A grid-connected hybrid energy storage control system for an off-grid hydrogen production system

Abstract

The application discloses a grid-connected type hybrid energy storage configuration of an off-grid hydrogen production system and a control method thereof, and relates to the technical field of renewable energy hydrogen supply. The system comprises a wind power generation unit, a photovoltaic power generation unit, a grid-connected type hybrid energy storage unit, an electrolytic cell unit and a controller. The wind power and the photovoltaic power generation are connected to an alternating current bus through a converter to provide renewable power for the system; the hybrid energy storage unit is composed of a super capacitor and a lithium battery, and is connected to the alternating current bus in a bidirectional mode through an energy storage converter; and the electrolytic cell is connected to the alternating current bus through an AC / DC converter. In the control method, the frequency of the alternating current bus is detected in real time, a frequency modulation dead zone is set, the super capacitor and the lithium battery are controlled to participate in frequency modulation adjustment in a time-sharing mode, and the frequency stability of the system and the continuity of electrolytic hydrogen production are ensured. The application has the advantages of fast frequency response capability, grid-connected operation capability and high-efficiency hydrogen production performance, and is suitable for the construction of green hydrogen energy systems in remote areas and in scenes without power grid access.

Description

Technical Field

[0001] This invention relates to the field of new energy hydrogen production, and in particular to a grid-type hybrid energy storage control system for an off-grid hydrogen production system. Background Technology

[0002] Against the backdrop of rapid development of renewable energy, clean energy sources such as wind and solar power are gradually becoming important supports for energy structure adjustment and the achievement of carbon reduction goals. However, due to the volatility and uncontrollability of natural resources, these energy sources face severe challenges in terms of output power and frequency stability, especially in isolated or off-grid operation scenarios, which can easily lead to system frequency fluctuations and voltage instability, seriously restricting the feasibility of large-scale off-grid applications. Meanwhile, water electrolysis for hydrogen production, as an important green hydrogen energy production route, still faces significant challenges in system coupling and coordinated control under off-grid conditions due to its high requirements for power supply stability and power continuity.

[0003] Existing off-grid renewable energy hydrogen production systems mostly employ wind-solar hybrid solutions, using wind and solar power systems to simultaneously power water electrolysis hydrogen production equipment. Some systems are equipped with batteries to mitigate output fluctuations from renewable energy sources. However, these systems typically rely on "follow-the-line" control, and the energy storage devices lack active grid connection capabilities. They cannot provide system-level frequency support and voltage reference in off-grid conditions, making the system highly susceptible to instability under power instability or load disturbances. Especially under conditions of drastic wind speed changes or severe solar radiation fluctuations, the system frequency often experiences short-term drops or rises. Traditional energy storage systems exhibit lag in response and low adjustment rates, making it difficult to meet the high power quality requirements of off-grid hydrogen production systems.

[0004] Furthermore, most conventional energy storage systems employ a single type of energy storage medium, such as lithium-ion batteries or lead-acid batteries, for energy storage and regulation. While these systems possess a certain energy density and storage capacity, their power density is relatively limited, making it difficult to respond to grid frequency fluctuations within milliseconds. Especially in off-grid conditions, load disturbances directly affect the grid frequency. A single energy storage medium cannot simultaneously address short-term and medium-to-long-term frequency regulation across different time scales, leading to decreased system frequency control accuracy and potentially triggering protective shutdowns of the electrolyzer equipment. This, in turn, impacts the continuity of the hydrogen production process and the overall system efficiency.

[0005] While existing literature proposes combining supercapacitors and battery systems to construct hybrid energy storage architectures to address frequency fluctuation issues, these structures are mostly applied to grid-connected scenarios. Their control strategies generally rely on voltage and frequency references provided by the external power grid, lacking grid-building capabilities and making it difficult to autonomously construct voltage and frequency references for the AC bus in islanded mode. Furthermore, most systems fail to achieve dynamic division of labor and frequency regulation logic switching between energy storage systems, and lack effective frequency regulation dead-zone ranges or critical point switching mechanisms. This results in control overlap, resource waste, and even mutual interference between supercapacitors and battery systems during frequency regulation, severely impacting system response efficiency and the lifespan of energy storage resources.

