Composite energy storage system utilizing gravity of abandoned mine and compressed air and control method

Abstract

The invention provides a composite energy storage system utilizing waste mine gravity and compressed air and a control method. The system comprises a waste mine vertical shaft, a giant piston assembly, a compressed air energy storage assembly, an electric power conversion assembly and a controller. The giant piston assembly is arranged in a vertical shaft of the abandoned mine and can reciprocate in the vertical direction. The giant piston assembly comprises a balance weight body, a piston rod and a sealing assembly. The giant piston assembly divides the vertical shaft of the abandoned mine into an upper cavity and a lower gas storage cavity. The piston rod is connected with and supports the balance weight body, and the sealing assembly is arranged between the balance weight body and the inner wall of a vertical shaft of the abandoned mine. The operation stability, the output continuity and the long-term safety of the abandoned mine composite energy storage system under the complex working condition can be improved, the method is suitable for scenes such as abandoned mine transformation, power grid peak regulation and frequency modulation and renewable energy consumption, and support is provided for building a novel energy storage system with high reliability and high adaptability.

Description

Technical Field

[0001] This invention relates to the field of energy storage technology, specifically to a composite energy storage system and control method utilizing the gravity and compressed air of abandoned mines. Background Technology

[0002] With the increasing proportion of intermittent renewable energy sources such as wind and solar power in the power system, the demand for large-scale, long-duration, and highly reliable energy storage technologies is becoming increasingly urgent. Current mainstream large-scale energy storage technologies, such as pumped hydro storage and compressed air energy storage (CAES), have specific geographical requirements, resulting in limitations in site selection, long construction periods, and high initial investment. On the other hand, with the depletion of mineral resources, a large number of abandoned mines and shafts are idle, not only occupying land but also posing certain safety hazards; their vast underground space and existing shaft structures are not being effectively utilized. Among existing technologies, gravity energy storage, as an emerging technology, stores / releases energy by lifting and lowering heavy objects in shafts, but the energy density of gravity storage alone is relatively limited. Compressed air energy storage (CAES) relies on large underground caverns to store high-pressure air, which has stringent geological requirements. Although there are ideas to combine gravity energy storage and compressed air energy storage, existing solutions are usually simple functional superpositions with loose system structures, failing to achieve deep coupling between core mechanical components and underground space, resulting in significant room for improvement in energy storage density per unit space and overall system efficiency. In addition, existing systems generally lack intelligent control capabilities that are linked to the real-time status of the power grid and power market signals, resulting in insufficient economic efficiency and operational flexibility. Summary of the Invention

[0003] Purpose of the Invention: To address the following problems existing in the gravity-compressed air hybrid energy storage system of abandoned mines: During system operation, there is a strong coupling relationship between the piston motion state, the air storage chamber pressure state, and the mechanical structure state. Frictional resistance, leakage, and sealing degradation dynamically change with operating conditions, making it difficult for traditional fixed-parameter control methods to accurately reflect the actual system state. Furthermore, the dynamic response speeds of the gravity energy storage branch and the compressed air energy storage branch differ, easily causing sudden pressure changes in the air storage chamber, piston speed fluctuations, and output torque oscillations during charging and discharging switching, dual-branch power switching, and operating mode switching, thus affecting system stability and equipment lifespan. This invention provides a hybrid energy storage system and control method utilizing the gravity and compressed air of abandoned mines to achieve online state identification, hierarchical collaborative control of the dual branches, and impact suppression during switching phases under complex operating conditions, thereby improving system operational stability, output continuity, and long-term safety.

[0004] The system includes an abandoned mine vertical shaft, a giant piston assembly, a compressed air energy storage assembly, a power conversion assembly, and a controller;

[0005] The giant piston assembly is installed inside the vertical shaft of the abandoned mine and can reciprocate in the vertical direction;

[0006] The giant piston assembly includes a counterweight, a piston rod, and a sealing assembly. The giant piston assembly divides the vertical shaft of the abandoned mine into an upper cavity and a lower air storage cavity. The piston rod connects to and supports the counterweight, and the sealing assembly is disposed between the counterweight and the inner wall of the vertical shaft of the abandoned mine. The sealing assembly serves as a physical carrier with dual energy storage functions, realizing the coupled storage and release of gravitational potential energy and compressed air energy.

[0007] The compressed air energy storage component is connected to the lower air storage chamber. The compressed air energy storage component includes a compressor, an air storage unit, an expander, and a valve group. The compressor is used to compress air into the air storage unit during charging. The expander is used to drive high-pressure air to generate electricity during discharging. A valve group is connected between the expander inlet and the air storage unit. The valve group is used to regulate the gas flow rate and direction to achieve energy storage and release control.

