Hot stand-by for battery systems

Abstract

The invention relates to a method for operating a submarine (10), wherein the submarine (10) has an on-board electrical system (20); the submarine (10) has n energy storage devices (30), n being a natural number which is greater than or equal to (4); the on-board electrical system (20) has a maximum network power; each energy storage device (30) is releasably electrically connected to the on-board electrical system (20) via a respective DC-to-DC converter (40), the DC-to-DC converters (40) being regulated via a current-voltage characteristic curve (100); the on-board electrical system (20) is operated using a partial load, said partial load being lower than the maximum network power; a first sub-group of m energy storage devices (30) is selected, m being a natural number and less than n and greater than or equal to (2); the first sub-group is connected to the on-board electrical system (20) so as to conduct a current; a first offset is selected for the current-voltage characteristic curve (100) of the DC-to-DC converters (40) of the first sub-group such that the product of the current and voltage and m corresponds to the partial load, resulting in a current on-board electrical system voltage; a second sub-group of l energy storage devices (30) is selected, l being a natural number and less than or equal to n-m and greater than or equal to (2); and the second sub-group is connected to the on-board electrical system (20) so as to not conduct a current such that a second offset is selected for the current-voltage characteristic curve (100) of the DC-to-DC converters (40) of the second sub-group such that the current-voltage characteristic curve (100) is shifted so that the current on-board electrical system voltage leads to a de-energized operation of the DC-to-DC converters (40) of the second sub-group.

Description

[0001] Hot standby for battery systems

[0002] The invention relates to a method for controlling DC / DC converters of energy storage devices, each of which is individually connected to the grid via separate DC / DC converters. A control system for the DC / DC converters ensures that at least one energy storage device feeds energy into the grid, and at least one further energy storage device, while electrically connected to the grid, does not supply any electrical power to the grid during normal operation. However, in the event of a grid overload, it is immediately switched to supply electrical energy to the grid. DC / DC converters are also known as DC-DC converters.

[0003] Submarines rely on an energy storage system as a crucial power source for underwater travel, currently most often a lead-acid battery. Since lead-acid batteries have a low voltage but a high current, they are typically connected in series to provide the voltage required for a propulsion motor, usually around 1000 V. However, newer technologies, such as lithium-ion batteries, are increasingly being used in submarines. Because their cells, while offering higher voltage, are generally smaller and therefore capable of generating lower currents, multiple energy storage devices are now being implemented, each individually connected to the submarine's electrical system.

[0004] A battery module is known from DE 10 2019 216 606 A1.

[0005] From DE 102019 216 608 A1 a battery module with monitoring of the thermal runaway of individual cells is known.

[0006] German patent DE 10 2020 205 327 A1 discloses a submarine with a situation-independent power supply for a string battery management system. German patent DE 10 2019 217 796 A1 discloses a bypass for a battery management system in a submarine in case of emergency.

[0007] From DE 10 2020 203 469 A1 a method for operating a lithium battery on an on-board electrical system designed for lead-acid batteries in a submarine is known.

[0008] A low-stray field battery module is known from DE 10 2021 200 765 A1.

[0009] From DE 10 2021 202 537 A1 a method for operating a submarine with a fuel cell and an accumulator is known.

[0010] The determination of the aging state of an energy storage device on board a submarine is known from DE 10 2021 203 947 A1.

[0011] From DE 10 2021 210 447 A1 a method for operating an on-board power network of a submarine under high loads is known.

[0012] From DE 10 2022 208 979 a method for increasing the range of a submerged submarine is known.

[0013] From DE 10 2022 205 773 A1 a submarine with two different battery systems and a method for operating it is known.

[0014] The DE 20 2022 102 716 U1 is known to have a submarine with two converters on the propulsion motor.

[0015] A battery module is known from EP 4 340 113 A1.

[0016] German patent DE 10 2022 132635 discloses a submarine with an energy storage device located outside the pressure hull. German patent WO 2020 / 030523 A1 discloses a method for controlling the power grid of an underwater vehicle and an underwater vehicle designed for such control.

[0017] A DC voltage converter for lithium batteries is known from DE 10 2017 009 527 A1.

[0018] From DE 10 2018 213 180 A1 a method for controlling the network of an underwater vehicle is known.

