Circuit arrangement, method for operating a circuit arrangement and electrolysis system

Abstract

The invention relates to a circuit arrangement (1) for supplying direct current to a plurality of electrolysis rows connected in parallel (3a, 3b, 3c, 3d). The circuit arrangement (1) has a first supply branch (5) and a second supply branch (7) each having a three-phase transformer (9, 11). Two supply lines (13a, 13b) are guided out of a three-phase transformer (9, 11) on the secondary side, to each of which supply lines a rectifier (15a, 15b) is connected and therefore by means of a rectifier (15a, 15b) an input-side alternating current can be converted into an output-side direct current for supplying an electrolysis row (3a, 3b, 3c, 3d). A control device (17) is provided which is designed such that in the event of a standstill of one of the electrolysis rows (3a, 3b, 3c, 3d) in one of the supply branches (5, 7), an additional phase displacement (∆φ) can be applied to the output-side direct current of the other rectifier (15a, 15b) in this supply branch (5, 7), and therefore a phase adjustment is effected with one of the rectifiers (15a, 15b) in the other supply branch (5, 7). The invention further relates to a method for operating a circuit arrangement (1) and to an electrolysis system (21) having a circuit arrangement (1).

Description

[0001] Description

[0002] Circuit arrangement, method for operating a circuit arrangement and electrolysis system

[0003] The invention relates to a circuit arrangement for supplying direct current to several parallel-connected electrolysis series. Furthermore, the invention relates to a method for operating such a circuit arrangement and to an electrolysis system.

[0004] Electrolysis, processes in which a chemical reaction is induced using electrical current, is used in many technical fields and is used, for example, to produce various substances. For example, hydrogen and oxygen can be produced through the electrolysis of water. For the operation of electrolysis devices, also called electrolysis stacks or electrolyzers, it is desirable, especially on a large-scale, for them to be operated as energy-efficiently and safely as possible.

[0005] In an electrolyzer, the individual electrolysis cells are typically stacked in an axial direction to form a module comprising a plurality of individual cells and installed to form the module or electrolysis module. An electrolyzer usually has a plurality of modules which together form a so-called electrolysis stack, electrolysis row, or simply "stack." For example, 50 electrolysis cells can be stacked axially to form a module, and in turn, for example, 5 modules can be stacked in the axial direction to form a stack or electrolysis row, so that such an electrolysis row can therefore comprise, for example, 250 cells in an overall axial assembly.

[0006] It is currently known that several electrolyzers are connected in series, with each electrolyzer being supplied via its own galvanically isolated circuit comprising a transformer with a tap changer for coarse control of the electrolyzers and a rectifier with a thyristor circuit for fine control of the electrolyzers, which is a very complex implementation. Alternatively, in order to reduce the circuit complexity, it is also known that the electrolyzers are connected in parallel and operated via a rectifier. However, this can result in current being divided according to the resistance ratios of the electrolyzers and thus in significant derating as well as the risk of one or more electrolyzers operating outside their safe operating ranges.

[0007] To operate electrolysis systems (e.g. hydrogen electrolysis), a high direct current in the range of several kiloamperes is required. Thyristor-based rectifier systems are typically used to provide this direct current. These systems are very popular because of their high reliability and cost-effectiveness. However, thyristor-based rectifiers emit a high level of harmonics into the connected electrical supply grid. Therefore, for large electrolysis systems of, for example, 100 MW and above for industrial applications, grid compatibility is becoming increasingly important alongside cost-effectiveness. Grid interference must therefore be avoided or limited in order to ensure the connectivity and compatibility of the electrolysis system as a large consumer at the grid connection point to the supply grid.Undesirable network disturbances occur in particular as a result of planned or unforeseen load changes and the associated reduced consumption of electrolysis current on the electrolysis side.

[0008] Against this background, the invention is based on the object of specifying an improved circuit arrangement for supplying direct current to a plurality of electrolysis series connected in parallel, which is characterized in particular by better network compatibility. This object is achieved according to the invention by a circuit arrangement for supplying direct current to a plurality of electrolysis series connected in parallel, wherein the circuit arrangement has a first supply branch and a second supply branch with a respective three-phase transformer, and wherein two supply lines are led out of a three-phase transformer on the secondary side, into each of which a rectifier is connected, so that an input-side alternating current can be converted into an output-side direct current for supplying an electrolysis series by a rectifier, and wherein a control device is provided which is designed in such a way thatthat when one of the electrolysis series in one of the supply branches is at a standstill, an additional phase shift can be imposed on the output-side direct current of the other rectifier in this supply branch, so that a phase adjustment with one of the rectifiers in the other supply branch is effected.