[0008] The power conversion component is connected to the giant piston assembly and the compressed air energy storage assembly. The power conversion component includes a reversible motor or generator and a power conversion unit. The reversible motor or generator is a bidirectional conversion device between electrical energy and mechanical energy. The power conversion unit is a power conversion and control system that realizes the electrical interface of the power grid, power regulation and protection. The reversible motor or generator and the power conversion unit are electrically connected and together constitute the power conversion component.

[0009] The controller is electrically connected to the displacement sensor, pressure sensor, flow sensor, power sensor, vibration sensor, and stress sensor, respectively.

[0010] The controller is used for:

[0011] Based on the multi-source operating signals collected by the displacement sensor, pressure sensor, flow sensor, power sensor, vibration sensor and stress sensor, a unified state vector of the composite energy storage system is constructed.

[0012] Based on a unified state vector, the friction state, leakage state, sealing attenuation state, and coupling hysteresis state between the gravity energy storage branch and the compressed air energy storage branch of the composite energy storage system are identified online. The giant piston assembly and related components that cooperate with it to achieve piston lifting and bidirectional conversion of mechanical and electrical energy constitute the gravity energy storage branch. The lower gas storage chamber, the compressed air energy storage assembly, and related components that cooperate with it to achieve gas compression, storage, and expansion energy release constitute the compressed air energy storage branch.

[0013] Based on the online identification results and the current operating conditions, the gravity energy storage branch and the compressed air energy storage branch are subjected to hierarchical coordinated control to determine the piston operation control quantity, compressor operation control quantity, valve group opening control quantity and expander output control quantity.

[0014] During the switching between charging and discharging, switching between gravity energy storage branch and compressed air energy storage branch, and switching between operating modes, the pressure change rate of the gas storage chamber, the piston speed change rate, and the output torque change rate of the power conversion component are jointly constrained to suppress system shock and output power fluctuations.

[0015] The unified state vector includes one or more of the following: piston displacement, piston velocity, gas storage chamber pressure, gas flow rate, system output power, output torque, structural vibration characteristic quantity, and structural stress characteristic quantity.

[0016] The online identification of the friction state, leakage state, sealing attenuation state, and coupling hysteresis state between the gravity energy storage branch and the compressed air energy storage branch of the composite energy storage system based on the unified state vector includes:

[0017] Identify the change in piston running resistance based on the dynamic relationship between piston displacement and gas storage chamber pressure;

[0018] Leakage trends can be identified by the deviation between changes in pressure in the gas storage chamber and changes in gas flow rate.

[0019] Identify the seal attenuation state based on changes in vibration and stress characteristic quantities;

[0020] The coupling lag state is identified based on the time deviation between the command response of the gravity energy storage branch and the command response of the compressed air energy storage branch.

[0021] The coupling lag state is identified based on the deviation between the time it takes for the gravity energy storage branch to reach the preset response amplitude after receiving the control command and the time it takes for the compressed air energy storage branch to reach the preset response amplitude after receiving the control command.

[0022] The operating conditions include one or more of the following: frequency regulation, peak shaving and valley filling, stable output, standby, and protection. The controller determines the current operating condition based on the grid load demand, system energy storage status, and online identification results.

[0023] The hierarchical collaborative control includes:

[0024] Upper-level mode decision-making is used to identify the current operating conditions and determine control objectives;

[0025] The middle layer power allocation is used to determine the power sharing ratio between the gravity energy storage branch and the compressed air energy storage branch based on the control objectives and the friction state, leakage state, sealing attenuation state and coupling hysteresis state.

[0026] The lower-level execution control is used to generate piston lifting speed commands, compressor start / stop commands, valve group opening commands, and expander adjustment commands based on the power load ratio.

[0027] The joint constraints implemented by the controller during the switching process include:

[0028] Set an upper limit threshold for the rate of change of pressure in the gas storage chamber;

[0029] Set an upper limit threshold for the rate of change of piston speed;

[0030] Set an upper limit threshold for the rate of change of output torque of the power conversion component;

[0031] And when any upper limit threshold is triggered, the power regulation rate of the corresponding branch is reduced.

[0032] The controller is also used to assess the health status of the system based on vibration characteristics, structural stress characteristics, leakage trends and sealing attenuation status, and to perform derating operation, speed limiting control, pressure limiting control and protective shutdown control when the health status is below a preset threshold.

[0033] The present invention also provides a control method for the system, comprising the following steps:

[0034] Step S1: Collect multi-source operating signals including piston displacement, gas storage chamber pressure, gas flow rate, system output power, output torque, structural vibration, and structural stress;

[0035] Step S2: Perform time synchronization processing on the multi-source operating signals and construct a unified state vector for the system, represented as:

[0036] ,

[0037] in, For a moment The unified state vector of the system; For a moment Piston displacement; For a moment Piston speed; For a moment Gas storage chamber pressure; For a moment Gas flow rate; For a moment System output power; For a moment Output torque; For a moment Structural vibration characteristic quantities; For a moment Structural stress characteristic quantity; T represents transpose;

[0038] Step S3: Based on the unified state vector, identify online the friction state, leakage state, sealing attenuation state, and coupling hysteresis state between the gravity energy storage branch and the compressed air energy storage branch of the composite energy storage system.

