Method for operating a plurality of energy stores of an on-board electrical system in a submarine

Abstract

The invention relates to a method for operating a submarine (10), wherein the submarine (10) has an on-board electrical system (20), the on-board electrical system (20) having a maximum network power; the submarine (10) has n energy storage devices (30), n being a natural number which is greater than or equal to (4); each energy storage device (30) is electrically separably connected to the on-board electrical system (20) via a respective DC-to-DC converter (40), each energy storage device (30) having a maximum storage power and a maximum storage capacity; the on-board electrical system 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 the first sub-group is connected to the on-board electrical system (20) so as to conduct a current.

Description

[0001] Method for operating multiple energy storage devices on an onboard electrical system in a submarine

[0002] The invention relates to a method for operating a submarine with several energy storage devices that are electrically compatible with and separable from each other and that can be independently connected to the ship's electrical system, in order to improve the use of the stored electrical energy.

[0003] Until now, submarines have used energy storage systems based on lead-acid batteries. These have the advantage of allowing for very large individual cells, which in turn enables a very high current at a very low voltage. Consequently, the lead-acid battery cells were previously connected in series and thus connected to the ship's electrical system as a single unit. This meant that there were practically only two states: the energy storage system connected to the electrical system, for example, during submersion, and the energy storage system disconnected from the electrical system, for example, when the diesel generator was running.

[0004] Increasingly, other types of energy storage cells are being used to build these devices, for example, lithium-based cells. This results in a different design. The cells are significantly smaller, which means that individual modules and strings have a higher voltage but a lower current. This allows the strings to be individually and selectively connected to or disconnected from the ship's electrical system. This, in turn, opens up considerably more options for utilizing the stored electrical energy. This is particularly relevant when the submarine is operating with very low energy requirements, for example, when submerged and moving at very low speeds.

[0005] A battery module is known from DE 10 2019 216 606 A1.

[0006] German patent DE 102019 216 608 A1 discloses a battery module with monitoring of the thermal runaway of individual cells. German patent DE 10 2020 205 327 A1 discloses a submarine with a situation-independent voltage supply for a string battery management system.

[0007] From DE 10 2019 217 796 A1, a bypass of a battery management system in a submarine in case of danger is known.

[0008] 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.

[0009] A low-stray field battery module is known from DE 10 2021 200 765 A1.

[0010] From DE 10 2021 202 537 A1 a method for operating a submarine with a fuel cell and an accumulator is known.

[0011] The determination of the aging state of an energy storage device on board a submarine is known from DE 10 2021 203 947 A1.

[0012] From DE 10 2021 210 447 A1 a method for operating an on-board power network of a submarine under high loads is known.

[0013] From DE 10 2022 208 979 a method for increasing the range of a submerged submarine is known.

[0014] From DE 10 2022 205 773 A1 a submarine with two different battery systems and a method for operating it is known.

[0015] The DE 20 2022 102 716 U1 is known to have a submarine with two converters on the propulsion motor.

[0016] A battery module is known from EP 4 340 113 A1. A submarine with an energy storage device arranged outside the pressure hull is known from DE 10 2022 132635.

[0017] From WO 2020 / 030523 A1 a method for regulating the network of an underwater vehicle and an underwater vehicle designed for such regulation are known.

[0018] Due to increasing complexity, it is important to develop a driving style that considers all components in order to extract the optimum amount of usable electrical power from the available maximum stored energy. In addition to the question of how much power can be drawn from a battery, the efficiency of all other electrical components and their operating mode also play a role. While this applies in principle to any battery system, in the case of a submarine it has a direct impact on dive time and range, thus increasing the submarine's overall utility.

[0019] From DE 10 2018 213 180 A1 a method for controlling the network of an underwater vehicle and an underwater vehicle which is designed for such control is known.

[0020] A battery power plant with a cooling system is known from DE 10 2017 123 730 A1.

[0021] From DE 10 2021 110 200 B3 an energy storage system with several energy storage devices connected in parallel and a method for operating an energy storage system is known.

[0022] The object of the invention is to provide a method that maximizes the electrical power that can be extracted from an energy storage system.

