A high flow rate liquid piston system

Abstract

The present invention discloses a high-flow-rate liquid piston system, which includes a power grid connected to a water pump, a generator connected to a water turbine, a hydraulic cylinder, and a reversible power device. The piston rod of each hydraulic cylinder is connected to a reversible power device. A water pool is connected to the hydraulic cylinder through a main pipeline. The input and output of the reversible drive device are connected to an external power grid. During operation, by controlling the working water flow rate of the water turbine to slow down and the working water flow rate of the water pump to speed up, kinetic energy recovery is achieved. A steady-flow control strategy is used to issue motion instructions to each reversible power device, enabling them to operate in a time-interleaved manner. The start-stop and commutation times of the hydraulic cylinders are staggered with each other, ensuring that the liquids flowing out of the parallel hydraulic cylinders compensate each other, and realizing the stable flow rate of the main pipeline on the water pool side at the target flow rate, thus forming a piston system with a stable flow rate, high flow rate, and recoverable kinetic energy.

Description

Technical Field

[0001] The present invention belongs to the field of hydraulic machinery, and particularly relates to a high-flow-rate liquid piston system. Background Art

[0002] During the operation of a hydraulic power system, the flow rate of the system pipeline is slow while the flow rate is large, which results in slow system operation and a large impact on the bottom of the water tank, reducing the service life of the equipment. Summary of the Invention

[0003] To address this problem, the present invention proposes a high-flow-rate liquid piston system that can be used in systems with high flow rate requirements to accelerate the system operation speed, stabilize the system flow rate, and reduce the impact of water flow on the bottom of the water tank.

[0004] A high-flow-rate liquid piston system includes a water pump, a water turbine, an electric motor, a generator, a first and a second water tank, a first and a second main liquid pipeline, a first and a second hydraulic cylinder, and a first and a second reversible power device; the electric motor connected to the water pump and the generator connected to the water turbine are both connected to an external power grid; the first reversible power device is connected to the piston of the first hydraulic cylinder through the piston rod of the first hydraulic cylinder, and the second reversible power device is connected to the piston of the second hydraulic cylinder through the piston rod of the second hydraulic cylinder; one end of the first hydraulic cylinder and the second hydraulic cylinder are both connected to the first main liquid pipeline, and the other ends are both connected to the second main liquid pipeline; the water pump connects the first main liquid pipeline and the first water tank, and the water turbine connects the second main liquid pipeline and the second water tank; characterized in that: during system operation, through a speed control strategy, the water pump is controlled to make the water flow rate from the first water tank into the first main liquid pipeline faster, and the water turbine is controlled to make the water flow rate from the second main liquid pipeline into the second water tank slower to achieve kinetic energy recovery; through a valve control strategy, the water volume entering and flowing out of the first and second hydraulic cylinders is kept stable; a steady flow control strategy is used to issue motion commands to the first and second reversible power devices to make them operate in a time-interleaved manner, and the start-stop and commutation times of the first and second hydraulic cylinders are staggered with each other, so that the liquid flowing out of the first and second hydraulic cylinders compensates each other in flow rate after converging into the second main pipeline on the second water tank side and achieves stability, and the total flow rate flowing into the second water tank from the second main pipeline remains stable.

[0005] Preferably, the specific implementation method of the speed control strategy is to issue commands for the guide vane opening degree and the water turbine control valve to the water pump and the water turbine in the form of pipeline flow rate detection.

[0006] Preferably, the specific implementation method of the steady flow control strategy is to issue speed commands to the first and second reversible power devices in the form of non-linear compensation control of a sine wave.

[0007] Optionally, the water turbine and the water pump in the system can be coaxially connected. Then, the system does not require an external power supply and a generator, and the kinetic energy of the water turbine is directly converted into mechanical energy and transmitted to the water pump after being recovered.

[0008] Optionally, both the water pump and the water turbine are reversible pump-turbines and are coaxially connected.

[0009] Optionally, both the first and second water pools are equipped with a water pump and a water turbine connected thereto.

[0010] Preferably, the first and second hydraulic cylinders are two or more groups of hydraulic cylinders connected in parallel.

[0011] Further preferably, each group of hydraulic cylinders is composed of a plurality of sub-hydraulic cylinders connected in series with the same rod.

[0012] Optionally, the reversible pump-turbine includes an axial-flow pump-turbine, a mixed-flow pump-turbine or a diagonal-flow pump-turbine.