[0039] Step S4: Identify the current operating conditions based on grid load demand, system energy storage status, and online identification results;

[0040] Step S5: Based on the current operating conditions and online identification results, determine the power bearing ratio of the gravity energy storage branch and the compressed air energy storage branch in layers, and generate piston operation control quantity, compressor operation control quantity, valve group opening control quantity and expander output control quantity.

[0041] Step S6: During the switching between charging and discharging, switching between gravity energy storage branch and compressed air energy storage branch, and switching between operating modes, the pressure change rate of the gas storage chamber, the piston speed change rate, and the output torque change rate are jointly constrained to suppress system impact and output power fluctuation.

[0042] Step S7: When the detected health status is lower than the preset threshold, perform derated operation, speed limit control, pressure limit control and protection shutdown control.

[0043] In step S3, the online identification of the leakage status includes: determining the leakage trend parameter based on the deviation between the actual pressure change in the gas storage chamber and the theoretical pressure change calculated based on the gas flow rate, expressed as: , in, For a moment Leakage trend parameters; The time interval between adjacent sampling times; The theoretical pressure value at the next moment is calculated based on the gas flow rate and the equilibrium model. This represents the actual pressure value of the gas storage chamber measured at the next moment;

[0044] The controller identifies the piston's running resistance based on the piston's kinematic state and the pressure states in the upper and lower chambers. The equivalent running resistance of the piston is expressed as:

[0045] ,

[0046] in, Let k be the equivalent running resistance of the piston at time k; The total mass of the giant piston assembly and its counterweights; This refers to piston acceleration; and These are the pressure in the upper chamber of the piston and the pressure in the lower gas storage chamber, respectively. This represents the effective pressure-bearing area of ​​the piston. It is the acceleration due to gravity;

[0047] The controller identifies the dual-branch coupled hysteresis state, and the coupling hysteresis parameter is expressed as:

[0048] ,

[0049] in, This is the lag time for the two-branch coupling; This refers to the time required for the compressed air energy storage branch to reach the preset response amplitude after receiving a control command. This refers to the time it takes for the gravity energy storage branch to reach the preset response amplitude after receiving a control command.

[0050] In step S5, the controller performs hierarchical power allocation for the gravity energy storage branch and the compressed air energy storage branch based on the system's target output power and the online identification results. The power allocation for the two branches is expressed as follows:

[0051] ,

[0052] ,

[0053] in, Let k be the power supplied by the gravity energy storage branch at time k. The power supplied by the compressed air energy storage branch at time k; The target output power of the system; The coefficients are dynamically allocated and satisfy the following conditions: ;

[0054] Dynamic allocation coefficient The calculation formula is:

[0055] ,

[0056] in, The energy storage status of the compressed air energy storage branch; The energy storage state of the gravity energy storage branch; For the preset allocation function;

[0057] In step S6, the joint constraint includes: the switching shock suppression constraint is expressed as:

[0058] ,

[0059] in, Threshold for the rate of change of pressure in the gas storage chamber; The threshold for the rate of change of piston speed; The threshold value for the rate of change of output torque is given by d, which represents the derivative.

[0060] when , or When any parameter reaches the corresponding upper limit threshold (i.e., satisfies the above inequality), the controller reduces the power regulation rate of the corresponding branch and delays the power increase or decrease action of the other branch to achieve a smooth transition during the switching process.

[0061] Beneficial effects: 1. This invention does not simply combine gravity energy storage and compressed air energy storage in abandoned mines. Instead, it constructs a unified state vector and identifies friction state, leakage state, sealing attenuation state and coupling hysteresis state online, enabling the controller to correct the system operating state description in real time, thereby improving the control accuracy and operational stability in complex working conditions and model mismatch scenarios.

[0062] 2. This invention avoids the response lag and power distribution imbalance problems that are prone to occur under the unified scheduling of a single optimizer by implementing a hierarchical collaborative control mechanism for the gravity energy storage branch and the compressed air energy storage branch, which includes upper-level mode decision-making, middle-level power allocation and lower-level execution control. This improves the collaborative operation capability and output continuity of the two branches.

[0063] 3. This invention effectively reduces pressure shocks, mechanical shocks, and power oscillations during the switching process by jointly constraining the rate of change of gas storage chamber pressure, the rate of change of piston speed, and the rate of change of output torque during the switching process of charging and discharging, dual-branch switching, and operating mode switching, thereby improving the system's operational stability and the lifespan of key components. Attached Figure Description

[0064] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention above and in other aspects will become clearer.