[0023] This problem is solved by the method with the features specified in claim 1. Advantageous embodiments are described in the dependent claims, the following description, and the drawings. The method according to the invention is for operating a submarine. The submarine has an onboard electrical system. The 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 onboard electrical system has a maximum power rating. This is the maximum electrical power for which the onboard electrical system is designed. This can also be referred to as the nominal power rating. The submarine has n energy storage devices. 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 accumulators connected in series and / or parallel. Each energy storage device is electrically disconnectable from the vehicle's electrical system via its own 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 makes it possible to connect several energy storage devices with different residual capacities to the vehicle's electrical system simultaneously.Furthermore, galvanic isolation can be achieved using DC-DC converters, which is advantageous, for example, in the event of a short circuit. Additionally, the DC-DC converter also enables an electrical, but currentless, connection if the DC-DC converter voltage is correctly selected relative to the vehicle electrical system voltage. Every energy storage device has a maximum storage capacity, the so-called nominal power, which is the maximum 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. According to the invention, the vehicle electrical system is operated at a partial load; at other times, the system can, of course, also be operated at full load. The partial load is lower than the maximum system power.Due to the partial load operation of the grid, electrical energy can be drawn from several energy storage devices in various ways, with the aim of optimizing the utilization of the stored electrical energy. A first subset of m energy storage devices is selected, where m is a natural number less than n. This is therefore a true subset of at least one energy storage device, but not all of them. The first subset is connected to the vehicle's electrical system. More precisely, the electrical system is supplied only via the first subset and not via any further subsets; or, put another way, the first subset comprises all energy storage devices connected to the vehicle's electrical system. "Connected" here means that a current is flowing at the specific time, i.e., that electrical power is actually being delivered from the energy storage devices to the vehicle's electrical system.An existing connection through which no current is supplied from the energy storage device to the vehicle electrical system or vice versa is therefore not current-carrying within the meaning of the invention.

[0024] To illustrate this, a purely hypothetical submarine with easily calculable numerical values ​​is used. Therefore, this example submarine has 100 energy storage devices. The onboard electrical system voltage is set at a nominal value of 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 system power of 1 MW.

[0025] If the submarine's partial load requirement is, for example, only 100 kW, then theoretically all energy storage devices can be operated at 10% load, i.e., with a current of 1 A. This has the advantage that as soon as higher power is required, 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. 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.

[0026] It is therefore advantageous not to connect all energy storage devices to the vehicle's electrical system. In the example given, this would result in a logical subset of m = 10, such that 10 energy storage devices each feed 10 A at 1000 V into the vehicle's electrical system, thus covering the 100 kW requirement. This is theoretically optimal.

[0027] This allows the DC / DC converters to be operated at their optimal operating point, and reliably prevents power outages caused by increased power demand.

[0028] Analogous to the first subgroup, a second subgroup of I energy storage devices is selected. I is a natural number less than or equal to nm. The second subgroup is not electrically connected to the vehicle's electrical system. This can mean that it is nevertheless electrically connected to the electrical system. Such a connection can be achieved, for example, by specifically choosing the voltage so that the energy storage device operates at a lower voltage level than the vehicle's electrical system. In this case, an electrical connection exists, but it is currentless, since no current can flow against the voltage rise. The advantage is that no switching operation is required during a voltage dip, and no time delay occurs due to a switching operation. This means that power can flow directly into the vehicle's electrical system during a voltage dip, and the load on the energy storage devices can be reduced during a load peak.Alternatively or additionally, for example with a third subgroup, an electrical disconnect device can be provided to interrupt the current flow. This disconnect device can then be, for example, a circuit breaker, a normally closed IGBTS, or a diode. However, a time delay still occurs due to the switching process, and the system is not purely passive; an active switching process must take place.

[0029] In a further embodiment of the invention, m is chosen such that m is minimal.

