Renewable energy off-grid hydrogen production system based on high-capacity hydrogen production power supply

Abstract

A renewable energy source off-grid hydrogen production system based on a high-capacity hydrogen production power source is characterized in that the hydrogen production system adopts a direct current collection-direct current transmission-direct current hydrogen production topological structure, and a wind power part and a photovoltaic part are arranged in a wind and light equipment area; the wind power part converts the output of a wind turbine generator into direct current through alternating current, then is connected with a direct current transformer in the direct current transformer area for boosting, and then is connected with an input end direct current bus in the direct current line area; an outgoing line of the combiner box is connected with a direct-current transformer in the direct-current transformer area for boosting and then connected with an input end direct-current bus in the direct-current line area. A novel DC off-grid hydrogen production topological structure is provided, the capacity of a hydrogen production power supply is improved on the basis of an off-grid condition, and a new scheme with advantages in the aspects of electric energy quality, stability, reliability, transmission efficiency and the like is provided; in the topology, a control protection and black-start strategy is provided. And a relatively complete system scheme is formed.

Description

Technical Field

[0001] The present invention relates to the technical field of power system topology structure, and in particular to a renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power source. Background Art

[0002] Hydrogen energy is the best way to store renewable energy on a large scale and for a long period of time. The cost of hydrogen storage containers is 10 times lower than that of fixed energy storage batteries. The midstream transportation method is flexible and the downstream application frequency domain is wide. In the future, the proportion of new energy in the power system will further increase, presenting a "wind and solar-based, diversified and coordinated" supply and demand pattern. However, the volatility of new energy poses a great challenge to the stability of the power grid. Stable and periodic storage and regulation are urgently needed to achieve cross-seasonal and long-term power regulation. Off-grid hydrogen production is an effective means.

[0003] Photovoltaic solar panels output direct current, and the power supply demand of electrolyzers is also direct current. Therefore, large-scale new energy can be concentrated through direct current to reduce the conversion link, improve transmission efficiency and reduce costs compared with the AC concentration scheme. In addition, compared with the AC hydrogen production scheme, the direct current hydrogen production system has higher power quality and better stability; fast and reliable power regulation; low transmission loss and other advantages, and is considered to be a more promising topology.

[0004] The large-capacity of renewable energy power generation has led to an increase in the capacity of the converter, which requires the use of power devices with larger power levels, or the use of a multi-converter parallel topology to meet the requirements of high-power conversion. Among them, the use of a multi-converter parallel structure has flexible redundant control characteristics, which can effectively improve the reliability of the system. However, when the load is low, its efficiency is much lower than the efficiency under rated conditions, and a control strategy is needed to optimize and improve the overall efficiency of the parallel system. At present, the power of the multi-converter parallel structure is generally less than 10MW; when the power increases to 10MW, more parallel connections increase the complexity of the system, power sharing control becomes more difficult, and the overall operating efficiency improvement faces challenges. The applicability of the parallel solution needs to be studied.

[0005] Overall, DC off-grid hydrogen production technology has received widespread attention around the world, and various countries have conducted in-depth research and launched many demonstration projects, making some progress. However, there is still no precedent for large-scale projects that have been connected to the grid, and the technology still faces some challenges. Summary of the invention

[0006] The present invention provides a renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power supply, and constructs a topological structure of the renewable energy off-grid hydrogen production system in view of the application requirements of a large power adjustment range, fast response speed, and adaptability to the volatility and intermittency of renewable energy. A large-capacity renewable energy off-grid hydrogen production power supply is applied in the topology to meet the application requirements of large-scale scenarios.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: A renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power supply. The hydrogen production system adopts a topological structure of DC collection-DC transmission-DC hydrogen production, including a wind and solar equipment area, a DC transformer area, a DC line area and a hydrogen production area connected in sequence. The wind and solar equipment area is provided with a wind power part and a photovoltaic part. The wind power part converts the output of the wind turbine set into DC through AC and then sends it to the DC transformer in the DC transformer area for boosting and then sends it to the input DC bus in the DC line area. The photovoltaic part is connected to a junction box after the photovoltaic components are connected in series and parallel. The output line of the junction box is connected to the DC transformer in the DC transformer area for boosting and then sent to the input DC bus in the DC line area. The DC voltage is transmitted from the input DC bus to the output DC bus on one side of the hydrogen production area, and the output DC bus is supplied to the electrolyzer in the hydrogen production area for hydrogen production.