[0013] Optionally, the reversible power device includes a pneumatic cylinder, an electric cylinder, a linear motor, a crank and connecting rod mechanism or an additional hydraulic drive system.

[0014] The beneficial effects of the present invention are as follows:

[0015] 1. By introducing a water pump, the present invention enables the water flow in the original piston system to flow rapidly, reduces the energy required for the original operation of the hydraulic transmission mechanism, and significantly accelerates the working speed of the liquid piston system. At the same time, when the kinetic energy of the system remains unchanged, the potential energy that the system needs to generate becomes smaller, so that more kinetic energy can be recovered, and it is expected to further increase the proportion of kinetic energy and improve the energy utilization rate.

[0016] 2. By introducing a water turbine, the present invention enables the kinetic energy of the water entering the water pool to be effectively utilized, realizes kinetic energy recovery, increases the energy utilization rate of the system, reduces the power loss, and at the same time greatly reduces the kinetic energy of the water when it enters the water pool, preventing the generation of eddy currents when the water enters the water pool and damaging the water pool and the surrounding pipelines. The dual functions of the water pump and the water turbine enable the water flow rate in the pipeline from the water pool to the hydraulic transmission mechanism to be controllable, reduce the damage to the pipeline system, and extend the service life of the system.

[0017] 3. By introducing two-way hydraulic cylinders, the present invention is beneficial to reducing the head loss in each pipeline during the power generation and pumping processes of the hydraulic equipment, reducing the use cost, and extending the service life of the equipment; the stable complementarity of the pipeline liquid flow enables the pressure change of the water outlet pipeline of the system water pool to be adjustable, thereby avoiding the use of an overflow valve, reducing the water energy loss, and improving the overall operation efficiency of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic structural diagram of a high-flow liquid piston system according to the first embodiment of the present invention;

[0019] Figure 2 It is the structural diagram of the PID speed control strategy adopted by the water pump and the water turbine in the first embodiment of the present invention;

[0020] Figure 3 It is the sine wave speed control curve diagram of the full compensation interleaved steady flow strategy in the first embodiment of the present invention;

[0021] Figure 4 It is the schematic structural diagram of a high-flow liquid piston system in the second embodiment of the present invention;

[0022] Figure 5 It is the schematic structural diagram of a high-flow liquid piston system in the third embodiment of the present invention. Specific embodiments

[0023] The present invention will be further described in detail below with reference to the accompanying drawings.

[0024] Figure 1 It is the schematic structural diagram of a high-flow liquid piston system in the first embodiment of the present invention. The liquid piston system includes: water pump A, water turbine B, motor C, generator D, water tank P1, water tank P2, liquid main pipelines (L1) and (L2), valves between the pipelines and the hydraulic cylinders, hydraulic transmission mechanism hydraulic cylinders H1 and H2, reversible power devices M1 and M2. Among them, the motor C connected to the water pump and the generator D connected to the water turbine are both connected to the external power grid; the reversible power device M1 is connected to the piston of the hydraulic cylinder H1 through the piston rod of the hydraulic cylinder H1, and the reversible power device M2 is connected to the piston of the hydraulic cylinder H2 through the piston rod of the hydraulic cylinder H2; one ends of the hydraulic cylinders H1 and H2 are both connected to the liquid main pipeline L1 on the side of the water tank P1, and the other ends are both connected to the liquid main pipeline L2 on the side of the water tank P2; the water pump A is connected to the liquid main pipeline L1 on the side of the water tank P1 and the water tank P1, and the water turbine B is connected to the liquid main pipeline L2 on the side of the water tank P2 and the water tank P2. During operation, the water pump A is controlled by a speed control strategy to make the water flow rate entering the liquid main pipeline L1 from the water tank P1 faster, and the water turbine is controlled to make the water flow rate entering the water tank P2 from the main pipeline L2 slower, so as to realize kinetic energy recovery. The water volume entering and flowing out of the hydraulic cylinders is kept stable through the valve control strategy; the steady flow control strategy is used to issue motion commands to each reversible power device, so that each reversible power device operates in a time-interleaved manner, and the start-stop and commutation times of the two hydraulic cylinders are staggered with each other, and the flows of the liquids flowing out of the two hydraulic cylinders are compensated with each other and stabilized after merging into the main pipeline L2 on the side of the water tank P2, and the total flow rate flowing into the water tank P2 from the main pipeline L2 remains stable.

