Buoyancy energy storage system based on piston drainage and operation method thereof

Abstract

The invention discloses a buoyancy energy storage system based on piston drainage and an operation method of the buoyancy energy storage system. The energy storage system comprises a high-pressure liquid storage tank, a low-pressure liquid storage tank, a control box and multiple sets of energy storage unit bodies. A variable hydraulic motor and a constant displacement pump are connected between the high-pressure liquid storage tank and the low-pressure liquid storage tank in parallel, the variable hydraulic motor is connected with a generator, a plurality of piston cylinders and motors are arranged in the energy storage unit, pistons are arranged in the piston cylinders, and the motors are sequentially connected with steel cables and the bottoms of the pistons through transmission chains. A control signal output end of the control box is connected with control signal input ends of the hydraulic motor, the metering pump and the motor, a pressure relief structure is arranged at the top of the piston cylinder, and the motor is arranged above the energy storage unit body. The system power input end is connected with the power output end of the offshore wind generating set; a modular buoyancy energy storage framework is adopted, flexible adjustment of the energy storage capacity is supported, and environment friendliness is achieved; the system can be integrated with offshore wind power infrastructures, reduces the investment cost, and meets the requirements of energy utilization and environmental protection.

Description

Technical Field

[0001] The present invention belongs to the technical field of long-term energy storage, and particularly relates to a buoyancy energy storage system based on piston drainage and an operation method thereof, which is applicable to scenarios such as grid frequency regulation and renewable energy consumption matching for supporting offshore wind power. Background Art

[0002] With the global energy structure transforming towards cleaner and lower-carbon, offshore wind power has become an important direction for renewable energy development due to its huge resource potential, high power generation efficiency, and proximity to load centers. However, affected by factors such as wind speed changes, extreme weather, and unit maintenance, the output of offshore wind power has significant volatility and intermittency. The grid connection power quality and grid stability are facing severe challenges. The inherent volatility and intermittency of offshore wind power output on the one hand make it difficult to match the power generation power with the grid load demand in real time, thus leading to problems such as grid connection difficulties and curtailment of wind power; on the other hand, it results in low power quality of the output, posing a severe challenge to grid stability. Energy storage can suppress the output fluctuations of offshore wind power and improve power quality, thereby enhancing the utilization rate of offshore wind energy. Therefore, technically speaking, energy storage is a powerful means to ensure the consumption of offshore wind power and promote the large-scale development of offshore wind power. Under this background, the high proportion of renewable energy consumption poses an urgent demand for large-scale energy storage technologies.

[0003] Traditional energy storage solutions such as electrochemical energy storage (such as lithium-ion batteries, lead-acid batteries, etc.) are prone to performance degradation and safety hazards in the harsh marine environment of high humidity, high salt spray, and strong corrosion, and the maintenance cost is high, making it difficult to meet the high-safety, long-cycle, and large-capacity energy storage requirements in the offshore wind power scenario; although pumped-storage energy has the advantage of high technology maturity, its characteristics of relying on specific geographical conditions have extremely low compatibility with the marine scenario, and the construction period is long and the project investment is large. Other energy storage technologies such as flywheel energy storage and compressed air energy storage are also limited in aspects such as energy storage cost and marine environment adaptability. In addition, the space on the offshore platform is limited, and the offshore wind power energy storage device should not occupy too much space on the offshore wind power platform. The Chinese patent with the publication number CN110608141A in the prior art provides a combined system of gravitational potential energy and buoyancy energy, which drives power generation through the mechanical gravitational potential energy of the floating cylinder freely falling in the wellbore, and then uses buoyancy to make the floating cylinder float and cycle for power generation. In essence, it is a direct energy conversion, and the movement of the floating cylinder is synchronized with power generation, without energy storage buffering ability; the energy output depends on the cycling speed of the floating cylinder, making it difficult to respond to changes in grid demand, relying on a fixed wellbore structure and water injection operation, suitable for small-scale power generation on land or in fixed water bodies, limited by geographical conditions; the mechanical transmission loss is relatively high, and the long-term operation and maintenance cost is large. Therefore, there is an urgent need to develop a new energy storage technology that can be deeply coupled with the marine environment and has both large-scale energy storage capacity and low-cost advantages. Summary of the Invention

