CN118353231A - Converter system, controller and control method thereof - Google Patents

Abstract

A converter system and a control method thereof are provided. The converter system includes: a modular converter comprising a plurality of converter modules, wherein each converter module is coupled between one of a plurality of secondary windings of a phase-shifting transformer and the electrolytic cell, and each converter module comprises a cascaded AC-DC converter and DC-DC converter; and a controller configured to control the DC-DC converter of at least one of the plurality of converter modules to regulate the direct current voltage supplied to the electrolytic cell.

Description

Converter system, controller and control method thereof

Technical Field

The present disclosure relates to the technical field of powering a hydrogen electrolyzer, and more particularly to a converter system for powering a hydrogen electrolyzer, a controller thereof, and a control method thereof.

Background technique

Green hydrogen is a climate-friendly solution. It offers the option of producing hydrogen from renewable energy sources such as solar or wind and storing it as an energy carrier. Depending on the need, it can be transported and converted into energy, or reconverted into electricity. Especially in geographical areas with abundant wind, water and sunshine, green hydrogen can be produced cost-effectively and transported elsewhere to meet future energy needs around the world.

The use of hydrogen electrolyzers (hereinafter referred to as electrolyzers) to produce hydrogen usually requires the provision of power supply at multiple voltage levels for the electrolyzers. In this regard, there are mainly three solutions in the prior art: 1) thyristor-based rectifiers; 2) diode rectifiers with DC-DC converters; 3) active rectifiers, among which thyristor-based 12-pulse or 24-pulse rectifiers are widely used due to their high efficiency and low cost. However, this solution has variable inductive reactive power and complex harmonic components, which require additional power quality equipment to handle. In addition, in a solution that includes a diode rectifier and a DC-DC converter and implements DC regulation through the DC-DC converter, although it has a lower reactive power demand, harmonics at the point of common connection (PCC) still exist. In addition, in a solution using an active rectifier, although it helps to achieve high power factor and low harmonic distortion, and no additional power quality equipment is required, this solution is often very expensive.

Summary of the invention

In view of the above-mentioned problems in the prior art, according to one aspect of the present disclosure, a converter system for powering an electrolyzer is provided, which comprises: a modular converter, comprising a plurality of converter modules, wherein each converter module is coupled between one of a plurality of secondary windings of a phase-shifting transformer and the electrolyzer, and each converter module comprises a cascaded AC-DC converter and a DC-DC converter; and a controller, configured to control the DC-DC converter of at least one converter module among the plurality of converter modules to adjust the DC voltage provided to the electrolyzer.

According to another aspect of the present invention, a method for controlling a converter system to supply power to an electrolyzer is provided, the converter system comprising a plurality of converter modules, wherein each converter module is coupled between one of a plurality of secondary windings of a phase-shifting transformer and the electrolyzer, and each converter module comprises a cascaded AC-DC converter and a DC-DC converter, the method comprising: controlling the DC-DC converter of at least one converter module among the plurality of converter modules to adjust the DC voltage supplied to the electrolyzer.

According to yet another aspect of the present invention, there is provided a controller for controlling a converter system to supply power to an electrolytic cell, comprising one or more processors configured to execute the method as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description in conjunction with the accompanying drawings will make the technical solution of the present invention clearer. It should be understood that these drawings are only used for exemplary description and are not intended to limit the scope of protection of the present invention.

FIG. 1 is a schematic block diagram of a converter system for powering an electrolyzer according to an embodiment of the present invention.

2-7 show some embodiments of modular converters of the converter system in FIG. 1 .

8 is a flow chart of a method for controlling a converter system to power an electrolyzer according to an embodiment of the present invention.

9-13 show some embodiments of the main steps of the method in FIG. 8 .

Detailed ways

Overview

Embodiments of the present invention relate to a solution for powering an electrolyzer, wherein the electrolyzer acts as a DC load in a power grid. According to an embodiment of the present invention, multiple converter modules implemented as multi-pulse rectifiers are coupled to multiple secondary windings of a phase-shifting transformer, and this structure is used as a power source to power the electrolyzer. Each converter module includes a partial power processing converter, that is, the DC-DC converter used for DC regulation only processes a small portion of the full power provided to the electrolyzer. Such a solution can greatly improve system efficiency and reduce the size of the converter module. Further, such a solution can also greatly reduce system cost, because the voltage or current that the power electronic devices constituting these converter modules need to withstand is greatly reduced, so that lower-cost power electronic devices can be selected and there are more options.

According to an embodiment of the present invention, since the modular converter is coupled with a phase shifting transformer (PST), harmonics at the PCC are eliminated by using the PST, thereby eliminating the passive filter.

According to an embodiment of the present invention, the rated value (e.g., rated current, rated voltage, or rated power) of the power electronic converter (e.g., DC-DC converter) of the converter module can be significantly smaller than the corresponding power value loaded on the electrolyzer. This further brings the advantages of more compact architecture, lower cost, and better power supply reliability.

According to the embodiments of the present invention, the DC voltage provided to the electrolyzer can be adjusted by controlling the DC-DC converter, and harmonics and imbalances between the multiple secondary windings of the PST can be compensated.

In general, the solution according to the embodiments of the present invention is very attractive for DC load applications that only require a smaller range of DC regulation in the power grid, because lower device costs can be achieved, which is crucial for meeting grid regulations.

