Design method of coupling power generation system of fan tower and underground aquifer pumped storage

Abstract

The application provides a design method of a coupling power generation system of a fan tower and a pumped storage system of an underground aquifer, which combines a wind turbine tower and a water tower as an upper reservoir of the pumped storage system, combines a large-capacity and large-flow water well of the aquifer as a lower reservoir of the pumped storage system, and uses water potential energy for pumped storage and power generation. During energy pumping, a submersible vertical turbine pump is used to pump water from the underground reservoir to the water-stored fan tower, so as to store water gravity potential energy. During energy release, the water stored in the fan tower is discharged to the underground aquifer through a turbine, and at this time, the turbine drives a generator to generate electricity. The application provides a coupling power generation system of wind energy and pumped storage double feed-in, and provides a reform design method of the underground water well system to improve the operation efficiency of the water pump / turbine, and simultaneously designs a control system function of the coupling power generation system. The application uses the flexible adjustment capacity of the pumped storage system to smooth the fluctuation of wind power, and improves the power generation capacity and consumption level of a single fan.

Description

Technical Field

[0001] This invention belongs to the field of small-scale underground pumped storage and distributed wind power generation system design, specifically involving a design method for a coupled power generation system of wind turbine tower and underground aquifer pumped storage. Background Technology

[0002] Pumped hydro storage enhances the flexibility and adaptability of new energy power generation systems, serving as a key means of constructing a new power system based on new energy sources and one of the most effective ways to promote green and low-carbon development. On one hand, the wind turbine industry may be entering an era of "high towers." As wind turbine tower height increases, wind speeds at the turbine blades rise significantly, resulting in increased single-unit power output, especially in low-wind-speed plains areas where turbine towers will become increasingly taller. Currently, the tallest wind turbine hub in my country has reached over 170 meters, and it is projected that by 2025, the hub height will reach 200 meters. On the other hand, the intermittent and random nature of wind power and other new energy sources necessitates the construction of a number of flexible energy storage facilities with characteristics such as rapid response, technological controllability, energy conservation, and environmental protection. Summary of the Invention

[0003] To address the issue of the inflexible adjustment capabilities required by wind power generation systems, this invention proposes a design method for a coupled power generation system combining wind turbine towers and underground aquifer pumped storage. The wind turbine tower and a water tower are combined as the upper reservoir of the pumped storage system, while a large-capacity, high-flow-rate well in the aquifer serves as the lower reservoir. Pumped storage and power generation are achieved using the potential energy of the water. This pumped storage system leverages its flexible adjustment capabilities to smooth wind power fluctuations and improve the absorption of power generated by a single wind turbine. Furthermore, the wind turbine and underground aquifer pumped storage are equated to near-synchronous generators, constructing a novel coupled synchronous power generation system. This invention utilizes the wind curtailment resources of a single wind turbine for pumped storage, which on the one hand helps smooth wind power fluctuations, and on the other hand, reduces the risk of wind power fluctuations while improving the absorption of renewable energy power generation.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A design method for a coupled power generation system of wind turbine tower and pumped storage in an underground aquifer includes the following steps:

[0006] Step 1: Design a pumped storage system that combines the wind turbine's water tower with an underground aquifer;

[0007] Step 2: Construct a variable-speed constant-frequency doubly-fed wind power generation system without a grid-side converter;

[0008] Step 3: Select the efficiency of the submersible vertical turbine pump and design the groundwater well system;

[0009] Step 4: Design the control system functions of the wind power pumped storage coupled power generation system.

[0010] Furthermore, in step 1, the flexible steel tower of the wind turbine is combined with a water tower to construct a water tower cylinder, which serves as the upper reservoir for pumped water storage. At the same time, a deep well with a large capacity and flow rate in the aquifer is used as an underground reservoir. When pumping water, a submersible vertical turbine pump is used to pump water from the underground reservoir into the water tower cylinder of the wind turbine to store the water's gravitational potential energy. When releasing the stored energy, the water stored in the wind turbine's water tower cylinder is discharged back to the underground aquifer through a pressure pipeline by the turbine. At this time, the submersible vertical turbine pump drives an electric motor / generator to generate electrical energy. An electrical center is also set up, including power electronic equipment, for control and protection.

