WO2025026628A1 - Method for operating a supply unit of an electrolyzer, supply unit, and electrolysis system - Google Patents

Abstract

The invention relates to a method for operating a supply unit (20) for an electrolyzer (10), having the steps of: - monitoring the insulation resistance (R_Iso) in a series connection of electrolysis cells (11) associated with the electrolyzer (10), wherein - if the insulation resistance (R_Iso) falls below a first threshold (R_TH,1) in a state in which a power converter (25) of the supply unit (20) is electrically connected to the electrolyzer (10), the power converter (25) of the supply unit (20) and the electrolyzer (10) are electrically disconnected in order to prevent a supply of power to the electrolyzer (10), and the supply unit (20) is converted to a fault state in which reconnection of the power converter (25) of the supply unit (20) and the electrolyzer (10) is suppressed and only enabled again after a fault-free state is confirmed, and - the supply unit (20) is prevented from being converted to the fault state if the insulation resistance (R_Iso) falls below the first threshold (R_TH,1) in a state in which the power converter (25) of the supply unit (20) is electrically disconnected from the electrolyzer (10). The invention also relates to a supply unit (20) for electrically supplying an electrolyzer (10) and to an electrolysis system (100).

Description

METHOD FOR OPERATING A SUPPLY UNIT OF AN ELECTROLYSER, SUPPLY UNIT AND ELECTROLYSIS SYSTEM

technical field

The invention relates to a method for operating a supply unit for an electrolyzer. The invention further relates to a supply unit designed for the method and an electrolysis plant with such a supply unit.

State of the art

In order to produce hydrogen from water using an electrolysis reaction, electrolysis systems are known in which an electrolyzer is supplied with electrical power from a power supply network via a power converter. Such electrolyzers are usually operated as direct current (DC) consumers during the electrolysis reaction and, depending on their size and design, can have nominal outputs of up to several 10 MW. The power converter can be used to specifically set a hydrogen production rate, i.e. the amount of hydrogen produced per unit of time. For this purpose, the power converter can be operated with a current setting at its DC connection connected to the electrolyzer. Depending on the design of the electrolyzer, an electrical DC voltage associated with the current set is applied to the DC connection of the electrolyzer and thus also to the DC connection of the power converter. The DC voltage usually increases with increasing hydrogen production rate and can assume values in the range between a few 100 V and 1500 V.

For safety reasons, it may be necessary, and in some cases even required by standards, to monitor a DC circuit comprising the electrolyzer and the DC connection of the power converter for a possible earth fault. For this purpose, a so-called ISO monitor can be used, for example, which permanently detects an insulation resistance Riso in the DC circuit. If the insulation resistance Riso in the DC circuit falls below a predefined threshold value, this is interpreted as an earth fault. In principle, the electrolyzer and the power converter supplying it in a previously unearthed DC circuit would still be functional even if there was a maximum of one earth fault in the DC circuit, and the electrolysis could also take place with the maximum of one existing Earth faults can continue. However, dangerous DC voltages compared to earth potential could occur in the DC circuit, so that contact with live components of the electrolysis system could result in personal injury. Due to this risk, an earth fault, even if it is a maximum of one earth fault in a previously unearthed DC circuit, is normatively classified as a critical fault in which a power flow from the power converter to the electrolyzer must be suppressed, for example by electrically isolating the power converter from the electrolyzer. In addition, if an earth fault has occurred in the DC circuit, it may be required to specifically prevent the power converter from being reconnected to the electrolyzer and only to allow it to be reconnected when a test, for example an on-site test by a specialist, confirms sufficient insulation in the DC circuit and the fault, in particular its elimination, is explicitly acknowledged.

However, particularly in the case of water electrolysis, it is apparent that the insulation resistance Riso of the electrolyzer - and thus the insulation resistance of the DC circuit - to earth potential is significantly dependent on its operating point. Factors such as flow rate, water pressure, amount of current supplied and hydrogen production rate play a significant role. For example, it has been observed that the insulation resistance Riso increases with increasing hydrogen production rate and sometimes decreases rapidly when hydrogen production is stopped, for example due to a deliberate stop. Even after a deliberate stop of the electrolysis, the insulation resistance Riso can temporarily drop so low that it falls below a threshold value effective for insulation monitoring, which causes the power converter to be permanently blocked. For safety reasons, the power converter can then only be reconnected to the electrolyzer after testing and confirmation that the system is error-free, e.g. after acknowledging the error. The insulation resistance Riso only drops temporarily, especially when the electrolysis is deliberately stopped, before rising again. A subsequent check of the system with an acknowledgement of the error, which must usually be done in order to restart the system, is complex. The publication DE 10 2020 121 593 A1 discloses a device for electrolysis from photovoltaically generated direct current power with an electrolyzer and a direct current converter. The direct current converter is designed to supply the electrolyzer with direct current power generated by a photovoltaic sub-generator via a DC bus. The sub-generator is connected to the direct current converter via a first isolating switch, wherein closing the first isolating switch requires a successful test for sufficient insulation of the sub-generator. The sub-generator has a main string, wherein a second isolating switch is arranged between the main string and the first isolating switch, which is coupled to a monitoring of a fault current of the main string in such a way that if a predeterminable limit value of the fault current is exceeded, the second isolating switch is opened. A method for operating a device for electrolysis from photovoltaically generated direct current power is also disclosed.

task of the invention

The invention is based on the object of specifying an improved method for operating a supply unit for an electrolyzer, which eliminates the disadvantages listed above, or at least reduces them. It is also the object of the invention to show a supply unit suitable for carrying out the method, as well as an electrolysis system with such a supply unit.