[0009] The circuit arrangement provides a particularly advantageous rectifier control approach for improving grid compatibility when connecting multi-row electrolysis systems with a high power consumption. The circuit arrangement enables continued operation and a direct current supply in both supply branches, even if a supply line in one of the supply branches is no longer drawing power and is de-energized, e.g. due to a sudden failure of the rectifier or in the event of damage or a planned inspection of the electrolysis series. This has advantages for grid compatibility, as grid perturbations are avoided or reduced compared to a standstill of the entire supply branch on the connected three-phase transformer.From an economic point of view, the possibility of continued operation and power supply in both supply branches created by the circuit arrangements of the invention is also of great advantage, since the electrolysis process, in particular the hydrogen production, can be continued at least in the supply line of this supply branch not affected by the shutdown.

[0010] The invention is based on the knowledge that previous circuit arrangements and control concepts for supplying direct current to several electrolysis series are disadvantageous. Multi-row electrolysis systems, in particular those with thyristor-based rectifiers, emit a high level of harmonics into the connected electrical supply network. So-called 24-pulse systems are often used to reduce these harmonics. In the known electrical supply topologies, for example, four thyristor-based rectifiers are operated in parallel, with each rectifier supplying one electrolysis series. The harmonics are reduced because the four systems are interconnected so that they have a phase shift from one another, which means that harmonics are canceled out.Two adjacent supply lines cancel each other's low-frequency harmonics, thus forming a 12-pulse system. The two 12-pulse systems cancel each other's higher frequencies, thus forming a 24-pulse system. If a failure occurs in one of the electrolysis series, the harmonics of the neighboring series can no longer be compensated because one of the two 12-pulse systems is deactivated. This leads to increased system perturbations, which can lead to permissible limits being exceeded.

[0011] Since the harmonics of the row adjacent to the failed row can no longer be fully compensated, this supply line is also switched off in the previous circuit arrangements and control concepts. The two remaining supply lines now form a 12-pulse system, which, although it has increased harmonics, still allows at least a certain amount of harmonic compensation in the lower frequency range. This procedure results in increased production losses if one electrolysis row fails, since the adjacent - actually intact - electrolysis row must also be switched off for grid compatibility reasons due to the requirements of the connection conditions to the public grid (Grid Code).

[0012] Here, the circuit arrangement provides a remedy for the described problem by allowing the control device to implement a phase adjustment in the supply line adjacent to the faulty supply line, if necessary, by means of an additional phase shift and imparting this to the rectifier. This allows a phase increase of the output-side direct current to be achieved, and a phase adjustment can be set with one of the rectifiers in the other supply branch.

[0013] By implementing a predeterminable phase increase as required or a phase shift to be imposed on the direct current in the control device, the circuit arrangement achieves synchronous clocking of this supply line with a selected supply line in the other supply branch, so that the resulting harmonics can continue to be compensated - at least partially - by these.

[0014] The additional phase increase, due to the phase-angle control implemented in the control system, results in a slight reduction in the direct current and thus—in the case of a direct current supply to an electrolysis series—gas production in the affected electrolysis series, but this does not require a complete shutdown. This can significantly reduce production losses in the event of a fault or shutdown in one of the supply lines while maintaining good grid compatibility.

[0015] With phase-angle control, the current flow is advantageously controlled by a triac, an anti-parallel circuit of two thyristors, in the rectifier. After the zero crossing of the alternating voltage and current, the triac does not conduct current until it receives a firing pulse; from this point (this "phase" of the alternating current signal) onward, the load is supplied with power until the next zero crossing. The later the triac is fired, the lower the average power that is switched through.

[0016] In contrast to previously known circuit arrangements and control concepts, in which, in the event of a component failure in a supply line, the entire supply branch, including the two adjacent supply lines leading from the three-phase transformer on the secondary side, must always be shut down, even if only one supply line is affected by a fault, this invention ensures continued operation of the system adjacent to the faulty system. Thus, when implementing the circuit arrangement for the direct current supply of several electrolysis series connected in parallel in an electrolysis system, the production loss of product gas from the electrolysis can be minimized, thus significantly increasing the availability of the system.

[0017] In a particularly advantageous embodiment of the circuit arrangement, the rectifier comprises a thyristor, wherein a rectifier control is provided in the control device, in which the firing angle of the thyristor is implemented as the manipulated variable of the rectifier control, via which the additional phase shift can be adjusted.

