Load shedding anti-overspeed control method during power grid decoupling of compressed air energy storage system

Abstract

The invention relates to the technical field of power grids, in particular to a load shedding anti-overspeed control method during power grid decoupling of a compressed air energy storage system. Acquiring rotating speed data of the compressed air energy storage system when the power grid is decoupled, and monitoring the rotating speed data; a load shedding mode is preset, and block valves and exhaust valves at the front ends of all stages of expansion machines are controlled; and executing a load shedding mode according to the change of the rotating speed data, and controlling the rotating speed of the system to be reduced to a preset range. The load shedding mode is divided into two stages, wherein in the first load shedding stage, rotating speed control is conducted by closing block valves at the front ends of all stages of expansion machines; and in the second load shedding stage, the residual working medium is discharged by opening the exhaust valve. A system standby recovery strategy is established, and stable transition of the system from an emergency state to a normal operation state is realized. According to the method, the problems of inaccurate rotating speed control, insufficient residual working medium treatment and the like during power grid decoupling of the CAES system in the prior art are effectively solved, and the operation safety and reliability of the system are improved.

Description

Technical Field

[0001] The invention relates to the technical field of power grids, and in particular to a load shedding and overspeed prevention control method when a compressed air energy storage system power grid is decoupled. Background Art

[0002] With the vigorous development of new energy, the scale of power generation represented by wind and solar power is constantly expanding. However, the biggest problem of wind and solar power generation is its unstable energy output and lack of inertial support, which brings huge challenges to the grid connection of clean electricity. Among many solutions, Compressed Air Energy Storage (CAES) has become an important energy storage method due to its large capacity, clean and low-carbon characteristics.

[0003] Existing CAES system research mainly focuses on active and reactive power regulation. For example, some studies have proposed replacing traditional throttle valves with combined valves and combining pressure reducing vessels to form a pressure control unit to improve the dynamic characteristics of the system; there are also studies based on variable domain fuzzy adaptive PI control strategies to cope with frequency fluctuations by adjusting the domain range. However, most of these studies focus on the normal operating status of the system, and there is a relative lack of research on emergency response, especially in terms of grid decoupling, black start and grid switching accident control.

[0004] When CAES is operating under rated conditions, if there is a sharp change or decoupling of the load on the grid side, the output power and load will lose balance, causing the speed to soar. At this time, emergency load shedding is required. The traditional load shedding control strategy has the following problems:

[0005] The existing control scheme mainly focuses on the speed control at a single moment, and fails to fully consider the speed control requirements at two key stages: the decoupling moment and the system recovery stage.

[0006] Traditional speed control strategies only focus on isolating the expander, ignoring the impact of residual high-temperature and high-pressure air in the system's internal pipelines and heat exchangers. These residual working fluids can cause the generator speed to soar again;

[0007] The existing technology lacks systematic research on the system response characteristics under different load conditions, and it is difficult to ensure good control effects under various conditions.

[0008] Therefore, it is urgent to propose a new compressed air energy storage load shedding and anti-overspeed control method to solve the above technical problems and ensure the safe operation of the CAES system in emergencies such as grid decoupling. Summary of the invention

[0009] In view of the problems existing in the prior art, the inventor proposed the present invention.

[0010] Therefore, the problem to be solved by the present invention is how to solve the problem that when the CAES is running under rated conditions, if there is a sharp change or decoupling of the grid side load, the output power and load lose balance, resulting in a surge in speed. At this time, emergency load shedding is required. The traditional load shedding control strategy has the following problems:

[0011] The existing control scheme mainly focuses on the speed control at a single moment, and fails to fully consider the speed control requirements at two key stages: the decoupling moment and the system recovery stage.

[0012] Traditional speed control strategies only focus on isolating the expander, ignoring the impact of residual high-temperature and high-pressure air in the system's internal pipelines and heat exchangers. These residual working fluids can cause the generator speed to soar again;

[0013] The existing technology lacks systematic research on the system response characteristics under different load conditions, making it difficult to ensure good control effects under various conditions.

[0014] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0015] In a first aspect, an embodiment of the present invention provides a load shedding and overspeed prevention control method for a compressed air energy storage system when the grid is decoupled, comprising: obtaining speed data of the compressed air energy storage system when the grid is decoupled, and monitoring the speed data;

[0016] Preset load rejection mode, including control of the cut-off valve and exhaust valve at the front end of each stage of expander;

[0017] According to the change of the rotational speed data, the load shedding mode is executed to control the rotational speed of the system to fall within a preset range.

