Active rectifier system for h2 electrolysis with combined precharge and protective voltage auxiliary rectifier

Abstract

The invention relates to a circuit arrangement (16) for electrically coupling an electrolysis device (12) to an energy supply network (14) which uses an alternating voltage, in order to supply the electrolysis device (12) with electrical energy during electrolysis operation as intended, said circuit arrangement comprising - an energy source connection (18), - an electrolysis device connection (20), - an isolation unit (22) which has at least one inverter connection (24), - an inverter (28) which has a DC link (26) and a AC voltage connection (30) electrically coupled to the inverter connection (24), - a control unit (32), and - an auxiliary circuit (34) which is designed to charge at least the DC link (26) at a time before the switching state of the isolation unit (22) is changed to a predefinable electric DC voltage as precharge voltage. According to the invention, the auxiliary circuit (34) is designed to apply a predefined, suitable protective voltage to the DC link (26) after the switching state of the isolation unit (22) has changed from the switched-on switching state to the switched-off switching state.

Description

[0001] Description

[0002] ACTIVE RECTIFIER SYSTEM FOR H2 ELECTROLYSIS WITH COMBINED PRECHARGE AND PROTECTIVE VOLTAGE AUXILIARY RECTIFIER

[0003] The invention relates to a circuit arrangement for electrically coupling an electrolysis device to a power supply network using an alternating voltage in order to supply the electrolysis device with electrical energy in a normal electrolysis operation, with an energy source connection for electrically connecting to the power supply network, an electrolysis device connection for connecting to the electrolysis device, a separation unit electrically coupled to the energy source connection, which has at least one inverter connection, wherein the separation unit is designed to establish an electrical connection between the energy source connection and the at least one inverter connection in a switched-on switching state and to separate the electrical connection between the energy source connection and the at least one inverter connection in a switched-off switching state,an inverter having a DC voltage intermediate circuit, wherein the inverter has at least one AC voltage connection electrically coupled to the at least one inverter connection, a control unit at least for controlling the inverter and the isolating unit, wherein the control unit is designed to control the isolating unit and the inverter, and an auxiliary circuit electrically coupled to the energy source connection and the DC voltage intermediate circuit, which is designedto charge at least the DC voltage intermediate circuit to a predeterminable electrical DC voltage as a pre-charging voltage prior to a change in the switching state of the separation unit from the switched-off switching state to the switched-on switching state. The invention further relates to an electrolysis system with an electrolysis device and a circuit arrangement for electrically coupling the electrolysis device to a power supply network using an AC voltage in order to supply the electrolysis device with electrical energy during normal electrolysis operation. Finally, the invention also relates to a method for electrically coupling an electrolysis device to a power supply network using an AC voltage by means of a circuit arrangement in order to supply the electrolysis device with electrical energy during normal electrolysis operation.wherein a separation unit of the circuit arrangement establishes an electrical connection between the power supply network and an inverter of the circuit arrangement in a switched-on switching state and separates the electrical connection between the power supply network and the inverter in a switched-off switching state, wherein a DC intermediate circuit of the inverter is electrically coupled to the electrolysis device, a control unit controls at least the separation unit and the inverter, and an auxiliary circuit electrically coupled to the power supply network and the DC intermediate circuit charges at least the DC intermediate circuit to a predetermined electrical DC voltage as a pre-charging voltage before a change in the switching state of the separation unit from the switched-off switching state to the switched-on switching state.

[0004] Generic circuit arrangements, electrolysis systems with such circuit arrangements, and generic methods are extensively known in the prior art, so that separate written documentation is not required. Electrolysis devices generally have a plurality of electrolysis cells, which serve in particular for the electrolysis of water into hydrogen and oxygen. Such an electrolysis cell is disclosed, for example, in DE19729529C1. The basic function of electrolysis, in particular water electrolysis, is known to those skilled in the art, which is why detailed explanations thereof are omitted here.

[0005] Electrolysis devices generally have at least one electrolysis cell, but usually the electrolysis devices have a large number of electrolysis cells that are at least partially connected in series. The electrolysis device serves, inter alia, to produce substances that can preferably be used on an industrial scale, for example hydrogen in water electrolysis, carbon monoxide in carbon dioxide electrolysis or the like. For this purpose, at least two electrodes of a respective electrolysis cell of the electrolysis device are supplied with a suitable small electrical direct voltage, which can be in the range of a few volts or possibly even less than one volt. Depending on the amount of substance to be provided by the electrolysis, a corresponding electrical direct current is provided as the electrolysis current by an electrolysis energy source.In series-connected electrolysis cells, this direct current flows through all of the series-connected electrolysis cells. The series connection is electrically coupled to the electrolysis energy source. Furthermore, it is also possible to connect electrolysis cells not only in series, but also, at least partially, in parallel.

[0006] The electrolysis energy source is often coupled to an energy supply network which supplies the electrolysis device with electrical energy. For the purpose of the electrical coupling, a circuit arrangement is generally provided which serves to couple the electrolysis device to the energy supply network. The circuit arrangement makes it possible to control an energy flow from the energy supply network to the electrolysis device, for example in that the electrical coupling can be activated or deactivated as required via the circuit arrangement. The energy supply network generally uses an alternating voltage which can be a single-phase, but preferably a multi-phase, in particular a three-phase, alternating voltage.

