Hydrogen production system and control method of off-grid new energy combined with ac-dc network

Abstract

The application relates to the technical field of new energy power generation hydrogen production, in particular to an off-grid new energy hydrogen production system with AC-DC combined network and a control method. The hydrogen production system comprises at least one new energy AC power generation network, at least one flexible DC converter, a DC power transmission unit, a hydrogen production unit and a DC energy storage unit. The at least one new energy AC power generation network generates AC power. The flexible DC converter is connected to the new energy AC power generation network and converts the AC power into sending-end DC power. The DC power transmission unit is connected to the at least one flexible DC converter to transmit the sending-end DC power. The hydrogen production unit receives the power transmitted by the DC power transmission unit and produces hydrogen. The DC energy storage unit is connected to the DC power transmission unit and adjusts the transmission voltage of the DC power transmission unit through charging and discharging to make the transmission voltage of the DC power transmission unit in a preset standard voltage interval. The flexible DC converter adopts a network construction control strategy to construct the voltage and frequency of the new energy AC power generation network.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy power generation hydrogen production, in particular to an off-grid new energy hydrogen production system with alternating current and direct current combined network and a control method. BACKGROUND

[0002] New energy power generation refers to a technology of generating power by using renewable energy such as wind, light, and tide. New energy power generation has the characteristics of randomness, volatility, and low inertia.

[0003] Water electrolysis hydrogen production is a clean, efficient and mature hydrogen production technology, which has the characteristics of flexible load adjustment and can well match the randomness and volatility of new energy power generation. Therefore, in the process of new energy power generation hydrogen production, that is, in the process of hydrogen production by using the power of new energy power generation, the load of water electrolysis hydrogen production and the power of new energy power generation can be flexibly adjusted, so that the supply and demand between power supply and load power consumption can be balanced.

[0004] Currently, in the new energy power generation hydrogen production technology, there are three modes for the connection between the new energy power generation system and the water electrolysis hydrogen production system, which are grid peak shaving mode, grid friendly mode and off-grid hydrogen production mode.

[0005] For the grid peak shaving mode and the grid friendly mode, the water electrolysis hydrogen production system not only needs to be connected with the new energy power generation system, but also needs to be connected with the power grid, and the water electrolysis hydrogen production is carried out by using the power provided by the new energy power generation and the power provided by the power grid. The hydrogen produced in this way is not completely green hydrogen, and the investment brought by the connection with the power grid and the power consumption is also increased.

[0006] Off-grid hydrogen production is a technology mode in which the power generated by renewable energy (such as wind power and photovoltaic power) is directly used for water electrolysis hydrogen production, without transmission through the traditional power grid. In this way, the investment cost brought by accepting power supply from the power grid can be reduced, and the production of green hydrogen can be scaled up.

[0007] Large-scale off-grid new energy hydrogen production technology is usually an alternating current off-grid large-scale new energy hydrogen production mode. In this alternating current off-grid large-scale new energy hydrogen production mode, the alternating current generated by new energy power generation is transmitted to the water electrolysis hydrogen production system in the form of alternating current, and the water electrolysis hydrogen production system performs rectification on the alternating current and then performs electrolysis to produce hydrogen.

[0008] However, the inventors found that in this alternating current off-grid large-scale new energy hydrogen production mode, the frequency and voltage of the alternating current need to be controlled to be stable. In a large-scale new energy hydrogen production system (for example, a hydrogen production system with a power generation capacity of hundreds of megawatts or more), there are many large-capacity new energy power generation units, so it is difficult to accurately control the frequency and voltage of the alternating current in this mode, thereby leading to a large control complexity and poor stability of this mode. Summary of the Invention

[0009] This application aims to provide an off-grid renewable energy hydrogen production system and control method using a combined AC / DC grid, in order to improve the stability of the renewable energy hydrogen production system.

[0010] According to one aspect of this application, an off-grid renewable energy hydrogen production system with AC / DC combined grid is proposed, comprising at least one renewable AC power grid, at least one flexible DC converter, a DC transmission unit, a hydrogen production unit, and a DC energy storage unit. At least one renewable AC power grid generates AC power. The flexible DC converter is connected to the renewable AC power grid to convert the AC power into DC power at the sending end. The DC transmission unit is connected to at least one flexible DC converter to transmit the DC power at the sending end. The hydrogen production unit is connected to the DC transmission unit, receives the electrical energy transmitted by the DC transmission unit, and produces hydrogen. The DC energy storage unit is connected to the DC transmission unit and adjusts the transmission voltage of the DC transmission unit through charging and discharging to keep the transmission voltage of the DC transmission unit within a preset standard voltage range. The flexible DC converter employs a grid-based control strategy to construct the voltage and frequency of the renewable AC power grid, thereby maintaining voltage and frequency stability.

[0011] According to some embodiments, a DC transmission unit includes at least one sending-end bus, at least one DC line, and a receiving-end bus.

[0012] The sending-end bus is connected to a flexible DC converter to receive sending-end DC power. At least one DC line is connected to the sending-end bus to receive and transmit sending-end DC power from the sending-end bus. The receiving-end bus is connected to at least one DC line and is connected to the hydrogen production unit. It receives and collects the sending-end DC power transmitted from the at least one DC line to obtain receiving-end high-voltage DC power, and then transmits the receiving-end high-voltage DC power to the hydrogen production unit.

[0013] According to some embodiments, the hydrogen production unit includes a high-voltage DC transformer, a low-voltage DC bus, at least one low-voltage DC transformer, at least one electrolyzer, and a hydrogen production common load. The high-voltage DC transformer is connected to the receiving-end bus and then to the hydrogen production unit, stepping down the receiving-end high-voltage DC power to obtain receiving-end low-voltage DC power. The low-voltage DC bus is connected to a DC transmission unit, receiving and collecting the receiving-end low-voltage DC power transmitted by the DC transmission unit. At least one low-voltage DC transformer is connected to the low-voltage DC bus, stepping down the receiving-end low-voltage DC power to obtain hydrogen-producing DC power. At least one electrolyzer is connected to the low-voltage DC transformer, receiving the hydrogen-producing DC power and using it for electrolysis to produce hydrogen. The hydrogen production common load is connected to the low-voltage DC bus, receiving the receiving-end low-voltage DC power provided by the low-voltage DC bus.

[0014] According to some embodiments, the DC energy storage unit includes a first energy storage device and / or at least one second energy storage device. The first energy storage device is connected to the receiving-end bus and charges and discharges according to the relative magnitude of the voltage of the receiving-end bus and a preset standard voltage, so that the voltage of the receiving-end bus is within the preset standard voltage range. The second energy storage device is connected to the sending-end bus and charges and discharges according to the relative magnitude of the voltage of the sending-end bus and a preset standard voltage, so that the voltage of the sending-end bus is within the preset standard voltage range.

[0015] According to some embodiments, the new energy hydrogen production system also includes an energy controller. The energy controller controls the power generation of at least one new energy AC power grid and the hydrogen production power of the hydrogen production unit based on the current maximum total power generation, the maximum hydrogen production power, and the current maximum rechargeable power of the DC energy storage unit. The current maximum total power generation is the sum of the maximum power generation currently achievable by at least one new energy AC power grid; the maximum hydrogen production power is the maximum hydrogen production power achievable by the hydrogen production unit.

[0016] According to some embodiments, when the current maximum total power generation, maximum hydrogen production capacity, and current maximum rechargeable power meet a first power condition, the energy controller controls the hydrogen production unit to produce hydrogen at its maximum hydrogen production capacity. The energy controller determines the first power generation capacity based on the current maximum rechargeable power and maximum hydrogen production capacity, and controls at least one new energy AC power grid to generate electricity at the first power generation capacity. The first power condition includes the current maximum power generation capacity being greater than the sum of the maximum hydrogen production capacity and the current maximum rechargeable power.