[0025] During operation, the water pump and the water turbine adopt a PID speed control strategy to control the water output and intake. The specific method is to control the opening degree of the guide vane and the control valve of the water turbine by detecting the water flow in the pipeline. Let x(t) be the actual water flow in the pipeline and x0 be the preset value of the water flow in the pipeline. Let e(t) be the water flow error in the pipeline, e(t) = x(t) - x0, and y(t) be the opening degree and rotational speed of the guide vanes of the water pump and the water turbine. The larger y(t) is, the larger the opening degree of the guide vane and the faster the rotational speed. The expression of y(t) in the continuous time domain is:

[0026]

[0027] Among them, y(t) represents the control variable, K p 、K i 、K d represent the proportional gain, derivative gain, and integral gain respectively. Adjusting K p can reduce the steady-state error of the system, improve the control accuracy of the system, and accelerate the action speed; adjusting K i can reduce the system damping and mitigate the adverse effects on the dynamic process; K d can characterize the change trend of the input signal and generate an early correction signal.

[0028] The frequency-domain expression is:

[0029]

[0030] The control structure is as Figure 2 shown. In this embodiment, there are two parallel hydraulic cylinders, namely the first hydraulic cylinder H1 and the second hydraulic cylinder H2, and both hydraulic cylinders are single sub-hydraulic cylinders. Therefore, they are also represented by the first hydraulic cylinder H1 and the second hydraulic cylinder H2.

[0031] During operation, the first reversible power device M1 and the second reversible power device M2 issue motion instructions, and the water pump A and the water turbine B operate in cooperation with the reversible power device to maintain the consistency of the total flow rate of the two water pools flowing in and out, forming a stable flow network to achieve the staggered operation of multiple hydraulic cylinders and the stable and complementary pipeline flow.

[0032] Let the operating cross-sectional areas of the hydraulic cylinders H1 and H2 be S A and S B , respectively. Then the velocity expressions of the two groups of hydraulic cylinders are:

[0033]

[0034]

[0035] During the operation of the fully staggered steady flow control strategy, as Figure 3As shown in the figure, a control form of a sine wave is adopted to send a motion command to the first reversible power device M1 and the second reversible power device M2. The driving device drives the piston rods in two hydraulic cylinders (the first hydraulic cylinder H1 and the second hydraulic cylinder H2) according to the motion command; the two piston rods of the two hydraulic cylinders move according to the speed command, and the speeds of the two piston rods cooperate with each other, so that the liquid flows flowing into the main pipeline L2 from the hydraulic cylinders are superimposed to achieve the effect of peak shaving and valley filling, forming a stable liquid flow; by controlling the inflow / outflow water volume of the main pipeline L2, the unsteady liquid flow can be suppressed, and the problem that the pipeline liquid flow cannot be completely constant in engineering applications can be avoided. Specifically, the two piston rods in the first hydraulic cylinder H1 and the second hydraulic cylinder H2 move alternately, and the speeds of the two piston rods cooperate with each other. The liquid flows flowing into the main pipeline L2 on the P2 side of the water tank from the first hydraulic cylinder pipeline L2 and the second hydraulic cylinder pipeline L2 are superimposed to achieve the effect of peak shaving and valley filling, forming a liquid flow with a constant speed.

[0036] During the working process, each valve cooperates with each other through a control strategy to keep the water flow rate entering the hydraulic cylinders H1 and H2 stable, so that the pressure in the hydraulic cylinders is easy to control.

[0037] The specific working process of power generation is as follows:

