Electrolysis device

Abstract

The invention relates to an electrolysis device (1) comprising a converter (2), an electrolyzer (3), and network connections (4). In order to improve the properties of the electrolysis, the electrolysis device (1) comprises two converters (2), wherein the converters (2) are arranged in a parallel circuit on the DC voltage side, the electrolyzer (3) is electrically connected to the DC voltage side of the converter (2), each phase (21) of the converters (2) is electrically connected to one of the network connections (4) via a choke (5), and the electrolysis device (1) has a controller (6) which is designed to clock the converters (2) with time offsets. The invention additionally relates to a method for operating such an electrolysis device (1), wherein the converters (2) are clocked with time offsets.

Description

[0001] Description

[0002] Electrolysis device

[0003] The invention relates to an electrolysis device comprising a power converter, an electrolyzer, and power connections. Furthermore, the invention relates to a method for operating such an electrolysis device.

[0004] With the help of an electrolyzer, a material transformation can be brought about as a chemical reaction. This is where electrolysis takes place. The electrolyzer is supplied with electrical energy from an energy source or a power grid. An alternating voltage from the energy source or the power grid is converted into a direct voltage for the electrolyzer by means of a power converter. This power converter is therefore also called a rectifier. Line-commutated power converters such as diode rectifiers or thyristor power converters, also known as thyristor-controlled power converters, are used as power converters. Self-commutated power converters, for example those based on IGBT semiconductors, are also known. These self-commutated power converters are also called pulsed power converters because of their pulsed operation.

[0005] Chokes can be designed as common-mode chokes. The choke has multiple windings that are magnetically coupled. The magnetic coupling suppresses common-mode currents. In contrast, a choke can also be designed as a differential-mode choke. In this case, the coupling suppresses differential-mode currents.

[0006] In the future, electrolysis will become increasingly important for the economical and environmentally friendly production of hydrogen, for example, as a synthetic fuel. Hydrogen is produced using an electrolyzer or a corresponding electrolysis device. This hydrogen-based fuel can significantly contribute to reducing climate-damaging CO2 emissions.

[0007] From the publication "Control methods for self-commutated power converters" (Felix Jenni, Dieter Wüest; Zurich: vdf, University Publishers at ETH Zurich; Stuttgart: Teubner, 1995) a staggered clocking of power converters is known.

[0008] The invention is based on the object of improving an electrolysis device.

[0009] This object is achieved by an electrolysis device having two power converters, an electrolyzer and mains connections, wherein the power converters are arranged in a parallel circuit on the DC voltage side, wherein the electrolyzer is electrically connected to the DC voltage side of the power converter, wherein each phase of the power converters is electrically connected to one of the mains connections via a choke, wherein the electrolysis device has a control device which is set up to clock the power converters in an offset manner. Furthermore, the object is achieved by a method for operating such an electrolysis device, wherein the power converters are clocked in an offset manner.

[0010] Further advantageous embodiments of the invention are specified in the dependent claims.

[0011] The invention is based, among other things, on the realization that the operation of an electrolyzer can be significantly improved if the voltage on the DC side of the converter, which is used to feed the electrolyzer, is ideally free of harmonics. Even a reduction in harmonics can sometimes lead to a significant increase in the efficiency of the electrolysis. The formation of harmonics is prevented or at least suppressed. The use of self-commutated converters allows the pulse frequency of these converters to be specified and varied. It is also possible to offset clock pulses between converters arranged in parallel.

[0012] A large proportion of harmonics, particularly low-frequency harmonics below 1 kHz, can be eliminated by designing the converter as a self-commutated converter. In other words, the converter is designed as a pulse-controlled converter. For consistent energy absorption from the power grid and easy transmission of electrical energy, it has proven advantageous for the converter to be three-phase, thus ensuring three-phase energy transfer between the grid connections and the converter.

[0013] To further reduce harmonics, at least two converters are installed in the electrolysis device to convert the alternating voltage from an energy source or a power grid (where the energy source can also be part of the power grid) into the direct voltage for powering the electrolyzer. These converters are arranged in parallel on the direct voltage side. The grid connections of the electrolysis device serve to connect the electrolysis device to a power grid.

