Photovoltaic storage direct-flexible system based on all-vanadium redox flow battery and its control method

Abstract

The present invention discloses a photovoltaic, energy storage, direct-current, and flexible system based on an all-vanadium liquid flow battery and its control method, relating to the field of photovoltaic, energy storage, direct-current, and flexible technologies. The present invention introduces a DC bus at the building terminal. The photovoltaic, energy storage, direct-current, and flexible system includes a photovoltaic unit, an all-vanadium liquid flow battery energy storage unit, a molten salt heat storage Carnot battery unit, a DC charging pile, a microgrid controller (EMS), and an AC-DC four-quadrant intelligent conversion unit. The photovoltaic unit, the all-vanadium liquid flow battery energy storage unit, the molten salt heat storage Carnot battery unit, the DC charging pile, the microgrid controller (EMS), and the AC-DC four-quadrant intelligent conversion unit are all connected to the DC bus, and the output end of the AC-DC four-quadrant intelligent conversion unit is connected to the AC bus. The present invention provides a near-zero-carbon energy system for buildings that combines photovoltaic and energy storage, solves the problems of energy storage safety, environmental friendliness, and short energy storage time, optimizes the coordinated control of source, grid, load, and storage, and improves the economy and reliability of the system.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic, energy storage, direct-flow and flexible technology, and in particular to a photovoltaic, energy storage, direct-flow and flexible system based on an all-vanadium redox flow battery and a control method thereof. Background Art

[0002] Climate change is a common challenge facing humanity, and it is related to human survival and development. In response to the energy crisis and global warming, countries around the world have pledged to strengthen the development of clean energy and reduce carbon dioxide emissions. Currently, the intermittent volatility caused by the high penetration of renewable energy has a serious impact on the power grid. To address the mismatch between the changes on the source side of the power grid and the load side, it is necessary to promote "solar storage direct current flexible" technology on the user side. Its characteristic is the organic combination of distributed photovoltaics, distributed energy storage and DC distribution buildings. The core is to place energy storage batteries on the load side or in the building, so that the building's electricity consumption is transformed from a rigid load to a flexible load. The purpose is to improve the ability to consume green and clean energy on site, while avoiding the double conversion of input and output, improving the power conversion efficiency, and reducing equipment investment and floor space.

[0003] Current "PV-storage, direct-flexible" systems being built in buildings rely on lithium iron phosphate batteries for energy storage. Due to the inherent characteristics of lithium batteries, these batteries present a high risk of explosion and ignition. Furthermore, current PV-storage, direct-flexible systems exhibit significant mismatches with peak and valley loads for building heating. These factors limit the application and development of PV-storage, direct-flexible technology in buildings and for industrial and commercial users.

[0004] The technology proposed in this patent is to establish a DC microgrid with flexible interactive functions at the building terminal or user end, and use the building rooftop photovoltaic and all-vanadium liquid flow batteries to sustainably supply electricity. At the same time, the system integrates molten salt heat storage devices and charging piles as high-power loads to fully absorb green electricity, providing electricity, steam or hot water for building users, reducing the use of fossil energy such as municipal electricity and natural gas, reducing carbon emissions and environmental pollution. It is a highly integrated green electricity and heat cogeneration system that achieves the "zero carbon" deep emission reduction goals of clean energy supply, low-carbon energy consumption, and safe energy security at the building user end.

[0005] The currently announced solar-storage-direct-flexible systems are lithium-ion battery-based systems. In terms of safety, the inherent characteristics of lithium batteries make their application in buildings subject to many safety hazards and environmental issues. In terms of economy, lithium batteries have a short storage time, making it difficult to form flexible interactions with different peaks and valleys in regional power supply and demand, and long-term off-grid operation, and their economy has not been well reflected. In terms of building load demand, if users have steam (hot water) heating needs, they need to configure a boiler and a supporting gas pipeline network, which requires large investment and low efficiency. As a result, the advantages of solar-storage-direct-flexible systems in directly and efficiently absorbing green electricity have not been truly reflected, and no application scenarios with strong adaptability and rich functions have been formed.

