EP3903396A1

EP3903396A1 - Electrolysis device having a converter and method for providing instantaneous reserve power for an ac voltage grid

Info

Publication number: EP3903396A1
Application number: EP19816599.5A
Authority: EP
Inventors: Andreas Falk; Christian Hardt
Original assignee: SMA Solar Technology AG
Current assignee: SMA Solar Technology AG
Priority date: 2018-12-27
Filing date: 2019-12-03
Publication date: 2021-11-03
Also published as: JP2022515821A; WO2020135975A1; US20240117513A1; JP7429698B2; DE102018133641A1; US11851776B2; CN113228448B; CN113228448A; US20210317588A1

Abstract

What is described is a method for operating an electrolysis device (10) having a converter (12) that is connected, at its AC voltage side, to an AC voltage grid (15) via a decoupling inductor (13) and draws an AC active power from the AC voltage grid (15), and an electrolyzer (11) that is connected, at its DC voltage side, to the converter (12) and, at a grid frequency that corresponds to a nominal frequency of the AC voltage grid (15) and is constant over time, is operated at an electric power that is between 50% and 100% of a nominal power of the electrolyzer (11), wherein the converter (12) is operated with voltage impression such that the AC active power drawn from the AC voltage grid (15) is changed directly depending on a change and/or a rate of change of the grid frequency in the AC voltage grid (15). What are also described are an electrolysis device and a method for providing instantaneous reserve power for an AC voltage grid.

Description

ELECTROLYSIS DEVICE WITH A CONVERTER AND METHOD FOR PROVIDING CURRENT RESERVE POWER FOR AN AC VOLTAGE NETWORK

TECHNICAL FIELD OF THE INVENTION

The invention relates to an electrolysis device with a converter, a method for operating an electrolysis device with a converter and a method for providing instantaneous reserve power for an AC voltage network.

STATE OF THE ART

In an AC voltage network that is constructed as a supra-regional interconnected network, deviations in the network frequency from a nominal frequency of the AC voltage network can occur due to an imbalance between the fed-in and the extracted electrical power. This imbalance and thus the frequency deviation can be counteracted by devices that feed electrical power into the AC network and / or can take from the AC network vary the power that they feed or withdraw. In particular, at frequencies which are above the nominal frequency, the power fed in can be reduced or the power drawn can be increased, while at frequencies which are below the nominal frequency, the power fed in can be increased or the power drawn off reduced.

The respective change in performance in direct or indirect response to a frequency deviation is referred to as control power. In some AC networks, particularly in the European interconnection network, the provision of this control power is organized in stages that build on one another in time. The first control stage, the so-called instantaneous control, is ensured by devices that change their output in direct and immediate reaction to a change in frequency. In the second control stage, the so-called primary control, which comes into play when the frequency deviation persists, devices are used which selectively adjust their output based on a characteristic curve as a function of the deviation of the mains frequency from the nominal frequency. In the third stage, the so-called secondary control, an expected or foreseeable power imbalance in the AC network is counteracted in a planned manner by devices being instructed by a higher-level control device to change their electrical power appropriately. Devices are known from the prior art which exchange electrical power between the AC voltage network and a DC unit operating with direct current. The DC unit can comprise an energy generator, for example a photovoltaic generator, the power of which is converted in an inverter and fed into the AC voltage network. DE102005046919A1 discloses a method for the temporary storage of electrical wind energy generated from wind power by means of an electrolysis device, so that the wind power plant can provide control power. EP2705175A1 discloses an energy management system comprising an electrolysis system with which control power can be provided.

The converters of such devices generally work in a current-impressing manner by converting a setpoint for the DC power into a corresponding setpoint for the AC current and feeding this AC current into the AC voltage network. The DC unit can also include a DC load, e.g. an ohmic resistor, a machine or an electrochemical system that is operated by means of a current-impressing converter that takes AC power from the AC network and makes it available to the DC load as DC power. This current-impressing converter is also given a setpoint for the DC power, which is transformed in a controller into a setpoint for an AC current to be drawn from the AC voltage network, so that the AC power is a function of the DC power.

Inverters of this type can in particular be designed as thyristor rectifiers or self-commutated IGBT inverters which synchronize themselves with the AC voltage network on the basis of a frequency measurement. In the event of a frequency change, this frequency measurement must first settle to the new frequency before the setpoint for the DC power and subsequently the AC power are adjusted to the new position. In this respect, a current-impressing converter cannot react immediately to a frequency change in the AC network. Because of this delayed reaction, DC loads which are connected to the AC voltage network via such a conventionally impressively operated converter are not suitable for providing instantaneous control power or instantaneous reserve.

DE1020161 15182A1 discloses a method for providing instantaneous reserve in an AC voltage network, in which the power of a current-impressing converter is set to an instantaneous reserve setpoint by means of a current regulator. The setpoint is generated from a phase error signal of a PLL control loop that uses the AC voltages of the AC network as input variables. A current-impressing converter proves to be advantageous here compared to a voltage-impressing converter, in particular in the case of photovoltaic generators as energy sources. From EP2182626A1 a method for operating a converter is known, in which semiconductor switches are controlled either selectively or in combination by means of a voltage impressing and / or a current impressing modulation. As a result, the properties of the various types of modulation, which are described in detail in EP2182626A1 and which result in voltage-impressing or current-impressing behavior of the converter, are to be advantageously combined with one another.

Devices which are used for the instantaneous control in the context of the first of the control stages mentioned at the beginning include, in particular, so-called synchronous generators which feed power into the network, or synchronous machines which take power from the network. Such synchronous generators and synchronous machines generally comprise rotating masses that have an inherent inertia. Synchronous machines and synchronous generators contribute to the stabilization of the network frequency by their electrical behavior, which is well known to the person skilled in the art, because their electrical power depends on the phase difference between the AC voltage of the AC network and the rotational frequency of the rotating mass due to the inherent inertia. In other words, due to its inertial inertia, a synchronous generator or a synchronous machine can react immediately to frequency changes and also counteract them directly.

