Comprehensive energy storage system for off-grid wind-solar hydrogen production and control strategy thereof

Abstract

The invention discloses a comprehensive energy storage system for off-grid wind-solar hydrogen production and a control strategy of the comprehensive energy storage system. The comprehensive energy storage system for off-grid type wind-solar hydrogen production is composed of power type energy storage, energy type energy storage and long-period energy storage, and the power type energy storage, the energy type energy storage and the long-period energy storage respectively meet the adjustment requirements of millisecond-second level adjustment, minute-hour level adjustment and hour-several-week adjustment time scales, the power type energy storage adopts a double-electrode-layer super capacitor, and the energy type energy storage adopts a double-electrode-layer super capacitor. Lithium ion battery energy storage is adopted for energy type energy storage, hydrogen energy storage is adopted for long-period energy storage, and a comprehensive energy storage system network structure wiring diagram is designed. Aiming at flexible control of the off-grid wind-solar hydrogen production comprehensive energy storage system, three layers of control strategies including a device-level control strategy, a system-level coordination strategy and a system-level recovery strategy are provided. In a system-level control strategy, a network construction coordination control strategy between energy storage of the double-electric-layer super capacitor and energy storage of the lithium battery is provided, and a network construction energy storage switching process of the comprehensive energy storage system is provided.

Description

Technical Field

[0001] The present invention relates to the field of hydrogen production from renewable energy, and more specifically, to a comprehensive energy storage system for off-grid wind-solar hydrogen production and a control strategy thereof. Background Art

[0002] According to the different carbon emissions in the hydrogen production process, hydrogen can be divided into three types: gray hydrogen, blue hydrogen, and green hydrogen. Hydrogen produced by electrolyzing water using renewable energy is called green hydrogen because it produces almost no carbon emissions during the production process. At present, there are many ways to produce hydrogen from renewable energy, including solar photolysis of water, wind photolysis of water, biomass conversion, and biological hydrogen production. Renewable energy hydrogen production is a method of producing hydrogen by electrolyzing water using renewable energy such as solar energy and wind energy. This method basically does not produce greenhouse gases during the production process and is one of the important ways to achieve carbon neutrality.

[0003] Off-grid hydrogen production is not restricted by grid access and interval resources, which reduces the investment in access and transmission links. At the same time, considering its high electricity cost, on the one hand, it avoids the difficulty of green hydrogen certification caused by using grid electricity to produce hydrogen, and on the other hand, it also reduces the unit hydrogen production cost caused by access equipment and transmission and distribution fees. At present, my country has carried out several off-grid renewable energy hydrogen production projects:

[0004] ① On December 21, 2023, CGN Lingwu's 1 million kilowatt new energy off-grid hydrogen production project was approved. The project plans to build a 1 million kilowatt photovoltaic system, 100MW / 200MWh energy storage and a corresponding scale of hydrogen production system. The project was included in the third batch of national large bases;

[0005] ② On January 5, 2024, the environmental impact assessment of the 600,000-kilowatt off-grid renewable energy hydrogen production phase I project (green hydrogen coupled with coal chemical industry) in the Pingshuo coal mining subsidence area of ​​China Coal was publicized for public participation. 3 / h water electrolysis hydrogen production, 3×1800m3 hydrogen storage tanks and supporting hydrogen compressors and other equipment;

[0006] ③ From January 8 to 9, 2024, the feasibility study report review meeting of Liaoning Huadian Diaobingshan off-grid wind power hydrogen production coupled with green ammonia-alcohol integrated demonstration project was held in Chengdu. The project scale is electrolytic water coupled with 200,000 tons / year of green ammonia, 100,000 tons / year of methanol and wind turbines, energy storage devices, electrolyzers and other supporting facilities;

[0007] ④ On January 15, 2024, the Ningxia Wuzhong off-grid hydrogen production project was signed with a total investment of about 8 billion yuan. The project will be developed and constructed in three phases, including a water electrolysis hydrogen production project, a green hydrogen production green ammonia project, and two comprehensive energy stations (single station scale 1000kg / day). After full production, the annual output value is expected to be 1.2 billion yuan;

[0008] ⑤On April 20, 2024, Liaoning Huadian Tieling Xintaizi Phase I 25MW off-grid energy storage and hydrogen production integrated project started commercial operation, providing high-purity hydrogen (high-purity hydrogen) for fuel cells to the society and solving the hydrogen demand for hydrogen fuel logistics heavy trucks;

[0009] ⑥ On July 10, 2024, Xinsichuang Hydrogen Energy won the bid for the first off-grid photovoltaic hydrogen and oxygen production project in plateau areas in China, which was initiated by the State Power Investment Group for public bidding. The project will provide technical reference for large-scale off-grid hydrogen production with renewable energy, and at the same time, provide solutions for diffuse oxygen supply to households in high-altitude areas. The project has the characteristics of high altitude, full DC off-grid, PEM electrolysis, and integrated energy management and control system of source, grid, load and storage.

[0010] At present, off-grid hydrogen production technology is in the initial demonstration stage, and there are the following problems:

[0011] a) Failure to fully utilize the technical advantages of different energy storage types has resulted in the rapid attenuation of energy storage life represented by lithium batteries, which has increased operation and maintenance costs;

[0012] b) The long-term hydrogen storage facilities in the off-grid renewable energy hydrogen production system are not fully utilized, resulting in the problem of over-configuration of energy units in the energy storage system and increased energy investment costs;

[0013] c) Failure to fully consider the switching strategy between different energy storage types has resulted in the configuration capacity of power energy storage represented by supercapacitors being too large, which has increased the power investment cost;

[0014] d) The energy recovery process of different energy storage types is not fully considered, resulting in the problem that the charge state of power-type energy storage and energy-type energy storage cannot be restored in time, affecting the operating performance. Summary of the invention

[0015] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a comprehensive energy storage system and a control strategy for off-grid wind-solar hydrogen production.

