Integrated system and method for brackish water desalination by optical storage direct drive

Abstract

The application relates to a light storage direct-drive brackish water desalination integrated system and method, and belongs to the technical field of brackish water desalination. The system comprises a pretreatment unit, a six-stage filtering membrane separation unit, a deep disinfection unit, a direct-current driving pump group, a photovoltaic energy storage power supply unit and an intelligent control unit. The pretreatment unit is used for impurity removal pretreatment of brackish water. The six-stage filtering membrane separation unit is communicated with the pretreatment unit and is used for step-by-step filtering and desalination of the pretreated water body, and the produced water is sent to the deep disinfection unit. The deep disinfection unit is used for sterilization and disinfection of the produced water. The direct-current driving pump group comprises at least one water pump provided with a speed controller and a direct-current brushless permanent magnet motor. The light storage direct-drive brackish water desalination integrated system and method combine the photovoltaic energy storage power supply unit and the direct-current driving pump group, realize full solar driving and zero external power grid operation, adapt to application requirements in remote power-free areas, and can reduce operation cost and carbon emission.

Description

Technical Field

[0001] This invention relates to the field of brackish water desalination technology, specifically to an integrated system and method for brackish water desalination using direct-drive photovoltaic storage. Background Technology

[0002] The global shortage of freshwater resources has become a core bottleneck hindering the sustainable development of society and economy. According to authoritative statistics from the United Nations, about 2 billion people around the world are currently facing the problem of chronic water scarcity. Among them, the distribution of brackish water resources in arid, desert, and low-lying coastal areas accounts for more than 40% of the total water-scarce areas, and many residents in remote areas have long been unable to obtain clean freshwater that meets national drinking water standards.

[0003] Currently, most mainstream brackish water desalination equipment on the market relies on fossil fuels or external power sources such as municipal power grids and diesel generators, which presents several technical challenges: First, fossil fuel power generation results in high carbon emissions and severe environmental pollution; second, power grid installation is costly and cannot cover remote areas without power grids, while diesel generators are noisy and fuel-intensive, leading to high overall maintenance costs; third, traditional desalination equipment uses a single water treatment process, and the pretreatment unit has weak anti-fouling capabilities, easily causing clogging and scaling of downstream membrane modules, shortening their lifespan; fourth, the energy and water treatment systems are independent, making it difficult to adapt to the intermittent and fluctuating nature of photovoltaic power generation, as changes in sunlight intensity can easily lead to equipment shutdowns and fluctuations in water quality, making it impossible to achieve continuous and stable operation 365 days a year; fifth, traditional water pumps operate on a fixed-speed drive mode, unable to dynamically adjust operating parameters according to energy supply, influent water quality, and water production demand, resulting in high energy consumption per ton of water and low resource utilization.

[0004] Existing photovoltaic desalination equipment simply combines photovoltaic modules with desalination equipment without intelligent energy storage regulation and multi-variable collaborative control strategies. This fails to address the industry pain points of unstable photovoltaic power output and large peak-valley differences. Furthermore, the water treatment process is outdated, with poor integration between pretreatment, filtration, and disinfection units, resulting in overall water production efficiency and quality that cannot meet the needs of large-scale residential water supply. Based on these technological shortcomings, there is an urgent need to develop an integrated, intelligent, low-energy-consumption, zero-carbon-emission photovoltaic-storage direct-drive brackish water desalination system. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an integrated system and method for brackish water desalination that combines photovoltaic and energy storage direct drive. It features intelligent collaborative operation, all-solar-driven operation, high efficiency and low consumption, and solves the problems of existing systems relying on external power sources, poor process integration, and inability to adapt to photovoltaic fluctuations.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an integrated system and method for direct-drive photovoltaic energy storage desalination of brackish water, comprising a pretreatment unit, a six-stage filtration membrane separation unit, a deep disinfection unit, a DC-driven pump group, a photovoltaic energy storage power supply unit, and an intelligent control unit;

[0007] The pretreatment unit is used to remove impurities from brackish water.

[0008] The six-stage filtration membrane separation unit is connected to the pretreatment unit and is used to filter and desalinate the pretreated water step by step. Its product water is sent to the deep disinfection unit.

[0009] The deep disinfection unit is used to sterilize and disinfect the produced water.

[0010] The DC-driven pump set includes at least one water pump equipped with a DC brushless permanent magnet motor and a speed controller.

[0011] The photovoltaic energy storage power supply unit supplies power to each speed controller via a DC bus.

[0012] The intelligent control unit adjusts the speed of each water pump based on photovoltaic forecasts, energy storage status, and water production requirements.

[0013] Furthermore, the pretreatment unit includes a coagulation sedimentation device and a micro-nano bubble flotation device connected in sequence. The coagulation sedimentation device is equipped with a reagent dosing port for adding polyaluminum chloride and polyacrylamide.

[0014] Furthermore, the six-stage filtration membrane separation unit includes a multi-media filter, an activated carbon filter, a precision filter, a composite refining component, a nanofiltration membrane component, and a reverse osmosis membrane component arranged in series along the water flow direction; its inlet end is connected to the outlet end of the pretreatment unit, and its product water end is connected to the deep disinfection unit.