[0017] According to some embodiments, when the current maximum total power generation capacity, maximum hydrogen production capacity, and current maximum rechargeable power meet a second power condition, the energy controller controls at least one new energy AC power grid to generate electricity at the maximum total power generation capacity. The energy controller controls the hydrogen production unit to produce hydrogen at the maximum hydrogen production capacity. The second power condition includes: the current maximum total power generation capacity is greater than the maximum hydrogen production capacity, and the current maximum total power generation capacity is less than the sum of the maximum hydrogen production capacity and the current maximum rechargeable power, and the current maximum rechargeable power is greater than a preset value.

[0018] According to some embodiments, the energy controller controls the hydrogen production unit to produce hydrogen at its maximum hydrogen production power when the current maximum total power generation, maximum hydrogen production power, and current maximum rechargeable power meet a third power condition. The energy controller ensures that the total power generation of at least one new energy AC power grid is not greater than the maximum hydrogen production power. The third power condition includes: the current maximum total power generation is greater than the maximum hydrogen production power, and the current maximum total power generation is less than the sum of the maximum hydrogen production power and the current maximum rechargeable power, and the current maximum rechargeable power is not greater than a preset value.

[0019] According to one aspect of this application, a control method for a hydrogen production system is proposed, applicable to an off-grid renewable energy hydrogen production system with AC / DC combined grid. The hydrogen production system includes at least one renewable AC power grid, a DC transmission unit, a hydrogen production unit, and a DC energy storage unit. The renewable AC power grid generates AC power; a flexible DC converter is connected to the renewable AC power grid to convert the AC power into DC power; the DC transmission unit is connected to at least one flexible DC converter to transmit the DC power; the hydrogen production unit is connected to the DC transmission unit, receives the electrical energy transmitted by the DC transmission unit, and produces hydrogen; the DC energy storage unit is connected to the DC transmission unit and adjusts the transmission voltage of the DC transmission unit by charging or discharging to keep the transmission voltage of the DC transmission unit within a preset standard voltage range; the flexible DC converter employs a grid-based control strategy to construct the voltage and frequency of at least one renewable AC power grid, thereby maintaining voltage and frequency stability.

[0020] The control method includes controlling at least one renewable AC power grid and a hydrogen production unit based on the current maximum total power generation and maximum hydrogen production capacity, thereby adjusting the power generation capacity of the renewable AC power grid and the hydrogen production capacity of the hydrogen production unit. The current maximum total power generation capacity is the sum of the maximum power generation capacity currently achievable by the at least one renewable AC power grid. The maximum hydrogen production capacity is the maximum hydrogen production capacity achievable by the hydrogen production unit.

[0021] According to some embodiments, based on the current maximum total power generation and maximum hydrogen production capacity, at least one new energy AC power grid and a hydrogen production unit are controlled. This includes controlling the hydrogen production unit to produce hydrogen at the maximum hydrogen production capacity when the current maximum total power generation, maximum hydrogen production capacity, and current maximum rechargeable power meet a first power condition. Based on the current maximum rechargeable power and maximum hydrogen production capacity, a first power generation capacity is determined, and at least one new energy AC power grid is controlled to generate electricity at the first power generation capacity.

[0022] The first power condition includes the condition that the current maximum power generation capacity is greater than the sum of the maximum hydrogen production capacity and the current maximum rechargeable capacity.

[0023] According to some embodiments, based on the current maximum total power generation and maximum hydrogen production capacity, at least one new energy AC power grid and a hydrogen production unit are controlled. This includes controlling the at least one new energy AC power grid to generate electricity at its maximum total power generation capacity when the current maximum total power generation capacity, maximum hydrogen production capacity, and current maximum rechargeable power meet a second power condition. The hydrogen production unit is controlled to produce hydrogen at its maximum hydrogen production capacity. The second power condition includes: the current maximum total power generation capacity is greater than the maximum hydrogen production capacity, and the current maximum total power generation capacity is less than the sum of the maximum hydrogen production capacity and the current maximum rechargeable power, and the current maximum rechargeable power is greater than a preset value.

[0024] According to some embodiments, based on the current maximum total power generation and maximum hydrogen production capacity, at least one new energy AC power grid and a hydrogen production unit are controlled. This includes controlling the hydrogen production unit to produce hydrogen at its maximum hydrogen production capacity when the current maximum total power generation, maximum hydrogen production capacity, and current maximum rechargeable power meet a third power condition. The total power generation capacity of the at least one new energy AC power grid is controlled to be no greater than the maximum hydrogen production capacity. The third power condition includes: the current maximum total power generation is greater than the maximum hydrogen production capacity, and the current maximum total power generation is less than the sum of the maximum hydrogen production capacity and the current maximum rechargeable power, and the current maximum rechargeable power is no greater than a preset value.

[0025] Beneficial effects

[0026] In the off-grid renewable energy hydrogen production system proposed in this application, a flexible DC converter is installed in the AC transmission network between the renewable AC power grid and the flexible DC converter. A grid-based control strategy for the flexible DC converter is used to construct and stabilize the voltage and frequency of the AC transmission network. A DC energy storage unit is installed in the DC transmission network composed of the DC transmission unit, DC energy storage unit, and hydrogen supply unit. The charging and discharging of the DC energy storage unit maintains the stability of the DC voltage of the DC transmission network.

[0027] In a DC transmission network, the hydrogen production system of this application only needs to adjust the amplitude of the DC power by the DC energy storage unit to achieve stable control of the power in the DC transmission network. There is no need to adjust frequency or phase angle, nor to consider the wideband oscillation problem caused by AC transmission. This simplifies control, thereby improving its accuracy and convenience, and ultimately enhancing the stability of the transmitted power.

[0028] In the AC transmission network, the hydrogen production system of this application does not require a single control device to uniformly control all new energy power generation units. Instead, the large-scale AC transmission network is divided into at least one medium- or small-scale AC transmission network. The voltage and frequency of the AC power in each medium- or small-scale AC transmission network are regulated by their respective flexible DC converters. This helps reduce control complexity, further improves the control accuracy of the AC power in the transmission network, thereby improving the transmission stability of the AC transmission network and, consequently, the stability of the hydrogen production system. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the architecture of an off-grid new energy hydrogen production system with AC / DC combined grid configuration according to an embodiment of this application;

[0031] Figure 2 This is a schematic diagram of the overall system architecture of the off-grid new energy hydrogen production system with AC / DC combined grid configuration according to an embodiment of this application;

[0032] Figure 3 This is a schematic diagram of the system structure of an off-grid new energy hydrogen production system with a first energy storage device, which is an embodiment of this application;

[0033] Figure 4 This is a schematic diagram of the system structure of an off-grid new energy hydrogen production system with a second energy storage device, which is an embodiment of this application;

[0034] Figure 5 This is a schematic diagram of the system structure of an off-grid new energy hydrogen production system with AC / DC combined grid configuration, which includes a first energy storage device and a second energy storage device, according to an embodiment of this application.

[0035] Figure 6 This is a schematic diagram of the flow framework of the control method for the hydrogen production system according to an embodiment of this application;

[0036] Figure 7 This is a flowchart of a first implementation of step S601 in an embodiment of this application;

[0037] Figure 8 This is a flowchart illustrating a second implementation of step S601 in an embodiment of this application.

[0038] Figure 9 This is a flowchart illustrating a third implementation of step S601 in an embodiment of this application.

[0039] Explanation of reference numerals in the attached figures:

[0040] 1. Hydrogen production unit; 11. High-voltage DC transformer; 12. Low-voltage DC bus; 13. Low-voltage DC transformer; 14. Electrolyzer; 15. Hydrogen production utility load; 2. DC transmission unit; 21. Sending-end bus; 22. DC line; 23. Receiving-end bus; 24. DC circuit breaker; 3. DC energy storage unit; 31. First energy storage device; 32. Second energy storage device; 4. Flexible DC converter; 5. New energy AC power grid; 51. AC bus; 52. AC line; 53. AC transformer; 54. New energy power generation unit. Detailed Implementation

[0041] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this application will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0042] The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of these specific details, or other methods, components, materials, devices, etc. In these cases, well-known structures, methods, devices, implementations, materials, or operations will not be shown or described in detail.

[0043] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0044] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order.

