Method of extending the dc voltage range of a rectifier, rectifier performing the method, and electrolysis plant

Abstract

This application describes a method for extending the DC voltage range of a rectifier for supplying power from an AC grid connected thereto to a DC load connected to the output of a DC rectifier. The AC / DC converter of the rectifier includes converter circuitry having a semiconductor switch and a freewheeling diode connected in anti-parallel thereto. An inductor is arranged between the AC / DC converter and the grid connection point, and the rectifier is connected to the AC grid via the grid connection point. The method includes the step of: adjusting a desired DC operating voltage U at the DC output of the AC / DC converter and / or at the output of the DC rectifier by driving the semiconductor switch of the AC / DC converter. DC,Soll Wherein, when the desired DC operating voltage U DC,Soll When the amplitude Û4 of the AC voltage at the AC input terminal of the AC / DC converter is lower than the value of the AC voltage, the semiconductor switch driving the AC / DC converter exchanges reactive power Q1(t) with the AC grid, which reduces the amplitude Û4 of the AC voltage. This application also includes a rectifier for performing the method and an electrolytic device having such a rectifier.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for extending the DC voltage range of a rectifier, a rectifier for carrying out the method and an electrolysis plant having such a rectifier. BACKGROUND

[0002] Hydrogen can be produced by an electrolysis reaction, in which water is decomposed into its components, i.e. hydrogen and oxygen, in an electrolyzer. The speed of the electrolysis reaction is adjusted by a DC voltage applied at the input of the electrolyzer. The DC voltage is usually generated by a rectifier, which is connected on the input side to an alternating current (AC) network and on the output side to the electrolyzer as a DC load. An actively controlled single-stage rectifier is usually used as a rectifier. Here, the converter circuit of the AC / DC converter assigned to the rectifier comprises a plurality of semiconductor switches, which each have a freewheeling diode connected in antiparallel to the semiconductor switch. The antiparallel connection of the freewheeling diodes causes the minimum DC voltage at the DC output of the AC / DC converter to be limited to the value of the amplitude of the alternating voltage applied at the input side of the AC / DC converter. In other words, the minimum DC voltage at the DC output of the AC / DC converter corresponds to the amplitude of the alternating voltage applied at the input side of the AC / DC converter. This is at least true for a predominantly capacitive DC load at the DC output of the AC / DC converter, which smoothes the DC voltage, so that the voltage ripple at the DC output is negligible. With increasing resistance components of the DC load, the voltage ripple at the DC output of the AC / DC converter becomes more pronounced, and the minimum DC voltage shifts to a somewhat smaller value. In this case, it is usually sufficient to describe the minimum DC voltage at the DC output with the so-called rectification value. The rectification value corresponds to the arithmetic mean of the rectified DC voltage and depends on the respective used topology of the rectifier, in particular of its AC / DC converter.

[0003] A conventional electrolyzer usually has a current-voltage characteristic curve (I-U characteristic curve) which characterizes it. The I-U characteristic curve can be divided into two regions. When the DC voltage applied at the input of the electrolyzer is below a critical voltage U cr , no electrolysis reaction and thus no steady-state current flow occurs. Rather, the electrolyzer exhibits here a predominantly capacitive behavior, which is caused by the formation of a double layer in the electrolysis cell. Only when the critical voltage U cr is exceeded does an electrolysis reaction occur, the speed of which increases with increasing DC voltage. A steady current flows in this region, which drives the electrolysis reaction, and the electrolyzer exhibits here a predominantly resistive behavior like a resistance load. The maximum DC voltage U DC,max allowed is limited by the rated power of the electrolyzer or by component properties. The critical voltage U crand the maximum permissible DC voltage U DC,max The value of U cr depends on the design of the electrolyzer and therefore usually differs from model to model.

[0004] It is generally desirable that, by means of the rectifier, the electrolyzer can be continuously adjusted and operated over the entire operating range of the DC voltage applied at the input, at least just below the critical voltage U DC,max up to the maximum permissible DC voltage U cr . It is furthermore desirable that a high reaction speed and the associated high DC voltage are produced at the input of the electrolyzer, while the conversion losses of the rectifier are as small as possible. In order to produce a DC voltage below the critical voltage U cr at the DC rectifier output in a single-stage rectifier, for example, the amplitude of the alternating voltage at the AC input of the converter circuit can be adjusted to a corresponding low value by means of a transformer. However, as a result, high conversion losses occur if a high DC voltage is required at the DC rectifier output in the operation of the electrolyzer.

[0005] From the prior art, for example from the document WO 2013 160486 A2, a method for voltage correction at a connection point of an AC grid is known, through which a renewable power plant is connected to the AC grid. Here, in the event of a deviation of the amplitude of the alternating voltage from its associated rated value, reactive power is exchanged between the renewable power plant and the AC grid. The exchanged reactive power counteracts the deviation in a manner that supports the grid and pursues the goal of minimizing the deviation.

[0006] The document DE 103 03 710 A1 discloses a method for adjusting an automatic commutated grid rectifier having a direct voltage output in the event of a grid overvoltage. In the method, a theoretical value of the reactive component of the grid current is preset in accordance with a determined value of the occurring grid overvoltage, so that the actual value of the modulation ratio of the automatic commutated grid rectifier is reduced. SUMMARY

[0007] It is the task of the present invention to give a method for expanding the DC voltage range of an active controlled rectifier, in particular a single-stage rectifier, with which the DC voltage at the DC output of the single-stage rectifier is adjusted to a value just below the critical voltage U cr , even if the critical voltage is below the rated value of the amplitude of the alternating voltage. Here, in addition, a high DC voltage should be adjustable at the DC rectifier output and the conversion losses should be as small as possible. The method should be performed as simply and cost-effectively as possible. Furthermore, it is the task of the present invention to indicate a rectifier suitable for performing the method and an electrolysis device having such a rectifier.