[0018] As a preferred scheme of the load shedding and anti-overspeed control method when the compressed air energy storage system grid is decoupled according to the present invention, the load shedding mode includes: in the first load shedding stage, the speed is controlled by closing the shut-off valves at the front end of each stage of the expander; in the second load shedding stage, the residual working fluid is discharged by opening the exhaust valve.

[0019] As a preferred solution of the load shedding and anti-overspeed control method during grid decoupling of the compressed air energy storage system described in the present invention, the first load shedding stage includes: detecting whether the system speed exceeds a preset threshold; when the system speed exceeds the preset threshold, closing the shut-off valves at the front end of each stage of the expander step by step in a preset order until the speed drops below 3000r / min.

[0020] As a preferred scheme of the load shedding and anti-overspeed control method during grid decoupling of the compressed air energy storage system described in the present invention, the second load shedding stage includes: determining whether there is residual working fluid in the pipelines and heat exchangers in the system; when there is residual working fluid, opening the exhaust valve to discharge the high-temperature and high-pressure air remaining in the system.

[0021] As a preferred solution of the load shedding and anti-overspeed control method during grid decoupling of the compressed air energy storage system described in the present invention, the execution of the load shedding mode includes: real-time monitoring of speed changes; when the speed drops below 3000r / min, locking the load shedding control system and maintaining the rotor speed through the speed regulating valve.

[0022] As a preferred solution of the load shedding and anti-overspeed control method during grid decoupling of the compressed air energy storage system described in the present invention, it also includes: evaluating the speed control effect of the system under different load conditions; and optimizing the execution strategy of the load shedding mode based on the evaluation results.

[0023] As a preferred solution of the load shedding and overspeed prevention control method during grid decoupling of the compressed air energy storage system described in the present invention, the load conditions include 100% load condition, 75% load condition and 50% load condition.

[0024] As a preferred scheme of the load shedding and anti-overspeed control method when the compressed air energy storage system grid is decoupled according to the present invention, the execution of the load shedding mode also includes: monitoring the working fluid parameters in the front end area of ​​each stage of the expander; adjusting the action timing of the shut-off valve and the exhaust valve according to the changes in the working fluid parameters.

[0025] As a preferred scheme of the load shedding and anti-overspeed control method when the compressed air energy storage system grid is decoupled according to the present invention, before executing the load shedding mode, it also includes: establishing a system recovery standby strategy; when the system needs to resume operation, control is performed according to the recovery standby strategy.

[0026] As a preferred solution of the load shedding and anti-overspeed control method during grid decoupling of the compressed air energy storage system described in the present invention, the load shedding mode also includes: real-time monitoring of the pressure and temperature of the residual working fluid in each area inside the system; and determining the opening timing and opening degree of the exhaust valve based on the monitoring results.

[0027] In a second aspect, an embodiment of the present invention provides a computer device, including a memory and a processor, wherein the memory stores a computer program, wherein: when the computer program instructions are executed by the processor, the steps of the load shedding and anti-overspeed control method when the compressed air energy storage system is decoupled from the power grid are implemented as described in the first aspect of the present invention.

[0028] In a third aspect, an embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein: when the computer program instructions are executed by a processor, the steps of the load shedding and anti-overspeed control method when the compressed air energy storage system is decoupled from the power grid are implemented as described in the first aspect of the present invention.

[0029] The beneficial effects of the present invention are as follows: by acquiring speed data and performing monitoring when the power grid is decoupled, comprehensive monitoring and prediction of the speed surge process are achieved for the first time, overcoming the defect of the prior art of only passively responding after the speed exceeds the limit, and improving the system's early warning capability.

[0030] The load shedding process is divided into a two-stage control strategy. In the first stage, the speed is controlled by closing the shut-off valves at the front end of each stage of the expander, and in the second stage, the residual working fluid is discharged by opening the exhaust valve. This solves the problem of the prior art of only focusing on speed control at a single moment and ignoring the system recovery stage, and effectively prevents the secondary speed surge caused by residual working fluid.

[0031] By evaluating and optimizing the speed control effect of the system under different load conditions, the adaptive adjustment of the control strategy is achieved, overcoming the problem of unstable control effect caused by fixed control parameters in the existing technology. Practical application shows that the new strategy can significantly reduce the maximum speed and shorten the system recovery time compared with the traditional strategy.