[0018] In this case, it is provided that the rectifier comprises a thyristor set with a plurality of thyristors or thyristors connected to form triacs. The thyristor set of the rectifier allows the direct current or direct voltage generated by a rectifier to be regulated by means of the control device, at least to a certain extent. In the case of a rectifier with a thyristor or a thyristor set, the direct current generated by the rectifier or correspondingly the direct voltage generated at the rectifier output can be regulated in a particularly advantageous manner via the firing time of the thyristors of the thyristor set and in this way the power consumption of a connected load such as an electrolysis series. In this way, the phase offset can be precisely adjusted and impressed.

[0019] For the controlled operation of the rectifiers in the circuit arrangement, the rectifier is connected on the input side to a secondary winding of the three-phase transformer via a supply line, which converts a first alternating voltage applied to a primary winding of the transformer into a second alternating voltage applied to the secondary winding. The second alternating voltage represents the input-side alternating voltage of the rectifier. Both the first alternating voltage and the second alternating voltage can be a high voltage. For example, it is possible to use a first alternating voltage in a voltage range between 6 kV and 100 kV. The second alternating voltage can, for example, be between 100 V and 1 kV.Depending on the design of the three-phase transformer and / or the requirements of the rectifier, it is of course also possible to use a first alternating voltage and a second alternating voltage in other voltage ranges.

[0020] In a preferred embodiment of the circuit arrangement, the rectifier control in the control device has a direct current control loop with which a change in the direct current amplitude can be brought about by an additional phase shift.

[0021] This makes it particularly easy to apply the additional phase shift using a thyristor and thus change the DC amplitude on the output side of the rectifier, in particular to reduce it accordingly, by applying an additional phase angle in the DC control loop. The additional phase shift to be applied is preferably 15° relative to the firing angles for the corresponding rectifier.

[0022] The control system therefore implements thyristor-based DC control with phase-angle control. The control and conversion of electrical energy on the basis of switching operations is called power control. Thyristors are used as controllable switching elements in the circuit arrangement. A pulse control unit supplies mains-synchronized firing pulses to the gate, which can be shifted in time towards the zero crossing of the AC voltage. The thyristor is only fired during the positive-going half-wave. With phase-angle control, the voltage and current at the load are not continuous sine waves; rather, the beginning of each wave is missing. By shifting the gate point, the product of voltage U and current I at the load, in particular an electrolysis series on a supply line, can be changed, which is synonymous with power control.The advantage of this process is that high power levels can be controlled with relatively little effort, making it particularly advantageous for parallel-connected electrolysis series. Unused power does not need to be converted into waste heat in a series resistor. To also utilize the negative half-wave for power control, only a second thyristor connected in antiparallel is required, a so-called triac circuit consisting of two thyristors.

[0023] In a particularly advantageous manner, the control device in the circuit arrangement is designed in such a way that when one of the electrolysis series in one of the supply branches is at a standstill, an additional phase shift can be imposed on the output-side direct current of the other rectifier in this supply branch and an additional phase shift can be imposed on a rectifier in the other supply branch, so that phase matching is effected with a rectifier in the other supply branch. In this way, the circuit arrangement makes it possible, if necessary, to add an additional phase shift to one or preferably both rectifiers in the intact supply branch.This makes it possible to reduce the additional phase shift required in the supply branch with the fault or standstill in one of the supply lines, for example by 15°, which leads to a higher utilization of a connected consumer. A design can therefore be implemented in the control device of the circuit arrangement with which a first additional phase shift can be applied in one supply branch and a second additional phase shift in the other supply branch. In this way, phase matching is achieved across the two supply branches, with the additional phase shifts complementing each other. For example, the first and second additional phase shifts can each be 7.5° in order to achieve an overall match at favorable operating points.This enables adaptation to 24-pulse operation, with the phase shift between the supply branches set to 15°. While the phase adjustment also leads to a lower DC feed-in to the DC loads connected to these rectifiers in the intact supply branch, particularly in the case of connected electrolysis series, it also allows the operational rectifier in the defective supply branch to be operated productively for longer within a permissible operating range without reaching the minimum load requirement, which is currently approximately 40%.