[0008] The method according to the invention aims to extend the DC voltage range of a rectifier used to supply power from an alternating current (AC) grid to a DC load connected to the output of the DC rectifier, wherein the AC rectifier input is connected to the AC grid via a grid connection point. Here, the rectifier has an AC / DC converter including an AC input and a DC output, the AC / DC converter including a converter circuit having a semiconductor switch and a freewheeling diode connected in anti-parallel therewith. The AC input of the AC / DC converter (if necessary via an AC disconnect unit) is connected to the AC rectifier input, and the DC output of the AC / DC converter is connected to the DC rectifier output (if necessary via a DC disconnect unit). An inductor L is arranged between the AC input of the AC / DC converter and the grid connection point. The method includes the following steps:

[0009] - By driving the semiconductor switch of the AC / DC converter, adjust the desired DC operating voltage U at the DC output terminal of the AC / DC converter and / or the output terminal of the DC rectifier. DC,Soll ,

[0010] - Wherein, if the desired DC operating voltage U DC,Soll If the amplitude Û4 of the AC voltage at the AC input of the AC / DC converter is lower than the value of the AC voltage at the AC input terminal, then the semiconductor switch of the AC / DC converter is driven to exchange reactive power Q1(t) with the AC grid. This exchange of reactive power Q1(t) reduces the amplitude Û4 at the AC input terminal of the AC / DC converter (and therefore also at the AC input terminal of the converter circuit). Through this voltage reduction, the amplitude Û4 of the AC voltage approaches the desired DC operating voltage U. DC,Soll Here, as long as reactive power exchange with the AC grid is permitted (e.g., as stipulated by the AC grid operator), the amplitude Û4 is made close to the desired DC operating voltage U. DC,Soll This enables the achievement of the desired DC operating voltage U. DC,Soll Here, the exchange of reactive power Q1(t) with the AC grid is carried out together with the electrical connection and / or electrical disconnection of the DC load and rectifier.

[0011] Herein, the term "together with" can be interpreted as meaning "during and / or shortly before". In particular, the rectifier can be a single-stage rectifier, which does not contain a DC / DC converter arranged between the AC / DC converter and the DC rectifier output. The rectifier can have only one phase connection on the AC side, but can alternatively also have multiple phase connections. Since the AC input of the AC / DC converter corresponds to the AC input of the converter circuit, at least with which it is connected with low impedance, the amplitude Û4 of the AC voltage applied at the AC input of the AC / DC converter also corresponds to the amplitude applied at the AC input of the converter circuit.

[0012] The amplitude Û4 of the AC voltage applied at the AC input of the AC / DC converter, and the amplitude Û7 of the AC voltage applied at the AC rectifier input of the rectifier, can each be the amplitude of the AC voltage at the phase line relative to the neutral point or star point of the transformer, i.e. the amplitude of the star voltage. This is all the more true when the converter circuit of the AC / DC converter is designed as a neutral point circuit. In this case, the output connection of the DC output can be connected with the neutral point of the transformer or the neutral line of the AC grid. Alternatively, the amplitude Û4 of the AC voltage applied at the AC input of the AC / DC converter is also the amplitude of the AC voltage present between the two phase lines of the AC grid, i.e. the amplitude of the cascade voltage. The same applies to the amplitude Û7 of the AC voltage applied at the AC rectifier input of the rectifier. This is all the more true when the converter circuit of the AC / DC converter is designed as a so-called bridge circuit. In this case, a transformer with a neutral point tap is not required at all, since the current only flows between the phase lines of the AC grid. For example, in a three-phase AC grid, the amplitudes of the star voltage and the cascade voltage are related to one another via the cascade factor 3.

[0013] The method according to the invention uses the knowledge that the exchange of reactive power between the AC / DC converter and the AC grid causes a change in the amplitude Û4 of the AC voltage applied at the AC input of the AC / DC converter by means of the inductance L arranged therebetween. In particular, the amplitude Û4 of the AC voltage can be reduced by exchanging a type of reactive power, for example inductive reactive power, while the amplitude Û4 of the AC voltage is increased by exchanging a compensatory type of reactive power, for example capacitive reactive power. Within the scope of the invention, the exchange of reactive power Q1(t) is deliberately used to change the amplitude Û4 of the AC voltage, in order thereby to influence the DC voltage at the DC output of the converter circuit and, in the case of the DC split unit being closed, also the DC voltage at the DC rectifier output. For example, if the DC operating voltage U DC,SollAdjusting the amplitude U4 of the AC voltage at the AC input of the AC / DC converter to less than the amplitude U4 of the AC voltage at the AC input of the AC / DC converter, temporarily exchanging reactive power Q1(t) with the AC power grid. Here, the current associated with the reactive power Q1(t) is passed via the inductance L and acts as a voltage reducer on the amplitude U4 of the AC voltage. In this way, the amplitude U4 of the AC voltage applied at the AC / DC converter is reduced. The reduced amplitude U4 likewise produces a reduced DC voltage value at the DC output of the converter circuit and thus at the DC rectifier output via the freewheeling diode of the converter circuit. By exchanging a certain amount of reactive power Q1(t), the percentage reduction or percentage increase of the amplitude U4 can be adjusted relative to the amplitude U4 present initially, i.e. before the reactive power was exchanged. At present, the temporary exchange of reactive power Q1(t) is carried out such that the amplitude U4 at the AC input of the AC / DC converter and thus the DC voltage at the DC output of the AC / DC converter approaches the desired DC operating voltage U DC,Soll and (depending on the maximum possible or permissible exchange of reactive power Q1(t)) also the desired DC operating voltage U DC,Soll .

[0014] Unlike the known prior art, the purpose of exchanging reactive power Q1(t) between the AC / DC converter and the AC power grid is not to counteract existing deviations of the amplitude of the AC voltage, thus supporting the AC power grid. In contrast to the prior art, here the purpose of exchanging reactive power Q1(t) is to intentionally deviate the amplitude U4 at least temporarily from its nominal value. According to the invention, the intentional deviation of the amplitude from its nominal value is caused in order to at least temporarily operate the DC load, in particular the electrolyzer, at the input thereof with a low DC voltage, which would otherwise not be achievable. Thus, the temporary change of the DC voltage, here the reduction of the DC voltage, is the actual goal of exchanging the reactive power Q1(t). In this way, it is possible to achieve a load-free connection or disconnection of the DC load, in particular the electrolyzer, from the rectifier, and thus a more gentle operation of the separation unit and the electrolyzer.