[0030] In the example shown above, this is precisely the case for m = 10. If the required partial load were 108 kW, then m would be, for example, 11. Here, m is preferably chosen such that the m energy storage devices operate in a power range where the electrical efficiency exceeds a minimum value. Typically, the efficiency is high at around 90% and above of the maximum storage power, and therefore the m energy storage devices are preferably operated in this range. In this range, the electrical efficiency of the DC-DC converter is optimal, representing an optimal operating point. The goal, therefore, is to select the fewest possible energy storage devices at the optimal operating point, i.e., to minimize the number of energy storage devices.The minimum number of energy storage devices is therefore a function of the current partial load and the optimal operating point, particularly in the case of a combination of energy storage devices and DC-DC converters. However, using the minimum number m results in the power reserve of the connected energy storage devices being minimal to non-existent. This is only possible because the second subgroup of energy storage devices, which are not connected to the vehicle's electrical system, can still provide this power reserve. Without the inventive combination with the non-current-carrying second subgroup, minimizing the first subgroup would be practically impossible, as any upward load fluctuation would lead to a momentary collapse of the vehicle's electrical system. Therefore, only the use of the second subgroup allows for the minimization of m in real-world applications.

[0031] In another embodiment, the electrical efficiency of the DC-DC converter is used as a criterion for selecting the number of energy storage devices. It can be provided that a specific electrical efficiency is predetermined. This specific electrical efficiency can be predefined, and the number of energy storage devices in the first subgroup is then selected such that the resulting operating point of the energy storage devices in the first subgroup meets or exceeds the specified electrical efficiency. The electrical efficiency of the DC-DC converter is a known quantity derived from the component. Alternatively, the efficiency of the DC-DC converter can be predetermined as a function of the current flow.The relationship between the operating point (current and voltage) and the efficiency can be pre-measured and stored in a function or table, or measured using suitable sensors. Efficiency is a function of the current flowing through the converter, decreasing significantly at very low currents. Therefore, high currents close to the DC-DC converter's nominal current are advantageous. However, the relationship is usually not linear; rather, in the high-current range, and thus with high efficiency, there is a region where the efficiency is only slightly dependent on the current flow. Even if a plateau does not form, this region can still be considered, for simplicity, as the area with the highest efficiency.Here, the number m is not chosen to be minimal, but rather selected such that the resulting current flow and the consequent efficiency of the DC-DC converters result in the lowest possible energy loss across the DC-DC converters. This is particularly advantageous when efficiency decreases again at very high currents. Depending on the efficiency, the targeted number m can thus be used to determine the current flow through each DC-DC converter that yields optimal efficiency for the overall system. Therefore, the minimum number m required for the first subgroup to achieve at least a specific efficiency can be determined. This specific efficiency can be greater than 0.9, preferably greater than 0.95, and most preferably greater than 0.98.It can be provided that the number m of energy storage devices in the first subgroup is chosen such that the efficiency for each energy storage device is exceeded, but the number m is chosen so that it just exceeds the required number of energy storage devices. In other words, a high efficiency is achieved that is at least as high as required, but the capacity of the energy storage devices is not fully utilized. Thus, a limited energy reserve exists without reducing efficiency.

[0032] In a further embodiment of the invention, m is chosen such that m is minimal, m is minimal + 1, or m is minimal + 2. In the example shown above, m is then exactly m = 10. m is minimal + 1 would then be m = 11, or m is minimal + 2 would then be m = 12. While this does not achieve the absolutely optimal efficiency, it does create a small power reserve even in the first subgroup. Here, m is minimal + 2 is preferably chosen only if n is greater than 100, preferably greater than 200. Here, m is minimal + 1 is preferably chosen only if n is greater than 50, preferably greater than 100.

[0033] In a further embodiment of the invention, the energy storage devices each have a time-varying characteristic parameter, the current value of which is determined. The members of the first subgroup are selected from all energy storage devices such that the characteristic parameter is closest to a minimum or maximum value compared to the characteristic parameters of the other energy storage devices.

[0034] In a further embodiment of the invention, the energy storage devices each have a residual capacity. The residual capacity is the electrical capacity of the energy storage device that is still available at the current time and lies between 0% and 100% of the maximum storage capacity. The respective residual capacity thus corresponds to the electrical capacity that can still be extracted from the respective energy storage device. The residual capacity is less than or equal to the maximum storage capacity. The members of the first subgroup from the totality of energy storage devices are selected such that the m energy storage devices with the highest remaining residual capacities are selected.

[0035] A consistent residual capacity ensures that maximum performance is maintained until the very end. If energy storage devices were discharged one after the other, the maximum available power would decrease proportionally with each discharged device, meaning, for example, that the submarine's top speed at full power would decrease with each discharged device. However, a consistent discharge allows the achievable top speed to be maintained until the end.