[0038] Assume that initially, the hydraulic cylinders H1 and H2 are filled with water, and all valves are in the closed state. At the beginning, the piston in the hydraulic cylinder H1 is at the leftmost end of the piston chamber, and the piston in the hydraulic cylinder H2 is in the middle of the piston chamber. When water flows from the pipeline on the P1 side of the water tank to the hydraulic cylinders, first open the valves F1, F4, F5, and F8. The pistons of the two hydraulic cylinders move to the right. The piston of the hydraulic cylinder H1 moves to the middle, and the piston of the hydraulic cylinder H2 moves to the rightmost end. Close the valves F5 and F8, and open the valves F6 and F7. The piston of the hydraulic cylinder H2 starts to move to the left. When the piston of the hydraulic cylinder H1 moves to the rightmost end and the piston of the hydraulic cylinder H2 moves to the middle, close the valves F1 and F4, and open the valves F2 and F3. The piston of the hydraulic cylinder H1 starts to move to the left. When the piston of the hydraulic cylinder H1 moves to the middle and the piston of the hydraulic cylinder H2 moves to the leftmost end, close the valves F6 and F7, and open the valves F5 and F8. The piston of the hydraulic cylinder H1 moves to the leftmost end, and the piston of the hydraulic cylinder H2 moves to the middle, completing one cycle. During this process, the water pump and the water turbine work to accelerate the water flow rate in the system. At the same time, the two hydraulic cylinders cooperate to keep the water flow rate entering the pipeline (L2) on the H2 side of the water tank stable, and at the same time keep the power generation of the reversible power devices M1 and M2 stable. After the process ends, the water pressure in the water tank P1 decreases, and the potential energy of the water is converted into electrical energy.

[0039] The specific switch schedule of the valves during the power generation working process is as follows:

[0040]

[0041] During the power generation process, the specific energy conversion process is as follows: Assume that initially the water in pool P1 has a speed of 0 and a pressure of P1. When it is pumped out by pump A and enters the pipeline, its speed is v1. Then the potential energy per unit volume of water is P1, and the kinetic energy is Control the opening and closing of the valve to increase the water pressure on one side of the hydraulic cylinder. The water pushes the piston to move, that is, P2 = P1 - P M , open the valve on the pool P2 side, and let the water enter the pipeline on the pool P2 side. Since the cross-sectional area of the pipeline decreases, the water speed returns to v1. Then the potential energy of the water when it enters pool B is P2, and the kinetic energy is The water turbine B works to recover the kinetic energy of the water. Then the potential energy of the water entering pool P2 is P2, and the kinetic energy is 0. At this time, the water pressure in the pool decreases, realizing power generation and kinetic energy recovery.

[0042] The specific working process of energy storage is as follows:

[0043] Assume that initially, the hydraulic cylinders H1 and H2 are filled with water, and all valves are in the closed state. At the beginning, the piston in the hydraulic cylinder H1 is at the leftmost end of the piston chamber, and the piston in the hydraulic cylinder H2 is in the middle of the piston chamber. First, open the valves F1, F5, and F8, and at the same time, the reversible power equipment operates to move the pistons of the two hydraulic cylinders to the right, increasing the pressure on the right side of the pistons of the two hydraulic cylinders. When the piston of the hydraulic cylinder A moves to the middle and the piston of the hydraulic cylinder H2 moves to the rightmost end, close the valves F5 and F8, open the valves F4 and F6, and M2 starts to drive the piston of the hydraulic cylinder H2 to move to the left. When the piston of the hydraulic cylinder H1 moves to the rightmost end and the piston of the hydraulic cylinder H2 moves to the middle, close the valves F1 and F4, open the valves F2 and F7, and M1 starts to drive the hydraulic cylinder H1 to move to the left. When the piston of the hydraulic cylinder H1 moves to the middle and the piston of the hydraulic cylinder H2 moves to the leftmost end, close the valves F6 and F7, open the valves F3 and F5, and M2 starts to drive the piston of the hydraulic cylinder H2 to move to the right. The piston of the hydraulic cylinder H1 moves to the leftmost end, and the piston of the hydraulic cylinder H2 moves to the middle, completing one cycle. During this process, the pump and the water turbine work to accelerate the water flow rate in the system. At the same time, the two hydraulic cylinders cooperate to keep the water flow rate in the pipeline (L2) on the pool P2 side stable. After the process ends, the water pressure in the pool P2 increases, and the electrical energy is converted into the potential energy of the water.

