Operating an energy storage device on board a submarine

Abstract

The present invention relates to a method for thermally optimising an energy storage device having at least two accumulators (10) of a submarine (1), wherein the energy storage device is cooled by means of an internal cooling circuit (20), wherein the internal cooling circuit (20) can be cooled using a seawater cooling circuit (30), wherein the temperature of the energy storage device is detected, wherein a minimum operating temperature is defined for an operating mode, wherein before the start of the operating mode, the detected temperature is compared with the minimum operating temperature, wherein the internal cooling circuit (20) is disconnected from the seawater cooling circuit (30) if the temperature falls below the minimum operating temperature, wherein charge is transferred between the at least two accumulators until the minimum operating temperature is reached.

Description

[0001] 19.11.2025 1 / 11

[0002] Operation of an energy storage device on board a submarine

[0003] The invention relates to a method for implementing temperature-sensitive operating modes on board a submarine.

[0004] A submarine typically has an energy storage device to draw energy from while underwater. However, the energy storage device can also be used when surfaced, for example, to achieve particularly high speeds.

[0005] Since heat is generated during charging and discharging, such energy storage devices in a submarine have a cooling system, which is ultimately cooled, for example, via a seawater cooling circuit. To avoid pumping seawater through the energy storage device, the cooling circuit is therefore usually separated into an internal closed cooling circuit and a seawater cooling circuit.

[0006] During normal operation, the energy storage device will always produce heat, so a sensible temperature range will automatically be established.

[0007] For example, it can become critical when the submarine is in port. During this time, power is usually supplied via the shore power connection, resulting in only minimal energy flow to the energy storage device. Consequently, the energy storage device can become comparatively cold, especially in low ambient temperatures.

[0008] There are operating modes that have a prescribed temperature range, such as the capacity test of the power supply device. These are often performed at the end of a period of inactivity. However, if the power supply device is too cold, these operating modes cannot be activated or carried out.

[0009] A battery module is known from DE 10 2019 216606 A1. 19.11.2025

[0010] 2 / 11

[0011] From DE 102020 205 327 A1 a submarine with a situation-independent voltage supply for a string battery management system is known.

[0012] From DE 10 2022 208 979 A1 a method for increasing the range of a submerged submarine is known.

[0013] From DE 10 2014214 313 A1 a device and a method for heating a battery as well as a corresponding battery, a battery system and a vehicle are known.

[0014] From US patent 2009 / 0195067A1, a power supply system, a vehicle with this system, a method for temperature increase control for an energy storage device, and a computer-readable recording medium with a program that causes a computer to perform the temperature increase control of the energy storage device are known.

[0015] A method for operating a battery system is known from DE 10 2020 003 062 A1.

[0016] The object of the invention is to provide a method to enable the use of appropriate operating modes even under these situations.

[0017] This problem is solved by the method with the features specified in claim 1. Advantageous further developments are described in the dependent claims, the following description, and the drawing.

[0018] The method according to the invention serves for the thermal optimization of an energy storage device with at least two accumulators and at least two DC-DC converters of a submarine. The at least two accumulators are each connected to an onboard electrical system of the submarine via a DC-DC converter. Each DC-DC converter is connected to at least one accumulator, such that the at least one accumulator is exclusively connected to the submarine's electrical system.

[0019] 3 / 11 feeds power into the ship's electrical system via the DC-DC converter. The energy storage device, consisting of batteries and DC-DC converters, is cooled by an internal, closed cooling circuit. This cooling circuit flows through or around both the batteries and the DC-DC converters. The internal cooling circuit is itself coolable. For example, the internal cooling circuit is directly connected to a seawater cooling circuit via a heat exchanger. The seawater cooling circuit can be flushed with ambient or seawater, thus cooling the internal cooling circuit. Alternatively, cooling can be achieved at the hull or via an air-to-water heat exchanger, with heat dissipated into the interior of the boat. The precise type of cooling is not essential to the invention itself; only a heat sink is required.This creates a separation between the seawater and the closed internal cooling circuit, allowing for either selective cooling or the ability to disconnect the connection between the internal and seawater cooling circuits. Separation can also be achieved by stopping the flow of seawater through the cooling circuit. This also allows for separation. The cooling circuit can be designed differently. Crucially, the cooling circuit must be switchable. For example, a pump can circulate the coolant, and the cooling circuit can be shut off by switching off the pump. The temperature of the energy storage device is monitored. This is preferably done directly in or on the accumulator. This is typically done anyway to detect, for example, thermal runaway. A minimum operating temperature is defined for each operating mode.This minimum operating temperature is usually determined by the design of the energy storage device, the operating mode, and the resulting expected current flows and heat generation. For example, commercially available batteries specify a temperature range for storage and another for use, representing two different operating modes, which vary depending on the battery technology. For instance, a minimum operating temperature is specified by the manufacturer for a capacity test. Before starting the operating mode, the measured temperature is compared to the minimum operating temperature. If the temperature falls below the minimum operating temperature, the battery is shut down.

