Hydrogen production power supply system and control method thereof

Abstract

The present application provides a hydrogen production power supply system and a control method thereof, including: an AC transformer, configured to distribute and output a second AC voltage after transforming a first AC voltage input from an AC power grid; a voltage regulating branch, configured to convert and adjust the second AC voltage to obtain a second DC voltage; a constant voltage branch, configured to convert the second AC voltage to obtain a first DC voltage; a switching device, configured to connect the output end of the voltage regulating branch and the output end of the constant voltage branch in series to form a total output voltage output to the electrolyzer; an energy storage device, configured to access the total output voltage and be connected in parallel to the electrolyzer; wherein the switching device is further configured to adjust the number of connected voltage regulating branches and / or constant voltage branches according to the working voltage of the electrolyzer. Through the above scheme, the hydrogen production power supply system of the present application can input a corresponding number of constant voltage branches and voltage regulating branches according to the load condition of the electrolyzer, thereby improving the operating efficiency of the hydrogen production power supply.

Description

Technical Field

[0001] The present application relates to the field of hydrogen production technology, and in particular to a hydrogen production power supply system and a control method thereof. Background Art

[0002] Hydrogen energy is a clean, carbon-free, flexible, efficient, and versatile secondary energy source and a key industrial raw material. Using renewable energy sources for power, water electrolysis is a convenient method for producing hydrogen. It offers environmental friendliness, flexibility, and high purity, making it an ideal green hydrogen production method. As the core device connecting the electrolyzer and the renewable energy grid, the control performance and reliability of the hydrogen power supply directly impact the efficiency and safety of the entire hydrogen production system.

[0003] At the same time, with the continuous improvement of the process and technology level of electrolyzer manufacturers, the hydrogen production capacity of alkaline electrolyzers has gradually increased from 1000Nm 3 / h increased to 3000Nm 3 / h、5000Nm 3 / h, the DC voltage and current specifications of the electrolyzer are constantly increasing, and the output voltage and current levels of the hydrogen production power supply compatible with the electrolyzer also need to be improved accordingly.

[0004] In related technologies, hydrogen production power supply solutions adopt three forms: thyristor rectification, diode rectification + insulated gate bipolar transistor (IGBT) chopping, and full IGBT rectification + chopping. Thyristor rectification is a one-stage topology, and the other two are two-stage topologies. When using a thyristor solution for rectification and power supply, in addition to injecting a large amount of low-order harmonics into the AC grid and absorbing a large amount of reactive power, its output DC voltage regulation speed is slow and contains a large amount of current ripple, which affects the efficiency of hydrogen production in the electrolyzer and is not suitable for application in the field of green electricity hydrogen production. When a two-stage topology circuit is used for rectification and power supply, multiple branches are usually required to be connected in parallel to meet the current and voltage requirements of the electrolyzer. The two-stage topology circuit has two energy conversion links: AC-DC conversion and the conversion of fixed DC voltage into variable DC voltage (DC-DC). Multiple branches supply power at the same time, which affects the overall efficiency of the hydrogen production power supply, especially under conditions where the hydrogen production of the electrolyzer is low.

[0005] In view of this, in order to promote the popularization and application of large-capacity electrolyzers in the field of green hydrogen, it is urgent to study new hydrogen production power supply topology solutions to meet the needs of green electricity hydrogen production systems for hydrogen production power supplies with high response speed, high efficiency, high power factor, wide output voltage and current range, and excellent grid-related characteristics. Summary of the Invention

[0006] The embodiments of the present application provide a hydrogen production power supply system and a control method thereof to solve the problem in the related art that multiple branches are used to supply power to meet the use requirements of the electrolyzer, which affects the overall efficiency of the hydrogen production power supply.

[0007] To solve the above problems, the technical solutions provided by this application are as follows:

[0008] In a first aspect, the present application provides a hydrogen production power supply system, comprising:

[0009] an AC transformer configured to transform a first AC voltage input from an AC power grid and distribute the transformed voltage to output a second AC voltage;

[0010] a voltage regulating branch, electrically connected to the AC transformer, the voltage regulating branch being configured to convert and adjust the second AC voltage to obtain a second DC voltage;

[0011] a constant voltage branch, electrically connected to the AC transformer, the constant voltage branch being configured to convert the second AC voltage into a first DC voltage;

[0012] a switching device configured to connect the output end of the voltage regulating branch and the output end of the constant voltage branch in series to form a total output voltage to be output to the electrolytic cell; and

[0013] an energy storage device configured to be connected to the total output voltage and in parallel with the electrolytic cell;

[0014] Wherein, the switching device is further configured to adjust the number of the connected voltage regulating branches and / or constant voltage branches according to the working voltage of the electrolytic cell.

[0015] In one embodiment, the hydrogen production power supply system includes one or two voltage regulating branches, and the voltage regulating branches include:

[0016] a first AC-DC converter configured to convert the second AC voltage into an initial DC voltage; and

[0017] A DC transformer is electrically connected to the first AC-DC converter, and the DC transformer is configured to adjust the initial DC voltage to obtain the second DC voltage.

[0018] In one embodiment, the DC transformer includes:

[0019] a chopper circuit configured to access and regulate the initial DC voltage; and

[0020] a discharge circuit electrically connected to the chopper circuit, the discharge circuit being configured to release electrical energy from the chopper circuit;

[0021] Wherein, the discharge circuit includes an insulated gate bipolar transistor and a power resistor connected in series.

[0022] In one embodiment, the hydrogen production power supply system includes multiple constant voltage branches, and the constant voltage branches include:

[0023] The second AC-DC converter is configured to convert the second AC voltage into a first DC voltage.

[0024] In one embodiment, the switching device includes a plurality of switching circuits, the plurality of switching circuits are connected in series with the electrolytic cell, and each of the voltage regulating branches and each of the constant voltage branches is connected to a switching circuit;

[0025] The switching circuit comprises a positive input terminal, a negative input terminal, a positive output terminal and a negative output terminal;

[0026] In adjacent switching circuits, the negative output terminal of one switching circuit is connected to the positive output terminal of another switching circuit.

[0027] In one embodiment, the switching circuit is a mechanical switching circuit; or

[0028] The switching circuit is an electronic switching circuit that realizes switching by controlling the on and off of the insulated gate bipolar transistor.