[0006] This invention is aimed at users of building buildings and realizes the in-depth comprehensive utilization of renewable energy such as solar energy. It innovatively proposes a combined heat and power generation system composed of DC bus distribution as the link, solar photovoltaic as the power source, all-vanadium liquid flow battery and Carnot battery (molten salt heat storage).

[0007] All-vanadium redox flow batteries are a new, green electrochemical energy storage technology. Due to their inherent advantages of safety and long life, they are ideal for applications requiring high safety, long life, and maintenance-free operation, as well as environmental protection. The Carnot battery (molten salt thermal storage) utilizes a new high-temperature, high-heat-flux molten salt heat transfer and storage medium. Electric heating raises the molten salt temperature, and when heating is needed, the stored heat (steam or hot water) is released in a heat exchanger. This fully utilizes green photovoltaic electricity and effectively utilizes the price differential between peak and valley electricity prices. Summary of the Invention

[0008] The main purpose of the present invention is to provide a photovoltaic, storage, direct-current and flexible system based on all-vanadium liquid flow batteries and its control method. At the same time, the photovoltaic, storage, direct-current and flexible system composed of distributed photovoltaic, molten salt heat storage and DC distribution network and its coordinated control algorithm can automatically adjust according to load changes. While providing green electricity, it realizes the joint storage and supply of electricity and heat to solve the problems raised in the above background.

[0009] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a photovoltaic storage direct-flexible system based on an all-vanadium liquid flow battery is introduced into a DC bus at the building terminal, and the photovoltaic storage direct-flexible system includes a photovoltaic unit, an all-vanadium liquid flow battery energy storage unit, a molten salt heat storage Carnot battery unit, a DC charging pile, a microgrid controller EMS and an AC-DC four-quadrant intelligent conversion unit. The photovoltaic unit, the all-vanadium liquid flow battery energy storage unit, the molten salt heat storage Carnot battery unit, the DC charging pile, the microgrid controller EMS and the AC-DC four-quadrant intelligent conversion unit are all connected to the DC bus, and the output end of the AC-DC four-quadrant intelligent conversion unit is connected to the AC bus; the photovoltaic unit is composed of a PV photovoltaic module and a DC power optimizer, and the DC power optimizer is an autonomous control module, and each mode switching and judgment is completed by the photovoltaic DC power optimizer. The PV photovoltaic module is combined in series and parallel by the photovoltaic panel according to the input power of the DC power optimizer; the all-vanadium liquid flow battery energy storage unit is composed of a battery pack and a bidirectional DC-DC converter. The device communicates through the CAN bus, and the DC converter can obtain the parameter information of the battery pack to perform corresponding actions; the molten salt heat storage Carnot battery unit is composed of a molten salt heat storage Carnot battery, and the molten salt heat storage Carnot battery acts as an AC load. The electric heater of the molten salt heat storage Carnot battery draws power from the AC bus, and the AC and DC realize flexible interactive complementarity; the DC charging pile acts as a DC load, and the DC charging pile draws power from the DC bus through a DC converter; the microgrid controller has a monitoring device, which is a terminal with Bluetooth or WiFi function, and can obtain the system parameter information through Bluetooth or WiFi and control it; the photovoltaic storage direct-flexible system uses the PSO-SQP framework to construct a multi-energy coupling algorithm model, and comprehensively regulates the all-vanadium liquid flow battery energy storage system according to the photovoltaic output and electrical and thermal load conditions, realizing intelligent scheduling and operation of the distribution network, real-time balance of power output and load, and taking load shedding measures when necessary to maintain the frequency and voltage stability of the photovoltaic storage direct-flexible system.

[0010] In terms of control algorithms, through the design of a multi-energy coupling algorithm, real-time balance between power output and load within the system is achieved under the photovoltaic + peak-valley electricity price mode, ensuring stable output of voltage and frequency.

