A micro-grid hybrid energy storage system based on wind power, tidal current energy and seawater desalination hydrogen production

Abstract

The application discloses a micro-grid hybrid energy storage system based on wind power, tidal current energy and seawater desalination hydrogen production, which comprises a wind-tide combined power generation system, a micro-grid hybrid energy storage system, a reverse osmosis seawater desalination system, an electric load and an alkali water electrolysis hydrogen production system, and simultaneously uses comprehensive power generation unit power smoothing control for steady-state control. As shown in the figure, the wind-tide combined power generation system provides energy for the hybrid energy storage system. The hybrid energy storage unit carries out seawater desalination under variable working conditions through the reverse osmosis seawater desalination system in the micro-grid background, can efficiently adjust the RO seawater operation load, recovers concentrated water to reduce energy consumption and cost. Meanwhile, the recovered water is stored through the alkali water electrolysis hydrogen production system to realize power storage and guarantee power supply.

Description

Technical Field

[0001] This invention belongs to the field of ocean energy power generation and application technology, specifically relating to a microgrid hybrid energy storage system based on wind power, tidal energy and seawater desalination for hydrogen production. Background Technology

[0002] Faced with the increasingly scarce global freshwater resources and my country's rapidly developing industrialization, seawater desalination technology plays a crucial role in alleviating the water crisis, while hybrid energy storage is vital for propelling my country's sustainable economic and social development to a new level. Meanwhile, against the backdrop of conventional energy shortages and ecological degradation, tidal power generation offers advantages such as being green, environmentally friendly, and highly predictable; wind power generation, as a renewable and pollution-free new energy technology, is gradually maturing; and ocean energy development receives strong policy support from my country. Seawater desalination for hydrogen production is an energy-intensive industry, and wind-tidal coupled power generation provides energy to the seawater desalination system, offering a dual benefit of alleviating the energy crisis and water scarcity. Therefore, exploring a wind-tidal-based hydrogen production and energy storage coupled system with seawater desalination is of great significance.

[0003] Existing technologies include hydrogen production and energy storage units operating as single power generation devices, and research has also been conducted on parameters and operating mechanisms of seawater desalination hydrogen production systems. However, further research is needed on utilizing multi-energy coupled power generation units at sea to achieve hydrogen production, energy storage, and seawater desalination, as well as applying seawater desalination hydrogen production technology to offshore microgrids. Furthermore, the poor power output stability of ocean energy coupled power generation and the high energy consumption of hybrid energy storage pose engineering challenges to the realization of coupled systems. Therefore, how to achieve steady-state control of the output power of wind and tidal current coupled power generation, how to efficiently realize hybrid energy storage, improve ocean energy utilization, and reduce energy consumption are all key issues for promoting the comprehensive development and utilization of ocean energy. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a microgrid hybrid energy storage system based on wind power, tidal energy, and seawater desalination for hydrogen production.

[0005] To address the shortcomings of existing technologies, the present invention adopts the following solution:

[0006] A microgrid hybrid energy storage system based on wind power, tidal energy and seawater desalination for hydrogen production includes an offshore wind power generation mechanism, a tidal energy generation mechanism, a seawater desalination mechanism, an electrolyzer, a hydrogen storage tank, a fuel cell and a battery.

[0007] The offshore wind power generation mechanism and the tidal turbine generator respectively use wind energy and tidal energy to power the electrolyzer and the reverse osmosis seawater desalination mechanism, and the excess power will be supplied to the storage battery; the seawater desalination mechanism desalinates seawater and then electrolyzes it in the electrolyzer to produce hydrogen, which is stored in a hydrogen storage tank and supplied to the hydrogen-oxygen fuel cell.

[0008] When the electrical energy generated by the wind power generation mechanism and the tidal power generation mechanism is insufficient to maintain the operation of the entire system, the battery is connected to the microgrid to continue supplying power.

[0009] Further optimization reveals the following power constraints for the microgrid hybrid energy storage system:

[0010] ∑P ore (t)+P pur (t)+P dis,bat (t)+P fc (t)=P load (t)+P cha,bat (t)+P el (t)+P de (t)

[0011] Among them, P pur (t) represents the power connected to the grid at time t, P ore (t) is the actual output power of the wind power generation mechanism and the tidal power generation mechanism, P load (t) represents the output power of the load end of this system (hydrogen production, seawater desalination, and supply required for the normal operation of this system); P de (t) represents the power consumption of the seawater desalination unit during time period t, P el (t) represents the power consumption of the electrolytic cell during time period t; P cha,bat (t) represents the charging power of the battery during time period t, P dis,bat (t) represents the discharge power of the battery during time period t.

[0012] Further optimization involves the main steps of seawater desalination and hydrogen production, including using a seawater desalination unit to desalinate seawater and electrolyzing the generated freshwater into hydrogen and oxygen, along with related byproducts such as liquid chlorine, caustic soda, and concentrated hydrochloric acid, through an electrolyzer.

[0013] The electricity consumption for desalinating seawater using reverse osmosis in a desalination plant is expressed as follows:

[0014] P de (t)=αP el (t)

[0015] Among them, P de (t) represents the power consumption of the seawater desalination unit during time period t, P el (t) represents the power consumption of the electrolyzer during time period t, and α is the ratio of the power consumption of the seawater desalination system to the power required for water electrolysis.