Solution

The object of demonstrating an improved method for operating a supply unit for an electrolyzer is solved by the subject matter of independent patent claim 1. The object of demonstrating a supply unit suitable for the method is solved by the subject matter of independent claim 8. The object of demonstrating an electrolysis system with such a supply unit is solved by the subject matter of claim 14. Advantageous embodiments of the method are given in claims 2 to 7. Advantageous embodiments of the supply unit are listed in claims 9 to 13. Description

A method for operating a supply unit for an electrolyzer comprises the steps:

Monitoring an insulation resistance of a series connection of electrolysis cells assigned to the electrolyzer, wherein, if the insulation resistance falls below a first threshold value in a state in which a power converter of the supply unit is electrically connected to the electrolyzer, the electrical connection between the power converter of the supply unit and the electrolyzer is severed in order to prevent power from being supplied to the electrolyzer, and the supply unit is transferred to a fault state in which a renewed connection of the power converter of the supply unit and the electrolyzer is suppressed and only released again after confirmation of a fault-free state, and wherein the transfer of the supply unit to the fault state is prevented if the insulation resistance falls below the first threshold value in a state in which the power converter of the supply unit is electrically separated from the electrolyzer.

The term "fall below" particularly characterizes the act of falling below the limit value, i.e. a change in the insulation resistance from a value above or at the level of the first threshold value to a value immediately below the first threshold value, and not the possibly longer-lasting state during which the insulation resistance is less than the first threshold value. Accordingly, the feature "if the insulation resistance falls below the first threshold value" also particularly characterizes the point in time at which the first threshold value is fallen below, and not the period of time during which the insulation resistance is less than the first threshold value. Therefore, the feature "if the insulation resistance falls below the first threshold value in a state in which the power converter of the supply unit is electrically separated from the electrolyzer" is to be understood in such a way that at the point in time at which the insulation resistance passes the first threshold value downwards, a state exists in which the Power converter is electrically separated from the electrolyzer, in particular galvanically separated. In concrete terms, this prevents the supply unit from entering the fault state if the insulation resistance only passes through the first threshold value after the power converter has already been electrically separated, in particular galvanically separated, from the electrolyzer. It may be that at the time of the electrical separation of the supply unit from the electrolyzer, the insulation resistance was still greater than or equal to the first threshold value.

In a corresponding manner, the feature "if the insulation resistance falls below a first threshold value in a state in which the power converter of the supply unit is electrically connected to the electrolyzer" is to be understood as meaning that at the time at which the insulation resistance passes the first threshold value downwards, a state exists in which the power converter is electrically connected to the electrolyzer, in particular galvanically and low-impedance connected.

A supply unit for the electrical supply of an electrolyzer has: an input for connecting a network, in particular an electrical supply network, an output for connecting the electrolyzer, a power converter which can be connected to the output via a separation unit and is designed to convert a power flowing via the input into a power flowing via the output, and a control unit for controlling the supply unit, in particular the power converter and the separation unit, wherein the supply unit comprises or can be connected to a measuring device for determining an insulation resistance of a series connection of electrolysis cells assigned to the electrolyzer, wherein the control unit is designed to operate the supply unit in a state connected to the electrolyzer according to the method according to one of the preceding claims. The method and the supply unit make it possible to ensure that the power converter of the supply unit can be reconnected to the electrolyzer without manual release after being disconnected from the electrolyzer if the insulation resistance of the electrolyzer has only fallen below the first threshold value due to the electrical separation of the power converter from the electrolyzer and the associated stopping or termination of the electrolysis process. The cause of the drop in insulation resistance can be determined by the method and the supply unit, and the supply unit can be prevented from entering the fault state if the insulation resistance is only undercut at a time when the power converter is already disconnected from the electrolyzer. The dependence of the insulation resistance on the operating point of the electrolyzer and/or the supply unit can thus be taken into account when the supply unit enters the fault state. In particular, it can be taken into account that the insulation resistance can fall below the first threshold value even without an actual fault, in particular an actual earth fault, and in particular temporarily, if the supply unit is already in a state in which it is separated from the electrolyzer. At the same time, operational reliability can continue to be guaranteed because the supply unit continues to be transferred to the fault state if the insulation resistance falls below the first threshold value in other operating states, for example the normal operating state with an electrical connection between the power converter of the supply unit and the electrolyzer, and when the electrolysis process is ongoing.

The electrolysis plant has the electrolyzer and the supply unit.

Confirmation of an error-free state can be done, for example, by activating a confirmation unit on the supply unit.

The supply unit of the electrolyzer can supply the electrolyzer with electrical DC power (DC direct current) from an electrical supply network. The electrical supply network can have a DC network or an AC network (AC alternating current). The supply unit can have a DC circuit on its output side for this purpose. In particular, the DC circuit can through the output of the supply unit and its connection to the electrolyzer and the electrolyzer. The insulation resistance of the electrolyzer can therefore correspond to the insulation resistance of the DC circuit, which is formed by the electrical connection of the output side of the supply unit and the electrolyzer. The insulation resistance refers to the electrical resistance of the DC circuit to earth potential. For an electrolysis system, a high insulation resistance is aimed for, which corresponds to the best possible electrical insulation of the electrolyzer and thus of the DC circuit to earth potential.