[0008] An energy storage device is connected to the DC busbar at the output end of the hydrogen production area.

[0009] The energy storage device mentioned above includes a bidirectional DC transformer connected to the DC bus at the output end, and an energy storage device connected to the bidirectional DC transformer.

[0010] The above-mentioned hydrogen production area includes a hydrogen production power supply connected to the DC bus at the output end. The hydrogen production power supply is DC / DC. The hydrogen production power supply is connected to multiple electrolyzers. The hydrogen production power supply reduces the DC bus voltage to the voltage required by the electrolyzer.

[0011] The above-mentioned wind power part includes 6 5MW AC wind turbines. The outputs of every two AC wind turbines are converted into DC through their respective wind power transformers and then connected to two 5MW step-up transformer modules in series. The two step-up transformer modules are connected in parallel on the low-voltage side and in series on the high-voltage side to form a 10MW DC transformer unit. The DC transformer outputs a voltage of ±10kV to the DC bus.

[0012] The photovoltaic part includes two 10MW photovoltaic systems. Each 10MW photovoltaic system is connected to three MPPT junction boxes by photovoltaic modules. The three MPPT junction boxes are connected to three IIOS structure step-up transformer modules. The three modules are connected in parallel on the low voltage side and in series on the high voltage side to form a 10MW step-up transformer. The output voltage of the whole machine is ±10kV to the DC bus. The total capacity of the step-up transformer is 10MW.

[0013] The control system of the above-mentioned hydrogen production system is divided into two levels, namely, a coordination control layer and a local control layer, according to the control scope and control function. The coordination control layer is the upper-level control, which determines that the DC collection system accepts power instructions, and sends control instructions and control reference values ​​to each device in the local control layer. At the same time, the control system realizes smooth switching between operating modes and coordinated processing when the AC system fails; the local control layer is the lower-level distributed control, which is controlled by each device such as the hydrogen production power supply, DC / DC transformer, i.e., DCT, MPPT junction box, etc. according to its own principles and characteristics.

[0014] The coordination control layer in the control system of the above-mentioned hydrogen production system is connected to the dispatching control layer. The dispatching control layer dispatches the energy flow of the source hydrogen storage equipment in the system according to the system flow distribution, generates the system operation mode instructions and their corresponding reference value instructions, and maintains the voltage stability and power balance of the whole system.

[0015] The protection system of the above-mentioned hydrogen production system is divided into a wind and solar equipment protection zone, a DC transformer protection zone, a DC line protection zone and a hydrogen production protection zone.

[0016] The above-mentioned protection system PSCAD simulation simulates and calculates the short-circuit current, and adopts a system protection device matched with a DC main network circuit breaker + a load side fuse. When the power outlet is short-circuited, the DC incoming line circuit breaker is instantaneously activated, and reverse current protection is provided to isolate the fault point from the DC main network. The DC transformer locks the pulse after a delay of 50ms and reduces the output to 0; when the ±10kV busbar is short-circuited, the DC incoming line circuit breaker is opened after a delay of 20ms to isolate the fault point; when the load side is short-circuited, the DC fuse is instantly blown to isolate the fault point.