[0006] Furthermore, traditional off-grid power systems for hydrogen production via water electrolysis often employ fixed-frequency, fixed-voltage control schemes to ensure stable operation of the electrolyzer, but they neglect the coupling characteristics between dynamic changes in system frequency and the energy storage system's regulation process, lacking real-time response mechanisms for frequency and power regulation. When the electrolyzer load changes abruptly or the system experiences frequency disturbances, existing solutions often cannot quickly provide the required active power through energy storage, leading to persistent system frequency deviations. This further triggers problems such as current surges in the electrolyzer, electrode aging, or reduced reaction efficiency, which is detrimental to the long-term stability of hydrogen production and energy efficiency.

[0007] Therefore, there is an urgent need to propose a hybrid energy storage configuration and control method with grid-connected capability. By rationally designing the energy storage structure, constructing a multi-timescale frequency regulation strategy, and achieving dynamic coordinated control with the electrolyzer load, the operational stability and energy efficiency of the entire off-grid hydrogen production system can be improved, thus promoting the widespread application of green hydrogen energy in off-grid scenarios. Summary of the Invention

[0008] One objective of this invention is to propose a grid-connected hybrid energy storage control system for off-grid hydrogen production systems. This invention fully integrates wind power generation, photovoltaic power generation, grid-connected hybrid energy storage, and water electrolysis hydrogen production technologies. It features a detailed design of a dual energy storage structure with coordinated frequency regulation of supercapacitors and lithium batteries, and constructs a multi-timescale frequency regulation control logic based on real-time frequency detection. This system can autonomously maintain the frequency stability and energy balance of the AC bus in off-grid conditions, ensuring the continuous and safe operation of the electrolyzer for hydrogen production. It has the advantages of fast frequency response, high system stability, and controllable hydrogen production rate.

[0009] A grid-connected hybrid energy storage control system for an off-grid hydrogen production system according to an embodiment of the present invention includes:

[0010] Wind power generation unit, used to provide renewable AC power;

[0011] Photovoltaic power generation units are used to provide renewable DC-to-AC power.

[0012] Grid-type hybrid energy storage units are used to achieve bidirectional energy regulation and frequency support for the system;

[0013] The electrolyzer unit, whose input is connected to the AC bus via an AC / DC converter, is used for hydrogen production by electrolysis of water in an off-grid state.

[0014] The controller is used to detect the real-time frequency of the AC bus and control the operating status of the supercapacitor energy storage converter and the lithium battery energy storage converter.

[0015] Optionally, the wind power generation unit includes a wind turbine, a wind power pitch control device, and an AC / AC converter. The wind turbine is used to convert wind energy into variable frequency and amplitude alternating current. The wind power pitch control device is used to adjust the wind turbine blade angle to adapt to wind speed changes and achieve power control. The AC / AC converter includes a rectifier module and an inverter module. The rectifier module converts the variable frequency alternating current output by the wind turbine into direct current, and the inverter module inverts the direct current into alternating current with the same frequency as the AC bus.

[0016] Optionally, the photovoltaic power generation unit includes a photovoltaic module array, a maximum power point tracking device, and a DC / AC converter. The photovoltaic module array is used to convert solar energy into direct current, the maximum power point tracking device is used to adjust the operating voltage in real time according to the irradiance and load conditions to obtain the maximum output power of the photovoltaic module, and the DC / AC converter is used to convert the DC power regulated by the maximum power point tracking into AC power that matches the AC bus frequency.

[0017] Optionally, the grid-type hybrid energy storage unit includes a supercapacitor and a lithium battery connected in parallel, respectively connected to a supercapacitor energy storage converter and a lithium battery energy storage converter. The supercapacitor has high power density and fast charging and discharging capability, and is used for response control of short-term frequency fluctuations and transient power disturbances in the system. The lithium battery has high energy density and large capacity characteristics, and is used for system energy balance and medium- and long-term frequency offset regulation. The supercapacitor energy storage converter and the lithium battery energy storage converter are bidirectionally connected to the AC bus, respectively, for energy injection and absorption according to the frequency regulation control strategy.

[0018] A method for controlling a grid-type hybrid energy storage system in an off-grid hydrogen production system according to an embodiment of the present invention includes the following steps:

[0019] S1. The AC power output from the wind power generation unit is converted by the AC / AC converter and then connected to the AC bus. The DC power output from the photovoltaic power generation unit is converted by the DC / AC converter and then connected to the AC bus, forming an AC power supply channel for renewable energy aggregation.