[0011] Preferably, the photovoltaic storage direct-flexible system operates in a "photovoltaic + peak-valley electricity price" mode. When the solar illumination is high during the day, the electricity generated by the photovoltaic unit is output to the AC380V AC bus through the AC-DC four-quadrant intelligent conversion unit to maintain the self-use of the cogeneration system and supply power to the outside; at the same time, the other path is rectified by the DC power optimizer and output to the DC750V DC bus, which is used to discharge the battery or take the peak electricity from the grid to supply power when there is no light or at night.

[0012] Preferably, the all-vanadium liquid flow battery energy storage unit charges the battery system through a bidirectional DC-DC converter. When the BMS detects that the battery system is fully charged, the charge and discharge main circuit contactor is disconnected and the circulation system stops running to avoid battery overcharging; when the solar light intensity is weak, the charge and discharge main circuit contactor is closed (the switching time is required to be less than 200ms), and the battery is discharged to the DC bus, running in parallel with the photovoltaic equipment and supplying power to the outside; when there is no light, the battery is discharged alone to maintain system operation.

[0013] The control method for a vanadium flow battery-based solar-storage direct-flexible system is based on an economic operation and scheduling strategy. By analyzing load and energy consumption data and matching different energy costs (photovoltaic power and peak and valley electricity prices), the optimal operation plan for the equipment is determined. The method includes the following steps:

[0014] Step 1: Determine the energy network structure of the PV-storage-direct-flexible system, calculate the power flow based on the electricity and heat load forecasts, and continuously adjust the DC injection power, PV output, battery energy storage output, DC charging pile output, and molten salt thermal storage Carnot battery output until the calculation converges.

[0015] Step 2: Check the constraints of the calculation results. If the constraints are not met, return to Step 1 until the constraints are met.

[0016] Step 3: Determine the electrical (thermal) output power of the multi-energy coupling device based on the coupling relationship and perform electrical (thermal) power flow calculations.

[0017] Step 4: Determine whether to enable molten salt heat storage based on load requirements. If enabled, calculate the electrical load of the molten salt heat storage Carnot battery based on the molten salt heat storage coupling relationship, add the electrical load output calculation, and perform power flow calculation based on the system energy network structure.

[0018] Step 5: Perform constraint verification to determine the electrical and thermal capacity of the equipment in the multi-energy coupling system and output the results.

[0019] The present invention has the following beneficial effects:

[0020] This invention, by establishing a photovoltaic-storage-direct-flexible system based on all-vanadium liquid flow batteries, provides buildings with a near-zero-carbon energy system that complements photovoltaics and energy storage. It solves the problems of energy storage safety, environmental protection and short energy storage time, optimizes the coordinated control of source, grid, load and storage, and improves the economy and reliability of the system.

[0021] The present invention realizes constant power supply, adopts photovoltaic + peak-valley electricity price operation mode, realizes new energy consumption, shifts peak power to fill valley power, optimizes energy consumption costs, and achieves the purpose of flexible electricity use in building terminals.

[0022] The present invention utilizes Carnot battery molten salt to store heat, which has a higher efficiency than storage batteries, can reduce battery capacity and cost, and realize the combined supply and storage of electricity, heat and electricity at the building terminal.

[0023] The present invention adopts a multi-energy coupling coordinated control algorithm based on the PSO-SQP framework, which can adjust the photovoltaic and energy storage output according to the fluctuation of electricity (heat) load.

[0024] The system of the present invention adopts high-precision controllable DC voltage and current source, flexible AC flexible control, and uses four-quadrant intelligent conversion technology to achieve deep integration and friendly interaction of source-grid-load-storage, changing the phenomenon of repeated conversion in the electricity consumption process in buildings, reducing losses, and providing conditions for energy intelligence, digitization, and networking, which is conducive to energy conservation and emission reduction in the construction field and is in line with the direction of future building development. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the system topology diagram of the solar-storage direct-flexible system based on all-vanadium redox flow batteries of the present invention;

[0026] Figure 2 This is a system principle diagram of the solar-storage direct-flexible system based on all-vanadium redox flow batteries of the present invention;

[0027] Figure 3 This is a flow chart of the multi-energy coupling control algorithm of the photovoltaic storage direct-flexible system based on all-vanadium redox flow batteries in the present invention.