[0017] The present invention provides a renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power supply, proposes a new DC off-grid hydrogen production topology structure, based on considerations and designs under off-grid conditions, and the stability meets the actual application needs; the hydrogen production power supply capacity is improved to meet the application needs under various working conditions and scenarios, more in line with the prospects for the development of large-scale projects, and adapted to the access of various mainstream and future development directions of electrolyzers on the market; the key technology of renewable energy off-grid hydrogen production is formed, and the above topology is replicable and scalable, providing a new solution with advantages in power quality, stability, reliability, transmission efficiency, etc. for large-scale off-grid hydrogen production projects such as the Shagohuang Base; in the above topology, control protection and black start strategies are proposed. A relatively complete system solution is formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Figure 1 Schematic diagram of the topological structure of the off-grid hydrogen production system of renewable energy of the present invention; Figure 2 This is a schematic diagram of the control system structure of the renewable energy off-grid hydrogen production system of the present invention; Figure 3 This is a schematic diagram of the protection system structure of the renewable energy off-grid hydrogen production system of the present invention; Figure 4 This is a schematic diagram of the AC collection-AC transmission-AC hydrogen production topology of a large-scale new energy off-grid hydrogen production system; Figure 5 This is a schematic diagram of the AC collection-DC transmission-AC hydrogen production topology of a large-scale new energy off-grid hydrogen production system; Figure 6 This is a schematic diagram of the AC collection-DC transmission-DC hydrogen production topology of a large-scale new energy off-grid hydrogen production system; Figure 7 Schematic diagram of DC collection-DC transmission-DC hydrogen production topology for large-scale new energy off-grid hydrogen production system Figure 8 It is a schematic diagram of series connection between DC transformers on the collection side; Fig. 9 It is a schematic diagram of parallel connection between DC transformers on the sink side; Fig.10 This is a schematic diagram of the hybrid connection between DC transformers on the sink side. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following content will systematically and completely describe the specific technical solutions of the present invention in combination with the drawings provided according to the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] like Figure 1 As shown in the figure, a renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power supply adopts a topological structure of DC collection-DC transmission-DC hydrogen production, including a wind and solar equipment area, a DC transformer area, a DC line area and a hydrogen production area connected in sequence. The wind and solar equipment area is provided with a wind power part and a photovoltaic part. The wind power part converts the output of the wind turbine set into DC through AC and then sends it to the DC transformer in the DC transformer area for boosting and then sends it to the input DC bus in the DC line area. The photovoltaic part is connected to the junction box after the photovoltaic components are connected in series and parallel. The outlet line of the junction box is connected to the DC transformer in the DC transformer area for boosting and then sent to the input DC bus in the DC line area. The DC voltage is transmitted from the input DC bus to the output DC bus on one side of the hydrogen production area, and the output DC bus is supplied to the electrolyzer in the hydrogen production area for hydrogen production.

[0021] An energy storage device is connected to the DC busbar at the output end of the hydrogen production area.

[0022] The energy storage device mentioned above includes a bidirectional DC transformer connected to the DC bus at the output end, and an energy storage device connected to the bidirectional DC transformer.

[0023] The above-mentioned hydrogen production area includes a hydrogen production power supply connected to the DC bus at the output end. The hydrogen production power supply is DC / DC. The hydrogen production power supply is connected to multiple electrolyzers. The hydrogen production power supply reduces the DC bus voltage to the voltage required by the electrolyzer.

[0024] The above-mentioned wind power part includes 6 5MW AC wind turbines. The outputs of every two AC wind turbines are converted into DC through their respective wind power transformers and then connected to two 5MW step-up transformer modules in series. The two step-up transformer modules are connected in parallel on the low-voltage side and in series on the high-voltage side to form a 10MW DC transformer unit. The DC transformer outputs a voltage of ±10kV to the DC bus.

[0025] The photovoltaic part includes two 10MW photovoltaic systems. Each 10MW photovoltaic system is connected to three MPPT junction boxes by photovoltaic modules. The three MPPT junction boxes are connected to three IIOS structure step-up transformer modules. The three modules are connected in parallel on the low voltage side and in series on the high voltage side to form a 10MW step-up transformer. The output voltage of the whole machine is ±10kV to the DC bus. The total capacity of the step-up transformer is 10MW.

