EP4150134A1

EP4150134A1 - Method for operating an electrolyzer, connection circuit, rectifier, and electrolysis system for carrying out the method

Info

Publication number: EP4150134A1
Application number: EP21725475.4A
Authority: EP
Inventors: Ralf Juchem; Alexander UNRU; Tobias Becker; Arno GERTH
Original assignee: SMA Solar Technology AG
Current assignee: SMA Solar Technology AG
Priority date: 2020-05-12
Filing date: 2021-05-10
Publication date: 2023-03-22
Also published as: DE102020112880A1; JP2023525117A; US20230045707A1; CN115552056B; CN115552056A; WO2021228770A1

Abstract

The invention relates to a method for operating an electrolyzer (40) which is designed to generate hydrogen from water by means of an electrolysis reaction and which is supplied by an AC voltage grid (AC - grid) (20) via an actively controlled rectifier (30), having the steps of: - operating the electrolyzer (40) with a largely ohmic behavior in a normal operating mode using an input voltage U_El above a no-load voltage U_LL, - operating the electrolyzer (40) with a largely capacitive behavior in a standby operating mode using an input voltage U_El below the no-load voltage U_LL, and - changing over from the standby operating mode to the normal operating mode during a first changeover duration Δt1, wherein the first changeover duration Δ_t1 is reduced in that the input voltage U_El at the input (41) of the electrolyzer (40) is kept above a first voltage threshold U_TH,1 differing from 0 V during the standby operating mode. The invention additionally relates to a connection circuit (1), to an actively controlled rectifier (30), and to an electrolysis system (60) for carrying out the method.

Description

_ WO 2021/228770 _ 1 liter _ PCT / EP2021 / 062341

Process for operating an electrolyzer, connection circuit, rectifier and electrolysis system for carrying out the process

Technical field of the invention

The invention relates to a method for operating an electrolyzer which is designed and set up to generate hydrogen from water by means of an electrolysis reaction, a connection circuit, a rectifier and an electrolysis system for carrying out the method

State of the art

Hydrogen is often generated using an electrolyser, which converts water into its elements hydrogen and oxygen by means of an electrolysis reaction. The electrolyser is supplied by an actively controlled rectifier from an alternating voltage network (AC network). An electrolyzer typically has a current-voltage characteristic curve which is divided into two areas via the so-called open circuit voltage ULL. Below the open circuit voltage ULL, the electrolyzer shows a predominantly capacitive behavior, which is caused by the formation of double layers on the electrodes of the electrolyzer. An electrolysis reaction does not yet take place at voltages below the open circuit voltage, or at least does not take place in a significant manner. At input voltages above the open circuit voltage ULL, the electrolyzer shows predominantly ohmic behavior, which is caused by the electrolysis reaction taking place at these voltages. The speed of the electrolysis reaction, and thus the rate of production of hydrogen, for example, is controlled via an input voltage of the electrolyzer and typically increases with increasing input voltage.

Rectifiers that have transistors, in particular insulated gate bipolar transistors (IGBT) or metal oxide field effect transistors (MOSFET) as actively controllable semiconductor switches, are increasingly being used as actively controlled rectifiers. A freewheeling diode is connected in anti-parallel to each of the transistors. The freewheeling diodes of the rectifier mean that a voltage range that can otherwise be set via the transistors at the DC converter output of the AC / DC converter is limited to a minimum DC voltage Uw, min. The limitation is mainly due to the fact that below the minimum DC _ WO 2021/228770 _ lÄl _ PCT / EP2021 / 062341 _

Voltage Uw, min at the output of the AC / DC converter at least one of the free-wheeling diodes has a conductive state, whereby a voltage applied on the anode side corresponds to a voltage applied on the cathode side of the free-wheeling diode except for a forward voltage of the free-wheeling diode. In addition, it is usually desired to supply the electrolyser with the lowest possible conversion losses on the part of the rectifier when the power consumption is close to its nominal power. The nominal output is to be understood here as the maximum output at which the electrolyzer can be operated continuously without damaging it. The nominal output can depend on various components of the electrolyser and their interaction with one another and is usually a manufacturer's specification.

The electrolysers in question usually have a large input voltage range between their open circuit voltage ULL and their nominal voltage. The nominal voltage is the voltage present at the input of the electrolyser at which the electrolyser is operated with its nominal power. If suitable measures, for example a suitable design of a transformer connected to an AC input of the rectifier, ensure that the minimum DC voltage Uw, min at the output of the AC / DC converter is below the no-load voltage ULL of the electrolyzer, so this is usually associated with high conversion losses of the actively controlled rectifier at high input voltages of the electrolyzer. The minimum DC voltage Uw, min is therefore often above the no-load voltage ULL of the electrolyzer, which, however, makes it more difficult for the electrolyzer to start up smoothly, as well as to slow it down gently.

When the electrolyzer is started, a considerable capacity of the electrolyzer must be charged. It is necessary to limit the current to a value during pre-charging in order to prevent damage to the freewheeling diodes. Specifically, the pre-charging takes place via a pre-charging resistor that limits the current. On the other hand, it is desirable to pre-charge the capacitance as quickly as possible, which requires the lowest possible resistance value. However, the lower the ohmic resistance, the higher its power loss and also its component costs. A break in, for example, hydrogen production is just over _ WO 2021/228770 _ IAl _ PCT / EP2021 / 062341 _ it is possible to separate the electrolyzer from the rectifier. However, due to leakage currents that cannot be completely suppressed, the electrolyzer discharges again - possibly significantly depending on the length of the pause - and has to be restarted. If the electrolyser is now operated within a consumer device, for example within an industrial company, such long charging and discharging times of the electrolyzer interfere and make efficient energy management of the consumer device more difficult. Specifically, under the given conditions it is not, at least with difficulty, possible to include the electrolyser in an energy management of the consumer device. For example, it is desirable to shorten, for example, hydrogen production as part of peak load shaving of the consumer device in a calculation period in order to instead continue it in the subsequent calculation period. This requires a precharge time in the range of a few seconds, advantageously for example a maximum of 2 s.

