Method and device for controlling the potential position of DC conductors

Abstract

Method for regulating the potential position of a first and a second DC conductor (DC+, DC-), wherein the DC conductors (DC+, DC-) are provided for supplying an electrolyzer (14) with electrical power and the electrical power can be transferred from an AC network (12) to the DC conductors (DC+, DC-) via a rectifier (20), wherein in a first operating mode the potential position of the first and the second DC conductor (DC+, DC-) is regulated such that both DC conductors (DC+, DC-) have the same polarity with respect to ground potential (GND).

Description

Technical area

[0001] The application relates to a method and a device for controlling the potential position of DC conductors (DC direct current) as well as to a DC network comprising such a device and an electrolyzer. background

[0002] Electrolyzers can be supplied with DC electrical power via DC connections to carry out electrolysis. The DC electrical power can be drawn from an AC grid and made available to the electrolyzer via a rectifier and DC conductors. The potential difference between the DC conductors corresponds to the DC voltage applied to the electrolyzer. The potential position of the respective electrical potentials of the DC conductors relative to ground depends on the type of AC grid and its grounding, as well as on the type of rectifier and, in particular, on whether or not it has galvanic isolation.

[0003] It is known from document DE 10 2020 121 593 A1 to earth electrolysis cells with an electrode, for example the negative pole.

[0004] During the operation of electrolyzers, it has been observed that an increasing current flows from the electrolyzer to ground over the course of its operating life, thus decreasing the electrolyzer's insulation resistance. For safety reasons, the electrolyzer's operation must be interrupted if the insulation resistance falls below a specified limit or the ground current exceeds a corresponding limit. Therefore, there is a desire to counteract such a gradual reduction in insulation resistance during ongoing electrolyzer operation, or to increase the insulation resistance back above the limit without the need for maintenance intervention, for example, by replacing electrolyzer parts. Overview

[0005] A first and a second DC conductor are provided to supply an electrolyzer with electrical power. The electrical power is transferred from an AC (alternating current) network to the DC conductors via a rectifier.

[0006] In a method for controlling the potential position of the first and second DC conductors, the potential position of the first and second DC conductors is controlled in a first operating mode such that both DC conductors have the same polarity with respect to earth potential.

[0007] A device for regulating the potential position of the first and second DC conductors is designed to regulate the potential position of the first and second DC conductors in a first operating mode such that both DC conductors have the same polarity with respect to ground potential.

[0008] The described control system enables targeted influence on the potential position of the DC conductors. In particular, the described control system can reduce so-called potential-induced degradation (PID) in electrolyzers, especially in electrolyzers with multiple electrolysis stacks. Due to the PID effect, the electrolyzer's insulation properties can be impaired by the migration of ions within the electrolyzer due to the potential position of the DC conductors. By specifically influencing the potential position of the DC conductors, this ion migration can be reduced or reversed, thus reducing or reversing the PID effect.

[0009] For example, the potential position of the DC conductors is adjusted by the device's power electronics so that the potential of both DC conductors has the same polarity relative to ground. This can reduce or prevent the PID effect, for example.

[0010] In one embodiment of the method, the potential level in the first operating mode is regulated to effect regeneration of the electrolyzer. Depending on the design of the electrolyzer, it may be necessary for both DC conductors to have a positive or negative potential relative to ground to effect regeneration. In one embodiment, the device regulates the potential level with the appropriate polarity.

[0011] During electrolyzer regeneration, the PID effect, specifically the unwanted migration of ions or the resulting chemical reaction, is at least partially reversed. For this purpose, the potential position of the DC conductors is specifically selected to achieve the reversal effect. In particular, the potentials of the DC conductors can be set as close together as possible, while maintaining a minimum distance from the ground potential.

[0012] In one embodiment of the method and / or device, the first operating mode has a first sub-operating mode in which the potential difference between the first and second DC conductors is regulated such that the voltage applied to the electrolyzer is below a threshold voltage. In this embodiment, the voltage applied to the electrolyzer is therefore below the threshold voltage, which can be selected, for example, with regard to the electrolyzer's characteristic curve, such that the electrolyzer assumes a predetermined operating range.