[0026] like Figure 2 As shown in , the control system of the above-mentioned hydrogen production system is divided into two levels, the coordination control layer and the local control layer, according to the control scope and control function. The coordination control layer is the upper control layer, which determines that the DC collection system accepts power instructions, and sends control instructions and control reference values ​​to each device in the local control layer. At the same time, the control system realizes smooth switching between operating modes and coordinated processing when the AC system fails; the local control layer is the lower decentralized control layer, which is controlled by each device such as the hydrogen production power supply, DC / DC transformer, i.e. DCT, MPPT junction box, etc. according to its own principles and characteristics.

[0027] The coordination control layer in the control system of the above-mentioned hydrogen production system is connected to the dispatching control layer. The dispatching control layer dispatches the energy flow of the source hydrogen storage equipment in the system according to the system flow distribution, generates the system operation mode instructions and their corresponding reference value instructions, and maintains the voltage stability and power balance of the whole system.

[0028] like Figure 3 As shown in , the protection system of the above-mentioned hydrogen production system is divided into a wind and solar equipment protection zone, a DC transformer protection zone, a DC line protection zone and a hydrogen production protection zone.

[0029] The above-mentioned protection system PSCAD simulation simulates and calculates the short-circuit current, and adopts a system protection device matched with a DC main network circuit breaker + a load side fuse. When the power outlet is short-circuited, the DC incoming line circuit breaker is instantaneously activated, and reverse current protection is provided to isolate the fault point from the DC main network. The DC transformer locks the pulse after a delay of 50ms and reduces the output to 0; when the ±10kV busbar is short-circuited, the DC incoming line circuit breaker is opened after a delay of 20ms to isolate the fault point; when the load side is short-circuited, the DC fuse is instantly blown to isolate the fault point.

[0030] Example: 1. The DC off-grid hydrogen production system can avoid the risks of frequency instability, power angle instability, sub-supersynchronous oscillation and other safe and stable operation risks in the AC power grid because there are no frequency, phase and phase-locking problems. With fewer power conversion and collection links, the system efficiency can be improved by more than 2%; the control is flexible, and active and reactive power are independently controlled without the need to configure SVG; the voltage support capacity can be enhanced without the need to configure a phase regulator. Therefore, the DC off-grid hydrogen production system is more suitable for the application scenario of large-scale wind power off-grid hydrogen production.

[0031] The system is constructed through the topological structure of DC collection-DC transmission-DC hydrogen production, which makes the system have higher power quality and better stability; fast and reliable power regulation; low transmission loss; high new energy consumption rate, etc. The specific topology is shown in the attached figure.

[0032] For DC collection, a hybrid series-parallel boosting solution is adopted on the new energy side; the DC transformer of the wind turbine adopts 2*5MW modules in series, and the DC transformer of the photovoltaic uses 3*3.3MW modules in series; after boosting, each DCT is connected in parallel to the medium-voltage bus.

[0033] For DC transmission, this topology is intended for scenarios where hydrogen production stations and new energy stations are close to each other. Due to the short transmission distance, a voltage transmission level of ±10kV is adopted.

[0034] For direct current hydrogen production, the receiving end adopts a solution of centralized transformation and then dividing the windings into electrolyzers. The hydrogen production power supply selects a 20MW large-capacity device, and 7 ports are set on the export side, namely 10MW*1+5MW*1+1MW*5; for the access of electrolyzers of various specifications; the load side is equipped with electrolyzers according to the capacity of 20MW, which correspond to the hydrogen production power supply ports one by one, namely 1 10MW alkaline electrolyzer, 1 5MW alkaline electrolyzer, and 5 1MWPEM electrolyzers.