[0007] Because of the high power requirements of electrolysis devices, which are associated with a correspondingly high current load, it has previously been common practice to use thyristor-based rectifier units to achieve the required direct current, for example in a range of around 7 kA to around 1 kOkA. However, thyristor-based rectifier units have proven disadvantageous in terms of feedback effects on the power grid, particularly at high power levels, because high current loads in particular cause severe distortions that cause harmonics in the power grid. It is therefore generally necessary to provide additional components, such as active and / or passive filters, power factor compensation units to meet power grid requirements, particularly with regard to harmonics, and reactive power compensation. However, this entails correspondingly high additional costs.

[0008] Therefore, circuit arrangements with transistor-based inverters are now increasingly being used. These allow the grid-side requirements to be largely met by appropriately controlling inverter switching elements of the inverter formed by transistors in switching mode, so that additional filters and compensation measures can be significantly reduced, if not completely eliminated.

[0009] For the inverter to function as intended, an inverse diode is generally connected in parallel with each transistor. The DC link of the inverter usually has an electrical capacitor with a sufficiently large electrical capacitance for its intended use in supplying an electrolysis device. When commissioning the electrolysis system formed by the electrolysis device in conjunction with the circuit arrangement, it is generally necessary to first precharge or charge the DC link to a predetermined DC link voltage as a pre-charging voltage before the inverter is electrically coupled to the power grid.If the inverter were connected to the power grid when the DC link is essentially discharged, a very large, almost unlimited current could flow through the freewheeling or inverse diodes, which could then become overloaded and fail. The result would be an inverter failure.

[0010] To avoid this problem, an appropriately large inductance connected to at least one AC voltage connection of the inverter could be selected. However, the size of the inductance is limited for the intended functional operation in order to be able to achieve the desired power using the inverter. Therefore, a large inductance cannot sufficiently limit any inrush current without disrupting normal operation. For this reason, a separate pre-charging circuit is provided which has a rectifier which is connected to the DC voltage intermediate circuit on the DC voltage side. On the AC voltage side, the rectifier is coupled to the power supply network via at least one electrical resistor.This makes it possible to precharge the intermediate circuit voltage to the specified DC link voltage before the electrical connection between the power grid and the inverter is established via the isolation unit. If the DC link voltage is precharged to the specified DC voltage, the problem described above can be largely avoided.

[0011] Even if the aforementioned circuit arrangement has proven itself, there is still room for improvement. One of the things that has proven to be at least partially critical for a particular electrolysis cell is a transition from or to an operating state that differs from the intended electrolysis state. This particularly applies to starting up the electrolysis system or the electrolysis device or shutting down the electrolysis system or the electrolysis device. Particularly during shutdown after intended operation, residual substances, in particular residual gases, may still be present in the electrolysis cells, which may under certain circumstances lead to fuel cell functionality occurring in the electrolysis cells. This can, however, cause irreversible damage to the electrolysis cells, which is why fuel cell functionality should be avoided at all costs.

[0012] Commissioning or shutting down the electrolysis plant therefore generally requires additional measures to ensure reliable operation. This cannot be achieved with the known circuit arrangement in conjunction with the pre-charging circuit, as these are not suitable for the required control functionality.

[0013] The invention is based on the object of developing a generic circuit arrangement in such a way that the reliability of the operation of the electrolysis system or electrolysis device can be improved.

[0014] As a solution, the invention proposes a circuit arrangement, an electrolysis system, and a method according to the independent claims. Advantageous further developments are provided by the features of the dependent claims.

[0015] With regard to a generic circuit arrangement, the invention proposes in particular that the auxiliary circuit is designed to apply a predetermined, suitable protective voltage to the DC voltage intermediate circuit following a change in the switching state of the isolating unit from the switched-on switching state to the switched-off switching state.

[0016] With regard to a generic electrolysis plant, it is proposed that the circuit arrangement is designed according to the invention.

[0017] With regard to a generic method, the invention proposes in particular that the auxiliary circuit applies a predetermined, suitable protective voltage to the DC voltage intermediate circuit following a change in the switching state of the isolating unit from the switched-on switching state to the switched-off switching state.

[0018] The invention is based, among other things, on the idea that the reliability of the operation of the electrolysis system or electrolysis device can be improved in particular by the circuit arrangement being able to provide not only a pre-charging function, but also a protective voltage if required. These functionalities can be implemented by a single common auxiliary circuit. It is therefore possible to apply a protective voltage, also called polarization voltage, to the electrolysis cells of the electrolysis device outside of the intended electrolysis operation, which protective voltage is selected such that the undesired fuel cell functionality can be largely avoided. In the case of a single electrolysis cell for electrolyzing water, the protective voltage can be, for example, approximately 1.25 V.Once the electrolysis cell has cooled sufficiently and residual gases have been removed, the protective voltage supply can be deactivated. Therefore, the invention does not require any additional protective circuitry or polarization circuit, because this function can also be implemented with the auxiliary circuit of the invention. This, of course, reduces not only the circuitry complexity but also the control technology complexity.