[0028] In the figure: 1. Battery pack; 2. Bidirectional DC-DC converter; 3. BMS; 4. Microgrid controller EMS; 5. PV photovoltaic module; 6. DC power optimizer; 7. AC-DC four-quadrant intelligent conversion unit; 8. DC charging pile; 9. DC converter; 10. Molten salt storage Carnot battery; 11. Electric heater; 12. DC bus; 13. AC bus. DETAILED DESCRIPTION

[0029] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0030] In the description of the present invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front end," "rear end," "both ends," "one end," "the other end," and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0031] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "provided with," "connected," etc., should be understood in a broad sense. For example, "connected" may refer to a fixed connection, a detachable connection, or an integral connection; it may refer to a mechanical connection or an electrical connection; it may refer to a direct connection or an indirect connection through an intermediate medium; it may refer to internal communication between two components. Those skilled in the art will be able to understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0032] Example 1:

[0033] Please refer to Figure 1-3 As shown: A photovoltaic, storage, direct-flexible system based on all-vanadium flow batteries introduces a DC bus 12 at the building terminal. The photovoltaic, storage, direct-flexible system includes a photovoltaic unit, an all-vanadium flow battery energy storage unit, a molten salt heat storage Carnot battery unit, a DC charging pile, a microgrid controller EMS4 and an AC-DC four-quadrant intelligent conversion unit 7. The photovoltaic unit, the all-vanadium flow battery energy storage unit, the molten salt heat storage Carnot battery unit, the DC charging pile 8, the microgrid controller EMS4 and the AC-DC four-quadrant intelligent conversion unit 7 are all connected to the DC bus 12, and the output end of the AC-DC four-quadrant intelligent conversion unit 7 is connected to the AC bus 13; the photovoltaic unit consists of a PV photovoltaic module 5 and a DC power optimizer 6. The DC power optimizer 6 is an autonomous control module, and the switching and judgment of each mode are completed by the photovoltaic DC power optimizer 6. The PV photovoltaic module 5 is connected in series and parallel by the photovoltaic panel according to the input power of the DC power optimizer 6; the all-vanadium flow battery energy storage unit consists of a battery group 1 and a bidirectional DC-DC converter 2. The battery group 1 and the DC converter 2 are connected through CA N bus for communication, the DC converter 2 can obtain the parameter information of the battery pack 1, and thus perform corresponding actions; the molten salt heat storage Carnot battery unit is composed of a molten salt heat storage Carnot battery 10, which serves as an AC load and the electric heater 11 of the molten salt heat storage Carnot battery 10 draws power from the AC bus 13, thus achieving flexible interactive complementarity between AC and DC; the DC charging pile 8 serves as a DC load and draws power from the DC bus 12 through the DC converter 9; the microgrid controller has a monitoring device, which is a terminal with Bluetooth or WiFi function, which can obtain the system parameter information through Bluetooth or WiFi and control it; the photovoltaic storage direct-flexible system uses the PSO-SQP framework to construct a multi-energy coupling algorithm model, and comprehensively regulates the all-vanadium liquid flow battery energy storage system according to the photovoltaic output and electrical and thermal load conditions, realizing intelligent scheduling and operation of the distribution network, real-time balance of power output and load, and taking load shedding measures when necessary to maintain the frequency and voltage stability of the photovoltaic storage direct-flexible system.

[0034] In terms of control algorithms, through the design of a multi-energy coupling algorithm, real-time balance between power output and load within the system is achieved under the photovoltaic + peak-valley electricity price mode, ensuring stable output of voltage and frequency.