[0011] Furthermore, in step 2, a variable-speed constant-frequency doubly-fed wind power generation system without a grid-side converter is adopted, and a stator-side converter for the pumped-storage motor / generator is added. That is, the wind power generation system adopts a doubly-fed variable-speed constant-frequency generator, and the aquifer underground pumped-storage system adopts a bidirectional permanent magnet motor / generator; the stator winding of the doubly-fed variable-speed constant-frequency generator is constant frequency, i.e., f s =50Hz AC power is directly connected to the external power grid. Its rotor circuit is controlled by a converter to achieve variable speed operation. Power is transmitted to the stator-side converter of the pumped storage motor / generator through the rotor-side converter. Power can also be transmitted in reverse. The rotor-side converter of the doubly-fed variable speed constant frequency generator transmits a maximum power of 30% of its stator rated power. The stator-side converter of the pumped storage motor / generator operates at full power.

[0012] Furthermore, in step 3, a submersible vertical turbine pump is used for forward pumping or in reverse turbine operation; the submersible vertical turbine pump includes a turbine and a water pump, and its efficiency results are: the efficiency in turbine operation is between 70% and 85%, and the efficiency in water pump operation is between 65% and 80%.

[0013] The redesign of groundwater well systems includes three methods:

[0014] 1) Increase the surface area in contact with the aquifer or increase the diameter of the deep well to increase the flow rate of injected water and achieve greater power generation.

[0015] 2) Replenishing aquifers with deep wells and storing water in aquifers, that is, water in deep wells seeps into aquifers to enrich the water or groundwater structure of aquifers, and combining a well network with a large number of wells with existing public water resources facilities on the surface.

[0016] 3) Install extension pipes at the bottom of the well, or excavate horizontally curved well pipes or seepage pits.

[0017] Furthermore, in step 4, the controllers for the converter and stator-side converters include the following functions:

[0018] 1) In pumping operation, the stator-side converter is controlled by a motor-driven strategy to perform DC inversion using a wind-driven electric motor / generator.

[0019] 2) Used to provide excitation for the doubly-fed variable-speed constant-frequency generator of wind turbine units, and simultaneously performs excitation and output rectification by controlling the converter and stator-side converter;

[0020] The converter and stator-side converter and their control system are located on the surface, while the submersible vertical turbine pump and electric motor / generator are located underground. A filter is used between the motor and the stator-side converter to reduce voltage spikes caused by the cable length. A supercapacitor is installed in the DC circuit between the converter and the stator-side converter to stabilize the DC bus voltage and improve transient performance. When operating off-grid, a small-capacity backup battery is connected in parallel between the converter and the stator-side converter for energy storage.

[0021] Beneficial effects:

[0022] This invention proposes a design method for a coupled power generation system of wind turbine towers and pumped-storage hydroelectric power generation, suitable for the construction of small-scale wind-hydroelectric complementary power generation and storage systems in the plains of southern my country. On one hand, pumped-storage hydroelectric power generation can smooth out wind power fluctuations, facilitating the effective absorption of the power generated by a single wind turbine. On the other hand, combining the wind turbine tower with the water tower effectively utilizes the gravitational potential energy of the water stored in the water tower, making efficient use of the space within the wind turbine tower. Attached Figure Description

[0023] Figure 1 A schematic diagram of a coupled power generation system of wind turbine and pumped storage in an underground aquifer;

[0024] Figure 2(a) is a schematic diagram of the large-capacity well modification of a non-confined groundwater well system;

[0025] Figure 2(b) is a schematic diagram of the horizontal well extension of a non-confined groundwater well system;

[0026] Figure 3 This is a schematic diagram of the control function logic of a coupled power generation system. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and formula derivations. It should be understood that the formula derivations described herein are merely for explaining the invention and are not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of the invention described below can be combined with each other as long as they do not conflict with each other.

[0028] The design method of a coupled power generation system of wind turbine tower and underground aquifer pumped storage according to the present invention includes the following steps:

[0029] Step 1: Design a pumped storage system that combines the wind turbine's water tower with an underground aquifer:

[0030] The current development trend for wind turbine towers is the adoption of flexible steel towers (flexible towers). When large-scale manufacturing enterprises possess strong process control capabilities and advanced production processes, they can combine wind turbine towers with water towers to create wind turbine water towers. The natural frequency of the water tower is designed to be significantly lower than the rotor rotation frequency and generator vibration frequency to avoid resonance between the two. Therefore, water tower 1 combines a flexible steel tower with a water tower, and enhances the tower's flexibility through water storage. This water tower 1 can serve as the upper reservoir for pumped storage, such as... Figure 1 As shown. The aquifer underground reservoir 2 can be realized using a large-capacity, high-flow-rate deep well, such as... Figure 1 As shown.