According to the prior art, it is assumed that the behavior of a synchronous generator can only be simulated with a device on the DC voltage side, which is connected directly to the network via a voltage-impressing converter. Such an inverter, in which the switching commands for power semiconductor switches are derived from an AC setpoint for the input AC voltage of the inverter, responds immediately, ie without control delays, to a change in the mains frequency. Therefore, the device on the DC voltage side must also be able to absorb or deliver energy directly and be connected directly to an intermediate circuit of the converter for this purpose. Such a device on the DC voltage side comprises, for example, a battery which is connected to the network via a voltage-setting converter and can directly absorb or emit energy. The voltage-impressing control would be severely hampered or even impossible by a control delay of any DC / DC converter to adjust the DC voltage. This applies in particular to a single-stage converter to which a photovoltaic generator is connected, which is operated with a PV voltage close to the grid rectification voltage, so that even small DC voltage drops can lead to considerable distortions of the alternating current fed in by the converter; Such dips must be prevented by means of suitable regulation of the DC source. DE102010030093A1 discloses a device and a method for controlling the exchange of electrical energy between an AC voltage network and a system connected to the AC voltage network, the system being able to contain a consumer, a generator and / or an energy store. The device comprises a converter in which the power exchanged with the AC voltage network can be set as a function of an active power frequency statics. In addition, the converter has a so-called synchronous machine emulator, by means of which the converter maps the dynamic behavior of a synchronous machine. As a result, in particular, network frequency support is to take place in the transient and / or subtransient time range, the reaction of the device to a network frequency change being able to take place differently, ie the change in power is greater the higher the rate of change of the network frequency over time. Ohmic resistors or machines are used as consumers, possibly in combination with a memory for thermal, mechanical or chemical energy. As a result, part of the performance of the consumers or part of the energy stored or storable in an energy store is available for network support.

Further embodiments of a synchronous machine emulation are known, for example, from DE102006047792A1, in which a so-called virtual synchronous machine (VISMA) is used for network support, the behavior of a synchronous machine being approximated by constant solution of differential equations, and from EP3376627A1, in which a voltage-impressing converter (voltage Source Inverter (VSI) is described, the control of which comprises a structure for generating a virtual inertia, so that the converter mimics the behavior of a synchronous generator.

A so-called droop mode control for an inverter is known from EP1286444B1, the inverter being operated on the basis of a frequency statics f (P) and a voltage statics U (Q), so that the inverter responds directly to frequency changes in the AC voltage network with a change in the Active power reacts and is therefore suitable for parallel operation with other inverters and in particular for setting up an island grid.

From US7645931 a device with a converter connected to an AC voltage network, a photovoltaic generator and an electrolyser is known, the electrolyser being operated permanently at an optimal operating point with a corresponding power, the electrical power for the operation of the electrolyser either from the PV generator is passed to the electrolyser via a DC converter or from the AC network via the converter. EP2894722B1 discloses an arrangement for supplying an electrolyser with direct current, in which semiconductor components of a rectifier, in particular its thyristors, are divided into two groups, one of the groups being arranged directly on one of the two direct current connections of the electrolyzer. The rectifier can be connected to a medium-voltage network via at least one transformer, and the output power of the rectifier can be set in a range between 20% and 50% of the maximum output power of the rectifier by means of a control of the thyristors.

OBJECT OF THE INVENTION

The invention has for its object to provide a method for operating an electrolysis device connected to an AC network and an electrolysis device with which an electrolyser can be operated and at the same time reserve power can be made available for stabilizing the network frequency of the AC network.

SOLUTION

The object is achieved by a method and a device with the features of independent claims 1 and 9 and a method with the features of claim 14. Preferred embodiments are defined in the dependent claims.

DESCRIPTION OF THE INVENTION

In a method for operating an electrolysis device with a converter that is connected to an AC voltage network via a decoupling inductor and draws AC active power from the AC network, and an electrolyser that is connected to the converter on the DC voltage side and at a network frequency that corresponds to a nominal frequency of Corresponds to the AC voltage network and is constant over time, is operated with an electrical power which is between 50% and 100% of a nominal power of the electrolyzer, the converter being operated in a voltage-impressing manner, so that the AC active power taken from the AC voltage network is immediately dependent on a change and / or a change rate of the network frequency in the AC network is changed. The method according to the invention is particularly distinguished from conventional methods for operating an electrolysis device in that the converter is operated in a voltage-impressing manner. This means, for example, that a setpoint for the input-side alternating voltage of the converter is specified in the control of the converter and the converter behaves in such a way that this setpoint voltage is achieved as far as possible, in particular regardless of the current then flowing. In addition, voltage-impressing operation of the converter includes that the AC current drawn from the AC network depends on the network frequency in such a way that a change in the network frequency leads to an immediate change in the power drawn from the AC network, in particular regardless of which sink on the AC network is opposite End of the converter is connected. The change in power can in particular be proportional to a change rate of the network frequency.

It is precisely this immediate change in performance as a function of a change in the mains frequency that is part of the inherent behavior of a synchronous machine. In contrast, current impressing operation has an inherent delay in that a setpoint for the AC current is specified, which setpoint can at best be adjusted indirectly in the event of frequency changes in order to stabilize the frequency, for example via a P (f) characteristic.

The immediate reactions to changes in the grid frequency in the form of changes in the active AC power drawn from the AC grid can be passed on to an electrolyser, although the electrolyser is not in a position to make a correspondingly rapid change in the converted power. Nevertheless, a change in the AC active power can be passed on directly to the electrolyzer via the converter, for example by means of a corresponding change in the DC voltage applied to the electrolyzer by the converter. The change in the DC voltage leads to a change in the power consumed by the electrolyzer via a voltage-current characteristic curve of the electrolyzer. According to the invention, the electrolyzer is switched on before the change, i.e. operate at a constant mains frequency between 50% and 100% of its nominal power, the nominal power of the electrolyzer being below a maximum power of the electrolyzer and in particular corresponding to the power with the maximum efficiency of the electrolyzer.