[0020] Once the minimum operating temperature is reached, the internal cooling circuit is switched off, for example, disconnected from the seawater cooling circuit. Furthermore, a charging cycle is performed between at least two batteries until the minimum operating temperature is reached. During this cycle, current flows from one battery through a DC-DC converter into the ship's electrical system and from the ship's electrical system through another DC-DC converter into the second battery. This charging cycle generates a certain amount of power loss, particularly in the DC-DC converters, which provides a small heating effect in the internal cooling circuit, allowing the batteries to be brought up to the required temperature gently. The effect of utilizing the waste heat from the DC-DC converters is significantly greater than the internal resistance of the batteries, resulting in a much faster and gentler heating process.

[0021] In another embodiment of the invention, the operating mode is a capacity test.

[0022] In a further embodiment of the invention, another operating mode is the starting up of the submarine in order to transfer it from harbor operation to ferry operation.

[0023] In a further embodiment of the invention, the submarine's energy storage device comprises a plurality of accumulators. An accumulator within the meaning of the invention can be a string or a module, which may include a plurality of unit cells for increasing current and voltage. The accumulator is preferably connected individually to the ship's electrical system via a DC-DC converter. The submarine may, for example, have two energy storage devices, for instance, in separate battery compartments.

[0024] In a further embodiment of the invention, the temperature of each battery is recorded. Since the batteries can be individually and differently loaded, they can also have different temperatures. For example, the batteries that are currently being fed into the vehicle's electrical system or being charged are measured. The charging process takes place between the batteries with the lowest temperature. This results in the greatest heating of these batteries; the other batteries are also heated, but to a lesser extent, via the internal cooling circuit.

[0025] In a further embodiment of the invention, the accumulator with the lower charge level is selected for charging and the accumulator with the higher charge level is selected for discharging. This simultaneously creates an equalization of charge levels between the accumulators, which is an advantageous side effect.

[0026] In a further embodiment of the invention, a priority is determined for each accumulator based on its state of charge and temperature. The priority is chosen to be higher the colder the accumulator is and the further its state of charge deviates from the average value.

[0027] In a further embodiment of the invention, the method is only carried out at an ambient water temperature of no more than 18 °C. This problem mainly occurs in winter and in northern waters (and southern waters in the other hemisphere), since the very low water temperature, down to the low single digits, can cause the power supply device to cool excessively.

[0028] In a further embodiment of the invention, the method is carried out while the submarine is moored. During this time, the charging and discharging processes of the energy storage device via the shore power connection are usually minimal, so that no significant waste heat is generated, resulting in a low temperature level of the energy storage device through active cooling.

[0029] In a further embodiment of the invention, the internal cooling circuit comprises at least one electric heating element. The heating element is preferably supplied with electrical energy by the energy storage device. The heating element allows for additional heating of the internal cooling circuit, thus accelerating the process. At the same time, this indirect heating reliably prevents local overheating. 19.11.2025 6 / 11

[0030] In a further embodiment of the invention, the internal cooling circuit is switched off in such a way that the cooling fluid continues to circulate within the internal cooling circuit, but no longer transfers heat to an external medium. The generated heat is thus distributed as evenly as possible within the energy storage device.

[0031] In a further embodiment of the invention, when the minimum operating temperature is exceeded, the internal cooling circuit is partially switched on again, i.e. connected to a heat sink, for example a seawater cooling system, in order to keep the temperature constant.

[0032] In a further embodiment of the invention, the vehicle electrical system voltage is reduced. Reducing the voltage increases the currents. The higher currents increase the power loss in the DC-DC converters, thus accelerating the process.

[0033] In a further embodiment of the invention, a lower power output is selected for the DC-DC converters. For the purposes of this invention, "low power output" is defined as less than 50% of the maximum power output, preferably less than 30%. This reduces the efficiency of the DC-DC converters, resulting in faster heating and thus accelerating the process. This can be adjusted by selecting the number of batteries used in the process. For example, if a submarine with an energy storage device has, say, 50 batteries, also called strings, then, for example, 5 batteries can be discharged and 5 batteries charged, or 10 batteries can be discharged and 10 batteries charged. Correspondingly, the batteries not used for the process remain available to supply the ship's electrical system.

