WO2024146702A1 - Converter system, and controller and control method thereof - Google Patents

Abstract

A converter system for powering an electrolyzer is provided. The converter system includes a modular converter comprising a plurality of converter modules. Each onverter module is coupled between the electrolyzer and one of a plurality of secondary windings of a transformer connected with the modular converter. Each converter module includes an AC-DC converter and a DC-DC converter. The converter system further includes a controller configured to c ntrol the DC-DC converter of at least one of the plurality of converter modules to adjust a DC voltage supplied to the electrolyzer.

Description

CONVERTER SYSTEM, AND CONTROLLER AND CONTROL METHOD THEREOF

TECHNICAL FILED

[0001] The present disclosure relates to the technical field of powering an electrolyzer (a hydrogen electrolyzer).

BACKGROUND

[0002] Green hydrogen is obtained by producing hydrogen from renewable sources such as solar or wind power and can be stored as an energy carrier. Thus, the green hydrogen is climate-friendly. The green hydrogen can be converted into energy, and also can be reconverted into electricity if needed. Especially in geographical regions with abundant wind, water or sunshine, green hydrogen can be produced cost-effectively and transported elsewhere to meet the world's future energy needs.

[0003] Using the hydrogen electrolyzer (hereinafter referred to as “electrolyzer”) to produce hydrogen requires a power supply of multiple voltage levels. In this regard, there are mainly three solutions for DC regulation in the prior art, i.e., 1 ) thyristor-based rectifier; 2) diode-based rectifier with DC-DC converter; and 3) active rectifier. In addition, 12-pulse or 24- pulse thyristor rectifiers are mostly used due to the high efficiency and low cost. However, these solutions have the problem of varying inductive reactive power and complex harmonic contents that need to be taken care of by additional power quality devices. In the solution of diode-based rectifier with DC/DC converter, the DC regulation is achieved by the DC-DC converter. This solution has low reactive power demand, but harmonics at the point of common coupling (PCC) still exhibit. The solution of active rectifier has the advantage of low harmonics and high PF operation without the need for additional power quality devices, however, this solution tends to be very costly.

SUMMARY

[0004] According to an aspect of the disclosure, a converter system for powering an electrolyzer is provided. The converter system includes a modular converter comprising a plurality of converter modules. Each converter module is coupled between the electrolyzer and one of a plurality of secondary windings of a transformer connected with the modular converter. Each converter module includes an AC-DC converter and a DC-DC converter. The converter system further includes a controller configured to control the DC-DC converter of at least one of the plurality of converter modules to adjust a DC voltage supplied to the electrolyzer.

[0005] According to another aspect of the disclosure, a method for controlling the above-mentioned converter system to power an electrolyzer is provided. The converter system includes a modular converter which comprises a plurality of converter modules. Each converter module includes an AC- DC converter and a DC-DC converter. The method includes the step of controlling the DC-DC converter of at least one of the plurality of converter modules to adjust a DC voltage supplied to the electrolyzer. [0006] According to yet another aspect of the disclosure, a controller for controlling a converter system to power an electrolyzer is provided. The controller includes one or more processors configured to execute the above-mentioned method.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The disclosed aspects will hereinafter be described in connection with the appended drawings that are provided to illustrate but not to limit the scope of the disclosure.

[0008] Figure 1 is a block diagram of a converter system for powering an electrolyzer according to an embodiment of the disclosure.

[0009] Figures 2~7 show examples of the converter system in Figure 1.

[0010] Figure 8 is a flow chart of a method for controlling the converter system to power an electrolyzer according to an embodiment of the disclosure.

[0011] Figures 9 — 13 show examples of the main step of the method in Figure 8.

DETAILED DESCRIPTION

Overview

[0012] Examples of the disclosure relate to systems and methods for powering an electrolyzer. The electrolyzer can be seen as a DC load in a power grid. According to an example of the disclosure, a plurality of converter modules are implemented as multi-pulse rectifiers and coupled with a plurality of secondary windings of a phase-shifting transformer. Each converter module includes a DC-DC converter implemented as a partial power processing converter for DC regulation. Such a solution can greatly improve system efficiency and reduce the size of the modular converter. Such a solution can also greatly reduce the system cost, because power electronic devices of converter modules just need to withstand a greatly reduced voltage or current and thus power electronic devices of lower cost can be selected.

[0013] According to an example of the disclosure, the modular converter is coupled to a phase-shifting transformer (PST). In this example, harmonics at the PCC can be eliminated by the use of PST, whereby passive filters can be omitted.

[0014] According to an example of the disclosure, the rated current or the rated voltage of each DC-DC converter can be much less than a supplied current or a supplied voltage to the electrolyzer. This further brings the advantages of more compact architecture, lower cost and better power supply reliability.

[0015] According to an example of the disclosure, powering of the electrolyzer can be controlled by controlling the DC-DC converter to adjust a supplied voltage and/or a supplied current to the electrolyzer.

[0016] In general, the solution according to examples of the disclosure is very attractive for DC load applications in a power grid that needs DC regulation (a small range of DC regulation). Such DC regulation is very important for powering the eletrolyzer in a best mode. Also, such DC regulation is meaningful for meeting requirements of grid specifications.

[0017] In addition, the converter system according to examples of the disclosure can also be used as a power supply in other applications to power DC loads, such as a power supply in a railway application, a power supply in a data center, a charging station for charging EV cars, and power supplies in other industrial applications.

[0018] In addition, according to examples of the disclosure, since the modular converter has a smaller size and a more compact structure, it can be integrated with the PST in the same housing, thereby forming an intelligent power supply equipment for powering DC loads.