A backup power supply for an electrolyser is known from the document FR2972200A1, which is used for the electrolysis of an aqueous NaCl solution. In such an electrolyser, it is necessary to polarize the input of the electrolyser even if its normal supply fails, which occurs from an AC network connected to a rectifier, even if the AC network fails. For this purpose, an input of the electrolyzer is connected to the AC network via a rectifier, a battery, a DC / DC converter and a diode. If the AC network fails as a normal supply, the input of the electrolyser remains polarized via the battery, the DC / DC converter and the diode.

The document DE 10 2019 200 238 A1 discloses a method for carbon dioxide reduction by means of an electrolyzer, in which salination is counteracted by recurring regeneration phases with applied protective potential and electrolyte flushing.

The document WO 2020 132064 A1 discloses a method for operating a carbon oxide (COx) reduction reactor. The method includes switching off, reducing or otherwise controlling the current during various stages of operation. The document DE 10 2014 224 013 A1 discloses a method for carbon dioxide utilization by means of an electrolytic cell, in which a protective voltage is applied to a cathode in a sleep mode and in which the electrodes would be attacked by the electrolyte solution without applying the protective voltage.

The publication WP 2019/246433 A1 discloses an operating method for a direct current distribution system. The method comprises a first voltage conversion using an active rectifier which converts a first AC input voltage into a first DC output voltage and supplies it to a DC bus. The first DC output voltage of the DC bus is fed to a second input of a buck converter as a second DC input voltage, which converts it into a second DC output voltage via a second voltage conversion and feeds it to a DC load, for example an electrolysis cell stack.

The document DE 102018 133641 A1 describes a method for operating an electrolysis device with a converter and an electrolyzer. On the AC voltage side, the converter is connected to an AC voltage network via a decoupling impedance and is operated with voltage input. The electrolyzer is connected to the converter on the DC voltage side. The electrolysis device is operated at a network frequency that corresponds to a nominal frequency of the AC voltage network and is constant over time, with an electrical power that is between 50% and 100% of a nominal power of the electrolyzer. With the method, an instantaneous reserve power can be provided for the AC voltage network.

Object of the invention

The invention is based on the object of specifying a method for operating an electrolyzer with which hydrogen production by the electrolyzer can be regulated in a highly dynamic manner by means of an electrolysis reaction carried out on water. In particular, when using an actively controlled rectifier of the type described at the outset, it should be possible on the one hand to temporarily pause the production of hydrogen. The temporary pause should be agreed upon over a period of a few minutes, if possible _ WO 2021/228770 _ lül _ PCT / EP2021 / 062341 _

Hours. In addition, a transition from a normal operating mode with electrolysis reaction, ie hydrogen production, to a standby operating mode with at least largely suppressed electrolysis reaction, ie hydrogen production, and vice versa, should take place as quickly as possible. It is also an object of the invention to provide a connection circuit suitable for carrying out the method and a rectifier with such a connection circuit. A further object of the invention is to show an electrolysis system which is suitable for carrying out the method.

solution

In a method of the type mentioned at the outset, the object is achieved according to the invention with the features of independent claim 1. The object of showing a connecting circuit according to the invention is achieved with the features of independent claim 11, and the object of showing an actively controlled rectifier according to the invention is achieved with the features of independent claim 15. The object of specifying an electrolysis system according to the invention is achieved with the features of independent claim 18. Advantageous embodiments of the method are reproduced in claims 2 to 10, advantageous embodiments of the connection circuit in the dependent claims 12 to 14. The dependent claims 16 and 17 aim at an advantageous embodiment of the actively controlled rectifier. The dependent claims 19 and 20 aim at advantageous embodiments of the electrolysis system.

Description of the invention

The method according to the invention relates to an operation of an electrolyzer which is designed and set up to generate hydrogen from water by means of an electrolysis reaction. The electrolyser is supplied from an alternating voltage network (AC network) via an actively controlled rectifier. The procedure consists of the following steps:

Operating the electrolyzer in a normal operating mode at an input voltage UEI above an open circuit voltage ULL of the electrolyzer with a predominantly ohmic behavior, _ WO 2021/228770 _ ll _ PCT / EP2021 / 062341 _

Operating the electrolyzer in a standby operating mode at an input voltage UEI below the open circuit voltage ULL of the electrolyzer with a predominantly capacitive behavior, and

Transition from the standby operating mode to the normal operating mode during a first transition period Dί-i, the first transition period Ati being reduced in that the input voltage UEI at the input of the electrolyzer during the standby operating mode is above a first voltage threshold value UTH different from 0V, I is held.

The electrolyzer is an electrolyzer that is set up to generate hydrogen from water by means of an electrolysis reaction. Such electrolysers are increasingly being operated in larger consumer facilities, for example industrial plants. In this case, they can be used on the one hand to cover the industrial company's hydrogen demand through local hydrogen production. On the other hand, it is desirable to regulate an electrical power consumption of the electrolyzer so dynamically that the electrolyzer can participate in a local energy management of the consumer device. For this purpose, the electrolyser has, on the one hand, the normal operating mode in which an electrolysis reaction, for example a hydrogen-generating decomposition of water, takes place. The electrolysis reaction takes place above the open circuit voltage ULL with an at least predominantly ohmic behavior of the electrolyser, possibly also with a completely ohmic behavior of the electrolyser. The speed of the electrolysis reaction influences the electrical power consumption of the electrolyzer and is controlled by means of the actively controlled rectifier via the input voltage UEI of the electrolyzer. In the standby operating mode with an input voltage UEI below the open circuit voltage ULL, the electrolyser has an at least predominantly capacitive behavior, possibly also a completely capacitive behavior. An electrolysis reaction does not take place here, at least not to a significant extent. Since the input voltage UEI of the electrolyser is kept above the first voltage threshold value UTH.I, which differs from 0V, in the standby operating mode, a capacity assigned to or inherent in the electrolyser remains precharged to a certain extent even in the standby operating mode. Hence a lesser one

