Providing a short-term power reserve in a submarine

Abstract

The present invention relates to a method for operating a submarine (20), wherein the submarine (20) comprises an on-board power network (60), at least one energy storage device (30), and an energy generation device (40), wherein the energy storage device (30) is connected to the on-board power network (60) via a DC-DC converter (50) and is electrically disconnectable therefrom, wherein the DC-DC converter (50) is controlled according to a current-voltage characteristic curve, wherein, in a first operating mode, the on-board power network (60) is supplied solely by the energy generation device (40), wherein, in a second operating mode, the on-board power network (60) is jointly supplied by the energy generation device (40) and the energy storage device (30), wherein, in the first operating mode, the on-board power network voltage of the on-board power network (60) is predefined by the current-voltage characteristic curve of the energy generation device (40), characterised in that, in the first operating mode, the energy storage device (30) is connected to the on-board power network (60) in a non-current-conducting manner such that an offset is applied to the current-voltage characteristic curve of the DC-DC converter (50) of the energy storage device (30) so that the current-voltage characteristic curve is shifted in such a manner that the present on-board power network voltage results in current-free operation of the DC-DC converter (50) of the energy storage device (30).

Description

[0001] Provision of a short-term power reserve in a submarine

[0002] The invention relates to a method for increasing the availability of electrical power during special operating conditions on board a submarine, for example in order to be able to quickly provide more propulsion power.

[0003] From the subsequently published German patent DE 10 2024 118 307, a hot standby mode for battery systems is known. This patent discloses 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. The DC / DC converters control at least one energy storage device, and at least one other 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, this second energy storage device is immediately switched to supply electrical energy to the grid. DC / DC converters are also known as DC-DC converters.

[0004] 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.

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

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

[0020] An energy storage device typically has multiple strings. Each string is connected to the vehicle's electrical system via a DC / DC converter, allowing each string to be individually connected and disconnected. This also allows for the equalization of voltage differences between the strings due to varying charge levels. The strings are thus electrically connected in parallel. For low power outputs (also known as partial load), the problem arises that the strings operate outside their optimal operating point and therefore have a lower efficiency. This leads to increased energy extraction from the energy storage device due to unused power losses, which, particularly in underwater vehicles, reduces the range or maximum possible dive times.A solution would be to switch off individual circuits, so that the total power to be supplied or received is distributed across fewer circuits. This would allow the remaining circuits to operate at a more efficient point, resulting in higher efficiency. However, if the unused circuits are switched off, a sudden increase in load in the vehicle's electrical system could lead to insufficient capacity provided by the switched-on circuits.

[0021] In addition to the energy storage system, there are typically two power generators: usually a diesel generator for surface operation (including snorkeling) and an air-independent system, such as a fuel cell or a water heater. For example, when surfaced, the diesel generator is often operated in island mode, meaning it is the sole power source for the ship's electrical system. During island mode, the energy storage system is disconnected from the electrical system. However, there are operating conditions, such as full power operation, that require more power than is available in island mode. Therefore, before this operating condition begins, the energy storage system must first be reconnected to the electrical system to provide sufficient power. This process takes time.

[0022] The purpose of the invention is to be able to provide full power at all times, even in island operation, while simultaneously reducing power loss.

[0023] 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 drawings.

[0024] The invention relates to a method for operating a submarine. The submarine has an onboard electrical system, at least one energy storage device, and an energy generation device, which are electrically connected to the onboard electrical system or can be electrically connected to it. The consumers, which for the sake of simplicity will not be considered further, are connected to the onboard electrical system, but which draw and consume power from it. One of the largest consumers is, for example, the propulsion motor. The onboard electrical system can also be designed with multiple components. For example, and typically, the onboard electrical system consists of two independently operable subnetworks to ensure redundancy. However, this is also not relevant to the method according to the invention, which can be carried out on a single onboard electrical system, on coupled subnetworks, or separately on separate onboard electrical systems.A submarine typically has not just one power generation device, but for redundancy and performance reasons, for example, two or four diesel generators. A submarine also often has an additional air-independent power generation device, which can also be multi-part or modular. Important examples of air-independent power generation devices are fuel cells, the Stirling engine, the Waiter engine, and the like. According to the invention, both island operation, for example of a diesel generator above water or, for example, of a fuel cell underwater, is possible and makes no difference to the further process. The energy storage device is connected to the ship's electrical system via a DC-DC converter and is electrically disconnectable. The DC-DC converter fulfills several functions.Firstly, it isolates the vehicle 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 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, but current-free, connection if a suitable current-voltage characteristic curve is defined for controlling the DC-DC converter.