[0031] When pumping water, the submersible vertical turbine pump 3 draws water from the underground aquifer source or the underground reservoir 3 into the water tower 1 for storage, storing the water's gravitational potential energy. When releasing the stored energy, the water stored in the water tower 1 is discharged back into the underground aquifer via the submersible vertical turbine pump 3 through the pressure pipeline 4. At this time, the submersible vertical turbine pump 3 drives the electric motor / generator 5 to generate electricity. This integrated energy storage system is best suited for use in series with variable renewable energy sources, such as wind turbine units 6, to buffer fluctuating output and reliably supply power to users. Therefore, the elements of the power generation system coupled with the water tower 1 and the underground pumped storage system include: power source (wind turbine, grid); water tank of the water tower 1; large-capacity, high-flow-rate deep well for storing water in the aquifer; integrated motor-pump-turbine generator unit; electrical center (power electronic equipment, control, protection), etc.

[0032] Step 2: Design a variable-speed constant-frequency doubly-fed wind power generation system without a grid-side converter:

[0033] In the underground pumping system based on wind power generation, the wind power generation of this invention adopts a doubly fed variable speed constant frequency generator, while the power generation system coupled with underground pumping and storage in the aquifer adopts a permanent magnet motor / generator.

[0034] like Figure 1 As shown, the motor / generator 5 is a doubly-fed variable-speed constant-frequency generator, employing a wound-rotor asynchronous motor. Its rotor windings are three-phase windings spatially out of phase by 120 degrees, with an applied frequency f. r The three-phase alternating current is used, while the stator winding is a constant frequency, i.e., f. s The 50Hz AC power is directly connected to the external power grid. Through conversion, the rotor winding frequency is the applied frequency f.r The alternating current has an equivalent rotational speed of N. r =60f r / N p The frequency in the stator winding is a constant frequency f. s The AC equivalent rotational speed is N. s =60f s / N p Then the rotor speed of the motor / generator is:

[0035] N = 60(f s -f r ) / N p (1)

[0036] In the formula, N p denoted as the number of rotor pole pairs.

[0037] The rotor circuit of a doubly-fed variable-speed constant-frequency generator can be achieved through, for example... Figure 1 The converter 7 shown is controlled to achieve variable speed operation. Furthermore, its power flow is bidirectional, with the direction of power depending on the system's operating conditions. Power can be transmitted from the rotor-side converter 7 to the stator-side converter 8 of the pumped-storage electric motor / generator 5, and power can also be transmitted in the reverse direction. The rotor-side converter of the doubly-fed variable-speed constant-frequency generator transmits a maximum power of 30% of its stator rated power, while the stator-side converter 8 of the pumped-storage electric motor / generator 5 operates at full power. Figure 1 As shown, the present invention omits the grid-side converter in the doubly fed variable speed constant frequency power generation system and replaces it with a stator-side converter 8 for the pumped storage electric motor / generator 5.

[0038] Under random wind speeds, the pumped storage system of this invention can change the input and output power of the water pump / turbine submersible vertical turbine pump 3 through the converter 7 and the stator-side converter 8, thereby adjusting the rotor speed of the doubly-fed variable speed constant frequency generator to achieve variable speed capture of more wind energy, while ensuring that the stator input power of the variable speed constant frequency generator to the power grid is adjustable.

[0039] Step 3: Select the efficiency of the submersible vertical turbine pump and design the groundwater well system:

[0040] The submersible vertical turbine pump 3 and the electric motor / generator 5 are the core components of the aquifer pumped storage system. This invention uses a standard centrifugal pump or a vertical turbine well pump, which can pump water in the forward direction or operate in reverse turbine mode. To improve the overall efficiency of the energy storage system, the efficiency of the pumping cycle of the pump turbine and the turbine cycle needs to be optimized. This invention mainly estimates based on data from the submersible vertical turbine pump, with the results showing that the efficiency in turbine mode is between 70% and 85%, and in pump mode it is between 65% and 80%. Electric generator sets generally have relatively high operating efficiency and are a mature and feasible technology; the electric generator used in this invention achieves an efficiency of over 96%. The rotational speed of the turbine-connected motor in the underground pumped storage system is one of the factors affecting the pumped storage efficiency of the power station. Simultaneously, the water pressure in the groundwater has a significant impact on pumping efficiency.