[0045] The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0046] According to one aspect of this application, this application provides an off-grid new energy hydrogen production system with AC / DC combined grid configuration. (Refer to...) Figure 1 The off-grid renewable energy hydrogen production system, which combines AC and DC power transmission, includes: a hydrogen production unit 1, a DC power transmission unit 2, a DC energy storage unit 3, at least one flexible DC converter 4, and at least one renewable AC power grid 5.

[0047] According to the example embodiment, refer to Figure 2 The new energy AC power grid 5 is an AC power generation network that collects AC power generated by at least one new energy power generation unit 54. The new energy power generation unit 54 is a unit that generates electricity using renewable energy sources, such as photovoltaic power generation units and wind power generation units.

[0048] According to the example embodiment, a new energy AC power grid 5 can correspond to a new energy power generation unit 54, or can correspond to multiple new energy power generation units 54, and each new energy power generation unit 54 may be the same or different, which is not limited here.

[0049] For example, a new energy AC power grid 5 may include multiple wind power generation units and multiple photovoltaic power generation units, or it may include multiple wind power generation units, or it may include multiple photovoltaic power generation units, without limitation.

[0050] According to some embodiments, refer to Figure 2 Each new energy AC power grid 5 may specifically include an AC bus 51, at least one AC line 52, at least one AC transformer 53, and at least one new energy power generation unit 54.

[0051] Each new energy power generation unit 54 corresponds to an AC transformer 53. The new energy power generation unit 54 is connected to the primary side of the corresponding AC transformer 53, and the secondary side of the AC transformer 53 is connected to the AC line 52.

[0052] Each AC line 52 can be connected to one AC transformer 53 at one end, or to at least two AC transformers 53, without limitation. The AC power generated by each new energy power generation unit 54 is stepped up by the corresponding AC transformer 53 and then input into the AC line 52 connected to that AC transformer 53. The AC line 52 collects all the stepped-up AC power received.

[0053] The other end of each AC line 52 is connected to the AC bus 51. The AC bus 51 receives and aggregates the boosted AC power collected by each AC line 52, and outputs the aggregated AC power.

[0054] Reference Figure 1The flexible DC converter 4 is connected to the new energy AC power grid 5, and converts the AC power output from the new energy AC power grid 5 into DC power for output.

[0055] According to the example embodiment, refer to Figure 1 Each new energy AC power grid 5 corresponds to only one flexible DC converter 4. That is, one new energy AC power grid 5 is connected to only one flexible DC converter 4, and not to multiple flexible DC converters 4 separately. For example, the first new energy AC power grid is only connected to the first flexible DC converter.

[0056] According to the example embodiment, each flexible DC converter 4 can be connected to one or more new energy AC power grids 5. For example, the first flexible DC converter can be connected not only to the first new energy AC power grid but also to the second new energy AC power grid, so as to collect the AC power from the first and second new energy AC power grids and convert the AC power into DC power at the sending end for output.

[0057] According to the example embodiment, the flexible DC converter 4 adopts a grid-based control strategy to construct the voltage and frequency of the new energy AC power grid 5. Grid-based control is a control method that simulates the characteristics of a synchronous generator, making the flexible DC converter 4 behave as a voltage source in terms of external characteristics. This means that the flexible DC converter 4 can actively control the amplitude, phase angle, and frequency of its output voltage, thereby becoming a stable support point for the power system.

[0058] In other words, the grid-type control strategy adopted by the flexible DC converter 4 enables the flexible DC converter 4 to adjust its output parameters when the system is disturbed, so as to provide voltage and frequency support for the system and thus enhance the stability and reliability of the power system.

[0059] In existing technology, the AC power output from each new energy power generation unit 54 in an off-grid AC new energy hydrogen production system is uniformly transmitted to the hydrogen production unit 1 through an AC transmission network. In order to improve the stability of the transmitted power, the voltage and frequency of the AC transmission network are uniformly adjusted by a control device. When the voltage and frequency of the AC transmission network fluctuate, the control device adjusts each new energy power generation unit 54 to regulate the voltage and frequency.

[0060] In this embodiment, each new energy power generation unit 54 is divided into each new energy AC power generation grid 5, and the voltage and frequency of each new energy AC power generation grid 5 are constructed by the flexible DC converter 4.

[0061] This approach is equivalent to dividing the existing large-scale AC transmission network into at least one independent medium- or small-scale AC transmission network. Furthermore, it transforms the existing control method of uniformly regulating the voltage and frequency of the entire large-scale AC transmission network into a method of separately regulating the voltage and frequency of each medium- or small-scale AC transmission network. This reduces control complexity and significantly improves control accuracy, thereby enhancing the stability of the AC transmission network.

[0062] Optionally, the flexible DC converter 4 can specifically consist of a flexible DC converter valve, a transformer, a bridge arm reactor, and switchgear. The flexible DC converter valve can be constructed using fully controllable power electronic devices as basic units, and it can employ a three-phase bridge inverter circuit structure. This structure gives the flexible DC converter valve high controllability and flexibility, enabling precise power conversion according to different operating requirements.

[0063] Optionally, the flexible DC converter valve can adopt a dual-level, three-level, or multi-level topology, which is not limited here.

[0064] Reference Figure 1 Each flexible DC converter 4 converts the received AC power into DC power at the sending end. The DC transmission unit 2 is connected to each of the flexible DC converters 4 and also to the hydrogen production unit 1. It receives the DC power output from each flexible DC converter 4 and transmits the received DC power to the hydrogen production unit 1 so that the hydrogen production unit 1 can produce hydrogen.

[0065] For example, a hydrogen production system includes a first flexible DC converter, a second flexible DC converter, and a third flexible DC converter. One end of the DC transmission unit 2 is connected to the first flexible DC converter, the second flexible DC converter, and the third flexible DC converter, respectively, and the other end of the DC transmission unit 2 is connected to the hydrogen production unit 1.

[0066] Optionally, the DC transmission unit 2 can specifically adopt a symmetrical unipolar topology, that is, there is no neutral line and zero potential line in each line of the DC transmission unit 2, only live line, neutral line and ground line, or only positive and negative lines.

[0067] Reference Figure 1 The DC energy storage unit 3 is connected to the DC transmission unit 2, and can discharge to the DC transmission unit 2 or receive electrical energy from the DC transmission unit 2 for charging.

[0068] The DC energy storage unit 3 adopts a constant voltage control strategy. That is, the DC energy storage unit 3 can charge and discharge according to the relative magnitude of the transmission voltage of the DC transmission unit 2 and the preset standard voltage. In this way, the DC energy storage unit 3 can adjust the transmission voltage of the DC transmission unit 2 through charging and discharging, so that the transmission voltage of the DC transmission unit 2 is within the preset standard voltage range.

[0069] For example, if the electrical energy transmitted by the DC transmission unit 2 exceeds the electrical energy consumption of the hydrogen production unit 1, the transmission voltage of the DC transmission unit 2 will be higher than the preset standard voltage. In this case, the DC energy storage unit 3 is charged to store the remaining electrical energy transmitted by the DC transmission unit 2, thereby gradually bringing the transmission voltage of the DC transmission unit 2 closer to the preset standard voltage, and thus stabilizing the transmission voltage of the DC transmission unit 2 within the preset standard voltage range.

[0070] Similarly, if the electrical energy transmitted by DC transmission unit 2 is less than the electrical energy used by hydrogen production unit 1, the transmission voltage of DC transmission unit 2 will be lower than the preset standard voltage. In this case, DC energy storage unit 3 discharges to stabilize the transmission voltage of DC transmission unit 2 within the preset standard voltage range.

[0071] In existing off-grid hydrogen production systems, the entire power transmission network is an AC power transmission network. Therefore, control devices are needed to control the voltage and frequency of the AC power in the entire power transmission network to keep it stable.

[0072] In addition, in conventional AC / DC off-grid hydrogen production systems, the AC power output from the new energy power generation unit 54 is first rectified into DC power by a rectifier, and then the DC power is converted into high-voltage DC power by a step-up transformer before being transmitted to the hydrogen production unit 1. The energy storage device is often connected to the AC side to directly charge and discharge energy, or connected to the inside of the hydrogen production unit 1 to charge and discharge energy inside the hydrogen production unit 1.

