Device and method for cooling components

Abstract

The invention relates to a device for cooling components (3) of an electric fuel cell drive system using stored liquid hydrogen (H₂(I)), wherein the liquid hydrogen (H₂(I)) is in thermally conductive contact with a cooling medium (Ne) via a heat exchanger (1), which cools the components (3). The method according to the invention is characterized in that the cooling medium (Ne) is a gaseous cooling medium (Ne) which retains its gaseous state even under the conditions prevailing in the heat exchanger (1) through which liquid hydrogen (H₂(I)) flows, wherein this cooling medium (Ne) is connected in at least one thermosiphon (6) to the heat exchanger (1) on the one hand and to the component (3) to be cooled on the other. According to the method, cooling is achieved to temperatures of -20°C to +30°C for the components (3) to be cooled.

Description

[0001] The invention relates to a device for cooling components of an electric fuel cell drive system according to the type defined in more detail in the preamble of claim 1. The invention also relates to a method for cooling components of an electric fuel cell drive system.

[0002] The cooling of components of an electric fuel cell drive system is known from the prior art. Generally, a cooling circuit is used, for example, a cooling circuit of the type known from US patent US 11,575,138 B1. This patent further describes how, in the event that additional cooling power is required, liquid hydrogen stored for use in the fuel cell system is heated and evaporated by means of the cooling circuit to provide additional cooling within the circuit.

[0003] JP 2022 - 114 463 A discloses a method for synchronizing transmission times of measurement signals of an energy conversion system to optimize the use of cold from liquefied fuel as well as monitoring and analysis.

[0004] Furthermore, the cooling of power electronic components or electric drive components typically requires much lower cooling medium temperatures than the fuel cell itself. This increases the complexity of the cooling circuit, as a rather intricate design results from a specific flow sequence through the components, as well as potentially valve systems and bypass lines around the relevant components.

[0005] JP 2005 - 44 631 A therefore describes a cooling of power electronic components such as an inverter by directing cryogenic liquid hydrogen from the hydrogen tank onto the power electronic components, so that their silicon substrate is directly cooled by the cryogenic hydrogen.

[0006] In principle, this can be advantageous, as lower temperatures are ideal for dissipating waste heat in power electronics. However, the temperatures that occur during direct cooling with liquid hydrogen are detrimental to most silicon substrates because temperatures below -100°C negatively affect the material, ultimately reducing its lifespan and simultaneously increasing the electrical resistance of the components. Therefore, such low temperatures have proven to be a significant disadvantage.

[0007] The object of the present invention is to improve the cooling of components in an electrically driven fuel cell system using liquid hydrogen by means of a simple and efficient system, in order to achieve an optimized efficiency of the corresponding components.

[0008] According to the invention, this problem is solved by a device having the features of claim 1, and in particular those of the characterizing part of claim 1. Advantageous embodiments and further developments are described in the dependent claims. Furthermore, a method for cooling components of an electric fuel cell drive system according to claim 7 solves the problem. Advantageous embodiments and further developments of this method are also described in the dependent claims.

[0009] The device according to the invention for cooling components of an electrically driven fuel cell system uses liquid hydrogen as a heat sink for cooling these components, similar to the system in the aforementioned prior art. In the device according to the invention, the liquid hydrogen flows through a heat exchanger in which it is in thermally conductive contact with a cooling medium, which then cools the component. According to the invention, this cooling medium is designed as a gaseous cooling medium, which retains its gaseous state even during heat-transferring contact with the liquid hydrogen in the heat exchanger. The cooling medium thus remains gaseous throughout operation. In the device according to the invention, it is brought into contact with the heat exchanger on the one hand and with the component to be cooled on the other hand via at least one thermosiphon.A thermosiphon is a setup in which heat is transferred via a pipe by the temperature-related density differences and the resulting convection of the gaseous cooling medium. Typically, the setup is such that the heat exchanger containing the liquid hydrogen used to cool the cooling medium is positioned higher than the component being cooled, in the direction of gravity. The cooled gaseous cooling medium then sinks down to the area of ​​the component being cooled and absorbs the heat from that component. This reduces the density of the gaseous cooling medium, causing it to rise back up to the heat exchanger, where it is cooled again and sinks once more to the component being cooled. Thus, without an external pump, the gaseous cooling medium can be circulated within the thermosiphon to cool the component being cooled.