[0041] To increase the power of underground pumped storage systems, the groundwater well system can be modified and seepage pits utilized. The following parameters or influencing factors need to be considered: the filtration coefficient or hydraulic conductivity of the geological structure surrounding the large-capacity well, the well depth, the well diameter, the well casing design, and the influence of confined or unconfined aquifers. Considering these factors, there are three main design methods for groundwater well systems: 1) Compared to the current groundwater well diameter of approximately 1.5 meters and its surface area of ​​approximately 943 square meters, the surface area in contact with the aquifer or the well diameter can be increased (as shown in the large-capacity well on the right in Figure 2), thereby increasing the flow rate of injected water and achieving greater power generation. Simultaneously, increasing the surface area connected to the aquifer and the effective radius of the well helps increase the filtration coefficient or hydraulic conductivity, thereby reducing the height of the injection cone generated during well drainage and ensuring effective head and turbine generator output power. 2) Water is replenished to the aquifer through wells and stored within the aquifer, i.e., water is enriched in the aquifer or underground structure by flowing water back into the well. This can be achieved by combining a well network containing numerous wells with existing surface water resource facilities. 3) The water level in the well changes significantly during pumping and drainage. To address the issue of depleted pumping conditions, extension pipes can be installed at the bottom of the well, or horizontally curved well pipes or infiltration pits can be excavated. For example, when a deep well is dry, treated drinking water needs to be used for replenishment through a supply pipe. It is worth noting that the upper surface of the aquifer is called the water table. When water is filtered or guided to the aquifer from a deep well, the water table closer to the deep well is higher than that farther away; this is known as the water cone effect. In this invention, a water cone can be formed during water injection / power generation. Depending on the surface area of ​​the deep well in contact with the aquifer, as shown in Figures 2(a) and 2(b), the water table of a deep well with a larger diameter water cone is lower than that of a deep well with a smaller diameter.

[0042] Step 4: Design the control system functions of the wind power pumped storage coupled power generation system:

[0043] The electrical system of a wind power pumped storage coupled power generation system needs to realize the function of underground pumped storage in the aquifer and connect the wind turbine, user load and the main grid.

[0044] In this invention, the controller of the stator-side converter 8 has two main functions: 1) In pumping operation, it uses a wind-driven motor to control the stator-side converter 8 for DC inversion via a motor-driven strategy; 2) It provides excitation for the doubly-fed variable-speed constant-frequency generator of the wind turbine, simultaneously performing excitation and output rectification by controlling the converter 7 and the stator-side converter 8. Furthermore, in this invention, the converter 7 and the stator-side converter 8 and their control system are located on the surface, while the submersible vertical turbine pump 3 and the motor / generator 5 are located underground. A filter is used between the motor / generator 5 and the stator-side converter 8 to reduce voltage spikes caused by the cable length. A supercapacitor is connected to the DC link between the converter 7 and the stator-side converter 8 to stabilize the DC bus voltage and improve transient performance. In actual operation, the system may operate off-grid, requiring a backup battery for energy storage in parallel with the DC link between the converter 7 and the stator-side converter 8. The converter 7 and the stator-side converter 8 and their controllers need to ensure the overall system functionality under the following operating conditions.

[0045] (1) If the electrical energy generated by the fan is not used by the load, the power is allocated to the electric motor 5 to drive the submersible vertical turbine pump 3 to pump water, and then the water is pumped to the water tower 1 of the fan until the water tower 1 is full.

[0046] (2) If the load power demand is large and the wind turbine power is too small, the underground pumped storage system is put into power generation mode to release the stored energy until the energy reserve is used up.

[0047] (3) If the power of the wind turbine is greater than the power used, and the water storage tank 1 of the wind turbine is full, the power will be “net metered” to the power grid.

[0048] like Figure 3 As shown, the wind turbine generates electricity and connects to an external transformer via the turbine interface and a circuit breaker, further supplying power to the load through the circuit breaker. On the other hand, the wind power is connected to the turbine-side rectifier-inverter and the motor / generator-side rectifier-inverter via the circuit breaker, supplying power to the motor M. Conversely, the motor M can act as a pumped-storage generator, supplying power to the external DC side via the motor / generator-side rectifier-inverter. On the DC side, a small-capacity battery can be connected to a supercapacitor for charging and discharging. Finally, the system sends commands to the system controller, wind turbine controller, etc., through system control, monitoring, and a user interface.