The DC power of the electrolyzer can thus be reduced or increased, which leads to a change in the metabolism in the electrolyzer. Due to its design, an electrolyser can withstand the short-term effects of a change in the DC power. Process or reduce sales only permanently if further measures for the operation of the electrolyzer take place, for example a change in the delivery rate of pumps for electrolyte circulation or the removal of produced gases. However, these further measures have a comparatively high inertia, so that stabilization of the operation of the electrolyzer is possible only after a sudden change in the applied voltage.

On the other hand, the voltage-impressing operation of the converter is characterized by the fact that the change in the active power drawn from the AC network essentially depends on the change and / or the rate of change in the network frequency, so that the active power returns to an initial value as soon as there is no change in the network frequency. especially if the rate of change is zero. As a result, the metabolism in the electrolyzer returns to the corresponding initial value as soon as the mains frequency has stabilized again.

If the network frequency stabilized in this way deviates from the nominal frequency of the AC network, primary control power is automatically provided and the instantaneous reserve power is no longer necessary. The electrolysis device therefore only provides instantaneous reserve power for a comparatively short period of time, so that the inertia of the material conversions in the electrolyzer, which makes it necessary to start up pumps and fans, does not yet play a role. The increase or decrease in turnover that takes place during the change in the mains frequency can therefore be buffered in the electrolyzer, for example by tolerating a short-term overpressure or underpressure in the electrolyzer and then reduced again by subsequent measures in the operation of the electrolyzer after the mains frequency has decreased has stabilized.

The invention is therefore based on the knowledge that a DC load connected to a voltage-setting converter does not necessarily have to be able to change the AC power obtained from the AC voltage grid just as quickly into a change in the DC power used for the intended purpose. Implement performance. Rather, it is sufficient if the DC load can process the changed DC power at least temporarily and can buffer it internally if necessary. In particular, an electrolyzer proves to be a particularly advantageous DC load, since on the one hand an electrolyzer can be prompted to change the DC power, for example by the converter changing the DC voltage on the electrolyzer, and on the other hand said buffering inherently takes place in an electrolyzer , so that the inertia of the electrolyser, which is also inherent, does not prevent at least a short-term change in the DC power. The voltage-impressing behavior of the electrolysis device can thus be achieved according to the invention, although neither an ohmic consumer, nor an energy source or an energy store is connected to the converter.

As part of the voltage-impressing operation of the converter, the converter can provide an instantaneous reserve power. For this purpose, a control structure can be used that simulates the behavior of a synchronous machine with respect to frequency changes. This behavior stabilizes the grid frequency in a way comparable to conventional power plants. Alternatively, a droop mode control mentioned at the outset, which comprises a frequency-power characteristic curve, can be used. Such a control system is also able to stabilize the grid frequency and can additionally include a voltage-reactive power characteristic, by means of which, in addition to the grid frequency, the grid voltage can also be stabilized and, if necessary, an island grid can be built or stabilized, into which further power generation units can be built can be involved.

The change in the AC active power drawn from the AC voltage network leads to a change in the DC voltage at the electrolyzer, the change in the DC voltage at the electrolyzer resulting in a change in a DC power consumed by the electrolyzer corresponding to the change in the AC active power. As a result, the change in the AC active power taken from the AC voltage network can be passed on to the electrolyzer directly as a change in the DC power consumed by the electrolyzer.

In one embodiment of the method, a voltage translation between the electrolyzer and the converter can be generated by means of a first direct voltage converter (DC / D converter). As a result, the setting range of the DC voltage on the electrolyzer can be expanded compared to the voltage range that can be set by the converter on the DC voltage side, so that the power consumption of the electrolyzer can also be set over a further range.

In addition, the converter can exchange electrical power with a PV generator connected on the DC voltage side, the PV generator being connected to a DC voltage intermediate circuit in parallel with the electrolyser. An electrical power generated by the PV generator is optionally fed into the electrolyzer or into the AC network. As a result, the electrolyzer can be supplied inexpensively with regeneratively generated electrical power that would otherwise have to be obtained from the AC network.

In a further embodiment of the method, the converter can exchange electrical power with a battery connected on the DC voltage side, the battery is connected to the DC link via a second DC / DC converter parallel to the electrolyser. The battery makes it possible to temporarily store electrical power and can decouple the power consumption from the network from the electrolyzer power.

In the embodiments of the method in which a DC / DC converter is arranged between the converter and a unit on the DC voltage side, the DC / DC converter can be used to stabilize the voltage of the DC voltage intermediate circuit. Specifically, regulation of the DC / DC converter can include a precontrol, with the precontrol being used to set a DC current setpoint of the DC / DC converter as a function of a phase difference between the mains voltage and the AC voltage at the input of the converter. The phase difference can be processed in a d-q coordinate system and is proportional to the power drawn from the network. This causes the DC / DC converter to change its power as soon as the phase difference changes and not only in response to a change in the voltage in the DC link.

The precontrol is used to modify the DC current setpoint of the DC / DC converter immediately as a function of a change in the mains frequency. As a result, a change in the voltage at the DC voltage intermediate circuit, which occurs due to a change in the AC active power in response to the change in the grid frequency, is anticipated. The regulation of the DC / DC converter is thus designed in such a way that the DC / DC converter immediately stabilizes the DC link when the mains frequency changes. With rapid changes in the network frequency, i.e. With high rates of change in the mains frequency, which result in correspondingly large phase differences and thus particularly large changes in the AC power, the DC / DC converter must supply or take away energy quickly in order to prevent the DC link voltage from sagging or becoming excessive. For this purpose, the DC current setpoint for the DC / DC converter is precontrolled by the phase phi between the mains voltage and the converter voltage, thus increasing the dynamics of the control.