[0065] Figure 1 This is a diagram of the architecture of the present invention.

[0066] Figure 2 This is a physical illustration of the present invention.

[0067] Figure 3 This is a flowchart of the optimization algorithm of the present invention.

[0068] Figure 4 This is a comparison chart of the core indicators of this invention.

[0069] Figure 5 This is a comparison chart of the attenuation curves of the present invention.

[0070] Figure 6 This is a comparison chart of the overall performance of the present invention. Detailed Implementation

[0071] like Figure 1 , Figure 2 , Figure 3 As shown, this embodiment of the invention provides a composite energy storage system and control method utilizing the gravity and compressed air of abandoned mines. In this embodiment, to achieve real-time sensing, online identification, and coordinated control of the operating status of the composite energy storage system, the controller first constructs a unified system state vector based on data collected by multiple source sensors. The unified state vector is represented as:

[0072] ,

[0073] in, For a moment The unified state vector of the system; This represents piston displacement; Piston speed; This refers to the pressure in the gas storage chamber. This refers to the gas flow rate; This refers to the system output power. This is the output torque; It is a characteristic quantity of structural vibration; It represents the characteristic quantity of structural stress.

[0074] By constructing the aforementioned unified state vector, the controller can integrate the piston's mechanical motion state, gas thermal state, and structural health state into the same state space, providing a basic input for subsequent online identification and hierarchical collaborative control.

[0075] In a preferred embodiment, the controller identifies the system leakage trend online based on the deviation between changes in the gas storage chamber pressure and changes in gas flow rate. The leakage trend parameter is expressed as:

[0076] ,

[0077] in, For a moment Leakage trend parameters; The time interval between adjacent sampling times; The theoretical pressure value at the next moment is calculated based on the gas flow rate and the equilibrium model. This represents the actual pressure value of the gas storage chamber measured at the next moment.

[0078] when A sustained increase in pressure indicates an increasing leakage trend in the system; conversely, a decrease indicates a relatively stable sealing state of the gas storage chamber. These parameters allow for dynamic characterization of the gas storage chamber's leakage status, rather than relying solely on a single pressure measurement to determine the system's operating condition.

[0079] In a preferred embodiment, the controller identifies the piston running resistance based on the piston kinematic state and the pressure state of the upper and lower chambers. The equivalent piston running resistance is expressed as:

[0080] ,

[0081] in, Let k be the equivalent running resistance of the piston at time k; The total mass of the giant piston assembly and its counterweights; This refers to piston acceleration; and These are the pressure in the upper chamber of the piston and the pressure in the lower gas storage chamber, respectively. This represents the effective pressure-bearing area of ​​the piston. This is the acceleration due to gravity.

[0082] Through the The continuous calculation can reflect the changes in factors such as frictional resistance, additional damping, or local jamming during piston operation in real time, and serve as the basis for subsequent power distribution and operating speed adjustment.

[0083] In a preferred embodiment, to characterize the dynamic response consistency between the gravity energy storage branch and the compressed air energy storage branch, the controller identifies the dual-branch coupling hysteresis state, and the coupling hysteresis parameter is expressed as:

[0084] ,

[0085] in, This is the lag time for the two-branch coupling; This refers to the time required for the compressed air energy storage branch to reach the preset response amplitude after receiving a control command. This refers to the time it takes for the gravity energy storage branch to reach the preset response amplitude after receiving a control command.

[0086] when When the value is large, it indicates a significant response mismatch between the two branches; when A smaller value indicates better consistency in the dynamic response of the two branches. The controller can then adjust accordingly. The size of the dual-branch control rhythm is dynamically adjusted to improve the system's collaborative operation capability.

[0087] In a preferred embodiment, the controller performs hierarchical power allocation for the gravity energy storage branch and the compressed air energy storage branch based on the system's target output power and online identification results. The dual-branch power allocation is expressed as follows: , , in, Let k be the power supplied by the gravity energy storage branch at time k. The power supplied by the compressed air energy storage branch at time k; The target output power of the system; The coefficients are dynamically allocated and satisfy the following conditions: .

[0088] The dynamic allocation coefficient The following parameters are dynamically determined based on leakage trend parameters, equivalent piston operating resistance, coupling hysteresis state, and system energy storage state:

[0089] ,

[0090] in, The energy storage status of the compressed air energy storage branch; The energy storage state of the gravity energy storage branch; This is the default allocation function.

[0091] Through the above power distribution method, the controller can dynamically determine the proportion of the dual branches to bear power under different operating conditions based on the real-time identification results, thereby avoiding the problem of response lag or output instability caused by a single fixed proportion distribution.

[0092] During charging / discharging switching, dual-branch switching, and operating mode switching, the controller implements joint constraints on the switching process to suppress sudden changes in gas storage chamber pressure, piston motion, and output torque. The switching impact suppression constraint is expressed as follows:

[0093] ,

[0094] in, Threshold for the rate of change of pressure in the gas storage chamber; The threshold for the rate of change of piston speed; This is the threshold for the rate of change of output torque.