[0025] The current-voltage characteristic of an energy storage device, to a first approximation, exhibits five voltage ranges. Each voltage range corresponds to a specific voltage range in the vehicle's electrical system. The voltage range is defined by a lower and an upper voltage value, with each voltage value within the range corresponding to a specific current. Alternatively, the voltage range, or its upper or lower limit value, may be predetermined based on other parameters. However, the voltage range remains greater than zero in this case. The first voltage range describes the discharge process of the energy storage device and therefore indicates a current flow in the direction of the vehicle's electrical system. This current direction is subsequently considered the positive current direction.The relationship between current and voltage is typically constant in this first voltage range, with higher currents generally occurring at lower electrical system voltages. The current is limited at the maximum current, so that the current does not increase further regardless of the decreasing voltage. This protects the energy storage device and the electrical system from damage. This can be defined as the second voltage range, in which the current is kept constant regardless of the voltage. Corresponding to the discharge process is the charging process, in which the current flows from the electrical system to the energy storage device; mathematically, the current has the opposite sign and flows in the negative direction.Here, too, there is a third voltage 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 voltage range follows, limiting the charging current and keeping it constant regardless of any further increases in voltage. This also reliably prevents damage to the energy storage device from excessive charging current. Finally, there is a fifth voltage range, which is currentless, meaning the rectifier neither draws power from nor supplies power to the energy storage device. This fifth voltage range connects the voltage range between the highest discharge voltage and the lowest charging voltage.

[0026] The current-voltage characteristic curve shows a fifth voltage range for the de-energized connection, in which the energy storage device is neither charged nor discharged. Furthermore, the current-voltage characteristic curve shows a first voltage range, in which power is delivered from the energy storage device to the ship's electrical system via the DC-DC converter. The DC-DC converter is controlled accordingly via the current-voltage characteristic curve. In a first operating mode, the ship's electrical system is supplied solely by the power generation device, the so-called island mode. This could be, for example, a diesel generator when operating on the surface or a fuel cell when operating underwater. In a second operating mode, the ship's electrical system is supplied jointly by the power generation device and the energy storage device. This results in a higher power output being available in the second operating mode.In the first operating mode, the vehicle electrical system voltage is determined by the current-voltage characteristic of the power generation device. This occurs automatically because only the power generation device is electrically connected to the vehicle electrical system and thus supplies all the electrical power. The power output of the power generation device is typically regulated to provide the power required by all consumers. As a result, the vehicle electrical system voltage automatically adjusts to the current-voltage characteristic of the power generation device. The current-voltage characteristic of a power generation device usually exhibits the highest voltage at no load (without current). As the power output increases, the voltage drops until a point is reached where, with further increases, the voltage decreases more sharply than the current, and consequently, the power output decreases.This point therefore represents the maximum power output of the energy generation device.

[0027] According to the invention, in the first operating mode, the energy storage device is not connected to the vehicle's electrical system in a current-carrying manner such that an offset is selected for the current-voltage characteristic of the DC-DC converter of the energy storage device, such that the current-voltage characteristic is shifted in such a way that the current vehicle electrical system voltage results in the DC-DC converter of the energy storage device operating without current. Operation thus takes place in the fifth voltage range of the current-voltage characteristic.

[0028] To prevent the energy storage device from being live when connected to the vehicle's electrical system, an offset is selected for the current-voltage characteristic curve of the energy storage device's DC-DC converter. This offset is chosen such that the current vehicle electrical system voltage lies within the fifth voltage range of the current-voltage characteristic curve. Thus, the current-voltage characteristic curve is shifted in such a way 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 supplied to the energy storage device. However, a large change in the vehicle electrical system voltage causes the fifth voltage range of the current-voltage characteristic curve to be left behind, and the energy storage device immediately switches to regulation mode, i.e., it draws or supplies current.In other words, this means that the energy storage device is electrically connected to the vehicle's electrical system, but due to the correspondingly shifted current-voltage characteristic, it exhibits a current flow of 0 A. This state can be described as hot standby and is the essential aspect of the invention. An energy storage device within the meaning of the invention can be, in particular, a string of, for example, and preferably, 4 to 8 modules, each module comprising a plurality of unit cells in parallel and series connection, as is known from the prior art. Such an arrangement is common for lithium-ion batteries. The energy storage device can also be a group of such strings. Alternatively, the energy storage device can be a series connection of large unit cells, as is currently common for lead-acid batteries on submarines.