[0073] For this type of conventional AC / DC off-grid hydrogen production system, when there are fluctuations in the AC and DC power transmission networks, the control device usually adjusts the voltage amplitude, frequency, and phase angle of each new energy power generation unit 54 in a unified manner to maintain the stability of the entire hydrogen production system.

[0074] The inventors discovered that both AC / DC off-grid hydrogen production systems and AC off-grid hydrogen production systems utilize a control device to uniformly control the voltage and frequency of the entire power transmission network. Regardless of which part of the power transmission network experiences fluctuations, the control device must regulate and adjust each new energy power generation unit 54 to maintain voltage and frequency stability. This approach results in high control complexity.

[0075] In the off-grid renewable energy hydrogen production system proposed in this application embodiment, a flexible DC converter 4 is installed in the AC transmission network between the renewable AC power grid 5 and the flexible DC converter 4. The grid-based control strategy of the flexible DC converter 4 is used to construct the voltage and frequency of the AC transmission network. When voltage and frequency fluctuate, the flexible DC converter 4 automatically adjusts its output to maintain the stability of the AC transmission network's voltage and frequency. A DC energy storage unit 3 is installed in the DC transmission network composed of the DC transmission unit 2, the DC energy storage unit 3, and the hydrogen supply unit. The charging and discharging of the DC energy storage unit 3 is used to maintain the stability of the DC voltage of the DC transmission network.

[0076] Firstly, in a DC transmission network, the hydrogen production system of this application only needs to adjust the amplitude of the DC power by the DC energy storage unit 3 to achieve stable control of the DC transmission network. There is no need to adjust frequency or phase angle, nor is it necessary to consider the wideband oscillation problem caused by AC transmission. This simplifies control, thereby improving control accuracy and convenience, and ultimately enhancing the stability of the transmitted electrical energy.

[0077] Secondly, in the AC power transmission network, the hydrogen production system of this application does not rely on a control device to control the new energy power generation unit 54 to regulate voltage and frequency and maintain stability. Instead, it relies on the voltage and frequency of the AC power transmission network constructed by the flexible DC converter 4, and the flexible DC converter 4 maintains the stability of the AC power transmission network's voltage and frequency. In the event of disturbances in the AC power transmission network, the flexible DC converter 4 automatically controls its own switching state, switching frequency, switching time, etc., to maintain the stability of the voltage and frequency output by the flexible DC converter 4.

[0078] Furthermore, the hydrogen production system of this application does not require a single control device to uniformly control all the new energy power generation units 54. Instead, the large-scale AC transmission network is divided into at least one medium- or small-scale AC transmission network. The voltage and frequency of the AC power in each medium- or small-scale AC transmission network are constructed by their respective flexible DC converters 4. This helps reduce control complexity, further improves the control accuracy of the AC power in the AC transmission network, thereby improving the transmission stability of the AC transmission network and, consequently, the stability of the hydrogen production system.

[0079] Thirdly, in the hydrogen production system of this application, the new energy power generation unit 54 and the flexible DC converter 4 can provide reactive power, thereby eliminating the need for reactive power compensation equipment to maintain power balance and saving investment in reactive power compensation equipment.

[0080] Fourthly, in the hydrogen production system of this application, in the event of a fault or voltage oscillation within the new energy AC power grid 5, the flexible DC converter 4 corresponding to the faulty new energy AC power grid 5 can automatically adjust its output to prevent the fault current output by the faulty new energy AC power grid 5 from flowing into other parts of the power transmission network. The remaining normal new energy AC power grid 5, DC transmission unit 2, DC energy storage unit 3, and hydrogen production unit 1 can operate normally without being affected, thereby improving the stability and reliability of the hydrogen production system and also improving the hydrogen production efficiency of hydrogen production unit 1.

[0081] Fifthly, because the flexible DC converter 4 has the characteristic of adjusting the magnitude and direction of the output current, it can offset the fault current in the AC transmission network. Therefore, it eliminates the need for relay protection devices in the AC transmission network, thus solving the problem of difficult relay protection setting in existing AC off-grid hydrogen production systems.

[0082] Sixthly, the flexible DC converter 4 used in this application embodiment not only possesses the characteristics of a conventional rectifier that converts AC to DC, but also allows for adjustment of the output DC voltage during the conversion process. Therefore, compared to existing AC / DC new energy hydrogen production systems, the hydrogen production system in this application embodiment does not require a step-up transformer, thus saving on the investment in step-up transformers.

[0083] According to some embodiments, refer to Figure 2 The DC transmission unit 2 may specifically include at least one sending-end bus 21, at least one DC line 22, and receiving-end bus 23.

[0084] According to the example embodiment, refer to Figure 1 and Figure 2 Each flexible DC converter 4 corresponds to only one sending-end bus 21 and only one DC line 22. The sending-end bus 21 is connected to the corresponding flexible DC converter 4 and receives the sending-end DC power output from the corresponding flexible DC converter 4. The sending-end bus 21 is connected to one end of the DC line 22 to transmit the sending-end DC power using the DC line 22.

[0085] The other end of each DC line 22 is connected to the receiving bus 23. The receiving bus 23 receives the sending DC power transmitted by each DC line 22 and collects the received sending DC power to obtain receiving high-voltage DC power. The hydrogen production unit 1 is connected to the receiving bus 23, receives the receiving high-voltage DC power, and uses the receiving high-voltage DC power to produce hydrogen.

[0086] For example, refer to Figure 2The hydrogen production system includes a first flexible DC converter, a second flexible DC converter, a first sending-end bus, a second sending-end bus, a first DC line, a second DC line, a receiving-end bus 23, and a hydrogen production unit 1. The first flexible DC converter is connected to the first sending-end bus. The first sending-end bus is connected to one end of the first DC line, and the other end of the first DC line is connected to the receiving-end bus 23. The second flexible DC converter is connected to the second sending-end bus. The second sending-end bus is connected to one end of the second DC line, and the other end of the second DC line is connected to the receiving-end bus 23.

[0087] The receiving-end bus 23 is also connected to the hydrogen production unit 1 to collect the sending-end DC power transmitted by the first DC line and the sending-end DC power transmitted by the second DC line to obtain receiving-end high-voltage DC power, and then transmit the receiving-end high-voltage DC power to the hydrogen production unit 1.

[0088] According to some embodiments, refer to Figure 2 The DC transmission unit 2 also includes at least one DC circuit breaker 24. The DC circuit breaker 24 is installed on the DC line 22 and disconnects to interrupt the fault current in the event of a fault in the DC line 22.

[0089] Optionally, the DC circuit breaker 24 may be any one of a diode cascade circuit, a mechanical circuit breaker, a hybrid DC circuit breaker 24, and a solid-state DC circuit breaker 24, without any limitation.

[0090] The DC circuit breaker 24 can interrupt fault current in the DC transmission network and clear faults quickly, within milliseconds, which helps reduce the impact of faults on the hydrogen production system and thus improves the stability and reliability of the hydrogen production system.

[0091] According to some embodiments, refer to Figure 3 In one possible implementation, the DC energy storage unit 3 may specifically include a first energy storage device 31.

[0092] The first energy storage device 31 is connected to the receiving bus 23 and charges and discharges according to the relative magnitude of the voltage of the receiving bus 23 and a preset standard voltage, so that the voltage of the receiving bus 23 is within the preset standard voltage range. For example, when the voltage of the receiving bus 23 is higher than the preset standard voltage, the first energy storage device 31 starts charging; when the voltage of the receiving bus 23 is lower than the preset standard voltage, the first energy storage device 31 starts discharging, so that the voltage of the receiving bus 23 is within the preset standard voltage range to maintain stability.

[0093] In this embodiment of the application, the voltage of the receiving bus 23 is regulated by the first energy storage device 31, so that the voltage of the entire DC transmission network can be kept stable.

[0094] According to some embodiments, refer toFigure 4 In another possible implementation, the DC energy storage unit 3 may specifically include at least one second energy storage device 32.

[0095] According to the example embodiment, one sending-end bus 21 corresponds to one second energy storage device 32. The second energy storage device 32 is connected to the corresponding sending-end bus 21 and charges and discharges according to the relative magnitude of the voltage of the sending-end bus 21 and a preset standard voltage, so that the voltage of the sending-end bus 21 is within the preset standard voltage range.