[0095] when , or When any parameter reaches its corresponding threshold, the controller reduces the power regulation rate of the corresponding branch and delays the power increase or decrease action of the other branch to achieve a smooth transition during the switching process. This effectively reduces pressure shocks, mechanical shocks, and power oscillations during system switching.

[0096] In this embodiment, as Figure 2 As shown in the figure, this embodiment provides a composite energy storage system utilizing the gravity and compressed air of an abandoned mine shaft, which is installed within a vertical shaft 3 of the abandoned mine shaft. The vertical shaft 3 is preferably an abandoned mine shaft that has undergone safety reinforcement and sealing treatment. A giant piston assembly capable of reciprocating vertically is installed within the shaft 3. The giant piston assembly mainly includes a giant piston body, a counterweight 1, and a piston rod 2. The giant piston body and counterweight 1 provide gravitational potential energy storage mass, and the piston rod 2 transmits mechanical force and connects to an external transmission mechanism. The giant piston assembly divides the internal space of the shaft 3 into an upper cavity and a lower air storage cavity, with the lower air storage cavity connected to the compressed air energy storage section. The compressed air energy storage section includes an expander 4, an air storage unit 5, a valve group 6, and a compressor 7. A controller 8 is used to collect system operation signals and perform coordinated control. A sealing assembly is installed between the giant piston body and counterweight 1 and the inner wall of the shaft 3 to ensure dynamic sealing between the upper and lower cavities when the piston assembly moves within the shaft 3.

[0097] The compressed air energy storage assembly includes a compressor 7, an air storage unit 5, an expander 4, and a valve group 6. The compressor outlet is connected to the lower air storage chamber and the air storage unit via a pipeline, and the expander inlet is connected to the air storage unit and the lower air storage chamber via the valve group. The power conversion assembly includes a reversible motor / generator and a power conversion unit. The reversible motor / generator is connected to the piston rod and the compressor via a mechanical transmission mechanism to convert electrical energy into mechanical energy during charging and mechanical energy into electrical energy during discharging. The controller is connected to displacement sensors, pressure sensors, flow sensors, power sensors, vibration sensors, and stress sensors to acquire multi-source operating signals during system operation.

[0098] In this embodiment, a displacement sensor is used to detect the current position and displacement trend of the giant piston assembly; a pressure sensor is used to detect the pressure state within the lower gas storage chamber and gas storage unit; a flow sensor is used to detect the gas flow rate at the compressor outlet or expander inlet; a power sensor is used to detect the system's output or input power; and vibration and stress sensors are used to detect the vibration or stress state of the piston rod, transmission mechanism, and key load-bearing components. After receiving the above multi-source operating signals, the controller performs time synchronization processing and constructs a unified system state vector. The unified state vector preferably includes at least piston displacement, piston velocity, gas storage chamber pressure, gas flow rate, system output power, output torque, structural vibration characteristics, and structural stress characteristics.

[0099] In a preferred embodiment, the controller performs online identification based on the unified state vector. The unified state vector can be represented as: Specifically, the controller identifies the change in piston running resistance based on the dynamic relationship between piston displacement and gas chamber pressure; and identifies the leakage trend based on the deviation between gas chamber pressure change and gas flow rate change. The parameters are expressed as follows: The system identifies the seal attenuation state based on changes in vibration and stress characteristics; and identifies the coupling hysteresis state based on the time deviation between the command responses of the gravity energy storage branch and the compressed air energy storage branch. After online identification, the controller can obtain key parameters reflecting the actual operating state of the system, no longer relying solely on fixed models or single sensor values ​​for control judgments.

[0100] During charging, the external power grid supplies power to the system. After the controller identifies the current condition as charging, it controls the reversible motor / generator to operate as a motor. This drives the piston rod upwards via a mechanical transmission mechanism, thereby lifting the giant piston assembly to store gravitational potential energy. Simultaneously, the controller controls the compressor to operate, compressing air and sending it into the lower air storage chamber and storage unit to store compressed air energy. During this process, the controller uses online identification of friction, leakage, and coupling hysteresis states. The coupling hysteresis parameter is expressed as follows: The power sharing ratio of the gravity energy storage branch and the compressed air energy storage branch is determined in layers, and piston rise speed command, compressor operation command and valve group opening command are generated respectively, so that the two energy storage branches work together during the charging phase.