[0016] The present invention discloses an integrated energy storage system for off-grid wind-solar hydrogen production and a control strategy thereof, which are realized by the following technical scheme and are composed of a renewable energy unit, an AC bus unit and a comprehensive energy storage unit. The renewable energy unit is composed of a wind power generation facility and a photovoltaic power generation facility. The AC bus unit includes an auxiliary equipment power supply interface and other AC load interfaces. The wind power generation facility is connected to the auxiliary equipment power supply interface through the AC bus, and the photovoltaic power generation facility is connected to other AC load interfaces through the AC bus. The comprehensive energy storage unit includes a supercapacitor energy storage device, a lithium battery energy storage device, and a hydrogen energy storage device. The supercapacitor energy storage device, the lithium battery energy storage device, and the hydrogen energy storage device are respectively connected to the AC bus.

[0017] The power supply interfaces of wind power generation facilities and auxiliary equipment are connected to the AC busbar through AC switches respectively; the photovoltaic power generation facilities and other AC load interfaces are connected to the AC busbar through AC switches respectively.

[0018] The supercapacitor energy storage device, the lithium battery energy storage device and the hydrogen energy storage device are connected to the AC busbar through AC switches respectively.

[0019] A control strategy for the integrated energy storage system using the above off-grid wind-solar hydrogen production method, which is composed of three control strategies: a device-level control strategy, a system-level coordination strategy, and a system-level recovery strategy;

[0020] ①Device-level control strategy:

[0021] a) Supercapacitor energy storage control strategy: The optimized Logistic function is used to control the charging and discharging power of the supercapacitor energy storage. The supercapacitor energy storage can be fully charged and discharged. Therefore, the state of charge SOC of the supercapacitor energy storage SC The range of variation is 0-1, and the optimized Logistic function is shown in the following formula;

[0022]

[0023] Where P SC.D.lim is the supercapacitor energy storage discharge power limit, P SC.C.lim is the supercapacitor energy storage charging power limit, P SCN is the rated power of supercapacitor energy storage, a, b, c are coefficients in the function, SOC SC The state of charge of the supercapacitor for energy storage;

[0024] b) Lithium battery energy storage control strategy: The lithium battery energy storage is divided into two parts, which are recorded as lithium battery energy storage A and lithium battery energy storage B. When the discharge power or charging power of the supercapacitor energy storage exceeds the discharge power limit or charging power limit shown in formula (1) and formula (2), the lithium battery energy storage A is switched to the grid-building control strategy, and the supercapacitor is switched to the recovery control strategy. The lithium battery energy storage A running in the grid-building control strategy uses an optimized Logistic function to control its charge and discharge power. The lithium battery energy storage is usually a non-100% DOD cycle. Therefore, the state of charge SOC of the lithium battery energy storage BS The range of variation is 0.1-0.9, and the optimized Logistic function is shown in the following formula;

[0025]

[0026] Where P BS.D.lim is the lithium battery energy storage discharge power limit, P BS.C.lim is the charging power limit of lithium battery energy storage, PBSN is the rated power of lithium battery energy storage running in the grid-building strategy, a, b, c are the coefficients in the function, SOC BS The state of charge of the lithium battery energy storage;

[0027] When lithium battery energy storage A operates in the grid-building control strategy, lithium battery energy storage B and hydrogen energy storage are used as peak-shaving resources to provide peak-shaving capability. When the discharge power or charging power of lithium battery energy storage A exceeds the discharge power limit or charging power limit shown in formula (3) and formula (4), lithium battery energy storage B is switched to the grid-building control strategy, and lithium battery energy storage A is switched to the peak-shaving control strategy and the recovery control strategy. At this time, lithium battery energy storage A and hydrogen energy storage are used as peak-shaving resources to provide peak-shaving capability.

[0028] c) Hydrogen energy storage control strategy: Due to the limitations of start-stop time and response speed, hydrogen energy storage only provides peak-shaving capability as a system peak-shaving resource and does not provide grid-building control capability; when lithium battery energy storage only operates in the grid-building state, only hydrogen energy storage is used as a peak-shaving resource to provide peak-shaving capability;

[0029] ②System-level coordination strategy

[0030] The system-level coordination strategy of the integrated energy storage system applied to off-grid wind-solar hydrogen production scenarios includes three coordination strategies, namely, the coordination strategy between double-layer supercapacitor energy storage and lithium battery energy storage, the coordination strategy between lithium battery energy storage and hydrogen energy storage, and the coordination strategy between fuel cell power generation and water electrolyzer in hydrogen energy storage through the coupling of hydrogen storage tanks;

[0031] Coordination strategy between double-layer supercapacitor energy storage and lithium battery energy storage: When the supercapacitor energy storage SOC exceeds the limit, the supercapacitor energy storage no longer has the ability to operate as a grid-forming energy storage. At this time, it is necessary to exit the supercapacitor energy storage grid-forming operation state. At the same time, the lithium battery energy storage of the same capacity needs to be switched to the grid-forming operation state to provide grid-forming support capabilities.