[0029] In one embodiment, the switching circuit further includes:

[0030] a bypass switch connected between the positive input terminal and the positive output terminal of the switching circuit, and / or connected between the negative input terminal and the negative output terminal of the switching circuit; and

[0031] A bipolar switch, wherein a first end of the bipolar switch is connected between the positive output end and the negative output end of the switching circuit.

[0032] In one embodiment, the bypass switch and the bipolar switch have different switching states.

[0033] In one embodiment, the first DC voltage and the second DC voltage satisfy:

[0034] Udc1=Udc2=Udc / (N+1), Udc≥Ups:

[0035] Wherein, Udc1 is the constant value of the first DC voltage, Udc2 is the maximum value of the second DC voltage, Udc is the maximum value of the total output voltage, N is the number of the constant voltage branches, and Ups is the operating voltage of the electrolytic cell.

[0036] In a second aspect, the present application provides a control method for a hydrogen production power supply system, which is implemented by the hydrogen production power supply system of any embodiment of the first aspect, including:

[0037] Boost control: raising the total output voltage of the hydrogen production power supply system from 0 to the operating voltage of the electrolyzer;

[0038] Buck control: reducing the total output voltage of the hydrogen production power supply system from the operating voltage of the electrolyzer to 0; and

[0039] Voltage regulation control: adjusting the output voltage of the hydrogen production power supply from the initial operating voltage of the electrolyzer to the target operating voltage.

[0040] In one embodiment, the voltage regulation branch includes a first voltage regulation branch and a second voltage regulation branch.

[0041] In one embodiment, the steps of the boost control include:

[0042] All the voltage regulation branches and the constant voltage branches are in the withdrawn state;

[0043] When Ups ≤ Udc2: unlock the first AC-DC converter and the DC transformer of the first voltage regulation branch or the second voltage regulation branch, put the voltage regulation branch in the unlocked state into operation, and gradually raise the voltage across the electrolyzer from 0 to Ups;

[0044] When Ups > Udc2 and Ups ≤ 2Udc2: unlock the first AC-DC converter and the DC transformer of the first voltage regulation branch and the second voltage regulation branch respectively, the output voltages of the first voltage regulation branch and the second voltage regulation branch are 0; then unlock one of the constant voltage branches, and the output voltage is Udc2; then put the first voltage regulation branch into operation, and gradually raise the voltage across the electrolyzer from 0 to Udc2; then withdraw the first voltage regulation branch, put one of the constant voltage branches in the unlocked state and the second voltage regulation branch into operation, one of the constant voltage branches in the unlocked state outputs a constant voltage Udc2, and the second voltage regulation branch gradually raises its output voltage from 0 to Ups - Udc2, and raises the voltage across the electrolyzer from Udc2 to Ups; lock the chopper circuit in the DC transformer of the first voltage regulation branch, and reduce the output voltage of the first voltage regulation branch to 0 through the discharge circuit;

[0045] When Ups > m * Udc2 and Ups ≤ (m + 1) * Udc2 (1 < m ≤ N, m is an integer), in accordance with the method of putting the constant voltage branches into operation and the method of switching and putting in and withdrawing the voltage regulation branches when Ups > Udc2 and Ups ≤ 2Udc2, put all the constant voltage branches into operation and one of the voltage regulation branches into operation in sequence, and gradually raise the voltage across the electrolyzer from 0 to Ups.

[0046] In one embodiment, the step-down control is to decrease the output voltage of the hydrogen production power supply from the voltage Ups corresponding to the current working condition of the electrolyzer to 0. The steps of the step-down control include:

[0047] When Ups ≤ Udc2: Assume that the first voltage regulating branch is in the unlocked and switched-in state, and adjust the output voltage of the first voltage regulating branch to gradually decrease the voltage across the electrolyzer from Ups to 0;

[0048] When Ups > Udc2 and Ups ≤ 2Udc2, assume that the second voltage regulating branch and one of the constant voltage branches are in the unlocked and switched-in state; First, unlock the first voltage regulating branch and output the voltage Udc2; Second, decrease the output voltage of the second voltage regulating branch from Ups - Udc2 to 0, and decrease the voltage across the electrolyzer from Ups to Udc2; Then, withdraw the one constant voltage branch and the second voltage regulating branch that are in the unlocked and switched-in state, and switch in the first voltage regulating branch; Next, adjust the output voltage of the first voltage regulating branch to decrease the voltage across the electrolyzer from Udc2 to 0;

[0049] When Ups > m * Udc2 and Ups ≤ (m + 1) * Udc2 (1 < m ≤ N, m is an integer), in accordance with the method of withdrawing the constant voltage branches and the method of switching, withdrawing, and switching in the voltage regulating branches when Ups > Udc2 and Ups ≤ 2Udc2, withdraw the constant voltage branches m to 1 in sequence and switch in one voltage regulating branch, and gradually decrease the voltage across the electrolyzer from Ups to 0.

[0050] In one embodiment, the steps of the voltage regulating control include:

[0051] Assume that the number of constant voltage branches switched in for the current output voltage Ups1 of the hydrogen production power supply is y, y = floor(Ups1 / Udc2), and determine that the number of constant voltage branches to be switched in for the target output voltage Ups2 of the hydrogen production power supply is z, z = floor(Ups2 / Udc2), where floor is the floor function;

[0052] When z = y, adjust the output voltage of the voltage regulating branch that is currently in the unlocked state to adjust the voltage across the electrolyzer from Ups1 to Ups2;

[0053] When z > y, in accordance with the method of switching in the constant voltage branches and the method of switching, withdrawing, and adjusting the voltage regulating branches in the step-up control, gradually increase the number of constant voltage branches switched in from y to z, and adjust the output voltage of the voltage regulating branch that is in the unlocked state to raise the voltage across the electrolyzer to Ups2;

[0054] When z < y, according to the constant voltage branch withdrawal method and the switching, connection / disconnection, and adjustment methods of the voltage regulation branch in the step-down control, gradually reduce the number of connected constant voltage branches from y to z, and adjust the output voltage of the voltage regulation branch in the unlocked state to reduce the voltage at both ends of the electrolyzer to Ups2.