[0015] Furthermore, the deep disinfection unit employs an advanced ultraviolet oxidation disinfection device, which includes a low-pressure ultraviolet lamp and a built-in photocatalytic module.

[0016] Furthermore, the DC-driven pump set includes an inlet pump, a high-pressure pump, and an outlet pump; the inlet pump is installed on the pipeline between the pretreatment unit and the six-stage filtration membrane separation unit, the high-pressure pump is installed on the pipeline between the nanofiltration membrane module and the reverse osmosis membrane module, and the outlet pump is installed on the product water side pipeline of the reverse osmosis membrane module.

[0017] Furthermore, the inlet pump, high-pressure pump, and outlet pump are all equipped with DC brushless permanent magnet motors with integrated Hall sensors, and each is equipped with an independent speed controller.

[0018] Furthermore, the photovoltaic energy storage power supply unit includes a photovoltaic array, a maximum power point tracking controller, a DC bus, an energy storage battery pack, and a bidirectional DC-DC converter; the photovoltaic array is electrically connected to the DC bus via the maximum power point tracking controller, and the energy storage battery pack is connected in parallel to the DC bus via the bidirectional DC-DC converter.

[0019] A method for integrated photovoltaic-storage-direct-drive brackish water desalination, applied to the integrated photovoltaic-storage-direct-drive brackish water desalination system according to any one of claims 1-7, comprises the following steps:

[0020] S1. Brackish Water Pretreatment: The raw brackish water is introduced into a coagulation and sedimentation device, and two flocculants, polyaluminum chloride and polyacrylamide, are added through the chemical dosing port to complete the flocculation and sedimentation of the water. The treated water is then sent to a micro-nano bubble flotation device, where 5μm to 50μm micro-nano bubbles adsorb and remove dissolved organic matter and heavy metal impurities from the water to obtain qualified pretreated effluent with a turbidity ≤0.5NTU.

[0021] S2. Multi-stage membrane filtration desalination: The inlet pump is started to deliver qualified pretreated water to a multi-media filter, activated carbon filter, precision filter, and composite refining component in sequence to complete the fine filtration of impurities at each stage; the water after preliminary purification flows into the nanofiltration membrane module for staged desalination, and then is pressurized by the high-pressure pump and sent to the reverse osmosis membrane module for deep desalination to prepare qualified purified water with a total dissolved solids content of <100mg / L;

[0022] S3. Deep sterilization and disinfection: The purified water produced by the reverse osmosis membrane module is transported to the ultraviolet advanced oxidation disinfection device. The hydroxyl radicals generated by the 254nm ultraviolet light in conjunction with the photocatalytic module are used to deeply inactivate harmful microorganisms in the water. After disinfection, the finished fresh water is transported to the clean water tank for storage.

[0023] S4. Intelligent Power Coordination and Regulation: The intelligent control unit collects photovoltaic power generation parameters, energy storage battery state of charge, water production flow rate and water quality indicators in real time through the data acquisition module; it relies on the long short-term memory neural network model to predict the changes in photovoltaic output in short cycles, and then dynamically adjusts the operating speed of the inlet pump, high-pressure pump and outlet pump through the multivariate fuzzy PID control algorithm; it matches the total power of photovoltaic power generation and energy storage power supply, balances the system's water production energy consumption, and realizes continuous and stable water production throughout the year under the all-solar-driven mode without external power grid reliance.

[0024] Furthermore, the specific steps for dynamic adjustment of the water pump speed in S4 are as follows:

[0025] S401, Parameter Comparison: Retrieve the future photovoltaic power prediction P_pred output from the photovoltaic power output prediction module, simultaneously obtain the rated energy consumption power P_load required by the system under the current water production conditions, and perform numerical comparison.

[0026] S402, Increased production and charging control: If P_pred≥P_load and the state of charge of the energy storage battery is lower than the preset charging threshold, the speed of the high-pressure pump is increased to increase the system water production flow, and the surplus photovoltaic power generation is directly used to charge the energy storage battery pack.

[0027] S403, Energy replenishment and stable production control: If P_pred < P_load, the high-pressure pump speed is gradually reduced to lower system energy consumption, while the energy storage battery pack is controlled to discharge, make up for the power gap, and ensure the continuous operation of the water production process.

[0028] S404 Synchronous and Coordinated Control: Based on the real-time speed of the high-pressure pump, the speed of the inlet and outlet pumps is synchronously and finely adjusted according to a preset ratio to stabilize the internal operating pressure of the six-stage filtration membrane separation unit, avoid damage to the membrane module due to pressure fluctuations, and ensure the filtration and desalination effect.

[0029] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0030] 1. The integrated system and method for direct-drive brackish water desalination, which combines photovoltaic energy storage power supply unit with DC drive pump group, achieves full solar drive and zero external grid connection, adapts to the application needs of remote areas without electricity, and can reduce operating costs and carbon emissions.

[0031] 2. The integrated system and method for direct-drive brackish water desalination using photovoltaic storage employs a six-stage filtration membrane separation unit for step-by-step purification, combined with micro-nano bubble flotation pretreatment and ultraviolet advanced oxidation disinfection, so that the effluent water quality can stably meet the national drinking water hygiene standards.