Advantageous embodiments are specified in the following description and the subclaims, the features of which can be used individually and in any combination with one another.

In one embodiment of the method, the transfer of the supply unit into the fault state is prevented if an electrolysis process taking place in the electrolyzer is intentionally and not due to a fault ended by separating the electrolyzer from the power converter of the supply unit. This can further improve the method, since only those separations of the electrolyzer from the power converter of the supply unit that were carried out by deliberate action, e.g. by an operator, prevent the fault state from being entered. In this embodiment, fault-related separations then continue to lead to the fault state being entered and/or the supply unit being transferred into the fault state.

In embodiments of the method, the deliberate and non-error-related termination of the electrolysis process triggers the expiration of a predefined period of time. The assumption of the error state by the supply unit or the transfer of the supply unit to the error state can only be prevented within the predefined period of time. After the expiration of the predefined period of time, the error state can then be assumed. The assumption of the error state after the expiration of the predefined period of time can then take place automatically or depend on additional conditions.

In this embodiment, it is possible, for example, to bridge a short-term, i.e. temporary, drop in the insulation resistance without the supply unit assuming the fault state or being transferred to it. In one embodiment of the method, the supply unit is transferred to the fault state if, after the time period has elapsed, the insulation resistance falls below a second threshold value. The supply unit does not enter the fault state if, after the time period has elapsed, the insulation resistance is equal to or greater than the second threshold value. The second threshold value can be identical to the first threshold value or different from the first threshold value. The second threshold value can therefore be equal to, greater than, or smaller than the first threshold value. This embodiment allows the entry into the fault state to be controlled even more precisely. In particular, it can be taken into account that if the electrolysis process is deliberately stopped and not due to a fault, the insulation resistance only drops briefly and then increases again.

In one embodiment of the method, an error state assumed by the supply unit is communicated by a communication unit and/or signaled visually and/or via an audio signal using a signaling device. In embodiments, the supply unit has a signaling device for signaling the error state and/or a communication unit for communicating the error state. This makes it possible for the state of the supply unit - i.e. its error state or its error-free state - to be recognizable from outside the supply unit. The communication unit can be designed for wired and/or wireless communication, in particular also via the Internet.

In one embodiment of the method, a third threshold value is provided which is smaller than the first threshold value. The supply unit is transferred to the fault state if the insulation resistance falls below the third threshold value in addition to the first threshold value, even if the power converter of the supply unit and the electrolyzer are in the electrically separated state. This embodiment makes it possible to take into account that a fault state can also exist or occur even if the electrolyzer and supply unit are separated. In this case, however, the insulation resistance drops below the third threshold value if there is an actual fault, in particular an actual ground fault, in the electrolyzer. The method monitors the first threshold value in an electrically connected state between the power converter of the supply unit and the electrolyzer. The method monitors the second threshold value after the time period has elapsed in an electrically separated state between the power converter of the supply unit and the electrolyzer. The method monitors the third threshold value in an electrically separated state between the power converter of the supply unit and the electrolyzer. The third threshold value is therefore preferably selected so that it is also lower than the second threshold value.

In one embodiment of the method, the first threshold value is selected such that, for a DC voltage that is present between the electrolyzer's DC lines at a nominal power of the electrolyzer, a current that flows from the DC lines to earth potential via an insulation resistance at the level of the first threshold value does not exceed a value of 600 mA. The DC lines are connected to the two DC inputs of the electrolyzer. The electrolyzer is supplied with direct electrical power from the supply unit via the DC inputs. The DC lines are connected to the output of the supply unit.

In one embodiment of the supply unit, its input for connecting a DC network is designed as an electrical supply network and the power converter has a DC/DC converter. In another embodiment of the supply unit, its input for connecting an AC network is designed as an electrical supply network and the power converter has an AC/DC converter. Depending on the design of the supply unit, the electrolyzer can therefore be supplied with direct electrical power from a DC network or from an AC network. In embodiments, the supply unit can also be designed in such a way that it enables both: supplying the electrolyzer from a DC network and/or supplying the electrolyzer from an AC network.

In one embodiment, the supply unit has a confirmation unit. By actuating the confirmation unit, a fault-free state of the supply unit and/or of an electrolysis system comprising the supply unit, in particular its DC circuit, which is formed by the output of the supply unit, the electrolyzer and the DC lines, can be confirmed. The actuation unit can also be used by maintenance personnel to confirm the elimination of a previously reported fault, in particular the elimination of a previously reported earth fault in the electrolysis system. The confirmation unit can also be used to confirm that the electrolysis system is in a fault-free state.

In one embodiment of the supply unit, the measuring device is designed to locate an earth fault within the series connection of electrolysis cells. The measuring device has one or more voltage sensors for this purpose. The measuring device detects an earth fault when it detects that the insulation resistance is below a predeterminable earth fault threshold value. An earth fault corresponds to a very small or too small insulation resistance.

Short description of the characters

In the following, embodiments of this application are further explained and described using figures. They show

Fig. 1 schematically shows an embodiment of an electrolysis plant;

Fig. 2 schematically shows another embodiment of the electrolysis plant;

Fig. 3 schematically shows an embodiment of a part of a measuring device

Fig. 4 schematically shows a method for operating a supply device for an electrolyzer.