Charge transport into the electrolyser is necessary in order to raise its input voltage UEI to a value above the open circuit voltage than would be the case, for example, if the electrolyser was restarted with a fully discharged capacity assigned to it. Since less charge has to be transported, a transition period Dίi between the standby operating mode and the normal operating mode can be kept very short with an otherwise similar current between the actively controlled rectifier and the electrolyzer. As a result of the short transition period Ati, the electrolysis reaction can be paused in the standby operating mode and a power-consuming electrolysis reaction in the normal operating mode can take place in a highly dynamic manner and without significant dead times. The short transition period Ati makes it possible to incorporate the operating behavior of the electrolyzer much better into an energy management of the consumer device than would be the case with long transition periods. Maintaining the input voltage UEI of the electrolyzer above the first voltage threshold value UTH, I cannot be done with any hardware, but at least with a reduced amount of hardware. For example, an already existing connection circuit can often be used, which is why no additional hardware expenditure is required in this case. Implementation of the method is therefore hardly associated with additional expenditure and can therefore be implemented extremely inexpensively.

By keeping the input voltage UEI of the electrolyzer in the standby operating mode above the first voltage threshold value UTH, I, which is different from 0V, the first transition period Ati from the standby operating mode to the normal operating mode can be minimized due to a lower associated charge transport. However, the charge transport required to change the operating mode to a lesser extent does not only have an effect during a transition from the standby operating mode to the normal operating mode. Rather, a second transition period DΪ2 from the normal operating mode to the standby operating mode can also be minimized as a result. An advantageous variant of the method can therefore include the step:

Transition from the normal operating mode to the standby operating mode during a second transition period DΪ2, the second transition period DΪ2 being reduced in that the input voltage UEI at the input of the _ WO 2021/228770 _ ll _ PCT / EP2021 / 062341 _

Electrolyser is kept above the first voltage threshold value UTH.I, which differs from 0V, during the standby operating mode.

The closer the first voltage threshold value UTH.I is to the no-load voltage, the shorter the first transition duration Ati can also be made. On the other hand, however, it must be taken into account that an electrolysis reaction does not start suddenly when the open-circuit voltage is exceeded. Rather, the electrolysis reaction will start in a narrowly limited area around the open circuit voltage ULL and there will continuously increase sharply with increasing input voltage UEI. In order to reliably pause the electrolysis reaction in the standby operating mode, a safety margin from the open circuit voltage must therefore be maintained. According to an advantageous variant of the method, the first voltage threshold value UTH.I can now correspond to a value of at least 80%, preferably of at least 90% of the open circuit voltage ULL of the electrolyzer. Alternatively or cumulatively, the input voltage UEI at the input of the electrolyzer can be kept in the standby operating mode by at least 5% below the no-load voltage ULL of the electrolyzer. These values correspond to a tolerance band for the input voltage UEI of the electrolyzer between a minimum of 80% and a maximum of 95%, particularly preferably between a minimum of 90% and a maximum of 95% of the open circuit voltage ULL of the electrolyzer. Within these tolerance bands, the first transition duration Ati from the standby operating mode to the normal operating mode can be limited to a value of a maximum of 10 s, preferably a maximum of 5 s.

According to an advantageous embodiment of the method, the input voltage UEI of the electrolyzer in the standby operating mode can be kept above the first voltage threshold value UTH.I by activating the input of the electrolyzer via a precharge resistor and / or an inductance in a clocked manner with a DC converter output of one of the controlled rectifier associated AC / DC converter is connected. The actively controlled rectifier can remain connected to the AC grid on the input side. In this way, in connection with free-wheeling diodes present within the AC / DC converter, a DC voltage is maintained at the DC converter output, which can be greater than the open circuit voltage ULL of the electrolyzer. The pulsed connection can be connected in series with the precharge resistor or in series with the _ WO 2021/228770 _ _ PCT / EP2021 / 062341 _

Inductance arranged disconnector take place. In a case in which the input of the electrolyzer is connected in a clocked manner via the precharge resistor to the DC converter output of the AC / DC converter, there are active time windows (with the isolating switch closed) with a current flow into the input of the electrolyzer and inactive ones Time window (with the isolating switch open) during which no current flows into the input of the electrolyzer. During the active time window, the input voltage UEI of the electrolyzer rises, while it drops again during the inactive time window, for example due to leakage currents that can never be completely prevented. According to a preferred variant of the method, the clocked connection of the input of the electrolyser to the DC converter output can take place in a voltage-controlled manner, in particular by means of a two-point control. The input voltage UEI of the electrolyzer can be used as a feedback signal for the control system. With the combination of actively controlled rectifier and electrolyzer in question, a pre-charging resistor with a disconnector arranged in series is often present anyway and therefore does not generate any additional costs. In a case in which the input of the electrolyser is connected in a clocked manner via the inductance to the DC converter output of the AC / DC converter, the inductance can be part of a DC / DC converter, in particular a buck converter, which is connected between the AC / DC converter and the DC output of the rectifier is arranged. When the isolating switch is closed, the increase in current is reduced by the inductance, and when the isolating switch is open there is a decrease in current driven by the inductance. The buck converter can operate in an intermittent or non-intermittent mode.

In a preferred embodiment of the method, a minimum DC voltage Uw, min at the DC converter output of the AC / DC converter can be above the no-load voltage ULL of the electrolyzer. This can be achieved, for example, via a suitable design of a transformer connected upstream of the actively controlled rectifier on the input side, via which the rectifier is connected to the AC network. Specifically, the transformer can be designed so that an AC voltage of the AC network with the amplitude UAC is transformed into an AC voltage with the amplitude U1 present at the AC input of the rectifier, the amplitude U1 in connection with the within of the AC / DC converter existing free-wheeling diodes a minimum DC voltage Uw, min at the DC- _ WO 2021/228770 _ ^'10' _ PCT / EP2021 / 062341 _

Transformer output generated, which is above the open circuit voltage ULL of the electrolyzer. Such a design with regard to the minimum DC voltage Uw, min applied to the DC converter output means, conversely, minimized conversion losses if the electrolyzer is to be operated with a high input voltage UEI.