[0014] Pulse converters with a DC link typically operate with capacitors in the DC link as energy storage devices. These capacitors are loaded with an alternating current during switching operations in the converter. The resulting losses and the permissible current-carrying capacity of the capacitors are a key dimensioning criterion.

[0015] The individual phases of the converters are each connected to one of the mains connections via a choke. The choke serves to decouple the two converters. To reduce DC-side currents and voltages, the two converters are clocked at an offset. This offset clocking compensates for the harmonics at the clock frequency.

[0016] In order to exploit the effect of the offset clocking, at least two converters are arranged in parallel on the DC side.

[0017] Today, electrolyzers are mostly powered by line-commutated converters, particularly thyristor or diode converters. These have a high energy density and can therefore provide high power for the electrolysis process. However, it has been shown that due to the low harmonic load, the electrolyzer can be operated much more efficiently. For the same yield from the chemical reaction in the electrolyzer, significantly less electrical power is required, so the high power density of line-commutated converters is no longer necessary. The same amount of material can also be produced through electrolysis with a lower total power of at least two self-commutated converters, i.e. pulse-controlled converters.

[0018] This effect is particularly clear for the production of hydrogen by electrolysis. Even with lower electrical power and a lower harmonic content in the direct voltage, the same, if not a larger, amount of hydrogen can be produced by the electrolyzer. This is particularly the case when harmonics below 50 kHz are eliminated by the staggered clocking. Even when harmonics in a frequency range up to 10 kHz are eliminated, a significantly improved and more efficient production of hydrogen can be demonstrated, measured in terms of the required electrical power. In other words, with a lower harmonic content, particularly with harmonics below 10 kHz or 50 kHz, significantly less electrical power is required for the electrolysis.

[0019] To date, grid-commutated converters with a direct current intermediate circuit have been predominantly used for hydrogen production. It is proposed, on the one hand, to use self-commutated pulse-controlled converters with a direct current intermediate circuit. It is also proposed to divide this overall converter, designed as a pulse-controlled converter, into several converters arranged in parallel on the DC side, and to operate the switching elements of the individual converters with a phase shift in order to optimize operation and dimensioning.

[0020] In an advantageous embodiment of the invention, the choke has two windings and three terminals, wherein a first of the windings is arranged between a first terminal of the three terminals and a second terminal of the three terminals, wherein a second of the windings is arranged between the first terminal of the three terminals and a third terminal of the three terminals, wherein the first terminal is electrically connected to one of the mains terminals, wherein the second terminal is electrically connected to a phase of a first power converter of the two power converters, wherein the third terminal is electrically connected to a phase of a second power converter of the two power converters, wherein the windings are magnetically coupled in such a way thatthat magnetic fields caused by a current in one direction from the first terminal to the second terminal of the choke and by a current in the direction from the first terminal to the third terminal at least partially compensate each other. With these coupled windings, a particularly simple and cost-effective decoupling of the two power converters can be achieved. The magnetic coupling of the two windings can, for example, be achieved by arranging them on the same core, which carries the magnetic field within the choke. The windings are aligned to one another in such a way that a current between the two power converters experiences a high inductance, while a current of the same size between the first terminal of the choke and the two power converters experiences a low inductance. A choke of this type is also referred to as a push-pull choke. This has the advantage that this choke, in particular the magnetic circuit of the choke,only needs to be designed for the harmonics between the converters. Due to the compensating effect of the current from the grid connection to the two converters, this plays no or almost no role in the design. Since the proportion of harmonics is very small compared to the current drawn from the power grid, the choke can be designed to be particularly small, compact, and cost-effective. Furthermore, due to its high inductance, this choke enables particularly good decoupling between the converters, especially if the electrolysis device has exactly two converters between the two converters. Furthermore, this decoupling is independent of the electrical power of the electrolysis device.

[0021] In this case, one such choke is provided for each phase, which is connected to one of the mains connections, a phase of the first converter and a phase of the second converter.

[0022] When using more than two converters, the chokes each have a corresponding number of windings, i.e., additional windings beyond the two. The number of windings per choke corresponds to the number of converters. One terminal of the additional windings is connected to the mains connection, and the other terminal is connected to a phase of the additional converter.