The same reference symbols are used in the figures for identical or similar elements. Representations in the figures may not be to scale.

character description

Fig. 1 shows an embodiment of an electrolysis system 100. The electrolysis system 100 has an electrolyzer 10 and a supply unit 20. The electrolyzer 10 has a plurality of electrolysis cells 11 connected in series. Within the series connection of all electrolysis cells 11, series connections with a smaller number of electrolysis cells 11 are combined to form a so-called electrolysis stack 12, wherein the plurality of electrolysis stacks 12 are in turn connected in series with one another via DC lines 2c. The electrolysis cells 11 and/or the electrolysis stacks 12 are usually surrounded by nearby housing components which are earthed, for example for protection reasons, i.e. connected to earth potential PE.

The series connection of the electrolysis stacks 12 has two external electrolysis stacks 12 and several internal electrolysis stacks 12. The positive pole of one of the two external electrolysis stacks 12 is connected via a positive DC line 2a to the positive pole at the output 21 of the supply unit 20. The negative pole of another of the two external electrolysis stacks 12 is connected via a negative DC line 2b to the negative pole at the output 21 of the supply unit 20. The supply unit 20 has a separation unit 24 and a power converter 25. The separation unit 24 is designed and configured to connect the electrolyzer 10 to the power converter 25 and to separate the electrolyzer 10 from the power converter 25.

The power converter 25 converts electrical power provided by a network 30 into direct electrical power. The electrolyzer 10 is supplied with electrical power for the electrolysis process via the power converter 25. The electrolyzer 10 is, for example, a hydrogen electrolyzer.

In the embodiment shown in Fig. 1, the network 30 is designed as an AC network 30a. The power converter 25 is designed as an AC/DC converter 25a, which converts electrical AC power from the AC network 30a into electrical DC power for the electrolyzer 10.

The supply unit 20 further comprises a control unit 27, which in particular controls the power converter 25 and the separation unit 24. The control of the power converter 25 comprises, for example, the control of semiconductor switches of an inverter bridge of the AC/DC converter 25a. The control of the separation unit 24 comprises, for example, opening and closing separation switches of the separation unit 24 in order to connect the power converter 25 to the electrolyzer 10 or to separate it from the electrolyzer 10.

The positive DC line 2a has a positive partial insulation resistance R _P with respect to earth potential PE. The negative DC line 2a has a negative partial insulation resistance R _n with respect to earth potential PE. The DC Connecting lines 2c between two adjacent electrolysis stacks 12 can have a respective partial insulation resistance with respect to ground potential PE (not explicitly shown in Fig. 1). The total insulation resistance Riso of the DC circuit, which is formed by the electrolyzer 10, the DC lines 2a, 2b, the DC connecting lines 2c and the output 21 of the supply unit 20, in other words the insulation resistance Riso of the series connection of the electrolysis cells 11 assigned to the electrolyzer 10, results from a parallel connection of all partial insulation resistances R _P , R _n . Both the positive DC line 2a and the negative DC line 2b can optionally have a respective fuse 51, which triggers, for example, in the event of a fault when the current is too high. The DC connecting lines 2c between the individual electrolysis stacks 12 can also optionally have a respective fuse 52, which triggers, for example. B. in the event of a fault, it is triggered by excessive currents. To indicate that the fuses 51, 52 are optional components, the fuses 51, 52 are shown in dashed lines in Fig. 1.

The positive partial insulation resistance R _P and the negative partial insulation resistance R _n can be recorded using a measuring device 40, and the total insulation resistance Riso of the DC circuit can be determined from this. The measuring device 40 can also be used to record the earth voltages U1, U2, U3, U4, i.e. the voltages relative to earth potential PE that are present on the individual DC connecting lines 2c between the electrolysis stacks 12. The measuring device 40 can thus be used to detect an earth fault 60 in one of the electrolysis stacks 12, which is indicated by the insulation resistance Riso of the DC circuit falling below one or more predefined threshold values. The location of the earth fault 60 can also be localized, or at least approximately localized, using the earth voltages U1, U2, U3, U4, using the measuring device 40. An actual earth fault 60 divides the entire series connection of the electrolysis stacks 12 into two substrings 13a, 13b. The DC connecting lines 2c of one substring 13a have predominantly positive earth voltages U1, U2, while the DC connecting lines 2c of the other substring 13b have predominantly negative earth voltages U3, U4.

In the embodiment of the electrolysis system 100 in Fig. 1, the supply unit 20 has the measuring device 40 for determining the insulation resistance Riso of the electrolyzer 10 or the series connection of its Electrolysis cells 11. Alternatively or additionally, the measuring device 40 can be connected to the electrolyzer 10 in order to determine the insulation resistance Riso of the electrolyzer 10 or the series connection of its electrolysis cells 11. The measuring device 40 can determine the insulation resistance Riso using the positive partial insulation resistance R _P , the negative partial insulation resistance R _n and ground voltages U1 , U2 , U3 , U3 of the DC connecting lines 2c between the electrolysis stacks 12. By means of the measuring device 40, for example, a ground fault 60 in the electrolysis stack 12 can be detected, which would divide the series connection of the electrolysis cells 11 into two substrings 13a, 13b. The location of the earth fault 60 within the series connection of the electrolysis cells can also be determined, or at least approximately determined, via the earth voltages U1, U2, U3, U4 by means of the measuring device 40.