[0019] From DE 10 2017 123 730 A1, an energy storage system with several energy storage devices connected in parallel and a method for operating an energy storage system are known.

[0020] A battery power plant with a cooling system is known from DE 10 201 110 200 B3.

[0021] Since several strings, each with an energy storage device and a DC-DC converter, are connected in parallel, a problem arises when dealing with small power demands (also known as partial load): the strings operate outside their optimal operating point and therefore have lower efficiencies. This leads to increased energy consumption, which reduces the maximum possible dive times, especially for underwater vehicles. A solution would be to disconnect individual strings, so that the total power demand is distributed across fewer strings. This would allow the remaining strings to operate at a better point and thus achieve higher efficiency.If the unused sections are switched off, a sudden increase in load in the vehicle electrical system can lead to the available capacity being too low to provide the necessary power.

[0022] This means that, especially in the partial load range, and particularly at very low loads, the challenge is to connect the correct number of energy storage devices to the vehicle electrical system in a meaningful way, where, for example, efficiency and power reserve can be conflicting design parameters.

[0023] The object of the invention is to provide a power reserve in an efficient manner that conserves battery life.

[0024] This problem is solved by the method with the features specified in claim 1 and by the energy supply system with the features specified in claim 3. Advantageous further developments are described in the dependent claims, the following description, and the drawings.

[0025] The method according to the invention is used to operate a submarine. The submarine has an onboard electrical system. This onboard electrical system can also be a subnetwork of several independent subnetworks, for example, to ensure redundancy of the electrical system via independent subnetworks. The method according to the invention can be applied independently to each subnetwork. The electrical consumers are connected to the onboard electrical system. The propulsion motor is usually the most powerful consumer, but its power consumption varies considerably depending on the speed and it has a very low energy requirement, especially when traveling at low speeds. Furthermore, a diesel generator is typically connected to the onboard electrical system for surface operation. The submarine has n energy storage devices, particularly for underwater operation. n is a natural number greater than or equal to 4; preferably, n is between 4 and 400.For the purposes of this invention, an energy storage device is understood to be one that can be individually and selectively connected to or disconnected from the vehicle's electrical system. Thus, an energy storage device is preferably a so-called string, which typically consists of 3 to 10 modules, each module comprising a plurality of batteries, particularly lithium-ion batteries, connected in series and / or parallel. The vehicle's electrical system has a maximum power rating. This is the maximum electrical power for which the electrical system is designed during continuous operation. This can also be referred to as the nominal power rating. Each energy storage device is electrically disconnectable from the vehicle's electrical system via a DC-DC converter. The DC-DC converter performs several functions. Firstly, it isolates the vehicle's electrical system voltage from the residual capacity-dependent charge of the energy storage device.This allows multiple energy storage devices with different residual capacities to be connected to the vehicle's electrical system simultaneously. Furthermore, the DC-DC converter can optionally provide galvanic isolation, which is advantageous, for example, in the event of a short circuit. Additionally, the DC-DC converter also enables an electrical connection without current flow if a corresponding current-voltage characteristic curve is defined for controlling the converter. For this purpose, the characteristic curve defines a voltage range within the vehicle's electrical system in which the energy storage devices are neither charged nor discharged.

[0026] Every energy storage device has a maximum storage capacity, the so-called nominal power, which is the maximum amount of electrical power the device is capable of delivering. Furthermore, every energy storage device has a maximum storage capacity, the so-called nominal capacity, which is the capacity between a full charge and a full discharge. The DC-DC converters are controlled by a current-voltage characteristic curve, as is familiar to those skilled in the art, for example, from WO 2020 / 030523 A1.

[0027] The current-voltage characteristic curve has, to a first approximation, five regions. Each region corresponds to a specific voltage range of the vehicle electrical system. The first region describes the discharge process of the energy storage device and therefore exhibits a current flow towards the vehicle electrical system. This region is typically continuous, with higher currents generally occurring at lower system voltages. The current is limited at the maximum current, so that the current intensity is not increased further, regardless of the voltage. This protects the energy storage device and the vehicle electrical system from damage. This can be defined as the second region. Corresponding to the discharge process is the charging process, in which the current flows from the vehicle electrical system to the energy storage device; mathematically, the current has the opposite sign.Here, too, there is a third range in which the relationship between charging current and vehicle electrical system voltage is typically constant; the higher the vehicle electrical system voltage, the greater the charging current of the energy storage device. A fourth range follows, limiting the charging current and keeping it constant regardless of the voltage. This also reliably prevents damage to the energy storage device from excessive charging current. Finally, there is a fifth range, which is currentless, meaning the rectifier neither draws power from nor supplies power to the energy storage device. This fifth range connects the range between the highest discharge voltage and the lowest charging voltage.