[0055] The embodiment of the present application provides a hydrogen production power supply system and its control method. The hydrogen production power supply system includes an AC voltage conversion device configured to convert the first AC voltage input from the AC power grid and then distribute and output the second AC voltage; a constant voltage branch electrically connected to the AC voltage conversion device, and the constant voltage branch is configured to convert the second AC voltage to obtain the first DC voltage; a voltage regulation branch electrically connected to the AC voltage conversion device, and the voltage regulation branch is configured to convert and adjust the second AC voltage to obtain the second DC voltage; a switching device configured to connect the output end of the voltage regulation branch in series with the output end of the constant voltage branch to form a total output voltage and output it to the electrolyzer; and an energy storage device configured to be connected to the total output voltage and be connected in parallel with the electrolyzer. Among them, the switching device is further configured to adjust the number of connected voltage regulation branches and / or constant voltage branches according to the working voltage of the electrolyzer. Through the above solution, according to the resistance load characteristics of the electrolyzer, the present application equally divides the output power capacity of the hydrogen production power supply, and inputs different numbers of power branches according to the operating conditions of the electrolyzer, improving the operating efficiency of the hydrogen production power supply and being beneficial to meeting the requirements for the hydrogen production power supply of large-capacity electrolyzers in the field of green hydrogen production. Description of the Drawings

[0056] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for description in the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0057] Attached Figure 1 is a schematic diagram of an optional hydrogen production power supply in the embodiment of the present application;

[0058] Attached Figure 2 is a schematic diagram of another optional hydrogen production power supply in the embodiment of the present application;

[0059] Attached Figure 3 is a schematic diagram of the two-level three-phase bridge circuit of the AC-DC converter in the embodiment of the present application;

[0060] Attached Figure 4 is a schematic diagram of the three-level three-phase bridge circuit of the AC-DC converter in the embodiment of the present application;

[0061] Attached Figure 5This is a circuit schematic diagram of a DC transformer based on a two-level three-phase AC-side parallel chopper circuit in an embodiment of the present application;

[0062] Attachment Figure 6 This is a circuit schematic diagram of a DC transformer based on a three-phase bridge diode rectifier chopper circuit in an embodiment of the present application;

[0063] Attachment Figure 7 Schematic diagram of a circuit of a DC transformer based on a dual active bridge resonant chopper circuit in an embodiment of the present application;

[0064] Attachment Figure 8 Schematic diagram of the circuit structure of the constant voltage branch in the embodiment of the present application;

[0065] Attachment Figure 9 Schematic diagram of the circuit structure of the voltage regulating branch in the embodiment of the present application;

[0066] Attachment Figure 10 This is a schematic diagram of a single two-level electronic switching circuit in an embodiment of the present application;

[0067] Attachment Figure 11 This is a schematic diagram of a plurality of two-level electronic switching circuits connected in parallel in an embodiment of the present application;

[0068] Attachment Figure 12 This is a schematic diagram of a single three-level electronic switching circuit in an embodiment of the present application;

[0069] Attachment Figure 13 This is a schematic diagram of a plurality of three-level electronic switching circuits connected in parallel in an embodiment of the present application;

[0070] Attachment Figure 14 A connection diagram of a two-level AC / DC converter and a switching circuit in an embodiment of the present application;

[0071] Attachment Figure 15 This is a connection diagram of a three-level AC / DC converter and a switching circuit in an embodiment of the present application;

[0072] Attachment Figure 16 A diagram showing the connection relationship between the voltage regulating branch and the switching circuit in an embodiment of the present application;

[0073] Attachment Figure 17 This is a circuit schematic diagram of multiple AC / DC converter modules connected in parallel in an embodiment of the present application;

[0074] Attachment Figure 18 This is a circuit schematic diagram of multiple parallel-connected DC transformer modules in an embodiment of the present application.

[0075] Description of reference numerals in the figures:

[0076] 1. Hydrogen production power system;

[0077] 100. AC transformer;

[0078] 200, constant voltage branch; 210, second AC / DC converter;

[0079] 300, voltage regulating branch; 310, first AC / DC converter; 320, DC transformer; 321, chopper circuit; 322, discharge circuit;

[0080] 400, switching device; 410, switching circuit; 411, bypass switch; 412, bipolar switch;

[0081] 500. Energy storage device. DETAILED DESCRIPTION

[0082] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0083] The terms "include" and "comprising" used in the description and claims of this application indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or collections thereof.

[0084] Reference Figure 1 and Figure 2 As shown, according to the first aspect of the present application, a hydrogen production power supply system 1 is provided, which can be applicable to a large-capacity electrolyzer. The hydrogen production power supply system 1 includes an AC transformer 100, a voltage regulating branch 300, a constant voltage branch 200, a switching device 400 and an energy storage device 500.

[0085] In which, the AC transformer 100 is configured to transform the first AC voltage input from the AC power grid and distribute it to output a second AC voltage. In some specific examples, the AC transformer 100 uses a multi-winding transformer, the primary winding of the multi-winding transformer is connected to the AC power grid, and each group of secondary windings is respectively connected to a voltage regulating branch 300 or a constant voltage branch 200.

[0086] The voltage regulating branch 300 is electrically connected to the AC transformer 100, and the voltage regulating branch 300 is configured to convert and adjust the second AC voltage to obtain a second DC voltage. Specifically, the voltage regulating branch 300 includes a first AC-DC converter 310 and a DC transformer 320. The first AC-DC converter 310 is configured to convert the second AC voltage into an initial DC voltage; the DC transformer 320 is electrically connected to the first AC-DC converter 310, and the DC transformer 320 is configured to adjust the initial DC voltage to obtain a second DC voltage. In addition to converting AC current into DC power with a constant voltage, the first AC-DC converter 310 can also perform reactive power compensation and harmonic suppression on the AC power grid, while the DC transformer 320 can convert the initial DC voltage with a constant voltage output from the first AC voltage conversion into a second DC voltage with a variable voltage amplitude. Figure 3 or Figure 4 As shown, in some embodiments of the present application, the circuit of the first AC-DC converter 310 is a two-level three-phase bridge circuit or a three-level three-phase bridge circuit based on insulated gate bipolar transistor pulse-width modulation (Insulated Gate Bipolar Transistor Pulse-Width Modulation, Insulated Gate Bipolar Transistor PWM) rectification.