[0032] By establishing a system recovery standby strategy, a smooth transition from emergency state to normal operation is achieved, and the system's safety protection mechanism is improved. Combined with real-time monitoring of working fluid parameters in the front-end area of ​​each level of expander, the action sequence of the cut-off valve and exhaust valve is dynamically adjusted to ensure the controllability and safety of the system in emergency situations. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 A flow chart of a load shedding and overspeed prevention control method when a compressed air energy storage system is decoupled from the power grid;

[0035] Figure 2 A computer equipment diagram of a load shedding and overspeed prevention control method for a compressed air energy storage system when the power grid is decoupled;

[0036] Figure 3 A schematic diagram of a thermal model of a load shedding and overspeed prevention control method when a compressed air energy storage system is decoupled from the power grid;

[0037] Figure 4 A schematic diagram of the speed climbing process of the load shedding and overspeed prevention control method when the compressed air energy storage system is decoupled from the power grid;

[0038] Figure 5 A schematic diagram of a grid module for a load shedding and overspeed prevention control method when a compressed air energy storage system is decoupled from the grid;

[0039] Figure 6 A schematic diagram of the pressure and temperature variation curve of the gas storage tank of the load shedding and overspeed prevention control method when the compressed air energy storage system is decoupled from the power grid;

[0040] Figure 7 A schematic diagram of the power ramp-up process of the load shedding and overspeed prevention control method when the compressed air energy storage system is decoupled from the power grid;

[0041] Figure 8 It is a line chart of the pressure before each level of expander of the load rejection and overspeed prevention control method when the compressed air energy storage system is decoupled from the power grid;

[0042] Fig. 9 It is a line chart of the output power of expanders at each level of the load rejection and overspeed prevention control method when the compressed air energy storage system is decoupled from the power grid;

[0043] Fig.10 It is a load variation line chart of the load shedding and overspeed prevention control method when the compressed air energy storage system is decoupled from the power grid;

[0044] Fig.11 It is a temperature variation curve diagram under rated working conditions of the load rejection and overspeed prevention control method when the compressed air energy storage system is decoupled from the power grid;

[0045] Fig.12 A comparison diagram of the effect of the cut-off valve action position on the load shedding and overspeed prevention control method during grid decoupling of a compressed air energy storage system;

[0046] Fig.13 This is a comparison chart of the effects of different load shedding actions on speed increase suppression of the load shedding and overspeed prevention control methods during grid decoupling of the compressed air energy storage system;

[0047] Fig.14 It is a comparison diagram of the parameters of the front area of ​​the cut-off valve after the action of different cut-off valves under the 100% load condition of the load rejection and overspeed prevention control method when the compressed air energy storage system is decoupled from the power grid;

[0048] Fig.15 It is a curve diagram showing the influence of residual gas on system speed recovery in the load shedding and overspeed prevention control method when the compressed air energy storage system is decoupled from the power grid;

[0049] Fig.16It is a schematic diagram of the optimized load shedding action operation logic of the load shedding and overspeed prevention control method when the compressed air energy storage system is decoupled from the power grid;

[0050] Fig.17 A schematic diagram of a load shedding regulation system for each valve in a load shedding and overspeed prevention control method when a compressed air energy storage system is decoupled from the power grid;

[0051] Fig.18 A schematic diagram of the system state when the new strategy of the load shedding and overspeed prevention control method during grid decoupling of the compressed air energy storage system is in action;

[0052] Fig.19 This is a comparison chart of the speed control effects of the traditional strategy and the new strategy of the load shedding and anti-overspeed control method under different working conditions when the compressed air energy storage system is decoupled from the power grid. DETAILED DESCRIPTION

[0053] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0054] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0055] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0056] Example 1

[0057] Reference Figure 1-2 , which is the first embodiment of the present invention, provides a load shedding and overspeed prevention control method when the compressed air energy storage system is decoupled from the power grid, comprising:

[0058] S100: acquiring rotation speed data of the compressed air energy storage system when the grid is decoupled, and monitoring the rotation speed data;

[0059] In the embodiment of the present application, the speed data includes the following parts: real-time system speed value, speed change rate, speed over-limit alarm signal and grid-side circuit breaker status signal. These data are mainly collected in real time by sensors installed at key points of the compressed air energy storage system.

[0060] Specifically, the real-time speed value is collected by the speed sensor installed on the generator shaft; the speed change rate is obtained by calculating the change in speed per unit time; the speed over-limit alarm signal is a Boolean signal generated based on the preset speed threshold; the grid-side circuit breaker status signal is used to determine the connection status between the system and the power grid.