In addition, according to the embodiments of the present invention, it is also possible to power other DC loads, for example, to be used as a DC power supply in railway applications, a power supply for large data centers, a high-power electric vehicle charging station, or other industrial applications.

In addition, according to an embodiment of the present invention, since the converter modules have a smaller size and a more compact structure, these converter modules can be integrated with the PST, for example, in the same housing, thereby realizing an intelligent power supply device for powering DC loads in the power grid.

Exemplary Systems

Fig. 1 schematically shows a converter system according to an embodiment of the present invention, which serves as a power source to supply power to an electrolyzer 5. The electrolyzer 5 serves as a DC load of the converter system.

Referring to FIG1 , the converter system includes a modular converter 1 and a controller 2. The modular converter 1 includes a plurality of converter modules 11-14. Each converter module is coupled between one of the plurality of secondary windings of the 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 32 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 to an AC source 4. The AC source 4 may be a point of common coupling (PCC). The AC source 4 may also be an AC grid (e.g., a grid connection from AC transmission or an off-grid from renewable energy) or coupled within a microgrid.

Continuing to refer to FIG. 1 , each converter module includes a cascaded AC-DC converter and a DC-DC converter, wherein the AC-DC converter is coupled between a secondary winding and the DC-DC converter, and the DC-DC converter is coupled between the AC-DC converter and the electrolytic cell. For example, the converter module 11 includes an AC-DC converter 111 and a DC-DC converter 112, wherein the AC-DC converter 111 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 111 and the electrolytic cell 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 converter 122 is coupled between the AC-DC converter 121 and the electrolytic cell 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 converter 142 is coupled between the AC-DC converter 141 and the electrolytic cell 5.

1 , for the sake of clarity, the side of the DC-DC converter of each converter module coupled to the AC-DC converter is referred to as the first side or “one side”, and the side coupled to the electrolyzer is referred to as the second side or “the other side”. The DC-DC converter of each converter module converts the first DC voltage _V1 of the one side into the second DC voltage _V2 of the other side, or converts the second DC voltage _V2 of the other side into the first DC voltage _V1 of the one side.

According to the topology of the converter module of an embodiment of the present invention, most of the power is directly transmitted to the electrolyzer through the AC-DC converter, and the DC-DC converter only processes a small part of the power, that is, the so-called partial power processing converter. When the load current flows from the first side of the DC-DC converter to the second side, the small part of the power is transmitted to the electrolyzer via the DC-DC converter. When the load current flows from the second side of the DC-DC converter to the first side, a small part of the power returns to the first side from the second side of the DC-DC converter. Such a partial power processing solution has many advantages. For example, the voltage or current that the power electronic device constituting the controllable switch of the DC-DC converter needs to withstand and the power transmitted can be reduced a lot. Therefore, such a modular converter can greatly reduce the cost of devices and reduce size.

1 , the DC-DC converter of each converter module can adjust at least one of the first voltage _V1 and the second voltage _V2 under the control of the controller 2. Based on such adjustment, the power supply to the electrolytic cell is controlled.

In addition, 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. The AC-DC converter can also be implemented as a semi-controlled device such as a thyristor to output an adjustable DC voltage. When the AC-DC converter is implemented as a semi-controlled device such as a thyristor, the DC voltage (for example, the first DC voltage V ₁ ) outputted by it can be adjusted under the control of the controller 2, thereby further increasing the adjustment range and adjustment flexibility of the power supply to the electrolyzer.

The controller 2 can receive feedback information, which includes at least one of the following: the state of the electrolyzer 5, the measurement result at the modular converter 1, and the measurement result at the phase-shifting transformer 3. In other words, the controller 2 can receive feedback information indicating at least one of the state of the electrolyzer 5, the measurement result at the modular converter 1, and the measurement result at the phase-shifting transformer 3. For example, the controller 2 can be connected to the electrolyzer 5, the modular converter 1, and the phase-shifting transformer 3 in communication, and exchange information with them. The controller 2 controls the modular converter 1 based on the received feedback information, so that the power supply to the electrolyzer 5 is controlled. The power supply control method implemented by the controller 2 will be specifically introduced in the exemplary method section below.

In one embodiment, the controller 2 is implemented in a distributed control system (not shown) including a plurality of controller nodes. For example, the distributed control system includes: a controller node on the transformer side, a controller node on the electrolyzer side, and a controller node on each converter module side. In this embodiment, the controller 2 can be integrated with the controller nodes on each converter module side as a control unit and communicate with other controller nodes in the distributed control system. The controller 2 can also be set in a computing device (e.g., a server computer) that is independent of the distributed control system and can communicate with each controller node of the distributed control system.

In another embodiment, the controller 2 can be implemented in a centralized control system (not shown), which includes a high-level controller (e.g., a central controller) and a plurality of low-level controllers capable of communicating with the high-level controller. For example, the low-level controller includes a low-level controller on the transformer side, a low-level controller on the electrolyzer side, and a low-level controller on each converter module side. In this embodiment, the controller 2 can be set in the high-level controller and can communicate with the low-level controller. The controller 2 can also be set in one of these low-level controllers and can communicate with the high-level controller.