[0015] According to the application, the exchange of reactive power Ql(t) takes place during and / or shortly before the DC load is electrically connected to the rectifier. Here, after the DC load has been electrically connected to the rectifier, in particular shortly after the connection, it is still possible, but not necessary, to exchange reactive power Ql(t) with the AC power grid. Specifically, in the case of an electrolyzer as the DC load, the voltage at the input of the electrolyzer can be reduced to just below the critical voltage Ucr. As a result, the connection and disconnection of the electrolyzer to the rectifier can take place as load-free and gentle as possible for the respective separation unit. Thus, the electrolysis reaction can also be started and / or terminated gently and controlled by means of a change in the exchanged reactive power Ql(t). Specifically, upon starting the electrolysis reaction, the exchanged reactive power Ql(t) can be reduced, while at the same time the converted active power P(t) is increased. In a corresponding manner, upon termination of the electrolysis reaction, the converted active power can be reduced, while at the same time the converted reactive power is increased, in order to further reduce the DC voltage at the DC output of the AC / DC converter. Furthermore, although not absolutely necessary, after the DC load has been disconnected from the rectifier, in particular shortly after the disconnection, it is still possible to exchange reactive power Ql(t) with the AC power grid. Thus, for example, the exchange of reactive power Ql(t) with the AC power grid can be continuously and controlled reduced, for example ramped controlled. In this way, sudden changes in the exchanged reactive power Ql(t) with the AC power grid and thus undesirable counteractions on the AC power grid can be prevented.

[0016] The inductance L is generally (at least to some extent) already a component of the rectifier. Specifically, in the rectifier in question, in order to attenuate high-frequency interference signals, a filter is provided between the AC rectifier input and the AC input of the AC / DC converter, which filter comprises one or more filter chokes. The one or more filter chokes can generally be used without adjustment (or at least with slight adjustment) as part of the inductance L via which the reactive power Ql(t) is exchanged with the AC power grid. Thus, often no additional hardware expenditure is required at all, or only a very small additional hardware expenditure. In terms of the semiconductor switches of the converter circuit, no hardware adjustment is required for the exchange of reactive power Ql(t), at most only a software adjustment of the clocking method. Overall, a relatively low-cost and low-expenditure adjustment of a conventional rectifier to carry out the method according to the application is obtained.

[0017] In an advantageous variant of the method, the reactive power Ql(t) exchanged between the AC / DC converter and the AC power grid is almost exclusively displacement reactive power, at least predominantly displacement reactive power. Correspondingly, the reactive power Ql(t) does not contain a distortion reactive power component, or only an unavoidable distortion reactive power component. Thereby, it is ensured that even when the reactive power Ql(t) is exchanged, the desired sinusoidal waveform of the AC voltage is maintained.

[0018] In another variant of the method, the reactive power Ql(t) can only be exchanged between the AC / DC converter and the AC power grid when the desired DC operating voltage U DC,Soll is below a value of the amplitude Û4 by a certain difference. For example, the reactive power Ql(t) is exchanged when the desired DC operating voltage U DC,Soll is below the rectified value of the amplitude Û4 of the AC voltage in addition to being below the value of the amplitude Û4. In this way, in the case of a DC load that is predominantly resistive, unnecessary exchange of the reactive power Ql(t) and the possibly undesirable counteraction on the power grid associated therewith can be reduced.

[0019] According to another variant of the method, the exchange of the reactive power Ql(t) is not only used to reduce the amplitude Û4 of the AC voltage, but also to increase the amplitude Û4 of the AC voltage. In the latter case, during certain operating conditions of the DC load, for example when the desired DC operating voltage U DC,Soll reaches or exceeds a voltage threshold U TH , the semiconductor switches of the AC / DC converter are driven for the exchange of additional reactive power Q2(t) with the AC power grid, such that the exchange of the additional reactive power Q2(t) has a voltage-boosting effect on the amplitude Û4 at the AC input of the converter circuit. In this way, the amplitude Û4 can also be brought close to the desired DC operating voltage U DC,Soll . The additional reactive power Q2(t) can be of the complementary type to the reactive power Ql(t). In other words, if the reactive power Ql(t) is inductive, the additional reactive power Q2(t) can be capacitive, and vice versa. In this case, it is necessary for the DC voltage applied at the DC output of the AC / DC converter to be slightly boosted in addition to the rectification of the AC voltage by the AC / DC converter. This can generally result in a reduction in the conversion losses of the AC / DC converter.

[0020] The exchange of reactive power Q1(t) and / or the exchange of further reactive power Q2(t) can comprise determining a theoretical value of the reactive power on the basis of a known voltage change characteristic u(Q), which is a function of the reactive power Q exchanged between the AC input of the AC / DC converter and the grid connection point of the AC grid. In particular, the correlation of the known voltage change characteristic u(Q) can be determined, for example, once and for all, by measurement and stored in a data memory connected to the control unit of the rectifier. Alternatively thereto, the exchange of reactive power Q1(t) and / or the exchange of further reactive power Q2(t) can be respectively self-adapting and by means of a regulating unit connected to the control unit. Here, the actual value of the DC voltage U DC,4 applied at the DC output of the AC / DC converter can be detected, the detected actual value can be compared to the desired DC operating voltage U DC,Soll , and the exchange of the respective reactive power Q 1,2 (t) can be regulated such that the actual value approximates the desired DC operating voltage U DC,Soll . The regulating unit can comprise a proportional regulator, an integral regulator and / or a differential regulator.

[0021] Whether the exchange of reactive power Q1(t) and / or the exchange of further reactive power Q2(t) is by means of a known voltage change characteristic u(Q) or self-adapting by means of a regulating unit, the exchange of reactive power Q1(t) and / or the exchange of further reactive power Q2(t) can cause a change of the amplitude Û4 at the AC input of the AC / DC converter of at least 10%, preferably at least 20%, particularly preferably at least 25% relative to the rated value of the amplitude Û4. Here, the amount of exchanged reactive power Q 1,2 (t) required to cause the respective amplitude Û4 change depends on the value of the inductance L between the AC / DC converter and the grid connection point. Here, the rated value of the amplitude Û4 is understood to be the value of the amplitude Û4 applied at the AC input of the AC / DC converter when no reactive power Q 1,2 (t) is exchanged between the AC / DC converter and the AC grid.