[0035] Among them, the photovoltaic storage direct-flexible system adopts the "photovoltaic + peak-valley electricity price" mode. When the solar illumination is high during the day, the power generated by the photovoltaic unit is output to the AC380V AC bus 13 through the AC-DC four-quadrant intelligent conversion unit 7, maintaining the self-use of the cogeneration system and supplying power to the outside; at the same time, the other path is rectified by the DC power optimizer 6 and output to the DC750V DC bus 12, which is used to discharge the battery or take the peak electricity from the grid to supply power when there is no light or at night.

[0036] Among them, the all-vanadium liquid flow battery energy storage unit charges the battery system through a bidirectional DC-DC converter 2. When the BMS3 detects that the battery system is fully charged, the charge and discharge main circuit contactor is disconnected and the circulation system stops running to avoid battery overcharging; when the solar light intensity is weak, the charge and discharge main circuit contactor is closed (the switching time is required to be less than 200ms), and the battery is discharged to the DC bus 12, running in parallel with the photovoltaic equipment and supplying power to the outside at the same time; when there is no light, the battery is discharged alone to maintain system operation.

[0037] The control method for a vanadium flow battery-based solar-storage direct-flexible system is based on an economic operation and scheduling strategy. By analyzing load and energy consumption data and matching different energy costs (photovoltaic power and peak and valley electricity prices), the optimal operation plan for the equipment is determined. The method includes the following steps:

[0038] Step 1: Determine the energy network structure of the PV-storage-direct-flexible system, calculate the power flow based on the electricity and heat load forecasts, and continuously adjust the DC injection power, PV output, battery energy storage output, DC charging pile output, and molten salt thermal storage Carnot battery output until the calculation converges.

[0039] Step 2: Check the constraints of the calculation results. If the constraints are not met, return to Step 1 until the constraints are met.

[0040] Step 3: Determine the electrical (thermal) output power of the multi-energy coupling device based on the coupling relationship and perform electrical (thermal) power flow calculations.

[0041] Step 4: Determine whether to enable molten salt heat storage based on load requirements. If enabled, calculate the electrical load of the molten salt heat storage Carnot battery based on the molten salt heat storage coupling relationship, add the electrical load output calculation, and perform power flow calculation based on the system energy network structure.

[0042] Step 5: Perform constraint verification to determine the electrical and thermal capacity of the equipment in the multi-energy coupling system and output the results.

[0043] The present invention provides a photovoltaic storage direct-flexible system and control method based on all-vanadium liquid flow batteries. The system design is reasonable, clear and innovative, providing a practical solution and approach for achieving near-zero-carbon buildings, and can achieve multiple benefits.

[0044] Safety Benefits: The use of all-vanadium redox flow batteries completely eliminates the potential explosion hazards associated with lithium batteries. Key technical indicators for all-vanadium redox flow batteries, including energy storage duration, cost per kilowatt-hour (kWh), energy efficiency, and operating life, must simultaneously meet the following requirements: energy storage duration ≥ 8 hours; energy storage cost per kilowatt-hour ≤ 0.6 yuan / kWh; system energy efficiency > 75% at rated power; and system operating life ≥ 20 years.

[0045] Economic benefits: The PV-storage direct-flexible system innovatively introduces a DC bus to achieve long-term energy storage, improve the ability to consume green energy locally, and reduce transformer redundancy. The overall equipment investment cost of the system is greatly reduced, and the construction area is also reduced, saving an overall 20-30% of the investment cost.

[0046] Environmental protection and comprehensive benefits: The goal of near-zero carbon production, supply and emissions of energy is achieved at the building terminal. The multi-energy complementary energy system composed of photovoltaics, energy storage and heat storage is responsible for the main power supply of regional buildings, saving a lot of electricity bills and power capacity costs, reducing energy costs, and realizing low-carbon and intelligent energy production, supply and consumption at the building terminal.

[0047] Example 2:

[0048] This implementation case is based on a 200-square-meter zero-carbon, ultra-low energy consumption green building in a villa-style commercial creative park in Shanghai, which was designed using this method.