[0096] For example, in the case where the hydrogen production system includes two sending-end buses 21, the hydrogen production system includes two second energy storage devices 32, each of which is connected to its corresponding sending-end bus 21. When the voltage of the corresponding sending-end bus 21 is greater than a preset standard voltage, the second energy storage device 32 begins to charge, thereby reducing the voltage of the sending-end bus 21; when the voltage of the corresponding sending-end bus 21 is lower than the preset standard voltage, it begins to discharge, thereby increasing the voltage of the sending-end bus 21.

[0097] In this embodiment, the voltage of each sending bus 21 is adjusted by the second energy storage device 32, which helps to maintain the voltage stability of the entire DC transmission network.

[0098] According to some embodiments, refer to Figure 5 In another possible implementation, the DC energy storage unit 3 may specifically include a first energy storage device 31 and at least one second energy storage device 32.

[0099] According to the example embodiment, the first energy storage device 31 is connected to the receiving end bus 23, and each second energy storage device 32 is connected to its corresponding sending end bus 21.

[0100] The voltage of the receiving bus 23 is adjusted by the first energy storage device 31, and the voltage of the sending bus 21 is adjusted by the second energy storage device 32, so that the voltage of the entire DC transmission network remains stable.

[0101] Optionally, the first energy storage device 31 and the second energy storage device 32 may specifically be high-voltage direct-connected DC energy storage devices. The high-voltage direct-connected DC energy storage device may specifically include multiple energy storage sub-modules connected in series. The energy storage sub-modules may specifically include energy storage elements, converter valves, reactors, starting circuits, and switching equipment, etc.

[0102] According to some embodiments, the first energy storage device 31 and the second energy storage device 32 may further include a step-down transformer and a low-voltage DC energy storage device. For example, for the first energy storage device 31, the primary side of the step-down transformer is connected to the receiving-end bus 23, and the secondary side is connected to the low-voltage DC energy storage device.

[0103] According to some embodiments, refer to Figure 2 The hydrogen production unit 1 in this embodiment may specifically include a high-voltage DC transformer 11, a low-voltage DC bus 12, at least one low-voltage DC transformer 13, and at least one electrolyzer 14. The low-voltage DC transformer 13 corresponds one-to-one with the electrolyzer 14. For example, if the hydrogen production unit 1 has five electrolyzers 14, then the hydrogen production unit 1 includes five low-voltage DC transformers 13.

[0104] The primary side of the high-voltage DC transformer 11 is connected to the receiving-end bus 23, and the secondary side is connected to the low-voltage DC bus 12. This allows the high-voltage DC power received from the receiving-end bus 23 to be stepped down in one stage to obtain the low-voltage DC power, which is then output to the low-voltage DC bus 12.

[0105] The primary side of each low-voltage DC transformer 13 is connected to the low-voltage DC bus 12, and the secondary side is connected to the corresponding electrolyzer 14. The low-voltage DC transformer 13 performs a two-stage step-down process on the low-voltage DC power received from the low-voltage DC bus 12 to obtain hydrogen-producing DC power, which is then output to the electrolyzer 14. The electrolyzer 14 can then use the power provided by the low-voltage DC transformer 13 to electrolyze and produce hydrogen.

[0106] In existing AC / DC off-grid new energy hydrogen production systems, the DC power transmitted through DC line 22 is directly fed into low-voltage DC transformer 13, which reduces the voltage of the DC power to the hydrogen production voltage. The resulting hydrogen production voltage is then used in electrolyzer 14 to produce hydrogen.

[0107] In the off-grid renewable energy hydrogen production system of this embodiment, the DC power transmitted through DC line 22 first undergoes a first-stage voltage reduction process via high-voltage DC transformer 11 to lower the DC power amplitude from high voltage to a level acceptable to the hydrogen production plant. The DC power after this first-stage voltage reduction then undergoes a second-stage voltage reduction process via low-voltage DC transformer 13 to obtain the hydrogen production voltage. This two-stage voltage reduction method allows the DC power transmitted through DC line 22 to be more easily input to the hydrogen production plant.

[0108] Optionally, the high-voltage DC transformer 11 can be an isolated unidirectional DC transformer or an isolated bidirectional transformer.

[0109] Optionally, the high-voltage DC transformer 11 may further include multiple transformer modules, with the high-voltage side of each transformer module connected in series and the low-voltage side connected in parallel. The connection between the transformer modules of the high-voltage DC transformer 11 can adopt an active bridge or a full-bridge LLC resonant topology, which is not limited here.

[0110] According to some embodiments, refer toFigure 2 The hydrogen production unit 1 may further include a hydrogen production utility load 15. For example, the hydrogen production utility load 15 may include loads such as lighting, air conditioning, and other industrial equipment power supplies.

[0111] The power supply for the hydrogen production utility load 15 can also be provided by the new energy AC power grid 5. The hydrogen production utility load 15 is connected to the low-voltage DC bus 12 and receives the receiving-end low-voltage DC power provided by the low-voltage DC bus 12. That is, the power supply for the hydrogen production utility load 15 is provided by the low-voltage DC bus 12.

[0112] Optionally, the electrolyzer 14 may specifically include an alkaline electrolyzer, a proton exchange membrane electrolyzer, an anion exchange membrane electrolyzer, and a solid oxide electrolyzer, without limitation.

[0113] According to some embodiments, the voltage level of the receiving-end bus 23 can be greater than or equal to 10KV. The voltage level of the low-voltage DC bus 12 can be less than or equal to 2KV, so that the electrical energy of the low-voltage DC bus 12 can be directly used to power the decommissioning tank 14, saving substation costs.

[0114] According to some embodiments, the off-grid renewable energy hydrogen production system with AC / DC combined grid also includes an energy controller.

[0115] The energy controller is connected to the new energy AC power grid 5, the hydrogen production unit 1, and the DC energy storage unit 3. The energy controller controls the power generation of at least one new energy AC power grid 5 and the hydrogen production power of the hydrogen production unit 1 based on the current maximum total power generation (P0), the maximum hydrogen production power (P2), and the current maximum rechargeable power (P1).

[0116] According to the example embodiment, the current maximum total power generation P0 is the sum of the maximum power generation of each new energy AC power grid 5 included in the hydrogen production system.

[0117] For example, the hydrogen production system includes a first new energy AC power grid and a second new energy AC power grid, which currently have a maximum total power output of 10MW and 12MW respectively, meaning that the first new energy AC power grid 5 can generate a maximum of 10MW of electricity. The current maximum total power output P0 is 22MW.

[0118] According to the example embodiment, the maximum hydrogen production power P2 is the maximum electrical power that hydrogen production unit 1 can use to produce hydrogen.

[0119] According to the example embodiment, the current maximum rechargeable power P1 is the maximum electrical power that the DC energy storage unit 3 can charge. This current maximum rechargeable power P1 reflects the rechargeability of the DC energy storage unit 3. The larger the current maximum rechargeable power P1, the higher the rechargeability of the DC energy storage unit 3. For example, if the DC energy storage unit 3 has stored sufficient electrical energy and cannot continue to be charged, the current maximum rechargeable power P1 is 0.

[0120] According to the example embodiment, the energy controller can coordinate and control the hydrogen production power of the hydrogen production unit 1 and the power generation power of the new energy AC power grid 5 based on the current maximum total power generation P0, the current maximum rechargeable power P1 and the maximum hydrogen production power P2, thereby coordinating and controlling the power transmission of the hydrogen production system.

[0121] According to some embodiments, the energy controller can specifically control the hydrogen production unit 1 to produce hydrogen at the maximum hydrogen production power P2 when the current maximum total power generation P0, the maximum hydrogen production power P2, and the current maximum rechargeable power P1 meet the first power condition.

[0122] According to the example embodiment, the first power condition includes the current maximum power generation P0 being greater than the sum of the maximum hydrogen production power P2 and the current maximum rechargeable power P1 (that is, P0>P1+P2).