[0029] In a further embodiment of the invention, in the first operating mode, a new on-board voltage is established by a load fluctuation on the on-board network, corresponding to the current-voltage characteristic of the

[0030] The power generation device is involved. As previously explained, the current-voltage characteristic of the power generation device results in a different current-voltage pair for each power output. A change in load therefore leads to an adjusted on-board voltage corresponding to the new load point, according to the current-voltage characteristic of the power generation device. However, this only applies once the power generation device has actually reached the new load point and is back in a steady state. Load fluctuations on the grid, however, usually occur more quickly, so that the load change on the on-board grid, with the previous setting of the power generation device, results in a change in the on-board voltage (if more power is required than generated, the on-board voltage drops; if less power is required than generated, the on-board voltage rises). This results in a dynamic, not a static, state.Depending on the originally selected offset for the energy storage device, the vehicle electrical system voltage reaches a value that lies within a continuous range of the DC-DC converter's current-voltage characteristic curve: the first voltage range when more power is required, or the third voltage range when less power is required. Thus, the energy storage device draws power from the vehicle electrical system (reduced load, third voltage range) or supplies power to the vehicle electrical system (increased load, first voltage range), in addition to the energy output of the energy generation device.Thus, on a very fast timescale and before the power generation device adjusts its load, the additional electrical power required is supplied by the energy storage device, or the unneeded but generated electrical energy is stored in the energy storage device. This stabilizes the vehicle electrical system at this operating point until the power generation device can be adjusted and has once again reached the static operating point for supplying the required electrical power. After reaching the new static state with the new vehicle electrical system voltage, a new offset is selected so that the current-voltage characteristic is shifted such that the new vehicle electrical system voltage results in the DC-DC converter of the energy storage device operating without current, provided the new vehicle electrical system voltage lies within the current-voltage characteristic of the power generation device.If the on-board voltage were to fall outside the current-voltage characteristic curve of the power generation device, a switch to the second operating mode would be necessary anyway, as the power output of the power generation device would no longer be sufficient, thus establishing a new operating point. If the new on-board voltage remains within the current-voltage characteristic curve of the power generation device, power will be briefly absorbed or supplied by the energy storage device during the transition until the new offset is established and the system is back in a new static operating point in the first operating mode, with the power being supplied exclusively by the power generation device.

[0031] In a further embodiment of the invention, the submarine has at least one additional energy storage device, for example, another string or a group of additional strings. This additional energy storage device is connected to the ship's electrical system via another DC-DC converter and is electrically disconnectable, entirely analogous to and usually identical in construction to the main energy storage device. The additional DC-DC converter is controlled by a current-voltage characteristic, entirely analogous to the DC-DC converter, but preferably independently of each other. In the first operating mode, the additional energy storage device is electrically disconnected from the ship's electrical system, i.e., not in the so-called hot standby mode described above. Here, the disconnection is as in the classic case.The additional energy storage device is electrically connected to the vehicle's electrical system as soon as the system voltage reaches the highest power point of the current-voltage characteristic curve of the energy generation device. This utilizes the fact that a power reserve is available through hot standby mode, and that drawing higher power from the electrical system, for example, and especially during strong acceleration using the traction motor, does not immediately draw the electrical power from the system but requires a ramp-up time. The hot standby mode of the energy storage device thus provides the time the electrical system needs to connect the additional energy storage device, enabling a rapid ramp-up of power, for example, from the traction motor.

[0032] The method according to the invention is explained in more detail below with reference to an embodiment shown in the drawings.

[0033] Fig. 1 Current-voltage characteristic curve of the energy generating device

[0034] Fig. 2 Current-voltage characteristic curve of the energy storage device

[0035] Fig. 3 Current-voltage characteristics

[0036] Fig. 4 Submarine

[0037] Figure 1 shows the current-voltage curve of the energy generation device 40, for example a fuel cell. The higher the current I, the more the voltage U decreases, until the maximum current of the energy generation device Imax.E is reached at maximum power.

[0038] Fig. 2 shows the current-voltage characteristic of the energy storage device 30. This is more complex because, in addition to energy output, energy can also be absorbed for charging. Therefore, the current-voltage characteristic of the energy storage device 30 has five voltage ranges 1, 2, 3, 4, 5. The first voltage range 1 is the power output up to the maximum discharge current l. ma The current is then limited to protect the energy storage device 30, resulting in the second voltage range 2. Analogously, this mirrors the process, creating the third voltage range, which acts as a charging range with a negative current flow (charging current) into the energy storage device 30 up to the maximum charging current lmax, 2, after which the fourth voltage range 4 begins. Between the first voltage range 1 and the third voltage range 3 is the currentless fifth voltage range 5, which can be used for hot standby.