[0044] The specific switch schedule of the valves during the energy storage process is as follows:

[0045]

[0046] During the energy storage process, the specific energy conversion process is as follows: Assume that initially the water in pool P1 has a speed of 0 and a pressure of P1. When it is pumped out by pump A and enters the pipeline, its speed is v1. Then the potential energy per unit volume of water is P1, and the kinetic energy is Ignoring the energy loss of water in the pipeline, the kinetic energy and potential energy before entering the hydraulic cylinder remain unchanged. After entering the hydraulic cylinder, due to the increase in the cross-sectional area of the hydraulic cylinder, the water flow velocity decreases, and part of the kinetic energy of the water is converted into potential energy. At this time, the power equipment pushes the piston to move, increasing the pressure on one side of the piston inside the hydraulic cylinder, that is, P2 = P1 + P M , open the valve on the P2 side of the water tank, and let the water enter the pipeline on the P2 side of the water tank. Since the cross-sectional area of the pipeline decreases, the water velocity returns to v1, so the potential energy of the water when it enters the water tank P2 is P2, and the kinetic energy is The water turbine B works to recover the kinetic energy of the water. Then the potential energy of the water entering the water tank P2 is P2, and the kinetic energy is 0. At this time, the pressure of the water in the water tank increases, realizing energy storage and kinetic energy recovery.

[0047] In the second embodiment of the present invention, the water turbine and the water pump are coaxially connected. Without an external power supply and generator, the system can operate integrally. After the kinetic energy of the water turbine is recovered, it is directly converted into mechanical energy and transmitted to the water pump for operation, as Figure 4 shown. The parts not described are the same as those in the first embodiment.

[0048] The liquid piston system in the second embodiment of the present invention includes: two water tanks P1 and P2, a water pump A and a water turbine B coaxially connected, a motor C, a hydraulic transmission mechanism hydraulic cylinders H1 and H2, and reversible power equipment M1 and M2. One end of the hydraulic cylinder H1 is connected to the main pipeline (L1) on the P1 side of the water tank, and the other end is connected to the main pipeline (L2) on the P2 side of the water tank. One end of the hydraulic cylinder H2 is connected to the main pipeline (L1) on the P1 side of the water tank, and the other end is connected to the main pipeline (L2) on the P2 side of the water tank; the water pump connects the main pipeline on the P1 side of the water tank to the water tank P1, and the water turbine connects the main pipeline on the P2 side of the water tank to the water tank P2.

[0049] The specific working process is as follows:

[0050] Water flows from the water tank P1 through the pipeline on the P1 side of the water tank and is divided into two paths to enter the first hydraulic cylinder H1 and the second hydraulic cylinder H2. At the same time, control the running speeds in the first hydraulic cylinder H1 and the second hydraulic cylinder H2 to match. The liquid flows in the pipeline on the P2 side of the first hydraulic cylinder water tank and the pipeline on the P2 side of the second hydraulic cylinder water tank converge and reach stability in the main pipeline on the P2 side of the water tank, and finally flow into the water tank P2. The water pump A and the water turbine B accelerate the whole process.

[0051] In the third embodiment, a reversible pump-turbine can be used to replace the water pump and the water turbine in the second embodiment respectively, and the two are coaxially connected, so that the working process of the system can be reversed. Reversible pump-turbines such as axial-flow pump-turbines, mixed-flow pump-turbines or diagonal-flow pump-turbines, etc., as Figure 5 shown. An axial-flow pump-turbine is used, and the parts not described are the same as those in Embodiment 1.

[0052] The liquid piston system in the third embodiment of the present invention includes: two water pools P1 and P2, a pump-turbine A and a pump-turbine B connected coaxially, a motor C, hydraulic transmission mechanism hydraulic cylinders H1 and H2, reversible power devices M1 and M2. Among them, one end of the hydraulic cylinder H1 is connected to the main pipeline (L1) on the side of the water pool P1, and the other end is connected to the main pipeline (L2) on the side of the water pool P2; one end of the hydraulic cylinder H2 is connected to the main pipeline (L1) on the side of the water pool P1, and the other end is connected to the main pipeline (L2) on the side of the water pool P2; the pump is connected to the main pipeline (L1) on the side of the water pool P1 and the water pool P1, and the turbine is connected to the main pipeline (L2) on the side of the water pool P2 and the water pool P2.

[0053] The specific working process when water flows from the water pool P1 to the water pool P2 is as follows:

[0054] Water flows from the water pool P1 through the pipeline on the side of the water pool P1 and is divided into two paths to enter the first hydraulic cylinder H1 and the second hydraulic cylinder H2. The pump-turbine A works in the pump state to accelerate the flow of water, control the running speeds in the first hydraulic cylinder H1 and the second hydraulic cylinder H2 to match, and the liquid flows in the pipeline on the side of the water pool P2 of the parallel first hydraulic cylinder and the pipeline on the side of the water pool P2 of the second hydraulic cylinder converge and reach stability in the main pipeline on the side of the water pool P2. Finally, the total flow rate flowing into the water pool P2 remains stable. The pump-turbine B works in the turbine state to decelerate the high-speed water flow and enter the water pool P2, reduce the kinetic energy of the water, and recover electric energy at the same time.