Example systems

[0019] Figure 1 schematically shows a converter system according to an embodiment of the disclosure. The converter system is used as a power supply for powering an electrolyzer 5.

[0020] Referring to Figure 1 , the converter system includes a modular converter 1 and a controller 2. The modular converter 1 includes a plurality of converter modules, for example, converter modules 11 -14 shown in Figure 1. Each converter module is coupled between one of a plurality of secondary windings of a transformer 3 and the electrolyzer 5. For example, the converter module 11 is coupled between the secondary winding 31 and the electrolyzer 5 ; the converter module 12 is coupled between the secondary winding 32 and the electrolyzer 5 ; the converter module 13 is coupled between the secondary winding 33 and the electrolyzer 5 ; and the converter module 14 is coupled between the secondary winding 34 and the electrolyzer 5. The primary winding 30 of the transformer 3 is coupled with an AC source 4. The AC source 4 can also be implemented as an AC grid (e.g., a gridconnection from AC transmission or off-grid from renewables) or coupled within a micro-grid. The AC source 4 can also be implemented as a PCC (point of common coupling) of a power system.

[0021] With continuing reference to Figure 1 , each converter module includes an AC-DC converter and a DC-DC converter, and the AC-DC converter and the DC-DC converter are cascaded. The AC-DC converter is coupled between one secondary winding of the transformer 3 and the DC-DC converter, and the DC-DC converter is coupled between the AC-DC converter and the electrolyzer 5. For example, the converter module 1 1 includes an AC-DC converter 1 11 and a DC-DC converter 112, wherein the AC-DC converter 11 1 is coupled between the secondary winding 31 and the DC-DC converter 112, and the DC-DC converter 112 is coupled between the AC-DC converter 11 1 and the electrolyzer 5. The converter module 12 includes an AC-DC converter 121 and a DC-DC converter 122, wherein the AC-DC converter 121 is coupled between the secondary winding 32 and the DC-DC converter 122, and the DC-DC 122 is coupled between the AC- DC converter 121 and the electrolyzer 5. The converter module 13 includes an AC-DC converter 131 and a DC-DC converter 132, wherein the AC-DC converter 131 is coupled between the secondary winding 33 and the DC-DC converter 132, and the DC-DC 132 is coupled between the AC-DC converter 131 and the electrolyzer 5. The converter module 14 includes an AC-DC converter 141 and a DC-DC converter 142, wherein the AC-DC converter 141 is coupled between the secondary winding 34 and the DC-DC converter 142, and the DC-DC 142 is coupled between the AC-DC converter 141 and the electrolyzer 5.

[0022] With continuing reference to Figure 1 , for clarity, the side of the DC-DC converter of each converter module that is coupled to the AC-DC converter is referred to as a first side or one side, and the side that is coupled to the electrolyzer is referred to as a second side or the other side. Said one side of the DC-DC converter of each converter module provides a first DC voltage Vi and said other side of the DC-DC converter of each converter module provides a second DC voltage V2. The DC-DC converter of each converter module converts the first DC voltage Vi into the second DC voltage V2, or converts the second DC voltage V2 into the first DC voltage Vi.

[0023] According to the topology of each converter module, most of the total power from the AC source 4 is directly transmitted to the electrolyzer through the AC-DC converter, and the DC-DC converter only processes a partial of the total power. Such a partial power processing solution has many advantages. For example, a voltage or current that power electronic devices of the DC-DC converter needs to withstand can be greatly reduced. Therefore, the cost as well as size of the modular converter can be greatly reduced.

[0024] With continuing reference to Figure 1 , the controller 2 controls the DC-DC converter of each converter module to adjust at least one of the first voltage Vi and the second voltage V2, such that powering of the electrolyzer can be controlled.

[0025] The AC-DC converter of each converter module can be implemented as an uncontrollable device such as a diode to output a fixed DC voltage. That is to say, when the AC-DC converter is implemented as a diode, the first DC voltage Vi is a fixed DC voltage. The AC-DC converter of each converter module can also be implemented as a half-controlled device such as a thyristor to output an adjustable DC voltage. That is to say, when the AC-DC converter is implemented as a thyristor, the first DC voltage Vi is an adjustable DC voltage. The thyristor can be controlled by the controller 2 to output the adjustable DC voltage, thereby further increasing the range and flexibility of adjustment to the powering of the electrolyzer.

[0026] The controller 2 can receive feedback information including at least one of information on a state of the electrolyzer 5, information on a measurement at the modular converter 1 , and information on a measurement at the phaseshifting transformer 3. For example, the controller 2 can communicate and exchange information with the electrolyzer 5, the modular converter 1 and the transformer 3. The controller 2 controls the modular converter 1 based on the received feedback information to adjust a supplied voltage and/or a supplied current to the electrolyzer 5, such that the powering of the electrolyzer 5 can be controlled.

[0027] In an example, the controller 2 is implemented in a distributed control system (not shown) including multiple controller nodes. For example, the distributed control system includes a controller node at the PST, a controller node at the electrolyzer, and a controller node at each converter module. In this example, the controller 2 can be integrated with the controller node at each converter module and in commutation with other controller nodes of the distributed control system. The controller 2 can also be provided in a computing device (e.g., a server computer) that is independent of the distributed control system, and in commutation with the controller nodes of the distributed control system.

[0028] In another example, the controller 2 can be implemented in a centralized control system (not shown) including a high-level controller (e.g., a supervisor controller) and a plurality of low-level controllers in communication with the high-level controller. For example, the low-level controllers include a low-level controller at the PST, a low- level controller at the electrolyzer and a low-level controller at each converter module. In this example, the controller 2 can be provided in the high-level controller, and in commutation with the low-level controllers. The controller 2 can also be provided in one of the plurality of low-level controllers, and in commutation with the high-level controller.