The network 30 is connected to an input 22 of the supply unit 20. The electrolyzer 10 is connected to the output 21 of the supply unit 20. The input 22 is designed to connect the AC network 30a. The supply unit 20 also has a signaling device for signaling a fault state and/or a communication unit 28 for communicating a fault state of the supply unit 20 and/or the electrolyzer 10 and/or the electrolysis system 100. The fault state can be triggered, for example, by a ground fault 60. The supply unit 20 also has a confirmation unit 29 for confirming a fault-free state of the supply unit 20 and/or the electrolyzer 10 and/or the electrolysis system 100.

The control unit 27 is designed to operate the supply unit 20 in a state connected to the electrolyzer 10. The power converter 25 of the supply unit 20 is connected to the electrolyzer 10 via the separation unit 24. The control unit 27 is designed to set a DC power flowing via the output 21 of the supply unit 20 in the direction of the electrolyzer by controlling semiconductor switches of the power converter 25. It is also designed to control the separation unit 24 of the supply unit 20 in order to electrically connect the power converter 25 of the supply unit 20 to the electrolyzer 10 and/or to electrically separate them from one another. The supply unit 20 is operated in such a way that the insulation resistance Riso of the electrolyzer 10 or the series connection of its electrolysis cells 11 is monitored. If the insulation resistance Riso falls below a first threshold value RTH when the separation unit 24 is closed, i.e. when the power converter 25 is electrically connected to the electrolyzer 10, the isolating switches of the separation unit 24 are opened and the electrical connection between the power converter 25 of the supply unit 20 and the electrolyzer 10 is severed. This can occur, for example, if an earth fault 60 occurs in the electrolyzer during the electrolysis process. By opening the separation unit 24, further power supply from the supply unit 20 to the electrolyzer 10 is reliably prevented.

Furthermore, the supply unit 20 is then transferred to an error state. In the error state, a renewed connection of the power converter 25 of the supply unit 20 and the electrolyzer 10 is suppressed and only made possible again after confirmation of an error-free state, which can be checked, for example, by maintenance personnel of the electrolysis system 100. Confirmation of the error-free state can be carried out via the confirmation unit 29. If, however, the insulation resistance Riso falls below the first threshold value RTH when the separation unit 24 is open, i.e. when the power converter 25 is electrically separated from the electrolyzer 10, the transfer of the supply unit 20 to the error state is prevented. This can occur, for example, in a case in which an electrolysis process is deliberately stopped or ended, and as a result the first threshold value RTH is only briefly undershot, before rising again to a value greater than or equal to the first threshold value RTH. In this case, no explicit confirmation of the error-free state via the confirmation unit 29 is required for a renewed connection of the power converter 25 of the supply unit 20 to the electrolyzer 10.

The supply unit 20 can, for example, be operated according to the method described with reference to Fig. 4.

Fig. 2 shows a further embodiment of the electrolysis system 100. The electrolysis system 100 comprises the electrolyzer 10 and the supply unit 20. The electrolyzer 10 comprises a plurality of series-connected Electrolysis cells 11. Within the series connection of all electrolysis cells 11, series connections with a smaller number of electrolysis cells 11 are combined to form an electrolysis stack 12, with the multiple electrolysis stacks 12 in turn being connected in series with one another via the DC connecting lines 2c. The electrolysis cells 11 and/or the electrolysis stacks 12 are usually surrounded by nearby housing components which are grounded, i.e. connected to earth potential, for example for protection reasons.

The series connection of the electrolysis stacks 12 has two external electrolysis stacks 12 and one or more internal electrolysis stacks 12. The positive pole of one of the two external electrolysis stacks 12 is connected via the positive DC line 2a to the positive pole at the output 21 of the supply unit 20. The negative pole of another of the two external electrolysis stacks 12 is connected via the negative DC line 2b to the negative pole at the output 21 of the supply unit. The supply unit 20 has the separation unit 24 and the power converter 25. The separation unit 24 is designed and configured to connect the electrolyzer 10 to the power converter 25 and to separate the electrolyzer 10 from the power converter 25.

The power converter 25 converts electrical power provided by the network 30 into direct electrical power. The electrolyzer 10 is supplied with electrical power for the electrolysis process via the power converter 25. The electrolyzer 10 is, for example, a hydrogen electrolyzer.

In the embodiment shown in Fig. 2, the network 30 is designed as a DC network 30b. The power converter 25 is designed as a DC/DC converter 25b, which converts electrical power from the DC network 30b into electrical DC power for the electrolyzer 10. The DC/DC converter 25b can be designed for step-up operation in order to convert a DC voltage applied to the input 22 of the supply unit 20 into a higher DC voltage applied to the output 21. Alternatively, the DC/DC converter 25b can be designed for step-down operation in which a DC voltage applied to the input 22 is converted into a smaller DC voltage applied to the output 21. Alternatively, it is also possible that the DC/DC converter is designed for both boost and buck operation.

The supply unit 20 further comprises the control unit 27, which in particular controls the power converter 25 and the separation unit 24. The control of the power converter 25 includes, for example, the control of semiconductor switches of a bridge circuit of the DC/DC converter 25b. The control of the separation unit 24 includes, for example, the opening and closing of the separation switches of the separation unit 24 in order to connect the power converter 25 to the electrolyzer 10 or to disconnect it from the electrolyzer 10.