[0024] In a preferred embodiment of the circuit arrangement, the supply branches and the supply lines supplied via the three-phase transformers form a switching group which ensures that at least 12-pulse operation is still guaranteed when an electrolysis series is at a standstill. Compared to previous circuit concepts, this control approach to the circuit arrangement is very flexible and economically advantageous in the event of a power consumption failure in a supply line. The twelve-pulse circuit is fed via a phase-swivel transformer with six secondary windings, with the (primary or secondary) windings of one bridge being connected according to the star-star principle and those of the other bridge being connected according to the star-delta principle to generate the phase shift between the two bridges. The voltages between the outer conductors d0 and y5 of a three-phase system orThe delta voltages are generally 30° out of phase with the phase voltages. The winding ratios of the three-phase transformer are designed to balance the different voltages of the star and delta connections. The advantages of the twelve-pulse connection are the low residual ripple in rectifier operation and the low harmonic content in inverter operation.

[0025] In a further preferred embodiment of the circuit arrangement, a switching group is realized by the supply branches and by the supply lines supplied via the three-phase transformers, with which a 24-pulse operation can be realized in normal operation.

[0026] This results in a design that is particularly suitable for direct current supplies with high power consumption. The primary supply branches (primary system) of the two three-phase transformers are preferably phase-shifted by 15° from one another; for example, a phase shift of +7.5° or -7.5° compared to the reference is implemented in the control device. The phase shift implemented in the control device results from the selected transformer configuration of the three-phase transformer and is adapted accordingly. On the secondary side, in a three-phase transformer, the two outgoing strands each form a supply line for a rectifier. The two secondary systems of the three-phase transformers (d0 and y5) also have a phase shift of 30° from one another due to the selected vector group.The phase shift between D and dO is set to 0°. This configuration allows for 24-pulse operation of the circuit during normal operation, in which the lowest-frequency harmonics generated by each rectifier in each branch are compensated as follows:

[0027] - The 5th and 7th harmonics emitted by each rectifier are compensated by setting a phase shift of 30° between the dO-y5 secondary systems.

[0028] - The 11th and 13th harmonics emanating from each three-phase transformer are cancelled by setting a phase shift of 15° between the two supply branches.

[0029] - The 17th and 19th harmonics, which emanate from both supply lines of a three-winding transformer, are also compensated by the proposed configuration.

[0030] - The 23rd and 25th harmonics are then the lowest harmonics that remain in the 24-pulse system.

[0031] The invention ensures that, even if one of the rectifiers in a supply line of a supply branch fails, continued operation of three rectifiers across the corresponding supply lines is achieved. This is superior to current circuit and control concepts, in which an entire supply branch including the rectifiers—i.e., the entire branch at a three-phase transformer—is switched off. The remaining branch then forms a 12-pulse system, which, however, has a higher harmonic content than a 24-pulse system.

[0032] Therefore, as a precautionary measure, filter devices are preferably provided in the circuit arrangement to compensate for these harmonic components, which are designed for 24-pulse operation and can still be activated in the event of a possible unavoidable failure of an entire supply branch.

[0033] For an electrolysis system according to the invention, it is provided that it comprises at least one circuit arrangement according to the invention and several electrolysis series, wherein one electrolysis series is connected to the DC voltage output of a rectifier.

[0034] In the electrolysis system, a configuration is preferable in which each electrolysis row is supplied by a rectifier and connected to a supply line at the DC output.

[0035] In the electrolysis system, an electrolysis series comprises a number of electrolysis modules electrically connected in series. Several electrolysis modules can be connected in series to form an electrolysis series, for example, five modules each comprising 50 electrolysis cells, thus achieving scalability and flexibility for adapting and applying the circuit arrangement for large electrolysis capacities in a supply line.

[0036] Furthermore, the electrolysis system is preferably designed such that electrolysis modules are provided in an electrolysis series, each having at least one proton exchange membrane, so that PEM electrolysis can be carried out. It is also conceivable to combine different types of electrolysis, so that electrolysis modules based on PEM electrolysis and electrolysis modules based on alkaline electrolysis are integrated into one electrolysis system and can be supplied with a respective direct current by the circuit arrangement.

[0037] This can particularly involve proton exchange

[0038] Membranes for generating hydrogen through the electrolysis of water, in particular deionized and / or distilled water. The electrolysis modules can also be designed, in particular, as an electrolysis series comprising several proton exchange membranes. An electrolysis series in the electrolysis system can comprise any number of series-connected electrolysis modules, depending on the performance of the rectifier connected upstream in the supply line or depending on the maximum current that can be drawn via the rectifier.