[0036] In a further embodiment of the invention, when the remaining capacity is ± 1% of the maximum storage capacity, the temperature of the DC-DC converter and / or the operating hours of the energy storage device are used as a second selection criterion. These secondary selection parameters serve, in particular, to optimize the service life. Preferably, an energy storage device with fewer operating hours is selected to achieve a balance in this respect. The temperature of the DC-DC converters is used as the second criterion, with the DC-DC converter with the lower temperature being selected preferably so that the DC-DC converter with the higher temperature is not conducting current and can thus cool down.

[0037] In a further embodiment of the invention, a reassignment is performed to achieve the most uniform state of charge possible across all energy storage devices. Therefore, the remaining capacity of all energy storage devices is compared. This comparison can be performed continuously or cyclically during operation. The reassignment of the energy storage devices to the first subgroup and the second subgroup occurs if the difference between the remaining capacity of the energy storage device with the lowest remaining capacity in the first subgroup and the remaining capacity of all energy storage devices not belonging to the first subgroup exceeds a certain threshold. The reassignment occurs when the difference between these remaining capacities is greater than a predetermined value, preferably greater than 20% of the maximum storage capacity, more preferably greater than 10% of the maximum storage capacity, and more preferably greater than 5% of the maximum storage capacity.Since the first subgroup discharges during operation, reassignment only occurs if its remaining capacity falls below that of the other energy storage devices. An excess, for example, because some energy storage devices initially have a significantly higher remaining capacity than others, would not trigger reassignment, as the goal is precisely to equalize the remaining capacity. The remaining capacity of each individual energy storage device is typically continuously recorded, monitored, or estimated. This estimation can be based on operating time and power output, or on characteristic curves, using methods already known. Determining the remaining capacity is usually done to obtain up-to-date information about the available energy reserve and, consequently, the operating range.This method allows for a simple, regular, but not unnecessarily frequent, reassignment of energy storage devices to the first and second subgroups. This regular reassignment ensures that all energy storage devices remain within a predefined band around a specific average residual capacity. A wider band, such as the aforementioned 20%, results in fewer reassignments of the energy storage devices connected to the vehicle's electrical system. A narrower band, such as the aforementioned 5%, leads to more reassignments but a more consistent residual capacity. This can result in a longer remaining operating time under full load.A particular advantage of this approach is that if individual energy storage devices fail, only the same fraction of energy is lost to the overall system, preventing the loss of exceptionally large amounts. The goal is therefore the cyclical redistribution of the subgroups within a tolerance band of the remaining capacity, ensuring that all energy storage devices are available for as long as possible. This allows, for example, in an emergency with maximum energy demand, all energy storage devices to be connected to the vehicle's electrical system to provide maximum power. This cyclical redistribution also occurs when the partial load of the vehicle's electrical system remains constant.

[0038] In a further embodiment of the invention, the energy storage devices are reassigned to the first subgroup and the second subgroup after a defined time interval. Even with very low load requirements, this can lead to a more even distribution of the thermal load on the energy storage devices and DC-DC converters, as well as equalizing their operating time, even if the reduction in residual capacity is small within the defined time interval.

[0039] In a further embodiment of the invention, the energy storage devices are reassigned to the first subgroup and the second subgroup if the partial load of the vehicle electrical system has changed by more than a predetermined value, preferably more than 10%, since the last assignment of the energy storage devices to the first subgroup and the second subgroup. The aim is to avoid unnecessarily long periods of stress on a single energy storage device and, if necessary, to allow it to cool down by switching devices. Reassignment can also occur if the partial load is greater than m times the maximum storage capacity, meaning that the energy storage devices already connected to the system are no longer sufficient to handle the new partial load. Similarly, reassignment can occur if the partial load becomes smaller than the (m-1) / m value of the previous partial load.In this case, it is advisable to reduce the number of electrically connected energy storage devices in order to return to an optimal operating point.

[0040] In a further embodiment of the invention, the offset, both the first and the second, is iteratively adjusted to the current partial load of the vehicle electrical system. Particularly in non-steady-state conditions (start-up, switching on and off of loads, etc.), the difference between power consumed and power supplied leads to voltage changes in the electrical system, for example, due to capacitors present in the system and their charging or discharging. Therefore, it is advantageous to adjust the current-voltage characteristics of both the first and second subgroups accordingly. Even with known load changes, such as changes in driving speed, the complexity of the vehicle electrical system with all its electrical components can make it difficult to predict an optimal operating point for voltage and current; it is often simpler to approach this point via an iterative process.