[0032] 3. The integrated system and method for direct-drive brackish water desalination using photovoltaic and energy storage achieves real-time dynamic adjustment of pump speed through the LSTM photovoltaic output prediction module and multivariable fuzzy PID controller built into the intelligent control unit. This effectively smooths out photovoltaic fluctuations, and the system power self-balancing adjustment time constant is no more than 15 minutes, which is conducive to ensuring continuous and stable water production throughout the year.

[0033] 4. The integrated system and method for direct-drive brackish water desalination using photovoltaic storage employs DC brushless permanent magnet motors with integrated Hall sensors for each water pump, and is powered directly by a DC bus. This eliminates the need for multiple AC-DC conversion steps, which helps improve the overall energy utilization efficiency. Furthermore, it features fast speed response and precise control. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall system structure of the present invention;

[0035] Figure 2 This is a schematic diagram of the preprocessing unit structure;

[0036] Figure 3 This is a schematic diagram of a six-stage filtration membrane separation unit.

[0037] Figure 4 This is a schematic diagram of the photovoltaic energy storage power supply unit structure of the present invention;

[0038] Figure 5 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0039] The technical solutions of the embodiments 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, and 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.

[0040] Example 1, please refer to Figures 1 to 4 This embodiment provides an integrated brackish water desalination system based on direct photovoltaic energy storage, comprising six major components: a pretreatment unit, a six-stage filtration membrane separation unit, a deep disinfection unit, a DC-driven pump group, a photovoltaic energy storage power supply unit, and an intelligent control unit.

[0041] The pretreatment unit, located at the front end of the system, performs preliminary impurity removal pretreatment on the raw brackish water. The inlet of the six-stage filtration membrane separation unit is connected to the outlet of the pretreatment unit via pipeline, and is used for step-by-step filtration and desalination purification of the pretreated water. The inlet of the deep disinfection unit is connected to the product water end of the six-stage filtration membrane separation unit, and is used for deep sterilization and disinfection of the product water after membrane separation. The DC-driven pump set includes an inlet pump, a high-pressure pump, and an outlet pump, respectively installed on key pipelines in the system, providing driving force for water transport between units and the membrane separation process. The photovoltaic energy storage power supply unit provides DC power to the entire system, while the intelligent control unit serves as the system control center, enabling coordinated operation and intelligent regulation of all units.

[0042] Detailed implementation of the preprocessing unit

[0043] The pretreatment unit includes a coagulation sedimentation device and a micro-nano bubble flotation device connected in sequence.

[0044] The coagulation and sedimentation unit is equipped with a reagent dosing port for adding two flocculants, polyaluminum chloride (PAC) and polyacrylamide (PAM), to the raw water. In actual operation, the raw brackish water is first introduced into the coagulation and sedimentation unit, and PAC and PAM are added in a predetermined ratio through the reagent dosing port. After stirring and mixing, flocculation and sedimentation are completed, removing large suspended solids and some colloidal substances from the water.

[0045] The water treated by coagulation and sedimentation is fed into a micro-nano bubble flotation device. This device uses a micro-nano bubble generator to produce micro-nano bubbles with diameters ranging from 5μm to 50μm. During operation, the micro-nano bubbles are dispersed in the water at a high density. Utilizing their large specific surface area and strong adsorption capacity, they can efficiently adsorb and remove dissolved organic matter and heavy metal impurities from the water.

[0046] Detailed Implementation of the Six-Stage Membrane Separation Unit

[0047] The inlet of the six-stage filtration membrane separation unit is connected to the outlet of the micro-nano bubble flotation device via a pipeline. This unit includes a multi-media filter, an activated carbon filter, a precision filter, a composite purification module, a nanofiltration membrane module, and a reverse osmosis membrane module, arranged in series along the water flow direction.

[0048] The specific configurations and functions of each component are as follows:

[0049] Multi-media filters are filled with multiple layers of filter media, including quartz sand and anthracite, to remove suspended impurities larger than 10μm from the water. Activated carbon filters are filled with high-quality granular activated carbon, which uses adsorption to remove organic matter, residual chlorine, and some odor-causing substances from the water, achieving a chemical oxygen demand (COD) removal rate of no less than 60%. Precision filters use melt-blown or pleated filter cartridges with a filtration precision of 5μm, used to remove solid particulate impurities larger than 5μm, protecting downstream membrane modules from physical damage by large particles.

[0050] The composite refining module uses hollow fiber ultrafiltration or microfiltration membranes with a filtration pore size of 0.01μm. Its water pollution index (SDI) is <3, which can effectively remove colloids, bacteria and macromolecular organic matter from the water, providing high-quality feed water for subsequent nanofiltration and reverse osmosis membrane modules.

[0051] The nanofiltration membrane module uses a nanofiltration membrane with a high rejection rate for divalent ions, achieving a rejection rate of no less than 98% for divalent ions in water and a rejection rate of 60%–80% for monovalent ions. The nanofiltration membrane module operates at relatively low pressure, achieving preliminary desalination and effectively reducing water hardness.