[0123] According to the example embodiment, when P0 > P1 + P2, the electrical energy provided by the current new energy AC power grid 5 can satisfy the hydrogen production unit 1's hydrogen production at maximum power, but will also exceed the electrical energy that the DC energy storage unit 3 can hold. Therefore, in this case, the energy controller can control the hydrogen production unit 1 to produce hydrogen at maximum power.

[0124] Furthermore, when P0 > P1 + P2, the energy controller can also determine the first power generation power in real time based on the current maximum rechargeable power P1 and the maximum hydrogen production power P2, and control at least one new energy AC power grid 5 to generate electricity at the first power generation power.

[0125] According to some embodiments, the first power generation can specifically be the sum of the current maximum rechargeable power P1 and the maximum hydrogen production power P2.

[0126] In this configuration, the power output of the new energy AC power grid 5 is P1+P2. The hydrogen production unit 1 produces hydrogen at its maximum power output P2, and the DC energy storage unit 3 charges at its current maximum rechargeable power output P1. Under these conditions, the hydrogen production unit 1 can produce hydrogen at its highest efficiency, and the DC energy storage unit 3 can charge at its maximum power output in real time until fully charged, thus maximizing the utilization of renewable energy for power generation.

[0127] According to some embodiments, the first power generation power can also be less than the sum of the current maximum rechargeable power P1 and the maximum hydrogen production power P2, so as to leave a certain margin for the energy storage of the DC energy storage unit 3, and reduce the probability of the situation that the DC energy storage unit 3 is damaged due to the over-full stored electric energy in the DC energy storage unit 3.

[0128] According to some embodiments, when the current maximum total power generation P0, the maximum hydrogen production power P2, and the current maximum rechargeable power P1 satisfy the second power condition, the energy controller controls at least one new energy AC power generation subnet 5 to generate power at the maximum total power generation. And the energy controller controls the hydrogen production unit 1 to produce hydrogen at the maximum hydrogen production power P2.

[0129] Among them, the second power condition includes: the current maximum total power generation P0 is greater than the maximum hydrogen production power P2, and the current maximum total power generation P0 is less than the sum of the maximum hydrogen production power P2 and the current maximum rechargeable power P1, and the current maximum rechargeable power P1 is greater than a preset value. That is, the second power condition is P2 < P0 < P1 + P2, and P1 > preset value.

[0130] According to an exemplary embodiment, when P2 < P0 < P1 + P2 and P1 > preset value, the electric energy that the current new energy AC power generation subnet 5 can provide at most can satisfy the hydrogen production unit 1 to produce hydrogen at the maximum hydrogen production power, and there is still remaining electric energy. And, the current DC energy storage unit 3 can continue to store electric energy, and the electric energy that the DC energy storage unit 3 can store is greater than the remaining electric energy.

[0131] Therefore, when P2 < P0 < P1 + P2 and P1 > preset value, the new energy AC power generation subnet 5 is controlled to perform maximum power tracking control, that is, the new energy AC power generation subnet 5 generates power in real time at the maximum total power generation corresponding to the current moment. The hydrogen production unit 1 produces hydrogen at the maximum hydrogen production efficiency P0. The DC energy storage unit 3 stores the remaining electric energy of the new energy AC power generation subnet 5 locally.

[0132] The remaining electric energy is the difference between the total generated electric energy generated by the new energy AC power generation subnet 5 and the hydrogen production electric energy consumed by the hydrogen production unit 1 for hydrogen production.

[0133] According to some embodiments, when the current maximum total power generation P0, the maximum hydrogen production power P2, and the current maximum rechargeable power P1 satisfy the third power condition, the energy controller controls the hydrogen production unit 1 to produce hydrogen at the maximum hydrogen production power P2; and controls the total power generation of at least one new energy AC power generation subnet 5 not to be greater than the maximum hydrogen production power P2.

[0134] Among them, the third power condition includes: the current maximum total power generation P0 is greater than the maximum hydrogen production power P2, and the current maximum total power generation P0 is less than the sum of the maximum hydrogen production power P2 and the current maximum rechargeable power P1, and the current maximum rechargeable power P1 is not greater than a preset value. That is, the third power condition is P2 < P0 < P1 + P2, and P1 ≤ preset value.

[0135] According to the exemplary embodiment, when P2 < P0 < P1 + P2 and P1 ≤ preset value, the electric energy that the current new energy AC power generation subnet 5 can provide at most can satisfy the hydrogen production unit 1 to produce hydrogen at the maximum hydrogen production power, and there is still remaining electric energy. And, the current DC energy storage unit 3 cannot continue to store electric energy.

[0136] Therefore, in this case, the energy controller controls the hydrogen production unit 1 to produce hydrogen at the maximum hydrogen production power P2 to ensure efficient hydrogen production.

[0137] And, in this case, the energy controller can also control the total power generation of the new energy AC power generation subnet 5 to be less than the maximum hydrogen production power P2, or equal to the maximum hydrogen production power P2, so as to reduce the probability of wasting resources caused by generating excess electric energy that cannot be stored.

[0138] It should be noted that for the case where the energy controller controls the total power generation of the new energy AC power generation subnet 5 to be less than the maximum hydrogen production power P2, part of the electric energy used by the hydrogen production unit 1 to produce hydrogen comes from the new energy AC power generation subnet 5, and the remaining electric energy that the new energy AC power generation subnet 5 cannot provide is provided by the discharge of the DC energy storage unit 3.

[0139] It should be noted that the preset value can be set by itself according to needs. For example, the preset value can be set to 0, and the current maximum rechargeable power P1 is 0, which means that the electric energy storage of the DC energy storage unit 3 is full and cannot continue to store electric energy. For example, the preset value can also be set to 2, and the current maximum rechargeable power P1 less than or equal to 2 means that the DC energy storage unit 3 stores more electric energy and is about to be full or already full. In this case, the DC energy storage unit 3 can no longer continue to store electric energy.

[0140] According to some embodiments, when the current maximum total power generation P0 is less than the maximum hydrogen production power P2, the electric energy that the new energy AC power generation subnet 5 can provide cannot support the hydrogen production unit 1 to produce hydrogen at the maximum hydrogen production power.

[0141] Therefore, when P0 < P2, the energy controller controls each new energy power generation unit 54 of the new energy AC power generation subnet 5 to perform in-situ maximum power tracking control. That is, the new energy AC power generation subnet 5 generates electricity in real time at the maximum power that can be generated.

[0142] Furthermore, the energy controller determines the current charging power of the DC energy storage unit 3 in real time, and calculates the difference between the current maximum total power generation P0 and the current charging power to obtain the current hydrogen production power. The energy controller controls the hydrogen production unit 1 to produce hydrogen at the current hydrogen production power.

[0143] According to the example embodiment, when the DC energy storage unit 3 is in a charging state, the current charging power is a positive number. When the DC energy storage unit 3 is in a discharging state, the current charging power is a negative number.

[0144] According to some embodiments, the energy controller determines the current charging power of the DC energy storage unit 3 in a specific way, including: determining the current charging power based on the current energy stored in the DC energy storage unit 3.

[0145] For example, when the current energy storage of DC energy storage unit 3 is sufficient, DC energy storage unit 3 can discharge appropriately. When DC energy storage unit 3 discharges, the current charging power determined by the energy controller is negative. The energy controller controls hydrogen production unit 1 to produce hydrogen at the current hydrogen production power (value equal to P0 + |current charging power|).

[0146] For example, when the current energy storage of DC energy storage unit 3 is insufficient, the current charging power of DC energy storage unit 3 can be 0, and the current hydrogen production power of hydrogen production unit 1 is P0. The energy controller controls hydrogen production unit 1 to produce hydrogen at the current hydrogen production power (value equal to P0).

[0147] For example, when the current energy storage of DC energy storage unit 3 is insufficient and the hydrogen production demand of hydrogen production unit 1 is low, DC energy storage unit 3 can also be appropriately charged. In this case, the current charging power determined by the energy controller is a positive number, and the energy controller can control hydrogen production unit 1 to produce hydrogen at the current hydrogen production power (the value is equal to P0 - |current charging power|).

