Power conversion system

Abstract

A power conversion system (1) for powering an electrolytic cell comprises K primary rectifier bridges (3), J auxiliary rectifier bridges (9) and Z DC / DC converters (15), each DC / DC converter being connected to the auxiliary rectifier bridge (9), where a first DC link (7) shared by the K primary rectifier bridges (3) is connected in series with Z second DC links (10) of the Z DC / DC converters (15), thereby forming an output of the power conversion system (1). Furthermore, the power conversion system (1) comprises a transformer (19) having secondary windings connected in various configurations to the K primary rectifiers (3) and the J auxiliary rectifiers (9).

Description

Technical Field

[0001] The present disclosure relates generally to power conversion systems, and more particularly to power conversion systems for powering electrolyzers. Background Art

[0002] The hydrogen economy has become an increasingly popular topic. There's consensus that green hydrogen production is the only way to enable this economy. Today, approximately 95% of hydrogen production is classified as grey, meaning it comes directly from fossil fuel sources and is carbon dioxide (CO2) intensive. Blue hydrogen adds carbon storage to current production methods, significantly reducing the CO2 footprint. However, green hydrogen, produced through electrolysis using energy from renewable resources, is the only sustainable way to produce hydrogen.

[0003] To meet the demand for hydrogen, large-scale electrolysis plants are planned to be deployed in the near future. Electrolyzers use low-voltage direct current (DC) to circulate current through water and separate hydrogen and oxygen molecules from the water. Therefore, large-scale electrolysis plants consume high current at low voltage. The most common way to generate this DC voltage is to use a controlled thyristor rectifier. This solution requires reactance and current harmonic compensation. Multi-pulse configurations can be used to reduce these current harmonics, but reactive power still requires additional compensation due to the firing angle taken into account throughout the lifetime. In addition, the magnetic components required on the electrolyzer side are considered to be very large in order to limit the peak-to-peak current ripple in the electrolyzer and limit the degradation of its lifetime and increase its hydrogen production capacity.

[0004] CN114499216A discloses a power supply system for powering an electrolysis cell. Power converters are connected to corresponding secondary windings of a transformer in Y and Δ configurations. One of the power converters is a single-stage AC / DC converter with an output connected to an electrolysis cell, while the other power converter comprises two cascaded power converters for precisely regulating the voltage supplied to the electrolysis cell within a narrow range. Summary of the Invention

[0005] In view of the above, a general object of the present disclosure is to provide a power conversion system that solves or at least alleviates the problems of the prior art.

[0006] Therefore, according to a first aspect of the present disclosure, there is provided a power conversion system for supplying power to an electrolyzer, comprising: K primary rectifier bridges, wherein K is an integer equal to or greater than 1, wherein if K is greater than 1, the K primary rectifier bridges are connected in parallel at their DC sides; a first DC link having a DC link capacitor, the first DC link being common to the K primary rectifier bridges; J auxiliary rectifier bridges, wherein J is an integer equal to or greater than 1; and Z DC / DC converters, wherein Z is an integer equal to or greater than 1, wherein the output terminal of each auxiliary rectifier bridge is connected to the input terminal of one of the Z DC / DC converters, wherein each DC / DC converter has a second DC link connected in series with the first DC link, the first DC link and the Z second DC links defining the power The output of the conversion system; and a transformer comprising N groups of M-phase secondary windings, wherein: A) if K=1, J=Z=1 or 2, and N=1, each auxiliary rectifier bridge is connected to a corresponding one of the DC / DC converters, and the M phases of the secondary windings are connected to the input terminals of the primary rectifier bridge, and are additionally connected to the input terminals of J auxiliary rectifier bridges, and wherein each auxiliary rectifier bridge includes six semiconductor switches for rectification; B) if K=1, J=Z=2, and N=3, each auxiliary rectifier bridge is connected to a corresponding one of the DC / DC converters, and the M phases of the first M-phase secondary winding of the three M-phase secondary windings are connected to the input terminals of the primary rectifier bridge, and the M phases of the second and third M-phase secondary windings are connected to the input terminals of the corresponding auxiliary rectifier bridges. C) if K is greater than 1, N=K+J, and Z=1, then the M phases of each of the K groups of M-phase secondary windings of the first winding set are connected to the input terminals of the corresponding primary rectifier bridge, and the M phases of each of the J groups of M-phase secondary windings of the second winding set separate from the first winding set are connected to the input terminals of the corresponding auxiliary rectifier bridge, wherein if J is greater than 1, the J auxiliary rectifier bridges are connected in parallel on their DC sides, and D) if K and Z are both greater than 1, J is greater than Z, and N=K+J, Then each of the Z-1 auxiliary rectifier bridges is connected to a corresponding one of the Z-1 DC / DC converters, and the remaining auxiliary rectifier bridges are connected in parallel on their DC sides, and the M phases of each group of M-phase secondary windings in the K groups of M-phase secondary windings of the first winding set are connected to the input terminals of the corresponding primary rectifier bridge, and the M phases of each group of M-phase secondary windings in the J groups of M-phase secondary windings of the second winding set separated from the first winding set are connected to the input terminals of the corresponding auxiliary rectifier bridge.