[0035] 2. On the DC bus, a high-voltage chain energy storage system is innovatively configured. The energy storage battery cluster is connected to the discrete half-bridge module DC port through an LC filter, and the other end is connected to the medium and high voltage DC grid by connecting the switch voltage port in series. In the grid-connected operation mode, the converter control level needs to include two control links, one is to control the current of the total port input / output current, and the other is to achieve battery SOC balance between modules, which is achieved by adjusting the duty cycle of the module. This further improves the reliability and robustness of the system. It also provides an interface for the self-use of DCT equipment.

[0036] 3. The hydrogen production power capacity is increased to 20MW level, and output ports of different capacities are configured at the outlet of the hydrogen production power supply to adapt to various mainstream 2000Nm³ / h (10MW) alkaline electrolyzers, 1000Nm³ / h (5MW) alkaline electrolyzers and 200Nm³ / h (1MW) PEM electrolyzers, so that electrolyzers of different types and capacities can be connected in parallel; on the one hand, the structure is simplified and the control system is simplified; on the other hand, the increase in the hydrogen production power capacity also provides a better foundation and support for the development of large-scale off-grid hydrogen production projects.

[0037] 4. Control architecture The control system solution is divided into two levels according to the control scope and control function, namely the coordination control layer and the local control layer. Among them: the coordination control layer is the upper control layer, which determines that the DC collection system accepts power instructions, including active and reactive instruction reference values, and sends control instructions and control reference values ​​to each key device in the local equipment control layer. At the same time, the control system realizes smooth switching between operating modes and coordinated processing when the AC system fails; the local equipment control layer is the lower decentralized control layer, which is controlled by each key device such as hydrogen power supply, DCT, MPPT according to its own principles and characteristics.

[0038] The dispatching control layer is located in the control center. It reasonably dispatches the energy flow of the source hydrogen storage equipment in the system according to the system flow distribution, generates the system operation mode instructions and their corresponding reference value instructions, maintains the voltage stability and power balance of the whole system, and ensures the long-term efficient and reliable operation of the off-grid hydrogen production system. The overall control architecture is as follows: Figure 2 shown.

[0039] Working mode and operation strategy of large-scale new energy off-grid hydrogen production system: (1) Energy storage in conjunction with total power input (hydrogen production) - the total power input is only used to supply hydrogen production in the electrolyzer. At this time, the total wind and solar power generation is less than the power demand of the hydrogen production device. The energy storage releases the stored power, and the electrolyzer power can be adjusted according to the wind and solar power generation and the energy storage power. (2) Wind and solar power only (hydrogen production) - the total wind and solar power generation only supplies hydrogen production in the electrolyzer. At this time, the total wind and solar power generation is less than the electricity demand of the hydrogen production device, and the remaining energy storage power is insufficient, so the ACB is disconnected, the energy storage is locked, and the electrolyzer power is adjusted according to the wind and solar power generation; (3) Only wind and solar power (hydrogen production + energy storage) - the total wind and solar power generation supplies electrolytic hydrogen production and energy storage. At this time, the total wind and solar power generation is greater than the electricity demand of the hydrogen production device, and the remaining energy storage capacity is sufficient, then the ACB is disconnected, the energy storage is charged, and all electrolyzers are put into use; (4) Wind and solar power only (hydrogen production) - the total wind and solar power generation only supplies hydrogen production in the electrolyzer. At this time, the total wind and solar power generation is greater than the electricity demand of the hydrogen production device, but the energy storage is full, so the ACB is disconnected, the energy storage is locked, and all electrolyzers are put into use; (5) Only wind and solar power (power storage) - the total wind and solar power generation only supplies energy storage power. At this time, the total wind and solar power generation cannot reach the starting power of the electrolyzer, so the ACB is disconnected, all electrolyzers are removed, and energy storage is charged; (6) Stop working - at this time, factors such as equipment failure, insufficient power supply, and economic considerations are considered.