[0052] The reverse osmosis membrane module uses a brackish water reverse osmosis membrane with a high desalination rate, which has a total dissolved solids (TDS) rejection rate of no less than 99.5%. After deep desalination treatment by the reverse osmosis membrane module, the final product water has a total dissolved solids content of less than 100 mg / L.

[0053] Detailed Implementation of Deep Disinfection Unit

[0054] The inlet of the deep disinfection unit is connected to the product water end of the reverse osmosis membrane module via a pipeline. The deep disinfection unit uses an advanced ultraviolet oxidation disinfection device, including a low-pressure ultraviolet lamp and a built-in photocatalytic module.

[0055] The low-pressure ultraviolet lamp emits ultraviolet light in a specific wavelength of 254nm, which has a good inactivation effect on microorganisms in water. Simultaneously, the built-in photocatalytic module generates hydroxyl radicals (·OH) under ultraviolet irradiation. These hydroxyl radicals have extremely strong oxidizing power and can indiscriminately oxidize and decompose residual trace organic matter and microbial cell structures in the water. The synergistic effect of ultraviolet light and hydroxyl radicals achieves deep sterilization and disinfection of the water produced after membrane separation.

[0056] Detailed implementation of DC-driven pump sets

[0057] The DC-driven pump set includes three pumps: an inlet pump, a high-pressure pump, and an outlet pump.

[0058] The feed water pump is installed on the pipeline between the pretreatment unit and the six-stage filtration membrane separation unit, used to deliver the qualified pretreated effluent to the six-stage filtration membrane separation unit. The high-pressure pump is installed on the pipeline between the nanofiltration membrane module and the reverse osmosis membrane module, used to pressurize the permeate from the nanofiltration membrane module to the operating pressure required by the reverse osmosis membrane module, ensuring the normal operation of the reverse osmosis process. The effluent pump is installed on the permeate side pipeline of the reverse osmosis membrane module, used to deliver the purified water produced by the reverse osmosis membrane module to the deep disinfection unit.

[0059] The inlet pump, high-pressure pump, and outlet pump are all equipped with DC brushless permanent magnet motors with integrated Hall effect sensors and independent speed controllers. DC brushless permanent magnet motors offer advantages such as high efficiency, good speed regulation performance, and easy maintenance. The integrated Hall effect sensors are used to detect the motor rotor position in real time, providing accurate speed feedback signals to the speed controllers. Each pump's speed controller receives pulse width modulation (PWM) control signals from the intelligent control unit, enabling precise adjustment of the pump speed.

[0060] Specific implementation methods of photovoltaic energy storage power supply units

[0061] The photovoltaic energy storage power supply unit includes a photovoltaic array, a maximum power point tracking (MPPT) controller, a DC bus, an energy storage battery pack, and a bidirectional DC-DC converter.

[0062] The photovoltaic array uses high-efficiency monocrystalline silicon photovoltaic modules with a photoelectric conversion efficiency of no less than 23.5%, with a total installed capacity of 4kWp. The photovoltaic array is installed on a sunny site or rooftop, facing due south, and the installation tilt angle is optimized according to the latitude of the project location to obtain the maximum annual solar irradiance.

[0063] The DC power output from the photovoltaic array is connected to the DC bus via a maximum power point tracking (MPPT) controller. The MPPT controller uses either the perturbation-observation method or the incremental conductance method to track the maximum power point of the photovoltaic array in real time, ensuring that the photovoltaic array always operates at maximum power output. The power conversion efficiency of the MPPT controller is no less than 98%.

[0064] The energy storage battery pack uses lithium iron phosphate batteries with a rated capacity of 2kWh. Lithium iron phosphate batteries are characterized by long cycle life, high safety, and excellent charge-discharge performance, with a cycle life exceeding 6000 cycles. The energy storage battery pack is connected in parallel to the DC bus via a bidirectional DC-DC converter. The bidirectional DC-DC converter enables bidirectional energy flow—when photovoltaic power generation is in surplus, the energy on the DC bus is stepped down and fed into the energy storage battery pack; when photovoltaic output is insufficient, the energy from the energy storage battery pack is stepped up and fed back to the DC bus to compensate for the system power shortfall. The bidirectional DC-DC converter has an energy conversion efficiency of no less than 98%.

[0065] Each pump's speed controller directly obtains its drive power from the DC bus, eliminating the multiple DC-AC-DC conversion steps in traditional solutions and enabling direct DC drive power supply to the system, effectively improving overall energy utilization efficiency.

[0066] Detailed Implementation of Intelligent Control Unit

[0067] The intelligent control unit is communicatively connected to the photovoltaic energy storage power supply unit, each speed controller, and water quality and flow sensors installed in the pipeline. The intelligent control unit includes a data acquisition module, a photovoltaic output prediction module, a multivariable fuzzy PID controller, and a speed control drive module.