[0019] In particular, the invention makes it possible to largely eliminate the need for the precharging circuit typically used in the prior art, because this functionality can be provided by the auxiliary circuit of the invention. Furthermore, the auxiliary circuit of the invention not only enables the DC link to be charged or precharged to the predeterminable DC voltage, but the auxiliary circuit also enables the electrolysis device to be subjected to a protective voltage, at least outside of the intended electrolysis operation, so that undesirable processes in the electrolysis cells of the electrolysis device, which could, for example, result in fuel cell operation, can be largely avoided.This makes it possible to achieve a complete protection and operating concept using a single additional circuit, namely the auxiliary circuit, which can ensure reliable operation of the electrolysis systems as a whole, even with frequently varying operating state changes or load changes, which can be caused, for example, by the availability of electrical energy from the power grid. At the same time, the auxiliary circuit makes it possible to create redundancy with regard to the reliability and safe operation of the electrolysis cells of the electrolysis device. This not only enables a coupling process with regard to the inverter with the power grid, but also simultaneously achieves a parallel auxiliary energy supply for the electrolysis device if, for example, the inverter fails or something similar.

[0020] An inverter is an electrical energy converter or energy transformer that electrically couples a DC voltage or DC intermediate circuit with an AC voltage. The AC voltage can be single-phase or multi-phase, particularly three-phase, AC voltage. The inverter has switching elements for energy conversion or energy transformation.

[0021] The transistor-based inverter can, for example, be designed as a two-level inverter. Furthermore, the inverter can, of course, also use more than just two electrical potentials for its conversion function. In an inverter that uses only two levels for voltage conversion, the two available electrical potentials roughly correspond to the electrical potentials provided by the DC link voltage at the DC link.

[0022] The inverter is designed here as a transistor-based inverter and has corresponding transistors as switching elements. The transistors of the inverter are operated in a switching mode by means of suitable control signals. The control signals implement a pulse width modulation method if the inverter is designed to use only two electrical potentials which essentially correspond to the electrical potentials available at the DC voltage intermediate circuit. This can of course vary with other inverter designs, for example when using a multi-level inverter (M2C) or the like. The inverter has at least one AC voltage connection electrically coupled to the at least one inverter connection. As a result, the inverter is connected on the AC voltage side to the energy source connection via the separation unit.The inverter is designed according to the number of phases of the alternating voltage used.

[0023] The switching elements of the inverter interact with an electrical energy storage device of the inverter, which is often formed by inductors arranged on the AC side. The inverter can be designed as a 2-level inverter, for which purpose the switching elements are arranged in the manner of half-bridge circuits for each of the phases of the AC voltage. The half-bridge circuits are connected in parallel to the DC link and each have center terminals that are connected to the inductors. The two electrical potentials of the DC link are provided at the center terminals depending on the respective switching states of the switching elements. In addition, inverters are known that can use more than the two aforementioned electrical potentials.

[0024] The switching operation of a transistor means that, when switched on, a very low electrical resistance is provided between the respective terminals forming the switching path, so that a high current flow is possible with a very low residual voltage. When switched off, the switching path of the transistor has a high impedance, i.e. it provides a high electrical resistance, so that even when a high electrical voltage is applied across the switching path, there is essentially no current flow, or only a very small, in particular negligible, current flow. This differs from linear operation, which is not generally used in inverters. The switching states of the transistor are achieved by a corresponding control signal at its control electrode.The inverter is preferably operated as a grid inverter, which means that at least one of its AC voltage connections is electrically coupled to the power grid.

[0025] For the purpose of coupling the AC voltage connection of the inverter to the power grid, the circuit arrangement generally has a separation unit that serves to establish the electrical connection between the power grid and the inverter. The DC voltage intermediate circuit of the inverter, however, can be coupled to the electrolysis device. During electrolysis operation, energy thus flows from the power grid via the at least one AC voltage connection of the inverter and the inverter to the DC voltage intermediate circuit, and from there to the electrolysis device.

[0026] The energy supply network is preferably a public energy supply network, which preferably provides a three-phase alternating voltage at a frequency of approximately 50 Hz or approximately 60 Hz. However, the invention is not limited to the use of such frequencies and can, among other things, also be used in alternating voltage networks that use a different frequency, for example approximately 16 Hz to approximately 17 Hz, but also in a range from approximately 200 Hz to approximately 500 Hz. In addition, the energy supply network can also be an island network, for example. The island network can be either a stationary network or a mobile network, for example an energy supply network of a vehicle, in particular a watercraft, an aircraft, a motor vehicle or the like.

[0027] During normal electrolysis operation, the electrolysis device is supplied with a suitable direct voltage required for normal electrolysis operation via the circuit arrangement. The circuit arrangement provides a corresponding electrolysis current so that the electrolysis cells of the electrolysis device can electrolyze the substance to be electrolyzed, for example water, into the electrolysis components, in the case of water, for example hydrogen and oxygen, in the intended manner. The energy source connection of the circuit arrangement can, for example, be a detachable connection with which the circuit arrangement or the electrolysis system can be detachably connected electrically to the energy supply network. The energy source connection can preferably provide a separate electrical connection for each phase of a multi-phase alternating voltage of the energy supply network.In addition, however, additional connections may also be provided, for example, for a neutral conductor, an earth connection, and / or the like. The energy source connection may also be fixed, i.e., non-detachable, for example, in a stationary system used to implement an electrolysis process on a large industrial scale.