The controller 2 can be implemented in hardware or software or a combination of software and hardware. For the hardware-implemented part, it can be implemented in one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, electronic units designed to perform their functions, or combinations thereof. For the software-implemented part, it can be implemented with the aid of microcodes, program codes, or code segments, and they can also be stored in machine-readable storage media such as storage components.

In one embodiment, the controller 2 includes a memory and a processor. Instructions are stored in the memory. When the instructions are executed by the processor, the processor executes the power supply control method according to the embodiment of the present disclosure.

It can be understood that the modular converter shown in Figure 1 includes four converter modules 11-14, each of which is coupled to one of the four secondary windings 31-34 of the transformer 3, but the number of converter modules in Figure 1 is only exemplary, and embodiments of the present invention may also include other numbers of converter modules, and the number of secondary windings of the transformer may also be configured accordingly.

For example, the transformer may be implemented as a phase-shifting transformer, and the modular converter may include 6 converter modules. In this example, each converter module is respectively coupled to one of the 6 secondary windings of the 36-pulse phase-shifting transformer. For another example, the transformer may be implemented as a phase-shifting transformer, and the modular converter may include 8 converter modules. In this example, each converter module is respectively coupled to one of the 8 secondary windings of the 48-pulse phase-shifting transformer.

In FIG. 2 and FIG. 4-FIG. 6, a modular converter including six converter modules is used as an example for illustration. In addition, FIG. 2 and FIG. 4-FIG. 6 show examples in which the transformer is implemented as a phase-shifting transformer. In the illustrations of these examples, the phase angle of the secondary winding should be understood as exemplary and not limiting.

FIG. 2 shows an example of the modular converter in FIG. 1 . As shown in FIG. 2 , the modular converter 1 includes 6 converter modules 11-16. The outputs of these converter modules are connected in parallel, and the electrolyzer 5 is connected across the two output terminals of these converter modules. The transformer 3 is implemented as a 36-pulse phase-shifting transformer, which has 6 secondary windings, and the phase angles of these secondary windings are staggered by a certain angle. The AC-DC converter of each converter module is implemented as a diode-based converter.

FIG3 shows another example of a modular converter 1. As shown in FIG2, a plurality of converter modules are connected in parallel. For example, the positive terminals on the second side of the converter modules 112-162 are electrically connected to each other, and the negative terminals on the second side of the converter modules 112-162 are electrically connected to each other. The electrolyzer 5 is connected across the positive terminals on the first side of the converter modules and the positive terminals on the second side of the converter modules. For example, the positive terminal of the electrolyzer 5 is electrically connected to the positive terminal on the first side of each converter module, and the negative terminal of the electrolyzer 5 is electrically connected to the positive terminal on the second side of each converter module.

According to the topology in FIG3 , the current flows as indicated by the dotted arrows, the current flowing through the electrolyzer 5 is the sum of the currents flowing through the various converter modules, and the voltage relationship is: V ₁ =V _L +V ₂ , wherein V ₂ is the second DC voltage on the second side of the DC-DC converter and is the input voltage, V ₁ is the first DC voltage on the first side of the DC-DC converter and is the output voltage, and V _L is the electrolyzer voltage (i.e., the voltage provided to the electrolyzer by the converter system, i.e., the voltage at the positive and negative ends of the electrolyzer). According to the topology in FIG3 , most of the power is directly transmitted to the electrolyzer through the AC-DC converter, and the DC-DC converter only processes a small portion of the power and transmits the small portion of the power from its second side to the first side.

According to the topology in FIG. 3 , the DC-DC converter of each converter module is implemented as an isolated DC-DC converter. FIG. 4 shows an example of the isolated DC-DC converter. In the example of FIG. 4 , the isolated DC-DC converter is implemented as an LLC resonant DC-DC converter. In addition, the isolated DC-DC converter can also be implemented as a dual active full bridge (DAB: DualActive Bridge) DC-DC converter (not shown). It can be understood that in FIG. 4 , the DC-DC converter 112 is used as an example for illustration, and the other DC-DC converters 122-162 can be implemented in the same manner as the DC-DC converter 112.

For the sake of clarity, an example of powering an electrolyzer using the topology in Figures 3 and 4 is described below. The numerical values in this example are only exemplary and not limiting.

In one embodiment, assuming that the current flowing through each converter module is 1000 A, the current flowing through the electrolyzer is the sum of the currents flowing through the six converter modules, that is, 6000 A. Next, the current and voltage processed by the DC-AC circuit 1121 and the AC-DC circuit 1123 are calculated according to the following two formulas: V ₁ =V _L +V ₂ , and V ₁ *I ₁ =V ₂ *I ₂ , where I ₁ and I ₂ are the current in the AC-DC circuit 1123 and the current in the DC-AC circuit 1121, respectively. For example, assuming that V ₁ is 1000 V, V ₂ is 100 V, and V _L is 900, then according to the above formula, it can be calculated that I ₁ is 100 A (100 V*1000 A/1000 V). It can be seen that for the DC-AC circuit 1121, what needs to be borne is a large current and a small voltage (for example, 1000A, 100V), and this can be achieved by connecting low-voltage devices in parallel. For the AC-DC circuit 1123, what needs to be borne is a small current and a large voltage (for example, 100A, 1000V). For the electrolytic cell, what is obtained is a large current, a large voltage and a high power (for example, 6000A, 900V, 6000A*900V).