[0004] In order to overcome the deficiencies of the above-mentioned existing technologies, the purpose of the present invention is to provide a buoyancy energy storage system based on piston drainage and its operation method, which can change the net buoyancy state of a sealed floating body, i.e., a piston, in seawater through an electric drive device, convert electrical energy into piston buoyancy potential energy for storage, and drive a generator to generate electricity when releasing energy. This technology has multiple advantages: directly using seawater as a natural pressure medium, with a theoretical energy density higher than that of compressed air energy storage; the energy storage medium is seawater, with a low risk of chemical substance leakage and outstanding environmental friendliness; it can be integrated and deployed with offshore wind power infrastructure (such as jacket foundations and floating platforms), reducing investment costs.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a buoyancy energy storage system based on piston drainage, including a high-pressure liquid storage tank, a low-pressure liquid storage tank, a control box, and multiple sets of energy storage unit bodies; a variable hydraulic motor and a fixed-displacement pump are connected in parallel between the high-pressure liquid storage tank and the low-pressure liquid storage tank, the variable hydraulic motor is connected to a generator, multiple piston cylinders and electric motors are arranged in the energy storage unit body, pistons are arranged in the piston cylinders, and the electric motor and the fixed-displacement pump drive chains are sequentially connected to the bottom of the piston through a steel cable; the control signal output of the control box is connected to the control signal input ends of the hydraulic motor, the fixed-displacement pump, and the electric motor, a pressure relief structure is arranged at the top of the piston cylinder, and the electric motor is arranged above the energy storage unit body; the power input end of the system is connected to the power output end of an offshore wind turbine generator set.

[0006] Further, the outlet of the high-pressure liquid storage tank, the inlet of the variable hydraulic motor, and the inlet of the low-pressure liquid storage tank are sequentially connected; the outlet of the low-pressure liquid storage tank, the inlet of the fixed-displacement pump, and the inlet of the high-pressure liquid storage tank are sequentially connected.

[0007] Further, the drive chain includes a drive chain on the electric motor side, a drive chain on the fixed-displacement pump side, a first clutch device, and a cable winch. The first clutch device is connected to one end of the cable winch, and the steel cable is wound around the cable winch; the other end of the cable winch, the second clutch device, and the input shaft of the fixed-displacement pump are sequentially connected.

[0008] Further, a pulley is arranged at the bottom end of the piston cylinder, and one end of the steel cable bypasses the pulley and is connected to the bottom of the piston.

[0009] Further, a corrosion-resistant piston ring is arranged between the piston and the piston cylinder.

[0010] Further, the piston cylinder, the pipelines connecting the high-pressure liquid storage tank, the low-pressure liquid storage tank, the fixed-displacement pump, and the variable hydraulic motor are all made of stainless steel material, with a pressure resistance of more than 25 MPa; the high-pressure liquid storage tank, the low-pressure liquid storage tank, and the pipelines connecting the high-pressure liquid storage tank and the low-pressure liquid storage tank are all filled with hydraulic oil.

[0011] Further, a pressure and temperature monitoring device is arranged in the high-pressure liquid storage tank; the pressure and temperature monitoring device is connected to the input end of the control box.

[0012] Furthermore, it can be integrally spliced and installed on the jacket foundation or floating platform of an offshore wind turbine generator, or connected to the offshore wind turbine generator platform through steel cables as an independent building. When the second construction method is adopted, the energy storage system should be subject to sufficient gravity to offset the buoyancy at the bottom of the piston in the deep sea.

[0013] Meanwhile, a method for operating the buoyancy energy storage system based on piston drainage as described above is provided, including the energy release process. Through the control box, the transmission chain on one side of the metering pump is controlled to be in the working state, and the transmission chain on the motor side is in the non - working state. The energy storage unit releases energy, and the metering pump pumps hydraulic oil into the high - pressure liquid storage tank. The high - pressure hydraulic oil in the high - pressure liquid storage tank enters the variable hydraulic motor under the action of pressure difference to drive the generator to generate electricity, and the pressure in the high - pressure liquid storage tank is kept constant; until the piston moves to the highest position, the energy release stage ends. The energy storage process: The control box controls the transmission chain on the motor side to be in the working state, and the transmission chain on the metering pump side is in the non - working state. By controlling the start and stop of the motor in the energy storage unit through the control box, the transmission chain on the motor side drives the steel cable to tow the piston to the lowest position.