[0016] During electrolysis, the output power of the electrolytic cell is expressed as:

[0017] P el,H (t)=η el Pel (t)

[0018] Among them, P el,H η is the hydrogen production power of the electrolyzer during time period t; el The hydrogen production efficiency of the electrolyzer;

[0019] The hydrogen storage tank is used to store hydrogen produced by water electrolysis and to provide hydrogen for the fuel cell. Its energy storage mathematical model is expressed as follows:

[0020]

[0021] in, The energy stored in the hydrogen storage tank during time period t. The hydrogen consumption power of the fuel cell during time period t. These represent the efficiency of hydrogen charging and discharging, respectively; Δt is the scheduling time.

[0022] The fuel cell converts clean hydrogen into electrical energy, and its mathematical model is expressed as follows:

[0023]

[0024] Among them, P fc (t) represents the power generation of the fuel cell during time period t, η fc The efficiency of hydrogen power generation from fuel cells.

[0025] Further optimization reveals that the power consumption in the hydrogen production and storage process is mainly from the water electrolysis process. The internal constraints on the power consumption of the electrolyzer during time period t primarily depend on the capacity and remaining capacity of the hydrogen storage tank. Furthermore, the hydrogen storage tank must satisfy the constraint of consistent initial and final states, thus resulting in the following three constraints:

[0026]

[0027] Among them, W el For the reserves of the electrolytic cell, These are the upper and lower limits of the hydrogen storage tank capacity, respectively. Let t be the amount of hydrogen stored in the hydrogen storage tank at time t. The initial and final states of the hydrogen storage tank.

[0028] Further optimization involves the fuel cell consuming hydrogen to generate electricity and power the system, as well as providing partial active power support. The constraint it must satisfy is that the fuel cell's output power depends on its capacity and the amount of hydrogen remaining in the hydrogen storage tank that can be supplied to the fuel cell at the current moment. Therefore, the constraint is:

[0029]

[0030] Among them W fc This refers to the capacity of the fuel cell.

[0031] Further optimization involves connecting the battery to the microgrid to continue supplying power when the electrical energy generated by the wind power generation mechanism and the tidal power generation mechanism is insufficient to sustain the operation of the entire system. The battery effectively mitigates fluctuations caused by sudden changes in load demand within the microgrid; its mathematical model is as follows:

[0032]

[0033] In the formula, P cha,bat (t), P dis,bat (t) represents the charging and discharging power of the battery during time period t; η cha,bat (t), η dis,bat (t) represents the battery charging and discharging efficiency; E bat (t) represents the stored energy of the battery during time period t; δ represents the battery's self-discharge loss rate.

[0034] The battery needs to meet the capacity constraint that is consistent with the initial and final states, and it also needs to meet the charge and discharge efficiency constraint. The specific constraint relationships are as follows:

[0035]

[0036] Among them, E bat,min E bat,max These represent the lower and upper limits of battery storage capacity, E bat (0), E bat (T) represent the initial and final states of the battery, respectively, and P represents the final state of the battery. cb,min P cb,max These represent the minimum and maximum charging power of the battery, respectively, P db,min P db,max These are the minimum and maximum discharge power of the battery, respectively.

[0037] Further optimization includes a raw water pretreatment device, a reverse osmosis device, an energy recovery device, and a post-treatment device. It can separate solutes and solvents in seawater using the reverse osmosis principle, adjust the RO seawater desalination operation load to adapt to changes in energy supply, and use the energy recovery device to recover the high-pressure energy at the concentrate outlet of the reverse osmosis device, thereby reducing energy consumption and desalination costs.

[0038] The pretreatment device includes a water intake pump, a seawater tank containing a flocculation device, a booster pump, a multi-media filter, an ultrafiltration membrane, and a security filter. After water purification and adjustment, the seawater is treated to a pH of 2-11; a pollution index SDI of <5; free chlorine of <0.1g / L; Mn of <1.0mg / L; and Fe of <0.1g / L.

[0039] The multi-media filter has a housing made of fiberglass and filter media made of anthracite and quartz sand; the ultrafiltration membrane has a membrane housing made of polyvinyl chloride and a membrane material made of polyvinylidene fluoride; the security filter has a filter housing made of PVC and a filter element made of PP cotton.

[0040] The reverse osmosis unit includes a reverse osmosis water supply pump, a high-pressure pump, and a reverse osmosis membrane (aromatic polyamide composite membrane). Utilizing the osmosis phenomenon and driven by a pressure difference, solvent molecules pass through the selectively permeable membrane, while solute molecules are retained at the inlet side, thus achieving solute and solvent separation and seawater desalination. The average desalination rate can reach 99.2%. The reverse osmosis membrane is an aromatic polyamide composite membrane.

[0041] Considering the instability of combined wind and tidal power generation, a variable-condition seawater desalination method is adopted. A frequency converter is used to change the speed of the high-pressure pump motor, thereby controlling the opening of the electric valve and the influent flow rate, thus adjusting the operating load of the reverse osmosis membrane seawater desalination system. A power-exchange energy recovery device is used to recover the pressure energy from the discharged concentrated brine and convert it into influent energy, achieving efficient energy utilization and reducing system energy consumption. By installing a post-treatment water storage device, the pH value of the reverse osmosis effluent can be adjusted to meet different requirements.