[0029] The controller 2 can be implemented by means of hardware or software or a combination of hardware and software, including code stored in a non-transitory computer- readable medium such as a memory and implemented as instructions executed by a processor. Regarding the part implemented by means of hardware, it may be implemented in an application-specific integrated circuit (ASIC), a digital signal processor (DSP), a data signal processing device (DSPD), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microcontroller, a microprocessor, an electronic unit, or a combination thereof. The part implemented by software may include a microcode, a program code or code segments. The software may be stored in a machine-readable storage medium, such as a memory.

[0030] In an example, the controller 2 can include a memory and a processor. The instructions are stored in the memory. The instructions, when executed by the processor, cause the processor to execute powering control methods according to examples of the disclosure.

[0031] As shown in Figure 1 , the modular converter 1 includes four converter modules 1 1- 14, and each converter module is connected to one of four secondary windings 31 -34 of the transformer 3. It is noted that the number of converter modules in Figure 1 is only exemplary. The number of converter modules of the modular converter can be implemented as more or fewer, and the number of secondary windings of the transformer can be configured accordingly.

[0032] In an example, the transformer 3 is implemented as a phase-shifting transformer, and the modular converter is implemented as including six converter modules. In this example, each converter module is connected with one of six secondary windings of the phase-shifting transformer which can be configured to provide a 36-pulse output. In another example, the transformer 3 is implemented as a phase-shifting transformer, and the modular converter is implemented as including eight converter modules. In this example, each converter module is connected with one of eight secondary windings of the phase-shifting transformer which can be configured to provide a 48-pulse output

[0033] In Figures 2, 3, 5 and 6, it is illustrated by taking the modular converter including six converter modules as an example. In addition, the transformer 3 is implemented as a phase-shifting transformer in examples of Figures 2, 3, 5 and 6. It is noted that phase angles shown in these figures should be understood as exemplary and not limiting.

[0034] Figure 2 shows an example of the converter system in Figure 1. As shown in Figure 2, the modular converter 1 includes six converter modules 1 1- 16. Outputs of these converter modules are connected in parallel, that is, the positive terminals of these converter modules are connected together and the negative terminals of these converter modules are connected together. A positive terminal and a negative terminal of the electrolyzer 5 are respectively coupled to one of two output terminals of each converter module. As shown in Figure 2, the transformer 3 has six secondary windings and is configured to provide a 36-pulse output. Phase angles of the six secondary windings are phase shifted relative to each other. The AC-DC converter of each converter module is implemented as a diode-based converter.

[0035] Figure 3 shows another example of the converter system in Figure 1. As shown in Figure 3, outputs of six converter modules of the converter modular are connected in parallel. For example, the positive terminals of the second sides of the six converter modules 1 12-162 are electrically connected together, and the negative terminals of the second sides of the six converter modules 1 12-162 are electrically connected together. A positive terminal and a negative terminal of the electrolyzer 5 are respectively coupled to one of two output terminals of each converter module. For example, the positive terminal of the electrolyzer 5 is electrically connected to the positive terminal of the first side of each converter module, and the negative terminal of the electrolyzer 5 is electrically connected to the positive terminal of the second side of each converter module.

[0036] According to the topology in Figure 3, the electric current flow direction is shown by a dotted line arrow. The electric current supplied to the electrolyzer 5 is equal to the sum of the electric current that flows through each converter module. For each converter module, the relation of voltages is: V I =VL+V2, where V2 is the input voltage at the second side of the DC-DC converter, Vi is the output voltage at the first side of the DC-DC converter, and VL is the electrolyzer voltage. According to the topology in Figure 3, most of the total power is transferred directly to the electrolyzer 5 through the AC-DC converter. The DC-DC converter processes only a partial of the total power and transfers the partial of the total power to the first side from the second side.

[0037] According to the topology in Figure 3, the DC-DC converter of each converter module is implemented as an isolated DC-DC converter. Figure 4 shows an example of the isolated DC-DC converter. In the example of Figure 4, the isolated DC-DC converter is implemented as an LLC resonant DC-DC converter. Alternatively, the isolated DC-DC converter can also be implemented as a dual active bridge (DAB) DC-DC converter (not shown). It is noted that, in Figure 4, the DC-DC converter 112 is taken as an example, and other DC-DC converters 122-162 can be implemented in the same manner as the DC-DC converter 112.

[0038] For clarity, an example of using the topology of Figures 3 and 4 to power the electrolyzer 5 is described below. The numerical values described below are exemplary and not limiting.

[0039] In an example, the current flowing through each converter module is 1000A, and the current flowing through the electrolyzer is the sum of the currents flowing through six converter modules, i.e., 6000A. Regarding the DC-AC circuit 1121 and the AC-DC circuit 1123, currents and voltages are calculated as follows: V I =VL+V2 (1 ) and Vi*Ii=V2*l2 (2), where Ii is the electric current flowing through the DC-AC circuit 1121 and D is the electric current flowing through the AC-DC circuit 1 123.

[0040] Assuming Vi is 1000V, V2 is 100V, and VL is 900 V, according to the above formulas (1) and (2), Ii is 100A (100V* 1000A/1000V). It is seen that the DC-AC circuit 1121 needs be able to withstand a high current (e.g., 1000A) and a small voltage (e.g., 100V), and thus the DC-AC circuit 1121 can be implemented by connecting low-voltage devices in parallel. The AC-DC circuit 1 123 needs to be able to withstand a small current (e.g., 100A) and a high voltage (e.g., 1000V). In this way, the electrolyzer can be provided with both a high current (e.g., 6000A) and a high voltage (e.g., 900V). Also, the electrolyzer can be provided with high power as well in the case of the high provided current and the high provided voltage.