[0022] In an advantageous variant of the method, a grid service exchange of reactive power between the AC / DC converter and the AC grid can take place under specified framework conditions, for example in order to maintain the voltage. In particular, a third reactive power Q3(t) is exchanged between the AC / DC converter and the AC grid during a state of the AC grid in which the amplitude of the alternating voltage Û7 at the AC rectifier input deviates from its rated value, the third reactive power Q3(t) being selected in such a way that it has a voltage-lowering or voltage-raising effect on the amplitude Û7 of the AC voltage in accordance with its quality. In order to maintain the voltage, the third reactive power Q3(t) is selected in such a way that it has an effect which counteracts the deviation from the rated value of the amplitude Û7. The specified framework conditions can include a ripple control signal from the operator of the AC grid and / or a contractual agreement with the operator of the AC grid.

[0023] According to an embodiment of the method, the inductance can include a filter choke arranged between the AC / DC converter and the AC rectifier input, via which the reactive power Q1(t) and / or the further reactive power Q2(t) is exchanged with the AC grid. Alternatively or additionally, the inductance can include a transformer winding of the secondary side of a transformer associated with the rectifier. This is in particular the case when the rectifier is connected to the AC grid via a transformer, wherein the rectifier is connected to the secondary side of the transformer and the AC grid is connected to the primary side of the transformer. In this configuration, at least one further device suitable for reactive power compensation can additionally be connected to the AC grid, i.e. on the primary side of the transformer, which device serves as a sink for the reactive power Q1(t) and / or the further reactive power Q2(t) exchanged by the AC / DC converter with the AC grid. The device suitable for reactive power compensation can be controlled in coordination with the rectifier, so that the exchange of reactive power with the AC grid by the device takes place at the same time. By the additional device serving as a sink for the reactive power exchanged by the AC / DC converter with the AC grid, the grid reaction of the exchanged reactive power on the AC grid can be eliminated or at least reduced. The operator of the AC grid therefore does not have to keep the additional device available in order to carry out reactive power compensation if necessary. The allowed share of the reactive power exchanged with the AC grid can therefore be increased if necessary.

[0024] The rectifier according to the application is formed by an active controlled rectifier, which is designed for supplying a DC load from an AC grid having an AC voltage. The rectifier comprises:

[0025] - an AC rectifier input having a plurality of input connections for connecting the AC grid and a DC rectifier output having two output connections for connecting the DC load, and

[0026] - an AC / DC converter having an AC input connected to the AC rectifier input, a DC output connected to the DC rectifier output and a converter circuit arranged between the AC input and the DC output. The converter circuit of the AC / DC converter has an actively controllable semiconductor switch and a freewheeling diode connected in antiparallel thereto. In addition to the rectifying function, the AC / DC converter is designed and set up for exchanging reactive power Q with the AC power grid 1,2 (t). The rectifier also comprises a control unit for controlling the AC / DC converter, in particular its semiconductor switch. The rectifier is characterized in that it is designed and set up for carrying out the method according to the application.

[0027] The plurality of input connection terminals of the rectifier can comprise only one phase connection terminal and one neutral connection terminal. Alternatively thereto, the plurality of input connection terminals can also comprise a plurality of phase connection terminals and no neutral connection terminal or one neutral connection terminal. The advantages already mentioned in connection with the method are obtained.

[0028] According to an advantageous embodiment, the rectifier can have an adjustment unit which, in conjunction with the control unit, is designed and set up to adjust the reactive power Q1(t) exchanged with the AC power grid and, if necessary, also the further reactive power Q2(t) such that the DC voltage at the DC output of the AC / DC converter approaches the desired DC operating voltage U DC,Soll as far as possible up to the attainment of the DC operating voltage U DC,Soll . In particular, the adjustment unit can be designed and set up to

[0029] - detect the DC voltage U DC,4 applied at the DC output of the AC / DC converter and / or applied at the DC rectifier output,

[0030] - compare the detected DC voltage U DC,4 with the desired DC operating voltage U DC,Soll , and

[0031] - control the AC / DC converter in conjunction with the control unit such that the detected DC voltage U DC,4 approaches the desired DC operating voltage U DC,Soll and as far as possible attains the desired DC operating voltage U DC,SollIn this way, the AC / DC converter is able to react in an adaptive manner to the currently existing voltage characteristic u(Q) between the AC input of the AC / DC converter and the grid connection point, without having to determine and, if necessary, store this voltage characteristic in advance. Alternatively, the voltage characteristic u(Q) can also be determined in advance from the reactive power Q and the reactive power Ql(t) and / or the further reactive power Q2(t) to be exchanged with the AC grid are adjusted in accordance with the determined voltage characteristic u(Q). For this purpose, the control unit of the rectifier can have or be connected to a data memory which is provided for storing the determined value pairs which reflect the previously determined voltage characteristic u(Q).

[0032] In an advantageous embodiment, the rectifier can have a filter unit with one filter choke or a plurality of filter chokes. Here, at least one filter choke can be arranged between the AC input of the AC / DC converter and the AC rectifier input. This at least one filter choke is thus at least part of the inductance through which the reactive power Ql(t) and / or the further reactive power Q2(t) is exchanged with the AC grid. Advantageously, the impedance of the filter choke can be determined such that, when the rated current I0 of the rectifier flows through the filter choke, a voltage drop of at least 25%, preferably at least 35%, particularly preferably at least 45% is caused with respect to the AC voltage applied at the AC rectifier input. The size of the impedance, and thus the size of the inductance L of the filter choke, is determined in such a way that, on the one hand, a particularly effective voltage drop with respect to the amplitude is achieved in the exchange of the reactive power Ql(t), and, on the other hand, an additional current limitation is also achieved in the event of a short circuit on the DC side. The additional current limitation minimizes the risk of damage to the freewheeling diode of the converter circuit in the event of a short circuit on the DC load. 1,2 (t) and, on the other hand, an additional current limitation is also achieved in the event of a short circuit on the DC side. The additional current limitation minimizes the risk of damage to the freewheeling diode of the converter circuit in the event of a short circuit on the DC load.