[0040] 5. Protect system architecture According to the principles of protection area division and the protected objects in the system, the protection area of ​​the DC hydrogen production system is divided as shown in the figure; the entire system is divided into wind and solar equipment protection area, DC transformer protection area, DC line protection area, and hydrogen production protection area.

[0041] Based on PSCAD simulation, the short-circuit current is simulated and calculated. A system protection device matching the DC main network circuit breaker + load side fuse is used. When the power outlet is short-circuited, the DC incoming line circuit breaker is instantaneously activated, reverse current protection is provided, and the fault point is isolated from the DC main network. The DC transformer locks the pulse after a delay of 50ms and reduces the output to 0; when the ±10kV busbar is short-circuited, the DC incoming line circuit breaker is opened after a delay of 20ms to isolate the fault point; when the load side is short-circuited, the DC fuse is instantly blown to isolate the fault point.

[0042] 6. Start-Stop Strategy In order to achieve the purpose of restoring power supply to other equipment through the self-starting power supply after failure shutdown or power outage maintenance, the following black start strategy is set: (1) Configure 10MW / 20MWh of energy storage as the power source for black start. The energy storage first supplies power to the medium-voltage DC bus to restore the ±10kV bus voltage. (2) After the bus voltage is established, the DCT is driven to work; (3) The wind turbine is unlocked for power generation. After the voltage at the output port of the wind turbine reaches the rated voltage and becomes stable, the AC / DC converter on the wind turbine side is started and the converter starts. The photovoltaic power generation subsystem is unlocked for power generation. After the voltage at each output port of the photovoltaic MPPT becomes stable, the DCB on the source side is closed and the wind and solar power sources are connected to the system.

[0043] (4) Close the load-side DCB and connect the hydrogen production power supply.

[0044] (5) After the voltage at the output port of the hydrogen production power supply reaches the rated voltage and stabilizes, unlock the hydrogen production power supply DC / DC and connect the electrolyzer.

[0045] The system of the present invention is compared and analyzed with the existing system as follows: A. AC / DC Comparative Analysis Large-scale new energy grid-connected hydrogen production involves multiple links such as inversion, voltage boosting and grid connection, transmission, voltage reduction, and rectification for hydrogen production, resulting in high system losses and high construction costs. In addition, large-scale new energy access requires the power grid to provide access points, and its volatility and randomness can easily affect the safe and stable operation of the power grid.

[0046] Based on the above problems, the topological structure of new energy hydrogen production systems at home and abroad can be divided into three major links: new energy collection link, centralized transmission link and hydrogen production and power supply link. Each link can adopt DC or AC mode, thus forming 4 main combined topologies.

[0047] like Figure 4 As shown in the figure, AC technology is considered in all three links of the hydrogen production power supply of the AC collection-AC transmission-AC hydrogen production topology scheme.

[0048] like Figure 5 As shown in, among the three links of hydrogen production power supply in the AC collection-DC transmission-AC hydrogen production topology scheme, AC technology is considered in the new energy collection link and hydrogen production link, and DC technology is considered in the transmission link.

[0049] like Figure 6 As shown in the figure, among the three links of hydrogen production power supply in the AC collection-DC transmission-DC hydrogen production topology scheme, AC technology is considered in the power transmission link, and DC technology is considered in the new energy collection link and transmission link.

[0050] like Figure 7 As shown in the , DC collection-DC transmission-DC hydrogen production topology scheme, all three links of hydrogen production power supply (new energy collection link, power transmission link, and hydrogen production link) consider DC technology.

[0051] A comprehensive comparison of their advantages and disadvantages is shown in Table 1: Table 1 Comparison of AC and DC topologies

[0052] The present invention specifically proposes a large-scale new energy DC collection-off-grid hydrogen production system solution; the large-scale new energy DC collection-off-grid hydrogen production system does not need to go through grid access approval, can greatly shorten the construction period, and has more flexible scale and capacity settings; the system has steps such as boosting, transmission, and pressure reduction for hydrogen production, the system efficiency is higher than that of grid-connected hydrogen production, and off-grid operation has no impact on the large power grid, which is very suitable for the application scenario of large-scale new energy off-grid hydrogen production.