[0032] Coordination strategy between lithium battery energy storage and hydrogen energy storage: Under the premise of maintaining the normal operation of the off-grid hydrogen production system and ensuring the consumption of renewable energy, the SOC of lithium battery energy storage is maintained at a reasonable level to ensure the ability of lithium battery energy storage to maintain the frequency and voltage stability of the system. The coordination strategy needs to consider both the upper limit of SOC and the lower limit of SOC;

[0033] The main coordination strategies for hydrogen energy storage include: a) When the hydrogen storage capacity in the hydrogen storage tank is less than the minimum hydrogen storage capacity requirement, all hydrogen produced by the water electrolyzer is supplied to the hydrogen storage tank, and the supply to the downstream hydrogen load is stopped; b) When the hydrogen storage capacity in the hydrogen storage tank is greater than the minimum hydrogen storage capacity requirement, the downstream hydrogen load can be supplied normally, but the minimum hydrogen storage capacity in the hydrogen storage tank should not be less than the minimum hydrogen storage capacity requirement; c) When the hydrogen storage capacity of the hydrogen storage tank does not reach the maximum hydrogen storage capacity, full use should be made of wind and solar power generation to increase the hydrogen storage capacity of the hydrogen storage tank on the basis of meeting the downstream hydrogen load;

[0034] ③ System-level recovery strategy: The capacity recovery of supercapacitor energy storage is provided by lithium-ion battery energy storage, the capacity recovery of lithium-ion battery energy storage is provided by hydrogen energy storage composed of fuel cell power generation, water electrolyzer and hydrogen storage tank, and the capacity recovery of hydrogen energy storage is provided by renewable energy power generation resources such as wind power generation and photovoltaic power generation;

[0035] a) Capacity recovery control of supercapacitor energy storage: When the supercapacitor energy storage is used as the voltage source in the system and operates in the grid-building state, due to its small capacity, its entire capacity is used to maintain the stability of the system voltage and frequency. When the supercapacitor energy storage SOC exceeds the limit, the lithium battery energy storage will provide voltage and frequency support. At this time, the supercapacitor energy storage enters the capacity recovery state and performs capacity recovery at a certain power value. The recovery power value is calculated according to formula (5) and formula (6). The power is provided by the lithium battery energy storage, that is, the lithium battery energy storage realizes the SOC recovery of the supercapacitor energy storage through charging and discharging. When the supercapacitor energy storage is charged, its recovery energy essentially comes from wind power and photovoltaic power generation;

[0036]

[0037] Where P SC.D.re , P SC.C.re are the supercapacitor energy storage recovery discharge power and recovery charging power, P SC.D.min , P SC.C.min are the minimum recovery discharge power and minimum recovery charging power of supercapacitor energy storage, P SC.D.max , P SC.C.max are the maximum recovery discharge power and maximum recovery charging power of supercapacitor energy storage, respectively, D , k C are the supercapacitor energy storage discharge recovery coefficient and charging recovery coefficient, P BS.D , P BS.C They are the discharge and charging power of lithium battery energy storage respectively;

[0038] b) Capacity recovery control of lithium-ion battery energy storage: When the lithium-ion battery energy storage completes the SOC recovery of the supercapacitor energy storage through the capacity recovery algorithm, the supercapacitor energy storage should switch back to the grid-type control, and the lithium battery energy storage should recover the power control mode. However, when the SOC of the supercapacitor energy storage has not recovered and the SOC of the lithium battery energy storage exceeds the limit, the hydrogen energy storage composed of fuel cell power generation, water electrolyzer and hydrogen storage tank provides the recovery energy of the lithium battery energy storage, and the capacity is restored at a certain power value. The recovery power value is calculated according to formula (7) and formula (8);

[0039]

[0040] Where P BS.D.re , PBS.C.re are the supercapacitor energy storage recovery discharge power and recovery charging power, P BS.D.min , P BS.C.min are the minimum recovery discharge power and minimum recovery charging power of supercapacitor energy storage, P BS.D.max , P BS.C.max are the maximum recovery discharge power and maximum recovery charging power of supercapacitor energy storage, m D 、m C are the supercapacitor energy storage discharge recovery coefficient and charging recovery coefficient, P HS.D , P HS.C are the lithium battery energy storage discharge and charging power, P HSN is the rated charging and discharging power of hydrogen energy storage;

[0041] c) Capacity recovery of hydrogen energy storage: Capacity recovery of hydrogen energy storage refers to the adjustment of the hydrogen storage capacity of the hydrogen storage tank. On the premise of meeting the downstream hydrogen load demand, the power of renewable energy generation is fully utilized, and the hydrogen production power of the electrolyzer is operated in a higher efficiency range to improve the hydrogen production efficiency. The recovery power is calculated according to formula (9);

[0042]

[0043] Where: P HS.C.re is the hydrogen energy storage and hydrogen production power, P W , P S are wind power and solar power generation respectively, P HS.C.min is the minimum hydrogen production power for hydrogen energy storage, P HS.C.max The maximum hydrogen production power for hydrogen energy storage.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] a) Solve the problem that existing technical solutions do not fully utilize the technical advantages of different energy storage types, and avoid the rapid attenuation of energy storage represented by lithium batteries and the increase in operation and maintenance costs;

[0046] b) Solve the problem that the existing technical solutions do not fully utilize the long-term hydrogen storage facilities in the off-grid renewable energy hydrogen production system, and avoid the energy storage system energy unit configuration being too high and increasing the energy investment cost;

[0047] c) Solve the problem that the existing technical solutions do not fully consider the switching strategies between different energy storage types, and avoid the configuration capacity of power energy storage represented by supercapacitors being too large, thereby increasing the power investment cost;

[0048] d) Solve the problem that the existing technical solutions do not fully consider the energy recovery process of different energy storage types, realize the timely recovery of the charge state of power-type energy storage and energy-type energy storage, and ensure the energy storage operation performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a wiring diagram of the off-grid wind-solar hydrogen production integrated energy storage system of the present invention;

[0050] Figure 2 It is a switching flow chart of the comprehensive energy storage system of the present invention. DETAILED DESCRIPTION

[0051] In order to be able to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other. In the following description, many specific details are set forth in order to fully understand the present invention, and the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the art without making creative work are within the scope of protection of the present invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by technicians in the technical field of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0052] 1. System structure

[0053] The off-grid wind-solar hydrogen production system is an independently operated wind power and photovoltaic hydrogen production system, with wind power and photovoltaic as power generation units and water electrolyzer as load unit. Since wind power and photovoltaic power generation are volatile and intermittent, they cannot meet the hydrogen production load demand in real time, and at the same time, they cannot establish a stable AC grid voltage and frequency. Therefore, for the off-grid wind-solar hydrogen production system, energy storage units are also required to provide power regulation and voltage support to avoid problems such as wind abandonment and system instability.