[0028] The same essentially applies to the electrolysis device connection, which electrically connects the circuit arrangement to the electrolysis device. This connection, too, can be detachable. However, given the typically high power, this connection is often not detachable. Both the energy source connection and the electrolysis device connection can be realized, for example, by means of screw connections, welded connections, clamp connections, and / or the like.

[0029] The circuit arrangement has a separation unit which is electrically coupled to the energy source connection. The separation unit can have at least one electromechanical or electronic switching element, for example a contactor, one or more thyristors, one or more transistors, combination circuits thereof and / or the like. The separation unit is preferably electrically connected directly to the energy source connection. The separation unit also has an inverter connection which is used to connect the inverter. The inverter is preferably designed to suit the number of phases of the energy supply network, so that the inverter connection and the energy source connection are also designed accordingly.

[0030] The isolating unit is designed to establish an electrical connection between the energy source connection and the at least one inverter connection in a switched-on switching state. In a switched-off switching state, the isolating unit is designed to disconnect the electrical connection between the energy source connection and the at least one inverter connection. In the case of a multi-phase alternating voltage, at least one separate individual switching element is preferably provided for each of the phases of the alternating voltage. The switching elements of the isolating unit can be controlled by means of a switching signal, for example a switch-on signal and / or a switch-off signal. The isolating unit can therefore assume the respective switching state depending on the switching signal.

[0031] The circuit arrangement further comprises a control unit which serves to control the inverter and the isolating unit. The control unit provides at least one switching signal for the isolating unit and at least the control signals for the transistors for the inverter, so that the desired functionality can be realized. The control unit is preferably designed as an electronic control unit and can be formed, for example, by a hardware circuit, a program-controlled computer unit, combinations thereof or the like. The circuit arrangement further comprises an auxiliary circuit which is electrically coupled on the AC voltage side to the energy source connection and on the DC voltage side to the DC voltage intermediate circuit of the inverter.The auxiliary circuit is designed to provide a direct voltage based at least on the alternating voltage provided via the energy source connection and to charge at least the direct voltage intermediate circuit to the predeterminable electrical direct voltage as a precharge voltage prior to a change in the switching state of the isolating unit from the switched-off switching state to the switched-on switching state. The precharge voltage is preferably selected such that the isolating unit can safely switch to the switched-on switching state without damaging the inverter, in particular its inverse diodes or freewheeling diodes.

[0032] For this purpose, the circuit arrangement, in particular the auxiliary circuit or the control unit, can have a suitable voltage sensor for detecting the intermediate DC voltage. The control unit can evaluate the corresponding sensor signal from the voltage sensor and use it in particular to control the isolating unit. Furthermore, the control unit can also control the auxiliary circuit depending on the sensor signal, for example by deactivating the auxiliary circuit as soon as the desired pre-charging voltage is reached or the like. It can also be provided that the control unit only activates the auxiliary circuit when, in addition to a higher-level activation signal, it can also be detected by means of the voltage sensor that the pre-charging voltage at the intermediate DC voltage link has not yet been reached.

[0033] One of the things that proves to be at least partially critical for a particular electrolysis cell is a transition from or to an operating state that differs from the intended operating state. This applies in particular to starting up the electrolysis cell or the electrolysis device as well as shutting down the electrolysis cell or the electrolysis device. Particularly during shutting down following intended operation, residual substances, in particular residual gases, may still be present in the electrolysis cell, which may under certain circumstances cause the electrolysis cell to display fuel cell functionality. However, this can cause irreversible damage to the electrolysis cell, which is why fuel cell functionality should be avoided at all costs.For this purpose, the electrolysis cell is subjected to a protective voltage, also called polarization voltage, outside of its intended operation. This voltage is selected so that the fuel cell functionality can be largely avoided. In an electrolysis cell for electrolyzing water, for example, the protective voltage can be approximately 1.25 V. Once the electrolysis cell has cooled down sufficiently and residual gases have been removed, the protective voltage can be deactivated.

[0034] The auxiliary circuit is designed to apply a predetermined, suitable protective voltage to the DC link following a change in the switching state of the separation unit from the switched-on state to the switched-off state. As a result, the electrolysis device can be supplied with an electrical DC voltage, namely the protective voltage, even after the intended electrolysis operation has ended, so that undesirable dangerous conditions in at least some of the electrolysis cells can be avoided, for example if substances or electrolysis products to be electrolyzed are still present in the electrolysis cells. In particular, during the pre-charging process it can be provided that the DC link voltage is measured and adjusted, for example using a predetermined ramp.In polarization operation, however, the intermediate circuit voltage is provided, for example, in such a way that the cell voltages of the electrolysis cells, for example provided from a cell voltage measurement or calculated from a stack voltage measurement, are evaluated and a cell current is increased until all electrolysis cells are above the protective voltage.

[0035] The invention therefore makes it possible to implement a protective function for the electrolysis device, in particular for its electrolysis cells, without the need for a separate, additional device. Rather, the auxiliary circuit, which serves, among other things, for the precharging process, can also be used to implement the corresponding protective functionality for the electrolysis device or its electrolysis cells outside of the intended electrolysis operation. For this purpose, the control unit can determine a corresponding operating state outside the intended operating state that requires a protective functionality and provide a corresponding control signal for the auxiliary circuit, so that the auxiliary circuit provides the protective voltage in a suitable manner.The protective voltage is usually different from the pre-charging voltage, so the auxiliary circuit is designed to be adjustable with regard to the voltage to be provided. The auxiliary circuit therefore not only implements a simple rectifier function to utilize electrical energy from the power grid, but is also capable of providing this energy in the form of a DC voltage that can be suitably adjusted. For example, an adjustable electrical resistor can be used for this purpose, with which the desired setting can be achieved.