[0053] B. Comparative analysis of the topology on the aggregation side The topology and structure adopted by the collection side include three commonly used solutions: series, parallel and hybrid. The respective topologies are as follows: like Figure 8 As shown, it is a series topology structure, which has the advantage that the high-voltage side voltage level of a single DC transformer is low, the overall equipment transformation ratio is small, and the economy is better.

[0054] like Fig. 9 As shown, it is a parallel topology structure. The advantage is that there is no connection between the branches. When a line device fails, it does not affect the normal operation of other parts. It has good robustness and is more flexible for subsequent expansion or connection to other equipment.

[0055] like Fig.10 As shown, it is a hybrid topology structure that combines the advantages of series and parallel. The common method is to first connect multiple boost transformers in series to reduce the transformation ratio of each boost transformer. Subsequently, multiple sets are connected in parallel to the DC bus.

[0056] C. Topological structure analysis The topology architecture is analyzed as follows: In terms of the new energy station array, the new energy side includes 30MW of wind power and 20MW of photovoltaic power. The wind power part consists of 6 5MW AC wind turbines. The DC boost converter is the most important power conversion device in the DC collection system. Its core function is to realize the voltage level increase from LVDC to MVDC. At the same time, according to the different collection system architecture and the converter's own topology, it can also have the functions of MPPT control and multi-branch energy collection. In order to achieve high-gain, high-efficiency DC power conversion and other auxiliary functions, different DC boost converter topology solutions can be selected according to the collection system architecture, actual system parameters, and operating conditions.

[0057] Under different DC collection system architectures, the DC boost converter should have the corresponding necessary performance characteristics to meet the needs of system operation.

[0058] The core issue on the DC transmission side is the determination of the DC voltage level. Different voltage levels will affect the DC transmission distance, capacity, equipment cost, etc. Currently, there is no unified standard for DC voltage at home and abroad.

[0059] Taking into account factors such as the short DC transmission distance, capacity, and equipment cost, the ±10kV scheme is the preferred transmission voltage after photovoltaic DC aggregation.

[0060] In summary, the system topology is temporarily designed as follows: the new energy side includes 30MW of wind power and 10MW of photovoltaic power; the wind power part consists of 6 5MW AC wind turbines, which are converted to DC by the converter and then boosted to ±10kV by the DC transformer; the photovoltaic part is connected to the junction box after the photovoltaic components are connected in series and parallel, and the outlet of the junction box is boosted to ±10kV by the DC transformer; the capacity of a single step-up transformer is 5MW, and the outlets of each transformer are connected in parallel to the ±10kV DC bus; the hydrogen production power supply on the chemical plant side reduces the DC power on the 10kV bus for use in the electrolyzer, and a total of 4 5MW alkaline electrolyzers are configured. In addition, 10MW / 20MWh of energy storage is directly connected to the 10kV bus for normal operation of equipment, storage and regulation of new energy power, and power supply for self-use of each equipment after inversion.

Claims

1. A renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power source, characterized in that: The hydrogen production system adopts a topological structure of DC collection-DC transmission-DC hydrogen production, including a wind and solar equipment area, a DC transformer area, a DC line area and a hydrogen production area connected in sequence. The wind and solar equipment area is equipped with a wind power part and a photovoltaic part. The wind power part converts the output of the wind turbine set into DC through AC and then sends it to the DC transformer in the DC transformer area for boosting and then sends it to the input DC bus in the DC line area. The photovoltaic part is connected to the combiner box after the photovoltaic components are connected in series and parallel. The output line of the combiner box is connected to the DC transformer in the DC transformer area for boosting and then sent to the input DC bus in the DC line area. The DC voltage is transmitted from the input DC bus to the output DC bus on one side of the hydrogen production area, and is supplied from the output DC bus to the electrolyzer in the hydrogen production area for hydrogen production.