[0013] The threshold voltage can depend on the electrolyzer's operating voltage and, in particular, correspond to the operating voltage. The electrolyzer's operating voltage refers to the voltage at which the electrolysis process in the electrolyzer begins. The operating voltage can also be referred to as the decomposition voltage. The threshold voltage can, in particular, lie in a range between 10% and 50% of the operating voltage. In this embodiment, the position of the potentials of the DC conductors is selected such that the voltage applied to the electrolyzer is so small that the electrolyzer does not carry out electrolysis. The potential position can be regulated such that other desired processes in the electrolyzer, for example the regeneration process, can take place without any significant electrolysis taking place during this time and without the power required for this having to be provided.

[0014] In one embodiment of the method and / or device, the DC conductors are disconnected from the AC grid in the first sub-operating mode. This is particularly advantageous when the AC grid has a fixed earth reference, which is the case, for example, with a TN grid. Provision can then be made for the electrical power required to regulate the potential level to be drawn from sources other than the AC grid, for example, from an auxiliary power supply that provides power with a supply voltage potential that is independent of the potentials of the AC grid and, in particular, galvanically isolated from it. The auxiliary power supply can draw the electrical power, for example, from a battery and / or an electrical generator.However, the auxiliary power supply can also have a galvanically isolated connection to the AC network, for example via a transformer, so that the auxiliary power supply still cannot draw power from the AC network.

[0015] In one embodiment of the method and / or device, the first operating mode has a second sub-operating mode. The first and second operating modes can be adopted alternatively. In the second sub-operating mode of the first operating mode, the electrolyzer is supplied with electrical power from the AC grid via the rectifier to carry out an electrolysis process, wherein in the second sub-operating mode, a potential difference between the first and second DC conductors is regulated as a function of the electrolysis process. This second sub-operating mode can be provided, in particular, to supply the electrolyzer with electrical power from the AC grid to carry out the electrolysis. At the same time, the potential regulation enables a reduction in the PID effect and / or regeneration of the electrolyzer.

[0016] In embodiments, in the second sub-operating mode, the potential difference between the first and second DC conductors can depend on an operating voltage of the electrolyzer. In particular, the potential difference can be regulated such that a voltage is applied to the electrolyzer that corresponds to the operating voltage of the electrolyzer. In this embodiment, the position of the potentials of the DC conductors is thus selected such that the voltage applied to the electrolyzer is large enough for the electrolyzer to perform electrolysis. The operating voltage of the electrolyzer is above the operating voltage and depends, among other things, on the type of electrolyzer.

[0017] In embodiments of the method and / or device, a second operating mode is provided in which the first or second DC conductor is grounded, wherein the electrolyzer is supplied with electrical power from the AC grid via the rectifier to carry out the electrolysis process. In the second operating mode, the potential difference between the first and second DC conductors is regulated depending on the electrolysis process. This second operating mode can be provided, in particular, to supply the electrolyzer with electrical power from the AC grid to carry out the electrolysis.In contrast to the first operating mode, in which the potentials of the two DC conductors are regulated so that they have the same polarity with respect to earth, i.e. both are on the same side of earth, in the second operating mode it is temporarily possible for the potentials of the two DC conductors to have different polarity, i.e. to be on different sides of earth.

[0018] In some embodiments, in the second operating mode, the potential difference between the first and second DC conductors corresponds to the operating voltage of the electrolyzer. In this embodiment, the position of the potentials of the DC conductors is selected such that the voltage applied to the electrolyzer is large enough for the electrolyzer to perform electrolysis.

[0019] In one embodiment of the method, the potential level is controlled by clocking a semiconductor switch arranged between the first DC conductor and the ground potential or between the second DC conductor and the ground potential. The clocking can be carried out, for example, by the device described. By connecting one of the DC conductors to ground via the semiconductor switch, which can be clocked, a so-called soft, current-carrying connection of one of the DC conductors to ground is enabled. The clocking can be used to control the current and thus regulate the potential level. So-called "soft grounding" can therefore be implemented using the semiconductor switch.

[0020] In one embodiment of the method, a ground current flowing through the semiconductor switch is monitored. The ground current is the current that flows between the DC conductor to which the semiconductor switch is connected and ground. Monitoring is carried out, for example, using the device described. Monitoring can be carried out in particular by detecting the ground current using an ammeter A, wherein the ammeter A can be arranged in the device. The magnitude of the ground current can then be determined in a computing device of the device, and a reaction can be triggered if the ground current becomes too large. This makes it possible to implement a grounding protection concept that can react to supercritical ground currents and thus earth faults.