[0020] S2. Connect the supercapacitor and lithium battery in the grid-type hybrid energy storage unit to the AC bus through the supercapacitor energy storage converter and the lithium battery energy storage converter respectively, so that the supercapacitor and lithium battery can perform bidirectional power interaction through the AC side power supply channel and dynamically adjust the system frequency.

[0021] S3. Connect the electrolyzer to the AC bus via an AC / DC converter, receive stable AC power from the AC power supply channel, and convert it into DC power via the AC / DC converter to drive the electrolyzer to perform the hydrogen production reaction.

[0022] S4. Detect the real-time operating frequency of the AC bus. Set target frequency and the frequency regulation dead zone range of lithium battery energy storage converter ;

[0023] S5. If the real-time operating frequency f is within the frequency modulation dead zone, control the supercapacitor energy storage converter to charge and discharge to adjust the system frequency, wherein when When the supercapacitor performs a discharge operation, the discharge power is the smaller value between the power required to adjust the frequency and the maximum discharge power of the supercapacitor; when When the supercapacitor performs a charging operation, the charging power is the smaller value between the power required to adjust the frequency and the maximum charging power of the supercapacitor.

[0024] S6. If the real-time operating frequency f is not within the frequency modulation dead zone, control the lithium battery energy storage converter to charge and discharge to adjust the system frequency, wherein when When the lithium battery performs a discharge operation, the discharge power is the smaller value between the power required to adjust the frequency and the maximum discharge power of the lithium battery; when When the lithium battery is charging, the charging power is the smaller value between the power required to adjust the frequency and the maximum charging power of the lithium battery.

[0025] S7. When the real-time operating frequency f recovers to the frequency regulation dead zone range, the control logic switches to the supercapacitor energy storage converter to continue the frequency regulation operation, and the lithium battery exits the frequency regulation process.

[0026] The beneficial effects of this invention are:

[0027] This invention improves the operational stability and system reliability of renewable energy hydrogen production in off-grid scenarios by constructing an off-grid hydrogen production system with grid-connection capabilities. Firstly, the invention introduces a hybrid energy storage unit composed of supercapacitors and lithium batteries into the system structure, each connected to a dedicated energy storage converter, achieving bidirectional energy regulation and rapid frequency response control. By using supercapacitors for rapid response to short-term frequency fluctuations and transient power disturbances, and lithium batteries for energy balance and medium- to long-term frequency offset regulation, a multi-timescale frequency regulation architecture that balances response speed and energy capacity is constructed, significantly improving the system's adaptability to fluctuating wind and solar power inputs.

[0028] Secondly, this invention establishes a clearly defined frequency regulation dead zone range and adjustment switching logic. It can automatically select between supercapacitors and lithium batteries to handle frequency regulation based on the real-time detected AC bus frequency, avoiding control overlap and resource waste between energy storage devices, and improving the efficiency of system frequency regulation and the lifespan of energy storage resources. When the frequency is within the frequency regulation dead zone, the fast-responding supercapacitor prioritizes frequency correction; when the frequency deviation exceeds the set range, the lithium battery intervenes to complete a larger amount of energy injection or absorption, realizing dynamic division of labor and automatic switching of the frequency regulation logic, enhancing the system's adaptability to complex operating conditions.

[0029] Furthermore, this invention unifies the connection of wind and photovoltaic power sources to the AC bus via converters and establishes an orderly energy flow path between the grid-type hybrid energy storage unit and the electrolyzer. This enables the water electrolysis hydrogen production process to obtain stable power supply support in an off-grid state, ensuring the continuous operation of the electrolyzer and maintaining hydrogen production efficiency under frequency disturbance conditions. Simultaneously, by using a controller to monitor the AC bus frequency in real time and coordinate the operation of the supercapacitor energy storage converter and the lithium battery energy storage converter, system-level intelligent control and frequency stabilization are achieved, providing crucial support for building a highly reliable green hydrogen energy system.