2. According to the renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power source as described in claim 1, it is characterized in that: An energy storage device is connected to the DC busbar at the output end on one side of the hydrogen production area.

3. According to the renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power source as described in claim 2, it is characterized in that: The energy storage device comprises a bidirectional DC transformer connected to the DC bus at the output end, and an energy storage device connected to the bidirectional DC transformer.

4. According to the renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power source as described in claim 3, it is characterized in that: The hydrogen production area includes a hydrogen production power supply connected to the output end DC bus, the hydrogen production power supply is DC / DC, the hydrogen production power supply is connected to multiple electrolyzers, and the hydrogen production power supply reduces the DC bus voltage to the voltage required by the electrolyzer.

5. According to the renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power source as described in claim 4, it is characterized in that: The wind power part includes 6 5MW AC wind turbines. The outputs of every two AC wind turbines are converted into DC by their respective wind power transformers and then connected to two 5MW step-up transformer modules connected in series. The low-voltage sides of the two step-up transformer modules are connected in parallel and the high-voltage sides are connected in series to form a 10MW DC transformer. The DC transformer outputs a voltage of ±10kV to the DC bus.

6. According to the renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power source as described in claim 5, it is characterized in that: The photovoltaic part includes 2 groups of 10MW photovoltaic systems, each 10MW photovoltaic system is connected to 3 MPPT junction boxes by photovoltaic modules, and the 3 MPPT junction boxes are connected to 3 IIOS structure step-up transformer modules. The 3 modules are connected in parallel on the low voltage side and in series on the high voltage side, together forming a 10MW step-up transformer. The output voltage of the whole machine is ±10kV to the DC bus, and the total capacity of the step-up transformer is 10MW.

7. According to the renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power source as described in claim 6, it is characterized in that: The control system of the hydrogen production system is divided into two levels, namely, a coordination control layer and a local control layer, according to the control scope and control function. The coordination control layer is the upper control layer, which determines that the DC collection system accepts power instructions and sends control instructions and control reference values ​​to each device in the local control layer. At the same time, the control system realizes smooth switching between operating modes and coordinated processing when the AC system fails; the local control layer is the lower decentralized control layer, which is controlled by each device such as the hydrogen production power supply, DC / DC transformer, i.e., DCT, MPPT junction box, etc. according to its own principles and characteristics.

8. According to the renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power source as described in claim 7, it is characterized in that: The coordination control layer in the control system of the hydrogen production system is connected to the dispatching control layer. The dispatching control layer dispatches the energy flow of the source hydrogen storage equipment in the system according to the system flow distribution, generates the system operation mode instructions and their corresponding reference value instructions, and maintains the voltage stability and power balance of the whole system.

9. According to the renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power source as described in claim 8, it is characterized in that: The protection system of the hydrogen production system is divided into a wind and solar equipment protection zone, a DC transformer protection zone, a DC line protection zone and a hydrogen production protection zone.

10. According to the renewable energy off-grid hydrogen production system based on a large-capacity hydrogen production power source as described in claim 8, it is characterized in that: The protection system PSCAD simulation performs simulation calculation on the short-circuit current and adopts a system protection device matched with a DC main network circuit breaker + a load side fuse. When the power outlet is short-circuited, the DC incoming line circuit breaker is instantaneously activated for reverse current protection to isolate the fault point from the DC main network. The DC transformer locks the pulse after a delay of 50ms and reduces the output to 0. When the ±10kV busbar is short-circuited, the DC incoming line circuit breaker is opened after a delay of 20ms to isolate the fault point. When the load side is short-circuited, the DC fuse is instantly blown to isolate the fault point.

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