[0010] According to a particularly advantageous embodiment, the gaseous medium can, in particular, comprise a noble gas or, more preferably, be configured as such. The noble gas neon is especially suitable, although other noble gases or mixtures thereof can also be used in principle. The noble gases have the advantage that they typically do not liquefy at the temperature of liquid hydrogen and thus always exist in the gaseous state, which is beneficial for the functionality of the thermosiphon. Furthermore, they are electrically non-conductive, which offers the advantage that, when used for cooling electrical components, they can flow around the component itself and / or its terminals without causing short circuits between the terminals.A single thermosiphon can therefore be used to directly cool the various electrical connections of a semiconductor component such as a transistor or diode, for example, such as the drain and source of a transistor, without causing a short circuit. By directly cooling these connection elements, which are in electrically and therefore also thermally conductive contact with the interior of the component, the heat generated there can be optimally dissipated.

[0011] According to a particularly advantageous embodiment of the device according to the invention, the area where the thermosiphon connects to the heat exchanger has at least one valve assembly to control the volume flow of the gaseous cooling medium. This valve assembly thus allows the cooling capacity and the target temperature of the component to be cooled to be adjusted.

[0012] The component can be designed as a power electronic component or as an electric drive component, such as an electric drive motor or its stator. This allows for independent cooling of these components from the rest of the cooling circuit. On the one hand, this enables a different temperature level to be achieved than if cooling had to be combined with, for example, the fuel cell. Additionally, the cooling circuit for the fuel cell itself can be relieved of some of its load, as it is already a relatively complex system to manage, since the typical temperature differences between the ambient air and the warm coolant are relatively small. Unlike, for example, internal combustion engine drive systems, where this temperature difference is significantly larger, a larger cooling surface area is therefore required to dissipate the resulting waste heat.The independent cooling of power electronic components, which thus relieves the regular cooling circuit, also has advantages with regard to the entire cooling system.

[0013] According to an advantageous embodiment, the power electronic component can be designed as a semiconductor device whose electrical terminals and / or substrate are in direct thermal contact with the gaseous cooling medium. Particularly when using a noble gas such as neon, as mentioned above, ideal cooling can be achieved in this way, since, for example, drain and source terminals can be cooled simultaneously via the gaseous cooling medium without the risk of electrical short circuits. Besides noble gases, other deionized gases would also be conceivable, with a noble gas such as the preferred neon mentioned above being very suitable because, by its very nature, it contains no ions and does not form any during operation.

[0014] The inventive method for cooling components of an electric fuel cell drive system now provides for the use of such a device to cool the components to be cooled to a temperature between -20°C and +30°C, which is an ideal operating temperature, especially for cooling power electronic components, at which, on the one hand, negative material changes of the silicon substrate due to excessively low temperatures are avoided, since these typically only occur at a level of about -100°C, and at which, on the other hand, heat-related losses can be reduced.

[0015] For example, the inventors found that cooling to a temperature of -10°C reduced losses in semiconductor switches by more than 8% and in diodes by up to 9%. Overall, this allows for a reduction in electrical losses of more than 8% at such temperatures. Even at slightly higher temperatures, such as 0°C, savings of 6% to 6.5% are still possible. This enables very efficient operation and allows for higher power outputs with the same chip size, or, if higher power is not required, a reduction in the chip's area or size.

[0016] According to a preferred embodiment of the inventive method, it is possible to influence the cooling temperature by means of the at least one valve arrangement according to the embodiment of the inventive device described above. Such influence can now be implemented, in particular, depending on the electrical power requirement, so that, for example, temperatures between -10°C and 0°C can be set depending on the load at a constant load, or that somewhat higher temperatures of, for example, 0°C to 20°C are permitted in the case of dynamic power requirements.

[0017] In addition to or as an alternative to controlling the temperature of the gaseous cooling medium via the valve device, according to a very advantageous further development of the method according to the invention, the amount of hydrogen introduced into the heat exchanger can also be adjusted accordingly in order to influence the cooling power to be transferred to the gaseous cooling medium.

[0018] According to a particularly advantageous embodiment of the method according to the invention, and this applies especially to the preferred use of the electric drive system in a vehicle application, it can further be provided that, during the initial cooling of the power electronic modules to a first preset temperature, the torque demand of the electric drive train is monitored. If an increased torque demand occurs, the cooling capacity can be increased accordingly via a feedforward control system in order to achieve, as quickly as possible, a corresponding increase in the waste heat in the components, which is to be expected with the higher torque demand. Subsequently, the temperature can then be controlled according to the torque demand in order to maintain the temperature in the area of ​​the power electronic components within a predefined temperature range.