[0028] The vehicle's electrical system is currently operating at partial load for the execution of the procedure. This means that not all energy storage devices need to be connected to the electrical system to provide full load (maximum grid power). The partial load is lower than the maximum grid power. Due to the partial load operation of the system, electrical energy can be drawn from several energy storage devices in various ways. A first subset of m energy storage devices is selected, where m is a natural number less than n and greater than or equal to 2. This is therefore a true subset of at least two energy storage devices, but not all of them. The first subset is connected to the vehicle's electrical system with current flowing through it. More precisely, the vehicle's electrical system is supplied only via the first subset and not via any other energy storage devices.Thus, the first subgroup comprises all energy storage devices connected to the vehicle's electrical system via a current-carrying connection. "Current-carrying" in this context means that a current is flowing at the specific time, i.e., that electrical power is actually being supplied from the energy storage devices to the vehicle's electrical system.

[0029] For the current-voltage characteristic of the DC-DC converters in the first subgroup, an initial offset is selected such that the product of current and voltage, and m, corresponds to the power input or output at the partial load. For example, assuming the vehicle electrical system voltage is selected and regulated within a range of 900 V to 1100 V, the offset of the first subgroup can be set so that the voltage is at 1000 V. If we further assume a maximum current of 10 A, then at a partial load of 55 kW, m could be set to 6. The offset is then adjusted, for example, so that the vehicle electrical system voltage is set to 916.7 V, resulting in the required power of 55 kW (916.7 V x 10 A x 6). For simplicity, it was assumed that current and voltage were independent.Taking this dependency into account simply makes the calculation more complex. This ensures that the subgroup provides precisely the required amount of energy. By varying the voltage between 900 V and 1100 V, a first subgroup with m = 6 would allow for an adjustment between 54 kW and 66 kW (this is a simplified explanation, as the achievable current would typically be lower and the range narrower at higher voltages). Therefore, a qualified technician can easily adjust the offset for a given power output. This results in a current on-board voltage. The offset represents a shift in the current-voltage characteristic curve along the on-board voltage.The offset allows the characteristic curve to be shifted to lower or higher voltages. In particular, different offsets can result in different DC-DC converters with otherwise identical current-voltage characteristics exhibiting different currents or power outputs. Therefore, m must be chosen such that the product of current, voltage, and the number of m can meet the energy requirement. Since the product is relevant, a small current would indeed lead to a higher voltage, but the individual power output would be low, necessitating a very large value for m. A more realistic approach is to choose a relatively high current, allowing for a smaller value for m. An example calculation would be to take the voltage at maximum current and determine a number of m such that the resulting power exceeds the required power output.The current can then be reduced, thereby increasing the voltage, until the product of current, voltage, and power (m) corresponds to the required power. The current-voltage characteristic curve for this first subgroup can then be adjusted to determine the operating point. To illustrate this, a purely hypothetical submarine with easily calculated numerical values ​​is used. This example submarine has 100 energy storage devices. The nominal onboard voltage is 1000 V. Each energy storage device can deliver a maximum current of 10 A, resulting in a maximum storage capacity of 10 kW and a maximum grid power of 1 MW.

[0030] If the submarine's partial load requirement is, for example, only 100 kW, then theoretically all energy storage devices could be operated at 10% load, i.e., with a current of 1 A. This has the advantage that as soon as higher power is needed, it is immediately and directly available up to the maximum grid capacity without any further regulation. However, this situation leads to the DC-DC converters operating in an unfavorable range where their efficiency is low. This, in turn, means that the maximum usable energy is reduced by electrical losses, for example, in the DC-DC converters, which in turn reduces the range and operating time underwater. Therefore, it is advantageous not to keep all energy storage devices connected to the ship's electrical system.In the example given, a logical subset of m = 11 would result, such that 11 energy storage devices would each feed approximately 9.1 A at 1000 V into the vehicle's electrical system, thus covering the 100 kW requirement. Assuming that the efficiency of the DC-DC converters is optimal at approximately 90% load, this results in the best possible energy efficiency. It is important to note that in this example, 90 energy storage devices are not actually connected to the vehicle's electrical system.