[0033] The electrolysis plant according to the application comprises a rectifier according to the application and an electrolyzer which is connected to the rectifier on the output side as a DC load. The electrolysis plant can additionally comprise a transformer whose secondary side is connected to the AC rectifier input and whose primary side is connected to the AC grid via the grid connection point. If the electrolysis plant has a transformer, the electrolysis plant can additionally comprise a device for reducing the counteraction on the grid which is suitable for reactive power compensation. Here, the device for reactive power compensation is connected to the AC grid on the primary side of the transformer and serves as a sink for the reactive power Ql(t) and / or the further reactive power Q2(t) exchanged by the AC / DC converter with the AC grid. The advantages already listed in connection with the method are also achieved here. BRIEF DESCRIPTION OF DRAWINGS

[0034] The application is explained below with the aid of the drawings. In which:

[0035] Figure 1 An embodiment of an electrolysis plant according to the application is shown with a rectifier according to the application;

[0036] Figure 2 An embodiment of a converter circuit of a rectifier according to the application is shown Figure 1

[0037] Figure 3 A time course of the method according to the application according to an embodiment is shown in a schematic manner. DETAILED DESCRIPTION

[0038] In Figure 1 , an embodiment of an electrolysis plant 50 according to the application is shown. The electrolysis plant 50 comprises an electrolyzer 22 as DC load 20, a rectifier 1 according to the application and a transformer 32. The primary side 32.P of the transformer 32 is connected with an alternating voltage (AC) grid 30 via a grid connection point 31. The secondary side 32.S of the transformer 32 is connected with the AC rectifier input 7 of the rectifier 1. The transformer 32 converts an AC voltage with an amplitude of Û Netz on the primary side into an AC voltage with an amplitude of Û7 on the secondary side and at the AC rectifier input 7. The DC rectifier output 8 of the rectifier 1 is connected with the input 21 of the electrolyzer 22.

[0039] The rectifier 1 is an active controllable rectifier which is designed to convert an AC voltage applied at the input side into a DC voltage applied at the DC rectifier output 8 in order to power the electrolyzer 22 with the DC voltage U DC,Last . To this end, the rectifier 1 comprises an AC / DC converter 4 with an AC input 4.1 and a DC output 4.2 which is controlled via a control unit 9. The AC input 4.1 is connected with a filter choke 3.1 and a filter capacitor 3.2 via a filter unit 3 and with the AC rectifier input 7 via an AC separation unit 2. The DC output 4.2 is connected with the DC rectifier output 8 via a DC separation unit 6. In parallel to the DC output 4.2, an output capacitor 5 is connected for smoothing the DC voltage U DC,4 ​The DC separation unit 6 comprises two current paths arranged in parallel. The first current path includes a series circuit of a pre-charge resistor and a circuit breaker, and is used for pre-charging the electrolyzer 22. The second current path, arranged in parallel, contains only one additional circuit breaker. After pre-charging is complete, the electrolyzer 22 operates within its resistance range, wherein the closed additional circuit breaker provides a low-impedance electrical connection between the DC output terminal 4.2 of the AC / DC converter 4 and the electrolyzer 22. The AC separation unit 2 and the DC separation unit 6 are driven by the control unit 9 of the rectifier 1.

[0040] The rectifier 1 according to the invention is designed to exchange reactive power Q with the AC grid 30 via the transformer 32 by correspondingly driving the semiconductor switches of the AC / DC converter 4. 1,2 (t). Here, it is related to the reactive power Q. 1,2 (t) The associated current flows through inductor L, which inductor L in Figure 1 In the case shown, it consists of the filter choke 3.1 of filter unit 3 and the winding of the secondary side 32.S of transformer 32. Reactive power Q 1,2 (t) is almost entirely displacement reactive power, or at least mostly displacement reactive power. For example, combined with... Figure 2 and Figure 3 The detailed explanation is based on reactive power Q. 1,2 The type of (t), reactive power Q 1,2 The switching of (t) affects the amplitude Û4 of the AC voltage applied to the AC input terminal 4.1 of the AC / DC converter 4, either by stepping down or boosting it, thereby expanding the DC voltage range of the rectifier 1, and particularly the DC voltage range of the AC / DC converter 4. On the one hand, the amount of reactive power switched can be adjusted, for example, by combining a known voltage change characteristic u(Q) determined once by the control unit 9. For this purpose, the rectifier 1 can have a data memory 11 for storing pairs of values ​​reflecting the previously determined voltage change characteristic u(Q). Alternatively or additionally, the rectifier 1 can also have a regulating unit 10 designed to detect the DC voltage U applied to the DC output terminal 4.2 of the AC / DC converter 4. DC,4 If necessary, it also detects the AC voltage with an amplitude of Û4 applied to the AC input terminal 4.1, and converts the detected DC voltage U DC,4 With the expected DC operating voltage U DC,Soll The comparison is performed, and the result is transmitted to the control unit 9. The control unit 9 then changes the reactive power Q exchanged between the AC grid 30 and the AC / DC converter 4 by correspondingly driving the semiconductor switch of the AC / DC converter 4. 1,2 (t), making the DC voltage U DC,4 Approaching the desired operating voltage U DC,SollAnd to achieve the desired operating voltage U as much as possible. DC,Soll .

[0041] exist Figure 1 In this embodiment, rectifier 1, transformer unit 32, and AC power grid are exemplarily shown as three-phase. However, according to the present invention, they can also be single-phase components. Furthermore, the control unit 9 of rectifier 1 can communicate with a communication unit (in... Figure 1 (Not shown in the diagram) Connection. In this way, the synchronous drive of additional equipment for reactive power compensation connected to the AC grid on the primary side of the transformer can be started and coordinated.

[0042] exist Figure 2 In the middle, it is shown in more detail. Figure 1 An implementation of the AC / DC converter 4 associated with rectifier 1. Figure 1 Similar to rectifier 1, AC / DC converter 4 is exemplarily designed as a three-phase AC / DC converter 4 and includes converter circuit 40 having a total of three bridge arms 45. Each bridge arm 45 has two series-connected semiconductor switches 41, each semiconductor switch having a freewheeling diode 42 connected in anti-parallel. The freewheeling diode 42 can be designed as an intrinsic diode of the corresponding semiconductor switch 41, or as a separate diode. The semiconductor switch 41 can be a MOSFET or IGBT semiconductor switch. According to the three-phase design of converter circuit 40, the AC input terminal 4.1 of AC / DC converter 4 includes three input connections, each of which is connected to the connection point 46 of the two semiconductor switches 41 assigned to its respective bridge arm 45. The DC output terminal 4.2 of AC / DC converter 4 includes a positive output connection (+) and a negative output connection (-).