The voltage at the DC link can be stabilized by the first DC / DC converter and the electrolyser connected to it and / or, if necessary, by the second DC / DC converter and the battery connected to it. The phase difference can act directly or via an appropriate filter on the clocking of the DC / DC converter.

An electrolysis device according to the invention with an electrolyzer which is connected to a converter and, via the converter, electrical AC active power from one Is removed from the AC voltage network, is characterized in that the converter is set up to operate in a voltage-impressing manner, so that a change in the network frequency in the AC network causes an immediate change in the AC active power drawn from the AC network. This invention is based on the knowledge that the direct reactions of the converter associated with the voltage-impressing operation to changes in the grid frequency in the form of changes in the AC active power taken from the AC voltage grid can be passed on directly to an electrolyzer. Although the electrolyser is not in a position to permanently make a correspondingly rapid change in the implemented power, it can be prompted to change the DC power directly, for example by the converter changing the DC voltage on the electrolyzer, and secondly a short-term one Buffer the deviation between an externally impressed power and a static DC power setpoint.

In one embodiment, the electrolysis device can comprise a first direct voltage converter (DC / DC converter), which is arranged between the electrolyzer and the converter. As a result, the setting range of the voltage on the electrolyzer can be expanded compared to the voltage range that can be set by the converter on the DC voltage side, so that the power consumption of the electrolyzer can also be set over a further range.

In a further embodiment, the electrolysis device can comprise a photovoltaic generator which is connected on the DC voltage side parallel to the electrolyser to a DC voltage intermediate circuit of the electrolysis device. By means of the photovoltaic generator, the electrolyser can be supplied inexpensively with regeneratively generated electrical power that would otherwise have to be obtained from the AC voltage network.

In a further embodiment, the electrolysis device can comprise a battery which is connected on the DC voltage side to the DC voltage intermediate circuit of the electrolysis device via a second DC / DC converter parallel to the electrolyzer. The battery makes it possible to temporarily store electrical power and can decouple the power consumption from the network from the electrolyzer power.

In a method for providing instantaneous reserve power for an AC voltage network by means of a converter which takes electrical AC power from the AC voltage network and supplies an electrolyser with electrical DC power, the converter is operated in a voltage-impressing manner, so that a change in the network frequency in the AC voltage network results in an immediate change of the AC active power drawn from the AC network. An electrolyzer proves to be advantageous DC load for the voltage-impressing converter, since on the one hand an electrolyzer can be prompted to change the DC power, for example by changing the DC voltage on the electrolyzer, and on the other hand there is buffering of electrical energy in the electrolyzer so that the electrolyzer despite its inherent inertia, a short-term change in the DC power is well tolerated and thus supports short-term changes in the AC active power to support the grid frequency as part of the instantaneous control.

In normal operation within the scope of the method according to the invention, i.e. In particular at a network frequency that corresponds to a nominal frequency of the AC voltage network, the power taken from the AC voltage network and supplied to the electrolyzer can correspond to between 50% and 100% of a nominal power of the electrolyzer. The electrolyzer has a maximum output that is above the nominal line, the nominal output being able to correspond in particular to an operating point which is characterized by a maximum efficiency of the electrolyzer. In principle, the electrolyzer can therefore take up a DC power that is above the nominal power, especially if the electrolyzer is only operated for a short time at this operating point.

In one embodiment of the method, the converter can exchange electrical power with a battery connected on the DC voltage side if a change in the mains frequency causes a change in the AC power and the DC power supplied to the electrolyzer would lie outside an operating range of the electrolyzer. The operating range can be limited by a lower input power between 10% and 20% of the nominal power and an upper maximum power between 1 10% and 120% of the nominal power of the electrolyzer. The battery can be connected via a DC / DC converter in parallel to the electrolyser to a DC link of the converter.

In a further embodiment of the method, the converter can exchange electrical power with a photovoltaic generator connected on the DC voltage side. In normal operation, that is to say in particular at a grid frequency which corresponds to a nominal frequency of the AC voltage network, the PV generator can be operated at a working point of maximum power and the electrolyzer with nominal power. The power of the PV generator is reduced if there is a change in the grid frequency, which causes the converter to reduce the AC power currently being fed in or to increase the AC power currently being drawn. If, however, a change in the grid frequency occurs, the converter leads to an increase in a current feed-in or a reduction in a current drawn AC power causes the DC power of the electrolyzer to be reduced. This means that the instantaneous reserve is available in both directions at all times.

BRIEF DESCRIPTION OF THE FIGURES

The invention is further explained and described below with reference to exemplary embodiments shown in the figures.

1 shows an electrolysis device according to the invention with a converter and an electrolyzer;

2 shows a device with a converter and a plurality of DC loads;

Fig. 3 shows a further electrolysis device with a converter, a DC voltage converter and an electrolyzer;

FIG. 4 shows an electrolysis device according to FIG. 3 with a control device;

FIG. 5 shows an electrolysis device according to FIG. 3 or 4 with a PV generator;

FIG. 6 shows a method for operating a device according to FIG. 3, 4 or 5;

FIG. 7 schematically shows the electrical powers in a device which is operated using a method according to FIG. 6;

8 shows a further electrolysis device with a converter, an electrolyzer, a DC voltage converter and an energy store; and

FIG. 9 shows an electrolysis device according to FIG. 8 with a further DC voltage converter and a PV generator.

FIGURE DESCRIPTION

1 shows an electrolysis device 10 with an electrolyser 11 and a converter 12. The converter 12 is connected to an AC voltage network 15 via an AC-side input 12a, a decoupling inductor 13, preferably a choke, and a network connection point 14 and takes electrical power from the AC network 15 Power. The electrolyzer 11 is connected to a DC-side output 12b of the converter 12 and is supplied with electrical power by the converter 12.