[0014] Furthermore, the displacement of the variable hydraulic motor is regulated in real - time by dynamically monitoring the pressure parameters of the hydraulic oil in the high - pressure liquid storage tank. The opening and closing states of the energy release of a single or several energy storage units are dynamically adjusted through the control box, and the metering pump is dynamically controlled to pump low - pressure hydraulic oil into the high - pressure liquid storage tank.

[0015] Compared with the prior art, the present invention has at least the following beneficial technical effects: Adopting a modular buoyancy energy storage architecture, it supports flexible adjustment of the energy storage capacity; the risk of chemical substance leakage is low, and it is environmentally friendly; it can be integrated and deployed with offshore wind power infrastructure, reducing investment costs, and meeting the increasingly strict requirements for energy utilization and environmental protection; the site selection is flexible, the application scenarios are wide, and it is easy to be implemented in engineering; by filling hydraulic oil in pipelines, high - pressure liquid storage tanks, and low - pressure liquid storage tanks, the power output of the power chain is ensured to be uninterrupted, and the system reliability is significantly improved through mechanical energy storage methods, specifically manifested in key indicators such as optimized floating body sealing performance and strengthened anti - fatigue structure; it helps to achieve the function of stabilizing the output fluctuation of wind power and improving the power quality of the energy storage system; in addition, the modular buoyancy energy storage architecture constructed based on the piston drainage principle provided by the present invention supports flexible adjustment of the energy storage capacity. When a small number of energy storage monomers fail, it does not affect the operation of the entire energy storage system, and the anti - risk ability is relatively high.

[0016] Furthermore, the pressure relief structure at the top of the piston cylinder is connected to the local atmosphere, so that the pressure in the upper space of the piston is the local atmospheric pressure to maintain a large pressure difference between the lower and upper surfaces of the piston.

[0017] Further, during the energy release process, the control box dynamically monitors the pressure parameter of the hydraulic oil in the high-pressure liquid storage tank, and intelligently adjusts the opening and closing state of the energy storage unit body to release energy, so as to realize the dynamic balance of the pressure in the high-pressure liquid storage tank; under the control of the control box, by dynamically monitoring the pressure parameter of the hydraulic oil in the high-pressure liquid storage tank, the displacement of the variable hydraulic motor is regulated in real time to ensure that the output power of the hydraulic motor remains constant.

[0018] Further, a pulley is installed at the lower part of the energy storage unit body, and the steel cable passes through the pulley to reduce frictional losses.

[0019] Further, a steel cable winch, a second clutch device, a fixed-displacement pump, connected pipelines, a high-pressure liquid storage tank, connected pipelines, a variable hydraulic motor, and a power generation mechanism are also provided to form a power transmission chain.

[0020] Further, as a common optimization method, a corrosion-resistant piston ring is provided between the piston and the piston cylinder in the energy storage unit body to ensure sealing. When the piston ring works, it first fits against the inner wall of the piston cylinder with its own elastic force, so that seawater cannot pass between the outer circle of the ring and the inner wall of the piston cylinder. A small amount of seawater enters the piston ring groove and acts on the back of the piston ring, increasing the pressure of the piston ring on the inner wall of the piston cylinder, and significantly improving the sealing performance of the piston ring.

[0021] Further, the system provided by the present invention can be integrally deployed with offshore wind power infrastructure (such as jacket foundations, floating platforms) to reduce investment costs.

[0022] Further, through the topological optimization of the energy storage unit body array and the vortex-induced vibration suppression device, the range of flow field disturbance can be limited within 600 meters, and the acoustic guidance technology can be used to avoid areas with dense marine organisms.

