Constant-speed pumped storage unit with adjustable working condition load of water pump and operation method of constant-speed pumped storage unit

Abstract

The invention discloses a constant-speed pumped storage unit with adjustable working condition load of a water pump and an operation method of the constant-speed pumped storage unit. Relates to the technical field of pumped storage. The unit is connected between an upstream reservoir and a downstream reservoir, and a complete loop composed of an upstream water tank, a water turbine, a downstream water tank and a water pump is communicated between the upstream reservoir and the downstream reservoir; the water turbine is coaxially connected with the water pump and is also coaxially connected with a generator motor, and the generator motor is connected into a power grid to obtain electric energy from the power grid or output the electric energy to the power grid; a valve is arranged between any two nodes; according to the operation method, a water flow path is changed by controlling opening and closing of a valve between an upstream reservoir and an upstream water tank, so that when the unit pumps and stores energy, part of water flows back to do work repeatedly; the working condition load of the water pump is adjusted; the water pumping working condition load can be continuously and rapidly adjusted within the rated power range of 20%-100%, and the flexibility of a power grid is greatly enhanced; meanwhile, the structure is compact, transformation is convenient, and the device is particularly suitable for efficiency-increasing and capacity-expanding transformation of existing small hydropower stations; and the absorption capability and the stability of the power distribution network on distributed photovoltaic and wind power volatility can be obviously improved.

Description

Technical Field

[0001] This invention relates to the field of pumped storage technology, and in particular to a constant-speed pumped storage unit with adjustable pump operating load and its operation method. Background Technology

[0002] Traditional constant-speed pumped-storage units have unadjustable loads under pumping conditions, resulting in insufficient regulation capabilities when combined with intermittent renewable energy sources (such as solar and wind power). This is particularly problematic in distribution networks where small hydropower resources are abundant but have poor regulation performance, making it difficult to meet the demands of high-proportion renewable energy integration. While existing three-unit pumped-storage systems possess both power generation and pumping functions, they cannot achieve wide-range power regulation under pumping conditions, limiting their application scenarios. Summary of the Invention

[0003] To address the problem of unadjustable load in existing constant-speed pumped-storage units under pumping conditions, this application provides a constant-speed pumped-storage unit with adjustable pump load and its operation method.

[0004] In a first aspect, this application provides a constant-speed pumped-storage unit with adjustable pump operating load, employing the following technical solution:

[0005] A three-unit constant-speed pumped storage unit with adjustable pump operating load is connected between an upstream reservoir and a downstream reservoir. The upstream and downstream reservoirs are connected by a complete circuit consisting of an upstream water tank, a water turbine, a downstream water tank, and a water pump. The water turbine and the water pump are coaxially connected, and a generator motor is also coaxially connected to the turbine. The generator motor is connected to the power grid to obtain electrical energy from the grid or to output electrical energy to the grid. A valve is provided between any two of the above nodes.

[0006] Optionally, the generator, turbine, and pump are arranged vertically and rigidly coaxially, with the main shaft rated at 750 rpm or 1000 rpm and rotating in the same direction.

[0007] Optionally, the installation elevation of the water turbine is at least 1.5 meters higher than that of the water pump.

[0008] Secondly, this application provides an operation method for a constant-speed pumped-storage unit with adjustable pump operating load, employing the following technical solution:

[0009] An operating method for a constant-speed pumped-storage unit with adjustable pump load, applied to the three-unit constant-speed pumped-storage unit with adjustable pump load as described in claim 3, has the following two operating modes:

[0010] Method 1: Conventional power generation and pumping operation;

[0011] Method 2: During pumping operation, hydraulic short-circuit operation is achieved by controlling the valves between the upstream reservoir and the upstream water tank. This includes two modes: partial hydraulic short-circuit operation and full hydraulic short-circuit operation. The valves are partially open for partial hydraulic short-circuit operation and fully closed for full hydraulic short-circuit operation. During pumping operation, water flows back to the turbine after passing through the upstream water tank. By coordinating the pump operation and the turbine guide vane opening, the turbine's auxiliary work is controlled, allowing for continuous adjustment of the unit's absorbed power within the pumping range of 20% to 100% of the rated power.

[0012] Optionally, during conventional power generation, relevant valves are opened to connect the upstream reservoir, upstream water tank, turbine, downstream water tank, and downstream reservoir; the turbine drives the generator motor to generate electricity and transmits it to the power grid.

[0013] Optionally, in pumped storage mode, relevant valves are opened to connect the upstream reservoir, upstream water tank, water pump, downstream water tank, and downstream reservoir; the generator motor obtains electrical energy from the grid to drive the water pump, which pumps water from the downstream water tank to the upstream water tank.