[0036] In addition, however, it is proposed that the auxiliary circuit have a rectifier circuit with at least one controllable electronic switching element. The electronic switching element can, for example, be a thyristor or a transistor which is operated in switching mode. The rectifier circuit is preferably designed as a full-bridge circuit. In the full-bridge circuit, all electronic switching elements are particularly preferably designed as thyristors or transistors. This makes it possible to adjust the intermediate circuit voltage at the DC voltage intermediate circuit almost continuously by means of the auxiliary circuit, so that both the pre-charging voltage and the protective voltage can be implemented independently of one another. The auxiliary circuit can be designed to provide either only the protective voltage or only the pre-charging voltage at a given time.Furthermore, it is of course also possible for the auxiliary circuit to provide the precharging voltage and the protection voltage at least partially simultaneously and to switch between the voltages to be provided as needed. For this purpose, a corresponding switching unit can be provided, which can also be controlled by the control unit.

[0037] Preferably, the control unit is configured to control at least the auxiliary circuit in a pre-charging mode and a protective mode. This allows a suitable control functionality to be implemented in a simple manner.

[0038] It is further proposed that at least the separation unit and the inverter are designed for operation on a multi-phase alternating voltage of the power supply network.

[0039] It is further proposed that the auxiliary circuit have an electrical energy store. The energy store makes it possible to operate the auxiliary circuit, at least temporarily, independently of the availability of electrical energy from the power supply network. This is particularly advantageous when the power supply network is unstable and disruptions, in particular power outages, can occur during normal electrolysis operation. As already explained, this can be disadvantageous for the electrolysis device. The energy store makes it possible, by means of the auxiliary circuit, in particular to provide the protective voltage independently of the availability of the power supply network, so that the protective voltage can be provided reliably by means of the auxiliary circuit even in the event of a sudden power failure.This proves particularly advantageous when the supply of electrical energy via the power grid suddenly fluctuates and fails. In this case, the auxiliary circuit can provide the required protective voltage almost immediately. The electrical energy storage device can be, for example, an accumulator or the like. However, the energy storage device can also comprise an electromechanical generator, which is driven, for example, by an internal combustion engine, a fuel cell device, or the like.

[0040] Furthermore, it is proposed that the pre-charging voltage and the protective voltage are different from one another. The pre-charging voltage and the protective voltage can thus be specified and provided essentially independently of one another. Preferably, at least one suitable control signal is required, which can preferably be provided by the control unit and on the basis of which the auxiliary circuit provides either the pre-charging voltage or the protective voltage. Of course, it can also be provided that the protective voltage and the pre-charging voltage are determined by the auxiliary circuit itself, for example can be fixed, and that the control unit only provides one control signal which tells the auxiliary circuit to provide the pre-charging voltage or the auxiliary voltage.In principle, it is of course also possible for the auxiliary circuit to be deactivated outside of its intended function of providing the pre-charging voltage and the protective voltage. For this purpose, the control unit can, for example, provide a suitable deactivation signal for the auxiliary circuit.

[0041] Furthermore, it is proposed that the control unit receives an activation signal for activating the electrolysis operation and, depending on the receipt of the activation signal, first activates the auxiliary circuit for providing the pre-charging voltage and then triggers a change in the switching state of the separation unit from the switched off switching state to the switched on switching state. The activation signal can come from a higher-level control of the electrolysis plant or the like. The activation signal can be provided, for example, by a control station. The control unit evaluates the activation signal and preferably determines a switch-on time or a switch-on period for the change in the switching state of the separation unit from the switched off switching state to the switched on switching state.Depending on this point in time or period, the auxiliary circuit is preferably activated in advance so that the auxiliary circuit can provide the pre-charging voltage by the specified point in time or period. This ensures reliable operation, particularly when the isolation unit changes from the switched-off state to the switched-on state. If the DC link is not completely discharged, this can be detected by the voltage sensor and taken into account when determining the activation of the auxiliary circuit. This makes it possible - depending on the charge state of the DC link - to achieve an adapted time offset between the activation of the auxiliary circuit to provide the pre-charging voltage and the triggering of the change in the switching state of the isolation unit.

[0042] It is further proposed that the protective voltage be provided by the auxiliary circuit for a predetermined period of time and that this provision is terminated after the predetermined period of time. It can be provided that the auxiliary circuit provides the pre-charging voltage for the predetermined period of time. After the predetermined period of time has elapsed, the auxiliary circuit can then be deactivated in order to terminate the provision of the predetermined pre-charging voltage. The auxiliary circuit therefore does not need to be in operation continuously during normal electrolysis operation. Rather, it can be deactivated, for example, when the switching state of the separation unit changes. Deactivation can also take place shortly after the switching state of the separation unit changes, for example in order to have a certain degree of temporal redundancy available.

[0043] The advantages and effects stated for the method according to the invention naturally also apply equally to the circuit arrangement according to the invention and the electrolysis system according to the invention, and vice versa. In this respect, method features can also be formulated as device features, and vice versa.