[0043] During conversion, AC / DC converter 4 can deliver active power P(t) from AC input terminal 4.1 to DC output terminal 4.2, and if necessary, also in the opposite direction from DC output terminal to AC input terminal 4.1. Furthermore, AC / DC converter 4 is designed to connect the AC input terminal 4.1 to the AC power grid 30 connected to AC input terminal 4.1 (in... Figure 2 The exchange of reactive power Q between (not explicitly shown in the text) 1,2 (t). For this purpose, semiconductor switch 41 is composed of (in) Figure 2 (Not explicitly shown) Control unit 9 is driven. The AC / DC converter 4 is able to convert the AC voltage applied to the AC input terminal 4.1 into the DC voltage U at the DC output terminal 4.2 via a corresponding clock from the semiconductor switch 41. DC,4 Here, the level of the converted DC voltage (in other words, the DC voltage range) can be taken as a value between the minimum DC voltage U. DC,minand maximum DC voltage U DC,max The value between. Minimum DC voltage U DC,min The voltage is downwardly limited to a value via the freewheeling diode 42, which excludes the forward voltage corresponding to the freewheeling diode 42 and corresponds to the amplitude Û4 of the AC voltage applied at the AC input terminal 4.1. Due to the freewheeling diode 42, the bridge circuit is thus able to generate a DC voltage U at the DC output terminal 4.2. DC,4 The DC voltage U DC,4 It is greater than, but not less than, and at least not significantly less than, the amplitude Û4 of the AC voltage applied on the input side. Here, the conversion loss increases with the DC voltage U applied on the output side. DC,4 The reactive power Q increases proportionally to the increase in the amplitude Û4 of the AC voltage applied on the input side. Now, the reactive power Q is exchanged with the AC grid 30 via the AC / DC converter 4 through the inductor L (e.g., the filter choke 3.1 and / or the inductance allocated to the secondary side of the transformer). 1,2 (t) has a voltage-boosting or voltage-reducing effect on the amplitude Û4 of the AC voltage applied to the AC input terminal 4.1. This is in Figure 3 This will be explained in more detail later.

[0044] exist Figure 2 The diagram exemplarily illustrates a two-stage converter circuit 40 with two voltage levels. However, within the scope of the invention, converter circuits with more than two voltage levels, such as three-stage or five-stage converter circuits, are also possible. Furthermore, within the scope of the invention, the converter circuit can be designed as a neutral point circuit. Here, the output connection (-) of the DC output terminal 4.2 can be connected to the neutral point tap of the transformer 32, via which the AC / DC converter 4 is connected to the AC power grid 30. Alternatively, the AC / DC converter 4 can also be connected to the neutral line of the AC power grid 30.

[0045] Figure 3 The time variation process of the method according to the invention in one embodiment is illustrated schematically, as can be performed using the adjustment unit 10. The time curves for the following items are shown here: DC voltage U at the DC output terminal 4.2 of the AC / DC converter 4. DC,4 The amplitude of the AC voltage Û4 at the AC input terminal 4.1 of the AC / DC converter 4 and the reactive power Q1(t) exchanged between the AC / DC converter 4 and the AC power grid 30 via the inductor L. Figure 3 In this process, the positive value of the exchanged reactive power Q1(t) has a voltage reduction effect on the amplitude Û4 of the AC voltage. For example, in... Figure 3 The various time curves, shown closer to the vertical axis, are presented with different line shapes. For example, the time curves reflect what might happen when the electrolyzer 22, acting as a DC load 20, is connected to the active controlled rectifier 1.

[0046] The starting point is the state in which the electrolyzer 22 is disconnected from the rectifier 1. However, the pre-charge of the electrolyzer 22 has already taken place, so that its input-side DC voltage U DC,Last corresponds to a value which is slightly below the threshold voltage U cr , so that no electrolysis reaction has yet taken place. In the time interval t < t I , no reactive power Ql(t) is initially exchanged between the AC / DC converter 4 and the AC network 30, i.e. for t < t I , Ql(t) = 0. The value of the amplitude of the AC voltage applied at the AC input 4.1, Û4, is above the threshold voltage, in order to produce as low a conversion loss as possible under the high-speed electrolysis reaction.

[0047] At the time point t I , a signal is issued to the electrolysis device 50, i.e. the rectifier 1 should be connected to the electrolyzer 22. In order to connect as load-free as possible, the connection is made at least in a reduced compensation current, from the time point t I , a first value of the desired DC operating voltage U DC,Soll,1 is also set to the currently present DC voltage U DC,Last at the input of the electrolyzer 22. The first value of the desired DC operating voltage U DC,Soll,1 is thus smaller than the amplitude of the AC voltage applied at the AC input 4.1, Û4, and since the DC voltage U DC,4 at the DC output 4.2 (excluding the forward voltage of the freewheeling diode 42) corresponds to the amplitude Û4, the first value of the desired DC operating voltage U DC,Soll,1 is also smaller than the DC voltage U DC,4 applied at the output side. The desired DC operating voltage U DC,Soll,1 and the DC voltage U DC,4 applied at the output side thus exist with a relatively large difference ΔU(t I ). The regulating unit 10 detects the DC voltage U DC,4 applied at the output side, compares it with the desired DC operating voltage U DC,Soll,1 and transmits the differential voltage ΔU(t I ) to the control unit 9. In response thereto, the control unit 9 controls the semiconductor switches 41 of the converter circuit 40 in accordance with an increase in the reactive power Ql(t I exchanged with the AC network 30. This exchanged reactive power Ql(t), in particular the current associated therewith and flowing through the inductance L, has a voltage- reducing effect on the amplitude of the AC voltage applied at the AC input 4.1, Û4. Thereby, the value of the amplitude Û4, and accordingly the DC voltage U DC,4 at the DC output 4.2 of the AC / DC converter 4, is reduced. In t I and tII During the time interval, the regulating unit 10 continuously detects the current DC voltage U. DC,4 (t), and compare it with the first value U of the desired DC operating voltage. DC,Soll,1 A comparison is made. The result of the comparison is a quantitative reduction in the difference ΔU(t), which is then transmitted to the control unit 9. The control unit 9 then drives the semiconductor switch 41 of the converter circuit 40 again, with the goal of further increasing the switched reactive power Q1(t). I and t II During the time interval, the reactive power Q1(t) increases, and the amplitude Û4 decreases accordingly, as does the DC voltage U at the DC output terminal 4.2 of the AC / DC converter 4. DC,4 Decrease until the DC voltage U at the DC output terminal 4.2 of AC / DC converter 4 is reached. DC,4 and the first value U of the desired DC operating voltage DC,Soll,1 The difference between them disappears. This ultimately leads to the disappearance of the difference at time point t. II The amplitude of the AC voltage on the input side Û4 and the DC voltage U at the DC output terminal 4.2 of the AC / DC converter 4. DC,4 The first value U of the desired DC operating voltage was achieved. DC,Soll,1 Therefore, electrolyzer 22 can operate at time point t. II The closed DC separation unit 6 is connected to the rectifier 1 with low impedance and as little load as possible.