[0087] Reference Figures 5 to 7 As shown, in some embodiments of the present application, the DC transformer 320 includes a chopper circuit 321 and a discharge circuit 322, wherein the chopper circuit 321 is configured to access and adjust the initial DC voltage, and the discharge circuit 322 is electrically connected to the chopper circuit 321. The discharge circuit 322 is configured to release the electrical energy of the chopper circuit 321, and the discharge circuit 322 includes an insulated gate bipolar transistor and a power resistor connected in series. Figure 5 As shown, the chopping branch can be a DC-DC converter based on multi-phase bridge arms interleaved in parallel, or it can be a reference Figure 6 The three-phase bridge diode rectifier DC-DC converter shown in the figure, or refer to Figure 7 In the dual active bridge resonant DC-DC converters shown, the positive electrodes of the output terminals of the chopper circuit 321 are connected to the positive electrodes of the discharge circuit 322 , and the negative electrodes are connected to the negative electrodes of the discharge circuit 322 .

[0088] The discharge circuit 322 is composed of an insulated gate bipolar transistor and a power resistor connected in series. The collector of the insulated gate bipolar transistor is connected to the positive terminal of the discharge circuit 322, the emitter of the insulated gate bipolar transistor is connected to one end of the power resistor, and the other end of the power resistor is connected to the negative terminal of the discharge circuit 322. It should be noted that the insulated gate bipolar transistor acts as a switch in the discharge circuit 322. When the voltage at the output end of the chopper circuit 321 is detected to be too high or when rapid energy release is required, the control system triggers the insulated gate bipolar transistor to turn on. Once the insulated gate bipolar transistor is turned on, a low-impedance path is formed in the circuit, allowing current to flow through the power resistor. The power resistor consumes excess energy by converting the current into heat energy, thereby reducing the voltage and current in the circuit. This process of consuming excess energy is fast and controllable, ensuring that the system responds quickly to overvoltage or overcurrent conditions.

[0089] The constant voltage branch 200 is electrically connected to the AC transformer 100, and the constant voltage branch 200 is configured to convert the second AC voltage to obtain a first DC voltage. It should be noted that in the hydrogen production power supply system 1 of the present application, a plurality of constant voltage branches 200 are provided, and the constant voltage branch 200 includes a second AC-DC converter 210, which is configured to convert the second AC voltage into a first DC voltage. Among them, since the output ends of the voltage regulating branch 300 and the constant voltage branch 200 are connected in series to power the electrolyzer, the current flowing through the output ends of the two are equal, so the voltage regulating branch 300 and the constant voltage branch 200 have the same active output capacity. Therefore, the second AC-DC converter 210 and the first AC-DC converter 310 can have the same circuit structure and effect, and this application will not repeat them here.

[0090] The switching device 400 is configured to connect the output of the voltage-regulating branch in series with the output of the constant-voltage branch to generate a total output voltage, which is then output to the electrolytic cell. The switching device 400 includes multiple switching circuits 410 connected in series with the electrolytic cell, with one switching circuit 410 connected to each voltage-regulating branch 300 and each constant-voltage branch 200.

[0091] Specifically, the switching circuit 410 includes a positive input terminal, a negative input terminal, a positive output terminal, and a negative output terminal. In adjacent switching circuits 410, the negative output terminal of one switching circuit 410 is connected to the positive output terminal of another switching circuit 410. Figure 8 As shown, the positive and negative poles of the DC input terminal of the switching circuit 410 are respectively connected to the positive and negative poles of the DC output terminal of the second AC-DC converter 210. Figure 9 As shown, the positive and negative DC output terminals of the first AC-DC converter 310 of the voltage regulating branch 300 are respectively connected to the positive and negative DC input terminals of the DC transformer 320, and the positive and negative DC output terminals of the DC transformer 320 are respectively connected to the positive and negative DC input terminals of the switching circuit 410.

[0092] In some embodiments of the present application, the switching circuit 410 is a mechanical switching circuit 410 , or the switching circuit 410 is an electronic switching circuit 410 that realizes switching by controlling the on and off of an insulated gate bipolar transistor.

[0093] In some embodiments of the present application, the switching circuit 410 further includes a bypass switch 411 and a bipolar switch 412, wherein the bypass switch 411 is connected between the positive input terminal and the positive output terminal of the switching circuit, and / or between the negative input terminal and the negative output terminal of the switching circuit, and the first end of the bipolar switch 412 is connected between the positive output terminal and the negative output terminal of the switching circuit. The bypass switch 411 is used to connect the constant voltage branch or the voltage regulating branch to the series circuit connected to the electrolytic cell, and the bipolar switch 412 is used to remove the constant voltage branch or the voltage regulating branch from the series circuit connected to the electrolytic cell. It should be noted that although the switching circuit 410 is divided into several switches in the embodiments of the present application, in actual application, it can be a general mechanical switch or an electronic switch composed of multiple IGBTs connected in series and parallel.

[0094] In addition, the switching device 400 is also configured to adjust the number of connected voltage regulating branches and / or constant voltage branches according to the working voltage of the electrolytic cell. According to this function of the switching circuit 410, the bypass switch 411 and the bipolar switch 412 need to have different switching states.

[0095] In some embodiments of the present application, the bypass switch 411 and the bipolar switch 412 are mechanical switches. Specifically, the bypass switch 411 includes a first switch and a second switch, and the bipolar switch 412 includes a third switch. The first switch is connected between the positive input and positive output of the switching circuit 410, and the second switch is connected between the negative input and negative output of the switching circuit 410. The first end of the third switch is connected to the connection line between the first switch and the positive output of the switching circuit, and the second end of the third switch is connected to the connection line between the second switch and the negative output of the switching circuit. In this embodiment, it is necessary for the first and second switches to have the same switching state, and the first and third switches to have different switching states. When the first and second switches are open and the third switch is closed, the voltage regulating branch 300 or the constant voltage branch 200 is connected to the external circuit. When the mechanical switching circuit 410 is deactivated, the first and second switches are closed and the third switch is open, disconnecting the voltage regulating branch 300 or the constant voltage branch 200 from the external circuit.

[0096] In some embodiments of the present application, when the switching circuit 410 is an electronic switching circuit 410 , the bipolar connection function and the branch bypass function are achieved by controlling the on and off of the IGBT.