[0068] The data acquisition module is used to collect real-time operating and water quality parameters such as photovoltaic power generation, state of charge (SOC) of the energy storage battery, DC bus voltage, permeate flow rate, permeate conductivity, and water turbidity. Sensors are strategically placed along the pipeline: light intensity and temperature sensors are installed near the photovoltaic array; voltage and current sensors are installed on the DC bus and the power supply circuits of each water pump; flow sensors are installed at the outlets of each water pump and in the main permeate pipeline; conductivity and turbidity sensors are installed at the pretreatment unit outlet, the reverse osmosis permeate end, and the finished water tank inlet.

[0069] The photovoltaic (PV) output prediction module embeds a Long Short-Term Memory (LSTM) neural network model. This model uses historical meteorological data such as solar irradiance, ambient temperature, and humidity as input, and after training, it continuously predicts PV output for future periods (typically 15 minutes to 4 hours). The model employs a time-series prediction method, fully exploiting the temporal dependence and periodicity of PV output, achieving a prediction accuracy of no less than 92%.

[0070] The multivariable fuzzy PID controller is the core control component of this invention. Its input variables include the predicted photovoltaic output, the state of charge of the energy storage battery, and the deviation between the preset and actual water production flow rates. The controller optimizes and adjusts the PID control parameters online through fuzzy control rules, outputs the setpoint for the high-pressure pump speed, and simultaneously calculates the optimal operating speeds of the inlet and outlet pumps.

[0071] The specific control logic of the multivariable fuzzy PID controller is as follows:

[0072] When the photovoltaic output is sufficient and the state of charge of the energy storage battery has not reached the set charging threshold, the controller increases the operating speed of the high-pressure pump to improve the system's water production efficiency. At the same time, the surplus photovoltaic power is charged into the energy storage battery pack through the bidirectional DC converter, so as to realize the full utilization of solar energy.

[0073] When the photovoltaic output is insufficient to meet the energy consumption requirements for water production, the controller reduces the operating speed of the high-pressure pump, switching the system to a low-water-production mode. Simultaneously, it controls the energy storage battery pack to discharge through the DC bus to compensate for the power shortfall, ensuring uninterrupted water production. This controller can achieve dynamic self-balancing of the system's internal electrical power, and the system's power self-balancing adjustment time constant does not exceed 15 minutes.

[0074] The speed control drive module is used to output pulse width modulation control signals to the speed controllers of each water pump, so as to control the actual speed of each water pump to accurately track the given speed parameters output by the multivariable fuzzy PID controller, thereby realizing closed-loop precise control of the water pump speed.

[0075] The working principle of this embodiment is as follows:

[0076] Raw water first enters a coagulation and sedimentation unit, where PAC and PAM flocculants are added and stirred to destabilize and settle large suspended solids and colloids. The effluent then enters a micro-nano bubble flotation unit, where numerous micro-nano bubbles with diameters of 5μm~50μm adsorb and carry dissolved organic matter and heavy metal ions upwards for separation, completing preliminary purification. The pretreated water then flows sequentially through a multi-media filter and an activated carbon filter, followed by a precision filter to intercept residual hard particles. The water then enters a composite refining module to remove colloids and bacteria, ensuring a SDI < 3 for the product water, guaranteeing the safety of subsequent membranes. Finally, the water is sent to a nanofiltration membrane module, where ≥98% of divalent ions are retained under lower pressure. The monovalent ion rejection rate is controlled at 60%~80% to achieve preliminary desalination. Finally, the nanofiltration permeate is pressurized by a high-pressure pump and enters the reverse osmosis membrane module, where a high-desalination membrane is used for deep desalination, so that the total dissolved solids (TDS) content of the final permeate is less than 100mg / L. The reverse osmosis permeate enters the deep disinfection unit, where low-pressure ultraviolet lamps emit 254nm ultraviolet light to inactivate microorganisms. At the same time, the photocatalytic module generates highly oxidizing hydroxyl radicals (·OH) under ultraviolet irradiation, which indiscriminately decompose residual trace organic matter and cell structures, achieving synergistic deep sterilization.

[0077] The photovoltaic array converts solar energy into direct current (DC). The MPPT controller tracks the maximum power point in real time, ensuring a stable supply of power to the DC bus. The lithium iron phosphate battery pack is connected in parallel to the DC bus via a bidirectional DC-DC converter. When photovoltaic power generation is excessive, the converter steps down the voltage to charge the batteries; when photovoltaic output is insufficient, the converter boosts the voltage to release battery power to the bus, making up for the power shortfall. The inlet pump, high-pressure pump, and outlet pump all use brushless permanent magnet DC motors, with their speed controllers directly connected to the DC bus for power. These motors do not require an inverter for DC-AC conversion and are driven directly by DC power.