[0101] Under discharge conditions, after the controller identifies the current condition as discharge, it controls the high-pressure air to enter the expander through the valve group to generate electricity. Simultaneously, it controls the piston assembly to move downwards under gravity and drive the reversible motor / generator to generate electricity. At this time, the controller determines whether there is a significant increase in friction, enhanced leakage, weakened sealing, or inconsistent response between the two branches based on the online identification results. Based on this, it adjusts the output ratio of the gravity energy storage branch and the compressed air energy storage branch to ensure that they work together to output enough electrical energy to meet the grid's demand. Unlike the original implementation which relied solely on a multi-objective optimization function to determine the output, this implementation adopts a hierarchical collaborative control mechanism. The power allocation between the two branches is expressed as follows: That is, the upper-level mode decision identifies the current operating condition and determines the control target, the middle-level power distribution calculates the output ratio of the two branches, and finally the lower-level execution control generates the piston running control quantity, the expander regulation control quantity, and the related valve group control quantity.

[0102] In a preferred embodiment, the operating conditions include at least frequency regulation, peak shaving and valley filling, stable output, standby, and protection. The controller determines the current operating condition based on grid load demand, system energy storage status, and online identification results. When the system is in frequency regulation mode, priority is given to improving the rapid response capability of the gravity energy storage branch; when the system is in peak shaving and valley filling mode, priority is given to considering the overall output efficiency of both branches; when the system is in protection mode, priority is given to reducing operating stress and suppressing the spread of abnormal states. Through operating condition identification, the system can switch control priorities for different task objectives.

[0103] During the switching between charging and discharging, switching between the gravity energy storage branch and the compressed air energy storage branch, and switching between operating modes, the controller performs switching impact suppression control, and its switching impact suppression constraint can be expressed as: Specifically, the controller sets upper thresholds for the rate of change of gas storage chamber pressure, the rate of change of piston speed, and the rate of change of output torque. When any parameter reaches its corresponding upper threshold, the controller reduces the power regulation rate of the corresponding branch and delays the power increase or decrease action of the other branch to achieve a smooth transition during the switching process. During the switching from charging to discharging, if the rate of change of gas storage chamber pressure exceeds the set threshold, the controller prioritizes slowing down the valve opening change rate and the expander loading speed; if the rate of change of piston speed is too large, the piston control increment is reduced; if the rate of change of output torque is too large, the torque regulation process of the reversible motor / generator is smoothed. Through the above combined constraints, pressure shocks, mechanical shocks, and power oscillations caused by switching can be effectively suppressed.

[0104] In another preferred embodiment, the controller also performs a system health status assessment. The controller calculates system health status indicators based on vibration characteristics, structural stress characteristics, leakage trends, and seal decay status. When the health status indicators fall below a preset threshold, the controller triggers a protection strategy. The protection strategy includes one or more of derating operation, speed limiting control, pressure limiting control, and protective shutdown control. For example, when a continuous deterioration in seal decay and a significant increase in leakage trends are detected, the controller prioritizes reducing the operating pressure and output power of the compressed air energy storage branch; when a continuous increase in piston rod structural stress characteristics is detected, the controller reduces the piston operating speed; when the overall system health status is detected to be below a safe lower limit, the controller executes a protective shutdown. This improves the long-term operational safety and reliability of the system in the complex environment of abandoned mines.

[0105] In this embodiment, the control method can be summarized as follows: First, multi-source operating signals such as piston displacement, gas storage chamber pressure, gas flow rate, system output power, output torque, structural vibration, and structural stress are collected; second, the multi-source operating signals are processed for time synchronization and a unified state vector is constructed; third, the friction state, leakage state, sealing attenuation state, and coupling hysteresis state are identified online based on the unified state vector; then, the current operating condition is identified based on the grid load demand, system energy storage status, and online identification results; subsequently, based on the current operating condition and online identification results, the power sharing ratio of the gravity energy storage branch and the compressed air energy storage branch is determined hierarchically, and piston operation control quantities, compressor operation control quantities, valve group opening control quantities, and expander output control quantities are generated; subsequently, the gas storage chamber pressure change rate, piston speed change rate, and output torque change rate are jointly constrained during the switching process; finally, when the health status is detected to be lower than a preset threshold, the corresponding protection strategy is executed.

[0106] Figure 4 This invention demonstrates a deep integration of gravity energy storage and compressed air energy storage within the same geographical space and core mechanical structure, compared to traditional compressed air energy storage systems. This optimizes energy storage density per unit space and the overall energy conversion efficiency of the system. The invention clearly demonstrates its breakthrough improvement in a single performance indicator, providing a data benchmark for subsequent comprehensive analysis.

[0107] Figure 5 The capacity and efficiency of existing compressed energy storage systems and gravity / compressed air hybrid energy storage systems were compared. The figures clearly demonstrate the superiority of this invention in long-term operational stability and durability, intuitively reflecting the intrinsic mechanism of extended equipment lifespan.

[0108] Figure 6 The system demonstrates how a multi-objective dynamic optimization algorithm in the intelligent control module dynamically coordinates piston movement, compressor power, and turbine opening, thereby optimizing grid power tracking accuracy, operational economy, and fatigue life of key mechanical components, achieving multi-objective collaborative optimization.