[0042] Further optimization yielded the following electrochemical reaction in the alkaline electrolyzer:

[0043] anode:

[0044] cathode:

[0045] overall:

[0046] Further optimization has led to diverse internal structures for alkaline water-to-hydrogen electrolyzers, which can be broadly categorized into bipolar plates, electrode frames, anode electrodes, cathode electrodes, diaphragms, and sealing gaskets. The external components of the alkaline water-to-hydrogen electrolyzer include a hydrogen-side outlet, an oxygen-side outlet, and an electrolyte inlet. During operation, the electrolyte enters the electrolyzer through the lower inlet, electrolyzing water into hydrogen and oxygen in each electrolysis chamber. The mixture of hydrogen and electrolyte flows out from the hydrogen-side outlet, and the mixture of oxygen and electrolyte flows out from the oxygen-side outlet. The bipolar plates are made of a metal resistant to alkaline corrosion and possessing good electrical conductivity. Their uneven structure increases current density, thereby improving hydrogen production efficiency. The electrode frames are rotationally symmetrical along their axis, reducing manufacturing difficulty and cost, and minimizing assembly problems caused by worker misalignment. The electrode material used for alkaline water electrolysis is nickel-based. It has rapid hydrogen absorption and dehydrogenation capabilities, stable material structure, and good conductivity; the molded electrode material has a high specific surface area, increasing the current density of the effective electrolysis apparent electrolysis area, and the electrode manufacturing cost is not too high.

[0047] Further optimization is needed. Energy consumption is the most important indicator for evaluating the performance of an electrolyzer. The formula for calculating the total voltage of an electrolyzer is:

[0048] E total =E(P,T)+E 0 (T)+E act，k +E ele +E el +E mem +E diff

[0049] In the formula, E total Let E(P,T) represent the total voltage, and E(P,T) represent the reversible overpotential. 0 (T) represents a variable reversible overpotential, E act，k This represents the activation overpotential; where k represents the combined anode and cathode, and E... ele E represents the ohmic overpotential of the electrode liquid. el E represents the ohmic overpotential of the electrode. mem E represents the ohmic overpotential of the diaphragm. diff Indicates concentration overpotential;

[0050] The overall efficiency of the entire electrolyzer system, also known as energy efficiency, is defined as:

[0051]

[0052] Among them U tn It is the thermal neutral potential of the electrolysis unit, U cell It is the instantaneous voltage of the electrolysis unit.

[0053] Further optimization is achieved by incorporating a wind power generation mechanism and a tidal current power generation mechanism into their steady-state control systems. These systems include a wind speed sensor, a wind speed and current velocity sensor, a speed and torque sensor, a turbine rotor-side controller, a wind turbine rotor-side controller, a clutch, and a speed protection module. A clutch is added to the tidal current turbine to address the impact of seawater resistance on the blades during flywheel energy storage. A speed protection module is incorporated into the coordinated control of speed, pitch, and angle to effectively prevent the rotor speed from remaining below the optimal speed for the given tidal current velocity after releasing kinetic energy, while also avoiding a decrease in system stability due to small disturbances.

[0054] By changing the operation mode of the tidal power generation mechanism, which has a higher predictability, the random power fluctuations of the integrated power generation unit caused by wind speed are compensated, thereby achieving smooth power control and stable output.

[0055] To achieve steady-state control of random power fluctuations in the integrated power generation unit, it is necessary to first collect the rotational speed n of the wind turbine's generating mechanism using a speed and torque sensor, and then obtain the corresponding real-time wind power P from the operating characteristics of the wind turbine's doubly-fed asynchronous generator. windBy using a first-order low-pass filter on the output power of the wind turbine, high-frequency noise, i.e., the random fluctuation power ΔP caused by wind, is extracted.

[0056] P smooth (k)=λP avg +(1-λ)P wind (k)

[0057]

[0058] ΔP=P smooth (k)-P wind (k)

[0059] Where P smooth (k) represents the low-frequency component of the total wind power generation, P wind (k) represents the measured power output of wind power generation, P avg Let λ be the average reference value of N state values, and let λ be the time constant of the first-order filter. In order to obtain a better smoothing effect, the average value of the first N state values ​​is taken as the reference value.

[0060] Further optimization revealed the maximum rotational kinetic energy E during the operation of the doubly-fed induction generator (DFIG):

[0061]

[0062] Where J is the moment of inertia of the DFIG generator rotor. The inertial time constant H is the time it takes for the DFIG generator to output rated power when supported by rotor kinetic energy, and its expression is:

[0063]

[0064] Where P n This refers to the rated active power of the DFIG unit. If the rotor speed ω... r When it performs overspeed or deceleration, or pitch control, it is capable of providing active power support for the integrated power generation system.

[0065] Further optimization aims to ensure the rotor speed remains at the maximum power point (MPPT) of the DFIG unit control system. However, the rotor kinetic energy available from a DFIG unit operating under MPPT is limited. Increasing the rotor speed would increase the stored kinetic energy, which can then be released when needed, providing active power support.