According to an advantageous embodiment of the method, the electrolyser can also be operated in a maintenance operating mode under predetermined framework conditions, in which the input voltage UEI of the electrolyser is below a voltage value that is critical to the risk. This is the case, for example, when repair and / or maintenance work is to be carried out on the electrolyzer and / or the active rectifier and personal injury due to an electric shock must be reliably ruled out. The risk-critical voltage values can be determined on a country-specific basis. In particular, it is possible that the input voltage of the electrolyzer is at a value of 0V. However, such a maintenance operating mode is then subsequently associated with an extended pre-charging time for the electrolyzer. However, since the maintenance operating mode is only adopted in a few cases, an associated extended charging time, possibly also an associated extended discharge time of the electrolyzer, can be tolerated.

In a further embodiment of the method, the electrolyser can be assigned to a consumer device, for example an industrial company, and together with other electrical consumers and / or generators of the consumer device can be connected to the AC network supplying the consumer device via a common network connection point. In the case of larger consumer facilities in particular, it is common to specify the maximum energy consumption permitted by the AC network within a calculation period. This gives an energy supplier of the consumer device a planning basis with regard to an electrical power to be generated on average over time during the calculation period. Compliance with the maximum energies agreed during the calculation periods is usually monitored and controlled via an energy management system EMS of the consumer device. The electrolyser represents an essential consumer of the consumer device. In one embodiment of the method, therefore, _ WO 2021/228770 _ ^{1 1} _ PCT / EP2021 / 062341 _ an operation of the electrolyser and / or an operation of at least one component that supplies the electrolyser with electrical power can be controlled via a control unit of the consumer device that carries out energy management. The at least one component that supplies the electrolyzer with power can in particular include the connection circuit described below and / or the active rectifier described below. At least one change between the normal operating mode and the standby operating mode of the electrolyzer can take place during a calculation period with the aim that a maximum energy DE agreed for the calculation period between the consumer device and an energy supplier is not exceeded. It is particularly advantageous if the first transition duration Ati, and possibly also the second transition duration At2, fall below a value of a maximum of 5%, in particular a maximum of 2% of a duration of the calculation period. In this way, the electrolyser can be integrated particularly efficiently into the EMS of the consumer device. The control unit of the consumer device can be designed as a separate control unit. As an alternative to this, however, it can also be implemented partially or completely in control units of components of the consumer device that already exist.

A connection circuit according to the invention is arranged between a DC source and an electrolyzer. It comprises: an input with two input connections for connecting the connection circuit to the DC source, as well as an output with two output connections for connection of the connection circuit with the input of the electrolyzer, a series connection made up of a precharge resistor and a disconnector or a series connection made up of an inductance and a Isolating switch, wherein the series circuit connects one of the input connections to a corresponding one of the output connections, a further isolating switch which is arranged in parallel to the precharge resistor, parallel to the series connection of the precharge resistor and disconnector or parallel to the series connection of inductance and disconnector, _ WO 2021/228770 _ ^'12' _ PCT / EP2021 / 062341 _ a measuring unit for determining a voltage difference between a DC voltage UEI present at the output and a DC voltage UQ present at the input, and a control unit for controlling the connection circuit , in particular the circuit breaker and the further circuit breaker. Characteristically, the connection circuit is designed and set up to operate the electrolyser according to the method according to the invention in conjunction with the DC source and, if necessary, a control unit of a consumer device that carries out energy management.

The DC source can in particular be a DC converter output of an AC / DC converter, which is connected to an AC network with its AC converter input. The AC / DC converter can be assigned to an actively controlled rectifier. The control unit of the connection circuit can be communicatively and / or technically connected to the control unit of the consumer device. The advantages already described in connection with the method result.

According to an advantageous embodiment of the connecting circuit, the isolating switch can comprise a semiconductor switch and / or an electromagnetic switch. The “and” stands for what is known as a hybrid switch, which comprises an electromechanical switch with a semiconductor switch arranged parallel to it. The hybrid switch can be used to suppress a switching arc that would otherwise occur if only an electromechanical switch were used. The same also applies to the further disconnector of the connection circuit. In one embodiment of the connection circuit, in which the series connection of the connection circuit is formed via the isolating switch and the inductance, the connection circuit can be designed and set up as a DC / DC converter, in particular as a step-down converter. For this purpose, the connection circuit can have a further semiconductor switch which connects another of the two input connections to a connection point of the isolating switch and the inductance. The further semiconductor switch can be a diode or an actively controlled semiconductor switch. _ WO 2021/228770 _ ¹³ _ PCT / EP2021 / 062341 _

A rectifier according to the invention is designed as an actively controlled rectifier. It is used to supply an electrolyser from an AC network with an AC voltage and comprises: an AC input with several input connections for connecting the AC network and a DC output with two output connections for connecting the electrolyser, an AC / DC Converter with a converter circuit comprising semiconductor switches with free-wheeling diodes connected in anti-parallel to this, as well as a rectifier (GR) control unit for controlling the semiconductor switches of the rectifier. The rectifier according to the invention also has a connecting circuit according to the invention as a characterizing feature.

The actively controlled rectifier can be a single-stage rectifier that is free of a DC / DC converter arranged between the AC / DC converter and the DC output of the rectifier. This is the case, for example, when the series circuit of the connection circuit is formed by the isolating switch and the precharge resistor. As an alternative to this, it is possible for the rectifier to be designed as a two-stage rectifier which comprises a DC / DC converter arranged between the AC / DC converter and the DC output of the rectifier. The DC / DC converter can in particular be a step-down converter. This is the case, for example, when the series circuit of the connection circuit is formed by the disconnector and the inductance arranged in series with the disconnector. The plurality of input connections of the rectifier can include a phase connection and a neutral conductor connection. Alternatively, it is possible for the multiple input connections to include multiple phase connections, in particular three phase connections. In the case of a plurality of phase connections, the input connections can additionally include a neutral conductor connection, but this is not absolutely necessary. The rectifier's AC / DC converter - and thus also the rectifier itself - can be operated bidirectionally with regard to the power flow it converts. It is possible that the AC / DC converter is operated in a voltage-setting manner. During voltage-setting operation, power can be exchanged between the AC / DC converter and the _ WO 2021/228770 _ ¹⁴ _ PCT / EP2021 / 062341 _ connected AC network can be controlled via one or more characteristics, for example an active power-frequency characteristic and / or a reactive power-voltage characteristic. This enables the active rectifier to operate as instantaneously as possible in a network-serving or network-supporting manner. The GR control unit can be designed to control other components of the rectifier in addition to the semiconductor switches of the rectifier, for example an AC isolating unit, which is arranged between the AC converter input of the AC / DC converter and the AC input of the rectifier. The control unit of the connection circuit can be designed as a separate control unit. As an alternative to this, it is possible that the control unit of the connection circuit is part of the GR control unit, provided that it is dimensioned accordingly. The advantages already listed in connection with the method result here as well.