[0049] This invention relates to a system layout circuit for protection and control systems, including wave-controlled circuit breakers. The circuit breakers utilize relays or contactors as isolation elements in the protection circuits. When a doubly-fed variable-speed constant-frequency generator is connected to a utility meter, the system controller must monitor and verify that its stator-side frequency and voltage waveforms are consistent with the power grid. When consistent with the power grid, the system controller uses a closed circuit breaker to connect the system to the grid.

[0050] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A design method for a coupled power generation system of a wind turbine tower and a pumped-storage aquifer, characterized in that, Includes the following steps: Step 1: Design a pumped storage system that combines the wind turbine's water tower with an underground aquifer. Combine the wind turbine's flexible steel tower with the water tower to construct a water tower, which serves as the upper reservoir for pumped storage. Simultaneously, utilize a large-capacity, high-flow-rate deep well in the aquifer as an underground reservoir; the deep well is directly connected to the aquifer. Step 2: Construct a grid-free, variable-speed, constant-frequency, doubly-fed wind power generation system. This system utilizes a grid-free, variable-speed, constant-frequency, doubly-fed wind power generation system, and adds a stator-side converter for the pumped-storage motor / generator. Specifically, the wind power generation system uses a doubly-fed variable-speed, constant-frequency generator, while the aquifer underground pumped-storage system uses a bidirectional permanent magnet motor / generator. The stator winding of the doubly-fed variable-speed, constant-frequency generator is a constant-frequency AC power supply (fs = 50Hz) directly connected to the external power grid. Its rotor circuit is controlled by a converter to achieve variable-speed operation. Power is transmitted through the rotor-side converter to the stator-side converter of the pumped-storage motor / generator, or in reverse. Step 3: Select the efficiency of the submersible vertical turbine pump, design the underground well system, and use the submersible vertical turbine pump for forward pumping or in reverse turbine mode; the submersible vertical turbine pump includes a turbine and a pump, and its efficiency results are: the efficiency in turbine mode is 70%~85%, and the efficiency in pump mode is 65%~80%; Step 4: Design the control system functions of the wind power pumped storage coupled power generation system. The rotor-side converter and stator-side converter and their control system are located on the ground, while the submersible vertical turbine pump and electric motor / generator are located underground. A filter is used between the motor and the stator-side converter to reduce voltage spikes caused by the cable line length. A supercapacitor is installed in the DC circuit between the rotor-side converter and the stator-side converter to stabilize the DC bus voltage and improve transient performance; when operating off-grid, a small-capacity backup battery is connected in parallel between the rotor-side converter and the stator-side converter for energy storage.

2. The design method for a coupled power generation system of wind turbine tower and underground aquifer pumped storage as described in claim 1, characterized in that: In step 1, when pumping water, a submersible vertical turbine pump is used to pump water from the underground reservoir into the water tower of the wind turbine used for water storage, so as to store the gravitational potential energy of the water; when releasing the stored energy, the water stored in the water tower of the wind turbine is discharged back to the underground aquifer through the pressure pipeline by the turbine. At this time, the submersible vertical turbine pump drives the electric motor / generator to generate electrical energy. At the same time, an electrical center is set up, including power electronic equipment, for control and protection.

3. The design method for a coupled power generation system of wind turbine tower and underground aquifer pumped storage as described in claim 2, characterized in that: In step 2, the rotor-side converter of the doubly fed variable speed constant frequency generator transmits a maximum power of 30% of its stator rated power, while the stator-side converter of the pumped storage electric motor / generator operates at full power.

4. The design method for a coupled power generation system of wind turbine tower and underground aquifer pumped storage as described in claim 3, characterized in that: Step 3, the modification design of the groundwater well system, includes three methods: 1) Increase the surface area in contact with the aquifer or increase the diameter of the deep well to increase the flow rate of injected water and achieve greater power generation. 2) Replenishing aquifers with deep wells and storing water in aquifers, that is, water in deep wells seeps into aquifers to enrich the water or groundwater structure of aquifers, and combining a well network with a large number of wells with existing public water resources facilities on the surface. 3) Install extension pipes at the bottom of the well, or excavate horizontally curved well pipes or seepage pits.

5. The design method for a coupled power generation system of wind turbine tower and underground aquifer pumped storage as described in claim 1, characterized in that, In step 4, the controllers for the rotor-side converter and the stator-side converter include the following functions: 1) In pumping operation, the stator-side converter is controlled by a motor-driven strategy to perform DC inversion using a wind-driven electric motor / generator. 2) Used to provide excitation for the doubly fed variable speed constant frequency generator of wind turbine units, and to simultaneously perform excitation and output rectification by controlling the rotor-side converter and the stator-side converter.

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