The converter 12 can have a DC voltage intermediate circuit and is preferably of three-phase design, so that the converter 12 can be connected to a three-phase AC voltage network 15 in order to draw three-phase electrical AC power from the AC voltage network 15. The converter 12 can in particular as self-guided transistor converter can be executed, the transistors of such a converter 12 may consist of IGBTs and / or MOSFETs.

The electrolyzer 11 essentially represents a DC load and is supplied with DC power by the converter 12. The DC power consumed by the electrolyzer 11 depends on a current-voltage characteristic curve from the voltage present at the electrolyzer 11, which corresponds here to the voltage at the output 12b of the converter 12. Depending on the type and design of the electrolyzer 11, the current-voltage characteristic curve can have different threshold voltages and gradients, with a monotonous relationship between current and voltage generally occurring in an allowable input voltage range for the electrolyzer 11, so that the one recorded by the electrolyzer 11 The higher the applied voltage, the higher the DC power.

The electrolyzer 11 has a nominal power at which the electrolyzer 11 can be operated with optimum efficiency. The nominal power is made up of a nominal voltage, which is within the permissible input voltage range of the electrolyser 1 1, and an associated nominal current. In principle, input voltages above the nominal voltage are also permissible and lead to a higher power consumption, the overall efficiency of the electrolyser 1 1 falling above the nominal power, for example due to the increased power requirement for auxiliary units such as pumps and the like.

The converter 12 supplies the electrolyser 11 with a DC power which can be set by the converter 12 as a function of the change in the current mains frequency of the AC network 15, in particular by the voltage at the output 12b of the converter 12 and thus the input voltage of the electrolyzer 1 1 is set by the converter 12 as a function of the change in the current network frequency of the AC network 15.

If the current line frequency corresponds to the nominal frequency and is constant, the converter 12 is operated in such a way that the electrolyser 11 is supplied with a DC power which is equal to or less than the nominal power of the electrolyzer 11. The DC power can preferably be set to a value between 50% and 100% of the nominal power of the electrolyzer at a constant mains frequency.

The converter 12 has semiconductor switches, not shown, which are arranged in a bridge circuit and are controlled by a control unit, not shown, in such a way that a flow of electrical power from the AC voltage network 15 via the converter 12 to the electrolyzer 11 is established. An alternating voltage can be applied to the line-side input 12a of the converter 12 by suitable timing of the semiconductor switches are regulated such that a phase difference is formed between the mains voltage in the AC network 15 and the AC voltage at the input 12a of the converter 12 via the decoupling inductor 13.

By means of such a regulation, a desired electrical AC active power can be set by specifying a setpoint for the phase difference. The desired electrical AC active power results from a setpoint value of the electrical DC power to be output by the converter 12 on the DC voltage side and to be supplied to the electrolyzer. This DC current setpoint is transformed in the control unit of the converter 12 into the corresponding setpoint for the phase difference between the mains voltage and the AC voltage on the input side at the converter 12, so that the setpoint for the phase angle is a function of the desired DC load current. In this case, the active electrical AC power which is drawn from the AC voltage network 15 by the converter 12 is approximately proportional to the phase difference which arises, provided that the phase difference is small compared to p.

On the other hand, the phase difference between the mains voltage and the alternating voltage at the input 12a of the converter 12 is regulated to the desired value by the converter 12 itself, the actual active AC power depending on which phase difference actually exists. As a result, a change in the grid frequency, which inevitably causes a change in the phase difference, leads directly to a largely proportional change in the active electrical AC power drawn from the AC network 15.

A frequency change in the AC network 15 thus correlates with a change in the phase angle, so that the AC active power drawn also changes immediately when the network frequency changes. In this respect, the converter 12 behaves in a voltage-impressing manner in that the active AC power that is drawn from the AC network 15 is immediately reduced when the frequency is reduced and is increased immediately when the frequency is increased.

FIG. 2 shows a device 20 with a plurality of DC loads 21, 22, 23 and a converter 12. The converter 12 is connected on the input side via a network connection point 14 to an AC voltage network 15 and takes electrical power from the AC voltage network 15. The DC loads 21, 22, 23 are each connected to the DC link 16 via one of the switches 21a, 22a, 23a and are supplied with electrical power by the converter 12. Both DC electrolysers 11 and ohmic loads, in particular heating resistors or other resistors which are used, for example, for surface finishing or metal processing, can be used here as DC loads 21, 22, 23. The DC loads 21, 22, 23 can each be connected to the converter 12 or separated from the converter 12 via the switches 21 a, 22a, 23a. As a result, the total DC power flowing at a given voltage at the DC link 16 of the converter 12 can be adjusted by supplying only a portion of the DC loads 21, 22, 23, with the switches 21a, 22a, 23a being controlled appropriately the specific part of loads 21, 22, 23 to be supplied is selected.

Fig. 3 shows an electrolysis device 10 with an electrolyser 1 1 and a converter 12 corresponding to FIG. 1, wherein a DC voltage converter or DC / DC converter 32 is additionally arranged between the electrolyser 11 and converter 12, which has a voltage translation between the voltage on the DC voltage side Output 12b of the converter 12 or on the DC link 16 and the voltage at the electrolyser 1 1 enables. The DC / DC converter 32 can be designed, for example, as a step-up converter, as a step-down converter or as a step-down converter and / or can be set up for a bidirectional power flow.

Such DC / DC converters 32 are known to the person skilled in the art in various embodiments, which mainly comprise clocked semiconductor switches for setting the voltage translation. In particular, the DC / DC converter 32 can be designed as a buck converter for a unidirectional power flow from the converter 12 to the electrolyser 11, which converts the voltage of the DC link 16 into a relatively lower voltage at the electrolyser 11, the transmission ratio being adjustable, for example, by means of a duty cycle is.