[0023] Further, during the power generation process, the pressure in the high-pressure liquid storage tank will decrease. Therefore, under the control of the control box, by dynamically monitoring the pressure parameter of the hydraulic oil in the high-pressure liquid storage tank, the displacement of the variable hydraulic motor is regulated in real time to ensure that the output power of the variable hydraulic motor remains constant. By dynamically monitoring the pressure parameter of the hydraulic oil in the high-pressure liquid storage tank through the control box, the opening and closing state of a single or several energy storage unit bodies to release energy is intelligently adjusted. Furthermore, the low-pressure hydraulic oil is pumped into the high-pressure liquid storage tank through the fixed-displacement pump in the energy storage unit body to realize the dynamic balance of the pressure in the high-pressure liquid storage tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is an isometric schematic diagram of a buoyancy energy storage system based on piston drainage provided by the present invention.

[0025] Figure 2 is Figure 1 a partial enlarged view of.

[0026] Figure 3Front elevation schematic view of a buoyancy energy storage system based on piston drainage provided by the present invention.

[0027] Figure 4 Left elevation schematic view of a buoyancy energy storage system based on piston drainage provided by the present invention.

[0028] Figure 5 Top view schematic view of a buoyancy energy storage system based on piston drainage provided by the present invention.

[0029] Figure 6 Bottom view schematic view of a buoyancy energy storage system based on piston drainage provided by the present invention.

[0030] Figure 7 Internal structure schematic view of the energy storage unit body in a buoyancy energy storage system based on piston drainage provided by the present invention.

[0031] Figure 8 Force schematic view of the piston in the energy storage unit body.

[0032] In the drawings, 1 - high-pressure liquid storage tank, 2 - low-pressure liquid storage tank, 3 - variable hydraulic motor, 4 - generator, 5 - control box, 6 - motor, 7 - first clutch device, 8 - cable winch, 9 - cable, 10 - second clutch device, 11 - fixed-displacement pump, 12 - fixed-displacement pump output pipeline, 13 - fixed-displacement pump input pipeline, 14 - piston cylinder, 15 - pulley, 16 - through hole, 17 - piston, 18 - piston ring, 19 - high-pressure liquid pipeline, 20 - low-pressure liquid pipeline. Detailed implementation manners

[0033] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0034] During the movement process of the piston in a single energy storage unit body from the lowest point to the highest point under the action of buoyancy, the average buoyancy force received by the piston can be expressed as: (1) In formula (1), ρ 液 , h and S respectively represent the density of seawater, the vertical distance that the piston moves from the lowest point to the highest point under the action of buoyancy, and the area of contact between the bottom of the piston and seawater.

[0035] During the process of releasing energy, the traction force exerted on the piston by the cable is expressed as: (2) In Equation (2), F f and G are the frictional force and the gravitational force acting on the piston between the piston and the wall surface, respectively.