[0066] Based on the operating characteristics of the doubly-fed induction generator (DFIG), steady-state control includes the following two operating conditions:

[0067] 1) When the tidal flow velocity collected by the velocity collector is less than the set start-up velocity, the tidal power generation mechanism is used as a flywheel energy storage device; the decoupling control of the power electronic converter of the tidal power generator set is used to realize the switching between motoring and power generation states of the tidal power generator; when the random power fluctuation ΔP>0, the generator works in motoring state, the rotor accelerates, and absorbs the fluctuating power to realize energy transfer; when ΔP≤0, the generator works in power generation state, the rotor decelerates, and converts the rotor kinetic energy into electrical energy to provide active power support;

[0068] 2) When the tidal current velocity is greater than the starting velocity, the coordinated control of the generator rotor speed and pitch angle of the tidal current power generation mechanism compensates for the random power fluctuations ΔP of the wind power. When ΔP > 0, the tidal current power generation mechanism first increases the active power output of the tidal current by reducing the pitch angle β, and then releases the rotor kinetic energy to make up for the missing active power support. When ΔP ≤ 0, the overspeed method is first used to transfer the rotor kinetic energy, and then the pitch angle control is used to complete the load reduction. This achieves real-time compensation of the fluctuating power of wind power on the platform and maintains the stability of the total output power of the integrated power generation unit.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] This invention applies seawater desalination hydrogen production technology to a microgrid system, proposing an optimized planning method for a hybrid energy storage system in a microgrid primarily powered by offshore wind power. This method achieves significant advantages in economic benefits and electricity utilization while ensuring safe and stable operation. The reverse osmosis (RO) seawater desalination system is used to adjust the RO desalination load in real time. An energy recovery device is employed to recover the high-pressure energy at the concentrate outlet of the RO unit, reducing energy consumption and desalination costs. An alkaline water electrolyzer is used, which is highly resistant to alkaline corrosion, has high hydrogen production efficiency, and is relatively low in cost. A steady-state control strategy for the random fluctuation power of the integrated power generation unit is applied, enabling the platform to compensate for the fluctuating power of wind power in real time, maintaining the stability of the total output power of the integrated power generation unit and alleviating the problem of poor stability in ocean energy power generation. Attached Figure Description

[0071] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0072] Figure 1 This is a block diagram of the reverse osmosis seawater desalination system described in this invention;

[0073] Figure 2 A schematic diagram of the steady-state control strategy for a wind power and tidal current integrated power generation unit;

[0074] Figure 3 This is a block diagram for coordinated control of the pitch angle of a tidal power unit. Detailed Implementation

[0075] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0076] A microgrid hybrid energy storage system based on wind power, tidal energy and seawater desalination for hydrogen production includes an offshore wind power generation mechanism, a tidal energy generation mechanism, a seawater desalination mechanism, an electrolyzer, a hydrogen storage tank, a fuel cell and a battery.

[0077] In this embodiment, a hybrid energy storage system design is adopted to make the system power supply more stable. The offshore wind power generation mechanism and the tidal current turbine generator use wind energy and tidal current power generation mechanism to power the electrolyzer and the reverse osmosis seawater desalination mechanism, respectively. The excess electricity will be supplied to the battery for storage. The seawater desalination mechanism desalinates seawater and then electrolyzes it in the electrolyzer to produce hydrogen. The hydrogen is stored in a hydrogen storage tank and supplied to the hydrogen-oxygen fuel cell.

[0078] When the electricity generated by the wind power and tidal power generation mechanisms is insufficient to sustain the operation of the entire system, the battery is connected to the microgrid to continue supplying power. Simultaneously, this hybrid energy storage system can also supply power to surrounding electrical systems (such as islands and reefs).

[0079] In this embodiment, a two-layer system planning model is adopted, including outer layer capacity configuration and internal operation scheduling.

[0080] In this embodiment, the outer layer capacity configuration is designed primarily with the system's economy in mind, and the objective function for design cost serves as a constraint:

[0081] minA all =A cm +A pun +A buy

[0082] A all A represents the total cost of this system. cm This represents the construction cost of the ORE marine energy multi-energy complementary system, which includes investment and construction costs as well as operation and maintenance costs. pun A represents the costs incurred by the ORE ocean energy power generation system due to wind and electricity curtailment. buyThe cost of purchasing electricity from the grid. Furthermore, the outer capacity configuration model is also based on the equipment capacity constraints of this hybrid energy storage system, with the constraint condition: W m,min ≤W m ≤W m,max W m W represents the actual capacity of the m-th device. m,min W m,max These are its upper and lower critical values, respectively.

[0083] In this embodiment, the internal operation scheduling mainly considers the energy storage system's ability to absorb wind and tidal energy. The power constraints for the system are as follows:

[0084] ∑P ore (t)+P pur (t)+P dis,bat (t)+P fc (t)=P load (t)+P cha,bat (t)+P el (t)+P de (t)

[0085] Among them, P pur (t) represents the power connected to the grid at time t, P ore (t) is the actual output power of the wind power generation mechanism and the tidal power generation mechanism, P load (t) represents the output power of the load end of this system (hydrogen production, seawater desalination, and supply required for the normal operation of this system); P de (t) represents the power consumption of the seawater desalination unit during time period t, P el (t) represents the power consumption of the electrolytic cell during time period t; P cha,bat (t) represents the charging power of the battery during time period t, P dis,bat (t) represents the discharge power of the battery during time period t.

[0086] In this embodiment, the main steps of seawater desalination and hydrogen production include using a seawater desalination device to desalinate seawater, and electrolyzing the generated freshwater into hydrogen and oxygen, as well as related byproducts such as liquid chlorine, caustic soda, and concentrated hydrochloric acid, through an electrolyzer.

[0087] The electricity consumption for desalinating seawater using reverse osmosis in a desalination plant is expressed as follows:

[0088] P de (t)=αP el (t)

[0089] Among them, P de (t) represents the power consumption of the seawater desalination unit during time period t, P el(t) represents the power consumption of the electrolyzer during time period t, and α is the ratio of the power consumption of the seawater desalination system to the power required for water electrolysis.