[0054] The power balance requirements of off-grid wind-solar hydrogen production systems involve multiple time scales. Maintaining the voltage and frequency stability of the power supply network requires millisecond-level regulation capabilities, economic scheduling and absorbing wind-solar power generation require minute-hour-level regulation capabilities, and long-term heat preservation of water electrolyzers and long-term power supply of system security loads require hours-weeks of regulation capabilities. Therefore, off-grid wind-solar hydrogen production systems put forward multiple time scale requirements for energy storage units. The present invention proposes a comprehensive energy storage system and its control strategy suitable for off-grid wind-solar hydrogen production scenarios. The comprehensive energy storage system consists of power-type energy storage, energy-type energy storage and long-term energy storage, corresponding to millisecond-level regulation, minute-hour-level regulation, and hour-week-level regulation time scales, respectively. Among them, power-type energy storage adopts double-layer supercapacitor energy storage (physical energy storage), energy-type energy storage adopts lithium-ion battery energy storage (electrochemical energy storage), and long-term energy storage adopts hydrogen energy storage (chemical energy storage). Among them, hydrogen energy storage mainly focuses on its power generation link, using proton exchange membrane (PEM) fuel cells for power generation, and its energy storage link is provided by water electrolysis hydrogen production and hydrogen storage facilities.

[0055] Figure 1 In the wiring diagram of the off-grid wind-solar hydrogen production integrated energy storage system shown, the system consists of three parts, namely, renewable energy unit, AC bus unit, and integrated energy storage unit. The renewable energy unit is mainly composed of wind power generation facilities and photovoltaic power generation facilities. The AC bus unit is mainly composed of AC bus, renewable energy unit interface, integrated energy storage system interface, auxiliary equipment power supply interface, other AC load interfaces, etc. The integrated energy storage unit includes supercapacitor energy storage equipment, lithium battery energy storage equipment, and hydrogen energy storage equipment. Each type of energy storage equipment is composed of several components.

[0056] 2. Control strategy

[0057] The off-grid wind-solar hydrogen production integrated energy storage control strategy consists of three levels of control strategies: device-level control strategy, system-level coordination strategy, and system-level recovery strategy.

[0058] ①Device-level control strategy

[0059] a) Supercapacitor energy storage control strategy

[0060] The device-level control strategy controls specific energy storage devices. Double-layer supercapacitor energy storage (power-type energy storage) has a high charging and discharging power, and the charging and discharging rate can reach 100C, but the energy density is low. It is suitable for high-power and high-frequency charging and discharging occasions. During the operation of the off-grid wind-solar hydrogen production system, the power fluctuation characteristics of wind power and photovoltaics will produce high-frequency power imbalances, causing frequency and voltage disturbances in the power supply system. Therefore, double-layer supercapacitor energy storage is used to smooth out short-time scale and high-frequency unbalanced power to avoid frequent charging and discharging of lithium battery energy storage and extend its operating life. The double-layer supercapacitor energy storage control strategy adopts a grid-type control strategy with fixed AC bus voltage and fixed AC bus frequency. At the same time, fixed AC power and fixed AC bus voltage are used as auxiliary control strategies for SOC recovery control when SOC exceeds the limit.

[0061] The optimized Logistic function is used to control the charging and discharging power of the supercapacitor energy storage. The supercapacitor energy storage can be fully charged and discharged. Therefore, the state of charge SOC of the supercapacitor energy storage SC The range of variation is 0-1, and the optimized Logistic function is shown in the following formula.

[0062]

[0063]

[0064] Where P SC.D.lim is the supercapacitor energy storage discharge power limit, P SC.C.lim is the supercapacitor energy storage charging power limit, P SCN is the rated power of supercapacitor energy storage, a, b, c are coefficients in the function, SOC SC It is the state of charge of the supercapacitor energy storage.

[0065] When the supercapacitor stores energy and discharges, the supercapacitor power P SC Should be less than P SC.D.lim When the supercapacitor is charging, the supercapacitor power P SC Should be less than P SC.C.lim From equations (1) and (2), it can be seen that when the supercapacitor energy storage charge state is around 0.5, P SC.D.lim and P SC.C.lim Both are close to P SCN , when the supercapacitor energy storage charge state is close to 0 or 1, the charging and discharging power of the supercapacitor energy storage is limited, and the shape of the Logistic function can be adjusted by the coefficients a, b, and c.

[0066] When supercapacitor energy storage operates in the grid control strategy, lithium battery energy storage and hydrogen energy storage are used as peak-shaving resources to provide peak-shaving capabilities.

[0067] b) Lithium battery energy storage control strategy

[0068] Lithium battery energy storage (energy storage) mainly responds to minute-hour level unbalanced power and optimization regulation needs, and mainly performs low-frequency power regulation to reduce the impact of high-frequency charging and discharging on its life. Lithium battery energy storage is composed of multiple energy storage converters (PCS), each of which needs to have fixed active power and fixed reactive power control strategies. At the same time, it needs to have a grid-type control strategy of fixed AC bus voltage and fixed AC bus frequency as an auxiliary control strategy when the double-layer supercapacitor energy storage SOC exceeds the limit.

[0069] The power capacity and energy capacity configuration of lithium battery energy storage are usually sufficient. The lithium battery energy storage can be divided into several parts, each of which can operate independently in the grid-building control strategy support system. The present invention temporarily divides the lithium battery energy storage into two parts, recorded as lithium battery energy storage A and lithium battery energy storage B. When the discharge power or charging power of the supercapacitor energy storage exceeds the discharge power limit or charging power limit shown in formula (1) and formula (2), the lithium battery energy storage A is switched to the grid-building control strategy, and the supercapacitor is switched to the recovery control strategy. The lithium battery energy storage A running in the grid-building control strategy uses an optimized Logistic function to control its charging and discharging power. The lithium battery energy storage is usually a non-100% DOD cycle. Therefore, the state of charge SOC of the lithium battery energy storage BS The range of variation is 0.1-0.9, and the optimized Logistic function is shown in the following formula.