It is worth noting that, when the electrolytic cell voltage V _L is relatively large, there will be a relatively large voltage difference between the DC voltages on both sides of the DC-DC converter (e.g., the first DC voltage V ₁ and the second DC voltage V ₂ ). For example, as in the above embodiment, the DC-DC converter needs to convert the second DC voltage V ₂ of 100V into the first DC voltage V ₁ of 1000V. In this way, the DC-DC converter needs to achieve a relatively large voltage conversion ratio. If it is achieved only by the DC-DC converter itself, the problem of low efficiency will occur. According to an embodiment of the present invention, the relatively large voltage conversion ratio can be achieved by both the voltage conversion of the DC-DC itself and the isolation transformer. For example, referring to FIG. 4 , a voltage conversion ratio of 1:10 can be achieved by the DC-DC converter itself to achieve a conversion ratio of 1:2, and by the isolation transformer to achieve a conversion ratio of 1:5.

According to such a solution, on the one hand, it is possible to provide high power to the electrolyzer, and at the same time, the DC-DC converter module can use a lower-cost and applicable power electronic switching device because the voltage or current it tolerates is significantly reduced. On the other hand, the power supply to the electrolyzer can be controlled by controlling the DC-DC converter, thereby meeting the customized power supply requirements of the electrolyzer. On the other hand, using such a converter topology to power the electrolyzer, the power that the DC-DC converter needs to process is very small. For example, when the electrolyzer is fully loaded, the power processed by the DC-DC converter is minimal; when the electrolyzer is lightly loaded, the ratio between the power processed by the DC-DC converter and the power supplied to the electrolyzer is relatively large, but because the power supplied to the electrolyzer is relatively small when lightly loaded, the power actually processed by the DC-DC converter is still very small. Therefore, in general, the power that the DC-DC converter actually needs to process is very small.

FIG5 shows another example of the modular converter in FIG1 . As shown in FIG5 , a plurality of converter modules are connected in parallel. For example, the positive terminals on the second side of the converter modules 112-162 are electrically connected to each other, and the negative terminals on the second side of the converter modules 112-162 are electrically connected to each other. The electrolyzer 5 is connected across the positive terminals on the second side of the converter modules and the negative terminals on the first side of the converter modules. For example, the positive terminal of the electrolyzer 5 is electrically connected to the positive terminal on the second side of each converter module, and the negative terminal of the electrolyzer 5 is electrically connected to the negative terminal on the first side of each converter module.

According to the topology in FIG5 , the current flows as indicated by the dotted arrows, the current flowing through the electrolyzer 5 is the sum of the currents flowing through the various converter modules, and the voltage relationship is: V ₁ +V ₂ =V _L , wherein V ₂ is the second DC voltage on the second side of the DC-DC converter, V ₁ is the first DC voltage on the first side of the DC-DC converter, and V _L is the electrolyzer voltage. According to this topology, most of the power is directly transmitted to the electrolyzer through the AC-DC converter of each converter module, and the DC-DC converter only processes a small portion of the power and provides the small portion of the power to the electrolyzer.

The DC-DC converters of the converter modules in Fig. 5 also use isolated DC-DC converters. The isolated DC-DC converters in this embodiment can be implemented using a circuit similar to that in Fig. 4 .

FIG6 shows another example of the modular converter in FIG1 . As shown in FIG6 , a plurality of converter modules are connected in parallel. For example, the positive terminals on the second sides of the converter modules 112-162 are electrically connected to each other, and the negative terminals on the second sides of the converter modules 112-162 are electrically connected to each other. The electrolyzer 5 is connected across the positive terminals on the second sides of the converter modules and the negative terminals on the second sides of the converter modules. For example, the positive terminal of the electrolyzer 5 is electrically connected to the positive terminal on the second side of each converter module, and the negative terminal of the electrolyzer 5 is electrically connected to the negative terminal on the second side of each converter module.

According to the topology in FIG6 , the current flows as indicated by the dotted arrows, the current flowing through the electrolyzer 5 is the sum of the currents flowing through the various converter modules, and the voltage relationship is: V _DC =V ₁ +V _L , wherein V _DC is the voltage on the DC side of the AC-DC converter of each converter module, V ₁ is the first DC voltage on the first side of the DC-DC converter, and V _L is the electrolyzer voltage. According to this topology, most of the power is directly transmitted to the electrolyzer through the AC-DC converter of each converter module, and the DC-DC converter only processes a small portion of the power and transmits the small portion of the power from the second side of the DC-DC converter to the first side.

The DC-DC converters of the converter modules in Fig. 6 also use isolated DC-DC converters. The isolated DC-DC converters in this embodiment can be implemented using a circuit similar to that in Fig. 4 .

FIG7 shows an application scenario of a converter system according to an embodiment of the present invention. As shown in FIG7 , each converter module in a plurality of converter modules is respectively coupled to an independent electrolytic cell stack and supplies power to the electrolytic cell stack. For example, converter module 11 is coupled to electrolytic cell stack 51 and supplies power to electrolytic cell stack 51, converter module 12 is coupled to electrolytic cell stack 52 and supplies power to electrolytic cell stack 52..... converter module 14 is coupled to electrolytic cell stack 54 and supplies power to electrolytic cell stack 54. According to the embodiment of FIG7 , a plurality of converter modules can simultaneously supply power to a plurality of independent electrolytic cell stacks, and adjust the power supply to the electrolytic cell stack according to the state of each electrolytic cell stack. In other words, by independently controlling the DC-DC converter of each converter module by the controller, individual adjustment of each electrolytic cell stack is achieved.