[0061] In an optional embodiment, the acquisition frequency of the speed data can be adjusted according to the response characteristics of the system. For example, a lower sampling frequency (such as 100 Hz) can be used during normal operation, and after detecting the grid decoupling signal, it automatically switches to a high-frequency sampling mode (such as 1 kHz) to obtain more accurate speed change information. This adaptive sampling strategy can reduce the burden of data storage and processing while ensuring the monitoring effect.

[0062] In an optional embodiment, in order to improve the reliability of data, redundant sensors can be configured at key locations. For example, photoelectric sensors and Hall sensors can be used simultaneously when measuring rotation speed, and the advantages of the two sensors can be combined through a data fusion algorithm to improve the accuracy and reliability of the measurement.

[0063] In an optional embodiment, the speed monitoring may also include a data preprocessing step, such as filtering and denoising the raw data. Specifically, a low-pass filter may be used to eliminate high-frequency noise, or a median filter may be used to remove mutation points to obtain a more stable speed signal.

[0064] It should be noted that this step realizes real-time monitoring of the system operation status and provides the necessary data basis for subsequent load shedding control. Through multi-dimensional data collection and preprocessing, the system can promptly detect and respond to abnormal situations, ensuring the timeliness and accuracy of control.

[0065] S101: The load shedding mode includes: a first load shedding stage, in which the speed is controlled by closing the shut-off valves at the front ends of the expanders at each stage; and a second load shedding stage, in which the residual working fluid is discharged by opening the exhaust valve.

[0066] S102: The first load shedding stage includes: detecting whether the system speed exceeds a preset threshold; when the system speed exceeds the preset threshold, closing the shut-off valves at the front end of each stage of the expander step by step in a preset order until the speed drops below 3000r / min.

[0067] S103: The second load shedding stage includes: determining whether there is residual working fluid in the pipelines and heat exchangers in the system; when there is residual working fluid, opening the exhaust valve to discharge the high-temperature and high-pressure air remaining in the system.

[0068] S200: preset load rejection mode, including control of the cut-off valve and exhaust valve at the front end of each stage of expander;

[0069] In the embodiment of the present application, the load shedding mode mainly includes two stages: the first load shedding stage and the second load shedding stage. In the first load shedding stage, the speed is quickly controlled by controlling the cut-off valves at the front end of each stage of the expander; and in the second load shedding stage, the residual working fluid in the system is processed by controlling the exhaust valve.

[0070] Specifically, the first load-shedding stage adopts the strategy of "quick cut-off + step-by-step closing": first, by quickly closing the shut-off valves at the front end of all expanders, the supply of high-pressure working fluid is cut off to achieve emergency braking of the speed increase; then, according to the change in speed, the opening of the shut-off valves at each level is adjusted step by step in a preset order to steadily reduce the system speed to a safe range.

[0071] The second load-shedding stage adopts the strategy of "zoned discharge + pressure balance": first identify the areas with more residual working fluid in the system; then gradually open the exhaust valves in the corresponding areas in a preset order to allow the residual working fluid to be discharged in an orderly manner; finally, achieve system balance by adjusting the pressure in each area.

[0072] In an optional embodiment, different control parameters can be set according to different load conditions (such as 100%, 75%, 50%). For example, under high load conditions, due to the large system inertia, a more aggressive valve control strategy can be adopted; while under low load conditions, a relatively mild control strategy can be adopted.

[0073] It should be noted that the design of the load shedding mode needs to comprehensively consider multiple factors such as system safety, response speed and control accuracy. By reasonably configuring the parameters of each control link, the optimal control effect can be achieved while ensuring system safety.

[0074] S201: The execution of the load rejection mode includes: real-time monitoring of the speed change; when the speed drops below 3000r / min, locking the load rejection control system and maintaining the rotor speed through the speed regulating valve.

[0075] In the embodiment of the present application, the first load shedding stage and the second load shedding stage are two main control stages performed in a time sequence. The system first performs the first load shedding stage to achieve rapid control of the speed, and then enters the second load shedding stage to deal with the residual working fluid problem.

[0076] Specifically, the execution process of the first load shedding stage is as follows:

[0077] When the system detects an abnormal increase in speed or a grid decoupling signal, it immediately triggers the first load shedding stage; the control system simultaneously sends a closing command to the shut-off valves at the front end of each level of expanders; the shut-off valves complete the closing action within 0.1s after receiving the command; the system continuously monitors the speed changes until the speed starts to drop.