[0007] The majority of the power passes through K primary rectifier bridges. This majority of power can, for example, be in the range of 60-80% of the total power fed to the electrolyzer. The remaining power passes through J auxiliary rectifier bridges and Z DC / DC converters. The Z DC / DC converters are configured to regulate the voltage and current fed to the electrolyzer.

[0008] Compared to conventional solutions with rectifier bridges that share the power equally, higher conversion efficiency can be achieved.

[0009] In alternatives BD, due to the configuration of multiple secondary-side transformer branches and their connection with K primary rectifier bridges and J auxiliary rectifier bridges, the performance of the grid side will be enhanced because fewer harmonics are injected into the grid.

[0010] According to alternatives A and B, when J and Z are equal to 2, a symmetrical voltage regulation of the electrolyzer can be obtained.

[0011] According to one embodiment, the semiconductor switch is a transistor. The transistor may be, for example, a metal oxide field effect transistor (MOS-FET) or an insulated gate bipolar transistor (IGBT). The MOS-FET or IGBT may be, for example, based on silicone, silicon carbide, or gallium nitride.

[0012] According to one embodiment, a power conversion system includes a control system configured to control semiconductor switches to perform rectification. The semiconductor switches may be controlled by pulse width modulation (PWM) to perform rectification.

[0013] According to one embodiment, the control system is configured to control the semiconductor switches to provide reactive power compensation.

[0014] According to one embodiment, the control system is configured to control the semiconductor switches to provide harmonic compensation.

[0015] In Alternative A, the same secondary winding is connected to the primary rectifier bridge and J auxiliary rectifier bridges. Through harmonic compensation and / or reactive power compensation performed by the six semiconductor switches of the J auxiliary rectifier bridges, the losses in the transformer can be reduced compared to the design disclosed in CN114499216A because the waveform on the secondary side of the transformer is cleaner / more sinusoidal.

[0016] Power conversion systems can be configured to deliver power in the megawatt range.

[0017] According to one embodiment, the power conversion system is a low voltage power conversion system.Low voltage in this context refers to a voltage of at most 1.5 kV, such as a voltage of at most 1 kV.

[0018] According to one embodiment, each primary rectifier bridge includes six semiconductor devices for rectification.

[0019] If K=1 and J=1, the power conversion system can be operated as a quasi-12-pulse rectifier. The term "quasi" is used because most of the power passes through the primary rectifier bridge, which can have six semiconductor devices, while six semiconductor switches can be used for rectification through the auxiliary rectifier bridge.

[0020] If K=2 and J=1, the power conversion system can operate as a quasi-18 pulse rectifier.If K=3 and J=1, the power conversion system can operate as a quasi-24 pulse rectifier.

[0021] According to one embodiment, the six semiconductor devices are diodes, thyristors or transistors such as MOS-FETs or IGBTs.

[0022] According to one embodiment, each primary rectifier bridge includes six semiconductor devices for rectification.

[0023] According to one embodiment, the six semiconductor devices are diodes, thyristors or transistors.