An electrolysis system according to the invention comprises an actively controlled rectifier and an electrolyzer connected on the output side to the actively controlled rectifier. The electrolysis system can be connected directly or with the interposition of a transformer assigned to the electrolysis system to the AC network supplying the electrolyser. In an advantageous embodiment, the electrolysis system can have a signal device which is designed to signal a current operating mode of the electrolyzer. In this way, reference can be made in particular to a standby operating mode of the electrolyzer, since there is no electrolysis reaction in this and - apart from the live input of the electrolyzer and possibly other live components of the electrolysis system - otherwise looks little different from the maintenance operating mode. Alternatively or cumulatively, the electrolysis system can also have a blocking device which is designed to prevent contact with live components of the electrolysis system in the standby operating mode and possibly also in the normal operating mode. It is possible that the blocking device only deactivates its blocking effect when the electrolyzer or other live components of the electrolysis system have been discharged to values below the dangerous voltage values. That way one can Personal injury, which could otherwise result from touching live components, can be safely ruled out.

According to an advantageous embodiment of the electrolysis system, the electrolysis system can be designed as part of a consumer device and can be controlled via a control unit of the consumer device that carries out energy management. In particular, the electrolyzer, the connection circuit and / or the rectifier of the electrolysis system can be controlled by the control unit assigned to the consumer device.

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

Brief description of the figures

The invention is illustrated below with the aid of figures. From these show

1 shows an embodiment of an electrolysis system according to the invention;

2a shows a first embodiment of a connection circuit according to the invention;

2b shows a second embodiment of a connection circuit according to the invention;

3 shows a circuit topology of an AC / DC converter of the actively controlled rectifier according to the invention in one embodiment;

4 shows a time profile of an input voltage UEI at the input of the

Electrolyzer according to one embodiment of the method according to the invention.

Fiqurenbeschreibunq

In Fig. 1, an embodiment of an electrolysis system 60 according to the invention is shown. The electrolysis system 60 contains an actively controlled rectifier 30, which is connected at its AC input 33 via a transformer 31 to an alternating voltage network (AC network) 20. A DC output 34 of the _ WO 2021/228770 _ ^'16' _ PCT / EP2021 / 062341 _

Rectifier 30 is connected to an input 41 of an electrolyzer 40. The actively controlled rectifier 30 comprises an AC separation unit 35, a filter unit 36 for reducing / damping the propagation of high-frequency interference signals in the AC network 20 and an AC / DC converter 37. The AC / DC converter 37 is set up, a to convert AC voltage present at an AC converter input 37.1 with the amplitude U ₃₇ into a DC voltage Uw present at a DC converter output 37.2. For this purpose, semiconductor switches of the AC / DC converter 37 are suitably controlled by a rectifier control unit (GR control unit) 39. The GR control unit 39 is also able to control the AC disconnection unit 35, and possibly also other components of the rectifier or the electrolysis system. A connection circuit 1 according to the invention is arranged between the DC converter output 37.2 and the DC output 34 of the rectifier, the input 5 of which is connected to the DC converter output 37.2 and its output 6 to the DC output 34 of the rectifier 30. The connection circuit 1 also includes a control unit 7 for controlling its components, which is exemplified in FIG. 1 as part of the GR control unit 39. Alternatively, however, it is also possible that the GR control unit 39 and the control unit 7 of the connection circuit 1 are each designed as separate control units. The electrolysis system 60 also includes a signaling device 42 for signaling a current operating mode of the electrolyzer 40. Optionally, it can also include a blocking device (not shown in FIG Normal operating mode of the electrolyzer 40 prevented.

With the connection circuit 1 according to the invention, which is explained in more detail in FIG. 2, the rectifier 30 is designed as a rectifier according to the invention and is set up to control operation of the electrolyzer 40 in accordance with the method according to the invention. The electrolyzer 40 can be operated in a normal operating mode at an input voltage UEI above its open circuit voltage ULL. In the normal operating mode, an electrolysis reaction takes place in the electrolyzer 40, for example a decomposition of water into its constituents hydrogen and oxygen, the _ WO 2021/228770 _ ^'17' _ PCT / EP2021 / 062341 _

Electrolyser 40 essentially behaves like an ohmic consumer. A speed of the electrolysis reaction is controlled by means of the rectifier 30 via a variation of the input voltage UEI of the electrolyzer 40. The electrolyzer 40 can also be operated in a standby operating mode below the open circuit voltage ULL, in which no, but at least no significant electrolysis reaction, and thus no - at least no significant - electrical power consumption of the electrolyzer 40 takes place.

In order to achieve a low value of a first transition period Dίi from the standby operating mode to the normal operating mode, as well as a low value of a second transition period DΪ2 from the normal operating mode to the standby operating mode, the input voltage UEI of the electrolyzer 40 is also held above a first threshold value UTH.I which differs from 0 V in the standby operating mode. The first threshold value UTH.I can be selected such that it is 80%, preferably 90% of the open circuit voltage ULL of the electrolyzer 40. However, the input voltage UEI should advantageously not exceed a value of 95% of the open circuit voltage of the electrolyzer. In this way, the first transition duration Dί-i, as well as the second transition duration DΪ2, can be limited to a value from 1s to a few seconds. By means of such a dynamic change in the operating states, the electrolysis system 60 can be efficiently integrated into an energy management system of a consumer device comprising the electrolysis system 60, for example an industrial company.