It can be understood that, in this embodiment, the adjustable range of each DC-DC converter should be limited to a smaller range, that is, the adjustment should be understood as fine-tuning.

Exemplary Methods

Based on the introduction of the above exemplary system, the schematic methods are now introduced. These methods can be performed using the above controller 2. It should be understood that the operations (steps) involved in the following methods do not have to be performed in the exact order described. Instead, multiple operations can be handled in different orders or simultaneously, and operations can be added or omitted.

FIG. 8 is a flow chart of a control method 800 according to an embodiment of the present invention.

8 , in box 810 , the controller 2 receives feedback information, which includes at least one of the following: a state of the electrolyzer 5 , a measurement result at the transformer 3 , and a measurement result at the modular converter 1 .

The feedback information may include status information from the electrolyzer indicating the status of the electrolyzer. The status information may be measured by a sensor on the electrolyzer side, or may be calculated based on the measurement results of the sensor and using an electrolyzer model. The status information may include, for example: the hydrogen production rate of the electrolyzer; the electrolyzer current flowing through the electrolyzer; the electrolyzer voltage at both ends of the electrolyzer; the operating efficiency of the electrolyzer; the state of health (SOH) of the electrolyzer; an aging index indicating the degree of aging of the electrolyzer; and the operating status of the electrolyzer. The operating status is one of a no-load state, a light-load state, a full-load state, and an overload state.

The feedback information may also include measurement information from the transformer and/or modular converter. The measurement information can reflect the fluctuation of the grid voltage and the harmonic condition of the system, and can also indirectly reflect the state of the electrolyzer. The measurement information may include the voltage and/or electrolyzer measured on the DC side of the converter, the voltage and/or current measured on the AC side of the converter, the voltage and/or current on the primary side of the transformer, and the voltage and/or current measured on the secondary side of the transformer.

In block 820, the controller 2 controls the DC-DC converter of at least one converter module among the plurality of converter modules according to the received feedback information to adjust the DC voltage provided to the electrolyzer, for example, to adjust at least one of the first DC voltage _V1 and/or the second DC voltage _V2 , so that the power supply to the electrolyzer is controlled. Some embodiments of block 820 are described below.

Figure 9 shows an embodiment of block 820 (block 821). In this embodiment, the controller 2 performs regulatory control based on the SOH of the electrolysis cell.

9 , at block 8211 , the controller determines whether the SOH of the electrolytic cell is degraded based on the received feedback information. For example, the controller 2 compares the current SOH of the electrolytic cell with the historical SOH stored in the controller to determine whether the SOH of the electrolytic cell is degraded.

In block 8212, when it is determined that the SOH of the electrolyzer is degraded, the controller 2 controls the DC-DC converter of at least one converter module among the plurality of converter modules to adjust the DC voltage provided to the electrolyzer. In one embodiment, the controller 2 controls the DC-DC converter of each converter module to adjust the DC voltage provided to the electrolyzer.

For example, after the SOH of the electrolyzer is degraded, the internal resistance of the electrolyzer increases. At this time, the DC-DC converter of each converter module is controlled by the controller, so that the voltage supplied to the electrolyzer is increased accordingly to ensure that the hydrogen production rate of the electrolyzer reaches the target hydrogen production rate at this time, and will not fail to reach the target hydrogen production rate due to the degradation of SOH.

In addition, in this embodiment, both the first DC voltage _V1 and the second DC voltage _V2 can be controlled by changing the tap position of the tap changer coupled to the primary side of the transformer, so that the hydrogen production rate of the electrolyzer reaches the target hydrogen production rate.

Fig. 10 shows another embodiment (block 822) of block 820. In this embodiment, the controller 2 performs regulatory control based on the actual operating state and the target operating state of the electrolytic cell.

Referring to FIG. 10 , in block 8221, the controller 2 determines the target operating state of the electrolyzer and the actual operating state of the electrolyzer based on the received feedback information. The target operating state of the electrolyzer may be determined by user demand, or may be determined by a high-level controller through coordinated control based on system and grid demand (e.g., active and reactive demand). The target operating state may be included in the feedback information and sent to the controller. The actual operating state of the electrolyzer may be determined by the electrolyzer state parameters measured by the sensor on the electrolyzer side. The actual operating state may be included in the feedback information and sent to the controller.

In block 8222, the controller 2 controls the DC-DC converter of at least one converter module among the plurality of converter modules to control the voltage provided to the electrolyzer, so that the operating state of the electrolyzer is controlled. For example, when the actual operating state of the electrolyzer meets the target operating state, the current control is maintained unchanged. When the actual operating state of the electrolyzer is inconsistent with the target operating state, the actual operating state of the electrolyzer is changed to the target operating state through control. Some examples of block 8222 are described below.

In one embodiment, if the target operating state of the electrolytic cell is full load, and the actual operating state of the electrolytic cell is also full load, the controller keeps the current control unchanged.