4 shows details of a control of the converter 12. A control device 41 generates control signals for the converter 12 and the DC / DC converter 32, which in particular predefine the control of the semiconductor switches of the converter 12 and the DC / DC converter 32. The control signals can be specified by the control device 41 as a function of a target value for an electrical DC power, an actual value of the DC power being able to be determined, for example, on the basis of a current and voltage measurement, in particular between the DC / DC converter 32 and the electrolyzer 11 can be arranged. The control device 41 determines a suitable duty cycle with which the DC / DC converter 32 has to be operated in order to set a suitable voltage on the electrolyzer 11 so that the electrolyzer 11 consumes the desired DC power. Since the voltage of the DC voltage intermediate circuit 16 is at least as high as the rectified mains voltage of the AC voltage network 15, the DC / DC converter 32 makes it possible, in contrast to the embodiment according to FIG. 1, to apply a significantly lower voltage than the rectified mains voltage to the electrolyzer 11 . Given a given duty cycle, the voltages on both sides of the DC / DC converter 32 are proportional to each other. Therefore, a change in the voltage of the DC link 16 leads to a proportional change in the voltage at the electrolyzer 1 1, provided that the duty cycle is not tracked. Conventional controls are able to track the duty cycle with a certain delay, whereby various higher-level control objectives can be pursued. In particular, the voltage at the electrolyzer 11 and thus the DC power can be kept constant. Alternatively, the voltage of the DC link 16 can be kept constant.

As explained in connection with FIG. 1, the converter 12 can work in a voltage-impressing manner in that the AC active power which is drawn from the AC voltage network 15, in particular as a function of the phase angle between the line voltage and the AC voltage at the input 12a of the converter 12, reduces and reduces the frequency immediately is increased immediately with a frequency increase. Such an immediate change in the active AC power leads to a corresponding change in the voltage of the DC link 16, provided the DC power remains unchanged. However, even a constant DC power is not sufficient to counteract a change in the voltage of the DC link 16 due to a change in the AC active power due to the frequency. Therefore, the DC power must be adapted to the AC power, wherein tracking the setpoint for the DC power as a function of the voltage of the DC link 16 to stabilize this voltage represents an indirect and correspondingly delayed response.

The control device 41 therefore determines the instantaneous phase difference between the line voltage in the AC voltage network 15 and the AC voltage at the input 12a of the converter 12 from time-resolved measurements of the voltages before and after the decoupling inductance 13. This phase difference can be used in the control device 41 for pre-controlling the setpoint of the DC / DC converter 32 are used. As a result, the setpoint for the DC power and thus the pulse duty factor of the DC / DC converter 32 is already adjusted in response to a change in the phase difference. This adaptation takes place before a significant change in the voltage of the DC link 16 occurs, which is accompanied by a change in the AC active power, in particular when the AC active power is changed in response to a change in the phase difference due to the voltage-impressing control of the converter 12. This significantly increases the dynamics of the entire control system. Fig. 5 shows an electrolysis device 10 with a PV generator 51, which is connected in parallel to the electrolyzer 11 with the DC link 16 of the converter 12. The electrical power of the PV generator 51 can be set via the voltage of the DC voltage intermediate circuit 16 and optionally fed into the electrolyser 11 or exchanged with the AC voltage network 15 via the converter 12. The operating point of the PV generator 51 is set on the basis of the voltage on the DC link 16, while the voltage on the electrolyser 11 can be set independently of this via the DC / DC converter 32.

FIG. 6 schematically shows an exemplary sequence of a method for providing control power by means of an electrolysis device 10 according to FIG. 5. In normal operation of the electrolysis device 10, for example with a balanced power balance in the AC network 15 with a network frequency that corresponds to the nominal frequency of the AC network 15 and is largely constant (step S1 in FIG. 5), the PV generator 51 can be operated at an operating point with the maximum possible power P_MPP and the electrolyser with its nominal power P_Nom (step S2).

In the event of a change in the grid frequency, the converter 12 of the electrolysis device 10 reacts with a change in the AC active power (step S3). From step S3, depending on the sign of the power imbalance that leads to the change in the network frequency, the method branches to steps S4a and S5a in the event of a power deficit in the AC network 15 and to steps S4b and S5b in the event of a power surplus in the AC network 15.

In step S5a, the change in the AC power in the electrolysis device 10, which counteracts the power deficit in the AC network 15, is implemented by reducing the DC power P_Last of the electrolyzer 11 compared to the rated power P_Nenn. The PV power P_PV of the PV generator 51 can remain unchanged at P_MPP.

In step S5b, the change in the AC power in the electrolysis device 10, which counteracts the excess power in the AC network 15, has the opposite sign and could be implemented by increasing the DC power P_Last of the electrolyzer 11 compared to the rated power P_Nenn. However, this proves to be disadvantageous in particular if the maximum output is only slightly above the nominal output of the electrolyzer 11 and / or the efficiency of the electrolyzer 11 drops significantly for DC outputs above its nominal output. Therefore, in addition or as an alternative, in step S5b the PV power P_PV is reduced compared to the maximum possible power P_MPP. Incidentally, this is possible at any time, especially at night when the maximum possible power P_MPP is zero by feeding DC power back into the PV generator 51.

The DC powers P load and P_PV can be set separately from one another, in particular in an electrolysis device 10 according to FIG. 5 or FIG. 9. The PV power P_PV is set via the voltage at the DC link 16, while the DC power P load of the electrolyser 1 1 results from the voltage at the DC link 16 and the adjustable transmission ratio of the DC / DC converter 32. By operating the electrolysis device 10 with the method according to FIG. 6, it is thus possible to provide instantaneous reserve power for stabilizing the AC voltage network 15, control power for eliminating a power deficit by reducing the DC power of the electrolyser 11 and control power for eliminating a power surplus by regulating the PV generator 51 is realized.