[0019] The device and method according to the invention can now be used in any type of electric fuel cell drive system that utilizes liquid hydrogen, whether for stationary or mobile drives. The electric drive system can particularly preferably serve to drive a vehicle, for example, a trackless or rail-bound land vehicle, such as a heavy commercial vehicle, or a watercraft.

[0020] Further advantageous embodiments of the device and method according to the invention also become apparent from the exemplary embodiment, which is described in more detail below with reference to the figures.

[0021] This shows: Fig. 1 a schematic representation of a possible embodiment of a device according to the invention; and Fig. 2 a software scheme on a control unit for implementing a possible embodiment of the method according to the invention.

[0022] In the presentation of the Fig. Figure 1 shows a section of an electric fuel cell drive system, which is known in principle to those skilled in the art. The core of the depicted section is a heat exchanger 1 through which liquid hydrogen H2 (I) from a cryogenic storage system, which is not shown here, flows. The amount of hydrogen flowing into the heat exchanger 1 can be adjusted accordingly via a metering valve 2. If this amount correlates with the amount required for the conversion in the fuel cell, a bypass (not shown here) can also be provided. This allows the total amount of hydrogen required for the fuel cell to be supplied, and this amount, or only a specific portion thereof, flows through the heat exchanger 1, with the remainder flowing through the bypass.

[0023] Liquid hydrogen or a mixture of liquid hydrogen H2 (I) and gaseous hydrogen H2 (g) then exits heat exchanger 1. Heat exchanger 1 now forms a heat sink at a correspondingly low temperature, for example, a temperature in the range of the boiling point of liquid hydrogen.

[0024] In the presentation of the Fig. 1. Further down, several power electronic components labeled 3, for example diodes and semiconductor switches or transistors, are shown. They are located on a surface shown in the diagram. Fig. Substrate 1, designated by 4. In the embodiment shown here, two layers of this substrate 4 are located adjacent to a free volume 5. This volume 5 is part of a thermosiphon, designated as a whole by 6, which, in addition to the volume 5, essentially comprises a power element 7 and optionally a valve assembly designated by 8. This thermosiphon 6 connects the heat exchanger 1 to the substrate 4, with the purpose of cooling the substrate and thus the power electronic components 3.

[0025] The thermosiphon 6, which is, for example, tubular in design, is filled with a gaseous cooling medium, in this case, neon (Ne). In the heat sink region of the heat exchanger 1, this neon is cooled by the liquid hydrogen, causing its density to increase and the neon to sink in the direction of the shear force g into the region of volume 5. There, the neon can absorb heat from the substrate 4, causing its density to decrease again and the heated neon to flow back upwards into the region of the heat exchanger 1. Without a conveying device or the like, heat transfer can thus be generated by the spontaneously occurring convection, which easily enables the cooling of the substrate 4 to temperatures on the order of -10°C to +10°C, for example, and thus contributes to the efficient functioning of the power electronic components 3.

[0026] The temperature itself can be adjusted in two ways, for example by adjusting the amount of liquid hydrogen dosed into the heat exchanger 1 via the metering valve 2, or by increasing or decreasing the flow of neon Ne through the thermosiphon 6 using the optional valve device 8, in order to influence the cooling capacity and ultimately the temperature in the area of ​​the substrate 4 by affecting the circulating volume flow of neon Ne in the thermosiphon 6.

[0027] This setup can now preferably be used in electric fuel cell drive systems for vehicles, for example, land or water vehicles. It is particularly preferred for use in heavy commercial vehicles. In such a case, according to a software scheme in the control unit of such a fuel cell system, the temperature T of the substrate 4 is set to, for example, 10°C. This is shown in the diagram. Fig. 2 is indicated accordingly by the circle labeled A. If, for example, the vehicle accelerates a, the drive system is signaled an increasing torque requirement. With increasing acceleration, the amount of liquid hydrogen H2(I) supplied to heat exchanger 1 is increased accordingly, as indicated in section B.

[0028] According to circuit C, the temperature T of substrate 4 is then measured, and the amount of liquid hydrogen H2(I) is adjusted under D to maintain the desired temperature range. Preferably, an approximately constant temperature T can be set in the area of ​​substrate 4, whereby two different temperature levels can be used: one between -10°C and 0°C for largely steady-state operation and a slightly higher temperature level in the range of 0°C to 20°C for dynamic load changes. Since higher cooling capacity requirements exist here, especially during acceleration, allowing the slightly higher temperature level provides a certain degree of flexibility, thus reducing the need for such dynamic adjustments to the cooling temperature and advantageously simplifying the control process.

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