In another embodiment, if the target operating state of the electrolyzer is full load, and the actual operating state of the electrolyzer is running at the minimum load, the DC-DC converter of each converter module is controlled by the controller to adjust the DC voltage provided to the electrolyzer, so that the actual operating state of the electrolyzer changes from running at the minimum load to running at full load. For example, if the converter system adopts 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 adopts the topology of Figure 5, the second DC voltage is adjusted to the maximum value within its adjustable range.

In yet another embodiment, if the target operating state of the electrolytic cell is light load, and the actual operating state of the electrolytic cell is also light load, the controller maintains the current control unchanged.

In another embodiment, if the target operating state of the electrolyzer is to operate at a minimum load, and the actual operating state of the electrolyzer is full load, the DC voltage provided to the electrolyzer is controlled by the controller to control the DC-DC converters of each converter module, so that the actual operating state of the electrolyzer changes from full load to minimum load. For example, if the converter system adopts a topology such as FIG. 3 or FIG. 6, the second DC voltage is adjusted to the maximum value within its adjustable range. If the converter system adopts a topology such as FIG. 5, the second DC voltage is adjusted to the minimum value within its adjustable range.

In addition, when the target operating state of the electrolytic cell is overload and the second DC voltage _V2 has been adjusted to the limit value (such as the maximum value or the minimum value) within its adjustable range, the controller can send a command signal to the controller node on the transformer side to change the tap position of the tap changer coupled to the primary side of the transformer so that both the first DC voltage _V1 and the second DC voltage _V2 are controlled, thereby changing the actual operating state of the electrolytic cell to overload.

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 power supply to the electrolytic cell can be further increased by controlling the semi-controlled device.

Fig. 11 is another example of block 820 (block 823). In this embodiment, the controller performs regulatory control with respect to grid voltage fluctuations, harmonic compensation, and power factor optimization.

11 , in block 8231 , the controller 2 receives measurement information from the transformer side, which includes measurement signals of the primary side and the secondary side of the transformer, such as measurement current and/or measurement voltage.

At block 8232 , the controller 2 determines fluctuations in a grid voltage of a grid coupled to the primary side of the transformer based on the received measurement information.

In box 8233, the controller 2 calculates the impact of the fluctuation on the hydrogen production rate and operating efficiency of the electrolyzer.

At box 8234, the controller 2 calculates an adjustment value for the electrolyzer voltage to compensate for this effect.

At block 8235 , the controller 2 controls the DC-DC converter of at least one converter module of the plurality of converter modules so that the voltage supplied to the electrolyzer is regulated at the regulated value.

In addition, when the AC-DC of the converter module is implemented as a full-bridge AC-DC converter, reactive power compensation can be achieved by controlling the full-bridge AC-DC converter. For example, the full-bridge AC-DC converters of each converter module are controlled to generate inductive or capacitive reactive power, thereby achieving reactive power compensation.

FIG. 12 is another example (frame 824) of frame 820. In this embodiment, controller 2 performs regulation control for the occurrence of unbalanced situations in multiple converter modules. Multiple converter modules are returned to a balanced state by regulation control. Such control is advantageous for a modular converter including multiple converter modules, because each converter module has the best harmonic performance when balanced. In addition, when the AC-DC converter of each converter is implemented as an active converter, it is important to consider that the aging, device stress and life of each converter module have consistency when balanced.

12 , at block 8241 , the controller 2 determines whether an unbalanced situation occurs in the plurality of converter modules based on the received feedback information.

In the embodiment of the present invention, "balance" should be understood as the power, current and voltage transmitted by each converter module reaching a stable state, that is, the power, current and voltage transmitted by each converter module are invariant over time. For the above-mentioned parallel converter modules, the main focus is on the current transmitted by each converter module. For example, if the current transmitted by each converter module is equal, it is considered that the multiple converter modules are in a balanced state.

In the embodiment of the present invention, "unbalanced" should be understood as that among the multiple converter modules, the power, current or voltage transmitted by at least one converter module is in an unstable state. The unstable state is, for example, that the current fluctuates irregularly over time. The unstable state is also, for example, that the current transmitted by at least one converter module is different from the current transmitted by other converter modules.

It is understandable that the above definitions of "balance" and "unbalance" constitute a rule for the controller to determine whether an unbalance situation occurs in multiple converter modules. The rule can be pre-stored in the controller.

In block 8242 , when it is determined that an unbalanced condition occurs in at least one converter module among the plurality of converter modules, the controller 2 controls the DC-DC converter of the at least one converter module to restore the converter module to a balanced state.

In one embodiment, the response to the unbalanced situation is achieved by compensating for the difference between the current in the unbalanced converter module and the current in other converter modules. Take the modular converter including 6 converter modules as an example. Under balanced conditions, the current flowing through each converter module is equal. Assume that such an unbalanced situation occurs: the current flowing through one converter module is not equal to the current flowing through the other five converter modules. At this time, the controller 2 calculates the difference between the current in the one converter module and the current in the other converter modules. Then, the controller 2 controls the DC-DC converter of the one converter module with the goal of compensating for the difference, so that the current in the one converter module is equal to the current in the other converter modules, that is, these converter modules return to a balanced state again.