The positive DC line 2a has the positive partial insulation resistance R _P with respect to ground potential PE. The negative DC line 2a has the negative partial insulation resistance R _n with respect to ground potential PE. The DC connecting lines 2c between two adjacent electrolysis stacks 12 can also have a respective partial insulation resistance with respect to ground potential PE (not explicitly shown in Fig. 2). The total insulation resistance Riso of the DC circuit, which is formed by the electrolyzer 10, the DC lines 2a, 2b, the DC connecting lines 2c and the output 21 of the supply unit 20, i.e. the insulation resistance Riso of the series connection of the electrolysis cells 11 assigned to the electrolyzer 10, results from a parallel connection of all partial insulation resistances R _P , R _n . Both the positive DC line 2a and the negative DC line 2b can optionally have a respective fuse 51, which e.g. B. triggers in the event of a fault if the current is too high. The DC connecting lines 2c between the individual electrolysis stacks 12 can also optionally have a respective fuse 52, which e.g. triggers in the event of a fault if the current is too high. To indicate that the fuses 51, 52 are optional components, the fuses 51, 52 are shown in dashed lines in Fig. 2.

In the embodiment of the electrolysis system 100 in Fig. 2, the supply unit 20 has the measuring device 40 for determining the insulation resistance Riso of the electrolyzer 10 or the series connection of its electrolysis cells 11. Alternatively or additionally, the measuring device 40 can be connected to the electrolyzer 10 in order to determine the insulation resistance Riso of the electrolyzer or the series connection of its electrolysis cells 11. The measuring device 40 can thereby determine the insulation resistance Riso using the positive partial insulation resistance R _P , the negative partial insulation resistance R _n and the earth voltages U1 , U2, U3, U3 of the DC connecting lines 2c between the electrolysis stacks 12. Using the measuring device 40, for example, an earth fault 60 in one of the electrolysis stacks 12 can be detected, which would divide the series connection of the electrolysis cells 11 into two substrings 13a, 13b. Using the earth voltages U1 , U2, U3, U4, the location of the earth fault 60 within the series connection of the electrolysis cells 11 can also be determined, or at least approximately determined, using the measuring device 40.

The network 30 is connected to the input 22 of the supply unit 20. The electrolyzer 10 is connected to the output 21 of the supply unit 20. The input 22 is designed to connect the DC network 30b. The supply unit 20 also has a signaling device for signaling an error state and/or a communication unit 28 for communicating the error state of the supply unit 20 and/or the electrolyzer 10 and/or the electrolysis system 100. The error state can be triggered, for example, by a ground fault 60. The supply unit 20 also has a confirmation unit 29 for confirming an error-free state of the supply unit 20 and/or the electrolyzer 10 and/or the electrolysis system 100.

The control unit 27 is designed to operate the supply unit 20 in a state connected to the electrolyzer 10. The power converter 25 of the supply unit 20 is connected to the electrolyzer 10 via the separation unit 24. The control unit 27 is designed to set a DC power flowing via the output 21 of the supply unit 20 in the direction of the electrolyzer 10 by controlling semiconductor switches of the power converter 25. It is also designed to control the separation unit 24 of the supply unit 20 in order to electrically connect the power converter 25 of the supply unit 20 to the electrolyzer 10 and/or to electrically separate them from one another.

The supply unit 20 is operated in such a way that the insulation resistance Riso of the electrolyzer 10 or the series connection of its electrolysis cells 11 is monitored. If the insulation resistance Riso falls below the first threshold value RTH when the isolating unit 24 is closed, i.e. when the power converter 25 is electrically connected to the electrolyzer 10, the isolating switches of the Separating unit 24 is opened and the electrical connection between the power converter 25 of the supply unit 20 and the electrolyzer 10 is severed. This can occur, for example, if an earth fault 60 occurs in the electrolyzer during the electrolysis process. By opening the separating unit 24, the further supply of power from the supply unit 20 to the electrolyzer 10 is safely prevented.

Furthermore, the supply unit 20 is then transferred to the error state. In the error state, a renewed connection of the power converter 25 of the supply unit 20 and the electrolyzer 10 is suppressed and only enabled again after confirmation of the error-free state, which can be checked, for example, by maintenance personnel of the electrolysis system 100. Confirmation of the error-free state can be carried out via the confirmation unit 29.

If, however, the insulation resistance Riso falls below the first threshold value RTH when the separation unit 24 is open, i.e. when the power converter 25 is electrically separated from the electrolyzer 10, the transfer of the supply unit 20 to the fault state is prevented. This can occur, for example, in a case in which an electrolysis process is deliberately stopped or ended and, as a result, the first threshold value RTH is only briefly undershot, before rising again to a value that is greater than or equal to the first threshold value RTH. In this case, no explicit confirmation of the fault-free state via the confirmation unit 29 is required for a renewed connection of the power converter 25 of the supply unit 20 to the electrolyzer 10.

The supply unit 20 can, for example, be operated according to the method described with reference to Fig. 4.

Fig. 3 schematically shows an embodiment of a part of the measuring device 40. The measuring device 40 as a whole is designed both for detecting and for locating the earth fault 60 within the electrolyzer 10. In concrete terms, however, Fig. 3 only shows that part of the measuring device 40 with which the earth fault 60 can be located or approximately located. The detection of whether an earth fault 60 is present in the electrolyzer 10 at all can be carried out using Application of known methods and is not explicitly shown in Fig.3.