[0055] The specific working process when water flows from the water pool P2 to the water pool P1 is as follows:

[0056] Water flows from the water pool P2 through the pipeline on the side of the water pool P2 and is divided into two paths to enter the first hydraulic cylinder H1 and the second hydraulic cylinder H2. The pump-turbine A works in the pump state to accelerate the flow of water, control the running speeds in the first hydraulic cylinder H1 and the second hydraulic cylinder H2 to match, and the liquid flows in the pipeline on the side of the water pool P1 of the parallel first hydraulic cylinder and the pipeline on the side of the water pool P2 of the second hydraulic cylinder converge and reach stability in the main pipeline on the side of the water pool P1. Finally, the total flow rate flowing into the water pool P1 remains stable. The pump-turbine A works in the turbine state to decelerate the high-speed water flow and enter the water pool P1, reduce the kinetic energy of the water, and recover electric energy at the same time.

[0057] To enable the system to operate reversely, another preferred implementation is that each side of the water pool can be equipped with a pump and a turbine at the same time. The pump and the turbine on each side are connected to the water pool at the same time.

[0058] In an alternative embodiment, the water pools P1 and P2 can be enclosed metal spherical tanks, steel pipes and other high-pressure containers or underground projects, or can also be enclosed containers such as chemical towers that store water and gas at the same time.

[0059] In the present invention, a hydraulic cylinder realizes the conversion between mechanical energy and water potential energy; the hydraulic cylinder has an upper port and a lower port, and the upper port of each hydraulic cylinder is respectively connected to a water pump through a valve and a pipeline, and the lower port of the hydraulic cylinder is connected to a water turbine through a valve and a pipeline.

[0060] The kinetic energy recovery device accelerates the water flow velocity in the pipeline, and at the same time slows down the velocity of the water when it enters the bottom of the water pool, reducing the influence of the eddy current effect on the bottom of the water pool and extending the service life, such as the water pump used in the embodiment of the present invention. In the present invention, a water pump refers to a device that converts mechanical energy into kinetic energy. Optionally, it can be a vane-type water pump, which can accelerate the water and pump it into the hydraulic cylinder.

[0061] In the present invention, water generates mechanical energy through a water turbine, and the water turbine is connected to a generator to generate electric energy, realizing kinetic energy recovery. Optionally, the water turbine can be an axial-flow pump turbine, a mixed-flow pump turbine or a diagonal-flow pump turbine. The pipeline is connected to the guide vane side of the water turbine and is of a fully sealed structure, and the water flows through the guide vane and the blade and enters the water pool.

[0062] In the present invention, a reversible power device refers to a device that can convert linear mechanical energy into other energies. Optionally, the reversible power device can be a pneumatic cylinder for compressing air, an electric cylinder, a linear motor, a crank-link mechanism or an additional hydraulic drive system.

[0063] In an alternative embodiment of the present invention, the two hydraulic cylinders can also be two groups of hydraulic cylinders, or multiple groups of hydraulic cylinders, and the two groups or multiple groups of hydraulic cylinders are connected in parallel. Each group of hydraulic cylinders can include multiple sub-hydraulic cylinders, and the multiple sub-hydraulic cylinders are connected in series with the same rod. At this time, the hydraulic cylinder can be regarded as a hydraulic cylinder with a variable area; the cross-sectional areas of each sub-hydraulic cylinder can be the same or different. One end of each sub-hydraulic cylinder is connected to the same pipeline through a valve and a pipeline, and the other end is connected to the same pipeline through a valve and a pipeline. When the hydraulic cylinder moves to the end point of the piston stroke, the connection states of the left and right chambers of each sub-hydraulic cylinder communicating with the water pool are interchanged, thereby pushing the piston in the hydraulic cylinder to move in the opposite stroke direction, so as to realize the reciprocating movement of the piston. During specific operation, each sub-hydraulic cylinder connected in series through the piston rod switches the connection states of the left and right chambers of the sub-hydraulic cylinder with the water pool by controlling its respective valve, so as to change the equivalent operating cross-sectional area of this path of hydraulic cylinder, and further change the flow rates of the main pipelines on one side of the water pool and the main pipelines on the other side of the water pool under the condition that the running speed of the piston rod remains unchanged.