[0090] During electrolysis, the output power of the electrolytic cell is expressed as:

[0091] P el,H (t)=η el P el (t)

[0092] Among them, P el,H η is the hydrogen production power of the electrolyzer during time period t; el The hydrogen production efficiency of the electrolyzer;

[0093] The hydrogen storage tank is used to store hydrogen produced by water electrolysis and to provide hydrogen for the fuel cell. Its energy storage mathematical model is expressed as follows:

[0094]

[0095] in, The energy stored in the hydrogen storage tank during time period t. The hydrogen consumption power of the fuel cell during time period t. These represent the efficiency of hydrogen charging and discharging, respectively; Δt is the scheduling time.

[0096] The fuel cell converts clean hydrogen into electrical energy, and its mathematical model is expressed as follows:

[0097]

[0098] Among them, P fc (t) represents the power generation of the fuel cell during time period t, η fc The efficiency of hydrogen power generation from fuel cells.

[0099] In this embodiment, the hydrogen production and storage unit produces hydrogen by electrolyzing water in an alkaline water electrolyzer, and then pressurizes and liquefies the hydrogen to store it in a hydrogen storage tank. Therefore, the power consumption of the hydrogen production and storage unit is mainly due to the water electrolysis process, and thus the internal constraints on the power consumption of the electrolyzer during time period t mainly depend on the capacity and remaining capacity of the hydrogen storage tank. Furthermore, the hydrogen storage tank needs to satisfy the constraint of consistent initial and final states, resulting in the following three constraints.

[0100]

[0101] Among them, W el For the reserves of the electrolytic cell, These are the upper and lower limits of the hydrogen storage tank's capacity. Let t be the amount of hydrogen stored in the hydrogen storage tank. This shows the initial and final states of the hydrogen storage tank.

[0102] In this embodiment, the fuel cell consumes hydrogen to generate electricity, providing power to the system and offering partial active power support. The constraint it needs to satisfy is that the fuel cell's output power depends on the fuel cell's capacity and the amount of hydrogen remaining in the hydrogen storage tank that can be supplied to the fuel cell at the current moment. Therefore, the constraint is...

[0103]

[0104] Among them W fc This refers to the capacity of the fuel cell.

[0105] In this embodiment, when the electrical energy generated by the wind power generation mechanism and the tidal power generation mechanism is insufficient to maintain the operation of the entire system, the battery is connected to the microgrid to continue supplying power; the battery can effectively smooth out fluctuations caused by sudden changes in load demand within the microgrid, and its mathematical model is as follows:

[0106]

[0107] In the formula, P cha,bat (t), P dis,bat (t) represents the charging and discharging power of the battery during time period t; η cha,bat (t), η dis,bat (t) represents the battery charging and discharging efficiency; E bat (t) represents the stored energy of the battery during time period t; δ represents the battery's self-discharge loss rate.

[0108] The battery needs to meet the capacity constraint, which must be consistent with the initial and final states, and also needs to meet the charge / discharge efficiency constraint. The specific constraint relationships are as follows:

[0109]

[0110] Among them, E bat,min E bat,max E represents the lower and upper limits of battery storage capacity. bat (0), E bat (T) represents the initial and final states of the battery, P cb,min P cb,max P represents the minimum and maximum charging power of the battery. db,min P db,max These represent the minimum and maximum discharge power of the battery.

[0111] This reverse osmosis seawater desalination system specifically includes a raw water pretreatment unit, a reverse osmosis unit, an energy recovery unit, and a post-treatment unit.

[0112] In this implementation example, such as Figure 1As shown in the figure, the raw water pretreatment device (with dashed box 1) includes a water intake pump, a seawater tank, a flocculation device, a multi-media filter (shell material: fiberglass; filter media material: anthracite, quartz sand), an ultrafiltration membrane (membrane shell material: polyvinyl chloride; membrane material: polyvinylidene fluoride), and a security filter (filter shell: PVC, filter element: PP cotton).

[0113] In this implementation example, the reverse osmosis unit includes a reverse osmosis water supply pump, a high-pressure pump, and a reverse osmosis membrane (aromatic polyamide composite membrane). The key condition for the operation of this unit is overcoming osmotic pressure, and the relevant calculation formula is as follows:

[0114] π = CRT (unit: kPa)

[0115]

[0116] Where π represents osmotic pressure, C represents ion concentration, R represents gas constant, T represents thermodynamic temperature, ΔPa1 represents the pressure difference across the membrane, Δπ represents the osmotic pressure difference across the membrane, and K represents the pressure difference across the membrane. w Q represents the pure water permeability coefficient; d represents the membrane separation layer thickness; Q represents the membrane separation layer thickness. w This represents the amount of water that passes through. This formula can be simplified to...

[0117] Q w =A×NDP

[0118] Where A is the water permeation constant of the membrane; NDP is the net driving force.

[0119]

[0120]

[0121]

[0122] Among them, Q S ΔC represents the salt permeation rate, ΔC represents the salt concentration difference across the membrane, B represents the salt permeation coefficient of the membrane, and C represents the salt permeation rate. P The value represents the permeate concentration, and SP represents the salt permeation rate. Therefore, it can be seen that the system's desalination rate increases with increasing pressure.

