METHOD FOR OPERATING AN ELECTROLYZER, CONNECTION CIRCUIT, RECTIFIER CIRCUIT, AND ELECTROLYSIS SYSTEM FOR CARRYING OUT THE METHOD

Abstract

The application describes a method for operating an electrolyzer to generate hydrogen from water using an electrolysis reaction, supplied with power from an AC grid via an actively controlled rectifier circuit. The method includes operating the electrolyzer in a normal operating mode with an input voltage U.sub.EI above a no-load voltage U.sub.LL with predominantly ohmic behavior, operating the electrolyzer in a standby operating mode with an input voltage U.sub.EI below the no-load voltage U.sub.LL with predominantly capacitive behavior, and transitioning from the standby operating mode to the normal operating mode during a first transition duration Δt.sub.1, wherein the first transition duration Δt.sub.1 is reduced by keeping the input voltage U.sub.EI at the electrolyzer input during the standby operating mode above a first voltage threshold value U.sub.TH,1 different from 0 V. The application furthermore describes a connection circuit, an actively controlled rectifier circuit and an electrolysis system for performing the method.

Claims

1. A method for operating an electrolyzer configured to generate hydrogen from water via an electrolysis reaction, and that is supplied with power from an AC voltage (AC) grid via an actively controlled rectifier circuit, comprising: operating the electrolyzer in a normal operating mode with an input voltage U.sub.EI applied thereto that is above a no-load voltage U.sub.LL of the electrolyzer, operating the electrolyzer in a standby operating mode with an input voltage U.sub.EI applied thereto that is below the no-load voltage U.sub.LL of the electrolyzer, and transitioning from the standby operating mode to the normal operating mode during a first transition duration Δt.sub.1, wherein the first transition duration Δt.sub.1 is dictated by keeping the input voltage U.sub.EI at an input of the electrolyzer during the standby operating mode above a non-zero first voltage threshold value U.sub.TH,1.

2. The method as claimed in claim 1, wherein the first voltage threshold value U.sub.TH,1 corresponds to a value of at least 80% of the no-load voltage U.sub.LL.

3. The method as claimed in claim 1, wherein the input voltage U.sub.EI at the input of the electrolyzer in the standby operating mode is kept at least 5% below the no-load voltage U.sub.LL of the electrolyzer.

4. The method as claimed in claim 1, further comprising: transitioning from the normal operating mode to the standby operating mode during a second transition duration Δt.sub.2, wherein the second transition duration Δt.sub.2 is dictated by keeping the input voltage U.sub.EI at the input of the electrolyzer during the standby operating mode above the non-zero first voltage threshold value U.sub.TH,1.

5. The method as claimed in claim 1, wherein the input voltage U.sub.EI of the electrolyzer in the standby operating mode is kept above the first voltage threshold value U.sub.TH,1 by connecting the input of the electrolyzer to a DC converter output of an AC/DC converter within the actively controlled rectifier circuit in a clocked manner via a precharging resistor and/or an inductor.

6. The method as claimed in claim 5, wherein the clocked connection of the input of the electrolyzer to the DC converter output is implemented using a two-point control.

7. The method as claimed in claim 5, wherein a minimum DC voltage U.sub.W,min at the DC converter output of the AC/DC converter is above the no-load voltage U.sub.LL of the electrolyzer.

8. The method as claimed in claim 1, wherein the electrolyzer is additionally operated in a maintenance operating mode under specified boundary conditions, wherein in the maintenance operating mode the input voltage U.sub.EI of the electrolyzer is below a hazardous voltage value.

9. The method as claimed in claim 1, wherein the electrolyzer is assigned to a consumer facility and wherein operation of the electrolyzer and/or operation of components that supply electric power to the electrolyzer is controlled via a control circuit of the consumer facility that performs energy management.

10. The method as claimed in claim 9, wherein at least one change between the normal operating mode and the standby operating mode of the electrolyzer takes place during a calculation period with an aim of ensuring that a maximum energy ΔE agreed between the consumer facility and an energy supplier for the calculation period is not exceeded.