[0023] In a further advantageous embodiment of the invention, an additional choke is arranged between the respective mains connections and the choke. The choke, which is equipped with two coupled windings, primarily acts on the harmonics that arise as a result of the switching operations between the power converters. In order to also influence and optimise the behaviour with regard to the mains connection, in particular with regard to the power consumption from the energy supply network, it has proven advantageous to arrange a corresponding component as an additional choke between the choke and the mains connection. This allows the control behaviour with regard to power consumption and the interference behaviour with regard to harmonics to be designed, dimensioned and improved separately from one another.The resulting chokes are correspondingly small and inexpensive to manufacture, since they are essentially designed to match the performance of the electrolysis device.

[0024] In a further advantageous embodiment of the invention, a transformer is arranged between the mains connections and the choke. With the help of the transformer, the electrolysis device is galvanically isolated from the power supply network or the power source. This arrangement has proven particularly advantageous in electrolysis because the electrodes always pose the risk of stray currents. These can lead, for example, to a current path being closed via the earth potential and to unwanted currents within the electrolysis device or the electrolyzer. With the help of the transformer, these currents can be effectively avoided. In addition, the transformer allows the voltage level of the electrolysis device to be adapted to the voltage level of the power supply network or the voltage source.

[0025] If the transformer provides separate windings for the connection to the respective converters, galvanic decoupling between the converters is also provided. This also allows compensating currents, particularly alternating current components in the compensating currents, to be avoided or reduced between the converters. This can contribute significantly to efficient operation of the electrolysis device. The invention is described and explained in more detail below with reference to the exemplary embodiments illustrated in the figures. They show:

[0026] FIG 1 to FIG 3 Examples of an electrolysis device

[0027] 1 shows an electrolysis device 1. This comprises an electrolyzer 3 which is fed by two pulse-controlled power converters 2 arranged in parallel on the DC voltage side. A capacitor 11 is arranged in the intermediate circuit to support the input voltage of the electrolyzer 3. The two pulse-controlled power converters 2 are self-commutated power converters 2 with turn-off semiconductors. These power converters 2 are controlled and / or regulated by a control device 6 which makes it possible to clock the two power converters 2 in an offset manner. On the input side, i.e. on the AC voltage side, the power converters 2 are three-phase. To absorb electrical energy, the power converters 2 are connected to mains connections 4 on the AC voltage side via a transformer 8 and chokes 5. Due to the three-phase nature, there are three mains connections 4.For reasons of clarity, however, only one is shown, and the three phases are indicated by corresponding lines on the electrical connection. The power converter 2 also has three inputs, which are also referred to as phases and are not shown in detail in FIG. 1. The mains connections 4 are also connected in three-phase fashion to an energy source 9 or a power supply network. The energy source 9 can be part of a power supply network.

[0028] With the help of the chokes 5, the power of the energy supply device can be regulated and controlled more easily and precisely. With the help of the transformer 8, the voltage level of the electrolysis device 1, i.e., the power converters 2 arranged therein, can be adapted to the voltage level of the energy source 9. Furthermore, the power converters 2 can be decoupled on the AC side by separate windings of the transformer 8. Furthermore, the chokes 5 also contribute to the decoupling of the power converters 2.

[0029] Alternatively, the electrolysis device 1 can also be connected to a single-phase power source 9. In this case, both the power converter 2 and the transformer 8 are single-phase. In this case, two mains connections 4 are present, one for the phase and one for the neutral conductor, which serves as the reference point.

[0030] FIG. 2 shows a further exemplary embodiment of an electrolysis device 1. To avoid repetition, reference is made to the description of FIG. 1 and to the reference symbols introduced. For reasons of clarity, the control device 6 for controlling or regulating the power converter 2 has been omitted.