[0036] During the movement of the piston in a single energy storage unit from the lowest point to the highest point under the action of buoyancy, the energy that can be released is expressed as: (3) Example 1, referring to Figure 1 、 Figure 2 and Figure 3, the present invention can provide a buoyancy energy storage system based on piston drainage, including a high-pressure liquid storage tank 1, a low-pressure liquid storage tank 2, a variable hydraulic motor 3, a generator 4, a control box 5, an electric motor 6, a first clutch device 7, a cable winch 8, a cable 9, a second clutch device 10, a fixed-displacement pump 11, a fixed-displacement pump output pipeline 12, a fixed-displacement pump input pipeline 13, a piston cylinder 14 of the energy storage unit body, a pulley 15 installed at the lower part of the energy storage unit body, through holes 16 around the energy storage unit body, a piston 17 in the energy storage unit body, a piston ring 18, a high-pressure liquid pipeline 19, and a low-pressure liquid pipeline 20; a steel pipe is connected between the high-pressure liquid storage tank 1 and the high-pressure oil inlet of the variable hydraulic motor 3, and a steel pipe is connected between the low-pressure oil outlet of the variable hydraulic motor 3 and the low-pressure liquid storage tank 2. A sufficient amount of high-pressure hydraulic oil is stored in the high-pressure liquid storage tank 1 to ensure continuous power supply to the variable hydraulic motor 3. The electric motor 6, the first clutch device 7, the cable winch 8, the cable 9, the second clutch device 10, and the fixed-displacement pump 11 are arranged at the upper part of the energy storage unit body. The first clutch device 7 connects the output shaft of the electric motor 6 and the shaft of the cable winch 8, and the second clutch device 10 connects the shaft of the cable winch 8 and the input shaft of the fixed-displacement pump 11. The control signal output end of the control box 5 is connected to the signal input ends of the electric motor 6, the first clutch device 7, the second clutch device 10, the cable winch 8, and the variable hydraulic motor 3. A plurality of piston cylinders 14 are arranged in the energy storage unit body, a piston 17 is arranged in the piston cylinder 14, and the lower surface of the piston 17 is connected to the cable 9. By adopting the buoyancy utilization method of piston drainage, the reliability of the energy storage system is significantly improved, which is specifically manifested in key indicators such as the optimization of the floating body sealing performance and the strengthening of the anti-fatigue structure. The material of the piston cylinder 14 in the energy storage unit body and the pipelines in the energy storage system is high-pressure-resistant stainless steel material, which needs to withstand a pressure of more than 25 Mpa. The fixed-displacement pump input pipelines 13 above the energy storage unit body are connected to each other, and the fixed-displacement pump input pipeline 13 is connected to the high-pressure liquid storage tank 1. The fixed-displacement pump output pipelines 12 above the energy storage unit body are connected to each other, and the fixed-displacement pump output pipeline 12 is connected to the low-pressure liquid storage tank 2. A pulley 15 is installed at the lower part of the energy storage unit body, and the cable 9 bypasses the pulley 15 to reduce frictional losses. The cable winch 8, the second clutch device 10, and the fixed-displacement pump 11 are connected to form a fixed-displacement pump side transmission chain, and the cable winch 8, the first clutch device 7, and the electric motor 6 form a transmission chain on the side of the electric motor 6. The pipelines, the high-pressure liquid storage tank 1, and the low-pressure liquid storage tank 2 in the energy storage system are all filled with hydraulic oil to ensure uninterrupted power output of the power chain. The upper space of the piston 17 is communicated with the local atmosphere through the through holes 16 opened around the energy storage unit body, so that the pressure in the upper space of the piston 17 is the local atmospheric pressure to maintain a large pressure difference between the lower surface and the upper surface of the piston 17. A corrosion-resistant piston ring 18 is arranged between the piston 17 and the piston cylinder 14 to ensure sealing.When the piston ring 18 is working, it first fits against the inner wall of the piston cylinder 14 with its own elastic force, preventing seawater from passing between the outer circumference of the ring and the inner wall of the piston cylinder 14. A small amount of seawater enters the groove of the piston ring 18 and acts on the back of the piston ring 18, increasing the pressure of the piston ring 18 against the inner wall of the piston cylinder 14, thus significantly improving the sealing performance of the piston ring 18. Through the topological optimization of the energy storage unit body array and the vortex-induced vibration suppression device, the range of flow field disturbance is limited within 600 meters, and the acoustic guidance technology is used to avoid the areas with dense marine organisms. When a small number of energy storage monomers fail, it does not affect the operation of the entire energy storage system. Therefore, the buoyancy energy storage system based on piston drainage has a high risk resistance. The through hole 16 serves as a pressure relief structure at the top of the piston cylinder 14 for reference. Figure 4 and Figure 8 。

[0037] reference Figure 3 、 Figure 4 and Figure 7 One end of the steel cable 9 bypasses the pulley 15 and is connected to the bottom of the piston 17, and the other end of the steel cable is wound around the steel cable winch 8.

[0038] As an example, for reference Figure 1 、 Figure 5 and Figure 6 The buoyancy energy storage system is composed of 100×100 energy storage unit bodies spliced in an array form, and is integrated and deployed with offshore wind power infrastructure such as jacket foundations and floating platforms to reduce the investment cost. The vertical distance that the piston 17 moves from the lowest point to the highest point under the action of buoyancy is 10 m, and the area of the bottom of the piston 17 in contact with seawater is 4 m 2 ². If during the energy release process, the traction force of the steel cable 9 on the piston 17 is approximately one-fourth of the average buoyancy force, then the energy that can be released by the upward floating of the piston 17 in a single energy storage unit body is about 0.278 kWh. Therefore, the total energy storage capacity of the buoyancy energy storage system composed of 10,000 energy storage unit bodies is 2.78 MWh.