[0021] The respective potential of each of the two DC conductors can have a specified minimum distance from ground potential. It can be stipulated that this minimum distance is maintained in each of the described operating modes. The minimum distance is set, in particular, by regulating the potential levels. Maintaining the minimum distance ensures that regeneration progress is achieved within a specified period or that degeneration is sufficiently counteracted.

[0022] A DC grid comprises the electrolyzer, the described device, and the first and second DC conductors. Optionally, the DC grid comprises an auxiliary power supply for supplying the device with electrical power as needed. A need to supply the device with electrical power may arise, for example, when the DC grid is disconnected from the AC grid and no electrical power can be drawn from the AC grid. The electrical power required to regulate the potential level can then be met, for example, by the auxiliary power supply. Character list

[0023] In the following, embodiments of this application are further explained and described with reference to the figures. Fig. 1 schematically shows a DC network with a device for regulating the potential level, Fig. 2 schematically shows a first embodiment of a potential position of DC conductors with an exemplary earth current profile, Fig. 3 schematically shows a second embodiment of a potential position of DC conductors, Fig. 4 schematically shows a third embodiment of a potential position of DC conductors, Fig. 5 schematically shows a fourth embodiment of a potential position of DC conductors, Fig. 6 schematically shows a fifth embodiment of a potential position of DC conductors.

[0024] The same reference numerals are used throughout the figures to refer to identical or similar elements. Representations in the figures may not be to scale. Character description

[0025] In Fig. Figure 1 schematically shows a device 10 for regulating the potential level of a first DC conductor DC+ and a second DC conductor DC-. A rectifier 20 can convert electrical AC power from an AC network 12 into electrical DC power and transmit it to the DC conductors DC+ and DC-.

[0026] A DC grid 30 comprises the device 10, the DC conductors DC+, DC-, DC switch 18, a fuse 24, and an electrolyzer 14. The electrolyzer 14 has several so-called electrolysis stacks 16 connected in series. Each electrolysis stack 16 has at least one electrolysis cell in which the desired electrolysis process takes place. The electrolysis can, for example, be the electrolysis of water to produce hydrogen and oxygen. The electrolyzer 14 is supplied with electrical DC power via the DC conductors DC+, DC-, which is drawn from the AC grid 12 via the rectifier 20. The AC grid 12 can be, for example, a public supply grid. The AC grid 12 can be single-phase or multi-phase. The AC grid 12 can be grounded or ungrounded.

[0027] The device 10 regulates the potential level of the two DC conductors DC+, DC- in a first operating mode so that both have the same polarity with respect to ground potential GND. The device is therefore designed to carry out a method which regulates the potential level of the two DC conductors DC+, DC- in a first operating mode so that both have the same polarity with respect to ground potential GND. For this purpose, the device 10 has a semiconductor switch 22 which is clocked by the device. The semiconductor switch establishes a connection to ground potential GND either between the first DC conductor DC+ or the second DC conductor DC-. This connection is clocked, i.e. the semiconductor switch 22 is opened and closed according to a duty cycle 26 so that the flowing current can be adjusted by the duty cycle 26 of the clocking.The timing of the semiconductor switch 22 can be such that the potential position of the two DC conductors DC+, DC- relative to each other and relative to ground potential GND can be specifically adjusted.

[0028] At the same time, the flowing current is optionally measured via an ammeter A. Using ammeter A, the device can measure the current flowing through the semiconductor switch and, if necessary, open the DC switches, for example, to disconnect the electrolyzer 14 from the rectifier 20. A fuse 24 additionally protects the DC network 30 against excessive ground currents.

[0029] A second operating mode is implemented alternatively to the first operating mode. The operation of the DC grid 30 can alternate between the first operating mode and the second operating mode. In the second operating mode, the potentials of the first and second DC conductors DC+, DC- are regulated such that the electrolysis process can be carried out in the electrolyzer 14. Electrical power is transferred from the AC grid 12 to the electrolyzer 14 via the DC conductors DC+, DC- to carry out the electrolysis. The voltage applied to the electrolyzer 14, which corresponds to the potential difference between the first DC conductor DC+ and the second DC conductor DC-, is greater than a starting voltage of the electrolyzer 14 and corresponds, for example, to an operating voltage of the electrolyzer 14.