[0031] In this exemplary embodiment, the choke 5 is designed with two windings 50 which are magnetically coupled and form a push-pull choke. The electrolysis device 1 has a choke 5 of this type for each phase 21 of the power converter 2. A first connection 51 of the choke 5 is connected to one of the mains connections 4, a second connection 52 of the choke 5 is connected to a first of the power converters 2, and a third connection 53 of the choke 5 is connected to a second of the power converters 2. The coupling of the windings 50 is designed such that a greater inductance results for a current between the second connection 52 and third connection 53 than for a current between the first connection 51 and the second connection 52 orbetween the first terminal 51 and the third terminal 53, since the magnetic fields generated in the choke 5 are at least partially compensated by a current from the first terminal 51 to the second terminal 52 and a current from the first terminal 51 to the third terminal 53. A choke 5 of this type is also referred to as a push-pull choke. The energy supply is, as shown, preferably three-phase, but can alternatively also be single-phase. The three phases of the energy source 9 are designated Lx, L2 and L3. The coupling of the windings 50 and the windings 50 themselves are designed such that the desired behavior results for the energy supply to the electrolyzer 3 and the decoupling of the two power converters 2. In this exemplary embodiment, too, the power converters 2 are preferably clocked in an offset manner.Due to the compensating effect of the currents from the first connection 51 to the second connection 52 and from the first connection 51 to the third connection 53, the magnetic circuit of the choke 5 only needs to be designed for the interference current behavior of the harmonics. For the behavior with regard to energy consumption, as shown in FIG 3, a further choke 7 can be arranged in the connection between the mains connection 4 and the choke 5, which improves the behavior of the energy consumption, in particular with regard to controllability and / or regulateability. Then only this further choke 7 needs to be designed in terms of its magnetic design for the current to the energy source 9. Furthermore, in order to adapt the voltage levels of the energy supply network 9 and the electrolysis device 1, as shown in FIG 3, a transformer 8 can be arranged in the electrolysis device 1 between the mains connections 4 and the further choke 7.To avoid repetition in the description of the embodiment of FIG. 3, reference is made to the description of FIGS. 1 and 2 and to the reference symbols introduced there.

[0032] In summary, the invention relates to an electrolysis device 1 with a power converter 2, an electrolyzer 3 and grid connections 4. In order to improve the electrolysis properties, it is proposed that the electrolysis device 1 comprises two power converters 2, wherein the power converters 2 are arranged in a parallel circuit on the DC voltage side, wherein the electrolyzer 3 is electrically connected to the DC voltage side of the power converter 2, wherein each phase 21 of the power converter 2 is electrically connected to one of the grid connections 4 via a choke 5, wherein the electrolysis device 1 has a control device 6 which is designed to clock the power converters 2 in an offset manner. Furthermore, the invention relates to a method for operating such an electrolysis device 1, wherein the power converters 2 are clocked in an offset manner.

Claims

Patent claims 1. Electrolysis device (1), comprising two self-commutated power converters (2), an electrolyzer (3) and mains connections (4), wherein the power converters (2) are arranged in a parallel circuit on the DC voltage side, wherein the electrolyzer (3) is electrically connected to the DC voltage side of the power converter (2), wherein each phase (21) of the power converters (2) is electrically connected to one of the mains connections (4) via a choke (5), wherein the electrolysis device (1) has a control device (6) which is set up to clock the power converters (2) in an offset manner.

2. Electrolysis device (1) according to claim 1, wherein the choke (5) has two windings (50) and three terminals (51, 52, 53), wherein a first of the windings (50) is arranged between a first terminal (51) of the three terminals (51, 52, 53) and a second terminal (52) of the three terminals (51, 52, 53), wherein a second of the windings (50) is arranged between the first terminal (51) of the three terminals (51, 52, 53) and a third terminal (53) of the three terminals (51, 52, 53), wherein the first terminal (51) is electrically connected to one of the mains terminals (4), wherein the second terminal (52) is electrically connected to a phase (21) of a first power converter of the two power converters (2), wherein the third terminal (53) is electrically connected to a phase (21) of a second power converter of the two power converters (2), wherein the windings (50) are magnetically coupled in such a waythat magnetic fields caused by a current in a direction from the first terminal (51) to the second terminal (52) of the choke (5) and by a current in the direction from the first terminal (51) to the third terminal (53) at least partially compensate each other.

3. Electrolysis device (1) according to one of claims 1 or 2, wherein a further choke (7) is arranged between the respective mains connections (4) and the choke (5).

4. Electrolysis device (1) according to one of claims 1 to 3, wherein a transformer (8) is arranged between the mains connections (4) and choke (5).

5. A method for operating an electrolysis device (1) according to one of claims 1 to 4, wherein the power converters (2) are clocked in an offset manner.

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