[0014] In summary, this application includes the following beneficial technical effects:

[0015] The pumping load of this application can be continuously and rapidly adjusted within the range of 20% to 100% of the rated power, greatly enhancing the flexibility of the power grid; at the same time, it has a compact structure and is easy to retrofit, making it particularly suitable for upgrading and expanding existing small hydropower plants; it can significantly improve the distribution network's ability to absorb and stabilize the fluctuations of distributed photovoltaic and wind power. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the constant-speed pumped-storage unit in this application;

[0017] Figure 2 This is a schematic diagram of some hydraulic short-circuit operation states in this application;

[0018] Figure 3 This is a schematic diagram of all hydraulic short-circuit operation states in this application.

[0019] Explanation of reference numerals in the attached figures:

[0020] A. Generator motor; B. Water turbine; C. Water pump; D1. Upstream water tank; D2. Downstream water tank; F1-F6. Valves; R1. Upstream reservoir; R2. Downstream reservoir. Detailed Implementation

[0021] The following is in conjunction with the appendix Figure 1-3 This application will be described in further detail.

[0022] This application discloses a three-unit constant-speed pumped-storage unit with adjustable pump operating load.

[0023] like Figure 1 As shown, the system of the present invention mainly includes a generator motor A, a water turbine B, a water pump C, an upstream water tank D1, a downstream water tank D2, an upstream inlet valve F1, and a tailrace valve F2.

[0024] Main shaft system: The generator motor A, water turbine B and water pump C are rigidly coaxially connected by flanges, forming a coaxial relationship of three machines with fixed rated speed and consistent direction of rotation (clockwise when viewed from above).

[0025] Installation elevation: Considering the water pump cavitation problem, the installation elevation of turbine B is at least 1.5 meters higher than that of water pump C.

[0026] Upstream water tank D1 and downstream water tank D2: D1 and D2 are pressure vessels, and their volume is designed according to the system flow rate. They can accommodate a flow rate of 5-10 seconds, effectively suppressing water hammer pressure during start-up, shutdown and regulation.

[0027] Valves: Upstream inlet valve F1 is a hydraulically controlled ball valve used for hydraulic short-circuit control; tailrace valve F2 is a conventional shut-off valve; during unit maintenance, upstream inlet valve F1 and tailrace valve F2 are used to cut off the water flow, keeping the unit section in a waterless state; valve F3 between upstream water tank D1 and turbine B, valve F5 between turbine B and downstream water tank D2, valve F4 between upstream water tank D1 and pump C, and valve F6 between pump C and downstream water tank;

[0028] The above-mentioned pumped-storage units can meet the following operating conditions:

[0029] Method 1: Regular Operation

[0030] 1. Power generation conditions

[0031] (1) Open valves F1, F2, F3 and F5, close valve F4 on the high-pressure side of water pump C and valve F6 on the low-pressure side, drain the water accumulated in the volute of water pump C, and keep the impeller of water pump C out of the air.

[0032] (2) When the unit starts up and runs, the movable guide vanes of the turbine B are opened. The water flow from the upstream reservoir R1 passes through F1, D1 and F3 and is controlled by the movable guide vanes of the turbine B to drive the turbine B to rotate, which drives the generator motor A to generate electricity and send the electrical energy into the power grid.

[0033] (3) The water after doing work flows through F5, D2, and F2 and is discharged into the downstream reservoir R2.

[0034] During this process, water pump C idles with the main shaft and does not function.

[0035] 2. Normal pumping operation (100% load)

[0036] (1) Open valves F2, F4 and F6, close turbine inlet valve F3 and tailwater valve F5, drain water from turbine B volute, and keep turbine B runner out of the air.

[0037] (2) When the unit starts up and runs, the movable guide vane is opened to the operating opening degree to enter the pressure building state. When the rated speed is reached or the pressure of the balance tank is close to the upstream water pressure, the main inlet valve F1 is opened. The generator motor A acts as the motor, absorbs the rated power from the power grid, and drives the main shaft to rotate.

[0038] (3) Pump C pumps water from downstream reservoir R2, and pumps it to upstream reservoir R1 via F2, D2, F6, pump C, F4, D1, and F1.

[0039] During this process, turbine B simply rotates idling with the main shaft without performing any work.

[0040] Method 2: Upstream hydraulic short-circuit operation (load regulation) under pumping conditions

[0041] This method is the core of the invention, used to continuously adjust the power absorbed by the unit from the power grid during pumping operations. Its principle is to utilize part or all of the water flow to drive the turbine in the forward direction, thereby assisting the electric motor in driving the pump, thus reducing the net power required from the power grid.

[0042] The following are implementation examples:

[0043] Initial state: The unit is in normal pumping operation, pump C is running at rated power P_pump, absorbing 100% of the rated power from the grid, and the guide vane opening of turbine B is 0%.

[0044] Step 1: Start power adjustment

[0045] (1) The unit control system receives a grid dispatch instruction requiring the absorption power to be reduced to 80%.