[0148] According to some embodiments, the energy controller controls the hydrogen production power of the hydrogen production unit 1 and the power generation power of the new energy AC power grid 5 in a manner that may specifically include: the energy controller sending corresponding power commands to the hydrogen production unit 1 and the new energy AC power grid 5 so that the hydrogen production unit 1 produces hydrogen at the corresponding hydrogen production power and the new energy AC power grid 5 generates electricity at the corresponding power generation power.

[0149] It should be clearly understood that this application describes how specific examples are formed and used, but this application is not limited to any details of these examples. Rather, based on the teachings of the disclosure of this application, these principles can be applied to many other embodiments.

[0150] According to one aspect of this application, a control method for a hydrogen production system is provided. This control method is applied to an off-grid new energy hydrogen production system with AC / DC combined grid connections.

[0151] Reference Figure 1 This off-grid renewable energy hydrogen production system, which combines AC and DC power generation, includes a hydrogen production unit 1, a DC transmission unit 2, a DC energy storage unit 3, at least one flexible DC converter 4, and at least one renewable AC power grid 5. The renewable AC power grid 5 generates AC power; the flexible DC converter 4 is connected to the renewable AC power grid 5 to convert the AC power into DC power at the sending end. The DC transmission unit 2 is connected to at least one flexible DC converter 4 to transmit the DC power at the sending end. The hydrogen production unit 1 is connected to the DC transmission unit 2, receives the electrical energy transmitted by the DC transmission unit 2, and produces hydrogen. The DC energy storage unit 3 is connected to the DC transmission unit 2 and adjusts the transmission voltage of the DC transmission unit 2 through charging and discharging to keep the transmission voltage of the DC transmission unit 2 within a preset standard voltage range.

[0152] The flexible DC converter 4 adopts a grid-type control strategy to construct the voltage and frequency of at least one new energy AC power grid 5, so that the voltage and frequency remain stable.

[0153] Reference Figure 6 The control method may specifically include step S601.

[0154] In step S601, based on the current maximum total power generation and maximum hydrogen production capacity, at least one new energy AC power grid 5 and hydrogen production unit 1 are controlled to adjust the power generation capacity of at least one new energy AC power grid 5 and the hydrogen production capacity of hydrogen production unit 1.

[0155] Among them, the current maximum total power generation is the sum of the maximum power generation that at least one new energy AC power grid 5 can currently generate; the maximum hydrogen production power is the maximum hydrogen production power that hydrogen production unit 1 can achieve.

[0156] According to some embodiments, refer to Figure 7 Step S601 may include steps Sa1 and Sa2.

[0157] In step Sa1, when the current maximum total power generation, maximum hydrogen production power, and current maximum rechargeable power meet the first power condition, the hydrogen production unit 1 is controlled to produce hydrogen at the maximum hydrogen production power.

[0158] In step Sa2, the first power generation capacity is determined based on the current maximum rechargeable power and the maximum hydrogen production capacity, and at least one new energy AC power grid 5 is controlled to generate electricity at the first power generation capacity.

[0159] The first power condition includes the condition that the current maximum power generation capacity is greater than the sum of the maximum hydrogen production capacity and the current maximum rechargeable capacity.

[0160] According to some embodiments, refer to Figure 8 Step S601 may also include steps Sb1 and Sb2.

[0161] In step Sb1, when the current maximum total power generation, maximum hydrogen production, and current maximum rechargeable power meet the second power condition, at least one new energy AC power grid 5 is controlled to generate electricity at the maximum total power generation.

[0162] In step Sb2, the hydrogen production unit 1 is controlled to produce hydrogen at its maximum hydrogen production power.

[0163] The second power condition includes: the current maximum total power that can be generated is greater than the maximum hydrogen production power, and the current maximum total power that can be generated is less than the sum of the maximum hydrogen production power and the current maximum rechargeable power, and the current maximum rechargeable power is greater than a preset value.

[0164] According to some embodiments, refer to Figure 9 Step S601 may also include steps Sc1 and Sc2.

[0165] In step Sc1, if the current maximum total power generation, maximum hydrogen production power, and current maximum rechargeable power meet the third power condition, the hydrogen production unit 1 is controlled to produce hydrogen at the maximum hydrogen production power.

[0166] In step Sc2, the total power generation of at least one new energy AC power grid 5 is controlled to be no greater than the maximum hydrogen production power.

[0167] The third power condition includes: the current maximum total power that can be generated is greater than the maximum hydrogen production power, and the current maximum total power that can be generated is less than the sum of the maximum hydrogen production power and the current maximum rechargeable power, and the current maximum rechargeable power is not greater than a preset value.

[0168] Those skilled in the art will understand that all or part of the steps of the above embodiments are implemented as a computer program executed by a CPU. When the computer program is executed by the CPU, it performs the functions defined by the methods provided in this application.

[0169] Finally, it should be noted that the above are merely preferred embodiments of this application and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions of the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An off-grid renewable energy hydrogen production system with AC / DC combined grid configuration, characterized in that, The system includes: At least one new energy AC power grid generates AC power; At least one flexible DC converter is connected to the new energy AC power grid to convert the AC power into DC power at the sending end. A DC transmission unit is connected to the at least one flexible DC converter to transmit the sending-end DC power; A hydrogen production unit is connected to the DC power transmission unit, receives electrical energy transmitted by the DC power transmission unit, and produces hydrogen. A DC energy storage unit is connected to the DC transmission unit and adopts a constant voltage control strategy. Based on the relative magnitude of the transmission voltage of the DC transmission unit and the preset standard voltage, the transmission voltage of the DC transmission unit is adjusted by charging and discharging to keep the transmission voltage of the DC transmission unit within the preset standard voltage range. The flexible DC converter adopts a grid-type control strategy to construct the voltage and frequency of the new energy AC power grid, so that the voltage and frequency are kept stable. This includes: when the system is disturbed, adjusting the output parameters of the flexible DC converter to provide voltage and frequency support for the system. The DC transmission unit includes: At least one sending-end bus is connected to the flexible DC converter and receives the sending-end DC power. At least one DC line is connected to the sending-end bus to receive and transmit sending-end DC power from the sending-end bus. The receiving-end busbar is connected to the at least one DC line and the hydrogen production unit. It receives and collects the sending-end DC power transmitted by the at least one DC line to obtain receiving-end high-voltage DC power, and then transmits the receiving-end high-voltage DC power to the hydrogen production unit. The DC transmission unit further includes at least one DC circuit breaker, which is installed on the DC line and disconnects to cut off the fault current in the event of a fault in the DC line. The DC energy storage unit includes a first energy storage device and / or at least one second energy storage device; The first energy storage device is connected to the receiving end bus and charges and discharges according to the relative magnitude of the voltage of the receiving end bus and the preset standard voltage, so that the voltage of the receiving end bus is within the preset standard voltage range. The second energy storage device is connected to the sending-end bus and charges and discharges according to the relative magnitude of the voltage of the sending-end bus and the preset standard voltage, so that the voltage of the sending-end bus is within the preset standard voltage range. The system also includes: An energy controller controls the power generation of the at least one new energy AC power grid and the hydrogen production power of the hydrogen production unit based on the current maximum total power generation, the maximum hydrogen production power, and the current maximum rechargeable power of the DC energy storage unit. Wherein, the current maximum total power generation is the sum of the maximum power generation that the at least one new energy AC power grid can currently generate; the maximum hydrogen production power is the maximum hydrogen production power that the hydrogen production unit can achieve; Wherein, when the maximum total power that can be generated is less than the maximum hydrogen production power, the energy controller controls each new energy power generation unit of the new energy AC power grid to perform local maximum power tracking control, so as to generate electricity in real time at the maximum power that can be generated. The energy controller determines the current charging power of the DC energy storage unit in real time, calculates the difference between the maximum total power that can be generated and the current charging power, obtains the current hydrogen production power, and produces hydrogen using the current hydrogen production power; The current charging power is determined based on the current energy stored in the DC energy storage unit.