[0078] The data acquisition module acquires parameters such as photovoltaic power, battery state of charge, DC bus voltage, water production flow rate, and conductivity in real time. Meanwhile, the LSTM neural network model embedded in the photovoltaic output prediction module uses historical meteorological data as input to predict the photovoltaic power generation for the next 15 minutes to 4 hours. The multivariate fuzzy PID controller takes "photovoltaic predicted output", "energy storage SOC" and "deviation between preset water production flow and actual flow" as input variables, optimizes PID parameters online through fuzzy rules, calculates and outputs the optimal operating speed of the high-pressure pump in real time, and synchronously matches the optimal speed of the inlet and outlet pumps. When the predicted output is sufficient and the battery has not reached the charging threshold, the controller automatically increases the speed of the high-pressure pump to increase the water production to make full use of solar energy and charge the excess electrical energy into the battery for storage. When the predicted output cannot meet the energy consumption for water production, the controller decreases the speed of the high-pressure pump, causing the system to switch to a low water production operation mode. At the same time, it instructs the energy storage battery to discharge through the DC bus to make up for the power gap and ensure uninterrupted water production in cloudy days or at night. The speed control drive module converts the speed setpoint output by the controller into a PWM signal and sends it to the speed controller of each water pump. The speed controller, combined with the real-time rotor position signal fed back by the Hall sensor, uses a closed-loop regulation to precisely follow the given value and achieve stable and efficient operation of the entire system.

[0079] Example 2, please refer to Figure 5 This embodiment provides an integrated method for direct-drive brackish water desalination using photovoltaic storage, applied to the aforementioned system, and specifically includes the following steps:

[0080] S1, Brackish Water Pretreatment

[0081] The raw brackish water is introduced into a coagulation and sedimentation device. Polyaluminum chloride and polyacrylamide are added in a predetermined ratio through the reagent dosing port. After stirring and mixing, flocculation and sedimentation are completed, causing suspended solids and colloidal substances in the water to form flocs and settle and separate. The treated water is then sent to a micro-nano bubble flotation device. Utilizing the strong adsorption properties of 5μm to 50μm micro-nano bubbles, dissolved organic matter and heavy metal impurities in the water are adsorbed and removed. The turbidity of the pretreated water is consistently below 0.5 NTU, resulting in qualified pretreated effluent.

[0082] The dosage of coagulant (PAC) and flocculant aid (PAM) needs to be determined based on the turbidity of the raw water. and traffic Dynamic adjustment:

[0083]

[0084] in, , The coefficient of the reagent. The turbidity influence index.

[0085] Removal rate of dissolved organic matter (DOM) and heavy metals (HM) by bubbles The formulas related to the specific surface area and residence time of bubbles are:

[0086]

[0087] in, The diameter of the bubble. For contact time, is the adsorption mass transfer coefficient.

[0088] The turbidity of the effluent must meet the following standards:

[0089]

[0090] in, It is a unit of scattering turbidity.

[0091] S2, Multi-stage membrane filtration desalination

[0092] The inlet pump is started, and the qualified pretreated water is sequentially delivered to the multi-media filter, activated carbon filter, precision filter, and composite purification component to complete the step-by-step fine filtration of impurities. Among them, the multi-media filter intercepts suspended solids with a particle size greater than 10μm, the activated carbon filter adsorbs and removes organic matter, the precision filter intercepts particulate matter with a particle size greater than 5μm, and the composite purification component further removes colloids and bacteria.

[0093] The pre-purified water flows into a nanofiltration membrane module for staged desalination. The nanofiltration membrane module has a rejection rate of no less than 98% for divalent ions and a rejection rate of 60%–80% for monovalent ions. The nanofiltration permeate is pressurized by a high-pressure pump and then sent to a reverse osmosis membrane module for deep desalination. The reverse osmosis membrane module has a rejection rate of no less than 99.5% for total dissolved solids, producing qualified purified permeate with a total dissolved solids content of less than 100 mg / L.

[0094] After passing through a multi-media filter (MMF), activated carbon (ACF), a precision filter (PF), and a composite purification component (CP), the effluent concentration exhibits an exponential decay formula as follows:

[0095]

[0096] in, The interception efficiency of each level of filter for suspended solids / colloids.

[0097] Nanofiltration (NF) and reverse osmosis (RO) desalination rates

[0098]

[0099]

[0100]

[0101] After being pressurized by the high-pressure pump, the flux of the solvent permeating through the membrane... Net driving force Decide:

[0102]

[0103] in, For operating pressure, For osmotic pressure difference, The viscosity of the solution. For membrane resistance, For water production flow rate, This represents the effective membrane area.

[0104] S3, Deep sterilization and disinfection

[0105] The purified water produced by the reverse osmosis membrane module is transported to an advanced ultraviolet oxidation disinfection unit. The unit's low-pressure ultraviolet lamps emit 254nm ultraviolet light, which, in conjunction with hydroxyl radicals generated by the photocatalytic module, deeply inactivates harmful microorganisms such as E. coli and Giardia lamblia in the water. After disinfection, the finished freshwater is transferred to a clean water tank for storage.

[0106] The biomechanical model for microbial inactivation by ultraviolet light (254nm) synergistically targeting hydroxyl radicals (·OH) is as follows:

[0107]

[0108] in, These represent the initial and time-based microbial counts, respectively. Ultraviolet radiation intensity, This represents the steady-state concentration of hydroxyl radicals generated by photocatalysis.