[0070]

[0071] Where P BS.D.lim is the lithium battery energy storage discharge power limit, P BS.C.lim is the charging power limit of lithium battery energy storage, P BSN is the rated power of lithium battery energy storage running in the grid-building strategy, a, b, c are the coefficients in the function, SOC BS The state of charge of the lithium battery.

[0072] When the lithium battery energy storage is discharged, the lithium battery power P running in the grid-building strategy BS Should be less than P BS.D.lim When the lithium battery energy storage is charged, the lithium battery power P running in the network strategy BS Should be less than P BS.C.lim From equations (3) and (4), it can be seen that when the supercapacitor energy storage charge state is around 0.5, P BS.D.lim and P BS.C.lim Both are close to P BSN,When the state of charge of the lithium battery energy storage is close to 0.1 or 0.9, the charging and discharging power of the supercapacitor energy storage is limited, and the shape of the Logistic function can be adjusted by the coefficients a, b, and c.

[0073] When lithium battery energy storage A operates in the grid-building control strategy, lithium battery energy storage B and hydrogen energy storage are used as peak-shaving resources to provide peak-shaving capability. When the discharge power or charging power of lithium battery energy storage A exceeds the discharge power limit or charging power limit shown in equation (3) and equation (4), lithium battery energy storage B is switched to the grid-building control strategy, and lithium battery energy storage A is switched to the peak-shaving control strategy and the recovery control strategy. At this time, lithium battery energy storage A and hydrogen energy storage are used as peak-shaving resources to provide peak-shaving capability.

[0074] c) Hydrogen energy storage control strategy

[0075] Hydrogen energy storage (long-term energy storage) mainly responds to unbalanced power and regulation needs of several hours to weeks. Hydrogen energy storage includes hydrogen production and power generation. The hydrogen production link includes hydrogen production transformers, hydrogen production power supplies, water electrolyzers, hydrogen storage tanks and other equipment. The hydrogen production link mainly adopts customized hydrogen power and customized hydrogen production control strategies. The hydrogen production power supply includes rectifier power supplies based on thyristor semi-controlled devices and rectifier power supplies based on IGBT fully controlled devices. Both types of rectifier power supplies can work in customized hydrogen power or customized hydrogen production control strategies; the power generation link includes hydrogen storage tanks, PEM fuel cells, interface converters, step-up transformers and other equipment. The power generation link mainly adopts a fixed power generation control strategy.

[0076] Due to the limitations of start-stop time and response speed, hydrogen energy storage only provides peak-shaving capability as a system peak-shaving resource and does not provide grid-building control capability. When lithium battery energy storage only operates in the grid-building state, only hydrogen energy storage is used as a peak-shaving resource to provide peak-shaving capability.

[0077] Double-layer supercapacitor energy storage (power-type energy storage) and lithium battery energy storage (energy-type energy storage) can both provide millisecond-level response times, and hydrogen energy storage (long-cycle energy storage) can provide second-level response times under normal operating conditions. The above three energy storage forms can respectively meet the requirements of different time scales in off-grid wind and solar hydrogen production scenarios.

[0078] ②System-level coordination strategy

[0079] The system-level coordination strategy of the integrated energy storage system applied to off-grid wind and solar hydrogen production scenarios includes three coordination strategies, namely, the coordination strategy between double-layer supercapacitor energy storage (power-type energy storage) and lithium battery energy storage (energy-type energy storage), the coordination strategy between lithium battery energy storage (energy-type energy storage) and hydrogen energy storage (long-cycle energy storage), and the coordination strategy between fuel cell power generation and water electrolyzer in hydrogen energy storage (long-cycle energy storage) through the coupling of hydrogen storage tanks.

[0080] The coordination strategy between double-layer supercapacitor energy storage (power-type energy storage) and lithium battery energy storage (energy-type energy storage) mainly considers making the supercapacitor energy storage operate in the grid-forming energy storage mode to maintain the frequency and voltage stability of the system. When the supercapacitor energy storage SOC exceeds the limit, the supercapacitor energy storage no longer has the ability to operate as a grid-forming energy storage. At this time, it is necessary to exit the supercapacitor energy storage grid-forming operation state. At the same time, it is necessary to switch the lithium battery energy storage of the same capacity (lithium battery energy storage A or lithium battery energy storage B) to the grid-forming operation state to provide grid-forming support capabilities.

[0081] The coordination strategy between lithium battery energy storage (energy-type energy storage) and hydrogen energy storage (long-cycle energy storage) mainly considers the connection between minute-to-hour regulation capability and hour-to-week regulation capability. The main purpose is to maintain the normal operation of the off-grid hydrogen production system and ensure the consumption of renewable energy. The SOC of lithium battery energy storage is maintained at a reasonable level to ensure the ability of lithium battery energy storage to maintain the frequency and voltage stability of the system. The coordination strategy needs to consider both the upper limit of SOC and the lower limit of SOC.

[0082] In hydrogen energy storage (long-term energy storage), fuel cell power generation and water electrolyzers are coupled through hydrogen storage tanks, and the coordinated operation between fuel cell power generation and water electrolyzers is crucial. Usually, in off-grid wind and solar hydrogen production scenarios, the installed capacity of water electrolysis hydrogen production equipment is much larger than that of fuel cell power generation. The configuration of hydrogen storage tanks mainly considers two factors: one is to provide a stable downstream hydrogen load supply capacity, and the other is to provide the system's basic operating load and insulation load needs, so that the water electrolyzer can quickly switch from the insulation state to the working state.