The part of the measuring device 40 shown in Fig. 3 has one or more connections 41.1 - 41.4 for the respective connection of a DC connecting line 2c and a connection 43 for the connection to earth potential PE. The part of the measuring device 40 shown in Fig. 3 also has one or more voltage sensors 42.1 - 42.4, by means of which the voltage between the respective DC connecting lines 2c and earth potential PE can be determined. For this purpose, the respective voltage sensors 42.1 - 42-4 are arranged to measure the voltage between the respective connections 41.1 - 41.4 and the connection 43 assigned to the earth potential PE. The respective earth voltages U1, U2, U3, U4 can be detected via the voltage sensors 42.1 - 42.4. By comparing the respective ground voltages U1, U2, U3, U4 with one another, the ground fault 60 can be localized or approximately localized within the series connection of the electrolysis cells 11. Specifically, the ground fault 60 is usually located near the DC connecting line 2c that has the lowest absolute value of the ground voltage. By determining the lowest absolute value of the ground potentials U1 - U4 and the DC connecting line assigned to this absolute value, it can therefore be determined between which electrolysis cells 11 and/or between which electrolysis stacks 12 the ground fault 60 is located.

Fig. 4 shows schematically an embodiment of a method for operating the supply device 20.

The process is started in S1. The starting point is a state of the electrolysis system 100 in which the separation unit 24 is in the open state and therefore the power converter 25 of the supply unit 20 is electrically separated from the electrolyzer 10. In S2, the insulation resistance Riso of the electrolyzer 10 is monitored. The electrolyzer 10 can comprise the series connection of electrolysis cells 11.

As long as it is detected in S3 that the insulation resistance Riso is less than the first threshold value RTH, branch “yes”, the monitoring is continued. The initially open state of the isolating unit 24 and thus the initial electrical separation between the power converter 25 and the electrolyzer 10 is maintained. If it is detected in S3 that the insulation resistance Riso is greater than or equal to the first threshold value RTH, branch "no", in S4 the electrolyzer 10 is connected to the power converter 25 of the supply unit 20 or - if the electrolyzer 10 is already connected to the power converter 25 - the connection between the electrolyzer 10 and the supply unit 20 is maintained. In S5 the power for the electrolyzer 10 is made available via the power converter 25 so that the electrolysis process can take place in the electrolyzer 10. A temporal rate of hydrogen production can be specified via a suitable control of the power flow into the electrolyzer 10 by the supply unit 20.

A deliberate stopping or deliberate termination of the electrolysis process can be signaled to the electrolysis system 100 via a stop command. If it is now detected in S6 that there is no stop command for the electrolysis system 100 (branch "no"), the electrolysis process is continued and the insulation resistance Riso of the electrolysis stack 12 is further monitored in S7. If it is detected in S8 that the insulation resistance Riso is greater than or equal to the first threshold value RTH (branch "no"), the system jumps to S4. The electrical connection between the power converter 25 and the electrolyzer 10 is maintained and the electrolysis process is continued.

If, however, it is detected in S8 that the insulation resistance Riso is smaller than the first threshold value RTH, branch "yes", it is concluded that the insulation resistance Riso has fallen below the first threshold value RTH AT a time when the power converter 25 was connected to the electrolyzer 10. This is interpreted by the control unit 27 as an actual earth fault 60. Consequently, in S8.1 the power converter 25 is deactivated and the electrolyzer 10 is separated from the power converter 25 of the supply unit by opening the separation unit 24 and the supply unit 20 is transferred to the error state in S13 or the supply unit 20 assumes the error state in S13. In concrete terms, the error state is assumed if there is no stop command during the electrolysis process and the insulation resistance Riso has fallen below the first threshold value RTH AT a time where there is an electrical connection between the power converter 25 of the supply unit 20 and the electrolyzer 10.

If it is detected in S6 that a stop command was present during the electrolysis process, branch "yes", i.e. the electrolyzer was deliberately stopped, the power converter 25 is deactivated in S9 and the power converter 25 of the supply unit 20 is separated from the electrolyzer 10 in S10 or such a separation, if it already exists, is maintained. In S11, the insulation resistance Riso of the electrolysis stack 12 is monitored.

If it is determined in S12 that the insulation resistance Riso detected in S11 is less than a third threshold value RTH,3 and/or if it is determined in S12 that the insulation resistance Riso detected in S11 is less than a second threshold value RTH,2 after a time period At has elapsed after leaving S6, branch "yes", it is concluded that an earth fault 60 is actually present and the supply unit 20 is transferred to the fault state in S13. The third threshold value RTH,3 can be less than the first threshold value RTH,I . In this case, the insulation resistance Riso detected in S11 is so small, even when the electrolysis process is deliberately terminated, that the fault state is assumed regardless of the state of the electrical connection between the electrolyzer 10 and the power converter 25 of the supply unit 20.

If, however, it is determined in S12 that the insulation resistance Riso is greater than or equal to the third threshold value RTH,3 and/or if it is determined in S12 that the insulation resistance Riso is greater than or equal to the second threshold value RTH,2 after the expiry of the time period At after leaving S6, branch "no", this is interpreted as only a short-term, temporary reduction in the insulation resistance Riso, which is accompanied by a renewed increase in the Riso and which can usually occur when the electrolysis process is deliberately terminated, in particular even without an actual earth fault 60. In this case, the system jumps to S14.