[0031] The problem is that if more power is suddenly required, for example, because an additional consumer is switched on, the necessary power can no longer be provided immediately, as switching on the energy storage devices, for example via an (electronic) switch, takes a certain amount of time. To solve this problem, a second subgroup of I energy storage devices is selected, where I is a natural number less than or equal to nm and greater than or equal to 2. The second subgroup is not connected to the vehicle's electrical system. The second subgroup can also be just a portion of the total number of energy storage devices not belonging to the first subgroup. The size of the second subgroup cannot be precisely determined in a simple way as described above.Rather, the size of the second subgroup represents a trade-off: keeping it as small as possible to maintain high flow rates, and keeping it as large as possible to maximize reserves. Therefore, the choice of the second subgroup's size will be highly mission-dependent. For example, if there is an immediate risk of detection, the probability of needing to accelerate to escape speed very quickly is high, requiring maximum power output in the short term. In such a mission profile, subgroup I would therefore be chosen to be comparatively large, even maximum. However, if no significant changes are expected because the submarine is in a secure position and is merely acting as an observation post for potential intruders, then the expected energy fluctuations will also be rather small, for example, due to the activation of the galley to prepare the next meal.In this mission profile, I will be chosen as small.

[0032] To prevent the second subgroup from being connected to the vehicle electrical system in a current-carrying manner, a second offset is selected for the current-voltage characteristic of the DC-DC converters of the second subgroup. This second offset is chosen such that the current vehicle electrical system voltage lies within the fifth region of the current-voltage characteristic. The essential aspect of the invention is therefore the determination of this offset of the second subgroup and thus the relative shift of the current-voltage characteristic of the first subgroup to the current-voltage characteristic of the second subgroup. The offset of the current-voltage characteristic of the first subgroup can be easily determined from the operating parameters, as described above. Thus, the current-voltage characteristic of the second subgroup is shifted such that the current vehicle electrical system voltage results in the DC-DC converter operating without current.This means that the current vehicle electrical system voltage, and preferably small fluctuations thereof, do not cause current to be drawn from or received by the energy storage devices belonging to the second subgroup. The offset of the current-voltage characteristic curve of the second subgroup is chosen precisely so that the current operating voltage lies in the fifth range and is therefore currentless. However, a large change in the vehicle electrical system voltage causes the fifth range of the current-voltage characteristic curve to be left behind, and the second subgroup immediately switches to regulation mode, meaning it draws or draws current. In other words, while the energy storage devices of the subgroup are electrically connected to the vehicle electrical system, they exhibit a current flow of 0 A due to the correspondingly shifted current-voltage characteristic curve.This state can be described as hot standby and is the essential point of the invention.

[0033] Knowing the operating point, the shift of the current-voltage characteristic of the second subgroup can be precisely determined using the first subgroup. The voltage resulting from the operating point of the first subgroup must therefore lie in the fifth region of the current-voltage characteristic of the second subgroup, and the shift of the current-voltage characteristic of the second subgroup must be selected accordingly. This can be done graphically using the diagrams or automatically using the underlying mathematical relationships.

[0034] If a slightly higher power output is required, the voltage in the vehicle's electrical system drops, but not enough to cause the DC-DC converters of the second subgroup to leave the fifth range. The required power is therefore supplied by the DC-DC converters of the first subgroup. If significantly more power is needed, the voltage in the vehicle's electrical system drops so low that the DC-DC converters of the second subgroup leave the fifth range and enter the first range. This means that not only the m energy storage devices of the first subgroup, but also the I energy storage devices of the second subgroup feed power into the vehicle's electrical system, thus distributing the load across m plus I energy storage devices. This immediately increases the current from the second subgroup. The power is therefore available instantly, even though the efficiency of the second subgroup is comparatively low due to the initially very low current.However, this protects the vehicle's electrical system and all connected devices from failure. Furthermore, the offsets can be readjusted based on the new voltage of the electrical system.