[0030] Therefore, this invention achieves efficient synergy between renewable energy power supply, energy storage frequency regulation, and hydrogen production load in an off-grid operating environment. It effectively solves the problems of insufficient grid construction capability, lagging frequency control, and inefficient utilization of energy storage resources in traditional technologies. It has beneficial effects such as strong system stability, fast frequency regulation response, controllable hydrogen production rate, and long energy storage life. It has broad engineering application prospects and significant economic and environmental value. Attached Figure Description

[0031] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0032] Figure 1This is a structural diagram of a grid-type hybrid energy storage control system for an off-grid hydrogen production system proposed in this invention;

[0033] Figure 2 This is an overall flowchart of a grid-type hybrid energy storage control method for an off-grid hydrogen production system proposed in this invention. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0035] refer to Figure 1 A structural diagram of a grid-type hybrid energy storage control system for an off-grid hydrogen production system, comprising:

[0036] Wind power generation unit, used to provide renewable AC power;

[0037] Photovoltaic power generation units are used to provide renewable DC-to-AC power.

[0038] Grid-type hybrid energy storage units are used to achieve bidirectional energy regulation and frequency support for the system;

[0039] The electrolyzer unit, whose input is connected to the AC bus via an AC / DC converter, is used for hydrogen production by electrolysis of water in an off-grid state.

[0040] The controller is used to detect the real-time frequency of the AC bus and control the operating status of the supercapacitor energy storage converter and the lithium battery energy storage converter.

[0041] This invention provides a grid-connected hybrid energy storage control system for an off-grid hydrogen production system, which plays a core role in constructing an off-grid renewable energy power supply platform and achieving efficient and stable hydrogen production operation. By integrating wind power generation units, photovoltaic power generation units, grid-connected hybrid energy storage units, electrolyzer units, and controllers, this system forms an integrated energy system with self-frequency support, autonomous energy regulation, and dynamic load adaptation capabilities. It can continuously output high-quality electrical energy in a completely off-grid state, meeting the stringent requirements for voltage, current, and frequency stability in the water electrolysis hydrogen production process.

[0042] In this embodiment, the wind power generation unit includes a wind turbine, a wind power pitch control device, and an AC / AC converter. The wind turbine is used to convert wind energy into variable frequency and amplitude alternating current. The wind power pitch control device is used to adjust the wind turbine blade angle to adapt to wind speed changes and achieve power control. The AC / AC converter includes a rectifier module and an inverter module. The rectifier module converts the variable frequency alternating current output by the wind turbine into direct current, and the inverter module inverts the direct current into alternating current with the same frequency as the AC bus.

[0043] In this embodiment, the photovoltaic power generation unit includes a photovoltaic module array, a maximum power point tracking device, and a DC / AC converter. The photovoltaic module array is used to convert solar energy into direct current. The maximum power point tracking device is used to adjust the operating voltage in real time according to the irradiance and load conditions to obtain the maximum output power of the photovoltaic module. The DC / AC converter is used to convert the DC power regulated by the maximum power point tracking into AC power that matches the AC bus frequency.

[0044] In this embodiment, the grid-type hybrid energy storage unit includes a supercapacitor and a lithium battery connected in parallel, respectively connected to a supercapacitor energy storage converter and a lithium battery energy storage converter. The supercapacitor has high power density and fast charging and discharging capability, and is used for response control of short-term frequency fluctuations and transient power disturbances in the system. The lithium battery has high energy density and large capacity characteristics, and is used for system energy balance and medium- and long-term frequency offset regulation. The supercapacitor energy storage converter and the lithium battery energy storage converter are bidirectionally connected to the AC bus, and are used for energy injection and absorption according to the frequency regulation control strategy.

[0045] The various functional modules in the system are interconnected via an AC bus. Wind and solar energy, after being standardized by converters, are jointly injected into the grid, providing a green power foundation for the system. The grid-connected hybrid energy storage unit undertakes the tasks of system frequency regulation and bidirectional power flow management, maintaining grid parameter stability under conditions of fluctuating wind and solar power output or sudden load changes. The controller enables intelligent real-time frequency monitoring and dynamic scheduling of the energy storage converter, giving the system proactive grid-connection capabilities and rapid disturbance response capabilities. The electrolyzer, as the load end, continuously carries out hydrogen production reactions under stable power supply conditions, realizing the conversion of clean energy into high-value-added hydrogen energy products.

[0046] Therefore, the grid-connected hybrid energy storage configuration of this off-grid hydrogen production system solves the problems of frequency fluctuation control difficulties, unstable power supply and system response lag in traditional off-grid hydrogen production schemes, and improves the system's independent operation capability, operational safety and hydrogen production efficiency.