[0097] Reference Figure 10As shown, in some embodiments of the present application, a two-level electronic switching circuit 410 is provided. When the relevant branch is put into operation, the upper IGBT tube Q1 is turned on and the lower tube Q2 is locked; when the relevant branch is exited, the upper IGBT tube Q1 is locked and the lower tube Q2 is turned on. In this embodiment, the Q1 tube is the bypass switch 411 and the Q2 tube is the bipolar switch 412. On this basis, referring to Figure 11 As shown, when the branch output current is large, multiple IGBTs can be directly connected in parallel to improve the current carrying capacity of the switching circuit 410.

[0098] Reference Figure 12 As shown, in some embodiments of the present application, a three-level electronic switching circuit 410 is also provided. When the relevant branch is put into operation, Q1 and Q4 are turned on, and Q2 and Q3 are locked; when the relevant branch is exited, Q1 and Q4 are locked, and Q2 and Q3 are turned on. In this embodiment, Q1 and Q4 are bypass switches 411, and Q2 and Q3 are bipolar switches 412. On this basis, referring to Figure 13 As shown, when the branch output current is large, multiple three-level bridge arms can be directly connected in parallel to improve the current-carrying capacity of the switching circuit 410.

[0099] In some embodiments of the present application, reference is made to Figure 14 As shown, when the second AC-DC converter 210 in the constant voltage circuit is a two-level three-phase bridge circuit, it can be connected to the two-level electronic switching circuit 410; Figure 15 As shown, when the second AC-DC converter 210 in the constant voltage circuit is a three-level three-phase bridge circuit, it can be connected to the three-level electronic switching circuit 410 .

[0100] Accordingly, refer to Figure 16 As shown, in the voltage regulation circuit, when the DC transformer 320 includes a two-level three-phase bridge arm interleaved parallel chopper circuit 321 , it can be connected to a two-level electronic switching circuit 410 .

[0101] In addition, in some embodiments of the present application, the first AC-DC converter 310 or the second AC-DC converter 210 may include one or more modules connected in parallel and using the same PWM rectifier current circuit for the AC side and the DC side. Figure 17 As shown, when a single PWM rectifier module cannot meet the power demand of the branch, multiple PWM rectifier modules can be connected in parallel on the AC side and the DC side to improve the power transmission capacity of the branch.

[0102] Similarly, in some embodiments of the present application, the DC transformer 320 in the voltage regulation circuit may also include one or more modules connected in parallel with the same chopper circuit 321 on the input side and output side. When the DC transformer 320 of the voltage regulation branch 300 needs to increase the transmission power, multiple chopper circuits 321 and the input and output sides of the discharge circuit 322 may be connected in parallel. The specific circuit structure is as follows: Figure 18 shown.

[0103] Energy storage device 500 is configured to be connected to the total output voltage and in parallel with the electrolyzer. In some specific examples, energy storage device 500 is a support capacitor, with the positive electrode of the support capacitor connected to the positive terminal of the electrolyzer and the negative electrode of the support capacitor connected to the negative terminal of the electrolyzer. By using the support capacitor as a transient energy storage device, the impact of sudden power changes on the system can be buffered, preventing interruptions in the hydrogen production process and ensuring stable hydrogen production efficiency.

[0104] It should be noted that, in the aforementioned embodiment, the total output voltage uout of the hydrogen production power supply ranges from 0 to Udc, the output voltage of the constant voltage branch 200 is constant at Udc1, the output voltage range of the voltage regulating branch 300 is from 0 to Udc2, and the output voltages of the voltage regulating branch 300 and the constant voltage branch 200 satisfy the following relationship: Udc1=Udc2=Udc / (N+1); the maximum voltage Udc output by the hydrogen production power supply is greater than or equal to the operating voltage Ups required by the electrolyzer.

[0105] In summary, this application provides the following two specific embodiments:

[0106] Example 1

[0107] Reference Figure 1 As shown, the hydrogen production power supply system 1 includes two voltage-regulating branches 300 and N constant-voltage branches 200. The AC input of each branch is connected to a set of secondary windings of a multi-winding isolation transformer. The positive and negative DC output terminals of adjacent branches are connected in series to the positive and negative terminals of a support capacitor, which in turn is connected to the positive and negative terminals of the electrolyzer. When the output voltage of the hydrogen production power supply changes, the first and second voltage-regulating branches are alternately switched on and off to achieve continuous output voltage regulation.

[0108] In this embodiment, the specific structures of the voltage regulating branch 300, the constant voltage branch 200 and the switching circuit 410 can adopt the circuit combination that can be implemented in the above embodiments, and this application does not limit it here.

[0109] Example 2

[0110] Reference Figure 2As shown, the hydrogen production power supply includes one voltage-regulating branch 300 and N constant-voltage branches 200. The AC input of each branch is connected to a set of secondary windings of a multi-winding isolation transformer. The positive and negative DC output terminals of adjacent branches are connected in series and then connected to the positive and negative terminals of the support capacitor. The positive and negative terminals of the support capacitor are connected to the positive and negative terminals of the electrolyzer. When the output voltage of the hydrogen production power supply decreases, if the output voltage of the voltage-regulating branch 300 reaches 0V, the voltage-regulating branch 300 is first deactivated. After the output voltage of the voltage-regulating branch 300 is adjusted to Udc2, the voltage-regulating branch 300 is activated and the number of activated constant-voltage branches 200 is reduced by one. When the output voltage of the hydrogen production power supply increases, if the voltage of the voltage-regulating branch 300 reaches Udc2, the voltage-regulating branch 300 is deactivated and the number of activated constant-voltage branches 200 is increased by one. The output voltage of the voltage-regulating branch 300 is reduced to 0V before being activated again.

[0111] In this embodiment, the specific structures of the voltage regulating branch 300, the constant voltage branch 200 and the switching circuit 410 may also adopt the circuit combination that can be implemented in the above embodiments, and this application does not limit this.

[0112] In a second aspect, the present application also provides a control method for a hydrogen production power supply system 1, including boost control, buck control and voltage regulation control.

[0113] Taking Example 1 as an example, the boost control is to raise the DC voltage output by the hydrogen production power supply from 0 to the voltage Ups required for the target operating condition of the electrolyzer. The steps of the boost control include:

[0114] 1) All voltage regulating branches 300 and constant pressure branches 200 are in the exit state;

[0115] 2) When Ups ≤ Udc2: the first AC-DC converter 310 and the DC transformer 320 of the first voltage regulating branch or the second voltage regulating branch are unlocked. At this time, the output voltage of the first voltage regulating branch or the second voltage regulating branch is 0. The unlocked voltage regulating branch 300 is put into operation to gradually raise the voltage across the electrolytic cell from 0 to Ups.