7 schematically shows an exemplary distribution of the provision of the control power as a function of the power balance in the AC network 15.

In the case of a balanced power balance, which can be expressed in particular by the fact that the grid frequency is constant and in particular corresponds to the nominal frequency of the AC network 15, the PV generator 51 is operated with the maximum possible power P_MPP and the electrolyzer 1 1 with the nominal power P_Nenn. The nominal power P_Nenn of the electrolyser 1 1 is a device property and can therefore be assumed to be largely constant. A current sum of the powers P_PV and P_Last and therefore also the AC power exchanged with the AC voltage network 15 via the converter 12 therefore depends essentially on the current solar radiation on the PV generator 51. Depending on the ambient conditions, the AC power can therefore lie between the nominal power P_Nenn of the electrolyzer 1 1 (e.g. at night, without sunlight) and the difference between the nominal power P_Nenn of the electrolyzer 1 1 and a nominal power of the PV generator 51. In a possible special case, in which the nominal powers of the electrolyzer 11 and the PV generator 51 are identical, the AC power in normal operation is therefore between P_nom and zero.

In the event of a power deficit in the AC network 15, the DC power P load supplied to the electrolyzer 11 is reduced, while the PV power P_PV can still correspond to the maximum possible PV power P MPP. In particular, a change rate of the network frequency can be used as a measure of the power deficit, so that the change in power is, for example, proportional to the change rate of the network frequency; this can apply analogously to a surplus in performance. In the event of an excess power in the AC network 15, the electrolyzer 11 continues to be operated with its nominal power P_Nom. In principle, the electrolyzer 11 could also be operated with a power greater than P_Nenn, but as a rule only with reduced efficiency and / or only for a short time. In order to counteract the excess power in the AC network 15, the power P_PV taken from the PV generator 51 is therefore additionally or alternatively reduced. The PV power P_PV can become zero and negative, ie DC power can be fed back into the PV generator 51 and consumed there. Since the maximum possible PV power P_MPP can be very small at times, as described, for example at night, the reduction in the PV power P_PV can also be implemented exclusively by the power fed into the PV generator 51 depending on the excess power in the AC network 15 is increased.

In a special configuration, the nominal power P_Nenn of the electrolyzer 11 can correspond approximately to the nominal power P_Peak of the PV generator 51. In this case, the complete nominal power P_Nenn of the electrolyser 11 is available for reacting to a power deficit in the AC network 15, while at least the complete nominal power P_Peak of the PV generator 51 is available at any time, in particular also at night, for reacting to a power surplus in the AC voltage network 15 . Overall, an electrolysis device 10 configured in this way thus provides an optimal symmetrical control power band with positive and negative control power in an identical order of magnitude.

In principle, many other configurations of the electrolysis device 10 are conceivable, for example intermediate variants with an electrolyser 11 as the main component, which is operated in normal operation at approximately 50% of the nominal power P_nom, and a PV generator 51 with a relatively small nominal power P_PV <P_nom. The PV generator 51 takes over part of the power change in response to a power surplus in the AC network 15. The greater the nominal power P_Peak of the PV generator, the higher the target power P_Last of the electrolyzer 11 can be selected in normal operation.

Another intermediate variant comprises an electrolysis device 10 with a PV generator 51 as the main component, which is operated in normal operation with the maximum possible power P MPP, and an electrolyzer 11 with a relatively low nominal power P_Nenn <P_Peak. The electrolyser 1 1 takes over the power change in response to a power deficit in the AC network 15, so that a symmetrical control power band can be offered, which is based on the nominal power P_Nenn of the electrolyser 1 1 on the one hand and, if necessary, the same reduction of the PV On the other hand, generator 51 is composed and thus only depends on the nominal power P_Nenn or makes it fully usable for the instantaneous reserve.

FIG. 8 shows a further embodiment of an electrolysis device 10 with a converter 12 and an electrolyzer 11. Compared to FIG. 1, the electrolysis device 10 according to FIG. 8 additionally comprises a battery 81, which is connected via a DC / DC converter 82 in parallel to the electrolyzer 11 is connected to the DC voltage intermediate circuit 16 of the converter 12. The DC / DC converter 82 can in particular control the power exchange between the DC voltage intermediate circuit 16 and the battery 81 in such a way that the voltage at the DC voltage intermediate circuit 16 is stabilized, a pilot control analogous to FIG. 4 possibly being used. In addition, a further degree of freedom is available for the specific configuration of the electrolysis device 10 according to FIG. 8 by the battery 81, in order to exclude individual contributions to the provision of a symmetrical control power band as an instantaneous reserve. For example, a power change in response to a power deficit in the AC network 15 can be implemented entirely by reducing the DC power P_Last of the electrolyzer 11 to a value below its nominal power P_Nenn, while a power change in response to a power surplus in the AC network 15 can be implemented entirely by feeding of DC power is realized in the battery 81; the energy thus stored in the battery can in turn be used to operate the electrolyser 11.

FIG. 9 shows a further embodiment of an electrolysis device 10 with a converter 12 and an electrolyser 11 connected to the converter 12 via a DC / DC converter 32. Compared to FIG. 3, the electrolysis device 10 according to FIG. 9 additionally includes a battery 81, which, analogously to FIG. 8, is connected to the DC voltage intermediate circuit 16 of the converter 12 via a further DC / DC converter 82, and a PV generator 51, which 5 is also connected to the DC voltage intermediate circuit 16 of the converter 12, possibly via a third DC / DC converter, not shown here. The electrolysis device 10 according to FIG. 9 essentially combines the features of the electrolysis devices 10 according to FIGS. 5 and 8 and therefore also has their advantages. REFERENCE SIGN LIST

10, 20 electrolysis device

11 electrolyzer

12 inverters

12a entrance

12b output

13 decoupling inductance

14 Grid connection point

15 AC network

21, 22, 23 DC load

21a, 22a, 23a switches

32, direct voltage converter (DC / DC converter)