[0041] It is noted that, in the case of the electrolyzer voltage VL being large, there will be a relatively large voltage difference between the DC voltage on one side of the DC-DC converter and the DC voltage on the other side of the DC-DC converter, that is, there will be a large difference between the first DC voltage Vi and the second DC voltage V2. For example, referring to Figure 4, the DC-DC converter 112 converts the second DC voltage V2 of 100V into the first DC voltage Vi of 1000V. In this case, the DC-DC converter 1 12 should achieve a relatively large voltage conversion ratio. If such a large voltage conversion ratio is realized only by the DC-DC converter 1 12, there will be a problem of low efficiency. According to an example of the disclosure, referring to Figure 4, this large voltage conversion ratio can be realized by both the voltage conversion of the DC-DC conversion and the voltage conversion of the isolation transformer 1 122. For example, a voltage conversion ratio of 1 : 10 can be achieved by a voltage conversion ratio of 1 :2 through the DC-DC conversion and a voltage conversion ratio of 1 :5 through the isolation transformer 1 122.

[0042] According to such a solution, firstly, high power can be provided to the electrolyzer, and the DC-DC converter module can adopt power electronic switching devices of lower cost, because the rated voltage and/or the rated current are significantly reduced. Secondly, powering of the electrolyzer can be controlled by controlling the DC-DC converter, and thus requiremnts of customized powering of the electrolyzer can be met. Thirdly, using such a topology to power the electrolyzer, the power that the DC-DC converter needs to process is very small. For example, in the case that the electrolyzer is operated at a full-load state, the power processed by the DC-DC converter is the smallest. In case that the electrolyzer is operated at a light-load state, the ratio of the power processed by the DC-DC converter to the power supplied to the electrolyzer is relatively large, but due to the power supplied to the electrolyzer at the light-load state is relatively small, so the actual power processed by the DC-DC converter is still very small. Therefore, the actual power that the DC-DC converter needs to process is very small.

[0043] Figure 5 shows another example of the converter system in Figure 1. As shown in Figure 5, outputs of a plurality of converter modules are connected in parallel. For example, at the second side, positive terminals of the converter modules 112- 162 are electrically connected together, and negative terminals of the converter modules 112- 162 are electrically connected together. A positive terminal and a negative terminal of the electrolyzer 5 is respectively coupled to one of the first side and the second side of each converter module. For example, the positive terminal of the electrolyzer 5 is electrically connected to the positive terminal of the second side of each converter module, and the negative terminal of the electrolyzer 5 is electrically connected to the negative terminal of the first side of each converter module.

[0044] According to the topology in Figure 5, the electric current flow direction is shown by a dotted line arrow. The electric current supplied to the electrolyzer 5 is equal to the sum of the electric current that flows through each converter module. For each converter module, the relation of voltages is: V I =VL+V2, where V2 is the second DC voltage provided by the second side of each DC-DC converter, Vi is the first DC voltage provided by the first side of each DC-DC converter, and VL is the electrolyzer voltage. According to the topology in Figure 5, most of the total power is transferred directly to the electrolyzer through AC-DC converters. Each DC-DC converter processes only a partial of the total power and transfers the partial of the total power to the electrolyzer 5.

[0045] The DC-DC converter of each converter module in Figure 5 can be implemented as an isolated DC-DC converter. The isolated DC-DC converter can be implemented by using the circuit in Figure 4.

[0046] Figure 6 shows yet another example of the converter system in Figure 1. As shown in Figure 6, outputs of a plurality of converter modules are connected in parallel. For example, at the second side, positive terminals of the converter modules 112- 162 are electrically connected together, and negative terminals of the converter modules 112- 162 are electrically connected together. A positive terminal and a negative terminal of the electrolyzer 5 is coupled to one of the first side and the second side of each converter module. For example, at the second side, the positive terminal of the electrolyzer 5 is electrically connected to the positive terminal of each converter module, and the negative terminal of the electrolyzer 5 is electrically connected to the negative terminal of each converter module.

[0047] According to the topology in Figure 6, the electric current flow direction is shown by a dotted line arrow. The electric current supplied to the electrolyzer 5 is equal to the sum of the electric current flowing through each converter module. For each converter module, the relation of voltages is: VDC=VI+VL, where VDC is the voltage at the DC side of the AC-DC converter of each converter module, Vi is the first DC voltage at the first side of each DC-DC converter, and VL is the electrolyzer voltage. According to the topology in Figure 6, most of the total power is transferred directly to the electrolyzer through AC-DC converters. Each DC-DC converter processes only a partial of the total power. The partial of the total power is transferred to the first side from the second side of the DC-DC converter of each converter module.

[0048] The DC-DC converter of each converter module in Figure 6 can be implemented as an isolated DC-DC converter. The isolated DC-DC converter can be implemented by using the circuit in Figure 4.

[0049] Figure 7 shows an application scenario of the converter system according to an example the disclosure. As shown in Figure 7, each of the plurality of converter modules is respectively coupled to one of a plurality of electrolysis stacks 51 -54 of the electrolyzer 5 and supplies power to the coupled electrolysis stack. For example, the converter module 11 is coupled to the electrolysis stack 51 and supplies power to the electrolysis stack 51. The converter module 12 is coupled to the electrolysis stack 52 and supplies power to the electrolysis stack 52. The converter module 13 is coupled to the electrolysis stack 53 and supplies power to the electrolysis stack 53. The converter module 14 is coupled to the electrolysis stack 54 and supplies power to the electrolysis stack 54. In the example of Figure 7, the plurality of electrolysis stacks can be powered at the same time and powering of each electrolysis stack can be independently controlled by controlling a corresponding DC-DC converter.