[0039] Figure 3 illustrates the selection of the offset for connecting the energy storage device 30 to the vehicle electrical system 60 without current. Since only the energy generation device 40 provides the energy for the vehicle electrical system 60, the current IB and the voltage UB are established at operating point 10 when a required power is applied. The offset is selected precisely so that the voltage UB at operating point 10 falls exactly within the fifth voltage range 5; the energy storage device 30 is electrically connected to the vehicle electrical system 60, but without current.

[0040] Fig. 4 shows a highly schematic representation of a submarine 20 for carrying out the method according to the invention. The submarine has a power generation device 40, for example a fuel cell, and another power generation device 41, for example a diesel generator, both of which are connected to the ship's electrical system 60. The propulsion motor 70 is shown as a consumer connected to the ship's electrical system, purely by way of example. The submarine 20 also has an energy storage device 30 and another energy storage device 31. The energy storage device 30 is connected to the ship's electrical system 60 via a DC-DC converter 50, and the other energy storage device 31 is connected to the ship's electrical system 60 via another DC-DC converter 51.

[0041] Reference sign

[0042] 1 first voltage range

[0043] 2 second voltage range

[0044] 3 third voltage range

[0045] 4 fourth voltage range

[0046] 5 fifth voltage range

[0047] 10 Operating point

[0048] 20 submarines

[0049] 30 energy storage devices 30 additional energy storage devices

[0050] 40 Energy generating device

[0051] 41 additional energy generating devices

[0052] 50 DC-DC converters 51 additional DC-DC converters

[0053] 60 On-board power supply

[0054] 70 drive motor

[0055] I Electricity

[0056] Imax.E maximum current of the energy generating device I max maximum discharge current lmax,2 maximum charging current

[0057] IB electricity at the operating point

[0058] U voltage

[0059] UB voltage at the operating point

Claims

Patent claims 1. Method for operating a submarine (20), wherein the submarine (20) has an onboard electrical system (60), at least one energy storage device (30) and an energy generation device (40), wherein the energy storage device (30) is connected to the onboard electrical system (60) via a DC-DC converter (50) and is electrically separable, wherein the DC-DC converter (50) is controlled via a current-voltage characteristic curve, wherein in a first operating mode the onboard electrical system (60) is supplied only by the energy generation device (40), wherein in a second operating mode the onboard electrical system (60) is supplied jointly by the energy generation device (40) and the energy storage device (30), wherein in the first operating mode the onboard electrical system voltage of the onboard electrical system (60) is determined by the current-voltage characteristic curve of the energy generation device (40), characterized in thatthat in the first operating mode the energy storage device (30) is not connected to the vehicle electrical system (60) in such a way that an offset is selected for the current-voltage characteristic of the DC-DC converter (50) of the energy storage device (30), such that the current-voltage characteristic is shifted in such a way that the current vehicle electrical system voltage leads to a currentless operation of the DC-DC converter (50) of the energy storage device (30).

2. Method according to claim 1, characterized in that, in the event of a load fluctuation on the vehicle electrical system (60) in the first operating mode, a new vehicle electrical system voltage is established by this load fluctuation according to the current-voltage characteristic of the energy generation device (40), wherein, according to the selected offset, the vehicle electrical system voltage reaches a continuous range (2, 4) of the current-voltage characteristic of the DC-DC converter (50), so that the energy storage device (30) absorbs power from or supplies power to the vehicle electrical system (60), wherein a new offset is selected such that the current-voltage characteristic is shifted in such a way that the new vehicle electrical system voltage leads to currentless operation of the DC-DC converter (50) of the energy storage device (30), provided that the new on-board voltage lies within the current-voltage characteristic curve of the power generation device (40).

3. Method according to one of the preceding claims, characterized in that the submarine (20) has at least one further energy storage device (31) has a further energy storage device (31) being connected to the vehicle electrical system (60) via a further DC-DC converter (51) and being electrically disconnectable, wherein the further DC-DC converter (51) is controlled via a current-voltage characteristic, wherein the further energy storage device (31) is electrically disconnected from the vehicle electrical system (60) in the first operating mode. The vehicle electrical system (60) is disconnected, with the additional energy storage device (31) being electrically connected to the vehicle electrical system (60) as soon as the vehicle electrical system voltage reaches the highest power point current-voltage characteristic of the energy generation device (40).

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