[0083] Therefore, the coordination strategy of coupling between fuel cell power generation and water electrolyzer through hydrogen storage tank is to ensure that the basic operating load and insulation load of the system are met in the hydrogen storage tank for continuous operation for a long period of time, and to maintain the supercapacitor energy storage SOC and lithium battery energy storage SOC at a reasonable level when the wind and solar output are limited for a long time. Since the configuration of the hydrogen storage tank has taken into account the provision of a stable downstream hydrogen load supply capacity, the hydrogen storage tank must meet the minimum hydrogen storage requirement. The main coordination strategies for hydrogen energy storage include: a) When the hydrogen storage in the hydrogen storage tank is less than the minimum hydrogen storage requirement, all hydrogen produced by the water electrolyzer is supplied to the hydrogen storage tank for storage, and the supply to the downstream hydrogen load is stopped; b) When the hydrogen storage in the hydrogen storage tank is greater than the minimum hydrogen storage requirement, the downstream hydrogen load can be supplied normally, but the minimum hydrogen storage in the hydrogen storage tank should not be less than the minimum hydrogen storage requirement; c) When the hydrogen storage in the hydrogen storage tank does not reach the maximum hydrogen storage capacity, wind and solar power generation should be fully utilized to increase the hydrogen storage capacity of the hydrogen storage tank on the basis of meeting the downstream hydrogen load.

[0084] ③System-level recovery strategy

[0085] The system-level recovery strategy mainly considers the coordination strategy of energy storage devices with different time scales and capacity scales in the capacity recovery link. The system-level recovery strategy adopts a downward compatible control strategy, which is divided into three levels, namely, the capacity recovery (SOC control) of supercapacitor energy storage is provided by lithium-ion battery energy storage, the capacity recovery (SOC control) of lithium-ion battery energy storage is provided by hydrogen energy storage composed of fuel cell power generation, water electrolyzer and hydrogen storage tank, and the capacity recovery (hydrogen storage control) of hydrogen energy storage is provided by renewable energy power generation resources such as wind power generation and photovoltaic power generation. The above three levels of system-level recovery processes are interconnected and interact with the device-level control strategy and system-level coordination strategy. In certain periods of the actual operation process, there will be a phenomenon of providing recovery energy across levels, which is caused by the coupling of recovery processes between levels.

[0086] a) Capacity recovery control of supercapacitor energy storage

[0087] Due to the loss and imbalance of charge and discharge during the operation of the energy storage system, the state of charge (SOC) of the energy storage system will gradually deviate from the ideal state. Too high or too low SOC will affect and limit the performance of the energy storage system. The capacity recovery (SOC control) of the supercapacitor energy storage is provided by the lithium-ion battery energy storage. When the supercapacitor energy storage is used as the voltage source in the system and operates in the grid state, due to its small capacity, its entire capacity is used to maintain the stability of the system voltage and frequency. When the supercapacitor energy storage SOC exceeds the limit, the lithium battery energy storage will provide voltage and frequency support. At this time, the supercapacitor energy storage enters the capacity recovery state and recovers the capacity at a certain power value. The recovery power value is calculated according to formula (5) and formula (6). The power is provided by the lithium battery energy storage, that is, the lithium battery energy storage realizes the SOC recovery of the supercapacitor energy storage through charging and discharging. When the supercapacitor energy storage is charged, its recovery energy essentially comes from wind power and photovoltaic power generation.

[0088]

[0089] Where P SC.D.re , P SC.C.re are the supercapacitor energy storage recovery discharge power and recovery charging power, P SC.D.min , P SC.C.min are the minimum recovery discharge power and minimum recovery charging power of supercapacitor energy storage, P SC.D.max , P SC.C.max are the maximum recovery discharge power and maximum recovery charging power of supercapacitor energy storage, respectively, D , k C are the supercapacitor energy storage discharge recovery coefficient and charging recovery coefficient, P BS.D , P BS.C They are the lithium battery energy storage discharge and charging power respectively.

[0090] b) Capacity recovery control of lithium-ion battery energy storage

[0091] When the lithium-ion battery energy storage completes the SOC recovery of the supercapacitor energy storage through the capacity recovery algorithm, the supercapacitor energy storage should switch back to the grid-type control, and the lithium battery energy storage should recover the power control mode. However, when the SOC of the supercapacitor energy storage has not recovered and the SOC of the lithium battery energy storage exceeds the limit, the hydrogen energy storage composed of fuel cell power generation, water electrolyzer and hydrogen storage tank provides the recovery energy of the lithium battery energy storage, and the capacity is restored at a certain power value. The recovery power value is calculated according to formula (7) and formula (8). The capacity recovery of the lithium battery energy storage can be achieved by adjusting the power generation of renewable energy, adjusting the hydrogen production power of the electrolyzer and adjusting the power generation of fuel cells. The method of adjusting the power generation of renewable energy and adjusting the hydrogen production power of the electrolyzer is preferred, and the stable supply of hydrogen to the downstream hydrogen load is guaranteed. If the SOC of the lithium battery energy storage is adjusted by fuel cell power generation, the overall operating efficiency of the system will be reduced. Therefore, this method has a lower priority.

[0092]

[0093] Where P BS.D.re , P BS.C.re are the supercapacitor energy storage recovery discharge power and recovery charging power, P BS.D.min , P BS.C.min are the minimum recovery discharge power and minimum recovery charging power of supercapacitor energy storage, P BS.D.max , P BS.C.max are the maximum recovery discharge power and maximum recovery charging power of supercapacitor energy storage, m D 、m C are the supercapacitor energy storage discharge recovery coefficient and charging recovery coefficient, P HS.D , P HS.C are the lithium battery energy storage discharge and charging power, P HSN is the rated charging and discharging power of hydrogen energy storage.