[0044] For use cases or application situations that may arise during the method and which are not explicitly described here, it may be provided that, in accordance with the method, an error message and / or a request to enter user feedback is issued and / or a standard setting and / or a predetermined initial state is set.

[0045] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identity are included.

[0046] The exemplary embodiments explained below are preferred embodiments of the invention. The features and combinations of features specified above in the description, as well as the features and combinations of features mentioned in the following description of exemplary embodiments and / or shown alone in the figures, can be used not only in the respective combination specified, but also in other combinations. Thus, embodiments are also encompassed by the invention or are to be regarded as disclosed which are not explicitly shown and explained in the figures, but which arise from and can be produced by separate combinations of features from the explained embodiments.The features, functions, and / or effects illustrated by the exemplary embodiments may, in and of themselves, represent individual features, functions, and / or effects of the invention that can be viewed independently of one another, and which also further develop the invention independently of one another. Therefore, the exemplary embodiments are intended to encompass combinations other than those in the embodiments explained. Furthermore, the described embodiments may also be supplemented by further features, functions, and / or effects of the invention already described.

[0047] In the figures, the same reference symbols denote the same features and functions.

[0048] It shows :

[0049] FIG 1 is a schematic diagram of an electrolysis plant connected to a power grid for electrolyzing water; and

[0050] FIG 2 is a schematic circuit diagram of an electrolysis plant for electrolyzing water, connected to a power supply network, which plant has an auxiliary circuit.

[0051] FIG 1 shows a schematic circuit diagram of an electrolysis system 10 which is connected via a first circuit arrangement 50 to a power supply network 14 which provides a three-phase alternating voltage. In the present case, the three-phase alternating voltage is a voltage with an effective value of approximately 900 V at a frequency of approximately 50 Hz. The first circuit arrangement 50 serves to supply the electrolysis device 12 with electrical energy during normal electrolysis operation. The electrolysis device 12 is used in the present case for the electrolysis of water to hydrogen and oxygen and has a large number of electrolysis cells (not shown in detail), which are at least partially connected in series.

[0052] The power supply network 14 provides the three-phase alternating voltage in this case. The circuit arrangement 50 has a power source connection 18 to which the power supply network 14, i.e., the three phases of the power supply network 14 in this case, are connected. Furthermore, the circuit arrangement 50 has an electrolysis device connection 20 to which the electrolysis device 12 is connected.

[0053] The circuit arrangement 50 also has a disconnection unit 22 which is connected to the energy source connection 18. The disconnection unit 22 also has an inverter connection 24. The disconnection unit 22 is designed to establish an electrical connection between the energy source connection 18 and the inverter connection 24 in an on-switched state and to disconnect the electrical connection between the energy source connection 18 and the inverter connection 24 in a off-switched state. The energy source connection 18 and the inverter connection 24 are designed in the present case to be adapted for operation on the three-phase alternating voltage. For this purpose, the disconnection unit 22 also has a respective electromechanical switching element in the form of a contactor for each of the phases of the alternating voltage.The circuit arrangement 50 further comprises a transistor-based inverter 28 which has a DC voltage intermediate circuit 26 and an AC voltage connection 30 electrically connected to the inverter connection 24. The inverter 28 is also designed in the present case for operation with a three-phase AC voltage. For the purpose of energy conversion functionality, the inverter 28 has three respective half-bridge circuits made up of respective transistors 54 which are connected in parallel to the DC voltage intermediate circuit 26. A respective inverse diode 56 is connected in parallel to each transistor 54. Center taps of the respective half-bridge circuits are connected via respective inductors 52 to respective phase connections of the AC voltage connection 30. In the present embodiment, it is provided that the transistors 54 can be formed by MOSFETs.In alternative embodiments, other transistors can of course also be used, for example bipolar transistors, field effect transistors or the like.

[0054] Both the switching elements 58 of the separation unit 22 and the transistors 54 of the inverter 28 can be operated by suitable control signals from a control unit 32. In the present case, the inverter 28 is designed as a 2-level inverter, and the control signals for the transistors 54 of the control unit 32 serve to implement a respective pulse width modulation for a respective phase of the alternating voltage. The functional principle of pulse width modulation in an inverter is known to a person skilled in the art, which is why further explanations in this regard are omitted here. The control unit 32 is a component of the electrolysis system 10, preferably of the circuit arrangement 50.

[0055] The inverter 28 is operated here as a grid inverter. A rectifier function can be implemented by means of the inverter 28 in order to charge the DC link 26 to a predetermined DC voltage for the intended electrolysis operation. For this purpose, the DC link 26 has an electrical capacitor 60.

[0056] During normal electrolysis operation, the separation unit 22 is in the switched-on state, so that the inverter 28, as a grid inverter, is electrically connected to the respective phases of the alternating voltage of the power supply network 14. By suitable operation of the transistors 54, an intermediate DC voltage is provided at the DC voltage intermediate circuit 26, which is passed to the electrolysis device 12 when a switching unit 62 is switched on. The electrolysis device 12 can be electrically separated from the circuit arrangement 50 via the switching unit 62, which can also have electromechanical switching elements or electronic switching elements. The switching elements of the switching unit 62 can basically be designed in the same way as the separation unit 22.