[0116] 3) When Ups > Udc2 and Ups ≤ 2Udc2: First, unlock the first AC-DC converter 310 and the DC transformer 320 of the first voltage regulation branch and the second voltage regulation branch respectively. At this time, the output voltage of the voltage regulation branch 300 is 0. Second, unlock the required constant voltage branch 200. It should be noted that the number of unlocked constant voltage branches 200 can be one, and it can be the first constant voltage branch adjacent to the voltage regulation branch. This constant voltage branch 200 is denoted as the first constant voltage branch, and the subsequent sequentially connected constant voltage branches 200 are denoted as the second to the Nth constant voltage branches in turn. At this time, the output voltage of the first constant voltage branch is Udc2. Then, put the first voltage regulation branch into operation, and gradually raise the voltage at both ends of the electrolytic cell from 0 to Udc2. Next, withdraw the first voltage regulation branch, put the first constant voltage branch and the second voltage regulation branch into operation. The first constant voltage branch outputs a constant voltage Udc2, and the second voltage regulation branch gradually raises its output voltage from 0 to Ups - Udc2, and raises the voltage at both ends of the electrolytic cell from Udc2 to Ups. In addition, lock the chopper circuit 321 in the DC transformer 320 of the first voltage regulation branch, and reduce the output voltage of the first voltage regulation branch to 0 through the discharge circuit 322.

[0117] 4) When Ups > m * Udc2 and Ups ≤ (m + 1) * Udc2 (1 < m ≤ N, m is an integer), in accordance with the method of putting the constant voltage branch 200 into operation and the method of switching and putting in and withdrawing the voltage regulation branch when Ups > Udc2 and Ups ≤ 2Udc2, sequentially put the 1st to the mth constant voltage branches 200 into operation and put one voltage regulation branch into operation, and gradually raise the voltage at both ends of the electrolytic cell from 0 to Ups.

[0118] Taking Embodiment 1 as an example, the step-down control is to reduce the output voltage of the hydrogen production power supply from the voltage Ups corresponding to the current working condition of the electrolytic cell to 0. The steps of the step-down control include:

[0119] 1) When Ups ≤ Udc2: Assume that the first voltage regulation branch is in the unlocked and put-in state, adjust the output voltage of the first voltage regulation branch, and gradually reduce the voltage at both ends of the electrolytic cell from Ups to 0.

[0120] 2) When Ups > Udc2 and Ups ≤ 2Udc2, assume that the second voltage regulation branch and the first constant voltage branch are in the unlocked and put-in state; First, unlock the first voltage regulation branch and output the voltage Udc2; Second, reduce the output voltage of the second voltage regulation branch from Ups - Udc2 to 0, and reduce the voltage at both ends of the electrolytic cell from Ups to Udc2; Then, withdraw the first constant voltage branch and the second voltage regulation branch, and put the first voltage regulation branch into operation; Next, adjust the output voltage of the first voltage regulation branch, and reduce the voltage at both ends of the electrolytic cell from Udc2 to 0; It should be noted that the constant voltage branch in the unlocked and put-in state can be the first constant voltage branch or any other constant voltage branch 200.

[0121] 3) When Ups > m * Udc2 and Ups ≤ (m + 1) * Udc2 (1 < m ≤ N, m is an integer), in accordance with the disconnection method of the constant voltage branch 200 and the switching, connection, and disconnection methods of the voltage regulation branch when Ups > Udc2 and Ups ≤ 2Udc2, disconnect the m~1st constant voltage branches 200 in sequence and connect one voltage regulation branch, gradually reducing the voltage at both ends of the electrolytic cell from Ups to 0.

[0122] Taking Embodiment 1 as an example, the voltage regulation control is to adjust the output voltage of the hydrogen production power supply from the voltage Ups1 corresponding to the current working condition of the electrolytic cell to the voltage Ups2 corresponding to the target working condition. The steps of the voltage regulation control include:

[0123] 1) Assume that the number of constant voltage branches 200 connected when the hydrogen production power supply outputs the current voltage Ups1 is y, y = floor(Ups1 / Udc2), and determine that the number of constant voltage branches 200 required to be connected when the hydrogen production power supply outputs the target voltage Ups2 is z, z = floor(Ups2 / Udc2), where floor is the floor function.

[0124] 2) When z = y, adjust the output voltage of the voltage regulation branch 300 that is currently in the unlocked state, and adjust the voltage at both ends of the electrolytic cell from Ups1 to Ups2.

[0125] 3) When z > y, in accordance with the connection method of the constant voltage branch 200 and the switching, connection, disconnection, and adjustment methods of the voltage regulation branch 300 in the boost control, gradually increase the number of connected constant voltage branches 200 from y to z, and adjust the output voltage of the voltage regulation branch 300 that is in the unlocked state to raise the voltage at both ends of the electrolytic cell to Ups2.

[0126] 4) When z < y, in accordance with the disconnection method of the constant voltage branch 200 and the switching, connection, disconnection, and adjustment methods of the voltage regulation branch in the buck control, gradually reduce the number of connected constant voltage branches 200 from y to z, and adjust the output voltage of the voltage regulation branch 300 that is in the unlocked state to reduce the voltage at both ends of the electrolytic cell to Ups2.