[0047] refer to Figure 2 A method for controlling a grid-type hybrid energy storage system in an off-grid hydrogen production system includes the following steps:

[0048] S1. The AC power output from the wind power generation unit is converted by the AC / AC converter and then connected to the AC bus. The DC power output from the photovoltaic power generation unit is converted by the DC / AC converter and then connected to the AC bus, forming an AC power supply channel for renewable energy aggregation.

[0049] S2. Connect the supercapacitor and lithium battery in the grid-type hybrid energy storage unit to the AC bus through the supercapacitor energy storage converter and the lithium battery energy storage converter respectively, so that the supercapacitor and lithium battery can perform bidirectional power interaction through the AC side power supply channel and dynamically adjust the system frequency.

[0050] S3. Connect the electrolyzer to the AC bus via an AC / DC converter, receive stable AC power from the AC power supply channel, and convert it into DC power via the AC / DC converter to drive the electrolyzer to perform the hydrogen production reaction.

[0051] S4. Detect the real-time operating frequency of the AC bus. Set target frequency and the frequency regulation dead zone range of lithium battery energy storage converter ;

[0052] S5. If the real-time operating frequency f is within the frequency modulation dead zone, control the supercapacitor energy storage converter to charge and discharge to adjust the system frequency, wherein when When the supercapacitor performs a discharge operation, the discharge power is the smaller value between the power required to adjust the frequency and the maximum discharge power of the supercapacitor; when When the supercapacitor performs a charging operation, the charging power is the smaller value between the power required to adjust the frequency and the maximum charging power of the supercapacitor.

[0053] S6. If the real-time operating frequency f is not within the frequency modulation dead zone, control the lithium battery energy storage converter to charge and discharge to adjust the system frequency, wherein when When the lithium battery performs a discharge operation, the discharge power is the smaller value between the power required to adjust the frequency and the maximum discharge power of the lithium battery; when When the lithium battery is charging, the charging power is the smaller value between the power required to adjust the frequency and the maximum charging power of the lithium battery.

[0054] S7. When the real-time operating frequency f recovers to the frequency regulation dead zone range, the control logic switches to the supercapacitor energy storage converter to continue the frequency regulation operation, and the lithium battery exits the frequency regulation process.

[0055] The method of this invention aims to achieve precise adjustment and stable control of the system frequency by dynamically scheduling the energy storage system, thereby ensuring the continuous and stable operation of the electrolyzer and the efficiency of hydrogen production in off-grid conditions. This method constructs an intelligent control strategy system for off-grid operation scenarios of renewable energy. Its core lies in utilizing the complementary characteristics of supercapacitors and lithium batteries in terms of power density and energy density to collaboratively complete frequency disturbance response tasks of different intensities and time scales through time-sharing and division of labor.

[0056] In this control method, the electrical energy output from the wind power generation unit and the photovoltaic power generation unit is first connected to a unified AC bus via their respective converters, forming a stable power supply channel within the off-grid system, serving as the power foundation for system frequency regulation and load power supply. Subsequently, the controller monitors the operating frequency of the AC bus in real time and, based on the set target frequency and frequency regulation dead zone, determines whether a supercapacitor or a lithium battery should participate in frequency regulation. If the frequency fluctuation is within the set dead zone, the control system prioritizes the faster-responding supercapacitor energy storage converter for small-amplitude, rapid adjustment; if the frequency fluctuation exceeds the set range, the lithium battery, with its larger energy capacity, intervenes for frequency regulation.

[0057] The method establishes a "primary-secondary frequency regulation" and "fast-slow coordination" control strategy, effectively preventing excessive response of energy storage resources and overlapping frequency control, thereby improving frequency regulation efficiency and the lifespan of the energy storage system. Simultaneously, by setting the charging and discharging power to the smaller value between the required power and the maximum allowable power, adaptive limiting during frequency regulation is achieved, avoiding overload or deep charging and discharging of the energy storage system and enhancing the safety and robustness of system operation.

[0058] When hydrogen production is carried out as the main load by water electrolysis, this control method ensures that the frequency of the AC bus can remain in a stable range even under conditions of large fluctuations in renewable energy input. This allows the electrolyzer to continuously receive a stable DC power supply (converted via an AC / DC converter), thereby ensuring the continuity and efficiency of hydrogen production and avoiding electrolyzer shutdowns or efficiency reductions caused by frequency disturbances.