[0024] According to one embodiment in the case of alternative A, the output terminals of each DC / DC converter are electrically isolated from the auxiliary rectifier bridge to which the DC / DC converter is connected. Short circuiting of the primary rectifier bridge and the J auxiliary rectifier bridges through the DC / DC converter can thus be avoided.

[0025] According to one embodiment in the case of alternative A, the power conversion system comprises a filter, wherein the filter is connected between the input terminals of the auxiliary rectifier bridge and the transformer.

[0026] The filter together with the J auxiliary rectifier bridges and the Z second DC links of the Z DC / DC converters may form an active filter.

[0027] The active filter may be configured to inject current harmonics into the grid that are opposite to the current harmonics in the primary rectifier bridge. The active filter may be controlled based on current measurements of the current of the primary rectifier bridge.

[0028] According to one embodiment, M=3.

[0029] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. Unless explicitly stated otherwise, all references to "a / an / the element, device, component, means, etc." should be interpreted openly as referring to at least one instance of that element, device, component, means, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Specific embodiments of the present inventive concept will now be described by way of example with reference to the accompanying drawings, in which:

[0031] Figure 1 A circuit diagram schematically illustrates an example of a power conversion system for powering an electrolyzer;

[0032] Figure 2 a circuit diagram schematically illustrating another example of a power conversion system for powering an electrolyzer; and

[0033] Figure 3 A circuit diagram of a general example of a power conversion system for powering an electrolyser is schematically shown. DETAILED DESCRIPTION

[0034] The concepts of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. However, the concepts of the present invention may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided as examples so that this disclosure will be thorough and complete and will fully convey the scope of the concepts of the present invention to those skilled in the art. Throughout the specification, like reference numerals represent like elements.

[0035] Figure 1 An example of a power conversion system 1 for powering an electrolyser is shown.

[0036] The power conversion system 1 includes a single primary rectifier bridge 3. The primary rectifier bridge 3 includes a plurality of semiconductor devices 5 for rectification. In this example, the number of semiconductor devices 5 is six. Each branch of the primary rectifier bridge 3 includes two semiconductor devices 5.

[0037] According to this example, the semiconductor device 5 is a diode. Alternatively, the semiconductor device 5 may be a thyristor or a transistor.

[0038] Primary rectifier bridge 3 includes a first DC link 7. First DC link 7 is arranged on the DC side of primary rectifier bridge 3. First DC link 7 includes a DC link capacitor C1. First DC link 7 has a first output terminal 7a and a second output terminal 7b. First output terminal 7a is a first power conversion system output terminal, i.e., the first output terminal of power conversion system 1. The first power conversion system output terminal may be a positive voltage terminal of power conversion system 1.

[0039] The power conversion system 1 includes an auxiliary rectifier bridge 9. The auxiliary rectifier bridge 9 is an active rectifier bridge. The auxiliary rectifier bridge 9 includes six semiconductor switches S. The semiconductor switches S are arranged to provide rectification. The semiconductor switches S may be thyristors or transistors, for example.

[0040] The power conversion system 1 may include a control system 11 configured to control the semiconductor switch S. The control system 11 is configured to control the switching of the semiconductor switch S so that the auxiliary rectifier bridge 9 performs rectification. For example, if the semiconductor switch S is a transistor, the control system 11 may be configured to control the switching of the transistor by means of a PWM modulation signal provided to the gate of the transistor.

[0041] The control system 11 may be configured to control the semiconductor switches S to perform rectification in addition to performing one or both of harmonic compensation and reactive power compensation. It will be apparent to those skilled in the art how to implement such control, and the details will not be further described herein.

[0042] The auxiliary rectifier bridge 9 includes a third output terminal and a fourth output terminal, and a second DC link 13 is formed across the third output terminal and the fourth output terminal.

[0043] The power conversion system 1 includes a DC / DC converter 15 having input terminals connected to the third output terminal and the fourth output terminal, respectively.

[0044] The control system 11 is configured to control the DC / DC converter 15 .