[0035] In the example above, l = n - m = 100 - 11 = 89 energy storage devices could be placed in hot standby, providing an extreme power reserve. However, these energy storage devices in the second subgroup would not be discharged during normal operation. Realistically, though, only a portion of these 89 energy storage devices would form the second subgroup, for example, I = 9, so the remaining 80 energy storage devices could be completely disconnected from the vehicle's electrical system.

[0036] The number of units (I) cannot be calculated or estimated in the same straightforward way as the number of units (m), but rather represents the safety margin. Therefore, it can be chosen depending on the situation. For example, if the need for escape is high, the risk of requiring a large amount of energy for propulsion in a short period would be very high. In this case, I would need to be very large, up to the maximum. If no sudden large energy demand is expected, for example, during the acoustic observation of whale migrations, then I can be chosen to be very small.

[0037] In a further embodiment of the invention, a third subgroup of k energy storage devices is selected, where k is a natural number less than or equal to n - m - l. The third subgroup is completely isolated from the vehicle's electrical system, for example, by switching off the DC-DC converters. This saves energy, but it takes longer to connect these energy storage devices to the vehicle's electrical system when needed. Furthermore, this requires active control intervention.

[0038] In a further embodiment of the invention, a fourth subgroup of i energy storage devices is selected, where i is a natural number less than or equal to n - m - l - i. The fourth subgroup is completely and permanently disconnected from the vehicle's electrical system, for example, because the energy storage devices are defective. Therefore, the energy storage devices of the fourth subgroup are not reconnected to the vehicle's electrical system without prior maintenance.

[0039] In a further embodiment of the invention, each energy storage device has a maximum storage power. Furthermore, each energy storage device has a maximum storage capacity.

[0040] After an increase in network load has led to a feed-in by the first subgroup and the second subgroup, new subgroups are advantageously formed. For example, m is increased to m* so that the first subgroup can again bear the full load. With a gradual increase, m can be increased by 1; with a steeper increase, the increase can be correspondingly greater. Here, I and / or k are reduced accordingly to I* and / or k*. After a reassignment, the method is then carried out again with the new subgroups according to the invention.

[0041] Similarly, an energy supply system for a submarine is disclosed. The energy supply system comprises an onboard electrical system, a data processing unit, n energy storage devices, and n DC-DC converters, where n is a natural number greater than or equal to 4. Each of the n energy storage devices is connected to the onboard electrical system via a DC-DC converter. The data processing unit can control the n DC-DC converters based on the current onboard electrical system voltage and a stored current-voltage characteristic curve for each DC-DC converter. Depending on the onboard electrical system voltage, the current-voltage characteristic curve provides for charging and discharging of the associated energy storage device, as well as a currentless operation of the DC-DC converter.When the vehicle electrical system is under partial load, the data processing unit can select m of the n DC-DC converters to provide the power for the partial load, where m is less than n, and shift the current-voltage characteristic of I of the n DC-DC converters such that a current vehicle electrical system voltage is assigned to the no-current operation of I of the DC-DC converters, where I is less than or equal to nm. The set of I and m DC-DC converters is disjoint. Furthermore, the data processing unit can execute the described procedure. The data processing unit can be a computer or a microcontroller.

[0042] In particular, the data processing unit can disconnect the remaining k energy storage devices from the vehicle electrical system, where k = n - m - I. This disconnection can be achieved, for example, by means of an electronic switch (per string), such as a power switch like a MOSFET, or by means of the corresponding DC-DC converters, provided these are equipped with a switch.

[0043] The method according to the invention is explained in more detail below with reference to an embodiment shown in the drawings.

[0044] Fig. 1 is a purely schematic representation of a submarine.

[0045] Fig. 2 shows an exemplary schematic current-voltage characteristic curve for controlling a DC-DC converter.

[0046] Fig. 3 shows an exemplary schematic representation of two current-voltage characteristic curves with an offset for an exemplary operating point; and

[0047] Fig. 4 shows a schematic simplified representation of a power supply system with control of a DC voltage converter using the current-voltage characteristic curve.