41 control device

51 photovoltaic generator (PV generator)

S1 -S3 process steps

S4a, S4b process steps

S5a, S5b procedural steps

81 battery

82 direct voltage converters (DC / DC converters)

Claims

PATENT CLAIMS

1. Method for operating an electrolysis device (10) with a converter (12), which is connected to an AC voltage network (15) via an uncoupling inductor (13) and takes an AC active power from the AC network (15), and an electrolyzer ( 1 1), which is connected on the DC voltage side to the converter (12) and is operated at an electrical power frequency that corresponds to a nominal frequency of the AC voltage network (15) and is constant over time with an electrical power that is between 50% and 100% of a nominal power of the electrolyser (11), the converter (12) being operated in a voltage-impressing manner, so that the active AC power drawn from the AC voltage network (15) is changed directly as a function of a change and / or a rate of change in the network frequency in the AC voltage network (15).

2. The method according to claim 1, wherein the converter (12) provides an instantaneous reserve power, the converter (12) simulating the behavior of a synchronous machine with respect to frequency changes or using a droop mode control which comprises a frequency-power characteristic.

3. The method according to claim 1 or 2, wherein the change in the AC power supply (15) taken from the AC active power leads to a change in a DC voltage at the electrolyzer (1 1), the change in the DC voltage at the electrolyzer (1 1 ) leads to a change in a DC power consumed by the electrolyzer (11) corresponding to the change in the AC active power.

4. The method according to claim 1 or 2, wherein a voltage translation between the electrolyzer (11) and the converter (12) is generated by means of a first DC-DC converter (32).

5. The method according to claim 4, wherein the converter (12) exchanges electrical power with a PV generator (51) connected on the DC voltage side, the PV generator (51) being connected in parallel with the electrolyzer (11) to a DC voltage intermediate circuit (16), wherein an electrical power generated by the PV generator (51) is optionally fed into the electrolyzer (11) or into the AC network (15).

6. The method according to any one of claims 1 to 5, wherein the converter (12) exchanges electrical power with a battery (81) connected on the DC voltage side, wherein the battery (81) is connected to the direct voltage intermediate circuit (16) via a second direct voltage converter (82) parallel to the electrolyzer (11).

7. The method according to any one of claims 4 to 6, wherein the first DC voltage converter (32) stabilizes the voltage of the DC voltage intermediate circuit (16) and a control of the first DC voltage converter (32) comprises a pilot control, wherein by means of the pilot control a DC current setpoint of the first DC voltage converter (32) is set depending on a phase difference between the mains voltage and the AC voltage at the input (12a) of the converter (12).

8. The method according to claim 6, wherein the second DC voltage converter (82) stabilizes the voltage of the DC voltage intermediate circuit (16) and a regulation of the second DC voltage converter (82) comprises a pilot control, wherein by means of the pilot control a DC current setpoint of the second DC voltage converter (82) in Depending on a phase difference between the mains voltage and the AC voltage at the input (12a) of the converter (12) is set.

9. Electrolysis device (10) with an electrolyzer (1 1), which is connected to a converter (12) and takes electrical AC active power from an AC voltage network (15) via the converter (12), characterized in that the converter (12 ) is set up to be operated in a voltage-impressing manner so that a change in the network frequency in the AC network (15) causes an immediate change in the active power drawn from the AC network (15).

10. electrolysis device (10) according to claim 9, wherein a first DC converter (32) between the electrolyzer (1 1) and converter (12) is arranged.

11. Electrolysis device (10) according to claim 9 or 10, wherein a photovoltaic generator (51) is connected on the DC voltage side parallel to the electrolyzer (1 1) with a DC voltage intermediate circuit (16) of the electrolysis device (10).

12. Electrolysis device (10) according to one of claims 9 to 1 1, wherein a battery on the DC voltage side via a second DC converter (82) parallel to the electrolyzer (1 1) is connected to a DC voltage intermediate circuit (16) of the electrolysis device (10).

13. A method for providing instantaneous reserve power for an AC voltage network (15) by means of a converter (12) which takes electrical AC power from the AC voltage network (15) and an electrolyzer (12) with electrical DC power supplied, the converter (12) being operated in a voltage-impressing manner, so that a change in the mains frequency in the AC voltage network (15) causes an immediate change in the AC power drawn from the AC voltage network (15).

14. The method according to claim 13, wherein at a network frequency that corresponds to a nominal frequency of the alternating voltage network (15), the active power removed from the alternating voltage network (15) and supplied to the electrolyzer (11) is between 50% and 100% of a nominal power of the electrolyzer (11) corresponds.

15. The method according to claim 13 or 14, wherein the converter (12) exchanges electrical power with a battery (81) connected on the DC voltage side when a change in the mains frequency causes a change in the AC power and the DC power supplied to the electrolyzer (11) is on the edge of an operating range of the electrolyzer (1 1), the operating range being limited by a lower insertion power between 10% and 20% of the nominal power and an upper maximum power between 80% and 100% of the nominal power of the electrolyzer (11), the battery (81) is connected to a DC voltage intermediate circuit (16) of the converter (12) in parallel to the electrolyzer (10) via a DC voltage converter.

16. The method according to claim 15, wherein the converter (12) exchanges electrical power with a photovoltaic generator (51) connected on the DC voltage side, the PV generator (51) at a working point at a grid frequency that corresponds to a nominal frequency of the AC voltage grid (15) maximum power and the electrolyzer (11) are operated at nominal power, the power of the PV generator (51) being reduced when a change in the grid frequency occurs, which causes the converter (12) to reduce a current feed-in or an increase in one induced AC power, and wherein the DC power of the electrolyser (11) is reduced when a change in the mains frequency occurs, which causes the converter (12) to increase a currently fed AC power or to reduce a currently drawn AC power prompted.