[0050] It is noted that, in the example of Figure 7, the adjustment amount of an output (an output voltage or an output current) of each DC-DC converter should be limited to a small range, that is, the adjustment to the output of each DC- DC converter should be understood as fine adjustment.

Example Methods

[0051] Further to example systems described above, example methods are now described. Such methods can be performed using the controller 2 described above. It should be understood that the operations involved in the following methods need not be performed in the precise order described. Rather, various operations may be performed in a different order or simultaneously, and operations may be added or omitted.

[0052] Figure 8 shows a flow diagram of a controlling method 800 according to an embodiment of the disclosure.

[0053] Referring to Figure 8, at block 810, the controller 2 receives feedback information including state information and/or measurement information. The state information includes information on a state of the electrolyzer 5. The measurement information includes information on a measurement at the transformer 3 and information on a measurement at the modular converter 1. [0054] The state of the electrolyzer 5 can be measured by one or more sensors associated with the electrolyzer 5. The state information can be obtained from the measurements of the sensors or calculated based on the measurements. The state information includes one or more of a hydrogen production rate of the electrolyzer, an electrolyzer current, an electrolyzer voltage, operating efficiency of the electrolyzer, a state of health of the electrolyzer, an aging degree of the electrolyzer, and an operating state of the electrolyzer. The operating state of the electrolyzer is one of a no-load state, a light-load state, a full-load state and an over-load state.

[0055] The measurement information can reflect fluctuations in grid voltage and harmonics of the system, and can also reflect the state of the electrolyzer. The measurement information can include a voltage and/or current measured at the DC side of each converter module. The measurement information can include a voltage and/or current measured at the AC side of each converter module. The measurement information can include a voltage and/or current measure at the primary side of the transformer. The measurement information can include a voltage and/or current measured at the secondary side of the transformer.

[0056] At block 820, the controller 2 controls the DC-DC converter of at least one of the plurality of converter modules according to the feedback information to adjust a DC voltage provided to the electrolyzer. For example, the controller 2 controls the DC-DC converter of at least one of the plurality of converter modules to adjust at least one of the first DC voltage Vi and the second DC voltage V2, so that powering of the electrolyzer is controlled. Some examples of block 820 are described below.

[0057] Figure 9 illustrates an example (block 821 ) of block 820. In this example, the controlling is performed based on an SOH of the electrolyzer.

[0058] Referring to Figure 9, at block 821 1 , the controller 2 determines whether the SOH of the electrolyzer is degraded based on the feedback information. For example, the controller 2 compares the current SOH of the electrolyzer and a history SOH of the electrolyzer that is previously stored in the controller 2 to determine whether the SOH of the electrolyzer is degraded.

[0059] At block 8212, if it is determined the SOH of the electrolyzer is degraded, the controller 2 controls the DC-DC converter of at least one of the plurality of the converter modules to adjust a DC voltage supplied to the electrolyzer, such that the powering of the electrolyzer can ensure a hydrogen production rate of the electrolyzer reaches a target hydrogen production rate in the case of degraded situation.

[0060] In addition, in this example, both the first DC voltage Vi and the second DC voltage V2 can be adjusted by changing a tap position of a tap changer coupled to the primary side of the transformer 3, so that the powering of the electrolyzer can be further controlled and that the hydrogen production rate of the electrolyzer reaches the target hydrogen production rate much faster.

[0061] Figure 10 illustrates another example (block 822) of block 820. In thi s example, the controlling is performed based on an actual operating state and a target operating state of the electrolyzer.

[0062] Referring to Figure 10, at block 8221 , the controller 2 obtains a target operating state of the electrolyzer and an actual operating state of the electrolyzer based on the feedback information.

[0063] The target operating state of the electrolyzer can be determined by a supervisor controller through coordinated control based on user’ s expectation or a grid demand (for example, an active power and reactive power demand). The information on the target operating state can be included in the feedback information to be sent to the controller 2. The actual operating state of the electrolyzer can be determined based on measurements from a sensor coupled with the electrolyzer. The information on the actual operating state can be included in the feedback information to be sent to the controller 2.

[0064] At block 8222, the controller 2 controls the DC-DC converter of at least one of the plurality of the converter modules so that the powering of the electrolyzer is controlled and that the operating state of the electrolyzer is controlled. For example, in the case that the actual operating state of the electrolyzer is consistent with the target operating state of the electrolyzer, controlling of the converters remains unchanged. In the case that the actual operating state of the electrolyzer is inconsistent with the target operating state of the electrolyzer, the controller 2 controls the DC-DC converter of at least one of the plurality of converter modules such that the actual operating state of the electrolyzer becomes consistent with the target operating state of the electrolyzer. Examples of block 8222 are described below. [0065] In an example, if the target operating state of the electrolyzer is a full-load state and the actual operating state of the electrolyzer is also a full-load state, the controller 2 keeps the controlling of the converters unchanged.

[0066] In another example, if the target operating state of the electrolyzer is a full-load state and the actual operating state of the electrolyzer is operating with the lowest load, the controller 2 controls the DC-DC converter of each converter module to adjust the supplied voltage to the electrolyzer, so that the actual operating state of the electrolyzer changes to the full-load state from the lowest-load-state. For example, if the converter system is implemented with the topology of Figure 3 or Figure 6, the second DC voltage is adjusted to the minimum value within its adjustable range. If the converter system is implemented with the topology of Figure 5, the second DC voltage is adjusted to the maximum value within its adjustable range.