[0123] In this implementation example, a variable operating condition seawater desalination method is adopted. Under different power supply conditions, the high-pressure pump speed is reduced proportionally by adjusting the inverter output frequency, as shown in the following formula:

[0124]

[0125]

[0126] Where, n 电机 Where P is the motor speed, P is the power consumption, ΔPa2 is the pump pressure difference, and Q is the motor speed. Vη represents the inlet water flow rate, and η represents the motor efficiency.

[0127] When the rotation speed changes, the opening of the electric valve is adjusted simultaneously. The relevant formula is as follows, which realizes the load adjustment of RO seawater desalination operation.

[0128]

[0129] in, This is the ratio of the valve's inlet flow rate to its maximum flow rate. A represents the relative opening of the valve, and A is a valve characteristic parameter.

[0130] In this embodiment, an energy recovery device is provided, such as... Figure 1 In box 2, the ultrafiltration effluent is supplied to the high-pressure pump and the energy recovery device respectively. This part of the low-pressure seawater is pressurized by the residual pressure of the reverse osmosis seawater (i.e., high-pressure concentrate), and then pressurized by the booster pump to enter the reverse osmosis device. The average energy recovery rate of this process can reach 32%.

[0131] In this embodiment, when the combined wind and tide power generation system is sufficient to maintain power supply, it supplies power to the alkaline electrolyzer. Excess power is supplied to the battery, while the hydrogen produced by electrolysis is stored in a hydrogen storage tank and supplied to the hydrogen-oxygen fuel cell. When the combined wind and tide power generation system is insufficient to maintain power supply, the battery and the hydrogen-oxygen fuel cell can be connected to the microgrid to continue supplying power.

[0132] In this embodiment, the seawater desalinated by the reverse osmosis desalination unit must be adjusted to a pH > 7.5 to prevent excessively low pH from accelerating corrosion of the metal substrate. The refined concentrated seawater enters the ion-exchange membrane electrolyzer from the anode side, while some fresh water from the desalination process is added to the cathode side. After electrolysis, brine and chlorine water are obtained on the anode side, and electrolyte and hydrogen gas are obtained on the cathode side. The brine and chlorine gas generated at the anode are cooled and separated into gas and liquid phases. The outflowing brine undergoes a dechlorination process to remove hypochlorous acid and can be reused in the concentrated seawater refining process. The chlorine gas can be liquefied and stored after cooling and drying, and the hydrogen gas can be stored in a hydrogen storage tank and supplied to hydrogen-oxygen fuel cells after drying. The electrolyte obtained at the cathode is evaporated to obtain solid caustic soda product.

[0133] In this embodiment, the turbine of the tidal power generation mechanism includes a housing, a shaft, and multiple blades. The shaft is rotatably mounted in the housing via bearings, with one end extending out of the housing and fixedly connected to a connecting member. The multiple blades are mounted on the connecting member. The other end of the shaft is connected to the rotor of a generator. A motor, the same number as the blades, is installed in the connecting member. The motor's output shaft is fixedly connected to the root of a corresponding blade within the cavity of the connecting member, enabling the motor to drive the blade to rotate relative to the connecting member. A support ring is fitted onto each blade near its root, and the support ring is rotatably connected to the blade via bearings. Multiple support rods are evenly arranged circumferentially on the support ring, with the other end of each support rod fixedly connected to the connecting member. An angle sensor is installed on the turbine to detect the deflection angle of the blades. A flow velocity collector is installed on the support frame of the tidal power generation mechanism.

[0134] The steady-state control system for the wind power generation mechanism and the tidal power generation mechanism includes a wind speed collector, a current velocity collector, a speed and torque sensor, a turbine rotor-side controller, a wind turbine rotor-side controller, a clutch, and a speed protection module. A clutch is added to the tidal turbine to address the impact of seawater resistance on the blades during flywheel energy storage. A speed protection module is incorporated into the coordinated control of speed, pitch, and angle to effectively prevent the rotor speed from remaining below the optimal speed for the tidal current velocity after releasing kinetic energy, while also avoiding a decrease in system stability due to small disturbances.

[0135] By changing the operation mode of the tidal power generation mechanism, which has a higher predictability, the random power fluctuations of the integrated power generation unit caused by wind speed are compensated, thereby achieving smooth power control and stable output.

[0136] In this embodiment, as Figure 2 As shown, to achieve steady-state control of random power fluctuations in the integrated power generation unit, it is necessary to first collect the rotational speed n of the generator in the wind power generation mechanism through a speed and torque sensor, and then obtain the corresponding real-time wind power P from the operating characteristics of the doubly-fed asynchronous generator. wind By using a first-order low-pass filter on the output power of the wind turbine, high-frequency noise, i.e., the random fluctuation power ΔP caused by wind, is extracted.

[0137] P smooth (k)=λP avg +(1-λ)P wind (k)

[0138]

[0139] ΔP=P smooth (k)-P wind (k)

[0140] Where P smooth (k) represents the low-frequency component of the total wind power generation, P wind(k) represents the measured power output of wind power generation, P avg Let λ be the average reference value of N state values, and let λ be the time constant of the first-order filter. In order to obtain a better smoothing effect, the average value of the first N state values ​​is taken as the reference value.

[0141] The maximum rotational kinetic energy E of the doubly-fed induction generator (DFIG) in the tidal current power generation mechanism during operation:

[0142]

[0143] Where J is the moment of inertia of the DFIG generator rotor. The inertial time constant H is the time it takes for the DFIG generator to output rated power when supported by rotor kinetic energy, and its expression is:

[0144]

[0145] Where P n This refers to the rated active power of the DFIG unit. If the rotor speed ω... r When it performs overspeed or deceleration, or pitch control, it is capable of providing active power support for the integrated power generation system.