[0109] This invention provides a composite energy storage system and control method utilizing the gravity and compressed air of abandoned mines. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A composite energy storage system utilizing gravity and compressed air from abandoned mines, characterized in that, This includes abandoned mine vertical shafts, giant piston assemblies, compressed air energy storage assemblies, power conversion assemblies, and controllers; The giant piston assembly is installed inside the vertical shaft of the abandoned mine and can reciprocate in the vertical direction; The giant piston assembly includes a counterweight, a piston rod, and a sealing assembly. The giant piston assembly divides the vertical shaft of the abandoned mine into an upper cavity and a lower air storage cavity. The piston rod connects to and supports the counterweight, and the sealing assembly is disposed between the counterweight and the inner wall of the vertical shaft of the abandoned mine. The sealing assembly serves as a physical carrier with dual energy storage functions, realizing the coupled storage and release of gravitational potential energy and compressed air energy. The compressed air energy storage component is connected to the lower air storage chamber. The compressed air energy storage component includes a compressor, an air storage unit, an expander, and a valve group. The compressor is used to compress air into the air storage unit during charging. The expander is used to drive high-pressure air to generate electricity during discharging. A valve group is connected between the expander inlet and the air storage unit. The valve group is used to regulate the gas flow rate and direction to achieve energy storage and release control. The power conversion component is connected to the giant piston assembly and the compressed air energy storage assembly. The power conversion component includes a reversible motor or generator and a power conversion unit. The reversible motor or generator is a bidirectional conversion device between electrical energy and mechanical energy. The power conversion unit is a power conversion and control system that realizes the electrical interface of the power grid, power regulation and protection. The reversible motor or generator and the power conversion unit are electrically connected and together constitute the power conversion component. The controller is electrically connected to the displacement sensor, pressure sensor, flow sensor, power sensor, vibration sensor, and stress sensor, respectively.

2. The system according to claim 1, characterized in that, The controller is used for: Based on the multi-source operating signals collected by the displacement sensor, pressure sensor, flow sensor, power sensor, vibration sensor and stress sensor, a unified state vector of the composite energy storage system is constructed. Based on a unified state vector, the friction state, leakage state, sealing attenuation state, and coupling hysteresis state between the gravity energy storage branch and the compressed air energy storage branch of the composite energy storage system are identified online. The giant piston assembly and related components that cooperate with it to achieve piston lifting and bidirectional conversion of mechanical and electrical energy constitute the gravity energy storage branch. The lower gas storage chamber, the compressed air energy storage assembly, and related components that cooperate with it to achieve gas compression, storage, and expansion energy release constitute the compressed air energy storage branch. Based on the online identification results and the current operating conditions, the gravity energy storage branch and the compressed air energy storage branch are subjected to hierarchical coordinated control to determine the piston operation control quantity, compressor operation control quantity, valve group opening control quantity and expander output control quantity. During the switching between charging and discharging, switching between gravity energy storage branch and compressed air energy storage branch, and switching between operating modes, the pressure change rate of the gas storage chamber, the piston speed change rate, and the output torque change rate of the power conversion component are jointly constrained to suppress system shock and output power fluctuations.

3. The system according to claim 2, characterized in that, The unified state vector includes one or more of the following: piston displacement, piston velocity, gas storage chamber pressure, gas flow rate, system output power, output torque, structural vibration characteristic quantity, and structural stress characteristic quantity.

4. The system according to claim 3, characterized in that, The online identification of the friction state, leakage state, sealing attenuation state, and coupling hysteresis state between the gravity energy storage branch and the compressed air energy storage branch of the composite energy storage system based on the unified state vector includes: Identify the change in piston running resistance based on the dynamic relationship between piston displacement and gas storage chamber pressure; Leakage trends can be identified by the deviation between changes in pressure in the gas storage chamber and changes in gas flow rate. Identify the seal attenuation state based on changes in vibration and stress characteristic quantities; The coupling lag state is identified based on the time deviation between the command response of the gravity energy storage branch and the command response of the compressed air energy storage branch. The coupling lag state is identified based on the deviation between the time it takes for the gravity energy storage branch to reach the preset response amplitude after receiving the control command and the time it takes for the compressed air energy storage branch to reach the preset response amplitude after receiving the control command.

5. The system according to claim 4, characterized in that, The operating conditions include one or more of the following: frequency regulation, peak shaving and valley filling, stable output, standby, and protection. The controller determines the current operating condition based on the grid load demand, system energy storage status, and online identification results.