[0067] In yet another example, if the target operating state of the electrolyzer is a light-load state and the actual operating state of the electrolyzer is also a light-load state, the controller 2 keeps the controlling of the converters unchanged.

[0068] In yet another example, if the target operating state of the electrolyzer is operating with the lowest load and the actual operating state of the electrolyzer is a full-load state, the controller 2 controls the DC-DC converter of each converter module to adjust the supplied voltage to the electrolyzer, so that the actual operating state of the electrolyzer changes to the lowest-load-state from the fullload state. For example, if the converter system is implemented with the topology of Figure 3 or Figure 6, the second DC voltage is adjusted to the maximum value within its adjustable range. If the converter system is implemented with the topology of Figure 5, the second DC voltage is adjusted to the minimum value within its adjustable range.

[0069] In addition, in the case that the target operating state of the electrolyzer is an overload state, and the second DC voltage V2 has been adjusted to the maximum value or the minimum value within a predetermined adjustable range, the controller 2 can generate a control signal for changing a tap position of a tap changer coupled to the primary side of the transformer so that both the first DC voltage Vi and the second DC voltage V2 are controlled and that the actual operating state of the electrolyzer can be implemented as the overload state.

[0070] In addition, when the AC-DC converter of each converter module is implemented as a semi-controlled device such as a thyristor, the adjustment range and adjustment flexibility of the powering of the electrolyzer can be further increased by controlling the semi-controlled device.

[0071] Figure 1 1 shows yet another example (block 823) of block 820. In thi s example, the controlling is performed based on fluctuations in grid voltage.

[0072] Referring to Figure 11 , at block 8231 , the controller 2 receives measurement information from the primary and/or secondary side of the transformer. In an example, the measurement information includes measured currents and voltages at the primary side of the transformer. The measurement information further includes measured currents and voltages at the secondary side of the transformer.

[0073] At block 8232, the controller 2 determines fluctuations in gird voltage of a power grid coupled with the primary side of the transformer based on the received measurement information.

[0074] At block 8233, the controller 2 calculates a negative impact of the fluctuations on the hydrogen production rate and operating efficiency of the electrolyzer.

[0075] At block 8234, the controller 2 calculates an adjustment amount of the electrolyzer voltage to compensate for the negative impact.

[0076] At block 8235, the controller 2 controls the DC-DC converter of at least one of the plurality of converter modules such that the electrolyzer voltage is adjusted by the adjustment amount.

[0077] In addition, in the case that the AC-DC converter of each converter module is implemented as a full-bridge AC-DC converter, reactive power compensation can be implemented by controlling the full-bridge AC-DC converter. For example, the controller 2 controls a full-bridge AC-DC converter of each converter module to generate inductive or capacitive reactive power, thereby realizing reactive power compensation.

[0078] Figure 12 shows yet another example (block 824) of block 820. In this example, if an imbalance arises among the plurality of converter modules, the controller 2 can control the plurality of converter modules to return to a balance state. Such control is especially advantageous for a scenario where two or more converter modules are operated, since the harmonic performance will be good when the converter modules are in balance state. Moreover, each converter module would have almost the same lifetime in case of the balance state.

[0079] In addition, in the case that the AC-DC converter of each converter module is implemented as an active converter, it is especially helpful that each converter module has the same aging speed, device stress and lifetime in the case of the balance state.

[0080] Referring to Figure 12, at block 8241 , the controller 2 determines whether an imbalance among the plurality of converter modules arises based on the feedback information.

[0081] In examples of the present disclosure, "balance" should be understood as the power, current and voltage transferred through each converter module are in a stable state, that is, the power, current and voltage transferred by each converter module have invariance in time. For example, as to converter modules coupled in parallel, the main factor is the current converted by individual converter modules. If the current transferred through each converter module is equal to each other, those converter modules are seen as in a balance state. As to converter modules coupled in serious, the main factor is the voltage converted by individual converter modules. If the voltage transferred through each converter module is equal to each other, those converter modules are seen as in a balance state.

[0082] In examples of the present disclosure, "imbalance" should be understood as the power, current or voltage converted by at least one converter module of the multiple converter modules is in an unstable state. The unstable state includes, for example, irregular fluctuations in current, voltage or power. The unstable state also includes, for example, that the power, current or voltage transferred through at least one converter module is different than that transferred through other converter modules. The unstable state also includes, for example, that the power, current or voltage converted by the at least one converter module deviates from a predetermined conversion ratio.

[0083] It is understood that the above definitions of "balance" and "imbalance" can be used as rules for determining whether an imbalance arises among multiple converter modules.

[0084] At block 8242, in the case that it is determined an imbalance arises among the plurality of converter modules, the controller 2 controls the DC-DC converter of at least one of the plurality of converter modules to remove the imbalance.

[0085] In an example, the imbalance is removed by removing the difference between supplied currents to the electrolyzer through different converter modules. For clarity, this example is further described with reference to Figure 1. As shown in Figure 1 , when the four converter modules 1 1 - 14 are in a balance state, the supplied current to the electrolyzer through each converter module should be equal to each other. Assuming that such an imbalance arises: the supplied current to the electrolyzer through the first converter module 1 1 is not equal to the current supplied to the electrolyzer through any of the other three converter modules. In this case, the controller 2 calculates a difference between the current supplied through the first converter module and the current supplied through any of the other three converter modules. Next, the controller 2 controls the DC-DC converter of the first converter module with the aim of removing the difference in supplied currents, so that the supplied current through each converter module will be equal to each other. Thus, the imbalance is removed.