[0094] When the SOC of the lithium battery energy storage recovers to the ideal state, the SOC recovery process of the supercapacitor energy storage is continued. Therefore, the grid-type control of the system voltage and frequency is jointly realized by the supercapacitor energy storage and the lithium battery energy storage. During normal operation, the system support power is mainly borne by the supercapacitor energy storage to extend the service life of the lithium battery energy storage and improve the investment and operation economy.

[0095] c) Capacity recovery of hydrogen energy storage

[0096] Since the hydrogen storage cost of hydrogen storage tanks is relatively low and the downstream hydrogen load demand must be met at the same time, the hydrogen storage capacity of hydrogen storage tanks is usually large. The capacity recovery of hydrogen energy storage refers to the adjustment of the hydrogen storage capacity of hydrogen storage tanks. On the premise of meeting the downstream hydrogen load demand, the power of renewable energy generation is fully utilized, and the hydrogen production power of the electrolyzer is operated in a higher efficiency range to improve the hydrogen production efficiency. The recovery power is calculated according to formula (9).

[0097]

[0098] Where: P HS.C.re is the hydrogen energy storage and hydrogen production power, P W , P S are wind power and solar power generation respectively, P HS.C.min is the minimum hydrogen production power for hydrogen energy storage, P HS.C.max The maximum hydrogen production power for hydrogen energy storage.

[0099] In the above three energy storage systems with different time scales, the priority order of energy storage (SOC) control is supercapacitor energy storage, followed by lithium battery energy storage, and hydrogen energy storage, which means that the stable operation and power quality indicators of the system are prioritized, and the system investment and operation costs are reduced to improve the economic efficiency of the whole life cycle. Since the energy source of the system is wind power and photovoltaic power generation, wind power and photovoltaic power are preferentially used to control the SOC of each energy storage to improve the operation efficiency.

[0100] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A comprehensive energy storage system for off-grid wind and solar hydrogen production, characterized in that: It consists of a renewable energy unit, an AC bus unit and an integrated energy storage unit. The renewable energy unit consists of wind power generation facilities and photovoltaic power generation facilities. The AC bus unit includes auxiliary equipment power supply interface and other AC load interfaces. The wind power generation facilities are connected to the auxiliary equipment power supply interface through the AC bus. The photovoltaic power generation facilities are connected to other AC load interfaces through the AC bus. The integrated energy storage unit includes supercapacitor energy storage equipment, lithium battery energy storage equipment, and hydrogen energy storage equipment. The supercapacitor energy storage equipment, lithium battery energy storage equipment, and hydrogen energy storage equipment are respectively connected to the AC bus.

2. The integrated energy storage system for off-grid wind-solar hydrogen production according to claim 1 is characterized in that: The power supply interfaces of wind power generation facilities and auxiliary equipment are connected to the AC busbar through AC switches respectively; the photovoltaic power generation facilities and other AC load interfaces are connected to the AC busbar through AC switches respectively.

3. The integrated energy storage system for off-grid wind-solar hydrogen production according to claim 1 is characterized in that: The supercapacitor energy storage device, the lithium battery energy storage device and the hydrogen energy storage device are connected to the AC busbar through AC switches respectively.