11. A connection circuit between a DC source and an electrolyzer, comprising: an input having two input connections configured to connect the connection circuit to the DC source, and an output having two output connections configured to connect the connection circuit to an input of the electrolyzer, a series connection of a precharging resistor and a circuit breaker or a series connection of an inductor and a circuit breaker, wherein the series connection connects one of the input connections to a corresponding one of the two output connections, a further circuit breaker arranged in parallel with the precharging resistor, or the inductor, or in parallel with the series connection, a measuring device configured to determine a voltage difference between a DC voltage U.sub.EI present at the output and a DC voltage U.sub.Q present at the input, and a control circuit configured to control the circuit breaker and the further circuit breaker of the connection circuit, wherein the connection circuit is configured to operate the electrolyzer in conjunction with the DC source or in conjunction with the DC source and a control circuit of a consumer facility that performs energy management, wherein the connection circuit is configured to: operate the electrolyzer in a normal operating mode with an input voltage U.sub.EI applied thereto that is above a no-load voltage U.sub.LL of the electrolyzer, operate the electrolyzer in a standby operating mode with an input voltage U.sub.EI applied thereto that is below the no-load voltage U.sub.LL of the electrolyzer, and transition from the standby operating mode to the normal operating mode during a first transition duration Δt.sub.1, wherein the first transition duration Δt.sub.1 is dictated by keeping the input voltage U.sub.EI at the input of the electrolyzer during the standby operating mode above a non-zero first voltage threshold value U.sub.TH,1.

12. The connection circuit as claimed in claim 11, wherein the circuit breaker comprises a semiconductor switch or an electromagnetic switch, or both.

13. The connection circuit as claimed in claim 11, wherein the further circuit breaker comprises an electromechanical switch or a combination of the electromechanical switch connected in parallel with a semiconductor switch.

14. The connection circuit as claimed in claim 11, wherein the series connection is formed via the circuit breaker and the inductor, and wherein the connection circuit further comprises a DC/DC converter.

15. An actively controlled rectifier circuit configured to supply power to an electrolyzer from an AC grid having an AC voltage, comprising: an AC input having multiple input connections for a connection to the AC grid and a DC output having two output connections for a connection to the electrolyzer, an AC/DC converter having a converter circuit that comprises semiconductor switches with freewheeling diodes connected in antiparallel therewith, and a rectifier control circuit configured to drive the semiconductor switches of the rectifier circuit, wherein the rectifier circuit additionally comprises a connection circuit, comprising: an input having two input connections configured to connect the connection circuit to a DC-source that is formed by a DC converter output of the AC/DC converter that is connected with its AC input to the AC grid, and an output having two output connections configured to connect the connection circuit to an input of the electrolyzer, a series connection of a precharging resistor and a circuit breaker or a series connection of an inductor and a circuit breaker, wherein the series connection connects one of the input connections to a corresponding one of the two output connections, a further circuit breaker arranged in parallel with the precharging resistor, or the inductor, or in parallel with the series connection, a measuring device configured to determine a voltage difference between a DC voltage U.sub.EI present at the output and a DC voltage U.sub.Q present at the input, and a control circuit configured to control the circuit breaker and the further circuit breaker of the connection circuit, wherein the connection circuit is configured to operate the electrolyzer in conjunction with the DC-source and a control circuit of a consumer facility that performs energy management, wherein the connection circuit is configured to: operate the electrolyzer in a normal operating mode with an input voltage U.sub.EI applied thereto that is above a no-load voltage U.sub.LL of the electrolyzer, operate the electrolyzer in a standby operating mode with an input voltage U.sub.EI applied thereto that is below the no-load voltage U.sub.LL of the electrolyzer, and transition from the standby operating mode to the normal operating mode during a first transition duration Δt.sub.1, wherein the first transition duration Δt.sub.1 is dictated by keeping the input voltage U.sub.EI at the input of the electrolyzer during the standby operating mode above a non-zero first voltage threshold value U.sub.TH,1.

16. The actively controlled rectifier circuit as claimed in claim 15, wherein the series connection of the connection circuit is formed by the circuit breaker and the precharging resistor and the rectifier circuit comprises a single-stage rectifier circuit.

17. The actively controlled rectifier circuit as claimed in claim 15 having a connection circuit as claimed in claim 13, such that the rectifier circuit comprises a two-stage rectifier circuit that comprises a DC/DC converter arranged between the AC/DC converter and the DC output of the rectifier circuit.