[0039] Embodiment 2, The present invention also provides an operation method for the above-mentioned buoyancy energy storage system based on piston drainage, including the following steps: In the process of releasing energy, first, the first clutch device 7 is adjusted to the disengaged state and the second clutch device 10 is adjusted to the engaged state through the control box 5. Second, the control box 5 controls the release of energy by a single or several energy storage unit bodies, and then the low-pressure hydraulic oil is pumped into the high-pressure liquid storage tank 1 through the metering pump 11 in the energy storage unit body. Third, the high-pressure hydraulic oil in the high-pressure liquid storage tank 1 enters the variable hydraulic motor 3 under the action of the pressure difference to drive the generator 4 to generate electricity. Fourth, during the power generation process, the pressure in the high-pressure liquid storage tank 1 will decrease. Therefore, under the control of the control box 5, the displacement of the variable hydraulic motor 3 is regulated in real time by dynamically monitoring the pressure parameter of the hydraulic oil in the high-pressure liquid storage tank 1 to ensure that the output power of the variable hydraulic motor 3 remains constant. Fifth, the control box 5 dynamically monitors the pressure parameter of the hydraulic oil in the high-pressure liquid storage tank 1, and intelligently adjusts the opening and closing state of a single or several energy storage unit bodies to release energy, and then the low-pressure hydraulic oil is pumped into the high-pressure liquid storage tank 1 through the metering pump 11 in the energy storage unit body to realize the dynamic balance of the pressure in the high-pressure liquid storage tank 1. Sixth, the energy release stage ends until the pistons 17 in each energy storage unit move to the highest position. In the energy release stage, by disengaging the first clutch device and engaging the second clutch device, the directional connection between the energy storage unit body and the hydraulic circuit is realized, and the metering pump drives the energy release in the transportation of hydraulic oil from low pressure to high pressure. The variable hydraulic motor maintains constant power generation by adjusting the displacement in real time, solves the problem of output fluctuation caused by the pressure attenuation of the liquid storage tank, and at the same time the system dynamically opens and closes the energy storage unit body based on the pressure parameter to ensure the pressure balance of the hydraulic system and improve the energy release efficiency and stability.

[0040] In the process of storing energy, first, the first clutch device 7 is adjusted to the engaged state and the second clutch device 10 is adjusted to the disengaged state through the control box 5; second, the start and stop of the motor 6 in the energy storage unit are regulated through the control box 5, and the pistons 17 are sequentially pulled to the lowest position by using the cable winches 8 of each unit, realizing the conversion of the electric energy output by the offshore wind turbine into the buoyancy potential energy of the energy storage system. In the energy storage stage, through the reverse of the clutch device state and the sequential control of the motor, the precise adjustment of the piston position by the cable winch is realized, and the efficient conversion of electric energy into buoyancy potential energy is completed. The whole set of control logic realizes the coordinated control of the hydraulic system and the mechanical actuator through a multi-level linkage mechanism while ensuring the power output of the system.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: still can modify the specific implementation manners of the present invention or make equivalent replacements, and any modification or equivalent replacement that does not deviate from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A buoyancy energy storage system based on piston drainage, characterized in that It includes a high-pressure liquid storage tank (1), a low-pressure liquid storage tank (2), a control box (5), and multiple sets of energy storage unit bodies; a variable hydraulic motor (3) and a fixed-displacement pump (11) are connected in parallel between the high-pressure liquid storage tank (1) and the low-pressure liquid storage tank (2), the variable hydraulic motor (3) is connected to a generator (4), multiple piston cylinders (14) and electric motors (6) are arranged in the energy storage unit bodies, pistons (17) are arranged in the piston cylinders (14), and the electric motor (6) and the fixed-displacement pump (11) are connected to the bottom of the piston (17) through a transmission chain in sequence by a steel cable (9); the control signal output end of the control box (5) is connected to the control signal input ends of the hydraulic motor (3), the fixed-displacement pump (11), and the electric motor (6), a pressure relief structure is arranged at the top of the piston cylinder (14), and the electric motor (6) is arranged above the energy storage unit body; the power input end of the system is connected to the power output end of an offshore wind turbine generator.