[0041] In a further embodiment of the invention, the method is carried out as soon as the partial load is below 50%, preferably below 25%, particularly preferably below 15% of the maximum network power.

[0042] In a further embodiment of the invention, the method is also used for charging the energy storage devices. During charging, the situation is correspondingly mirror-symmetrical; the current flows in the opposite direction (opposite sign), and the offset leads to higher voltages (the voltage of the energy storage devices of the second subgroup in hot standby is higher than the voltage of the actively charged energy storage devices of the first subgroup).

[0043] In a further embodiment of the invention, the DC-DC converters are controlled via a current-voltage characteristic curve, as is familiar to those skilled in the art from prior art, for example, WO 2020 / 030523 A1. The current-voltage characteristic curve has, to a first approximation, five regions. A first region describes the discharge process and exhibits a voltage and current flow towards the vehicle's electrical system. This region is typically continuous, with lower voltage generally occurring at higher currents. At the maximum current, the current is limited so that, regardless of the voltage, the current is not increased further. This protects the energy storage device and the vehicle's electrical system from damage. This can be defined as the second region.Symmetrical to the discharge process is the charging process, in which the current flows from the vehicle's electrical system to the energy storage device, meaning the current has the opposite sign mathematically. Here, too, there is a third region where the relationship between current and voltage is typically continuous; the higher the magnitude of the charging current, the higher the corresponding voltage generally is. A fourth region follows, limiting the charging current and maintaining it regardless of the voltage. This also reliably prevents damage to the energy storage device from excessive charging current. Finally, there is a fifth region, which is currentless and connects the range between the highest discharge voltage and the lowest charging voltage.For the current-voltage characteristic of the DC-DC converters in the first subgroup, a first offset is selected such that the product of current and voltage corresponds to the partial load. This results in a current on-board voltage. The offset represents a shift of the current-voltage characteristic along the voltage curve; the offset allows the characteristic to be shifted to lower or higher voltages. In particular, different offsets allow different DC-DC converters with the same current-voltage characteristic to be switched differently. For the current-voltage characteristic of the DC-DC converters in the second subgroup, a second offset is selected such that the voltage of the continuous part of the discharge current corresponds to the current on-board voltage.This means that the energy storage devices are electrically connected to the vehicle's electrical system, but due to their current-voltage characteristic, they exhibit a current flow of 0 A. This state can be described as hot standby. As soon as even a minimal increase in power is drawn, the voltage in the vehicle's electrical system drops, but this immediately causes the current from the second subgroup to rise. The power is therefore available instantly and directly, 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 consumers from failure.

[0044] The problem is that if even a minimal increase in power is required, for example because an additional consumer is switched on, the necessary power can no longer be provided.

[0045] 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. The second subgroup is not electrically connected to the vehicle's electrical system. This means that the second subgroup can be electrically isolated from the electrical system but kept ready for rapid activation, for example, if a power surge or a resulting voltage drop in the electrical system needs to be detected. Alternatively, the second subgroup can be electrically connected to the electrical system, but, for example, by selecting a suitable voltage, such that no current flows from the energy storage devices of the second subgroup into the electrical system, while the second subgroup immediately takes over the power supply, for example, in the event of a power surge and associated voltage drop in the electrical system.This state is called hot standby because the second subgroup does not directly supply power, i.e., it is in standby mode, but is nevertheless directly connected (hot). While the first variant requires more active monitoring and control, the second variant places higher demands on the settings of the DC-DC converters. In the example above, l = n - m = 100 - 10 = 90 energy storage devices could then be put into hot standby, providing an extremely large power reserve, while these energy storage devices in the second subgroup are not discharged during normal operation.