[0086] In another example, the modular converter is implemented with the topology of Figure 7, where the transformer 3 is implemented as a phase shifting transformer, and each converter module is coupled with one of a plurality of electrolysis stacks. In this example, the controller 2 calculates a first current distribution for the plurality of converter modules to remove the imbalance.

[0087] For example, the controller 2 calculates harmonic components based on phase angles of winds (the primary winding and the secondary windings) of the PST and further based on the supplied current to each electrolysis stack through each converter module. Then, the controller 2 determines the first current distribution for the plurality of converter modules and controls each converter module based on the determined first current distribution. The first current distribution is determined such that: 1 ) the harmonic requirement of the PCC point (e.g., the harmonic distortion at the PCC point is required to be less than 3%) can be met; 2) the supplied current to each electrolysis stack is adapted to the SOH state of the electrolysis stack (e.g., the supplied current to each electrolysis stack is controlled such that the electrolysis stack with worse SOH is operated to work at a light-load state, while the electrolysis stack with better SOH is operated to work at a full-load state); 3) the total hydrogen production generated by all the electrolysis stacks is maximized (e.g., some electrolysis stacks have decreased hydrogen production and others have increased hydrogen production, and the total hydrogen production generated by all the electrolysis stacks is maximized).

[0088] In this example, an optimization model can be stored in the controller 2. Phase angles of the primary winding and secondary windings of the phase-shifting transformer as well as the supplied current to each electrolysis stack are input to the optimization model, and the first current distribution can be output from the optimization model. The optimization model can be a machine learning model, a multiphysics model, or a relation table, or a combination thereof.

[0089] Figure 13 shows yet another example (block 825) of block 820. In this example, if one or more of the plurality of converter modules coupled in parallel fail and the system cannot be shut down quickly, the controller 2 controls corresponding converter modules such that harmonics at the PCC point are minimized and that hydrogen production with the powering by the normal converter modules can reach a predetermined percentage.

[0090] Referring to Figure 13, at block 8251 , the controller 2 determines whether any of the plurality of converter modules is a faulty converter module based on the feedback information.

[0091] Here, the "faulty converter module" refers to a converter module that cannot work, that is, a broken one. There will be no current flowing through the secondary winding connected with a faulty converter module, which will cause an imbalance among the secondary windings, and thus the problem of harmonics arises. The control strategy of block 8252 can solve this problem.

[0092] At block 8252, if it is determined that at least one converter module is a faulty converter module, the controller 2 controls the DC-DC converters of other converter modules (normal converter modules other than said faulty one) so that these normal converter modules supply unbalanced currents to the electrolyzer for damping the harmonic distortion of the system to a minimal level. Also, the hydrogen production of the electrolyzer can reach a predetermined hydrogen production level in the case that the electrolyzer is powered by such unbalanced currents. For example, when the electrolyzer is powered by six converter modules, the hydrogen production of the electrolyzer is 100%. If one of the six converter modules fails, the electrolyzer will be powered by five converter modules. A predetermined hydrogen production level of 80% is pre-defined. In this case, a combination of unbalanced currents supplied by the five converter modules is determined to ensure the hydrogen production level of the electrolyzer reaches the predefined level, i.e., 80%.

[0093] In an example, the transformer 3 is implemented as a phase shifting transformer, and the controller 2 determines, based on phase angles of windings of the phase shifting transformer, a second current distribution for the normal converter modules is determined.

[0094] For example, the controller 2 calculates harmonic components based on phase angles of the primary winding and the secondary windings and further based on the supplied currents through the normal converter modules. Then, the controller 2 determines the second current distribution for the normal converter modules and controls each of the normal converter modules based on the determined second current distribution. The second current distribution is determined such that: 1) the harmonic requirement of the PCC point can be met; and; 2) the hydrogen production of the electrolyzer is maximized when at least one converter module is a faulty one.

[0095] Similarly, an optimization model can be used to determine the second current distribution. The optimization model can be a machine learning model, a multiphysics model, or a relation table, or a combination thereof.

[0096] In addition, in the case that the AC-DC converter of each converter module is implemented as a semi-controlled device such as a thyristor, an additional control margin can be provided by controlling the AC-DC converter, which can help to realize the combination of the above-mentioned unbalanced currents.

[0097] An example of the disclosure provides a machine readable medium comprising instructions stored in a memory and executed by one or more processors to carry out the above-mentioned methods.

[0098] In the above, examples where the controller controls at least one converter to adjust a supplied voltage to the electrolyzer are described. It is noted that examples where the controller controls at least one converter to adjust a supplied current to the electrolyzer can be implemented in a similar way. Where the supplied current or supplied voltage or both to the electrolyzer can be controlled, the power supplied to the electrolyzer can also be controlled.

[0099] The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein. All structural and functional equivalent transformations to the elements of the various aspects of the disclosure, which are known or to be apparent to those skilled in the art, are intended to be covered by the claims.

Claims

WHAT IS CLAIMED IS:

1. A converter system for powering an electrolyzer, comprising: a modular converter comprising a plurality of converter modules, each converter module being coupled between the electrolyzer and one of a plurality of secondary windings of a transformer connected with the modular converter, each converter module comprising an AC-DC converter and a DC- DC converter; and a controller configured to control the DC-DC converter of at least one of the plurality of converter modules to adjust a DC voltage supplied to the electrolyzer.