[0030] If the DC network 30 with the electrolyzer 14 is operated on an AC network 12, which is designed as a TN network, then in the second operating mode the voltage of the first DC conductor DC+ and the second DC conductor DC- is symmetrical with respect to ground potential GND when the DC network 30 is connected via the rectifier 20 to the AC network 12, which is designed, for example, as a TN network, for example, as a star-grounded AC network 12. As a result, the second DC conductor DC- has a negative voltage with respect to ground GND. This negative voltage can cause negatively charged ions to flow to ground, thereby degrading the electrolyzer 14 due to a PID effect and potentially significantly reducing its service life. As in Fig. If, as shown in Figure 1, several electrolysis stacks 16 are connected in series to form a string, this effect can be significantly increased.

[0031] Even if the electrolyzer 14 is connected to a galvanically isolated AC grid 12, for example, an IT grid, via a rectifier, a PID effect can be observed. Here, too, a voltage can arise between the two DC conductors DC+ and DC- in the second operating mode if their potential is symmetrical or approximately symmetrical with respect to ground potential GND. The PID effect can therefore occur in various types of AC grids 12, such as TN grids or IT grids.

[0032] The described device 10 and the described method offer the advantage that in the first operating mode such a PID effect can be reduced, reduced or even reversed.

[0033] In Fig. Figure 2 shows an example of a further embodiment of the potential position of the first DC conductor DC+ and the second DC conductor DC- in the second operating mode. The second operating mode can be used alternately with the first operating mode. The following describes how the method and device 10 can function as a ground current monitor in the second operating mode.

[0034] In this embodiment, the DC network 30 is supplied via the rectifier 20 from a galvanically isolated AC network 12, for example, an IT network. One of the DC conductors, in the example shown, the second DC conductor DC-, is grounded. The first DC conductor is regulated to a potential level such that the voltage between the conductors is high enough to operate the electrolysis in the electrolyzer 14.

[0035] By grounding one DC conductor, in this case the second DC conductor DC-, the PID effect can be reduced or eliminated. Which of the two DC conductors, DC+ and DC-, is grounded may depend, for example, on the type of rectifier 20 used.

[0036] Shown is the middle graph of Fig. 2 a possible course of the duty cycle 26 of the clocking of the semiconductor switch 22. In the lower graph of Fig. 2 shows a possible course of the earth current 28.

[0037] By means of the method and the device for regulating the potential level, the potential level is controlled by clocking the semiconductor switch 22, as shown in the upper graph of Fig. 2. To maintain the potential level, the timing must be adjusted over time, for example due to a fault, and the ground current 28 increases, for example due to the fault. If the ground current 28 reaches the first threshold 32, the timing is stopped and, for example, the electrolyzer 14 is disconnected from the rectifier 20 by opening the DC switch 18. If the ground current 28 continues to rise, for example due to the severity of the fault, the fuse 24 trips, for example when the threshold 34 is reached.

[0038] In Fig. Figure 3 shows a first exemplary embodiment of a first sub-mode of the first operating mode. The potential for ground GND and the potential corresponding to a maximum DC voltage 36 for the DC grid 30 are shown.

[0039] The potential of the first DC conductor DC+ and the second DC conductor DC- are regulated by device 10 so that they are both positive relative to ground potential GND. Thus, both have a positive polarity relative to ground potential GND.

[0040] The potential difference between the first DC conductor DC+ and the second DC conductor DC- is regulated so that the voltage applied to the electrolyzer 14 is below a threshold voltage. The threshold voltage is below a threshold voltage of the electrolyzer 14, so that no electrolysis takes place in the electrolyzer 14 in the first sub-operating mode. The threshold voltage can, for example, be in a range between 10% and 50% of the threshold voltage.

[0041] Since no electrolysis takes place in the electrolyzer 14 in the first sub-mode of operation, the DC conductors DC+, DC- of the DC grid 30 can be separated from the AC grid 12 in the first sub-mode of operation. This also makes it possible to implement the first sub-mode of operation regardless of the type of AC grid 12. The first sub-mode of operation is therefore possible for different types of AC grid 12, for example, a TN grid or an IT grid.