[0057] If the electrolysis device 12 is to be supplied with electrical energy via the circuit arrangement 50 and the DC voltage intermediate circuit 26 or its capacitor 60 is discharged, a change in the switching state of the separating unit 22 from the off switching state to the on switching state would result in the phases of the AC voltage acting directly on the capacitor 60 via the inverse diodes 56 and causing a large current flow, for example, in the manner of a short circuit. This could overload the inverse diodes 56, and there is a risk of destruction.

[0058] To remedy this situation, the electrolysis plant

[0059] 10 has a pre-charging circuit 46 which is connected on the one hand to the energy source connections 18 and on the other hand to the DC voltage intermediate circuit 26. The pre-charging circuit 46 has a further isolating unit 40 which in the present case also has electromechanical switching elements in the manner of a contactor. The isolating unit 40 is connected via electrical resistors 42 for each of the phases to an AC voltage side of a three-phase bridge rectifier 48. The three-phase bridge rectifier 48 has diodes 44. On the DC voltage side, the bridge rectifier 48 is connected to the DC voltage intermediate circuit 26. In the present case, it is provided that the pre-charging circuit 46 is connected to all three phases of the AC voltage. In alternative embodiments, however, it can be provided that the pre-charging circuit 46 is connected to at least one of the three phases of the AC voltage.

[0060] To commission the inverter 28, it is now provided that the separation unit 40 is first switched into the switched-on state by means of a corresponding pre-charging switch-on signal from the control unit 32, before the separation unit 22 changes to the switched switching state. As a result, the alternating voltage of the energy supply network 14 can charge the direct voltage intermediate circuit 26 to a pre-charging voltage via the electrical resistors 42 and the bridge rectifier 48. The pre-charging voltage is preferably selected such that a change in the switching state of the separation unit 22 to the switched-on state avoids the aforementioned disadvantage when switching on the inverter 28. The pre-charging voltage is preferably selected substantially corresponding approximately to an amplitude of the alternating voltage of the energy supply network 14.

[0061] As soon as the pre-charging voltage is reached at the DC intermediate circuit 26, the control unit can control the isolating unit 22 accordingly, so that it changes to the switched-on state and thus electrically couples the inverter 28 to the power supply network 14.

[0062] After the coupling between the power supply network 14 and the inverter 28 has been established, the control unit 32 can deactivate the pre-charging circuit 46 if necessary by controlling the separation unit 40 accordingly with a pre-charging shutdown signal, so that the separation unit 40 changes to the switched-off state.

[0063] Although the precharging circuit 46 enables the implementation of a precharging function for the DC link 26, this circuit is not suitable for also providing a protective voltage for the electrolysis device 12, for example, to enable the electrolysis device 12 to start up its intended electrolysis operation or shut down after the intended electrolysis operation of the electrolysis device 12 has ended. This would require a protective voltage that differs from the precharging voltage.

[0064] FIG. 2 shows, in a further schematic circuit diagram like FIG. 1, a schematic circuit diagram of an electrolysis system 10 with a circuit arrangement 16 instead of the circuit arrangement 50, in which an auxiliary circuit 34 is installed instead of the precharging circuit 46 and with whose aid it is possible to implement both the precharging functionality and the protection functionality. In this case, the auxiliary circuit 34 is also connected to the control unit 32 for this purpose in order to be controlled accordingly. The auxiliary circuit 34 is preferably a component of the circuit arrangement 16.

[0065] 1, which is why only the differences to the design according to FIG. 1 are explained below. The circuit arrangement 16 according to FIG. 2 differs from the circuit arrangement 50 according to FIG. 1 in that the pre-charging circuit 46 is replaced by the auxiliary circuit 34. Furthermore, the auxiliary circuit 34 differs from the pre-charging circuit 46 in that the resistors 42 and the bridge rectifier 48 are replaced by a rectifier circuit 36 ​​which is essentially also based on a circuit structure of a three-phase bridge circuit, but in which the diodes of the bridge rectifier 48 are replaced by thyristors 38. The thyristors 38 are controlled by suitable control signals from the control unit 32.

[0066] By using thyristors and omitting the electrical resistors 42, it is possible not only to provide the pre-charging voltage with the auxiliary circuit 34, but also to implement a corresponding protective voltage for a protective functionality of the electrolysis device 12 outside of the intended electrolysis operation. For this purpose, the thyristors 38 can be controlled accordingly, so that the capacitor 60 of the DC voltage intermediate circuit 26 can be charged successively with the smallest possible voltage differences between the voltage values ​​present at the respective ignition times and a current DC intermediate circuit voltage. This makes it possible to achieve the pre-charging voltage at the DC voltage intermediate circuit 26 in a simple manner. By using the thyristors 38, it is also possible to shorten the charging process and thus implement a charging process that is as efficient and short as possible.This can be achieved with comparatively little hardware effort.

[0067] In addition, it is possible that after deactivation of the inverter 28 and a change of the switching state of the separation unit 22 from the switched-on switching state to the switched-off switching state, a suitable protective voltage for the electrolysis device 12 can be provided by means of suitable control signals for the thyristors 38, so that the problems mentioned above when shutting down the electrolysis system 10 after the end of the intended electrolysis process can be avoided.