[0046] In a further embodiment of the invention, a third subgroup of k energy storage devices is selected, where k is a natural number including 0 and less than or equal to nml, i.e., less than or equal to the total number of energy storage devices minus the active ones and minus the ones in hot standby. The third subgroup is electrically isolated from the vehicle's electrical system. This isolation can be permanent, for example, because the devices are defective or indicators have suggested an increased risk of thermal runaway. However, it can also be temporary, for example, to perform maintenance and / or servicing cycles on the batteries, such as internal recharging processes for targeted charging and discharging. Accordingly, this third subgroup can also consist of 0 energy storage devices; it is not necessarily required in every case.

[0047] In a further embodiment of the invention, the method includes a switching step. In the switching step, the subgroup of energy storage devices currently supplying the vehicle electrical system with electrical energy is disconnected from the vehicle electrical system, and a new subgroup of energy storage devices is connected to the vehicle electrical system.

[0048] In a first embodiment of the switching step, the second subgroup is initially connected to the vehicle's electrical system. During this phase, both the first and second subgroups are connected to the electrical system. This is preferably implemented such that the power supply from the first and second subgroups provides a constant current. After a transition phase, the first subgroup is then disconnected from the electrical system, and the second subgroup becomes the new first subgroup. Preferably, a third subgroup is placed in standby mode and thus becomes the new second subgroup.In a second iteration of the switching process, the first and second subgroups are swapped. The former first subgroup becomes the new second subgroup and is thus de-energized in standby mode, while simultaneously the former second subgroup becomes the new first subgroup and takes over the supply of electrical energy to the vehicle's electrical system. Subsequently, the former (now more heavily discharged) first subgroup is completely disconnected from the vehicle's electrical system, and a former third subgroup takes over as the new second subgroup in standby mode.

[0049] The first configuration is preferred for higher partial loads of the vehicle electrical system, and the second variant for lower partial loads of the vehicle electrical system.

[0050] The method according to the invention is explained in more detail below with reference to an embodiment shown in the drawings.

[0051] Fig. 1 Submarine

[0052] Fig. 2 Current-voltage characteristic curve

[0053] Fig. 3 Operating point

[0054] 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, which consists of 3 to 10 modules, with a plurality of accumulators connected in series and parallel in each module. In this way, both current and voltage within the module can be increased. The modules are usually connected in series within the string to increase the voltage. The energy storage devices 30 are each connected to the ship's electrical system via a DC-DC converter 40. The DC-DC converter 40 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 and thus to connect energy storage devices 30 with different residual capacities to the ship's electrical system 20.A ship battery management system 60 directly or indirectly controls the DC-DC converters 40 via string battery management systems (not shown) and thereby selectively connects and disconnects energy storage devices 30 to the ship's electrical system 20 in order 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 battery management system 60.

[0055] 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 up and down in the figure.

[0056] 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 higher currents I resulting in a lower voltage U. At the maximum current l maIn this section, the 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 section 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). Here, too, there is a third section 3, in which the relationship between current I and voltage U is continuous; the higher the magnitude of the charging current I, the higher the corresponding voltage U. A fourth section 4 follows, which limits the charging current lmax, 2 and keeps it independent 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 area 5, which is currentless and connects the area between the highest discharge voltage U and the lowest charging voltage U.

[0057] Fig. 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 ordinate, i.e. the voltage.

[0058] Let us now consider again the example above of a submarine 10 with 100 energy storage devices 30 (n = 100). The onboard electrical system voltage is nominally 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 system power of 1 MW. As an example, a power of 108 kW is drawn from the onboard electrical system 20. Thus, m = 11 energy storage devices 30 are selected for the first subgroup, with the 11 energy storage devices 30 having the highest remaining residual capacity being chosen for this 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 at operating point 100, the voltage at operating point UB, and the number m result in the current load: UB ■ IB ■ m = 108 kW

[0059] Thus, the voltage of the on-board network 20 is 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 lies at the value UB for I = 0.

[0060] If the load on the on-board network 20 changes, the operating point and, if applicable, the number m of the first subgroup are adjusted, and thus the offset of the current-voltage characteristic of the first subgroup 101 and the offset of the current-voltage characteristic of the second subgroup 102 are adjusted accordingly. Likewise, the m members of the first subgroup are regularly reselected from the total number of n energy storage devices 30.