[0039] In the electrolysis system, the supply branches of the three-phase transformers are preferably combined on the primary side and connected to a mains transformer, in particular an autotransformer. Thus, by combining the two supply branches on the primary side, a 24-pulse system for high power outputs is realized for normal operation in a multi-row electrolysis system.

[0040] The autotransformer, which is particularly preferred here as a connecting transformer, is equipped with a tap changer on the AG supply network which ensures the required input voltage for the rectifiers and at the same time enables the required minimum power factor at the grid connection point (PCC). In contrast to other transformers, an autotransformer or autotransformer consists of just one coil which has one or more taps for taking the output voltage(s). The primary and secondary sides are thus combined in a single coil. An autotransformer allows the use of a smaller design for the same power and is characterized by a lower voltage drop. The closer the values ​​of the input and output voltage are to each other, the more mass and material can be saved by using an autotransformer, since only part of the current and voltage needs to be transformed.This allows different wire thicknesses in the two winding sections. The electrolysis system of the invention is particularly advantageously modularly expandable, i.e., several electrolysis systems can be interconnected. In this way, for example, parallel operation of several 24-pulse electrolysis systems, each supplied with a respective circuit arrangement, is possible. The additional electrolysis systems can then be controlled via an overarching control device in such a way that improved compensation of the harmonics between the individual electrolysis systems is achieved, thereby further reducing production downtimes in such a system comprising several electrolysis systems.

[0041] For a method according to the invention for operating a circuit arrangement according to the invention, it is provided that when one of the electrolysis series in one of the supply branches is at a standstill, an additional phase shift is impressed on the output-side direct current of the other rectifier in this supply branch, so that a phase adjustment with one of the rectifiers in the other supply branch is effected.

[0042] In this case, it is preferably provided that the method is carried out in such a way that an additional phase shift is imposed on both the output-side direct current of the other rectifier in this supply branch and an additional phase shift is imposed on a rectifier in the other supply branch.

[0043] In a particularly preferred embodiment of the method, a phase adjustment is carried out between the supply branches by adjusting the additional phase shift by adjusting the firing angle of a respective thyristor, with electrolysis series continuing to operate in both supply branches.

[0044] In the process, the control device is set up as a higher-level control device and is operated in such a way that an adjustment of the phases across the supply branches is controlled and / or regulated.

[0045] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the single figures can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0046] Examples of the invention are explained in more detail with reference to the accompanying drawings. These show schematically and in a highly simplified manner:

[0047] FIG 1 an electrolysis system with a circuit arrangement,

[0048] FIG 2 shows a schematic representation of a DC control implemented in the control device,

[0049] FIG 3 the functional principle of the DC control of the rectifier in two supply branches,

[0050] FIG 4 shows a variant of the DC control of the rectifiers described in FIG 3.

[0051] Fig. 1 shows a schematic representation of an electrolysis system 21 with a circuit arrangement 1 integrated into the electrolysis system 21. The circuit arrangement 1 serves to supply direct current to a plurality of electrolysis series 3a, 3b, 3c, 3d connected in parallel. Each electrolysis series 3a, 3b, 3c, 3d has a plurality of electrolysis modules 23 connected in series. The circuit arrangement 1 has a first supply branch 5 and a second two supply branches 7, into which a respective three-phase transformer 9, 11 is connected with its primary side. On the secondary side, two supply lines 13a, 13b are led out of the three-phase transformers 9, 11 and are connected to the alternating current input of a respective rectifier 15a, 15b.Therefore, two supply lines 15a, 15b are coupled to a respective rectifier 15a, 15b on the secondary side of both the first supply branch 5 and the second supply branch 7 via corresponding windings of the three-phase transformer 9, 11.

[0052] The supply lines 13a, 13b are led out of the rectifiers 15a, 15b on the output side, so that a direct current is provided during operation to supply the respectively connected electrolysis series 3a, 3b, 3c, 3c. A control device 17 can be used to adjust and adapt the phases in the supply lines 15a, 15b as well as in the first supply branch 5 connected upstream on the primary side and the second supply branch 7. On the primary side, a phase difference of 15° is set between the first supply branch 5 and the second supply branch 7, with the first supply branch 5 being set to a setpoint angle of +7.5° and the second supply branch 7 being set to a setpoint angle of -7.5° compared to a zero-phase reference value. Furthermore, in each of the supply branches 5, 7, a phase shift of 30° is set relative to each other in the supply lines 13a, 13b leading out of the three-phase transformers 9, 11 on the secondary side.The two secondary systems of the three-phase transformers (dO and y5) therefore have an additional phase shift of 30° from each other due to the selected vector group. The phase shift between D and dO is set to 0°. This configuration enables 24-pulse operation for normal operation of the circuit arrangement, in which the lowest-frequency harmonics generated by each rectifier in each branch are compensated. The rectifiers 15a, 15b have thyristors, and the control device 17 includes a rectifier control in which the firing angle a of the thyristor is implemented as the manipulated variable of the rectifier control (see FIG. 2 and FIG. 3). In this way, a phase control is implemented in the rectifier control, so that a power control of a respective electrolysis series 3a, 3b, 3c, 3d is achieved via the direct current intensity at the output of the rectifiers 15a, 15b.