2. The converter system of claim 1 , wherein one side of the DC-DC converter of each converter module is coupled with the AC-DC converter and provides a first DC voltage, and the other side of the DC-DC converter of each converter module is coupled with the electrolyzer and provides a second DC voltage; and the controller is configured to control the DC-DC converter of at least one of the plurality of converter modules to adjust at least one of the first DC voltage and the second DC voltage.

3. The converter system of claim 1 or 2, wherein the controller is configured to: receive feedback information comprising at least one of information on a state of the electrolyzer, information on a measurement at the transformer, and information on a measurement at the modular converter; and control the DC-DC converter of at least one of the plurality of converter modules based on the feedback information to adjust the DC voltage supplied to the electrolyzer.

4. The converter system of claim 3, wherein the controller is configured to: determine whether a state of health of the electrolyzer is degraded based on the feedback information; and in the case that it is determined the state of health the electrolyzer is degraded, control the DC-DC converter of at least one of the plurality of converter modules to adjust the DC voltage supplied to the electrolyzer, so that a hydrogen production rate of the electrolyzer is controlled.

5. The converter system of claim 3 or 4, wherein the controller is configured to: determine whether an actual operating state of the electrolyzer is consistent with a target operating state of the electrolyzer based on the feedback information; and in the case that it is determined the actual operating state of the electrolyzer is inconsistent with the target operating state of the electrolyzer, control the DC-DC converter of at least one of the plurality of converter modules to adjust the DC voltage supplied to the electrolyzer, so that the actual operating state of the electrolyzer becomes coincident with the target operating state of the electrolyzer.

6. The converter system of claim 2, wherein the controller is configured to: in the case that the second DC voltage provided by the DC-DC converter of each converter module has been adjusted to a minimum value or maximum value within a predetermined adjustable range, generate a command signal for changing a tap position of a tap changer coupled with the transformer, so that the DC voltage supplied to electrolyzer is further controlled.

7. The converter system of any one of claims 3-6, wherein the controller is configured to: determine fluctuations in grid voltage of a power grid coupled to a primary side of the transformer based on the feedback information; calculate an impact of the fluctuations on a hydrogen production rate and operating efficiency of the electrolyzer; determine an adjustment amount of the DC voltage supplied to the electrolyzer to compensate for the impact of the fluctuations; and control the DC-DC converter of at least one of the plurality of converter modules such that the DC voltage supplied to the electrolyzer is adjusted by the adjustment amount.

8. The converter system of any one of claims 3-7, wherein the controller is configured to: control at least one of the plurality of converter modules based on the feedback information to provide reactive power for power factor correction.

9. The converter system of any one of claims 3-8, wherein the controller is configured to: determine whether an imbalance arises among the plurality of converter modules based on the feedback information; and in the case that it is determined the imbalance arises, control the DC-DC converter of at least one converter module to remove the imbalance.

10. The converter system of claim 9, wherein in the case that the transformer is a phase shifting transformer and the electrolyzer comprises a plurality of electrolysis stacks, the controller is configured to: determine a fist current distribution for the plurality of converter modules based on phase angles of a primary winding and a plurality of secondary windings of the phase shifting transformer, such that the total hydrogen production generated by all the electrolysis stacks is maximized.

11. The converter system of any one of claims 3-9, wherein the controller is configured to: determine whether any of the plurality of converter modules is a faulty one based on the feedback information; and if it is determined that at least one converter module is a faulty one, control DC-DC converters other than the faulty one to supply unbalanced currents to the electrolyzer for damping harmonic distortion of the converter system to a minimal level.

12. The converter system of claim 11 , wherein in the case that the transformer is a phase shifting transformer, the controller is configured to: determine, based on phase angles of a primary winding and a plurality of secondary windings of the phase shifting transformer, a second current distribution for the DC-DC converters other than the faulty one such that a hydrogen production of the electrolyzer is maximized in the case that the electrolyzer is power by the DC-DC converters other than the faulty one.

13. The converter system of any one of claims 1- 12, wherein the AC-DC converter of each converter module is a diodebased converter or a thyristor-based converter, and the DC-DC converter of each converter module is an isolated DC-DC converter.

14. The converter system of claim 2, wherein outputs of the plurality of converter modules are connected in parallel; and a positive terminal of said one side of the DC-DC converter of each converter module is connected to a positive terminal of the electrolyzer, and a positive terminal of said other side of the DC-DC converter of each converter module is connected to a negative terminal of the electrolyzer.

15. The converter system of claim 2, wherein outputs of the plurality of converter modules are connected in parallel; and a positive terminal of said other side of the DC-DC converter of each converter module is connected to a positive terminal of the electrolyzer, and a positive terminal of said one side of the DC-DC converter of each converter module is connected to a negative terminal of the electrolyzer.

16. The converter system of claim 2, wherein outputs of the plurality of converter modules are connected in parallel; and a positive terminal of said other side of the DC-DC converter of each converter module is connected to a positive terminal of the electrolyzer, and a positive terminal of said other side of the DC-DC converter of each converter module is connected to a negative terminal of the electrolyzer.

17. A method for controlling the converter system of any one of claims 1 - 16 to power an electrolyzer, the converter system comprising a modular converter which comprises a plurality of converter modules, each converter module comprising an AC- DC converter and a DC-DC converter, the method comprising the step of: controlling the DC-DC converter of at least one of the plurality of converter modules to adjust a DC voltage supplied to the electrolyzer.

18. The method of claim 17, the method further comprising: controlling the DC-DC converter of at least one of the plurality of converter modules to further adjust a current supplied to the electrolyzer.

19. A controller for controlling a converter system to power an electrolyzer, the controller comprising one or more processors configured to execute the method of claim 17 or 18.