18. An electrolysis system comprising an actively controlled rectifier circuit as claimed in claim 15 and an electrolyzer connected to the actively controlled rectifier circuit on an output side thereof.

19. The electrolysis system as claimed in claim 18, comprising a signalling apparatus that is configured to signal a current operating mode of the electrolyzer, and wherein the electrolysis system additionally comprises a blocking apparatus that is configured to prevent touching of live components of the electrolysis system in the standby operating mode and optionally also in the normal operating mode.

20. The electrolysis system as claimed in claim 18, wherein the electrolysis system comprises a part of a consumer facility that is controlled via a control circuit of the consumer facility that performs energy management.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0030] The disclosure is illustrated below with the aid of figures. In the figures

[0031] FIG. 1 shows one embodiment of an electrolysis system according to the disclosure;

[0032] FIG. 2a shows a first embodiment of a connection circuit according to the disclosure;

[0033] FIG. 2b shows a second embodiment of a connection circuit according to the disclosure;

[0034] FIG. 3 shows a circuit topology of an AC/DC converter of the actively controlled rectifier circuit according to the disclosure in one embodiment;

[0035] FIG. 4 shows a temporal profile of an input voltage U.sub.EI at the input of the electrolyzer according to one embodiment of the method according to the disclosure.

DETAILED DESCRIPTION

[0036] FIG. 1 illustrates one embodiment of an electrolysis system 60 according to the disclosure. The electrolysis system 60 contains an actively controlled rectifier circuit 30 that is connected to an AC voltage grid (AC grid) 20 at its AC input 33 via a transformer 31. A DC output 34 of the rectifier circuit 30 is connected to an input 41 of an electrolyzer 40. The actively controlled rectifier circuit 30 comprises an AC disconnection circuit 35, a filter circuit 36 for reducing/damping the propagation of high-frequency interfering signals in the AC grid 20, and an AC/DC converter 37. The AC/DC converter 37 is circuitry configured to convert an AC voltage with the amplitude .Math..sub.37 present at an AC converter input 37.1 into a DC voltage U.sub.W present at a DC converter output 37.2. For this purpose, semiconductor switches of the AC/DC converter 37 are driven appropriately by a rectifier control circuit 39. The rectifier control circuit 39 is also able to drive the AC disconnection circuit 35, and possibly also other components of the rectifier circuit 30 or of the electrolysis system 60. A connection circuit 1 according to the disclosure is arranged between the DC converter output 37.2 and the DC output 34 of the rectifier circuit and is connected to the DC converter output 37.2 at its input 5 and to the DC output 34 of the rectifier circuit 30 at its output 6. The connection circuit 1 additionally comprises a control circuit 7 for driving its components, which control circuit is embodied in one embodiment as part of the rectifier control circuit 39 in FIG. 1, by way of example. As an alternative, however, it is also possible for the rectifier control circuit 39 and the control circuit 7 of the connection circuit 1 each to be embodied as separate control circuits. The electrolysis system 60 additionally comprises a signalling circuit, device, or apparatus 42 for signalling a current operating mode of the electrolyzer 40. It may additionally optionally comprise a blocking apparatus (not illustrated in FIG. 1), which prevents people coming into contact with live components of the electrolysis system 60 in the standby operating mode and/or in the normal operating mode of the electrolyzer 40.

[0037] With the connection circuit 1 according to the disclosure, which is explained in more detail in one embodiment in FIG. 2, the rectifier circuit 30 is configured as a rectifier circuit according to the disclosure and configured to control operation of the electrolyzer 40 in accordance with the method according to the disclosure. The electrolyzer 40 may in this case be operated in a normal operating mode with an input voltage U.sub.EI above its no-load voltage U.sub.LL. In the normal operating mode, an electrolysis reaction takes place in the electrolyzer 40, for example, a decomposition of water into its components, hydrogen and oxygen, wherein the electrolyzer 40 essentially behaves like an ohmic consumer. In this case, a speed of the electrolysis reaction is controlled by means of the rectifier circuit 30 by varying the input voltage U.sub.EI of the electrolyzer 40. The electrolyzer 40 may additionally be operated below the no-load voltage U.sub.LL in a standby operating mode in which there is no, but at least no significant electrolysis reaction, and thus no—at least no significant—electric power consumption of the electrolyzer 40.