[0068] In addition, the auxiliary circuit 34 can also be used, for example, to start up the electrolysis device 12 by providing a suitable protective voltage before the separation unit 22 changes from the switched off state to the switched on state. For this purpose, it can be provided that, as soon as the control unit 32 has determined a time for the change of the switching state of the separation unit 22 from the switched off state to the switched on state, a pre-charging of the DC voltage intermediate circuit to the pre-charging voltage can be carried out shortly before this time by means of the auxiliary circuit 34. This can be done very quickly using the auxiliary circuit 34, so that negative effects on the electrolysis device 12 can be largely avoided.As soon as the precharge voltage is reached, the switching state of the separating unit 22 is changed by means of a suitable switch-on signal from the control unit 32, so that the switched-on switching state is assumed. By activating the inverter 28, the desired energy supply functionality for the intended electrolysis operation can then be initiated, so that the intended electrolysis operation can be realized by the electrolysis device 12.

[0069] By means of the auxiliary circuit 34 according to the invention, it is thus possible to provide a protective voltage not only after the termination of the intended electrolysis operation, but also for the start-up of the electrolysis device 12 to commence the intended electrolysis operation. This can be achieved cost-effectively with limited effort. The exemplary embodiments serve exclusively to explain the invention and are not intended to limit it.

Claims

Patent claims 1. Circuit arrangement (16) for electrically coupling an electrolysis device (12) to a power supply network (14) using an alternating voltage in order to supply the electrolysis device (12) with electrical energy in a normal electrolysis operation, with - an energy source connection (18) for electrical connection to the energy supply network (14), - an electrolysis device connection (20) for connection to the electrolysis device (12), - a separation unit (22) electrically coupled to the energy source connection (18) and having at least one inverter connection (24), wherein the separation unit (22) is designed to establish an electrical connection between the energy source connection (18) and the at least one inverter connection (24) in a switched-on switching state and to separate the electrical connection between the energy source connection (18) and the at least one inverter connection (24) in a switched-off switching state, - an inverter (28) having a DC voltage intermediate circuit (26), wherein the inverter (28) has at least one AC voltage connection (30) electrically coupled to the at least one inverter connection (24), - a control unit (32) at least for controlling the inverter (28) and the separation unit (22), wherein the control unit is designed to control the separation unit (22) and the inverter (28), and - an auxiliary circuit (34) which is electrically coupled to the energy source connection (18) and the DC voltage intermediate circuit (26), which is designed to switch at least the DC voltage intermediate circuit (26) on to a to charge a predeterminable electrical direct voltage as a pre-charging voltage, characterized in that the auxiliary circuit (34) is designed to apply a predetermined, suitable protective voltage to the direct voltage intermediate circuit (26) following a change in the switching state of the separating unit (22) from the switched-on switching state to the switched-off switching state.

2. Circuit arrangement according to claim 1, characterized in that the auxiliary circuit (34) has a rectifier circuit (36) with at least one controllable electronic switching element (38).

3. Circuit arrangement according to one of the preceding claims, characterized in that the control unit (32) is designed to control at least the auxiliary circuit (34) in a pre-charging mode and a protection mode.

4. Circuit arrangement according to one of the preceding claims, characterized in that at least the separation unit (22) and the inverter (28) are designed for operation on a multi-phase alternating voltage of the power supply network (14).

5. Circuit arrangement according to one of the preceding claims, characterized in that the auxiliary circuit (34) has an electrical energy storage device.

6. Electrolysis system (10) with an electrolysis device (12) and a circuit arrangement (16) for electrically coupling the electrolysis device (12) to a power supply network (14) using an alternating voltage in order to supply the electrolysis device (12) with electrical energy in a normal electrolysis operation, characterized in that the circuit arrangement (16) is designed according to one of the preceding claims.

7. A method for electrically coupling an electrolysis device (12) to a power supply network (14) using an alternating voltage by means of a circuit arrangement (16) in order to supply the electrolysis device (12) with electrical energy in a normal electrolysis operation, wherein - a separation unit (22) of the circuit arrangement (16) establishes an electrical connection between the power supply network (14) and an inverter (28) of the circuit arrangement (16) in a switched-on switching state and separates the electrical connection between the power supply network (14) and the inverter (28) in a switched-off switching state, wherein a DC voltage intermediate circuit (26) of the inverter (28) is electrically coupled to the electrolysis device (12), - a control unit (32) controls at least the separation unit (22) and the inverter (28), and - an auxiliary circuit (34) electrically coupled to the power supply network (14) and the DC intermediate circuit (26) charges at least the DC intermediate circuit (12) to a predetermined electrical DC voltage as a pre-charging voltage before a change in the switching state of the isolating unit (22) from the switched-off switching state to the switched-on switching state, characterized in that the auxiliary circuit (34) applies a predetermined, suitable protective voltage to the DC intermediate circuit (26) following a change in the switching state of the isolating unit (22) from the switched-on switching state to the switched-off switching state.

8. Method according to claim 7, characterized in that the pre-charging voltage and the protection voltage are different from each other.

9. The method according to claim 7 or 8, characterized in that the control unit (32) receives an activation signal for activating the electrolysis operation and, depending on the receipt of the activation signal, first activates the auxiliary circuit (34) for providing the pre-charging voltage and then triggers a change in the switching state of the separating unit (22) from the switched-off switching state to the switched-on switching state.

10. Method according to one of claims 7 to 9, characterized in that the protective voltage is provided by the auxiliary circuit (34) for a predetermined period of time and the provision is terminated after the predetermined period of time.

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