[0109] S4, Intelligent Power Coordination Regulation

[0110] The intelligent control unit collects photovoltaic power generation parameters, energy storage battery state of charge, water production flow rate, and water quality indicators in real time through the data acquisition module. The photovoltaic output prediction module uses an LSTM neural network model to predict changes in photovoltaic output over short periods. The multivariate fuzzy PID controller dynamically adjusts the operating speeds of the inlet pump, high-pressure pump, and outlet pump based on the prediction results and real-time operating data, matching the total power of photovoltaic power generation and energy storage power supply, balancing the system's water production energy consumption, and achieving continuous and stable water production throughout the year under a fully solar-driven mode without external grid connection.

[0111] The system's global real-time power balance equation is:

[0112]

[0113] in, Real-time photovoltaic power generation. The right side represents the energy storage charging and discharging power, while the right side represents the total power consumption of the load and the line loss.

[0114] The recursive formula for the state of charge (SOC) of an energy storage battery is:

[0115]

[0116] in, For the battery's rated capacity, This refers to the charge / discharge efficiency.

[0117] The ultra-short-term prediction equation for photovoltaic power output using a Long Short-Term Memory (LSTM) neural network is as follows:

[0118]

[0119] in, For predicting rolling windows (e.g., the next 15-30 minutes). The total horizontal radiation intensity. These are the training weights for the network.

[0120] To predict power deviation and its rate of change As input, dynamically adjust the pump unit speed. :

[0121]

[0122]

[0123] in, , , It is not a fixed constant, but a nonlinear gain coefficient calculated online through a fuzzy rule table.

[0124] The formula relating pump shaft power to flow rate and head is:

[0125]

[0126] By adjusting the speed It can be changed in real time. and This allows for matching the fluctuating power of the photovoltaic input, thus enabling flexible water production.

[0127] The comprehensive constraints are as follows:

[0128]

[0129] And meet real-time water quality hard constraints: .

[0130] The specific process for dynamically adjusting the water pump speed in step S4 is as follows:

[0131] S401. Parameter Comparison: Retrieve the future photovoltaic power prediction P_pred output from the photovoltaic power output prediction module, simultaneously obtain the rated energy consumption power P_load required by the system under the current water production conditions, and perform a numerical comparison. The rated energy consumption power P_load includes the total energy consumption of the inlet pump, high-pressure pump, outlet pump, and control system.

[0132] S402. Increased Production and Charging Control: If P_pred ≥ P_load, and the state of charge (SOC) of the energy storage battery is below the preset charging threshold, it indicates that there is surplus photovoltaic power generation. At this time, the controller increases the operating speed of the high-pressure pump to increase the system's water production flow, using the surplus photovoltaic power for increased water production. Simultaneously, the excess power is charged into the energy storage battery bank via a bidirectional DC-DC converter, achieving solar energy storage. The charging threshold SOC is typically set to ≤90%.

[0133] S403, Energy Supplement and Stable Production Control: If P_pred < P_load, it indicates that photovoltaic power generation is insufficient to meet the current water production energy consumption. At this time, the controller gradually reduces the operating speed of the high-pressure pump to reduce system energy consumption, causing the system to switch to a low water production operation mode; at the same time, it controls the energy storage battery pack to discharge through the bidirectional DC converter, and supplements the power gap through the DC bus to ensure the continuous and uninterrupted operation of the water production process.

[0134] S404 Synchronous and Coordinated Control: Based on the real-time speed of the high-pressure pump, the speed of the inlet and outlet pumps is synchronously and finely adjusted according to a preset ratio to stabilize the internal operating pressure of the six-stage filtration membrane separation unit, avoid damage to the membrane components due to pressure fluctuations, and ensure the stability of the filtration and desalination effect.

[0135] Through the above control strategy, the system can dynamically adjust its operating status according to the real-time changes in photovoltaic output. When photovoltaic power is sufficient, it can produce water and store energy at full load. When photovoltaic power is insufficient, the energy storage can supplement the power supply and reduce the water production load, so as to achieve continuous and stable water production throughout the year under the full solar-driven mode.

[0136] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0137] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A direct-drive photovoltaic-storage system for brackish water desalination, characterized in that, It includes a pretreatment unit, a six-stage filtration membrane separation unit, a deep disinfection unit, a DC-driven pump set, a photovoltaic energy storage power supply unit, and an intelligent control unit; The pretreatment unit is used to remove impurities from brackish water. The six-stage filtration membrane separation unit is connected to the pretreatment unit and is used to filter and desalinate the pretreated water step by step. Its product water is sent to the deep disinfection unit. The deep disinfection unit is used to sterilize and disinfect the produced water. The DC-driven pump set includes at least one water pump equipped with a DC brushless permanent magnet motor and a speed controller. The photovoltaic energy storage power supply unit supplies power to each speed controller via a DC bus. The intelligent control unit adjusts the speed of each water pump based on photovoltaic forecasts, energy storage status, and water production requirements.

2. The integrated brackish water desalination system based on direct-drive photovoltaic storage as described in claim 1, characterized in that, The pretreatment unit includes a coagulation sedimentation device and a micro-nano bubble flotation device connected in sequence. The coagulation sedimentation device is equipped with a reagent dosing port for adding polyaluminum chloride and polyacrylamide.