[0059] Therefore, in practical implementation, this control method realizes the orderly scheduling and intelligent frequency regulation of hybrid energy storage devices, and plays a comprehensive role in frequency support, system stability and load protection. It is a key technical support means to build the safe, efficient and long-cycle operation capability of the entire off-grid hydrogen production system.

[0060] Example 1:

[0061] To verify the feasibility of this invention in practice, it was applied to an off-grid photovoltaic-hydrogen storage integrated demonstration project in a certain region. This project is located in an area rich in wind and solar energy resources but far from the main power grid coverage, representing a typical scenario of "abundant renewable energy but limited energy consumption." The region has an average annual wind speed of 6.8 m / s and over 3000 hours of sunshine annually, possessing natural advantages for coupling wind-solar hybrid power generation with off-grid hydrogen production. However, due to the lack of grid connection, the existing photovoltaic hydrogen production system suffers from large power supply fluctuations, frequent electrolyzer shutdowns, and unstable hydrogen production rates, severely restricting the efficient production and resource utilization of green hydrogen.

[0062] In this application scenario, this invention deploys a grid-connected hybrid energy storage off-grid hydrogen production system. It includes 300kW photovoltaic modules and a 200kW wind turbine generator, along with a hybrid energy storage system comprising a 150kWh lithium battery and a 50kWh supercapacitor. The energy storage converters are bidirectional three-phase full-bridge structures with rated powers of 100kW and 30kW, respectively. The system is connected to an independent AC bus, with all power generation equipment connected and coordinated by the controller of this invention. Simultaneously, a 50Nm³ / h alkaline electrolyzer is connected to this bus via an AC / DC converter to achieve hydrogen production.

[0063] In actual operation, the system is primarily powered by solar energy from 6:30 AM to 8:30 PM daily, while at night it relies mainly on wind power to maintain AC bus power supply. The controller samples the AC bus frequency five times per second. When the frequency fluctuates slightly within ±0.1Hz, the system prioritizes the use of supercapacitors for rapid adjustment, restoring the frequency to the target value of 50Hz within ±0.05Hz. When the frequency fluctuates significantly due to inconsistent sunlight, such as a deviation of ±0.3Hz, the system automatically switches to lithium battery control for frequency regulation, stabilizing the output or absorbed power between 60 and 80kW, effectively suppressing power instability caused by frequency fluctuations.

[0064] Through the above implementation examples, the present invention effectively solves the problems of difficult frequency control, severe power fluctuations, frequent electrolyzer shutdowns, and low hydrogen production efficiency in off-grid hydrogen production systems. It significantly improves the stability of system operation, frequency regulation capability, and energy utilization efficiency, and verifies the engineering feasibility and application value of this technology in the scenario of integrating renewable energy and hydrogen energy.

[0065] Table 1: Statistical Table of Comparative Data of Application Demonstration Projects of the Invention

[0066] Project Indicators Traditional solution (without energy storage deployment) This invention provides a solution for deploying grid-based hybrid energy storage. Total system uptime (hours) 1884 2063 Effective operating time of the electrolytic cell (hours) 1457 1937 Electrolytic cell availability 77.3% 93.9% Average number of automatic shutdowns of electrolytic cells per week 6.5 times 0.2 times Electrolyzer current fluctuation rate (±) ±12% ±3% Daily hydrogen production (Nm³) 38 46 Hydrogen production efficiency improvement (%) — +21.1% System energy conversion efficiency (solar-wind to hydrogen, %) 39.5% 48.7% Energy utilization rate of energy storage system (%) 61.8% 82.5% Sudden disturbance recovery time (within ±0.2Hz, seconds) >10 seconds <2 seconds Lithium-ion battery deep cycle count (within 90 days) 210 times 124 times

[0067] From the comparison data of off-grid hydrogen production system operation shown in Table 1 above, it can be clearly observed that the grid-type hybrid energy storage control method proposed in this invention has achieved significant optimization effects on several key operating performance indicators, especially in terms of frequency stability, electrolyzer availability, hydrogen production efficiency and energy utilization of the energy storage system, all of which demonstrate superior system performance.