[0042] If the DC network 30 is separated from the AC network in the first sub-operating mode, the electrical power used to regulate the potential position can be obtained from an auxiliary power supply 21 of the DC network 30.

[0043] In Fig. 4 shows a second embodiment of the first sub-operating mode of the first operating mode.

[0044] The potential of the first DC conductor DC+ and the second DC conductor DC- are regulated by device 10 so that they are both negative relative to ground potential GND. Thus, both have a negative polarity relative to ground GND.

[0045] The potential difference between the first DC conductor DC+ and the second DC conductor DC is regulated so that the voltage applied to the electrolyzer 14 is below the threshold voltage. The threshold voltage is below a threshold voltage of the electrolyzer 14, so that no electrolysis takes place in the electrolyzer 14 in the first sub-mode of operation. The threshold voltage can, for example, be in a range between 10% and 50% of the threshold voltage.

[0046] Since no electrolysis takes place in the electrolyzer 14 in the first sub-mode of operation, the DC conductors DC+, DC- of the DC grid 30 can also be separated from the AC grid 12 in the first sub-mode of operation. This also allows the first sub-mode of operation to be implemented independently of the type of AC grid 12. The first sub-mode of operation is therefore possible for various types of AC grid 12, for example, a TN grid or an IT grid.

[0047] If the DC network 30 is separated from the AC network in the first sub-operating mode, the electrical power used to regulate the potential position can be obtained from an auxiliary power supply 21 of the DC network 30.

[0048] In Fig. Figure 5 shows a first embodiment of the second sub-mode of operation of the first operating mode. In the second sub-mode, the electrolyzer 14 is supplied with electrical power from the AC grid 12 via the rectifier 20 to carry out the electrolysis process in the electrolyzer 14.

[0049] The potential of the first DC conductor DC+ and the second DC conductor DC- are regulated by device 10 so that they are both positive relative to ground potential GND. Thus, both have a positive polarity relative to ground potential GND.

[0050] The potential difference between the first DC conductor DC+ and the second DC conductor DC- in the second sub-operating mode is regulated such that, in the second sub-operating mode, the potential difference between the first DC conductor DC+ and the second DC conductor DC- corresponds to an operating voltage of the electrolyzer 14. At least the potential difference between the first DC conductor DC+ and the second DC conductor DC- corresponds approximately to the operating voltage of the electrolyzer 14, and such that the electrolysis process can take place in the electrolyzer 14.

[0051] In Fig. Figure 6 shows a second embodiment of the second sub-operating mode of the first operating mode. In the second sub-operating mode, the electrolyzer 14 is supplied with electrical power from the AC grid 12 via the rectifier 20 to carry out the electrolysis process in the electrolyzer 14.

[0052] The potential of the first DC conductor DC+ and the second DC conductor DC- are regulated by device 10 so that they are both negative relative to ground potential GND. Thus, both have a negative polarity relative to ground potential GND.

[0053] The potential difference between the first DC conductor DC+ and the second DC conductor DC- in the second sub-operating mode is regulated such that, in the second sub-operating mode, the potential difference between the first DC conductor DC+ and the second DC conductor DC- corresponds to an operating voltage of the electrolyzer 14. At least the potential difference between the first DC conductor DC+ and the second DC conductor DC- corresponds approximately to the operating voltage of the electrolyzer 14, and such that the electrolysis process can take place in the electrolyzer 14. Reference symbol 10 Device 12 AC network 14 Electrolyzer 16 electrolysis stack 18 DC switches 20 rectifiers 21 Auxiliary power supply 22 clocked semiconductor switches 24 Security 26 Duty cycle semiconductor switch 28 Earth current 30 DC network 32 first threshold 34 second threshold 36 maximum DC voltage A ammeter DC+, DC- DC conductor GND ground potential