[0127] In related technologies, hydrogen production power supply solutions employ three types of topologies: thyristor rectification, diode rectification + insulated gate bipolar transistor (IGBT) chopping, and full IGBT rectification + chopping. Thyristor rectification is a single-stage topology, while the other two are two-stage topologies. When using a thyristor solution for rectification and power supply, since the thyristor rectifier is a nonlinear load and adjusts the output voltage by controlling the conduction angle, this control method causes the current waveform to deviate from a sinusoidal waveform, generating harmonics. Furthermore, since the thyristor begins conducting after the voltage crosses zero, the current lags behind the voltage. This phase difference results in the absorption of reactive power. In addition to injecting a large amount of low-order harmonics into the AC grid and absorbing a large amount of reactive power, its output DC voltage has a slow regulation speed and contains a large amount of current ripple, which affects the efficiency of hydrogen production in the electrolyzer and makes it unsuitable for application in the field of green electricity hydrogen production. When a two-stage topology circuit is used for rectification and power supply, multiple branches are usually required to be connected in parallel to supply power to meet the current and voltage requirements of the electrolyzer. The two-stage topology circuit has two energy change links: AC to DC (AC-DC) and the conversion of a fixed DC voltage into a variable DC voltage (DC-DC). Multiple branches supply power at the same time, which affects the overall efficiency of the hydrogen production power supply. However, the present application divides the output power capacity of the hydrogen production power supply into equal parts according to the resistive load characteristics of the electrolyzer, and invests different numbers of power branches according to the operating conditions of the electrolyzer, thereby improving the operating efficiency of the hydrogen production power supply. At the same time, the present application provides a hydrogen production power supply solution with fast response speed, excellent grid-related characteristics, and high overall efficiency for large-capacity electrolyzers by connecting in series a voltage regulation branch 300 based on a two-stage topology circuit with a voltage regulation function and a constant voltage branch 200 based on a one-stage topology circuit that outputs a constant voltage, thereby meeting the demand for large-capacity electrolyzer hydrogen production power supplies in the field of green electricity hydrogen production.

[0128] In summary, although the present application has been disclosed as above with preferred embodiments, the above preferred embodiments are not intended to limit the present application. Ordinary technicians in this field can make various changes and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be based on the scope defined by the claims.

Claims

1. A hydrogen production power supply system, characterized in that: Comprising: An AC voltage transformation device configured to transform the first AC voltage input from an AC power grid and then distribute and output the second AC voltage; A constant voltage branch electrically connected to the AC voltage transformation device, the constant voltage branch being configured to convert the second AC voltage to obtain a first DC voltage; A voltage regulation branch electrically connected to the AC voltage transformation device, the voltage regulation branch being configured to convert and adjust the second AC voltage to obtain a second DC voltage; A switching device configured to connect the output end of the voltage regulation branch in series with the output end of the constant voltage branch to form a total output voltage and output it to an electrolytic cell; And An energy storage device configured to be connected to the total output voltage and be connected in parallel with the electrolytic cell; Wherein, the switching device is further configured to adjust the number of the voltage regulation branch and / or the constant voltage branch connected according to the working voltage of the electrolytic cell; The voltage regulation branch includes: a first AC-DC converter configured to convert the second AC voltage into an initial DC voltage; and a DC transformer electrically connected to the first AC-DC converter, the DC transformer being configured to adjust the initial DC voltage to obtain the second DC voltage; The voltage regulation branch includes a first voltage regulation branch and a second voltage regulation branch; The boost control of the hydrogen production power supply system includes the following steps: Controlling all the voltage regulation branches and the constant voltage branches to be in an off state; When Ups ≤ Udc2: Unlock the first AC-DC converter and the DC transformer of the first voltage regulation branch or the second voltage regulation branch, the voltage regulation branch in the unlocked state is put into operation, and the voltage at both ends of the electrolytic cell is gradually raised from 0 to Ups; When Ups > Udc2 and Ups ≤ 2Udc2: Unlock the first AC-DC converter and the DC transformer of the first voltage regulation branch and the second voltage regulation branch respectively, the output voltages of the first voltage regulation branch and the second voltage regulation branch are 0; then unlock one of the constant voltage branches, and the output voltage is Udc2; then put the first voltage regulation branch into operation, and gradually raise the voltage at both ends of the electrolytic cell from 0 to Udc2; then withdraw the first voltage regulation branch, put one of the constant voltage branches in the unlocked state and the second voltage regulation branch into operation, one of the constant voltage branches in the unlocked state outputs a constant voltage Udc2, the second voltage regulation branch gradually raises the output voltage from 0 to Ups - Udc2, and raises the voltage at both ends of the electrolytic cell from Udc2 to Ups; lock the chopper circuit in the DC transformer of the first voltage regulation branch, and reduce the output voltage of the first voltage regulation branch to 0 through a discharge circuit; When Ups > mUdc\(_2\) and Ups ≤ (m + 1)Udc\(_2\) (1 < m ≤ N, m is an integer), according to the method of putting in the constant voltage branch and the method of switching and putting in and withdrawing the voltage regulation branch when Ups > Udc2 and Ups ≤ 2Udc2, put in all the constant voltage branches and one of the voltage regulation branches in sequence, and gradually raise the voltage at both ends of the electrolytic cell from 0 to Ups; where N is the number of the constant voltage branches, Ups is the working voltage of the electrolytic cell, and Udc\(_2\) is the maximum value of the second DC voltage.

2. The hydrogen production power supply system according to claim 1, characterized in that: The DC transformer comprises: a chopper circuit configured to access and regulate the initial DC voltage; and a discharge circuit electrically connected to the chopper circuit, the discharge circuit being configured to release electrical energy from the chopper circuit; Wherein, the discharge circuit includes an insulated gate bipolar transistor and a power resistor connected in series.

3. The hydrogen production power supply system according to claim 1, characterized in that: The hydrogen production power supply system includes multiple constant voltage branches, and the constant voltage branches include: The second AC-DC converter is configured to convert the second AC voltage into a first DC voltage.

4. The hydrogen production power supply system according to claim 3, characterized in that: The switching device includes a plurality of switching circuits, the plurality of switching circuits are connected in series with the electrolytic cell, and each of the voltage regulating branches and each of the constant voltage branches is connected to a switching circuit; The switching circuit comprises a positive input terminal, a negative input terminal, a positive output terminal and a negative output terminal; In adjacent switching circuits, the negative output terminal of one switching circuit is connected to the positive output terminal of another switching circuit.

5. The hydrogen production power supply system according to claim 4, characterized in that: The switching circuit is a mechanical switching circuit; or The switching circuit is an electronic switching circuit that realizes switching by controlling the on and off of the insulated gate bipolar transistor.

6. The hydrogen production power supply system according to claim 5, characterized in that: The switching circuit further includes: a bypass switch connected between the positive input terminal and the positive output terminal of the switching circuit, and / or connected between the negative input terminal and the negative output terminal of the switching circuit; and A bipolar switch, wherein a first end of the bipolar switch is connected between the positive output end and the negative output end of the switching circuit.