[0068] Taking the availability of electrolyzers as an example, in traditional off-grid systems without hybrid energy storage, the drastic fluctuations in wind and solar power output and the lagging frequency control mechanism cause frequent shutdowns due to over- or under-frequency triggering of protection mechanisms, resulting in up to 6.5 operational interruptions per week, directly impacting hydrogen production efficiency. The present invention, however, introduces a dynamic control strategy of "fast and slow coordination, main and auxiliary frequency regulation," enabling the supercapacitor to correct frequency disturbances with millisecond-level response, while the lithium battery smoothly takes over after exceeding the frequency regulation dead zone. This effectively avoids drastic frequency shifts and significantly improves system stability. In 90 consecutive days of actual operation, the electrolyzer accumulated 1937 hours of effective operation, achieving an availability rate of 93.9%, far exceeding the 77.3% of the traditional solution, demonstrating the excellent frequency disturbance suppression capability of this control method.

[0069] In terms of hydrogen production performance, this invention also demonstrates a significant improvement. Benefiting from stable power input and low-frequency fluctuating current, the electrolyzer current fluctuation rate is reduced from ±12% to ±3%, significantly improving the stability and continuity of the electrolysis reaction and avoiding frequent electrode polarization, current surges, and fluctuations in hydrogen production caused by fluctuations. Under these conditions, the average daily hydrogen production increases from 38 Nm³ to 46 Nm³, with a hydrogen production efficiency improvement of over 21%. This change not only demonstrates that the system can achieve high-quality power support without relying on the power grid, but also reflects the adaptability of the control method to the power supply of the end-point hydrogen production load.

[0070] In terms of energy efficiency, the system's integrated solar-wind-hydrogen energy conversion efficiency has increased from 39.5% in the traditional structure to 48.7%, mainly due to the energy storage device's participation in the frequency regulation process, which reduces power loss within the system and optimizes load operating conditions. Simultaneously, the energy utilization rate of the energy storage system itself has increased from 61.8% to 82.5%, with the supercapacitor undertaking over 87% of the instantaneous frequency regulation task, averaging up to 170 responses per day, significantly reducing the burden of deep discharge on the lithium battery. Under the control strategy, the number of deep charge-discharge cycles of the lithium battery within 90 days has decreased from 210 to 124, indirectly extending its lifespan and performance maintenance period, thus ensuring the economy and maintainability of engineering deployments.

[0071] It is worth noting that under complex meteorological conditions, including repeated sudden wind speed surges (such as instantaneous wind speeds exceeding 12 m / s) and widespread photovoltaic shading (such as high-altitude clouds causing a sudden drop in array output voltage), the system frequency exhibited a deviation trend exceeding ±0.25 Hz. Failure to adjust in time could easily trigger the electrolytic cell shutdown. However, in the solution of this invention, the supercapacitors were able to complete the frequency correction to the ±0.2 Hz range within 2 seconds. Subsequently, the controller automatically switched to the lithium battery for relay compensation, ensuring that the system frequency stabilized within ±0.05 Hz within 10 seconds. This verifies the closed-loop efficiency of this control strategy in multi-timescale frequency modulation.

[0072] In summary, the actual deployment of this invention in this embodiment verifies its adaptability to fluctuations in power supply from multiple renewable energy sources, its rapid response to frequency disturbances, its stable support for terminal loads, and its efficient allocation of energy storage resources. By constructing an AC bus network with autonomous grid-building capabilities and supplementing it with an intelligent energy storage scheduling mechanism, this system solves the problems of large frequency fluctuations, unstable operation, low hydrogen production efficiency, and poor energy storage utilization in traditional off-grid hydrogen production systems. It improves the overall operational quality and energy efficiency of the system, providing strong technical support for green hydrogen production in remote areas, microgrids, and island energy systems.

[0073] The results of this embodiment fully demonstrate the systematic advantages of the present invention in multiple aspects, including optimization of grid-type hybrid energy storage architecture, power supply adaptation to electrolytic loads, multi-source frequency regulation and coordinated control, improvement of energy conversion efficiency, and extension of energy storage life. It possesses broad promotional value and practical application prospects. The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention should fall within the scope of protection of the present invention.