2. The buoyancy energy storage system based on piston drainage according to claim 1, wherein The outlet of the high-pressure liquid storage tank (1), the inlet of the variable hydraulic motor (3), and the inlet of the low-pressure liquid storage tank (2) are connected in sequence; the outlet of the low-pressure liquid storage tank (2), the inlet of the fixed-displacement pump (11), and the inlet of the high-pressure liquid storage tank (1) are connected in sequence.

3. The buoyancy energy storage system based on piston drainage according to claim 1, wherein The transmission chain includes a transmission chain on the side of the electric motor (6), a transmission chain on the side of the fixed-displacement pump (11), a first clutch device (7), and a steel cable winch (8), one end of the first clutch device (7) is connected to the steel cable winch (8), and the steel cable (9) is wound around the steel cable winch (8); the other end of the steel cable winch (8), a second clutch device (10), and the input shaft of the fixed-displacement pump (11) are connected in sequence.

4. The buoyancy energy storage system based on piston drainage according to claim 1, wherein A pulley (15) is arranged at the bottom end of the piston cylinder (14), and one end of the steel cable (9) bypasses the pulley (15) and is connected to the bottom of the piston (17).

5. The buoyancy energy storage system based on piston drainage according to claim 1, wherein A corrosion-resistant piston ring (18) is arranged between the piston (17) and the piston cylinder (14).

6. The buoyancy energy storage system based on piston drainage according to claim 1, wherein, The piston cylinders (14), and the pipelines connecting the high-pressure liquid storage tank (1), the low-pressure liquid storage tank (2), the fixed-displacement pump (11), and the variable hydraulic motor (3) are all made of stainless steel and have a pressure resistance of more than 25 Mpa; the high-pressure liquid storage tank (1), the low-pressure liquid storage tank (2), and the pipelines connecting the high-pressure liquid storage tank (1) and the low-pressure liquid storage tank (2) are all filled with hydraulic oil.

7. The buoyancy energy storage system based on piston drainage according to claim 1, wherein A pressure and temperature monitoring device is arranged in the high-pressure liquid storage tank (1); the pressure and temperature monitoring device is connected to the input end of the control box (5).

8. The buoyancy energy storage system based on piston drainage according to claim 1, wherein, It is integrally spliced and installed on the jacket foundation or floating platform of an offshore wind turbine generator, or is connected to the platform of the offshore wind turbine generator through a steel cable as an independent building.

9. The operation method of the buoyancy energy storage system based on piston drainage according to any one of claims 1-8, characterized in that, It includes an energy release process. By controlling the control box (5), the transmission chain on the side of the fixed-displacement pump (11) is in the working state, the transmission chain on the side of the electric motor (6) is in the non-working state, the energy storage unit body releases energy, and the fixed-displacement pump (11) pumps hydraulic oil into the high-pressure liquid storage tank (1); The high-pressure hydraulic oil in the high-pressure liquid storage tank (1) enters the variable hydraulic motor (3) under the action of the pressure difference to drive the generator (4) to generate electricity, and keeps the pressure in the high-pressure liquid storage tank (1) constant; until the piston (17) moves to the highest position, the energy release stage ends; Energy storage process: The control box (5) controls the drive chain on one side of the motor (6) to be in the working state, and the drive chain on one side of the metering pump (11) to be in the non-working state. The start and stop of the motor (6) in the energy storage unit are regulated through the control box (5). The drive chain on one side of the motor (6) drives the steel cable (9) to pull the piston (17) to the lowest position.

10. The operating method of the buoyancy energy storage system based on piston drainage according to claim 9, characterized in that, The displacement of the variable hydraulic motor (3) is regulated in real time by dynamically monitoring the pressure parameters of the hydraulic oil in the high-pressure liquid storage tank (1). The opening and closing states of the release of energy from a single or several energy storage unit bodies are dynamically adjusted through the control box (5), and the metering pump (11) is dynamically controlled to pump low-pressure hydraulic oil into the high-pressure liquid storage tank (1).

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