[0045] The DC / DC converter 15 has output terminals 15a and 15b that are galvanically isolated from the auxiliary rectifier bridge 9. The DC / DC converter 15 may include a DC / AC converter stage, an AC / DC converter stage, and a transformer connected between the DC / AC converter stage and the AC / DC converter stage to provide galvanic isolation.

[0046] DC / DC converter 15 has a second DC link capacitor C2 connected across its output terminals 15a and 15b to form a second DC link 10. First DC link 7 and second DC link 10 are connected in series, and the output of power conversion system 1 is defined by the two DC links 7 and 10. That is, the electrolyzer to be powered by power conversion system 1 is connected across the two DC links 7 and 10. Output terminal 15a is connected to second output terminal 7b of DC link 7. The other output terminal 15b forms the second power conversion system output terminal, i.e., the second output terminal of power conversion system 1. The negative side of DC link capacitor C1 is connected to the positive side of second DC link capacitor C2. The negative side of second DC link capacitor C2 is connected to the second power conversion system output terminal. The second power conversion system output terminal can be the negative voltage terminal of power conversion system 1. An electrolyzer can be connected to both the first and second power conversion system output terminals to power the electrolyzer. The electrolyzer is thus powered by power conversion system 1, with the majority of the power flowing through primary rectifier bridge 3 and a smaller portion flowing through auxiliary rectifier bridge 9 and DC / DC converter 15.

[0047] The power conversion system 1 further comprises a transformer 19. The transformer 19 has a primary side configured to be connected to a power grid (such as a medium voltage power grid). The transformer 19 has a secondary side configured to be connected to the primary rectifier bridge 3 and at least indirectly to the auxiliary rectifier bridge 9. To this end, the power conversion system 1 may optionally include a filter 21 connected between the transformer 19 and the input of the auxiliary rectifier bridge 9. The filter 21 may be a passive filter. When the control system 11 controls the semiconductor switch S in an appropriate manner, the filter 21, together with the auxiliary rectifier bridge 9 and the second DC link 13, becomes an active filter. Thus, according to the control of the semiconductor switch S, the active filter can inject current harmonics into the power grid that are opposite to the current harmonics generated by the primary rectifier bridge 3.

[0048] Transformer 19 includes a set of M-phase secondary windings 19a. M-phase secondary windings 19a are the secondary-side windings of transformer 19. In this example, M=3, so transformer 19 includes a single set of three secondary windings. Each of these secondary windings is connected to a corresponding input terminal of primary rectifier bridge 3. Furthermore, each secondary winding 19a is connected to a corresponding input terminal of auxiliary rectifier bridge 9, either directly or, if present, via filter 21.

[0049] Figure 2 Another example of a power conversion system for powering an electrolyzer is shown.

[0050] according to Figure 2 In the example in FIG. 1 , the power conversion system 1 ′ includes two primary rectifier bridges 3 ′ and 3 ″. The first primary rectifier bridge 3 ′ is the same as the primary rectifier bridge 3 described above.

[0051] The second primary rectifier bridge 3 ″ is identical to the first primary rectifier bridge 3 ′. The first and second primary rectifier bridges 3 ′ share a first DC link 7 .

[0052] The power conversion system 1' further includes an auxiliary rectifier bridge 9' and a DC / DC converter 15' connected to the output terminals of the auxiliary rectifier bridge 9'. Similar to the first example, one of the output terminals of the DC / DC converter 15' is connected to the second output terminal 7b, while the other output terminal forms the second power conversion system output terminal.

[0053] The DC / DC converter 15' may include a plurality of semiconductor switches S for DC / DC conversion, such as thyristors or transistors. In the case where the semiconductor switches are transistors, they may be, for example, silicon-based, silicon carbide-based, or gallium nitride-based MOS-FETs or IGBTs.

[0054] Each of the two primary rectifier bridges 3', 3" and the auxiliary rectifier bridge 9' includes a plurality of semiconductor devices 5. The semiconductor devices 5 may be diodes, such as Figure 2 As shown, or they can be semiconductor switches (such as thyristors or transistors). In the case where the semiconductor switches are transistors, they can be, for example, silicon-based, silicon carbide-based or gallium nitride-based MOS-FETs or IGBTs.