Claims

[1] Method for regulating the potential position of a first and a second DC conductor (DC+, DC-), wherein the DC conductors (DC+, DC-) are provided for supplying an electrolyzer (14) with electrical power and the electrical power can be transferred from an AC network (12) to the DC conductors (DC+, DC-) via a rectifier (20), wherein in a first operating mode the potential position of the first and the second DC conductor (DC+, DC-) is regulated such that both DC conductors (DC+, DC-) have the same polarity with respect to earth potential (GND). [2] Method according to claim 1, wherein the potential position in the first operating mode is controlled such that both DC conductors (DC+, DC-) have a positive polarity with respect to ground potential (GND). [3] Method according to claim 1, wherein the potential position in the first operating mode is controlled such that both DC conductors (DC+, DC-) have a negative polarity with respect to ground potential (GND). [4] Method according to claim 1, 2 or 3, wherein the first operating mode has a first sub-operating mode in which the potential difference between the first and second DC conductors (DC+, DC-) is controlled such that the voltage applied to the electrolyzer (14) is below a threshold voltage. [5] Method according to claim 4, wherein the threshold voltage depends on a starting voltage of the electrolyzer (14), wherein the threshold voltage is in particular in a range between 10% and 50% of the starting voltage. [6] Method according to claim 4 or 5, wherein the DC conductors (DC+, DC-) are separated from the AC network (12) in the first sub-operating mode. [7] Method according to one of claims 4 to 6, wherein the electrical power used to regulate the potential position is obtained from an auxiliary power supply (21). [8] Method according to one of the preceding claims, wherein the first operating mode has a second sub-operating mode in which the electrolyzer (14) is supplied with electrical power from the AC network (12) via the rectifier (20) to carry out an electrolysis process, wherein in the second sub-operating mode a potential difference between the first and second DC conductors (DC+, DC-) is regulated as a function of the electrolysis process. [9] Method according to claim 8, wherein in the second sub-operating mode the potential difference between the first and second DC conductors (DC+, DC-) depends on an operating voltage of the electrolyzer. [10] Method according to one of the preceding claims, wherein a second operating mode is provided in which the first or the second DC conductor (DC+, DC-) is earthed, wherein the electrolyzer (14) is supplied with electrical power from the AC network (30) via the rectifier (20) for carrying out the electrolysis process and wherein in the second operating mode the potential difference between the first and second DC conductors (DC+, DC-) is regulated as a function of the electrolysis process. [11] Method according to one of the preceding claims, wherein the regulation of the potential position takes place via the clocking of a semiconductor switch (22) which is arranged between the first DC conductor (DC+) and the ground potential (GND) or between the second DC conductor (DC-) and the ground potential (GND). [12] Method according to claim 11, wherein a ground current (28) flowing via the semiconductor switch (22) is monitored. [13] Method according to one of the preceding claims, wherein the respective potential of each of the two DC conductors (DC+, DC-) has a minimum distance from earth potential (GND). [14] Device (10) for regulating the potential position of a first and a second DC conductor (DC+, DC-), wherein the DC conductors (DC+, DC-) are provided for supplying an electrolyzer (14) with electrical power and the electrical power can be transferred from an AC network (12) to the DC conductors (DC+, DC-) via a rectifier (20), wherein the device (10) is designed to regulate the potential position of the first and the second DC conductor (DC+, DC-) in a first operating mode such that both DC conductors (DC+, DC-) have the same polarity with respect to ground potential (GND). [15] Device according to claim 14, wherein the device (10) is arranged to regulate the potential position in the first operating mode such that both DC conductors (DC+, DC-) have a positive polarity with respect to ground potential (GND). [16] Device according to claim 14, wherein the device (10) is arranged to regulate the potential position in the first operating mode such that both DC conductors (DC+, DC-) have a negative polarity with respect to ground potential (GND). [17] Device according to claim 14, 15 or 16, wherein the device (10) is designed to clock a semiconductor switch (22) for regulating the potential position, which is arranged between the first DC conductor (DC+) and the ground potential (GND) or between the second DC conductor (DC-) and the ground potential (GND). [18] Device according to one of claims 14 to 17, wherein the device (10) is designed to monitor a ground current (28) flowing via the semiconductor switch (22). [19] DC network (30) comprising an electrolyzer (14), a device (10) according to one of claims 14 to 18, and the first and second DC conductors (DC+, DC-). [20] DC network (30) according to claim 19, further comprising an auxiliary power supply (21) for supplying the device (10) with electrical power as needed.

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