7. The hydrogen production power supply system according to claim 6, characterized in that: The bypass switch and the bipolar switch have different switching states.

8. The hydrogen production power supply system according to claim 1, characterized in that: The first DC voltage and the second DC voltage satisfy: Udc1=Udc2=Udc / (N+1), Udc≥Ups: Wherein, Udc1 is the constant value of the first DC voltage, Udc2 is the maximum value of the second DC voltage, Udc is the maximum value of the total output voltage, N is the number of the constant voltage branches, and Ups is the operating voltage of the electrolytic cell.

9. A control method for a hydrogen production power supply system, implemented based on the hydrogen production power supply system according to any one of claims 1 to 8, characterized in that: include: Boost control: increasing the total output voltage of the hydrogen production power system from 0 to the operating voltage of the electrolyzer; Voltage reduction control: reducing the total output voltage of the hydrogen production power supply system from the operating voltage of the electrolyzer to 0; and Voltage regulation control: adjust the output voltage of the hydrogen production power supply from the initial operating voltage of the electrolyzer to the target operating voltage.

10. The control method according to claim 9, characterized in that: The voltage regulating branch includes a first voltage regulating branch and a second voltage regulating branch.

11. The control method according to claim 10, characterized in that: The step of boost control includes: All the voltage regulating branches and the constant pressure branches are in the exit state; When \(U_{ps}\leq U_{dc2}\): Unlock the first AC / DC converter and the DC transformer of the first voltage regulation branch or the second voltage regulation branch, and put the voltage regulation branch in the unlocked state into operation. Gradually raise the voltage across the electrolyzer from 0 to \(U_{ps}\). When \(U_{ps}>U_{dc2}\) and \(U_{ps}\leq 2U_{dc2}\): Unlock the first AC / DC converter and the DC transformer of the first voltage regulation branch and the second voltage regulation branch respectively. The output voltages of the first voltage regulation branch and the second voltage regulation branch are 0. Then unlock one of the constant voltage branches, and the output voltage is \(U_{dc2}\). Then put the first voltage regulation branch into operation, and gradually raise the voltage across the electrolyzer from 0 to \(U_{dc2}\). Then withdraw the first voltage regulation branch, and put one of the constant voltage branches in the unlocked state and the second voltage regulation branch into operation. One of the constant voltage branches in the unlocked state outputs a constant voltage \(U_{dc2}\), and the second voltage regulation branch gradually raises the output voltage from 0 to \(U_{ps}-U_{dc2}\), and raises the voltage across the electrolyzer from \(U_{dc2}\) to \(U_{ps}\). Block the chopper circuit in the DC transformer of the first voltage regulation branch, and reduce the output voltage of the first voltage regulation branch to 0 through the discharge circuit. When \(U_{ps}>mU_{dc2}\) and \(U_{ps}\leq(m + 1)U_{dc2}\) (\(1 < m\leq N\), \(m\) is an integer), in accordance with the method of putting the constant voltage branches into operation and the method of switching and putting in and withdrawing the voltage regulation branches when \(U_{ps}>U_{dc2}\) and \(U_{ps}\leq 2U_{dc2}\), put all the constant voltage branches into operation and one of the voltage regulation branches into operation in sequence, and gradually raise the voltage across the electrolyzer from 0 to \(U_{ps}\).

12. The control method according to claim 11, characterized in that: The step of the step-down control is to reduce the output voltage of the hydrogen production power supply from the voltage \(U_{ps}\) corresponding to the current working condition of the electrolyzer to 0. The steps of the step-down control include: When \(U_{ps}\leq U_{dc2}\): Assume that the first voltage regulation branch is in the unlocked and put-in state, and adjust the output voltage of the first voltage regulation branch to gradually reduce the voltage across the electrolyzer from \(U_{ps}\) to 0. When \(U_{ps}>U_{dc2}\) and \(U_{ps}\leq 2U_{dc2}\), assume that the second voltage regulation branch and one of the constant voltage branches are in the unlocked and put-in state. First, unlock the first voltage regulation branch and output a voltage \(U_{dc2}\). Secondly, reduce the output voltage of the second voltage regulation branch from \(U_{ps}-U_{dc2}\) to 0, and reduce the voltage across the electrolyzer from \(U_{ps}\) to \(U_{dc2}\). Then withdraw one of the constant voltage branches and the second voltage regulation branch in the unlocked and put-in state, and put the first voltage regulation branch into operation. Then adjust the output voltage of the first voltage regulation branch to reduce the voltage across the electrolyzer from \(U_{dc2}\) to 0. When \(U_{ps}>mU_{dc2}\) and \(U_{ps}\leq(m + 1)U_{dc2}\) (\(1 < m\leq N\), \(m\) is an integer), in accordance with the method of withdrawing the constant voltage branches and the method of switching and putting in and withdrawing the voltage regulation branches when \(U_{ps}>U_{dc2}\) and \(U_{ps}\leq 2U_{dc2}\), withdraw \(m\) of the constant voltage branches and put one of the voltage regulation branches into operation in sequence, and gradually reduce the voltage across the electrolyzer from \(U_{ps}\) to 0.

13. The control method according to claim 12, characterized in that: The steps of the voltage regulation control include: Assume that the number of the constant - voltage branches input when the hydrogen - production power supply outputs the current voltage Ups1 is y, and y = floor(Ups1 / Udc2). Determine that the number of the constant - voltage branches required to be input when the hydrogen - production power supply outputs the target voltage Ups2 is z, and z = floor(Ups2 / Udc2), where floor is the floor operator. When z = y, adjust the output voltage of the voltage - regulating branch that is currently in the unlocked state, and adjust the voltage across the electrolyzer from Ups1 to Ups2. When z > y, according to the method of inputting the constant - voltage branches in the boost control and the methods of switching, inputting, withdrawing, and adjusting the voltage - regulating branch, gradually increase the number of input constant - voltage branches from y to z, and adjust the output voltage of the voltage - regulating branch that is in the unlocked state to raise the voltage across the electrolyzer to Ups2. When z < y, according to the method of withdrawing the constant - voltage branches in the buck control and the methods of switching, inputting, withdrawing, and adjusting the voltage - regulating branch, gradually reduce the number of input constant - voltage branches from y to z, and adjust the output voltage of the voltage - regulating branch that is in the unlocked state to lower the voltage across the electrolyzer to Ups2.

Images