[0048] From time point t II Initially, the desired first value of the DC operating voltage U DC,Soll,1 The second value U of the desired DC operating voltage DC,Soll,2 Instead, the electrolysis reaction should now take place at the second value. Therefore, in time period t... II To t IV Internally, the DC voltage U at the DC output terminal 4.2 of AC / DC converter 4 DC,4 The current effective second value U approaches the desired DC operating voltage in a ramp-like manner. DC,Soll,2 During time period t II -t III This is accompanied by a gradual decrease in reactive power Q1(t) to a value of 0. From time point t... III Initially, the AC / DC converter 4 and the AC grid 30 no longer exchange reactive power Q1(t), and the amplitude Û4 of the AC voltage at the AC input terminal 4.1 of the AC / DC converter returns to its initial value at t=0.

[0049] exist Figure 3 The reactive power Q1(t) and the DC voltage U at the DC output terminal 4.2 of the AC / DC converter 4 are shown in the figure.DC,4 The sloping curve can also extend more steeply than shown in the figure, and has an almost step-like time variation.

[0050] exist Figure 3 The method according to the invention is shown, which can be implemented adaptively by means of the adjustment unit 10. Here, a detailed understanding of the voltage variation characteristic u(Q) between the grid connection point 31 of the AC grid 30 and the AC input terminal 4.1 of the AC / DC converter is not required. However, within the scope of the invention, the method can also be performed using a known voltage variation characteristic u(Q). Based on the known voltage variation characteristic u(Q), when the DC voltage U applied at the DC output terminal 4.2 of the AC / DC converter 4 is detected... DC,4 And compare it with the first value of the desired DC operating voltage. DC,Soll,1 After comparison, the corresponding differential voltage ΔU(t) can be determined. I The determined differential voltage ΔU(t) I By comparing the voltage change characteristic u(Q) with the known voltage change characteristic, the desired DC operating voltage U can be determined. DC,Soll,1 The required reactive power Q1(t) is determined. In response, the control unit 9 can drive the semiconductor switch 41 of the AC / DC converter 4 to exchange the required reactive power Q1(t). The method according to the invention has been described above with the electrolyzer 22 connected to the rectifier 1 as close to no-load connection as possible. However, alternatively or additionally, it can also be performed by disconnecting the electrolyzer 22 from the rectifier 1 by disconnecting the DC disconnection unit 6 to remove the load. Specifically, by temporarily exchanging the reactive power Q1(t), the DC voltage U at the DC output terminal of the AC / DC converter 4... DC,4 (When rectifier 1 is connected to electrolyzer 22 with low impedance, this DC voltage also exists at input terminal 21 of electrolyzer 22.) It can be reduced to the critical voltage U required to maintain the electrolysis reaction shortly before and during the disconnection of DC separation unit 6. cr the following.

[0051] List of references signs

[0052]

[0053] .

Claims

1. A method for extending the DC voltage range of a rectifier (1), the rectifier being used to supply power from an AC power grid (30) connected to an AC rectifier input terminal (7) of the rectifier (1) via a power grid connection point (31) to a DC load (20) connected to a DC rectifier output terminal (8) of the rectifier (1), in, The rectifier (1) has an AC / DC converter (4) having an AC input terminal (4.1) and a DC output terminal (4.2). The AC / DC converter (4) includes a converter circuit (40) having a semiconductor switch (41) and a freewheeling diode (42) connected in antiparallel to the semiconductor switch. An inductor L is arranged between the AC input terminal (4.1) of the AC / DC converter (4) and the power grid connection point (31). The method includes the following steps: By driving the semiconductor switch (41) of the AC / DC converter (4), the desired DC operating voltage U at the DC output terminal (4.2) of the AC / DC converter (4) and / or at the DC rectifier output terminal (8) is adjusted. DC,Soll , Wherein, when the desired DC operating voltage U DC,Soll When the amplitude Û4 of the AC voltage at the AC input terminal (4.1) of the AC / DC converter (4) is lower than the value of the AC voltage amplitude Û4, the semiconductor switch (41) of the AC / DC converter (4) is driven to exchange reactive power Q1(t) with the AC grid (30). The reactive power Q1(t) reduces the amplitude Û4 of the AC voltage at the AC input terminal (4.1) of the AC / DC converter (4), making the amplitude Û4 closer to the desired DC operating voltage U. DC,Soll And to achieve the desired DC operating voltage U as much as possible. DC,Soll ,as well as During and shortly before the DC load (20) is electrically connected and / or disconnected from the rectifier (1), the reactive power Q1(t) is exchanged with the AC grid (30).

2. The method according to claim 1, wherein, The reactive power Q1(t) exchanged between the AC / DC converter (4) and the AC grid (30) is mostly displacement reactive power.

3. The method according to claim 1, wherein, The inductor includes a filter choke (3.1) arranged between the AC / DC converter (4) and the input terminal (7) of the AC rectifier and / or a transformer winding on the secondary side (32.S) of the transformer (32) associated with the rectifier (1).

4. The method according to claim 2, wherein, The inductor includes a filter choke (3.1) arranged between the AC / DC converter (4) and the input terminal (7) of the AC rectifier and / or a transformer winding on the secondary side (32.S) of the transformer (32) associated with the rectifier (1).