In another embodiment, the transformer is implemented as a phase-shifting transformer, and each converter module supplies power to an independent electrolyzer stack. In such a scenario, the controller calculates the optimal current distribution for each converter module according to the phase shift angles of multiple windings of the phase-shifting transformer, thereby coping with the unbalanced situation.

For example, the controller 2 calculates the harmonic components according to the phase angles of the primary winding of the phase-shifting transformer and each of the multiple secondary windings and the current in the converter module coupled to each secondary winding. Then, the controller 2 calculates the optimal current distribution for each converter module. That is, the current distribution of the secondary windings for each phase angle. The optimal current distribution enables: 1) the harmonic elimination result to meet the harmonic requirements at the PCC point (for example, the harmonics at the PCC point need to be less than 3%); 2) the current provided to each electrolyzer stack is adapted to the SOH state of the electrolyzer stack (for example, the electrolyzer stack can operate in a light load, full load or overload state according to its SOH, and this factor is taken into consideration when distributing the current); 3) the total hydrogen production rate of each electrolyzer stack is maximized (for example, although the hydrogen production rate of some electrolyzer stacks decreases and the hydrogen production rate of some electrolyzer stacks increases, the total hydrogen production rate of these electrolyzer stacks is the largest). Then, the controller 2 controls each converter module so that each converter module achieves the optimal current distribution. In this embodiment, an optimization model may be stored in the controller 2, and the phase angles of the primary winding of the phase-shifting transformer and each of the multiple secondary windings and the current in the converter module coupled to each secondary winding are input into the optimization model. After model processing, the optimal current distribution for each converter module is output from the optimization model.

Fig. 13 is another example of block 820 (block 825). In this embodiment, the controller 2 performs regulation control for the situation that one or more of the multiple converter modules connected in parallel fail, so that when a failure occurs and the fast shutdown condition cannot be met, the system harmonics are minimized.

13 , in block 8251 , the controller 2 determines whether a fault condition, such as a circuit breaker fault, occurs in a plurality of converter modules based on the received feedback information.

Here, the converter module "failure" means that the converter module cannot work, that is, it is usually called "broken". At this time, there is no current in the secondary winding connected to the faulty converter module, so it will cause harmonic problems at the PCC point. In this regard, according to the control strategy of the following block 8252, such harmonic problems can be dealt with.

In box 8252, when it is determined that at least one converter module among the multiple converter modules fails and cannot work, the controller 2 controls the DC-DC converters of other converter modules so that other converters output unbalanced currents, and the combination of unbalanced currents provided by other converter modules can minimize the PCC point harmonics under the current conditions. In addition, the combination of unbalanced currents also maximizes the hydrogen production rate of the electrolyzer under the current conditions, or makes the hydrogen production rate of the electrolyzer under the current state at least reach the predetermined hydrogen production rate under the conditions. For example, when working with 6 converter modules, the hydrogen production rate of the electrolyzer is 100%. If one of the converter modules fails, it works with 5 converter modules, and the predetermined hydrogen production rate is 80%, that is, the combination of unbalanced currents for the 5 converter modules should make the hydrogen production rate of the electrolyzer reach at least 80%.

In one embodiment, the transformer is implemented as a phase-shifting transformer, and the controller 2 calculates the optimal current distribution for other converter modules according to the phase-shifting angles of multiple windings of the phase-shifting transformer, thereby coping with fault situations.

For example, the controller 2 calculates the optimal current distribution for other converter modules (i.e., converter modules that are not faulty and can work normally) based on the phase angles of the primary winding of the phase-shifting transformer and each of the multiple secondary windings and the current in the converter module coupled to each secondary winding. That is, the optimal current distribution for the secondary windings at each phase angle. The optimal current distribution enables: 1) the harmonic elimination result to meet the harmonic requirements at the PCC point (for example, the harmonics at the PCC point need to be less than 3%); 2) the hydrogen production rate of the electrolyzer is maximized. Similar to the above embodiment, an optimization model can be stored in the controller 2, and the phase angles of the primary winding of the phase-shifting transformer and each of the multiple secondary windings and the current in the converter module coupled to each secondary winding are input into the optimization model. After model processing, the optimal current distribution is output from the model.

It can be understood that in the above embodiments, the optimization model includes forms such as machine learning models, multi-physics field models, relationship tables, etc.

In addition, in box 7252, when the AC-DC converter of each converter module is implemented as a semi-controlled device such as a thyristor, additional control margin can be further provided by controlling the AC-DC converter, which helps to achieve the combination of the above-mentioned unbalanced currents to minimize the harmonics at the PCC point.

The above description is provided to enable any person skilled in the art to implement the various aspects described herein. Various modifications to these aspects are apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects. Therefore, the claims are not intended to be limited to the aspects shown herein. All structural and functional equivalents of elements of various aspects described in this disclosure that are known or to be known to those skilled in the art will be expressly included herein by reference and are intended to be covered by the claims.