[0078] In an optional embodiment, the closing sequence of the cut-off valves in the first load shedding stage may adopt different strategies:

[0079] Synchronous closing strategy: all shut-off valves are closed at the same time, which is suitable for situations where the working fluid supply needs to be cut off urgently; step-by-step closing strategy: closing in sequence from high pressure to low pressure can reduce the impact on the system; group closing strategy: divide the shut-off valves into several groups and close them simultaneously to balance the response speed and system impact.

[0080] The execution process of the second load shedding stage includes:

[0081] The second load shedding stage is triggered after the system speed drops to a safe range; the control system identifies the distribution of the residual working fluid through the pressure sensor; the opening sequence of the exhaust valve is determined according to the pressure distribution; the exhaust valve opening is controlled according to the preset strategy to achieve orderly discharge of the residual working fluid.

[0082] It should be noted that the timing of switching between the two stages is very critical. Entering the second stage too early may lead to insufficient speed control, while switching too late will prolong the system recovery time. Therefore, the system sets dual trigger conditions based on speed and pressure. The second stage will only be entered when the following conditions are met at the same time: the system speed drops below 3000r / min; the speed change rate is less than the preset threshold; the residual pressure in the system exceeds the preset value.

[0083] In an optional embodiment, in order to cope with possible special situations, the system is also equipped with an emergency switching mechanism. When the following situations are detected, the second load shedding stage can be triggered in advance: abnormal pressure increase in a certain area; failure of the cut-off valve; system vibration exceeds the limit.

[0084] S202: Also includes: evaluating the speed control effect of the system under different load conditions; and optimizing the execution strategy of the load shedding mode according to the evaluation results.

[0085] In the embodiment of the present application, the detection and control of the system speed is a real-time closed-loop process. The control system samples the speed value every 1ms and compares it with the preset multi-level thresholds, and takes corresponding control measures according to the degree of over-limit.

[0086] Specifically, the preset thresholds are divided into three levels: Level 1 warning threshold: 3100r / min, triggering a software alarm signal; Level 2 warning threshold: 3200r / min, initiating preventive control measures; Emergency threshold: 3300r / min, triggering an emergency cut-off action.

[0087] The preset shutdown sequence is determined based on system characteristics and simulation analysis, and mainly considers the following factors: pressure level of each stage of expanders; working fluid flow distribution; energy conversion efficiency; and dynamic response characteristics of the system.

[0088] In an optional embodiment, the closing sequence can be dynamically adjusted according to the operating conditions: under 100% load conditions, the high-pressure stage shut-off valve is closed first; under 75% load conditions, the stage-by-stage closing strategy is adopted; under 50% load conditions, closing starts from the low-pressure stage.

[0089] It should be noted that the closing action of each level of shut-off valve is not a simple switch operation, but involves complex flow and pressure control logic: pressure balance calculation before closing; control of the valve closing rate to avoid pressure shock; real-time monitoring of pressure fluctuations during the closing process; and adjustment of the action timing of subsequent valves according to pressure changes.

[0090] S203: The load conditions include a 100% load condition, a 75% load condition and a 50% load condition.

[0091] In the embodiment of the present application, the processing of residual working fluid involves the pressure and temperature monitoring inside the system. By arranging pressure and temperature sensors at key areas such as the front end of the first-stage expander, the front end of the second-stage expander, the front end of the third-stage expander, and the front end of the fourth-stage expander, a comprehensive monitoring of the state of the residual working fluid is achieved. When the pressure in any area is monitored to exceed 0.5MPa or the temperature exceeds 50°C, the system determines that there is residual working fluid in the area that needs to be processed.

[0092] In an optional embodiment, the discharge process of the residual working fluid can be controlled in stages. First, the area with the highest pressure is discharged, and the flow rate is smoothly changed by controlling the opening of the exhaust valve to avoid violent vibration of the system due to excessive exhaust speed. When the pressure in this area drops to a safe level, the residual working fluid in other areas is processed in turn. In addition, during the exhaust process, the system will monitor the temperature changes of the pipeline in real time to prevent local overheating due to heat accumulation.

[0093] It should be noted that the treatment of residual working fluid is crucial to the safe operation of the system. If the residual working fluid cannot be discharged in a timely and effective manner, the speed may soar again when the system resumes operation. Therefore, the system sets strict criteria for the completion of residual working fluid treatment: the pressure of each monitoring area must drop below 0.3MPa, the temperature must drop below 40℃, and remain stable for more than 10 seconds before the residual working fluid treatment is considered complete.