[0064] In an embodiment of the present invention, the inlet diameter d of the water turbine is 1 m, the outlet diameter D is 4 m, and the water flow rate is 50 m 3 / s, then the kinetic energy recovery efficiency can reach 99.6%.

[0065] The above embodiments are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A high-flow liquid piston system, comprising a water pump, a water turbine, an electric motor, a generator, a first and a second water tank, a first and a second main liquid pipelines, a first and a second hydraulic cylinders, a first and a second reversible power devices; the electric motor connected to the water pump and the generator connected to the water turbine are both connected to an external power grid; the first reversible power device is connected to the piston of the first hydraulic cylinder through the piston rod of the first hydraulic cylinder, and the second reversible power device is connected to the piston of the second hydraulic cylinder through the piston rod of the second hydraulic cylinder; one end of the first hydraulic cylinder and the second hydraulic cylinder are both connected to the first main liquid pipeline, and the other ends are both connected to the second main liquid pipeline; the water pump is connected to the first main liquid pipeline and the first water tank, and the water turbine is connected to the second main liquid pipeline and the second water tank; characterized in that: During system operation, through the speed regulation control strategy, the water pump is controlled to make the water flow rate from the first water tank into the first liquid main pipeline faster, and the water turbine is controlled to make the water flow rate from the second liquid main pipeline into the second water tank slower, so as to realize kinetic energy recovery; the water volume entering and flowing out of the first and second hydraulic cylinders is kept stable through the valve control strategy; the steady flow control strategy is adopted, that is, a non-linear compensation control form of sine wave is used to send motion commands to the first and second reversible power devices, so that they operate in a time-interleaved manner, and the start-stop and commutation times of the first and second hydraulic cylinders are staggered with each other, so that the flow rates of the liquids flowing out of the first and second hydraulic cylinders are compensated with each other and stabilized after merging into the second main pipeline on the second water tank side, and the total flow rate flowing into the second water tank from the second main pipeline is kept stable; the speed regulation control strategy is as follows: the PID speed regulation control strategy is adopted to control the water output and water input, and the opening degree of the guide vane and the water turbine control valve are controlled by detecting the pipeline water flow rate; let x(t) be the actual pipeline water flow rate and x0 be the preset pipeline water flow rate; let e(t) be the pipeline water flow error, e(t)=x(t)-x 0， y(t) represents the control variable. The larger y(t) is, the larger the opening degree of the guide vanes of the water pump and the water turbine and the faster the rotation speed. The expression of y(t) in the continuous time domain is: Among them, K p , K i , and K d represent the proportional gain, derivative gain, and integral gain respectively; Adjusting K p can reduce the steady-state error of the system, improve the control accuracy of the system, and accelerate the acting speed; Adjusting K i can reduce the damping of the system and mitigate the adverse effects on the dynamic process; K d can characterize the change trend of the input signal and generate an early correction signal; The frequency-domain expression is as follows:

2. The high-flow liquid piston system according to claim 1, characterized in that The water turbine and the water pump in the system can be coaxially connected, so that the system does not require an external power supply and a generator, and the kinetic energy of the water turbine is directly converted into mechanical energy and transmitted to the water pump after being recovered.

3. The high-flow liquid piston system according to claim 1, characterized in that Both the water pump and the water turbine are reversible pump-turbines and are coaxially connected.

4. The high-flow liquid piston system according to claim 1, characterized in that Both the first and second water pools are equipped with water pumps and water turbines connected thereto.

5. The high-flow liquid piston system according to any one of claims 1-4, characterized in that The first and second hydraulic cylinders are two or more groups of hydraulic cylinders connected in parallel.

6. The high-flow liquid piston system according to claim 5, characterized in that Each group of hydraulic cylinders is composed of a plurality of sub-hydraulic cylinders connected in series with the same rod.

7. The high-flow liquid piston system according to claim 3, characterized in that The reversible pump-turbine includes an axial-flow pump-turbine, a mixed-flow pump-turbine or a diagonal-flow pump-turbine.

8. The high-flow liquid piston system according to claim 1, characterized in that The reversible power device includes a pneumatic cylinder, an electric cylinder, a linear motor, a crank and connecting rod mechanism or an additional hydraulic drive system.

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