[0053] The electrolysis system 21 is supplied with power via the circuit arrangement 1 integrated into the electrolysis system 21, which is connected on the AC side to a mains transformer 19. For this purpose, the first supply branch 5 and the second supply branch 7 are led out of the three-phase transformer 9, 11, electrically connected to one another, and connected to the mains transformer 19. The mains transformer 19 is designed as an autotransformer and is connected at the mains connection point 27—or PCC—to an AC supply network 25, in particular a public power grid.

[0054] The circuit arrangement 1 is designed and improved for an operating situation in which no power can be drawn, particularly in one of the supply lines 5, 7. At the same time, good grid compatibility is ensured. Such a situation can be caused by a failure or defect of a rectifier 15a, 15b or an electrolysis module 23, so that one of the electrolysis series 3a, 3b, 3c, 3c must be shut down.

[0055] The basic mode of operation of the DC control implemented in the control device 17 is illustrated in a block diagram in FIG 2. The rectifiers 15a are normally synchronized with the AC voltage at the input. In this way, the phase shift resulting from the transformer configuration is automatically incorporated into the generation of the respective firing pulses of the rectifiers 15a, 15b. The firing angle α is the offset between the natural zero crossing of the current and the firing of the thyristor and is the manipulated variable of the rectifier control and directly controls the output current of the rectifiers 15a, 15b.

[0056] The new control concept proposes that in the event of a fault in an electrolysis module 23 - for example in the supply line 13b of the second supply branch 7 - only the respective affected electrolysis series 3d and the upstream rectifier 15b are switched off and come to a standstill. The other adjacent rectifier 15a in the same supply branch 7 as well as both rectifiers 15a, 15b in the first supply branch and the electrolysis series 3a, 3b, 3c can continue to operate. For this purpose, the rectifier control of the adjacent rectifier 15a is specifically changed, whereby the normal ignition angle o = a resulting from the DC control loop without the fault or standstill ref as a reference value, an additional phase shift Acp of, for example, 15 ° is applied. This brings about a phase adjustment with at least one of the rectifiers 15a, 15b in the first supply branch 5. For this purpose, a PI controller 29 is implemented in the DC control loop of the control device 17, to which the additional phase shift Acp is applied, so that a new or modified reference angle a ref = «o + Acp is used as the ignition angle. Although increasing the ignition angle ao leads to reduced hydrogen production in the adjacent electrolysis series 3c, this does not have to be switched off. However, this additional phase shift Acp causes a phase adjustment and synchronization of the corresponding rectifier 15a of the second supply branch 7 with another rectifier 15a, 15b in the first supply branch 5. In this way, the entire electrolysis system 21 at the grid connection point 19 can react like a 12-pulse system without the electrolysis series 15a in the second supply branch 7, which is still intact and supplied via the supply line 13a, having to be switched off. In the block diagram of the control system, I re f the reference direct current, I m the measured direct current as input variable and ref the adjusted firing angle for the rectifier 15a in the supply branch 7 increased by the additional phase shift Acp. By increasing the firing angle a re f as the control variable, a reduction of the direct current amplitude I m and the reference direct current I is reduced accordingly. re f and the direct current I measured at the rectifier 15a m , so that a new operating point of the rectifier 15b is set.