[0146] In this embodiment, the control objective of the DFIG unit control system is to ensure that the rotor speed always operates at the maximum power point (MPPT), i.e., control is performed according to the MPPT strategy. The rotor kinetic energy provided by a DFIG unit operating under MPPT is limited. If the rotor speed can be increased, the kinetic energy stored in the rotor can be increased and released when needed, thus providing active power support.

[0147] Based on the operating characteristics of the doubly-fed asynchronous generator in the tidal power generation mechanism, steady-state control includes the following two operating conditions:

[0148] 1) When the tidal flow velocity collected by the flow velocity collector is less than the set start-up velocity, the tidal power generation mechanism is used as a flywheel energy storage device; the decoupling control of the power electronic converter of the tidal power generator set is used to realize the switching between motoring and power generation states of the tidal power generator; when the random power fluctuation of wind power ΔP>0, the generator works in motoring state, the rotor accelerates, and absorbs the fluctuating power to realize energy transfer; when the random power of wind power ΔP≤0, the generator works in power generation state, the rotor decelerates, and converts the rotor kinetic energy into electrical energy to provide active power support;

[0149] 2) When the tidal current velocity is greater than the starting velocity, the coordinated control of the generator rotor speed and pitch angle of the tidal current power generation mechanism compensates for the random power fluctuations ΔP of the wind power. When ΔP > 0, the tidal current power generation mechanism first increases the active power output of the tidal current by reducing the pitch angle β, and then releases the rotor kinetic energy to make up for the missing active power support. When ΔP ≤ 0, the overspeed method is first used to transfer the rotor kinetic energy, and then the pitch angle control is used to complete the load reduction. This achieves real-time compensation of the fluctuating power of wind power on the platform and maintains the stability of the total output power of the integrated power generation unit.

[0150] In this embodiment, the speed protection module is as follows: Figure 3 As shown, the speed and torque sensor transmits a signal to the module. If the actual speed of the motor is less than the minimum speed and the duration exceeds the set value, the multiplication coefficient is set to 1 and enters the PI controller to continuously adjust the active power parameter value of the unit to make the speed reach the optimal speed as soon as possible, so as to prevent the speed from being lower than the optimal speed under the current flow rate for a long time after the rotor releases kinetic energy.

[0151] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A microgrid hybrid energy storage system based on wind power, tidal energy, and seawater desalination for hydrogen production, characterized in that, This includes offshore wind power generation systems, tidal power generation systems, seawater desalination systems, electrolyzers, hydrogen storage tanks, fuel cells, and batteries; The offshore wind power generation mechanism and the tidal turbine generator respectively use wind energy and tidal energy to power the electrolyzer and the reverse osmosis seawater desalination mechanism, and the excess electricity will be supplied to the storage battery. The seawater desalination unit desalinates seawater and then electrolyzes it to produce hydrogen. The hydrogen is stored in a hydrogen storage tank and supplied to the hydrogen-oxygen fuel cell. When the electrical energy generated by the wind power generation mechanism and the tidal power generation mechanism is insufficient to maintain the operation of the entire system, the battery is connected to the microgrid to continue to supply power. The seawater desalination system includes a raw water pretreatment device, a reverse osmosis device, an energy recovery device, and a post-treatment device. The pretreatment device includes a water intake pump, a seawater tank containing a flocculation device, a booster pump, a multi-media filter, an ultrafiltration membrane, and a security filter. After water purification and adjustment, the seawater is treated to a pH of 2-11; a pollution index SDI < 5; free chlorine < 0.1 g / L; Mn < 1.0 mg / L; and Fe < 0.1 g / L. The reverse osmosis unit includes a reverse osmosis water supply pump, a high-pressure pump, and a reverse osmosis membrane; By adopting a variable operating condition seawater desalination method, the speed of the high-pressure pump motor is changed by using a frequency converter, thereby controlling the opening of the electric valve and the influent flow rate, and thus adjusting the operating load of the reverse osmosis membrane seawater desalination. A power-exchange type energy recovery device is used to recover the pressure energy in the discharged concentrated brine and convert it into influent energy; By setting up a post-treatment water storage device, the pH value of the reverse osmosis effluent can be adjusted to meet different requirements; The steady-state control system of the wind power generation mechanism and the tidal power generation mechanism includes a wind speed collector, a wind speed and flow rate collector, a speed and torque sensor, a turbine rotor-side controller, a wind turbine rotor-side controller, a clutch, and a speed protection module. By changing the operation mode of the tidal power generation mechanism, which has a higher predictability, the random power fluctuations of the integrated power generation unit caused by wind speed are compensated, thereby achieving smooth power control and stable output. To achieve steady-state control of random power fluctuations in the integrated power generation unit, it is necessary to first collect the rotational speed of the wind power generation mechanism using a speed and torque sensor. The real-time power of the wind is obtained from the operating characteristics of the doubly-fed asynchronous generator of the wind turbine. By using a first-order low-pass filter on the output power of the wind turbine, high-frequency noise, i.e., the random power fluctuations caused by wind, can be extracted. : ； ； ； in The low-frequency component of the total wind power generation. This is a measured power meter for wind power generation. The average baseline value of N state values. is the time constant of the first-order filter. In the formula, the average value of the first N state values ​​is taken as the reference value in order to obtain a better smoothing effect. Based on the operating characteristics of the doubly-fed asynchronous generator, steady-state control includes the following two operating conditions: 1) When the tidal flow velocity collected by the velocity collector is less than the set starting velocity, the tidal power generation mechanism is used as a flywheel energy storage device; the decoupling control of the power electronic converter of the tidal power generator set is used to realize the switching between motoring and power generation states of the tidal power generator; when the wind power random power fluctuations When the wind power is in a stochastic state, the generator operates in an electric state, the rotor accelerates, and absorbs fluctuating power to achieve energy storage; when the wind power random power... At this time, the generator is in generating mode, the rotor decelerates, and the rotor kinetic energy is converted into electrical energy to provide active power support; 2) When the tidal current velocity is greater than the starting velocity, the coordinated control of the generator rotor speed and pitch angle of the tidal current power generation mechanism is used to compensate for the random fluctuations in wind power. ;when At that time, tidal power generation mechanisms prioritize reducing the pitch angle. This increases the active power output of the tidal current, and secondly, releases the rotor's kinetic energy to compensate for the lack of active power support; when The system first uses the overspeed method to transfer rotor kinetic energy, and then uses pitch angle control to reduce load, thus enabling the platform to compensate for the fluctuating power of wind power in real time and maintain the stability of the total output power of the integrated power generation unit.