[0034] In a further embodiment of the invention, the method equalizes the state of charge. Thus, the batteries with the highest state of charge are preferably selected for discharging, and the batteries with the lowest state of charge are selected for charging. 19.11.2025 7 / 11

[0035] The method according to the invention is explained in more detail below with reference to an embodiment shown in the drawing.

[0036] Fig. 1 Submarine

[0037] Figure 1 shows a highly schematic representation of an exemplary submarine 1 for carrying out the method according to the invention. The submarine 1 has, by way of example, four accumulators 10, which are preferably strings of four to eight modules, wherein the modules have a plurality of unit cells connected both in parallel and in series. Typically, a submarine will have 20 to 100 strings. The accumulators 10 are each connected to the ship's electrical system via a DC-DC converter 12. The DC-DC converter enables the decoupling of the accumulator voltage and the ship's electrical system voltage, which in turn makes it possible to connect accumulators 10 with different states of charge and consequently different voltages to the ship's electrical system 50. Each accumulator 10 has a string battery management system 14, which can detect the temperature of the accumulator 10 by means of a thermocouple 16.All string battery management systems are connected to the central boat battery management system 60. Furthermore, the submarine 1 has a shore power connection 70, which is connected to the ship's electrical system.

[0038] To dissipate the waste heat generated during operation, the submarine has an internal cooling circuit 20, which circulates a heat exchange fluid through or along the accumulators 10 in a closed loop. The internal cooling circuit 20 can be connected to the seawater cooling circuit 30 via a heat exchanger 40.

[0039] For example, if submarine 1 is in port and powered via shore power connection 70, there is no significant electrical load on the accumulators 10, allowing them to cool down. If, for instance, a capacity test is to be performed before the submarine sets sail again, the accumulators 10 may be colder than required for the test. To still be able to perform the test, heat exchanger 40 is deactivated, and assuming the same temperature, the following applies: 19.11.2025 8 / 11

[0040] The battery with the highest remaining charge is discharged, and the battery with the lowest remaining charge is charged. This charging process generates some heat, which is distributed via the internal cooling circuit and gently warms the other batteries as well. The advantage is that no additional components, such as heating elements, are required.

[0041] Reference sign

[0042] 1 submarine

[0043] 10 Accumulator

[0044] 12 DC / DC converters

[0045] 14-strand battery management system

[0046] 16 Thermocouple

[0047] 20 internal cooling circuit

[0048] 30 Seawater cooling circuit

[0049] 40 heat exchangers

[0050] 50 On-board power supply

[0051] 60 Boat battery management system

[0052] 70 Shore power connection

Claims

November 19, 2025 9 / 11 Patent claims 1. Method for the thermal optimization of an energy storage device with at least two accumulators (10) and at least two DC-DC converters (12) of a submarine (1), wherein the at least two accumulators (10) are each connected to an on-board electrical system (50) of the submarine via a DC-DC converter (12), wherein the energy storage device is cooled by an internal cooling circuit (20), wherein the internal cooling circuit (20) is coolable, wherein the temperature of the energy storage device is detected, wherein a minimum operating temperature for an operating mode is set, wherein before the start of the operating mode the detected temperature is compared with the minimum operating temperature, wherein if the minimum operating temperature is undershot the internal cooling circuit (20) is switched off, wherein a recharging process is carried out between the at least two accumulators until the minimum operating temperature is reached.

2. Method according to claim 1, characterized in that the operating mode is a capacity test.

3. Method according to one of the preceding claims, characterized in that the energy storage device of the submarine (1 ) has a plurality of accumulators (10).

4. Method according to claim 3, characterized in that the temperature for each accumulator (10) is recorded, wherein the recharging between the accumulators (10) with the lowest temperature takes place.

5. Method according to one of claims 3 to 4, characterized in that the accumulator (10) with the lower state of charge is selected for charging and the accumulator (10) with the higher state of charge is selected for discharging.

6. Method according to one of claims 3 to 5, characterized in that a priority is formed for each accumulator (10) from state of charge and temperature. November 19, 2025 10 / 11 7. Method according to one of the preceding claims, characterized in that the method is only carried out at a water ambient temperature of at most 18 °C.

8. Method according to one of the preceding claims, characterized in that the method is carried out while the submarine is moored.

9. Method according to one of the preceding claims, characterized in that the on-board network voltage is reduced.

10. Method according to one of the preceding claims, characterized in that a low power rating of the DC-DC converter is selected.

11. Method according to one of the preceding claims, characterized in that the method results in an equalization of the state of charge.

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