4. A control strategy for an off-grid wind-solar hydrogen production integrated energy storage system using any one of claims 1-3, which consists of three control strategies: a device-level control strategy, a system-level coordination strategy, and a system-level recovery strategy; ①Device-level control strategy: a) Supercapacitor energy storage control strategy: The optimized Logistic function is used to control the charging and discharging power of the supercapacitor energy storage. The supercapacitor energy storage can be fully charged and discharged. Therefore, the state of charge SOC of the supercapacitor energy storage SC The range of variation is 0-1, and the optimized Logistic function is shown in the following formula; Where P SC.D.lim is the supercapacitor energy storage discharge power limit, P SC.C.lim is the supercapacitor energy storage charging power limit, P SCN is the rated power of supercapacitor energy storage, a, b, c are coefficients in the function, SOC SC The state of charge of the supercapacitor for energy storage; b) Lithium battery energy storage control strategy: The lithium battery energy storage is divided into two parts, which are recorded as lithium battery energy storage A and lithium battery energy storage B. When the discharge power or charging power of the supercapacitor energy storage exceeds the discharge power limit or charging power limit shown in formula (1) and formula (2), the lithium battery energy storage A is switched to the grid-building control strategy, and the supercapacitor is switched to the recovery control strategy. The lithium battery energy storage A running in the grid-building control strategy uses an optimized Logistic function to control its charge and discharge power. The lithium battery energy storage is usually a non-100% DOD cycle. Therefore, the state of charge SOC of the lithium battery energy storage BS The range of variation is 0.1-0.9, and the optimized Logistic function is shown in the following formula; Where P BS.D.lim is the lithium battery energy storage discharge power limit, P BS.C.lim is the charging power limit of lithium battery energy storage, P BSN is the rated power of lithium battery energy storage running in the grid-building strategy, a, b, c are the coefficients in the function, SOC BS The state of charge of the lithium battery energy storage; When lithium battery energy storage A operates in the grid-building control strategy, lithium battery energy storage B and hydrogen energy storage are used as peak-shaving resources to provide peak-shaving capability. When the discharge power or charging power of lithium battery energy storage A exceeds the discharge power limit or charging power limit shown in formula (3) and formula (4), lithium battery energy storage B is switched to the grid-building control strategy, and lithium battery energy storage A is switched to the peak-shaving control strategy and the recovery control strategy. At this time, lithium battery energy storage A and hydrogen energy storage are used as peak-shaving resources to provide peak-shaving capability. c) Hydrogen energy storage control strategy: Due to the limitations of start-stop time and response speed, hydrogen energy storage only provides peak-shaving capability as a system peak-shaving resource and does not provide grid-building control capability; when lithium battery energy storage only operates in the grid-building state, only hydrogen energy storage is used as a peak-shaving resource to provide peak-shaving capability; ②System-level coordination strategy The system-level coordination strategy of the integrated energy storage system applied to off-grid wind-solar hydrogen production scenarios includes three coordination strategies, namely, the coordination strategy between double-layer supercapacitor energy storage and lithium battery energy storage, the coordination strategy between lithium battery energy storage and hydrogen energy storage, and the coordination strategy between fuel cell power generation and water electrolyzer in hydrogen energy storage through the coupling of hydrogen storage tanks; Coordination strategy between double-layer supercapacitor energy storage and lithium battery energy storage: When the supercapacitor energy storage SOC exceeds the limit, the supercapacitor energy storage no longer has the ability to operate as a grid-forming energy storage. At this time, it is necessary to exit the supercapacitor energy storage grid-forming operation state. At the same time, the lithium battery energy storage of the same capacity needs to be switched to the grid-forming operation state to provide grid-forming support capabilities. Coordination strategy between lithium battery energy storage and hydrogen energy storage: Under the premise of maintaining the normal operation of the off-grid hydrogen production system and ensuring the consumption of renewable energy, the SOC of lithium battery energy storage is maintained at a reasonable level to ensure the ability of lithium battery energy storage to maintain the frequency and voltage stability of the system. The coordination strategy needs to consider both the upper limit of SOC and the lower limit of SOC; The main coordination strategies for hydrogen energy storage include: a) When the hydrogen storage capacity in the hydrogen storage tank is less than the minimum hydrogen storage capacity requirement, all hydrogen produced by the water electrolyzer is supplied to the hydrogen storage tank, and the supply to the downstream hydrogen load is stopped; b) When the hydrogen storage capacity in the hydrogen storage tank is greater than the minimum hydrogen storage capacity requirement, the downstream hydrogen load can be supplied normally, but the minimum hydrogen storage capacity in the hydrogen storage tank should not be less than the minimum hydrogen storage capacity requirement; c) When the hydrogen storage capacity of the hydrogen storage tank does not reach the maximum hydrogen storage capacity, full use should be made of wind and solar power generation to increase the hydrogen storage capacity of the hydrogen storage tank on the basis of meeting the downstream hydrogen load; ③ System-level recovery strategy: The capacity recovery of supercapacitor energy storage is provided by lithium-ion battery energy storage, the capacity recovery of lithium-ion battery energy storage is provided by hydrogen energy storage composed of fuel cell power generation, water electrolyzer and hydrogen storage tank, and the capacity recovery of hydrogen energy storage is provided by renewable energy power generation resources such as wind power generation and photovoltaic power generation; a) Capacity recovery control of supercapacitor energy storage: When the supercapacitor energy storage is used as the voltage source in the system and operates in the grid-building state, due to its small capacity, its entire capacity is used to maintain the stability of the system voltage and frequency. When the supercapacitor energy storage SOC exceeds the limit, the lithium battery energy storage will provide voltage and frequency support. At this time, the supercapacitor energy storage enters the capacity recovery state and performs capacity recovery at a certain power value. The recovery power value is calculated according to formula (5) and formula (6). The power is provided by the lithium battery energy storage, that is, the lithium battery energy storage realizes the SOC recovery of the supercapacitor energy storage through charging and discharging. When the supercapacitor energy storage is charged, its recovery energy essentially comes from wind power and photovoltaic power generation; Where P SC.D.re , P SC.C.re are the supercapacitor energy storage recovery discharge power and recovery charging power, P SC.D.min , P SC.C.min are the minimum recovery discharge power and minimum recovery charging power of supercapacitor energy storage, P SC.D.max , P SC.C.max are the maximum recovery discharge power and maximum recovery charging power of supercapacitor energy storage, respectively, D , k C are the supercapacitor energy storage discharge recovery coefficient and charging recovery coefficient, P BS.D , P BS.C They are the discharge and charging power of lithium battery energy storage respectively; b) Capacity recovery control of lithium-ion battery energy storage: When the lithium-ion battery energy storage completes the SOC recovery of the supercapacitor energy storage through the capacity recovery algorithm, the supercapacitor energy storage should switch back to the grid-type control, and the lithium battery energy storage should recover the power control mode. However, when the SOC of the supercapacitor energy storage has not recovered and the SOC of the lithium battery energy storage exceeds the limit, the hydrogen energy storage composed of fuel cell power generation, water electrolyzer and hydrogen storage tank provides the recovery energy of the lithium battery energy storage, and the capacity is restored at a certain power value. The recovery power value is calculated according to formula (7) and formula (8); Where P BS.D.re , P BS.C.re are the supercapacitor energy storage recovery discharge power and recovery charging power, P BS.D.min , P BS.C.min are the minimum recovery discharge power and minimum recovery charging power of supercapacitor energy storage, P BS.D.max , P BS.C.max are the maximum recovery discharge power and maximum recovery charging power of supercapacitor energy storage, m D 、m C are the supercapacitor energy storage discharge recovery coefficient and charging recovery coefficient, P HS.D , P HS.C are the lithium battery energy storage discharge and charging power, P HSN is the rated charging and discharging power of hydrogen energy storage; c) Capacity recovery of hydrogen energy storage: Capacity recovery of hydrogen energy storage refers to the adjustment of the hydrogen storage capacity of the hydrogen storage tank. On the premise of meeting the downstream hydrogen load demand, the power of renewable energy generation is fully utilized, and the hydrogen production power of the electrolyzer is operated in a higher efficiency range to improve the hydrogen production efficiency. The recovery power is calculated according to formula (9); Where: P HS.C.re is the hydrogen energy storage and hydrogen production power, P W , P S are wind power and solar power generation respectively, P HS.C.min is the minimum hydrogen production power for hydrogen energy storage, P HS.C.max The maximum hydrogen production power for hydrogen energy storage.

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