As an example, the transformer 31, like the rectifier 30, is shown in FIG. 1 as a three-phase rectifier 30. As an alternative to this, however, it is also possible that the AC network, the transformer 31 and also the rectifier 30 are designed as single-phase components and each have a phase conductor and a neutral conductor connection. It is also possible for them to have a different number of phase conductors, for example two phase conductors. In the context of the invention, a direct connection of the rectifier 30 to the AC network 20 without the interposition of the transformer 31 is also possible. _ WO 2021/228770 _ ¹⁸ _ PCT / EP2021 / 062341 _

In Fig. 2a a first embodiment of a connection circuit 1 according to the invention is shown. The connection circuit 1 comprises an input 5 with two input connections 5.1, 5.2 for connecting a DC source 10, as well as an output 6 with two output connections 6.1, 6.2 for connecting the electrolyzer 40 an AC network 20 connected AC / DC converter 37 act. 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 precharge resistor 2 and a disconnector 3. Another isolating switch 4 is arranged parallel to the series connection. The connection circuit 1 also includes a measuring unit 8 with a voltage sensor 9.2 for detecting a DC voltage UEI present at the output 6 and thus also at the electrolyzer 40, as well as a further voltage sensor 9.2 for detecting a DC voltage present at the input 5 UQ. In addition, the measuring unit 8 has a current sensor 9.1 for detecting a current I (t) flowing via the output 6. The disconnector 3 and the further disconnector 4 are controlled by the control unit 7 of the connection circuit 1. In addition, the control unit 7 is set up to communicate with the measuring unit 8 and to control the measuring unit 8, which is symbolized by a control line shown in dashed lines.

In the normal operating mode of the electrolyzer 40, the further isolating switch 4 of the connection circuit 1 is permanently closed, so that the electrolyzer 40 is connected to the DC source 10 with low resistance. The disconnector 3 can be open or also closed. In the standby operating mode of the electrolyzer 40, the further isolating switch 4 is permanently open. The circuit breaker 3 is closed and opened again in a clocked manner. The clocked opening and closing of the isolating switch 3 can take place as a function of the detected DC voltage UEI present at the output 6 and thus the DC voltage UEI present at the input 41 of the electrolyzer 40. In this way, a 2-point control of the input voltage UEI of the electrolyzer 40 can be implemented, which leads to a time curve of the input voltage UEI of the electrolyzer, as will be explained in more detail in connection with FIG. _ WO 2021/228770 _ ^'19' _ PCT / EP2021 / 062341 _

FIG. 2b illustrates a second embodiment of the connection circuit 1 according to the invention, which has many features in common with the first embodiment of the connection circuit according to FIG. 2a. In the following, therefore, mainly the differences from the first embodiment of the connection circuit are explained, while reference is made to the explanations under FIG. 2a with regard to the similarities.

According to the second embodiment, the connection circuit 1 is designed as a DC / DC converter, in particular as a step-down converter 14. The first input connection 5.1 of the connection circuit 1 is connected to the corresponding output connection 6.1 via a series circuit of the isolating switch 3 and an inductance 11. The isolating switch 3 is designed as an actively controllable semiconductor switch in FIG. Furthermore, the connection circuit 1 has a further semiconductor switch 12, which connects a connection point 13 between the isolating switch 3 and the inductance 11 to the other input terminal 5.2 of the connection circuit 1. In FIG. 2 b, the further semiconductor switch 12 is designed as an actively controllable semiconductor switch which is also controlled by the control unit 7. As an alternative to this, however, it is also possible for the further semiconductor switch 12 to be designed as a diode. The further isolating switch 4 of the connecting circuit 1 is designed as an electromechanical isolating switch and is arranged parallel to the series circuit comprising isolating switch 3 and inductance 11.

During the standby operating mode of the electrolyzer 40, the DC voltage UQ applied to the input 5 can be converted into a DC voltage UEI applied to the output 6 by suitable control of the isolating switch 3 and the further semiconductor switch 12. The further disconnector 4 is permanently open and the output voltage UEI is kept above the first voltage threshold value UTH.I via clocked operation of the disconnector 3 and the further semiconductor switch 12. During the normal operating mode, the further isolating switch 4 is permanently closed, so that the first input connection 5.1 has low impedance with the first output connection 6.1 _ WO 2021/228770 _ ²⁰ _ PCT / EP2021 / 062341 _ is connected. The further semiconductor switch 12 is permanently open in the normal operating mode.

FIG. 3 shows an embodiment of an AC / DC converter 37 of the actively controlled rectifier 30 from FIG. 1. Corresponding to the rectifier 30 from FIG Semiconductor switches 52, each of which is assigned an anti-parallel connected free-wheeling diode 53. The freewheeling diode 53 can be designed as an intrinsic diode of the respective semiconductor switch 52, or as a separate diode. The semiconductor switches 52 can be MOSFET or IGBT semiconductor switches. Corresponding to the three-phase configuration 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 arm 51 assigned to them. The DC converter output 37.2 of the AC / DC converter 37 comprises a positive (+) and a negative output connection (-).

The AC / DC converter 37 is designed to convert an active power P (t) from its AC converter input 37.1 to its DC converter output 37.2, possibly also in the opposite direction from its DC converter output 37.2 to its AC converter input 37.1 to transport. In addition, the AC / DC converter 37 can be designed, a reactive power Q (t) between the AC converter input 37.1 of the AC / DC converter 37 and an AC network 20 connected to the AC converter input 37.1 (not in FIG. 3 explicitly shown). For the purpose of power conversion, the semiconductor switches 52 are suitably controlled by the GR control unit 39 of the rectifier (not explicitly shown in FIG. 3). The level of the converted DC voltage Uw, in other words the DC voltage range, can assume values between a minimum DC voltage Uw, min and a maximum DC voltage Uw.max. The minimum DC voltage Uw, min is limited by the freewheeling diodes 53 to a value which - apart from one _ WO 2021/228770 _ ²¹ _ PCT / EP2021 / 062341 _

Forward voltage of the freewheeling diodes 53 - corresponds to the amplitude U37 of the AC voltage present at the AC converter input 37.1. Due to the free-wheeling diodes 53, the converter circuit 50 is thus able to generate a DC voltage Uw at the DC converter output 37.2, which is larger, but not smaller, at least not significantly smaller than the amplitude U37 of the AC voltage applied on the input side. The conversion losses increase as the ratio of the DC voltage Uw applied on the output side to the amplitude U37 of the AC voltage applied on the input side increases. In order 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, can be above the no-load voltage ULL of the electrolyzer. This can be done, for example, by appropriately designing a transformer 31 via which the AC / DC converter 37 is connected to the AC network 29.

