA . G . Mo connects or separates from them

M

Factor to the second voltage U2 is greater than the first voltage U1

Mo

Traction motor, DC takes the second voltage U2 on

N

Factor to the third voltage U3 is greater than the first voltage U1

O

Factor to the second voltage U2 is greater than the third voltage U3 , O = M / N

U1

first voltage, voltage of the first voltage source (fuel cell system BZ ) supplied direct current

U2

second voltage, voltage of the driver motor and the second voltage source (battery system Ba ) as well as from the generator G supplied direct current

U3

third voltage, voltage of the system V electrical consumer recorded DC

V

System of electrical consumers, takes DC of the third voltage U3 on

Vb

electrical connection between the fuel cell system BZ and the two DC-DC converters G.1 and G.2

Claims (12)

Watercraft with - a first voltage source (BZ), - a driving network with a traction motor (Mo), - a system (V) electrical consumers, - a first DC-DC converter (G.1) and - a second DC-DC converter (G.2), wherein the first voltage source (BZ) is configured to provide direct current of a first voltage (U1), wherein the drive network with the drive motor (Mo) is configured to be operated with direct current of a second voltage (U2), the system (V) electrical load is designed to be operated DC of a third voltage (U3) and wherein these two voltages (U2, U3) differ from each other and from the first voltage (U1), characterized in that the first DC-DC converter (G.1) - is configured to convert direct current of the first voltage (U1) into direct current of the second voltage (U2), and - is electrically connected to the first voltage source (BZ) and to the driving network (Mo), and the zw DC-DC converter (G.2) - configured to convert direct current of the first voltage (U1) into direct current of the third voltage (U3), and - electrically connected to the first voltage source (BZ) and to the electrical load system (V) , and wherein the two DC-DC converters (G.1, G.2) are connected in parallel with each other. Watercraft after Claim 1 , characterized in that the first voltage (U1) is smaller than the third voltage (U3) and the third voltage (U3) is smaller than the second voltage (U2). Vessel according to one of the preceding claims, characterized in that at least temporarily turned on the first DC-DC converter (G.1) and simultaneously the second DC-DC converter (G.2) is switched off or at least temporarily the second DC-DC converter (G.2) and at the same time the first DC-DC converter (G.1) is switched off. Vessel according to one of the preceding claims, characterized in that the vessel comprises at least a third DC-DC converter (G.3) which is - configured to convert direct current of the first voltage (U1) into direct current of the second voltage (U2), and - with the first voltage source (BZ) and to the driving network (Mo) is electrically connected, wherein the third DC-DC converter (G.3) is connected in parallel to the first DC-DC converter (G.1) and parallel to the second DC-DC converter (G.2). Vessel according to one of the preceding claims, characterized in that the vessel comprises two parallel-connected third DC-DC converter (G.3), wherein each third DC-DC converter (G.3) - is configured to direct current of the first voltage (U1) in direct current of the second Voltage (U2), and - is electrically connected to the first voltage source (BZ) and with the driving network (Mo), each third DC-DC converter (G.3) parallel to the first DC-DC converter (G.1) and parallel to the second DC-DC converter ( G.2) is switched. Watercraft after Claim 5 , characterized in that at least temporarily turned on a third DC-DC converter (G.3) and at the same time the other third DC-DC converter (G.3) is turned off. Vessel according to one of the preceding claims, characterized in that the vessel comprises a fourth DC-DC converter (G.4) which is designed to convert direct current of the second voltage (U2) into direct current of the third voltage (U3), and - with the first DC-DC converter (G.1) and is electrically connected to the system (V) electrical loads. Watercraft after Claim 7 , characterized in that the underwater vehicle comprises a second voltage source (Ba) which - direct current supplies the second voltage (U2) and - is connected to the driving network (Mo), wherein the fourth DC-DC converter (G.4) in addition to the second voltage source (Ba) is electrically connected. Watercraft according to one of the preceding claims, characterized in that the first voltage source (BZ) comprises at least one fuel cell. Vessel according to one of the preceding claims, characterized in that the underwater vehicle comprises a second voltage source (Ba) which supplies direct current of the second voltage (U2), wherein the first DC-DC converter (G.1) - additionally connected to the second voltage source (Ba) is and - is designed as a bidirectional DC-DC converter and wherein the second DC-DC converter (G.2) with the electrical connection (Vb) between the first voltage source (BZ) and the first voltage converter (G.1) is electrically connected. Watercraft after Claim 10 , characterized in that the second voltage source (Ba) is adapted to store electrical energy, and the second DC-DC converter (G.2) - is additionally connected to the second voltage source (Ba) and - is designed as a bidirectional DC-DC converter. Method for operating a watercraft, wherein the watercraft - a first voltage source (BZ), - a driving network with a traction motor (Mo), - a system (V) electrical consumers, - a first DC-DC converter (G.1) and - a second DC-DC converter (G.2), the method comprising the steps of - providing the first voltage source (BZ) with direct current of a first voltage (U1), - consuming the driving network (Mo) with direct current of a second voltage (U2), and - the system ( V) consumes electrical load DC a third voltage (U3), wherein the second voltage (U2) is greater than the third voltage (U3) and wherein these two voltages (U2, U3) differ from the first voltage (U1), characterized in that the first DC-DC converter (G.1) is electrically connected to the first voltage source (BZ) and to the driving network (Mo) and the second DC-DC converter (G.2) to the first voltage source (BZ) and to the S ystem (V) electrical load is electrically connected, wherein the two DC-DC converter (G.1, G.2) are connected in parallel and wherein the method comprises the further steps that - the first DC-DC converter (G.1) DC of the first voltage (U1) converts to direct current of the second voltage (U2) - the second DC-DC converter (G.2) converts direct current of the first voltage (U1) into direct current of the third voltage (U3).

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