[0055] The power conversion system 1' comprises a transformer 19'. The transformer 19' has a primary side configured to be connected to a power grid (such as a medium voltage power grid). The transformer 19' has a secondary side configured to be connected to the primary rectifier bridge 3', 3" and the auxiliary rectifier bridge 9'.

[0056] Transformer 19' includes a first winding set comprising K groups of M-phase secondary windings 19a', where K is 2 in this example, and a second winding set comprising J groups of M secondary windings 19b', where J is an integer equal to 1 in this example. Thus, each group includes M secondary windings, one for each phase. The first and second winding sets comprise the secondary-side windings of transformer 19'. In this example, M = 3. The three phases of each of the two groups of secondary windings 19a' in the first winding set are connected to the corresponding input terminals of the primary rectifier bridge 3', 3", and the three phases of the secondary winding 19b' in the second winding set are connected to the input terminals of the auxiliary rectifier bridge 9'. Typically, the transformer 19' can have three branches, one for each phase, and each branch is equipped with three secondary windings. A group of M-phase secondary windings connected to one of the primary rectifier bridges 3', 3" can be connected in Δ, while the other group connected to the other primary rectifier bridge 3', 3" can be connected in Wye shape. Thereby, the 5th, 7th and 11th harmonics can be eliminated.

[0057] If the auxiliary rectifier bridge has semiconductor switches, the control system can control the semiconductor switches to provide harmonic compensation for higher harmonics, such as the 13th, 17th, etc.

[0058] The control system 11 may be configured to control the DC / DC converter 15' using staggered operation. This reduces the ripple to the electrolysis cell.

[0059] according to Figure 2 In a variation of the illustrated example, the power conversion system may additionally include a third primary rectifier bridge. In this case, the transformer would have four sets of secondary windings 19a' and 19b', three of which are connected to the input terminals of a respective primary rectifier, and the fourth connected to the input terminals of the auxiliary rectifier spine. The power conversion system can then operate as a quasi-24-pulse rectifier.

[0060] More generally, reference Figure 3 The power conversion system 1" may include K primary rectifier bridges 3' and J auxiliary rectifier bridges 9', where K is an integer equal to or greater than 1, and J is an integer equal to or greater than 1.

[0061] Furthermore, the power conversion system 1" includes Z DC / DC converters 15', where Z is an integer equal to or greater than 1 and at most equal to J. Z may be smaller than J. Figure 3 In the example in , Z = 2.

[0062] In general, if Figure 3 As shown, the transformer 19' has two winding sets of M-phase secondary windings 19a' and 19'b. The number of sets of M-phase secondary windings 19a' in the first winding set is equal to K, and the number of sets of M-phase secondary windings 19b' in the second winding set is equal to J. The primary bridge rectifiers 3' are connected in parallel on their DC sides and therefore share a common first DC link 7. All auxiliary rectifier bridges 9' connected to the same DC / DC converter 15' are connected in parallel on their DC sides. In the case where Z is greater than 1, then Z auxiliary rectifier bridges 9' can be connected to corresponding DC / DC converters among the Z DC / DC converters 15'. If J is greater than Z, then JZ auxiliary rectifier bridges 9' can be connected to the same DC / DC converter 15'. The second DC link 10 of the Z DC / DC converters 15' is connected in series with the first DC link 7. The output of the power conversion system 1" is formed across the DC links 7 and 10.

[0063] The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept as defined by the appended claims.