In S14, the system waits for a start command. Without a start command, branch "no", the system jumps from S14 to S10. In S10, the power converter 25 of the supply unit 20 is separated from the electrolyzer 10 or such a separation is maintained. If a start command is present, branch "yes", the system jumps to S4. The error state assumed by the supply unit 20 in S13 can be communicated by the communication unit 28 and/or signaled visually and/or via an audio signal by means of a signaling device.

The first threshold value RTH can be selected such that it depends on the nominal power of the electrolyzer 10. For example, the first threshold value RTH can be selected such that, at a voltage that is present between the positive and negative DC lines 2a, 2b of the electrolyzer 10 at a nominal power, a current that flows from the DC lines 2a, 2b via an insulation resistance Riso at the level of the first threshold value RTH against earth potential PE does not exceed a value of 600 mA.

The flow chart in Fig. 4 shows that the detection of the insulation resistance within the resulting loop runs takes place at successive points in time. However, the time intervals between two successive detections or between two successive determinations of the insulation resistance Riso can be so short that this is equivalent to continuous monitoring of the insulation resistance. In this respect, the method according to the invention also includes continuous monitoring of the insulation resistance Riso.

list of reference symbols

Claims

patent claims 1 . Method for operating a supply unit (20) for an electrolyzer (10) with the steps: Monitoring an insulation resistance (Riso) of a series connection of electrolysis cells (11) assigned to the electrolyzer (10), wherein, when the insulation resistance (Riso) falls below a first threshold value (RTH) in a state in which a power converter (25) of the supply unit (20) is electrically connected to the electrolyzer (10), the electrical connection between the power converter (25) of the supply unit (20) and the electrolyzer (10) is separated in order to prevent a power supply to the electrolyzer (10), and the supply unit (20) is transferred to a fault state in which a renewed connection of the power converter (25) of the supply unit (20) and the electrolyzer (10) is suppressed and only released again after confirmation of a fault-free state, and wherein the transfer of the supply unit (20) to the fault state is prevented when the insulation resistance (Riso) falls below the first threshold value (RTH) in a state in which the power converter (25) of the supply unit (20) is electrically separated from the electrolyzer (10). 2. Method according to claim 1, wherein the transfer of the supply unit (20) into the fault state is prevented if an electrolysis process running in the electrolyzer (10) is terminated intentionally and not due to a fault. 3. Method according to claim 2, wherein the deliberate and non-fault-related termination of the electrolysis process triggers the expiration of a predefinable time period (At), and wherein the supply unit (20) is prevented from entering the fault state within the predefinable time period (At). 4. Method according to claim 3, wherein the supply unit (20) is transferred to the fault state if, after expiration of the time period (At), the insulation resistance (Riso) falls below a second threshold value (RTH,2), and wherein the assumption of the fault state by the supply unit (20) is omitted if the insulation resistance (Riso) is equal to or greater than the second threshold value (RTH,2) after expiration of the time period (At). 5. Method according to one of the preceding claims, wherein an error state assumed by the supply unit (20) is communicated by a communication unit (28) and/or is signaled visually and/or via an audio signal by means of a signaling device. 6. Method according to one of the preceding claims, wherein a third threshold value (RTH,3) is provided which is smaller than the first threshold value (RTH ), and wherein the supply unit (20) is transferred to the fault state when the power converter (25) of the supply unit (20) and the electrolyzer (10) are in a separated state and the insulation resistance (Riso) also falls below the third threshold value (RTH,3). 7. Method according to one of the preceding claims, wherein the first threshold value (RTH ) is selected such that, at a voltage which is present between the DC lines (2a, 2b) of the electrolyzer (10) at a nominal power, a current which flows from the DC lines (2a, 2b) via an insulation resistance (Riso) at the level of the first threshold value (RTH ) to earth potential (PE) does not exceed a value of 600 mA. 8. Supply unit (20) for the electrical supply of an electrolyzer (10), comprising: an input (22) for connecting a network (30), an output (21) for connecting the electrolyzer (10), a power converter (25) which can be connected to the output (21) via a separating unit (24) and is designed to convert a power flowing via the input (23) into a power flowing via the output (21), and a control unit (27) for controlling the supply unit (20), in particular the power converter (25) and the separating unit (24), wherein the supply unit (20) comprises a measuring device (40) for determining an insulation resistance (Riso) of a series connection of electrolysis cells (11) assigned to the electrolyzer (10) or is connectable to this, and wherein the control unit (27) is designed to connect the supply unit (20) in a state according to the method of any one of the preceding claims. 9. Supply unit (20) according to claim 8, wherein the input (22) is designed for connection to a DC network (30b) and the power converter (25) has a DC/DC converter (25b). 10. Supply unit (1) according to claim 8, wherein the input (22) is designed for connection to an AC network (30a) and the power converter (25) has an AC/DC converter (25a). 11. Supply unit (20) according to one of claims 8 to 10, comprising a signaling device for signaling an error state and/or a communication unit (28) for communicating an error state. 12. Supply unit (20) according to one of claims 8 to 11, further comprising a confirmation unit (29) for confirming an error-free state of the supply unit (20) and/or the electrolysis system (100). 13. Supply unit (20) according to one of claims 8 to 12, wherein the measuring device (40) is designed to localize an earth fault (60) within the series connection of electrolysis cells (11) and for this purpose has one or more voltage sensors (42.1 - 42.4). 14. Electrolysis system (100) comprising an electrolyzer (10) and a supply unit (20) according to one of claims 8 to 13, which supplies the electrolyzer (10) from a network (30).