[0061] Reference sign

[0062] 1 first area

[0063] 2 second area

[0064] 3 third area

[0065] 4 fourth area

[0066] 5 fifth area

[0067] 10 submarine

[0068] 20 On-board power supply

[0069] 30 Energy storage device

[0070] 40 DC / DC converters

[0071] 60 Ship battery management system 101 Current-voltage characteristic of the first subgroup

[0072] 102 Current-voltage characteristic of the second subgroup

[0073] 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 onboard electrical system (20) has a maximum power rating, wherein the submarine (10) has n energy storage devices (30), where n is a natural number greater than or equal to 4, wherein each energy storage device (30) is electrically disconnectable from the onboard electrical system (20) via a DC-DC converter (40), wherein each energy storage device (30) has a maximum storage power, wherein each energy storage device (30) has a maximum storage capacity, wherein the onboard electrical system is operated at a partial load, the partial load being 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, wherein the first subgroup is connected to the onboard electrical system (20) with current flowing.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, wherein the second subgroup is not connected to the vehicle electrical system in a current-carrying manner.

2. Method according to claim 1, characterized in that m is chosen such that m is minimal.

3. Method according to one of the preceding claims, characterized in that the energy storage devices (30) each have a time-varying characteristic parameter, the current value of which is determined, and the members of the first subgroup are selected from the totality of the energy storage devices (30) such that the characteristic parameter is closest to a minimum value or a maximum value compared to the characteristic parameters of the other energy storage devices (30).

4. A method according to one of the preceding claims, characterized in that the energy storage devices (30) each have a residual capacity, wherein the respective residual capacity corresponds to the electrical capacity still extractable from the respective energy storage device (30), wherein the residual capacity is less than or equal to the maximum storage capacity, wherein the members of the first subgroup are selected from the totality of energy storage devices (30) such that the m energy storage devices (30) with the highest remaining residual capacity are selected.

5. Method according to claim 4, characterized in that, for ± 1 % of the maximum storage capacity, the temperature of the DC-DC converter and / or the previous operating hours of the energy storage device (30) are used as a second selection criterion.

6. Method according to one of claims 4 to 5, characterized in that the energy storage devices (30) are reassigned to the first subgroup and the second subgroup if the difference in residual capacity between the energy storage device (30) with the lowest residual capacity of the first subgroup and the energy storage device (30) with the highest residual capacity of the second subgroup is greater than a predetermined value of the maximum storage capacity, preferably greater than 20% of the maximum storage capacity, preferably greater than 10% of the maximum storage capacity, preferably greater than 5% of the maximum storage capacity.

7. Method according to one of the preceding claims, characterized in that a reassignment of the energy storage devices (30) to the first subgroup and to the second subgroup takes place if the partial load of the on-board network has changed by more than a predetermined value since the last assignment of the energy storage devices (30) to the first subgroup and to the second subgroup, or the partial load is greater than m times the value of the maximum storage power, or the partial load becomes less than (m- 1 ) / m of the previous partial load.

8. Method according to one of the preceding claims, characterized in that the method is carried out as soon as the partial load is below 50%, preferably below 25%, of the maximum network power.

9. Method according to one of the preceding claims, characterized in that the method is also used for charging the energy storage devices (30).

10. A method according to one of the preceding claims, characterized in that a second subgroup of I energy storage devices (30) is selected, wherein I is a natural number and less than or equal to nm, wherein the first subgroup is connected to the vehicle electrical system (20) in such a way that the DC-DC converters (40) are controlled via a current-voltage characteristic, wherein a first offset is selected for the current-voltage characteristic 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 vehicle electrical system voltage, wherein the second subgroup is not connected to the vehicle electrical system in such a way that a second offset is selected for the current-voltage characteristic of the DC-DC converters (40) of the second subgroup such that the voltage of the continuous part of the discharge current corresponds to the current-voltage characteristic of the current vehicle electrical system voltage.

11. Method according to claim 10, characterized in that the offset is iteratively adjusted to the current partial load of the vehicle electrical system.

12. Method according to one of the preceding claims, characterized in that the on-board network voltage is monitored and, if the on-board network voltage drops, the second subgroup is connected to the on-board network (20) in a current-carrying manner.

13. Method according to one of the preceding claims, characterized in that a third subgroup of k energy storage devices (30) is selected, wherein k is a natural number and less than or equal to nml, wherein the third subgroup is electrically separated from the vehicle electrical system (20).

Images