Claims

1. A power conversion system (1; 1'; 1"), including: K primary rectifier bridges (3; 3', 3"), wherein K is an integer equal to or greater than 1, wherein if K is greater than 1, the K primary rectifier bridges (3'; 3") are connected in parallel on the DC side of the K primary rectifier bridges, a first DC link (7) having a DC link capacitor (C1), wherein the first DC link (7) is shared by the K primary rectifier bridges (3; 3', 3"); J auxiliary rectifier bridges (9; 9'), where J is an integer equal to or greater than 1, Z DC / DC converters (15; 15'), Z being an integer equal to or greater than 1, wherein the output terminal of each auxiliary rectifier bridge (9; 9') is connected to the input terminal of one DC / DC converter among the Z DC / DC converters (15; 15'), wherein each DC / DC converter (15; 15') has a second DC link (10) connected in series with the first DC link (7), the first DC link (7) and the Z second DC links (10) defining the output of the power conversion system (1; 1'), and A transformer (19; 19') comprising N groups of M-phase secondary windings (19a; 19a'), wherein: A) if K=1, J=Z=1 or 2, and N=1, each auxiliary rectifier bridge (9; 9') is connected to a corresponding one of the DC / DC converters (15; 15'), and the M phases of the secondary winding (19a) are connected to the input terminals of the primary rectifier bridge (3) and additionally to the input terminals of the J auxiliary rectifier bridges (9), and wherein each auxiliary rectifier bridge (9) includes six semiconductor switches (S) for rectification, B) if K=1, J=Z=2, and N=3, each auxiliary rectifier bridge (9; 9') is connected to a corresponding one of the DC / DC converters (15; 15'), the M phases of a first M-phase secondary winding (19a') of the three M-phase secondary windings (19a') are connected to the input terminals of the primary rectifier bridge (3'; 3"), and the M phases of a second M-phase secondary winding (19a') and a third M-phase secondary winding (19a') are connected to the input terminals of the corresponding auxiliary rectifier bridge (9'), C) if K is greater than 1, N=K+J and Z=1, the M phases of each group of M-phase secondary windings (19a') in K groups of M-phase secondary windings (19a') of the first winding set are connected to the input terminals of the corresponding primary rectifier bridge (3'; 3"), and the M phases of each group of M-phase secondary windings (19b') in J groups of M-phase secondary windings (19b') of the second winding set separated from the first winding set are connected to the input terminals of the corresponding auxiliary rectifier bridge (9'), wherein if J is greater than 1, J auxiliary rectifier bridges (9; 9') are connected in parallel on the DC sides of the J auxiliary rectifier bridges, D) If K and Z are both greater than 1, J is greater than Z, and N=K+J, each of the Z-1 auxiliary rectifier bridges (9; 9') is connected to a corresponding one of the Z-1 DC / DC converters (15; 15'), and the remaining auxiliary rectifier bridges (9; 9') are connected in parallel on the DC side of the remaining auxiliary rectifier bridges, and wherein the M phases of each group of M-phase secondary windings in the K groups of M-phase secondary windings (19a') of the first winding set are connected to the input terminals of the corresponding primary rectifier bridge (3'; 3"), and the M phases of each group of M-phase secondary windings in the J groups of M-phase secondary windings (19b') of the second winding set separated from the first winding set are connected to the input terminals of the corresponding auxiliary rectifier bridge (9').

2. The power conversion system (1; 1'; 1") according to claim 1, wherein the semiconductor switch (S) is a transistor.

3. The power conversion system (1; 1") according to claim 1 or 2, wherein the power conversion system (1) comprises a control system (11) configured to control the semiconductor switches (S) to perform rectification.

4. The power conversion system (1; 1") according to claim 3, wherein the control system (11) is configured to control the semiconductor switches (S) to provide reactive power compensation.

5. A power conversion system (1; 1") according to claim 3 or 4, wherein the control system (11) is configured to control the semiconductor switches (S) to provide harmonic compensation.

6. The power conversion system (1; 1'; 1") according to any one of the preceding claims, wherein each primary rectifier bridge (3; 3', 3") comprises six semiconductor devices (5) for rectification.

7. The power conversion system (1; 1'; 1") according to claim 6, wherein the six semiconductor devices (5) are diodes, thyristors or transistors.

8. A power conversion system (1) according to any of the preceding claims, wherein in the case of alternative A, the output terminals (15a), (15b) of each DC / DC converter (15) are electrically isolated from the auxiliary rectifier bridge (9) to which the DC / DC converter (15) is connected.

9. A power conversion system (1) according to any one of the preceding claims, wherein in the case of alternative A, the power conversion system comprises a filter (21), wherein the filter (21) is connected between the input terminals of the auxiliary rectifier bridge (9) and the transformer (19).

10. The power conversion system (1; 1'; 1") according to any one of the preceding claims, wherein M=3.

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