Claims (18)

1. A converter system for powering an electrolyzer, comprising: A modular converter, comprising a plurality of converter modules, wherein each converter module is coupled between one of a plurality of secondary windings of a transformer and the electrolytic cell, and each converter module comprises a cascaded AC-DC converter and a DC-DC converter; and A controller is configured to control a DC-DC converter of at least one converter module among the plurality of converter modules to adjust a DC voltage provided to the electrolyzer. 2. The converter system of claim 1, wherein a side of the DC-DC converter of each converter module close to the AC-DC converter provides a first DC voltage, and another side away from the AC-DC converter provides a second DC voltage; And wherein the controller is configured to control a DC-DC converter of at least one converter module among the plurality of converter modules to adjust at least one of the first DC voltage and the second DC voltage. 3. The converter system according to claim 1 or 2, wherein the controller is configured to: receiving feedback information including at least one of a status of the electrolyzer, a measurement at the transformer, and a measurement at the modular converter; and A DC-DC converter of at least one converter module among the plurality of converter modules is controlled according to the received feedback information to adjust a DC voltage provided to the electrolyzer. 4. The converter system according to claim 3, wherein the controller is configured to: determining whether the health status of the electrolytic cell is degraded based on the feedback information; and When it is determined that the health state of the electrolyzer is degraded, the DC-DC converter of at least one converter module among the plurality of converter modules is controlled to adjust the DC voltage provided to the electrolyzer, so that the hydrogen production rate of the electrolyzer is controlled. 5. The converter system according to claim 3 or 4, wherein the controller is configured to: When it is determined based on feedback information that the actual operating state of the electrolytic cell is inconsistent with the target operating state, the DC-DC converter of at least one converter module among the multiple converter modules is controlled to adjust the DC voltage provided to the electrolytic cell, so that the actual operating state of the electrolytic cell becomes the target operating state. 6. The converter system according to any one of claims 3 to 5, wherein the controller is configured to: When the DC voltage output by the DC-DC converter of each converter module has been adjusted to the limit value of the adjustable range, a command signal is generated to change the tap position of the shaft head converter coupled to the primary side of the transformer, so that the DC voltage output by the DC-DC converter of each converter module is further adjusted. 7. The converter system according to any one of claims 3 to 6, wherein the controller is configured to: determining a fluctuation of a grid voltage of a grid coupled to a primary side of the transformer based on the feedback information; Calculating the effect of the fluctuation on the hydrogen production rate and operating efficiency of the electrolyzer; determining a desired adjustment value of the cell voltage to compensate for said influence; and A DC-DC converter of at least one converter module among the plurality of converter modules is controlled so that a voltage supplied to the electrolytic cell is adjusted by the adjustment amount. 8. The converter system according to any one of claims 3 to 7, wherein the controller is configured to: At least one converter module among the plurality of converter modules is controlled based on the feedback information to provide reactive power required for power factor correction. 9. The converter system according to any one of claims 3 to 8, wherein the controller is configured to: determining whether an unbalanced state occurs in the plurality of converter modules based on the feedback information; When it is determined that at least one converter module is in an unbalanced state, a DC-DC converter of the at least one converter module is controlled to return the at least one converter module to a balanced state. 10. The converter system according to claim 1, wherein the controller is configured to execute, for a case where the transformer is a phase-shifting transformer: The optimal current distribution for the plurality of converter modules is calculated according to the phase shift angles of the plurality of windings of the phase shift converter, so as to maximize the hydrogen production rate of the electrolyzer when the unbalanced state occurs. 11. The converter system according to any one of claims 3 to 10, wherein the controller is configured to: determining whether a fault has occurred in the variator system based on the feedback information; and When it is determined that a fault has occurred in the converter system, a DC-DC converter of at least one converter module among the plurality of converter modules is controlled to minimize harmonics at a PCC coupled to the primary side of the transformer and to maximize a hydrogen production rate of the electrolyzer under current conditions. 12. The converter system according to claim 11, wherein the controller is configured to execute, for a case where the transformer is a phase-shifting transformer: The optimal current distribution for other converter modules is calculated according to the phase shift angles of the multiple windings of the phase shift converter, so as to maximize the hydrogen production rate of the electrolyzer when the short circuit fault occurs. 13. The converter system according to any one of claims 1 to 12, wherein the AC-DC converter of each converter module is a diode-based 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 the plurality of converter modules are connected in parallel; And wherein, the positive terminal of the one side of the DC-DC converter is connected to the positive terminal of the electrolytic cell, and the positive terminal of the other side of the DC-DC converter is connected to the negative terminal of the electrolytic cell. 15. The converter system of claim 2, wherein the plurality of converter modules are connected in parallel; And wherein, the positive terminal of the other side of the DC-DC converter is connected to the positive terminal of the electrolytic cell, and the negative terminal of the one side of the DC-DC converter is connected to the negative terminal of the electrolytic cell. 16. The converter system of claim 2, wherein the plurality of converter modules are connected in parallel; And wherein, the positive terminal of the other side of the DC-DC converter is connected to the positive terminal of the electrolytic cell, and the negative terminal of the other side of the DC-DC converter is connected to the negative terminal of the electrolytic cell. 17. A method for controlling a converter system to supply power to an electrolyzer, the converter system comprising a plurality of converter modules, wherein each converter module is coupled between one of a plurality of secondary windings of a transformer and the electrolyzer, and each converter module comprises a cascaded AC-DC converter and a DC-DC converter, the method comprising: A DC-DC converter of at least one converter module among the plurality of converter modules is controlled to adjust a DC voltage provided to the electrolyzer. 18. A controller for controlling a converter system to supply power to an electrolyser, comprising one or more processors configured to perform the method of claim 17.