[0048] Figure 1 shows a submarine 10 with an example of eight energy storage devices 30. In reality, the number will be higher. An energy storage device is typically a so-called string, consisting of 3 to 10 modules, each containing a plurality of accumulators connected in series and parallel. In this way, both current and voltage within the module can be increased. The modules within the string are usually connected in series to increase the voltage. The energy storage devices 30 are each connected to the ship's electrical system via a DC-DC converter 40.A DC-DC converter 40, or preferably a separate (electronic) switch, for example a MOSFET (metal-oxide semiconductor field-effect transistor), makes it possible to separate the residual capacity-dependent voltage of the energy storage devices 30 from the voltage of the ship's electrical system 20, thus allowing energy storage devices 30 with different residual capacities to be connected to the ship's electrical system 20. A ship's battery management system 60 controls the DC-DC converters 40 directly or indirectly via string battery management systems (not shown) and thereby selectively connects and disconnects energy storage devices 30 from the ship's electrical system 20 to supply the electrical power required by the ship's electrical system 20. This is state of the art without any special procedure in the ship's battery management system 60.

[0049] Fig. 2 shows a single current-voltage characteristic curve. This is essentially identical for all DC-DC converters 40; to regulate the energy flow, this current-voltage characteristic curve is shifted by an offset along the voltage axis, i.e., shifted to the right or left in the figure.

[0050] The current-voltage characteristic curve has five sections 1, 2, 3, 4, 5. A first section 1 describes the discharge process and exhibits a voltage U and a current flow I in the direction of the vehicle electrical system 20. This first section 1 is continuous, with a lower vehicle electrical system voltage U resulting in a lower current I. At the maximum current l maThe current I is limited so that, regardless of the voltage U, the current I does not increase further. This protects the energy storage device 30 from damage. This is the second area 2. Mirroring the discharge process, there is the charging process, in which the current I flows from the vehicle electrical system 20 to the energy storage device 30, meaning the current I has the opposite sign (-1). There is also a third area 3 in which the relationship between current I and voltage U is continuous; the higher the vehicle electrical system voltage, the higher the magnitude of the charging current I. A fourth area 4 then follows, limiting the charging current lmax, 2 and maintaining it regardless of any voltage U. This also reliably prevents damage to the energy storage device 30 caused by an excessively high charging current I.Then there is a fifth region 5, which is currentless and connects the region between the highest discharge voltage U and the lowest charging voltage U. Figure 3 shows the current-voltage characteristic of the first subgroup 101 and the current-voltage characteristic of the second subgroup 102, which differ from each other only by a different offset, i.e., a shift along the abscissa, i.e., the voltage.

[0051] Consider, for example, a submarine 10 with 100 energy storage devices 30 (n = 100). The nominal onboard voltage is 1000 V. Each energy storage device 30 can deliver a maximum current of 10 A, resulting in a maximum storage power of 10 kW and a maximum network power of 1 MW. As an example, a power of 108 kW is drawn from the onboard network 20. Thus, m = 11 energy storage devices 30 are selected for the first subgroup. For this first subgroup, the offset is then chosen such that the operating point 110 is positioned such that the current at operating point IB, the voltage at operating point UB, and the number m result in the current load, and thus: U B ■ IB ■ m = 108 kW

[0052] Thus, the voltage of the vehicle electrical system 20 is given by UB. Now, the offset of the current-voltage characteristic of the second subgroup 102 is chosen precisely so that the voltage of the first region 1 for I = 0 lies at the value UB, i.e., in the fifth region 5 or, as shown here, at the intersection of the first region 1 and the fifth region 5.

[0053] If the load on the ship's electrical system 20 changes, the voltage drops because the first subgroup 101 does not provide sufficient power. This drop causes the second subgroup 102, which is in hot standby due to the characteristic curve shift, to enter the range where it supplies current and thus contributes to the power supply without requiring any control intervention. Therefore, the second subgroup 102 is in hot standby precisely when the characteristic curve is such that the voltage UB, and thus the voltage present on the ship's electrical system before the load increase, is selected at the intersection of the first range 1 and the fifth range 5. Fig. 4 shows a simplified schematic representation of part of a power supply system 70 for a submarine 10. It depicts the control of a single DC-DC converter 40 of the n DC-DC converters using the current-voltage characteristic curve 100.This means that, as an example, a string, i.e., an energy storage device 30, is shown, which is electrically connected to the ship's electrical system 20 by means of a DC-DC converter 40. The control of the DC-DC converter 40 is carried out by a data processing unit 61. The ship's battery management system 60 or a string battery management system can also be part of the data processing unit 61. Accordingly, the data processing unit 61 can be a central data processing unit or a string data processing unit. Based on a current on-board electrical system voltage UL, a corresponding input and output current is defined in the current-voltage characteristic curve 100, which the DC-DC converter 40 is to realize into and out of the energy storage device 30. Control can be achieved by means of pulse-width modulation 63.Optionally, the data processing unit also monitors the current flow and regulates the DC voltage converter 40, especially under constant load and thus constant on-board voltage, also based on the current flow, so that, for example, the correct pulse width ratio is set.