6. The system according to claim 5, characterized in that, The hierarchical collaborative control includes: Upper-level mode decision-making is used to identify the current operating conditions and determine control objectives; The middle layer power allocation is used to determine the power sharing ratio between the gravity energy storage branch and the compressed air energy storage branch based on the control objectives and the friction state, leakage state, sealing attenuation state and coupling hysteresis state. The lower-level execution control is used to generate piston lifting speed commands, compressor start / stop commands, valve group opening commands, and expander adjustment commands based on the power load ratio.

7. The system according to claim 6, characterized in that, The joint constraints implemented by the controller during the switching process include: Set an upper limit threshold for the rate of change of pressure in the gas storage chamber; Set an upper limit threshold for the rate of change of piston speed; Set an upper limit threshold for the rate of change of output torque of the power conversion component; And when any upper limit threshold is triggered, the power regulation rate of the corresponding branch is reduced.

8. The system according to claim 7, characterized in that, The controller is also used to assess the health status of the system based on vibration characteristics, structural stress characteristics, leakage trends and sealing attenuation status, and to perform derating operation, speed limiting control, pressure limiting control and protective shutdown control when the health status is below a preset threshold.

9. A control method for the system as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Step S1: Collect multi-source operating signals including piston displacement, gas storage chamber pressure, gas flow rate, system output power, output torque, structural vibration, and structural stress; Step S2: Perform time synchronization processing on the multi-source operating signals and construct a unified state vector for the system, represented as: ， in, For a moment The unified state vector of the system; For a moment Piston displacement; For a moment Piston speed; For a moment Gas storage chamber pressure; For a moment Gas flow rate; For a moment System output power; For a moment Output torque; For a moment Structural vibration characteristic quantities; For a moment Structural stress characteristic quantity; T represents transpose; Step S3: Based on the unified state vector, identify online the friction state, leakage state, sealing attenuation state, and coupling hysteresis state between the gravity energy storage branch and the compressed air energy storage branch of the composite energy storage system. Step S4: Identify the current operating conditions based on grid load demand, system energy storage status, and online identification results; Step S5: Based on the current operating conditions and online identification results, determine the power bearing ratio of the gravity energy storage branch and the compressed air energy storage branch in layers, and generate piston operation control quantity, compressor operation control quantity, valve group opening control quantity and expander output control quantity. Step S6: During the switching between charging and discharging, switching between gravity energy storage branch and compressed air energy storage branch, and switching between operating modes, the pressure change rate of the gas storage chamber, the piston speed change rate, and the output torque change rate are jointly constrained to suppress system impact and output power fluctuation. Step S7: When the detected health status is lower than the preset threshold, perform derated operation, speed limit control, pressure limit control and protection shutdown control.

10. The method according to claim 9, characterized in that, In step S3, the online identification of the leakage status includes: determining the leakage trend parameter based on the deviation between the actual pressure change in the gas storage chamber and the theoretical pressure change calculated based on the gas flow rate, expressed as: ， in, For a moment Leakage trend parameters; The time interval between adjacent sampling times; The theoretical pressure value at the next moment is calculated based on the gas flow rate and the equilibrium model. This represents the actual measured pressure value of the gas storage chamber at the next moment; The controller identifies the piston's running resistance based on the piston's kinematic state and the pressure states in the upper and lower chambers. The equivalent running resistance of the piston is expressed as: ， in, Let k be the equivalent running resistance of the piston at time k; The total mass of the giant piston assembly and its counterweight; This refers to piston acceleration; and These are the pressure in the upper chamber of the piston and the pressure in the lower gas storage chamber, respectively. This represents the effective pressure-bearing area of ​​the piston. It is the acceleration due to gravity; The controller identifies the dual-branch coupled hysteresis state, and the coupling hysteresis parameter is expressed as: ， in, This is the lag time for the two-branch coupling; This refers to the time required for the compressed air energy storage branch to reach the preset response amplitude after receiving a control command. This refers to the time it takes for the gravity energy storage branch to reach the preset response amplitude after receiving a control command; In step S5, the controller performs hierarchical power allocation for the gravity energy storage branch and the compressed air energy storage branch based on the system's target output power and the online identification results. The power allocation for the two branches is expressed as follows: ， ， in, Let k be the power supplied by the gravity energy storage branch at time k. The power supplied by the compressed air energy storage branch at time k; The target output power of the system; The coefficients are dynamically allocated and satisfy the following conditions: ; Dynamic allocation coefficient The calculation formula is: ， in, The energy storage state of the compressed air energy storage branch; The energy storage state of the gravity energy storage branch; For the preset allocation function; In step S6, the joint constraint includes: the switching shock suppression constraint is expressed as: ， in, Threshold for the rate of change of pressure in the gas storage chamber; The threshold for the rate of change of piston speed; The threshold value for the rate of change of output torque is given by d, which represents the derivative. when , or When any parameter reaches its corresponding upper limit threshold, the controller reduces the power regulation rate of the corresponding branch and delays the power increase or decrease action of the other branch to achieve a smooth transition during the switching process.

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