3. The integrated brackish water desalination system based on direct-drive photovoltaic storage according to claim 1, characterized in that, The six-stage filtration membrane separation unit includes a multi-media filter, an activated carbon filter, a precision filter, a composite refining component, a nanofiltration membrane component, and a reverse osmosis membrane component arranged in series along the water flow direction. Its inlet is connected to the outlet of the pretreatment unit, and its product water is connected to the deep disinfection unit.

4. The integrated photovoltaic-storage direct-drive brackish water desalination system according to claim 1, characterized in that, The deep disinfection unit employs an advanced ultraviolet oxidation disinfection device, which includes a low-pressure ultraviolet lamp and a built-in photocatalytic module.

5. The integrated brackish water desalination system based on direct-drive photovoltaic storage according to claim 1, characterized in that, The DC-driven pump set includes an inlet pump, a high-pressure pump, and an outlet pump; the inlet pump is installed on the pipeline between the pretreatment unit and the six-stage filtration membrane separation unit, the high-pressure pump is installed on the pipeline between the nanofiltration membrane module and the reverse osmosis membrane module, and the outlet pump is installed on the product water side pipeline of the reverse osmosis membrane module.

6. The integrated photovoltaic-storage direct-drive brackish water desalination system according to claim 5, characterized in that, The inlet pump, high-pressure pump, and outlet pump are all equipped with DC brushless permanent magnet motors with integrated Hall sensors, and each has its own independent speed controller.

7. The integrated brackish water desalination system based on direct-drive photovoltaic storage according to claim 1, characterized in that, The photovoltaic energy storage power supply unit includes a photovoltaic array, a maximum power point tracking controller, a DC bus, an energy storage battery pack, and a bidirectional DC-DC converter; the photovoltaic array is electrically connected to the DC bus via the maximum power point tracking controller, and the energy storage battery pack is connected in parallel to the DC bus via the bidirectional DC-DC converter.

8. A method for integrated photovoltaic-storage-direct-drive brackish water desalination, applied to the integrated photovoltaic-storage-direct-drive brackish water desalination system according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Brackish Water Pretreatment: The raw brackish water is introduced into a coagulation and sedimentation device, and two flocculants, polyaluminum chloride and polyacrylamide, are added through the chemical dosing port to complete the flocculation and sedimentation of the water. The treated water is then sent to a micro-nano bubble flotation device, where 5μm to 50μm micro-nano bubbles adsorb and remove dissolved organic matter and heavy metal impurities from the water to obtain qualified pretreated effluent with a turbidity ≤0.5NTU. S2. Multi-stage membrane filtration desalination: The inlet pump is started to deliver qualified pretreated water to a multi-media filter, activated carbon filter, precision filter, and composite refining component in sequence to complete the fine filtration of impurities at each stage; the water after preliminary purification flows into the nanofiltration membrane module for staged desalination, and then is pressurized by the high-pressure pump and sent to the reverse osmosis membrane module for deep desalination to prepare qualified purified water with a total dissolved solids content of <100mg / L; S3. Deep sterilization and disinfection: The purified water produced by the reverse osmosis membrane module is transported to the ultraviolet advanced oxidation disinfection device. The hydroxyl radicals generated by the 254nm ultraviolet light in conjunction with the photocatalytic module are used to deeply inactivate harmful microorganisms in the water. After disinfection, the finished fresh water is transported to the clean water tank for storage. S4. Intelligent Power Coordination and Regulation: The intelligent control unit collects photovoltaic power generation parameters, energy storage battery state of charge, water production flow rate and water quality indicators in real time through the data acquisition module; it relies on the long short-term memory neural network model to predict the changes in photovoltaic output within a short period of time, and then dynamically adjusts the operating speed of the inlet pump, high-pressure pump and outlet pump through the multivariate fuzzy PID control algorithm; it matches the total power of photovoltaic power generation and energy storage power supply, balances the system's water production energy consumption, and realizes continuous and stable water production throughout the year under the all-solar-driven mode without external grid connection.

9. The method according to claim 8, characterized in that, The specific steps for dynamic adjustment of the water pump speed in S4 are as follows: S401, Parameter Comparison: Retrieve the future photovoltaic power prediction P_pred output from the photovoltaic power output prediction module, simultaneously obtain the rated energy consumption power P_load required by the system under the current water production conditions, and perform numerical comparison. S402, Increased production and charging control: If P_pred≥P_load and the state of charge of the energy storage battery is lower than the preset charging threshold, the speed of the high-pressure pump is increased to increase the system water production flow, and the surplus photovoltaic power generation is directly used to charge the energy storage battery pack. S403, Energy replenishment and stable production control: If P_pred < P_load, the high-pressure pump speed is gradually reduced to lower system energy consumption, while the energy storage battery pack is controlled to discharge, make up for the power gap, and ensure the continuous operation of the water production process. S404 Synchronous and Coordinated Control: Based on the real-time speed of the high-pressure pump, the speed of the inlet and outlet pumps is synchronously and finely adjusted according to a preset ratio to stabilize the internal operating pressure of the six-stage filtration membrane separation unit, avoid damage to the membrane module due to pressure fluctuations, and ensure the filtration and desalination effect.

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