[0038] In order then to achieve a small value of a first transition duration Δt.sub.1 from the standby operating mode to the normal operating mode (e.g., a quick transition), as well as a small value of a second transition duration Δt.sub.2 from the normal operating mode to the standby operating mode, the input voltage U.sub.EI of the electrolyzer 40 is kept above a first threshold value U.sub.TH,1 different from 0 V in the standby operating mode as well. The first threshold value U.sub.TH,1 may be selected in one embodiment such that it is 80%, preferably 90%, of the no-load voltage U.sub.LL of the electrolyzer 40. The input voltage U.sub.EI should however advantageously not exceed a value of 95% of the no-load voltage of the electrolyzer according to one embodiment. The first transition duration Δt.sub.1, as well as the second transition duration Δt.sub.2, may thereby be limited to a value of 1 s to a few seconds. By means of such a dynamic change in the operating states, the electrolysis system 60 is able to be efficiently integrated into an energy management system of a consumer facility, for example, an industrial plant, that comprises the electrolysis system 60.

[0039] The transformer 31 and also the rectifier circuit 30 in FIG. 1 are illustrated in one embodiment as a three-phase rectifier circuit 30 by way of example. As an alternative thereto, however, it is also possible for the AC grid, the transformer 31 and also the rectifier circuit 30 to be embodied as single-phase components and each have a phase conductor and a neutral connection. It is also possible for them to have a different number of phase conductors, for example, two phase conductors. Within the scope of the disclosure, a direct connection of the rectifier circuit 30 to the AC grid 20 without the interposition of the transformer 31 is also possible.

[0040] FIG. 2a illustrates a first embodiment of a connection circuit 1 according to the disclosure. The connection circuit 1 comprises an input 5 having two input connections 5.1, 5.2 for the connection of a DC source 10, and an output 6 having two output connections 6.1, 6.2 for the connection of the electrolyzer 40. The DC source 10 may, in one embodiment, be an AC/DC converter 37 connected to an AC grid 20 on the input side. One of the input connections 5.1, 5.2 of the connection circuit 1 is connected to a corresponding one of the output connections 6.1, 6.2 via a series connection of a precharging resistor 2 and a circuit breaker 3. A further circuit breaker 4 is arranged in parallel with the series connection. The connection circuit 1 additionally comprises a measuring circuit or device 8 having a voltage sensor 9.2 for detecting a DC voltage U.sub.EI present at the output 6 and thus also at the electrolyzer 40, and a further voltage sensor 9.2 for detecting a DC voltage U.sub.Q present at the input 5. The measuring circuit or device 8 additionally has a current sensor 9.1 for detecting a current I(t) flowing via the output 6. The circuit breaker 3 and the further circuit breaker 4 are controlled by the control circuit 7 of the connection circuit 1. The control circuit 7 is additionally configured to communicate with the measuring circuit or device 8 and to drive the measuring circuit or device 8, which is symbolized by a control line illustrated in dashed form.

[0041] In the normal operating mode of the electrolyzer 40, the further circuit breaker 4 of the connection circuit 1 is permanently closed, such that the electrolyzer 40 is connected with low resistance to the DC source 10. The circuit breaker 3 may in this case be open or likewise closed. In the standby operating mode of the electrolyzer 40, the further circuit breaker 4 is permanently open. The circuit breaker 3 is closed and opened again in a clocked manner. The clocked opening and closing of the circuit breaker 3 may in this case take place depending on the detected DC voltage U.sub.EI present at the output 6, and thus present at the input 41 of the electrolyzer 40. It is thereby possible to implement a two-point control of the input voltage U.sub.EI of the electrolyzer 40, which leads to a temporal profile of the input voltage U.sub.EI of the electrolyzer, as will be explained in more detail in connection with FIG. 4.

[0042] FIG. 2b illustrates a second embodiment of the connection circuit 1 according to the disclosure, which has many features in common with the first embodiment of the connection circuit according to FIG. 2a. The differences from the first embodiment of the connection circuit are therefore mainly explained below, while reference is made to the explanations under FIG. 2a for the features in common.