[0054] Reference sign

[0055] 1 first area

[0056] 2 second area 3 third area

[0057] 4 fourth area

[0058] 5 fifth area

[0059] 10 submarine

[0060] 20 On-board electrical system 30 Energy storage device

[0061] 40 DC / DC converters

[0062] 60 ship battery management system

[0063] 61 Data processing unit

[0064] 63 Pulse width modulator 70 Power supply system

[0065] 100 Current-voltage characteristic curve

[0066] 101 Current-voltage characteristic of the first subgroup

[0067] 102 Current-voltage characteristic of the second subgroup

[0068] 110 operating point

Claims

Patent claims 1. Method for operating a submarine (10), wherein the submarine (10) has an onboard electrical system (20), wherein the submarine (10) has n energy storage devices (30), where n is a natural number greater than or equal to 4, wherein the onboard electrical system (20) has a maximum power rating, wherein each energy storage device (30) is connected to the onboard electrical system (20) via a DC-DC converter (40) and is electrically separable, wherein the DC-DC converters (40) are controlled via a current-voltage characteristic (100), wherein the onboard electrical system (20) is operated at a partial load, wherein the partial load is less than the maximum power rating, wherein a first subgroup of m energy storage devices (30) is selected, where m is a natural number less than n and greater than or equal to 2, wherein the first subgroup is connected to the onboard electrical system (20) with current flowing.wherein a first offset is chosen for the current-voltage characteristic (100) of the DC-DC converters (40) of the first subgroup such that the product of current and voltage and m corresponds to the partial load, resulting in a current on-board voltage, wherein a second subgroup of I energy storage devices (30) is selected, where I is a natural number and less than or equal to nm and greater than or equal to 2, wherein the second subgroup is connected to the on-board network (20) in such a way that a second offset is chosen for the current-voltage characteristic (100) of the DC-DC converters (40) of the second subgroup such that the current-voltage characteristic (100) is shifted such that the current on-board voltage results in currentless operation of the DC-DC converters (40) of the second subgroup.

2. Method according to claim 1, characterized in that each energy storage device (30) has a maximum storage power, wherein each energy storage device (30) has a maximum storage capacity.

3. Energy supply system (70) for a submarine (10) with the following features: - an on-board electrical system (20) - n-energy storage devices (30), where n is a natural number greater than or equal to 4 - n DC voltage converters (40), wherein each energy storage device (30) of the n energy storage devices (30) is connected to the on-board network (20) by means of a DC voltage converter (40); - a data processing unit (61) wherein the data processing unit (61) is configured to control the n DC voltage converters (40) based on a current on-board voltage and a stored current-voltage characteristic curve (100) per DC voltage converter (40), wherein the current-voltage characteristic curve (100) provides, depending on the on-board voltage, a charging operation and a discharging operation of the associated energy storage device (30) as well as a currentless operation of the DC voltage converter (40); - wherein the data processing unit (61) is configured when the on-board network (20) is operating at partial load, m DC-DC converters (40) of the n DC-DC converters (40) are selected to provide the power for the partial load, where m is less than n and greater than or equal to 2; and - wherein the data processing unit (61 ) is configured to shift the current-voltage characteristic (100) of I further DC voltage converters (40) of the n DC voltage converters (40) such that a current on-board voltage is assigned to the currentless operation of the I DC voltage converters (40), where I is less than or equal to nm and greater than or equal to 2.

4. Energy supply system (70) according to claim 3, wherein the data processing unit (61) is formed, the remaining k to disconnect energy storage devices (30) from the on-board network (20), where k equals nml.

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