[0049] The building's rooftop is equipped with photovoltaic panels. The power generated by the PV panels, via MPPT, is integrated into a 750V DC busbar through a DC power optimizer, supplying power to the system. This power is used by the molten salt thermal storage Carnot battery and DC charging station, while excess power is stored in vanadium flow batteries. This ensures 100% self-generation and self-use. The system utilizes AC-DC four-quadrant intelligent power technology for flexible interaction with the AC busbar.

[0050] Technical requirements for the configuration of a PV-storage direct-flexible system:

[0051] 1. The optimized system configuration is 20kW photovoltaic power generation, 10kW / 80kWh all-vanadium liquid flow battery, 10kW / 90kWh molten salt thermal storage Carnot battery, and 10kW DC charging pile;

[0052] 2. A structure that complements the three new energy sources of photovoltaic power generation, flow battery, and Carnot battery;

[0053] 3. The system can be charged at constant power. The energy conversion efficiency of the flow battery in constant power mode is greater than 80%. The power factor is adjustable, ranging from 0.9 leading to 0.9 lagging.

[0054] 4. The measurement error of current, voltage and electrolyte flow is ≤0.5%, the measurement error of active and reactive power is ≤1.0%; the frequency measurement error is ≤0.01Hz.

[0055] Based on the PV capacity and charging load, this system features a 10kW all-vanadium redox flow battery energy storage system with a capacity of 80kWh, enabling eight hours of long-term charging and discharging. The system is highly integrated within a 10-foot container. The integrated equipment includes the battery stack, liquid storage tank, electrolyte circulation system (piping, circulation pump, heat exchanger, chiller), and electrical system (electrical control cabinet and DC / DC cabinet).

[0056] The system operates in two modes. In daytime mode, during periods of abundant sunlight, the PV panels initially supply power to the DC loads via the DC power optimizer. When the total output power of the DC converter exceeds the power demanded by the DC loads, the DC converter begins charging the vanadium liquid flow battery pack. When the total output power of the four-quadrant DC-AC inverter exceeds the sum of the power demanded by the AC and DC loads and the battery pack charging power, the inverter begins connecting to the 380V AC mains. The battery pack discharges, supplying power to the AC loads and AC loads on the 380V AC mains line via the inverter. In nighttime mode, when the PV panels have no power output, the battery pack discharges, supplying power to the DC loads via the DC converter. When the battery pack discharge power falls below the power demanded by the AC loads, the 380V AC mains returns power to the AC loads.

[0057] After testing, the system's energy conversion efficiency in constant power mode is higher than 75%, the electrolyte flow measurement error is <0.36%, the voltage measurement error is <0.47%; the active power measurement error is <0.06%, the reactive power measurement error is <0.5%; the frequency measurement error is <0.002Hz; the coordinated control of the photovoltaic storage direct and flexible combined power and heat supply has initially met the technical requirements, laying the foundation for promoting the technological progress and industrialization of photovoltaic storage direct and flexible.