In FIG. 3, a two-stage converter circuit 50 with only two voltage stages is shown as an example. In the context of the invention, however, a converter circuit 50 with more than two voltage stages, for example a three-stage or a five-stage converter circuit, is also possible. It is also possible within the scope of the invention for the converter circuit to be designed as a midpoint circuit. Here, an output connection, for example the negative output connection (-), of the DC converter output 37.2 can be connected to a center point of a transformer 31 connected to the AC converter input 37.1. Alternatively, the negative output connection (-) can also be connected to a neutral conductor of the AC network 20.

4 illustrates a time curve of the input voltage UEI of the electrolyzer 40 during a transition from its standby operating mode to its normal operating mode according to an embodiment of the method according to the invention. Furthermore, FIG. 4 shows time curves of the input voltage UEL as they can occur in the standby operating mode arranged temporally before the transition and in the normal operating mode arranged temporally after the transition using the connection circuit 1 from FIG. 2a. _ WO 2021/228770 _ ^'22' _ PCT / EP2021 / 062341 _

In the standby operating mode, the input voltage UEI has a sawtooth-like curve as a function of time, which varies between a lower limit value - formed from the first voltage threshold value UTH.I - and an upper limit value. The upper limit value is selected such that it corresponds to 95% of the open circuit voltage ULL of the electrolyzer 40. The sawtooth-like curve results from a clocked closing and opening of the isolating switch 3 with the further isolating switch 4 of the connecting circuit 1 permanently open. It includes temporary charging phases of the electrolyzer 40, during which the input voltage UEI increases. In this case, a capacitance assigned to the electrolyser 40 is charged by means of the closed isolating switch 3 of the connecting circuit 1 and a current I (t) made possible by this and flowing through the precharge resistor 2. The increases in the input voltage UEI are each followed by discharge phases with associated voltage decreases. The voltage decreases result from a leakage current that cannot be completely prevented within the electrolyzer 40. In FIG. 4, the illustrated steepness of the voltage decreases is purely exemplary and, depending on the level of the leakage current, can also be significantly lower than shown in FIG is.

At time to, the actively controlled rectifier 30 is signaled, for example by an energy management system of a consumer device comprising the electrolysis system 60, that the electrolyser 40 should be switched to its normal operating mode. For this purpose, the further isolating switch 4 of the connection circuit 1 is closed and the electrolyser 40 is connected with low resistance to the DC source 10, formed from the AC / DC converter 37 with an upstream AC network 20. At the same time, the semiconductor switches 52 of the AC / DC converter 37 are controlled via the GR control unit 39 in such a way that the AC / DC converter 37 has a DC voltage at the DC converter output 37.2 that corresponds to a voltage desired in the normal operating mode. Setpoint UEI.SOII for its input voltage. Since the input voltage UEI of the electrolyzer 40 is already close to the open circuit voltage ULL in the standby operating mode, only a significantly reduced voltage change is required until the voltage setpoint UEI SOII is reached, and therefore only a significantly reduced charge transport into the electrolyzer 40. The first transition period Ati between the _ WO 2021/228770 _ ²³ _ PCT / EP2021 / 062341 _

The standby operating mode and the normal operating mode are therefore significantly reduced relative to a pre-charging of the electrolyzer from 0V. The same applies accordingly to the second transition duration DΪ2 in the case of a transition from the normal operating mode to the standby operating mode of the electrolyzer 40.

If the second embodiment according to FIG. 2b is used instead of the first embodiment of the connection circuit 1, the result is a time curve similar to that shown in FIG. The sawtooth-like curve in the standby operating mode can, however, have extremely small and negligible voltage differences, so that an approximately constant DC voltage can be set there.

_ WO 2021/228770 24 -PCT / EP2021 / 062341 _

Reference list

1 connection circuit

2 precharge resistor

3 circuit breakers

4 circuit breakers

5 entrance

5.1, 5.2 input connector

6 exit

6.1, 6.2 output connection

7 control unit

8 measuring unit

9.1 Current sensor

9.2 Voltage sensor 10 DC source 11 Inductance 12 Semiconductor switch

13 connection point

14 power converter 20 AC network

30 rectifiers

31 transformer

33 AC input

34 DC output

35 AC disconnection unit

36 filter unit

37 AC / DC converter

37.1 AC converter input

37.2 DC converter output

39 Rectifier (GR) control unit

40 electrolyser

41 input (of the electrolyzer) _ WO 2021/228770 _ - 25 - PCT / EP2021 / 062341 _

50 converter circuit

51 bridge branch

52 semiconductor switches

53 freewheeling diode

Claims

_ WO 2021/228770 _ '26' _ PCT / EP2021 / 062341 _ claims

1. A method for operating an electrolyzer (40) which is designed and set up to generate hydrogen from water by means of an electrolysis reaction and which is supplied from an alternating voltage (AC) network (20) via an actively controlled rectifier (30), with the steps:

Operating the electrolyzer (40) in a normal operating mode at an input voltage UEI above an open circuit voltage ULL with a predominantly ohmic behavior,

Operating the electrolyzer (40) in a standby operating mode at an input voltage UEI below the open circuit voltage ULL with predominantly capacitive behavior, and

Transition from the standby operating mode to the normal operating mode during a first transition period AU, the first transition period AU being reduced in that the input voltage UEI at the input (41) of the electrolyzer (40) during the standby operating mode is above a value different from 0V first voltage threshold value UTH.I is held.