5. The method according to any one of claims 1 to 4, wherein, When the desired DC operating voltage U DC,Soll Reaching or exceeding the voltage threshold U TH At the same time, the semiconductor switch (41) of the AC / DC converter (4) is driven to exchange additional reactive power Q2(t) with the AC grid (30), such that the exchange of additional reactive power Q2(t) boosts the amplitude Û4 of the AC voltage applied at the AC input terminal (4.1) of the AC / DC converter (4), thereby bringing the amplitude Û4 closer to the desired DC operating voltage U. DC,Soll .

6. The method according to any one of claims 1 to 4, wherein, The exchange of reactive power Q1(t) and / or the exchange of additional reactive power Q2(t) includes: determining the theoretical value of reactive power based on the known voltage variation characteristic u(Q), which is a function of the reactive power Q exchanged between the AC input terminal (4.1) of the AC / DC converter (4) and the grid connection point (31) of the AC grid (30).

7. The method according to any one of claims 1 to 4, wherein, The DC voltage U applied at the DC output terminal (4.2) of the AC / DC converter (4) is detected. DC,4 The actual value, wherein the actual value is compared with the expected DC operating voltage U. DC,Soll The comparison is performed, and the corresponding reactive power Q is adjusted by means of the adjustment unit (10) connected to the control unit (9). 1,2 The exchange of (t) makes the actual value closer to the desired DC operating voltage U. DC,Soll .

8. The method according to any one of claims 1 to 4, wherein, The exchange of the reactive power Q1(t) and / or the exchange of the additional reactive power Q2(t) causes the amplitude Û4 at the AC input terminal (4.1) of the AC / DC converter (4) to change by at least 10% relative to the rated value of the amplitude Û4.

9. The method according to any one of claims 1 to 4, wherein, During the state of the AC grid (30) under specified framework conditions and when the amplitude Û7 of the AC voltage at the input terminal (7) of the AC rectifier deviates from its rated value, a third reactive power Q3(t) is exchanged between the AC / DC converter (4) and the AC grid (30) to counteract the deviation of the amplitude Û7 from its rated value.

10. The method according to any one of claims 1 to 4, wherein, When the desired DC operating voltage U DC,Soll The exchange of reactive power Q1(t) between the AC / DC converter (4) and the AC grid (30) only occurs when the rectified value of the AC voltage is lower than the value of the amplitude Û4, in addition to being lower than the value of the amplitude Û4.

11. The method according to claim 8, wherein, The change is at least 20%.

12. The method according to claim 8, wherein, The change is at least 25%.

13. An active controlled rectifier (1) for supplying power from an AC grid (30) having an AC voltage to a DC load (20), the rectifier comprising: An AC rectifier input terminal (7) has multiple input terminals for connecting to the AC power grid (30) and a DC rectifier output terminal (8) has two output terminals for connecting to the DC load (20). AC / DC converter (4), the AC / DC converter having an AC input terminal (4.1) connected to the AC rectifier input terminal (7) on the AC side, a DC output terminal (4.2) connected to the DC rectifier output terminal (8) on the DC side, and a converter circuit (40) arranged between the AC input terminal (4.1) and the DC output terminal (4.2). The AC / DC converter (4) includes a converter circuit (40) comprising an active controllable semiconductor switch (41) and a freewheeling diode (42) connected in anti-parallel to the active controllable semiconductor switch. The AC / DC converter (4) is designed to exchange reactive power Q with the AC power grid (30). 1,2 (t), and The rectifier (1) also includes a control unit (9) for controlling the AC / DC converter (4). Its features are, The rectifier (1) is designed and configured to perform the method according to any one of claims 1-12.

14. The rectifier (1) according to claim 13, characterized in that, The rectifier (1) has a regulating unit (10) which is designed and configured to detect the DC voltage U applied at the DC output terminal (4.2) of the AC / DC converter (4) and / or at the output terminal (8) of the DC rectifier. DC,4 The detected DC voltage U DC,4 With the expected DC operating voltage U DC,Soll The comparison is performed, and the control unit (9) controls the AC / DC converter (4) so ​​that the detected DC voltage U DC,4 Approximately the desired DC operating voltage U DC,Soll And to achieve the desired DC operating voltage U as much as possible. DC,Soll .

15. The rectifier (1) according to claim 13, characterized in that, The control unit (9) has a data memory (11) or is connected to a data memory (11), the data memory being configured to store voltage change characteristics u(Q) related to the reactive power Q.

16. The rectifier (1) according to claim 14, characterized in that, The control unit (9) has a data memory (11) or is connected to a data memory (11), the data memory being configured to store voltage change characteristics u(Q) related to the reactive power Q.

17. The rectifier (1) according to any one of claims 13 to 16, characterized in that, The rectifier (1) also has a filter unit (3) with a filter choke (3.1), wherein the impedance of the filter choke (3.1) is measured such that when the rated current I0 flows through the filter choke (3.1), it causes a voltage drop of at least 25% relative to the AC voltage U7 applied at the input terminal (7) of the AC rectifier.

18. The rectifier (1) according to claim 17, characterized in that, The voltage drop is at least 35%.

19. The rectifier (1) according to claim 17, characterized in that, The voltage drop is at least 45%.

20. The rectifier (1) according to claim 13, characterized in that, The control unit (9) is used to control the semiconductor switch (41) of the AC / DC converter.

21. An electrolysis apparatus (50) having a rectifier (1) according to any one of claims 13 to 20 and an electrolyzer (22) connected to the rectifier (1) on the output side as a DC load (20).

22. The electrolysis apparatus (50) according to claim 21 further includes a transformer (32), the secondary side (32.S) of the transformer being connected to the input terminal (7) of the AC rectifier, and the primary side (32.P) of the transformer being connected to the AC power grid (30) via the power grid connection point (31).

23. The electrolysis apparatus (50) according to claim 22 further includes a device for reducing the reaction to the power grid for reactive power compensation, the device being connected to the AC power grid (30) on the primary side (32.P) of the transformer (32), and the device serving as a sink for reactive power Q(t) and / or additional reactive power Q2(t) exchanged between the AC / DC converter (4) and the AC power grid (30).

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