[0058] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. The solar-storage direct-flexible system based on all-vanadium flow batteries is characterized by: A DC bus (12) is introduced at the building terminal. The photovoltaic storage direct-flexible system includes a photovoltaic unit, a vanadium liquid flow battery energy storage unit, a molten salt heat storage Carnot battery unit, a DC charging pile, a microgrid controller EMS (4) and an AC-DC four-quadrant intelligent conversion unit (7). The photovoltaic unit, the vanadium liquid flow battery energy storage unit, the molten salt heat storage Carnot battery unit, the DC charging pile (8), the microgrid controller EMS (4) and the AC-DC four-quadrant intelligent conversion unit (7) are all connected to the DC bus (12). The output end of the AC-DC four-quadrant intelligent conversion unit (7) is connected to the AC bus (13). The photovoltaic unit is composed of a PV photovoltaic assembly (5) and a DC power optimizer (6). The DC power optimizer (6) is an autonomous control module. Each mode switching and judgment is completed by the photovoltaic DC power optimizer (6). The PV photovoltaic assembly (5) is connected in series and parallel by photovoltaic panels according to the input power of the DC power optimizer (6). The all-vanadium liquid flow battery energy storage unit is composed of a battery pack (1) and a bidirectional DC-DC converter (2). The battery pack (1) and the DC converter (2) communicate via a CAN bus. The DC converter (2) can obtain parameter information of the battery pack (1) and thereby perform corresponding actions. The molten salt heat storage Carnot battery unit is composed of a molten salt heat storage Carnot battery (10), the molten salt heat storage Carnot battery (10) serves as an AC load, and the electric heater (11) of the molten salt heat storage Carnot battery (10) draws power from an AC bus (13), so that AC and DC achieve flexible interactive complementarity; The DC charging pile (8) serves as a DC load, and the DC charging pile (8) draws power from the DC bus (12) via a DC converter (9); The microgrid controller has a monitoring device, which is a terminal with Bluetooth or WiFi function, and can obtain system parameter information through Bluetooth or WiFi and control it; The PV-storage direct-flexible system uses the PSO-SQP framework to construct a multi-energy coupling algorithm model, and comprehensively regulates the all-vanadium liquid flow battery energy storage system according to the photovoltaic output and electrical and thermal load conditions, realizing intelligent scheduling and operation of the distribution network, real-time balance of power output and load, and taking load shedding measures when necessary to maintain the frequency and voltage stability of the PV-storage direct-flexible system.

2. The solar-storage direct-flexible system based on all-vanadium flow batteries according to claim 1 is characterized by: The photovoltaic storage direct-flexible system operates in a "photovoltaic + peak-valley electricity price" mode. When the solar illumination is high during the day, the power generated by the photovoltaic unit is output to the AC380V AC bus (13) through the AC-DC four-quadrant intelligent conversion unit (7) to maintain the self-use of the combined heat and power generation system and supply power to the outside. At the same time, the other power is rectified by the DC power optimizer (6) and output to the DC750V DC bus (12) for power supply when there is no light or at night, discharged by the battery or taken from the grid during the off-peak period.

3. The solar-storage direct-flexible system based on all-vanadium redox flow batteries according to claim 1 is characterized by: The all-vanadium liquid flow battery energy storage unit charges the battery system through a bidirectional DC-DC converter (2). When the BMS (3) detects that the battery system is fully charged, the charge and discharge main circuit contactor is disconnected and the circulation system stops running to avoid overcharging of the battery. When the solar light intensity is weak, the charge and discharge main circuit contactor is closed, and the switching time is required to be less than 200ms. The battery is discharged to the DC bus (12) and is connected to the photovoltaic equipment for grid operation while supplying power to the outside. When there is no light, the battery is discharged alone to maintain the system operation.

4. A control method for a photovoltaic, energy storage, direct-flexible system based on an all-vanadium redox flow battery, applied to the photovoltaic, energy storage, direct-flexible system according to any one of claims 1 to 3, characterized in that: Based on the economic operation scheduling strategy, by analyzing the load and energy consumption data and matching different energy costs, the optimal operation plan for the equipment is determined, including the following steps: Step 1: Determine the energy network structure of the PV-storage-direct-flexible system, calculate the power flow based on the electricity and heat load forecasts, and continuously adjust the DC injection power, PV output, battery energy storage output, DC charging pile output, and molten salt thermal storage Carnot battery output until the calculation converges. Step 2: Check the constraints of the calculation results. If the constraints are not met, return to Step 1 until the constraints are met. Step 3: Determine the electrical or thermal output power of the multi-energy coupling device based on the coupling relationship and perform electrical or thermal power flow calculations; Step 4: Determine whether to enable molten salt heat storage based on load requirements. If enabled, calculate the electrical load of the molten salt heat storage Carnot battery based on the molten salt heat storage coupling relationship, add the electrical load output calculation, and perform power flow calculation based on the system energy network structure. Step 5: Perform constraint verification to determine the electrical and thermal capacity of the equipment in the multi-energy coupling system and output the results.

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