[0046] (2) The control system keeps the pump running status unchanged and slowly opens the guide vanes of turbine B.

[0047] Step 2: Partial hydraulic short-circuit operation

[0048] (1) As the guide vane opening of turbine B increases, some of the pressurized water (from R1) that should have flowed to pump C flows through turbine B instead.

[0049] (2) This water flow drives the turbine B to rotate, generating a positive torque M_turbine. This torque is in the same direction as the motor driving torque M_motor, and together they drive the water pump C.

[0050] At this point, the net driving torque required by the motor is reduced to: M_motor = M_pump - M_turbine.

[0051] According to the power formula P = M * ω (ω is a fixed speed), the active power P_absorbed by the motor from the grid decreases proportionally.

[0052] By precisely controlling the guide vane opening, P_absorb can be stabilized at the target value (e.g., 80% of rated power).

[0053] Step 3: Full hydraulic short-circuit operation (extreme low load)

[0054] When it is necessary to reduce the absorption power to a minimum, completely close the inlet valve F1.

[0055] At this point, the water flow from upstream reservoir R1 is completely cut off, and the pumping system is isolated from the upstream. The water flow forms a closed loop between balance tank D1, turbine B, pump C, and balance tank D2. There is water exchange between balance tank D2 and downstream reservoir R2. All the water pumped by pump C flows through turbine B to do work before being discharged to the tailrace.

[0056] In this mode, turbine B operates near its optimal efficiency point, providing maximum auxiliary power P_turbine_max.

[0057] Considering the pump efficiency η_pump (90%), the turbine efficiency η_turbine (90%), and the system hydraulic loss η_loss (2%), the system's net absorbed power can reach its minimum point:

[0058] P_absorb_min = P_pump - P_turbine_max * η_pump * η_turbine * (1 - η_loss) ≈ 20% P_rated.

[0059] Therefore, this system can achieve a wide range of continuous adjustment from 20% to 100% of the rated power under pumping conditions.

[0060] During normal power generation, relevant valves are opened to connect the upstream reservoir, upstream water tank, turbine, downstream water tank, and downstream reservoir; the turbine drives the generator motor to generate electricity and transmits it to the power grid.

[0061] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A three-unit constant-speed pumped-storage unit with adjustable pump operating load, connected between an upstream reservoir and a downstream reservoir, characterized in that: The upstream and downstream reservoirs are connected by a complete loop consisting of an upstream water tank, a water turbine, a downstream water tank, and a water pump; the water turbine and the water pump are coaxially connected, and a generator motor is also coaxially connected to the turbine motor, which is connected to the power grid to obtain electrical energy from the grid or to output electrical energy to the grid; a valve is provided between any two of the above nodes.

2. The three-unit constant-speed pumped-storage unit with adjustable pump operating load according to claim 1, characterized in that: The generator, turbine, and pump are arranged vertically and rigidly coaxially, with a rated main shaft speed of 750 rpm or 1000 rpm and the same direction of rotation.

3. The three-unit constant-speed pumped-storage unit with adjustable pump operating load according to claim 1, characterized in that: The installation elevation of the water turbine is at least 1.5 meters higher than that of the water pump.

4. An operating method for a constant-speed pumped-storage unit with adjustable pump load, applied to the three-unit constant-speed pumped-storage unit with adjustable pump load as described in claim 3, characterized in that: It has the following two operating modes: Method 1: Conventional power generation and pumping operation; Method 2: Under pumping conditions, hydraulic short-circuit operation is achieved by controlling the valves between the upstream reservoir and the upstream water tank. This includes two modes: partial hydraulic short-circuit operation and full hydraulic short-circuit operation. The valves are partially open for partial hydraulic short-circuit operation and fully closed for full hydraulic short-circuit operation. Under pumping conditions, water flows back to the turbine after passing through the upstream water tank. By coordinating the operation of the pumps and the opening of the turbine guide vanes, the turbine's auxiliary work is controlled to continuously adjust the unit's absorbed power within the range of 20% to 100% of the rated power under pumping conditions.

5. The operating method of a constant-speed pumped-storage unit with adjustable pump operating conditions according to claim 4, characterized in that: During normal power generation, relevant valves are opened to connect the upstream reservoir, upstream water tank, turbine, downstream water tank, and downstream reservoir; the turbine drives the generator motor to generate electricity and transmits it to the power grid.

6. The operating method of a constant-speed pumped-storage unit with adjustable pump operating conditions according to claim 5, characterized in that: In pumped storage operation, relevant valves are opened to connect the upstream reservoir, upstream water tank, water pump, downstream water tank, and downstream reservoir; the generator motor obtains electrical energy from the grid to drive the water pump, which pumps water from the downstream water tank to the upstream water tank.

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