Claims

1. A network-constructing type hybrid energy storage control system of an off-grid hydrogen production system, characterized by, The application relates to a renewable energy supply system, which comprises the following units: a wind power generation unit for providing renewable AC power supply; a photovoltaic power generation unit for providing renewable DC-to-AC power supply; a network-constructing hybrid energy storage unit for realizing bidirectional energy regulation and frequency support of the system; an electrolytic cell unit, the input end of which is connected with an AC bus through an AC / DC converter, for electrolyzing water to produce hydrogen in an off-grid state; a controller for detecting the real-time frequency of the AC bus and controlling the working state of a super capacitor energy storage converter and a lithium battery energy storage converter; the application further comprises the following steps: S1, AC power output by the wind power generation unit is connected with the AC bus through an AC / AC converter, and DC power output by the photovoltaic power generation unit is connected with the AC bus through a DC / AC converter, so as to form an AC side power supply channel for renewable energy collection; S2, the super capacitor and the lithium battery in the network-constructing hybrid energy storage unit are respectively connected with the AC bus through a super capacitor energy storage converter and a lithium battery energy storage converter, so that the super capacitor and the lithium battery can realize bidirectional energy interaction through the AC side power supply channel and dynamically regulate the system frequency; S3, the electrolytic cell is connected with the AC bus through an AC / DC converter, receives stable AC power supply from the AC side power supply channel, and is converted into DC power through the AC / DC converter to drive the electrolytic cell to carry out hydrogen production reaction; S4, detecting real-time operation frequency of the AC bus , setting target frequency and frequency modulation dead zone range of the lithium battery energy storage converter ; S5, if the real-time running frequency f is in the frequency modulation dead zone range, the super capacitor energy storage converter is controlled to charge and discharge to adjust the system frequency, wherein when the super capacitor performs discharging operation, and the discharging power is the smaller value between the power required for adjusting the frequency and the maximum discharging power of the super capacitor; when the super capacitor performs charging operation, and the charging power is the smaller value between the power required for adjusting the frequency and the maximum charging power of the super capacitor. S6、if the real-time operating frequency f is not in the frequency modulation dead zone range, control the lithium battery energy storage converter to charge and discharge to adjust the system frequency, wherein when the lithium battery performs discharging operation, and the discharging power is the smaller value between the power required for adjusting the frequency and the maximum discharging power of the lithium battery; when the lithium battery performs charging operation, and the charging power is the smaller value between the power required for adjusting the frequency and the maximum charging power of the lithium battery. S7, when the real-time operation frequency f returns to the frequency regulation dead zone, the control logic is switched to the super capacitor energy storage converter to continue the frequency regulation operation, and the lithium battery exits the frequency regulation process.

2. The grid-connected hybrid energy storage control system of the off-grid hydrogen production system according to claim 1, characterized in that, The wind power generation unit comprises a wind driven generator, a wind energy variable pitch control device and an AC / AC converter, the wind driven generator is used for converting wind energy into variable frequency and variable amplitude AC power, the wind energy variable pitch control device is used for adjusting the blade angle of the wind wheel to adapt to the change of wind speed and realize power control, and the AC / AC converter comprises a rectification module and an inversion module, the rectification module converts the variable frequency AC power output by the wind driven generator into DC power, and the inversion module inverses the DC power into AC power consistent with the frequency of the AC bus.

3. The grid-connected hybrid energy storage control system of the off-grid hydrogen production system according to claim 1, characterized in that, The photovoltaic power generation unit comprises a photovoltaic module array, a maximum power point tracking device and a DC / AC converter, the photovoltaic module array is used for converting solar energy into DC power, the maximum power point tracking device is used for adjusting the working voltage in real time according to the irradiation intensity and the load condition to obtain the maximum output power of the photovoltaic module, and the DC / AC converter is used for converting the DC power adjusted by the maximum power point tracking into AC power matched with the frequency of the AC bus.

4. The grid-connected hybrid energy storage control system of claim 1, wherein, The network-constructing hybrid energy storage unit comprises a super capacitor and a lithium battery connected in parallel, and is respectively connected with a super capacitor energy storage converter and a lithium battery energy storage converter, the super capacitor has high power density and fast charging and discharging capacity and is used for responding to short-time frequency fluctuation and transient power disturbance of the system, the lithium battery has high energy density and large capacity characteristics and is used for energy balance and medium and long-term frequency offset regulation of the system, and the super capacitor energy storage converter and the lithium battery energy storage converter are respectively bidirectionally connected with the AC bus and are used for energy injection and absorption according to a frequency regulation control strategy.

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