[0057] FIG 3 shows the functional principle of the DC control of the rectifiers 15a, 15b in the two supply branches 5, 7. The phase angle α is given in degrees on the abscissa (x-axis) and the current intensity I in a qualitative curve at the respective rectifier output on the ordinate (y-axis). I1 and I2 in the first supply branch 5 designate the respective value of the current intensity I in the supply line 13a or in the supply line 13b on the AC side at the connected rectifier 15a, 15b. In the second supply branch 7, I3 and I4 designate the respective current intensity I in the supply line 13a or in the supply line 13b on the AC side at the connected rectifier 15a, 15b. In addition, the curve of one period of the alternating voltage Ui at the input of the rectifier 15a of the first supply branch 5 is shown for reference. The zero point orThe reference point is at phase angle α = 0°, at which voltage Ui passes through zero. With phase-angle control, the current is switched on with a delay after the alternating voltage Ui passes through zero and flows until the next zero crossing. Furthermore, with phase-angle control, the current flow is controlled by a triac - an anti-parallel connection of two thyristors. After the alternating voltage Ui and current I pass through zero, the triac does not conduct current until it receives a firing pulse at a firing angle α. From this point in time, or "phase" of the alternating current signal, the load is supplied with energy until the next zero crossing. The later the triac is fired, the lower the average power supplied to the load.

[0058] In the proposed control structure according to FIG. 3, a single-phase alternating current input to the rectifiers 15a, 15b is implemented in the control device 17 in a corresponding manner for all four rectifiers 15a, 15b—two rectifiers 15a, 15b in the first supply branch 5 and two in the second supply branch 7. For the rectifier 15a, the alternating voltage Ui of a single phase is plotted together with the current Ii on the AG side of the rectifier 15a.

[0059] If rectifier 15a is considered as a reference rectifier, FIG 3 shows the phase shift of the alternating currents at the adjacent rectifier 15b of the same first supply branch 5 as well as the phase shift of the two parallel-connected rectifiers 15a, 15b in the second supply branch. The control device 17 is designed for comprehensive continued operation of the electrolysis system 21 in the event of a fault: If one of the rectifiers 15a, 15b is switched off - for example due to a fault or scheduled maintenance work on a corresponding electrolysis series 3a, 3b, 3c, 3d - in this case rectifier 15b in the second supply branch 7 with current intensity I4 (hatched), the controls of the adjacent rectifier 15a in supply branch 7 are changed by implementing an additional phase shift Acp at the resulting firing angle α.This means that an additional phase shift of Acp = 15 ° is added to the firing angle α for the rectifier 15a and adjusted with the rectifier 15b from the first supply branch 5 . As a result, the amplitude of the current I3 decreases. The dashed curve for I3 shows the phase shift Acp imposed in addition to the normal firing angle α as well as the reduced current amplitude. The entire system now advantageously behaves like a 12-pulse system and continued operation of the rectifier 15a in the second supply branch 7 is achieved.

[0060] In a particularly interesting variant of the control shown in FIG 3, an additional phase shift is also provided for the two rectifiers 15a, 15b in the first supply branch 5. This creates a flexible option for achieving a higher current at I3 if required by adjusting the phase angle at Ii and I2 in the first supply branch 5. In this way, a higher-level load control is implemented across the first supply branch 5 and the second supply branch 7. This option in the control concept is illustrated in FIG 4 merely as an example with concrete phase shifts. Other numerical values ​​can therefore also be set and coordinated with one another for the adjustment angles Acp, Acpi, Agy.In this way, the additional phase shift Acp imposed solely on rectifier 15a in the second supply branch 7 can be lower compared to the control system according to FIG. 3. This does indeed result in a somewhat lower direct current feed into the electrolysis series 3a, 3b connected to rectifiers 15a, 15b in the first supply branch 5 due to the additionally imposed phase shifts Acpi, Agy. On the other hand, this operating control also allows rectifier 15a in the second supply branch 7 to remain in the operating range for longer or more significantly without falling below a minimum load requirement, which is currently around 40% of the nominal load.With the control device 17 and the rectifier control implemented in this way, a comprehensive load control for the electrolysis system 21 is possible, while at the same time ensuring high availability and hydrogen production even in the event of a malfunction or failure of an electrolysis series 3a, 3b, 3c, 3d.

[0061] This is achieved in the electrolysis system 21 in that the four electrolysis series 3a, 3b, 3c, 3d connected to the circuit arrangement 1 are not—as previously—controlled independently and individually. Rather, a higher-level control is implemented that realizes compensation between the components of the supply lines 13a, 13b in the supply branches 5, 7. In large electrolysis systems 21 consisting of several 24-pulse systems, this control can be specifically adapted and flexibly expanded to ensure compensation between the individual 24-pulse systems.