2. The system according to claim 1, characterized in that, The hydrogen production unit includes: A high-voltage DC transformer is connected to the receiving-end bus and the hydrogen production unit to step down the high-voltage DC power at the receiving end to obtain low-voltage DC power at the receiving end. A low-voltage DC bus is connected to the DC transmission unit to receive and collect the receiving-end low-voltage DC power transmitted by the DC transmission unit. At least one low-voltage DC transformer is connected to the low-voltage DC bus to step down the low-voltage DC power at the receiving end to obtain hydrogen-producing DC power. At least one electrolyzer is connected to the low-voltage DC transformer to receive the hydrogen-producing DC power and to use the hydrogen-producing DC power to electrolyze and produce hydrogen. The hydrogen production utility load is connected to the low-voltage DC bus and receives the receiving-end low-voltage DC power provided by the low-voltage DC bus.

3. The system according to claim 1, characterized in that: When the current maximum total power generation, the maximum hydrogen production power, and the current maximum rechargeable power meet the first power condition, the energy controller controls the hydrogen production unit to produce hydrogen at the maximum hydrogen production power. The energy controller determines the first power generation capacity based on the current maximum rechargeable power and the maximum hydrogen production capacity, and controls the at least one new energy AC power grid to generate electricity at the first power generation capacity. The first power condition includes the current maximum power generation being greater than the sum of the maximum hydrogen production power and the current maximum rechargeable power.

4. The system according to claim 1, characterized in that: When the current maximum total power generation, the maximum hydrogen production power, and the current maximum rechargeable power meet the second power condition, the energy controller controls the at least one new energy AC power grid to generate electricity at the maximum total power generation. The energy controller controls the hydrogen production unit to produce hydrogen at the maximum hydrogen production power. The second power condition includes: the current maximum total power that can be generated is greater than the maximum hydrogen production power, and the current maximum total power that can be generated is less than the sum of the maximum hydrogen production power and the current maximum rechargeable power, and the current maximum rechargeable power is greater than a preset value.

5. The system according to claim 1, characterized in that: When the current maximum total power generation, the maximum hydrogen production power, and the current maximum rechargeable power meet the third power condition, the energy controller controls the hydrogen production unit to produce hydrogen at the maximum hydrogen production power. The energy controller ensures that the total power generation of the at least one new energy AC power grid is not greater than the maximum hydrogen production power. The third power condition includes: the current maximum total power that can be generated is greater than the maximum hydrogen production power, and the current maximum total power that can be generated is less than the sum of the maximum hydrogen production power and the current maximum rechargeable power, and the current maximum rechargeable power is not greater than a preset value.

6. A control method for a hydrogen production system, characterized in that, The method is applied to an off-grid renewable energy hydrogen production system with AC / DC combined grids. The system includes a DC transmission unit, a hydrogen production unit, a DC energy storage unit, at least one renewable AC power grid, and at least one flexible DC converter. The renewable AC power grid generates AC power. The flexible DC converter is connected to the renewable AC power grid to convert the AC power into DC power. The DC transmission unit is connected to the at least one flexible DC converter to transmit the DC power. The hydrogen production unit is connected to the DC transmission unit, receives the electrical energy transmitted by the DC transmission unit, and produces hydrogen. The DC energy storage unit is connected to the DC transmission unit and employs a constant voltage control strategy. Based on the relative magnitude of the transmission voltage of the DC transmission unit and a preset standard voltage, the transmission voltage of the DC transmission unit is adjusted by charging or discharging to keep the transmission voltage of the DC transmission unit within the preset standard voltage range. The flexible DC converter adopts a grid-type control strategy to construct the voltage and frequency of the at least one new energy AC power grid, so that the voltage and frequency are kept stable. This includes: when the system is disturbed, adjusting the output parameters of the flexible DC converter to provide voltage and frequency support for the system. The DC transmission unit includes at least one sending-end bus, at least one DC line, and a receiving-end bus. The sending-end bus is connected to the flexible DC converter and receives the sending-end DC power. The DC line is connected to the sending-end bus and receives and transmits the sending-end DC power from the sending-end bus. The receiving-end bus is connected to the at least one DC line and is connected to the hydrogen production unit. It receives and collects the sending-end DC power transmitted by the at least one DC line to obtain receiving-end high-voltage DC power, and transmits the receiving-end high-voltage DC power to the hydrogen production unit. The DC transmission unit further includes at least one DC circuit breaker, which is installed on the DC line and disconnects to cut off the fault current in the event of a fault in the DC line; the DC energy storage unit includes a first energy storage device and / or at least one second energy storage device. The first energy storage device is connected to the receiving end bus and charges and discharges according to the relative magnitude of the voltage of the receiving end bus and the preset standard voltage, so that the voltage of the receiving end bus is within the preset standard voltage range. The second energy storage device is connected to the sending-end bus and charges and discharges according to the relative magnitude of the voltage of the sending-end bus and the preset standard voltage, so that the voltage of the sending-end bus is within the preset standard voltage range. The control method includes: Based on the current maximum total power generation and maximum hydrogen production capacity, control the at least one new energy AC power grid and the hydrogen production unit to adjust the power generation capacity of the at least one new energy AC power grid and the hydrogen production capacity of the hydrogen production unit. Wherein, the current maximum total power that can be generated is the sum of the maximum power that the at least one new energy AC power grid can currently generate; The maximum hydrogen production power is the maximum hydrogen production power that the hydrogen production unit can achieve; The step of controlling the at least one new energy AC power grid and the hydrogen production unit based on the current maximum total power generation capacity and the maximum hydrogen production capacity, so as to adjust the power generation capacity of the at least one new energy AC power grid and the hydrogen production capacity of the hydrogen production unit, includes: When the maximum total power that can be generated is less than the maximum hydrogen production power, the energy controller controls each new energy power generation unit of the new energy AC power grid to perform local maximum power tracking control, so as to generate electricity in real time at the maximum power that can be generated. The energy controller determines the current charging power of the DC energy storage unit in real time, calculates the difference between the maximum total power that can be generated and the current charging power to obtain the current hydrogen production power, and produces hydrogen using the current hydrogen production power. Based on the current energy storage of the DC energy storage unit, the current charging power is determined.

7. The method according to claim 6, wherein controlling at least one new energy AC power grid and the hydrogen production unit based on the current maximum total power generation capacity and the maximum hydrogen production capacity comprises: When the current maximum total power generation, the maximum hydrogen production power, and the current maximum rechargeable power meet the first power condition, the hydrogen production unit is controlled to produce hydrogen at the maximum hydrogen production power. Based on the current maximum rechargeable power and the maximum hydrogen production power, a first power generation power is determined, and the at least one new energy AC power grid is controlled to generate electricity at the first power generation power. The first power condition includes the current maximum power generation being greater than the sum of the maximum hydrogen production power and the current maximum rechargeable power.

8. The method according to claim 6, characterized in that, The step of controlling at least one new energy AC power grid and the hydrogen production unit based on the current maximum total power generation capacity and the maximum hydrogen production capacity includes: When the current maximum total power generation, the maximum hydrogen production power, and the current maximum rechargeable power meet the second power condition, the at least one new energy AC power grid is controlled to generate electricity at the maximum total power generation. The hydrogen production unit is controlled to produce hydrogen at the maximum hydrogen production power. The second power condition includes: the current maximum total power that can be generated is greater than the maximum hydrogen production power, and the current maximum total power that can be generated is less than the sum of the maximum hydrogen production power and the current maximum rechargeable power, and the current maximum rechargeable power is greater than a preset value.

9. The method according to claim 6, characterized in that, The step of controlling at least one new energy AC power grid and the hydrogen production unit based on the current maximum total power generation capacity and the maximum hydrogen production capacity includes: When the current maximum total power generation, the maximum hydrogen production power, and the current maximum rechargeable power meet the third power condition, the hydrogen production unit is controlled to produce hydrogen at the maximum hydrogen production power. The total power generation of the at least one new energy AC power grid shall not exceed the maximum hydrogen production power. The third power condition includes: the current maximum total power that can be generated is greater than the maximum hydrogen production power, and the current maximum total power that can be generated is less than the sum of the maximum hydrogen production power and the current maximum rechargeable power, and the current maximum rechargeable power is not greater than a preset value.

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