[0043] According to the second embodiment, the connection circuit 1 is embodied as a DC/DC converter, for example, as a buck converter 14. In this case, the first input connection 5.1 of the connection circuit 1 is connected to the corresponding output connection 6.1 via a series connection of the circuit breaker 3 and an inductor 11. The circuit breaker 3 is designed, in FIG. 2b, as an actively controllable semiconductor switch and is driven by the control circuit 7. The connection circuit 1 furthermore has a further semiconductor switch 12 that connects a connection point 13 between the circuit breaker 3 and the inductor 11 to the other input connection 5.2 of the connection circuit 1. In FIG. 2b, the further semiconductor switch 12 is configured as an actively controllable semiconductor switch that is likewise driven by the control circuit 7. As an alternative thereto, however, it is also possible for the further semiconductor switch 12 to be embodied as a diode. The further circuit breaker 4 of the connection circuit 1 is designed as an electromechanical circuit breaker and is arranged in parallel with the series connection of the circuit breaker 3 and the inductor 11.

[0044] During the standby operating mode of the electrolyzer 40, the DC voltage U.sub.Q present at the input 5 is able to be converted into a DC voltage U.sub.EI present at the output 6 through appropriate driving of the circuit breaker 3 and the further semiconductor switch 12. The further circuit breaker 4 is in this case permanently open and the output voltage U.sub.EI is kept above the first voltage threshold value U.sub.TH,1 through clocked operation of the circuit breaker 3 and the further semiconductor switch 12. During the normal operating mode, the further circuit breaker 4 is permanently closed, such that the first input connection 5.1 is connected with low impedance to the first output connection 6.1. The further semiconductor switch 12 is permanently open in the normal operating mode.

[0045] FIG. 3 illustrates one embodiment of an AC/DC converter 37 of the actively controlled rectifier circuit 30 from FIG. 1. In a manner corresponding to the rectifier circuit 30 from FIG. 1, the AC/DC converter 37 is configured, for example, as a three-phase AC/DC converter 37 without a separate neutral connection and comprises a converter circuit 50 having a total of three bridge branches 51. Each of the bridge branches 51 has two series-connected semiconductor switches 52, each of which is assigned a freewheeling diode 53 connected in antiparallel. The freewheeling diode 53 may be an intrinsic diode of the respective semiconductor switch 52, or a separate diode. The semiconductor switches 52 may be MOSFET or IGBT semiconductor switches, for example. In a manner corresponding to the three-phase embodiment of the converter circuit 50, the AC converter input 37.1 of the AC/DC converter 37 comprises three input connections, which are each connected to a connection point 54 of the two semiconductor switches 52 of the bridge branch 51 assigned thereto. The DC converter output 37.2 of the AC/DC converter 37 comprises a positive (+) and a negative (−) output connection.

[0046] The AC/DC converter 37 is configured, when converting power, to transport active power P(t) from its AC converter input 37.1 to its DC converter output 37.2, and possibly also in the opposite direction from its DC converter output 37.2 to its AC converter input 37.1. The AC/DC converter 37 may additionally be configured to exchange reactive power Q(t) between the AC converter input 37.1 of the AC/DC converter 37 and an AC grid 20 (not illustrated explicitly in FIG. 3) connected to the AC converter input 37.1. For the purpose of the power conversion, the semiconductor switches 52 are appropriately driven by the rectifier control circuit 39 (not shown explicitly in FIG. 3) of the rectifier circuit. A level of the converted DC voltage U.sub.W, in other words the DC voltage range, may in this case adopt values between a minimum DC voltage U.sub.W,min and a maximum DC voltage U.sub.W,max. The minimum DC voltage U.sub.W,min is limited via the freewheeling diodes 53 to a value that—apart from a forward voltage of the freewheeling diodes 53—corresponds to the amplitude U.sub.37 of the AC voltage present at the AC converter input 37.1. On account of the freewheeling diodes 53, the converter circuit 50 is thus able to generate a DC voltage U.sub.W at the DC converter output 37.2 that is larger, but not smaller, at least not significantly smaller than the amplitude .Math..sub.37 of the AC voltage present on the input side. The conversion losses in this case increase as the ratio of the DC voltage U.sub.W present on the output side to the amplitude .Math..sub.37 of the AC voltage present on the input side increases. In order then to reduce the conversion losses at high DC voltages, the AC voltage at the AC converter input 37.1, and thus also the minimum DC voltage at the DC converter output 37.2, may be above the no-load voltage U.sub.LL of the electrolyzer. This may be achieved, for example, through an appropriate design of a transformer 31 by way of which the AC/DC converter 37 is connected to the AC grid 20.