2. The microgrid hybrid energy storage system based on wind power, tidal energy, and seawater desalination for hydrogen production according to claim 1, characterized in that, The power constraints for a microgrid hybrid energy storage system are: ； in, Let be the power fed into the grid at time t. This refers to the actual output power of wind power generation mechanisms and tidal power generation mechanisms. This refers to the output power at the load end of this system; For time period The power consumption of a seawater desalination unit For time period The power consumption of the electrolytic cell; For time period Battery charging power, For time period The discharge power of the battery.

3. The microgrid hybrid energy storage system based on wind power, tidal energy, and seawater desalination for hydrogen production according to claim 2, characterized in that, The main steps of seawater desalination and hydrogen production include using a seawater desalination unit to desalinate seawater, and electrolyzing the produced freshwater into hydrogen and oxygen, along with related byproducts such as liquid chlorine, caustic soda, and concentrated hydrochloric acid, through an electrolyzer. The electricity consumption for desalinating seawater using reverse osmosis in a desalination plant is expressed as follows: ； in, For time period The power consumption of a seawater desalination unit For time period The power consumption of the electrolytic cell This is the ratio of the electricity consumption of the seawater desalination system to the electricity required for water electrolysis. During electrolysis, the output power of the electrolytic cell is expressed as: ； in, For time period Hydrogen production capacity of the electrolyzer; The hydrogen production efficiency of the electrolyzer; Hydrogen storage tanks are used to store hydrogen produced by water electrolysis and to supply hydrogen to fuel cells. Their energy storage mathematical model is expressed as follows: ； in, The energy stored in the hydrogen storage tank during time period t. For time period The hydrogen consumption power of fuel cells, , These represent the efficiency of hydrogen filling and releasing, respectively. For scheduling time; The fuel cell converts clean hydrogen into electrical energy, and its mathematical model is expressed as follows: ； in, For time period The power generation capacity of fuel cells, The efficiency of hydrogen power generation from fuel cells.

4. The microgrid hybrid energy storage system based on wind power, tidal energy, and seawater desalination for hydrogen production according to claim 3, characterized in that, The power consumption in the hydrogen production and storage process is mainly from the water electrolysis process. The internal constraints of the electrolyzer's power consumption during time period t mainly depend on the capacity and remaining capacity of the hydrogen storage tank. In addition, the hydrogen storage tank needs to satisfy the constraint of consistent initial and final states, thus there are the following three constraints: ； in, For the reserves of the electrolytic cell, These are the upper and lower limits of the hydrogen storage tank capacity, respectively. Let t be the amount of hydrogen stored in the hydrogen storage tank at time t. The initial and final states of the hydrogen storage tank.

5. The microgrid hybrid energy storage system based on wind power, tidal energy, and seawater desalination for hydrogen production according to claim 4, characterized in that, The fuel cell is used to consume hydrogen to generate electricity and power the system, as well as provide some active power support. The constraint it needs to meet is that the output power of the fuel cell depends on its capacity and the amount of hydrogen remaining in the hydrogen storage tank that can be supplied to the fuel cell at the current moment. Therefore, the constraint is: ； in This refers to the capacity of the fuel cell.

6. The microgrid hybrid energy storage system based on wind power, tidal energy, and seawater desalination for hydrogen production according to claim 5, characterized in that, When the electrical energy generated by the wind power generation mechanism and the tidal power generation mechanism is insufficient to sustain the operation of the entire system, the battery is connected to the microgrid to continue supplying power; the battery can effectively smooth out fluctuations caused by sudden changes in load demand within the microgrid, and its mathematical model is as follows: ； In the formula, , For time period The charging and discharging power of the battery; , To improve the charging and discharging efficiency of the battery; For time period The energy stored in a battery; This refers to the battery's self-discharge loss rate. The battery needs to meet the capacity constraint that is consistent with the initial and final states, and it also needs to meet the charge and discharge efficiency constraint. The specific constraint relationships are as follows: ； in, These represent the lower and upper limits of battery storage capacity, respectively. These represent the initial and final states of the battery. These are the minimum and maximum charging power of the battery, respectively. These are the minimum and maximum discharge power of the battery, respectively.

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