2. The method according to claim 1, wherein the first voltage threshold value UTH.I corresponds to a value of at least 80%, preferably of at least 90% of the open circuit voltage ULL.

3. The method according to claim 1 or 2, wherein the input voltage UEI at the input (41) of the electrolyzer (40) in the standby operating mode is kept at least 5% below the open circuit voltage ULL of the electrolyzer (40).

4. The method according to any one of the preceding claims, comprising the step:

Transition from the normal operating mode to the standby operating mode during a second transition period At2, the second transition period At2 being reduced in that the input voltage UEI at the input (41) of the electrolyzer (40) during the standby operating mode is above the value different from 0V first voltage threshold value UTH.I is held. _ WO 2021/228770 _ ²⁷ _ PCT / EP2021 / 062341 _

5. The method according to any one of the preceding claims, wherein the input voltage UEI of the electrolyzer in the standby operating mode is kept above the first voltage threshold value UTH.I by its input (41) via a precharge resistor (2) and / or an inductance (11) in is connected in a clocked manner to the DC converter output (37.2) of an AC / DC converter (37) assigned to the rectifier (30).

6. The method according to claim 5, wherein the clocked connection of the input (41) of the electrolyzer (40) with the DC converter output (37.2) takes place by means of a two-point control.

7. The method according to any one of the preceding claims, wherein a minimum DC voltage Uw, min at the DC converter output (37.2) of the AC / DC converter (37) is above the open circuit voltage ULL of the electrolyzer (40).

8. The method according to any one of the preceding claims, wherein the electrolyzer (40) is also operated in a maintenance operating mode under predetermined framework conditions, in which the input voltage UEI of the electrolyzer (40) is below a critical voltage value, in particular at a value of 0V.

9. The method according to any one of the preceding claims, wherein the electrolyzer (40) is assigned to a consumer device, for example an industrial company, and wherein an operation of the electrolyzer (40) and / or an operation of components that the electrolyzer (40) with electrical power supply, is controlled via a control unit of the consumer device that carries out energy management.

10. The method according to claim 9, wherein at least one change between the normal operating mode and the standby operating mode of the electrolyzer (40) takes place during a calculation period with the aim that a maximum energy DE agreed for the calculation period between the consumer device and an energy supplier is not is exceeded.

11. Connection circuit (1) between a DC source (10), in particular between a DC converter output (37.2) of an AC / DC converter (37), which with its AC converter input (37.1) is connected to an AC network (20 ) is connected, and an electrolyzer (40) comprising: _ WO 2021/228770 _ ²⁸ _ PCT / EP2021 / 062341 _ an input (5) with two input connections (5.1, 5.2) for connecting the connection circuit (1) to the DC source (10), and an output (6) with two output connections (6.1, 6.2) for connecting the connection circuit (1) to the input (41) of the electrolyzer (40), a series circuit made up of a precharge resistor (2) and a disconnector (3) or a series circuit made up of an inductance (11) and a disconnection switch (3), the series circuit connecting one of the input connections (5.1, 5.2) to a corresponding one of the output connections (6.1, 6.2), a further disconnection switch (4) connected in parallel to the precharge resistor (2), the inductance (11) or is arranged parallel to the series circuit, a measuring unit (8) for determining a voltage difference between a DC voltage UEI applied to the output (6) and a DC voltage UQ applied to the input (5), and a control unit (7) to steer tion of the connecting circuit (1), in particular the isolating switch (3) and the further isolating switch (4), characterized in that the connecting circuit (1) is designed and set up in connection with the DC source and, if necessary, a control unit carrying out an energy management Consumer device to operate the electrolyzer (40) according to the method according to one of the preceding claims

12. Connection circuit (1) according to claim 11, wherein the isolating switch (3) comprises a semiconductor switch and / or an electromagnetic switch.

13. Connection circuit (1) according to claim 11 or 12, wherein the further isolating switch (4) is formed by an electromechanical switch, which is optionally connected in parallel with a semiconductor switch.

14. Connection circuit (1) according to one of claims 11 to 13, wherein the series circuit is formed via the disconnector (3) and the inductance (11), and wherein the connection circuit (1) as a DC / DC converter, in particular as a buck converter ( 14) is designed and set up.

15. Actively controlled rectifier (30) for supplying an electrolyzer (40) from an AC network (20) having an AC voltage, comprising: _ WO 2021/228770 _ ²⁹ _ PCT / EP2021 / 062341 _ an AC input (33) with several input connections for connecting the AC network (20) and a DC output (34) with two output connections for connecting the electrolyzer (40 ) as well as an AC / DC converter (37) with a converter circuit comprising semiconductor switches (52) with free-wheeling diodes (53) connected in anti-parallel, and a rectifier (GR) control unit (39) for controlling the semiconductor switches (52) of the rectifier (30), characterized in that the rectifier (30) also has a connection circuit (1) according to one of claims 11 to 14.

16. An actively controlled rectifier (30) according to claim 15, characterized in that the series circuit of the connecting circuit (1) is formed by the isolating switch (3) and the precharge resistor (2) and the rectifier (30) is designed as a single-stage rectifier (30) is.

17. Actively controlled rectifier (30) according to claim 15 with a connecting circuit (1) according to claim 13, so that the rectifier (30) is designed as a two-stage rectifier (30), the one between the AC / DC converter (37) and comprises the DC / DC converter arranged at the DC output (6) of the rectifier (30).

18. Electrolysis system (60) comprising an actively controlled rectifier (30) according to one of claims 15 to 17 and an electrolyzer (40) connected on the output side to the actively controlled rectifier (30).

19. Electrolysis system (60) according to claim 18, with a signaling device (42) which is designed to signal a current operating mode of the electrolyzer (40), and wherein the electrolysis system (60) optionally additionally has a blocking device which is designed in to prevent contact with live components of the electrolysis system (60) in the standby operating mode and possibly also in the normal operating mode.

20. The electrolysis system (60) according to claim 18 or 19, characterized in that the electrolysis system (60) is designed as part of a consumer device which is controlled by a control unit of the consumer device which carries out an energy management.