[0047] FIG. 3 shows one example of a two-level converter circuit 50 having only two voltage levels. However, a converter circuit 50 having more than two voltage levels, for example a three-level or five-level converter circuit, is also possible within the scope of the disclosure. It is furthermore possible, within the scope of the disclosure, for the converter circuit to be configured as a center tap circuit. In this case, an output connection, for example the negative output connection (−), of the DC converter output 37.2 may be connected to a center tap of a transformer 31 connected to the AC converter input 37.1. As an alternative, the negative output connection (−) may also be connected to a neutral conductor of the AC grid 20.

[0048] FIG. 4 illustrates a temporal profile of the input voltage U.sub.EI of the electrolyzer 40 during a transition from its standby operating mode to its normal operating mode according to one embodiment of the method according to the disclosure. FIG. 4 also illustrates temporal profiles of the input voltage UES as may occur in the standby operating mode chronologically before the transition and in the normal operating mode chronologically after the transition using the connection circuit 1 from FIG. 2a, for example.

[0049] In the standby operating mode, the input voltage U.sub.EI as a function of time has a sawtooth-like profile that moves between a lower limit value—formed from the first voltage threshold value U.sub.TH,1—and an upper limit value. The upper limit value is in this case chosen such that it corresponds to 95% of the no-load voltage U.sub.LL of the electrolyzer 40. The sawtooth-like profile results from clocked closing and opening of the circuit breaker 3 with a permanently open further circuit breaker 4 of the connection circuit 1. It comprises temporary charging phases of the electrolyzer 40 during which the input voltage U.sub.EI rises. In this case, a capacitor assigned to the electrolyzer 40 is charged by means of the closed circuit breaker 3 of the connection circuit 1 and a current I(t) enabled thereby flowing through the precharging resistor 2. The rises in the input voltage U.sub.EI are each followed by discharging phases having voltage decreases associated therewith. The voltage decreases result from a leakage current within the electrolyzer 40 that cannot be completely prevented. In FIG. 4, the illustrated gradient of the voltage decreases is of a purely exemplary nature and may, depending on the level of the leakage current that occurs, also turn out to be significantly lower than illustrated in FIG. 4.

[0050] At the time to, it is signalled to the actively controlled rectifier circuit 30, for example, by an energy management system of a consumer facility comprising the electrolysis system 60, that the electrolyzer 40 should be put into its normal operating mode. For this purpose, the further circuit breaker 4 of the connection circuit 1 is closed and the electrolyzer 40 is connected with low resistance to the DC source 10, formed from the AC/DC converter 37 with the AC grid 20 connected upstream. At the same time, the semiconductor switches 52 of the AC/DC converter 37 are driven via the rectifier control circuit 39 such that the AC/DC converter 37 has a DC voltage at the DC converter output 37.2 that corresponds to a setpoint voltage value U.sub.EI,Soll that is desirable in the normal operating mode for its input voltage. Since the input voltage U.sub.EI of the electrolyzer 40 is already close to the no-load voltage U.sub.LL in the standby operating mode, only a significantly reduced voltage change is required until reaching the voltage setpoint value U.sub.EI,Soll, and therefore also only significantly reduced charge transport into the electrolyzer 40 is required. The first transition duration Δt.sub.1 between the standby operating mode and the normal operating mode is therefore significantly reduced in relation to precharging of the electrolyzer that takes place from 0 V. The same applies analogously to the second transition duration Δt.sub.2 during a transition from the normal operating mode to the standby operating mode of the electrolyzer 40.

[0051] If, instead of the first embodiment of the connection circuit 1, the second embodiment according to FIG. 2b is used, then this results in a similar temporal profile as illustrated in FIG. 4. However, the sawtooth-like profile in the standby operating mode may have extremely small and negligible voltage differences, meaning that an approximately temporally constant DC voltage is able to be set there.