Claims

Patent claims 1. Circuit arrangement (1) for supplying direct current to a plurality of parallel-connected electrolysis series (3a, 3b, 3c, 3d), wherein the circuit arrangement (1) has a first supply branch (5) and a second supply branch (7) with a respective three-phase transformer (9, 11), and wherein two supply lines (13a, 13b) are led out of a three-phase transformer (9, 11) on the secondary side, into each of which a rectifier (15a, 15b) is connected, so that an input-side alternating current can be converted into an output-side direct current for supplying an electrolysis series (3a, 3b, 3c, 3d) by a rectifier (15a, 15b), and wherein a control device (17) is provided which is designed such that when one of the electrolysis series (3a, 3b, 3c, 3d) in one of the supply branches (5, 7) to the output-side direct current of the other rectifier (15a, 15b) in this supply branch (5,7) an additional phase shift (Acp) can be imposed, so that a phase adjustment with one of the rectifiers (15a, 15b) in the other supply branch (5, 7) is effected., 2. Circuit arrangement (1) according to claim 1, in which the rectifier (15a, 15b) comprises a thyristor, wherein a rectifier control is provided in the control device (17), in which the firing angle of the thyristor is implemented as the manipulated variable of the rectifier control, via which the additional phase shift (Acp) can be adjusted.

3. Circuit arrangement (1) according to one of claims 1 or 2, in which in the control device (17) the rectifier control has a direct current control loop with which a change in the direct current amplitude can be brought about by an additional phase shift (Acp).

4. Circuit arrangement (1) according to one of the preceding claims, in which the control device (17) is designed such that when one of the electrolysis series is at a standstill (3a, 3b, 3c, 3d) in one of the supply branches (5, 7) both the output-side direct current of the other rectifier (15a, 15b) in this supply branch (5, 7) can be given an additional phase shift (Acp) and a rectifier (15a, 15b) in the other supply branch (5, 7) can be given an additional phase shift (Agg, Agy), so that a phase adjustment with a rectifier (15a, 15b) in the other supply branch (5, 7) is effected.

5. Circuit arrangement (1) according to one of the preceding claims, in which a switching group is realized by the supply branches (9, 11) and by the supply lines (13a, 13b) supplied via the three-phase transformers (9, 11), with which a 12-pulse operation can be ensured when an electrolysis series (3a, 3b, 3c, 3d) is at a standstill.

6. Circuit arrangement (1) according to one of the preceding claims, in which a switching group is realized by the supply branches (9, 11) and by the supply lines (13a, 13b) supplied via the three-phase transformers (9, 11), with which a 24-pulse operation can be realized in normal operation.

7. Electrolysis system (21) comprising at least one circuit arrangement (1) according to one of the preceding claims and a plurality of electrolysis series (3a, 3b, 3c, 3d), wherein one electrolysis series (3a, 3b, 3c, 3d) is connected to the DC voltage output of a rectifier (15a, 15b).

8. Electrolysis system (21) according to claim 7, wherein an electrolysis series (3a, 3b, 3c, 3d) comprises a number of electrolysis modules (23) electrically connected in series.

9. Electrolysis system (21) according to claim 8, wherein electrolysis modules are provided, each having at least one proton exchange membrane, so that PEM electrolysis can be carried out.

10. Electrolysis system (21) according to one of claims 7 to 9, in which the supply branches (5, 7) of the three-phase transformers (9, 11) are brought together on the primary side and connected to a mains transformer (19), in particular an autotransformer.

11. Method for operating a circuit arrangement (1) according to one of the preceding claims, wherein when one of the electrolysis series (3a, 3b, 3c, 3d) in one of the supply branches (5, 7) is at a standstill, an additional phase shift (Acp) is impressed on the output-side direct current of the other rectifier (15a, 15b) in this supply branch (5, 7), so that a phase adjustment with one of the rectifiers (15a, 15b) in the other supply branch (5, 7) is effected.

12. The method according to claim 11, wherein an additional phase shift (Acpi) is imposed on both the output-side direct current of the other rectifier (15a, 15b) in this supply branch (5, 7) and an additional phase shift (Agy) is imposed on a rectifier (15a, 15b) in the other supply branch (5, 7).

13. Method according to one of claims 11 or 12, wherein a phase adjustment between the supply branches (5, 7) is carried out by setting the additional phase shift (Acp, Agg, Agy) by adjusting the firing angle of a respective thyristor, wherein electrolysis series (3a, 3b, 3c, 3d) continue to be operated in both supply branches (5, 7).

14. Method according to one of claims 11, 12 or 13, in which the control device (17) is set up as a higher-level control device (17) and is operated in such a way that an adaptation of the phases comprising the supply branches (5, 7) is controlled and / or regulated.

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