[0094] S204: The execution of the load rejection mode further includes: monitoring the working fluid parameters of the front end area of ​​each level of expanders; and adjusting the action timing of the shut-off valve and the exhaust valve according to the change of the working fluid parameters.

[0095] In the embodiment of the present application, the monitoring of working fluid parameters mainly includes key physical quantities such as pressure, temperature, and flow rate. In order to achieve accurate monitoring, multiple sensors are arranged in the front end area of ​​each level of expander: the pressure sensor is used to monitor the change of working fluid pressure, with a range of 0-10MPa; the temperature sensor monitors the working fluid temperature, with a measurement range of 0-200℃; the flow sensor monitors the working fluid flow rate in real time, with a measurement range of 0-100kg / s.

[0096] In an optional embodiment, the valve action sequence is adjusted using an adaptive control strategy. When the working fluid pressure changes rapidly, the system will correspondingly speed up the closing speed of the shutoff valve; when an abnormal temperature rise is detected in a certain area, the exhaust valve in that area will be opened first to cool it down. This control method based on real-time feedback of working fluid parameters can effectively deal with various abnormal situations in system operation.

[0097] It should be noted that the accuracy of working fluid parameter monitoring directly affects the control effect. The system uses data verification and fault diagnosis algorithms to identify and eliminate abnormal data by comparing the parameter change trends of adjacent measuring points. At the same time, redundant measurement methods are used for important parameters to improve the reliability of monitoring. These measures together ensure that the control system can make correct control decisions based on accurate working fluid parameter information.

[0098] S205: Before executing the load shedding mode, the method further includes: establishing a system recovery standby strategy; and performing control according to the recovery standby strategy when the system needs to resume operation.

[0099] In the embodiment of the present application, the system recovery standby strategy mainly considers three key factors: speed state, working fluid state and system temperature. After the speed drops below 3000r / min and runs stably for 10 seconds, the system begins to evaluate whether the conditions for resuming operation are met. Specifically, it includes: checking whether the residual working fluid in each area is completely discharged, whether the system temperature returns to the normal range, and whether the status of key equipment is normal.

[0100] In an optional embodiment, the system recovery process adopts a step-by-step startup method. First, the equipment status self-check is performed to confirm that all monitoring and control components are working normally; then the shut-off valves are opened step by step to slowly restore the working fluid supply; finally, the load is gradually increased according to the system response. During the entire recovery process, the system closely monitors the speed changes and immediately initiates protection measures if an abnormality occurs.

[0101] It should be noted that the design of the system recovery standby strategy must fully consider safety. Strict inspection conditions are set for each recovery step, and the next step can only be entered after the previous step is completely stable. At the same time, the system also has multiple protection mechanisms. If any abnormality is found during the recovery process, it can immediately switch to a safe state to ensure the reliability of the system recovery process.

[0102] S300: Executing the load shedding mode according to the change of the rotational speed data, and controlling the rotational speed of the system to drop to a preset range.

[0103] In the embodiment of the present application, the execution of the load shedding mode is a dynamic adjustment process, and the system adaptively adjusts the control parameters according to the speed data collected in real time. When the speed exceeds 3000r / min, the control system first activates the first load shedding stage, and suppresses the speed increase by closing the cut-off valves at the front end of each level of expander. When the speed starts to decrease, the system dynamically adjusts the control strategy according to the speed change rate to ensure that the speed can be smoothly reduced to a safe range.

[0104] In an optional embodiment, the system adopts an adaptive adjustment mechanism based on fuzzy control. According to the two key parameters of speed deviation and speed change rate, the correction value of the control amount is calculated in real time. When the speed deviation is large, the system adopts a larger control amount to speed up the response speed; when the speed is close to the target value, a smaller control amount is adopted to avoid over-adjustment. Through this adaptive adjustment mechanism, good control effects can be achieved under different working conditions.

[0105] It should be noted that the speed control process needs to balance the response speed and system stability. Overly aggressive control may cause system oscillation, while overly conservative control will prolong the adjustment time. Therefore, when the system executes the load shedding mode, it will comprehensively consider multiple factors such as the speed overlimit degree and load conditions, and select the most suitable control parameters to ensure the control effect while avoiding additional impact on the equipment.

[0106] S301: The load shedding mode further includes: real-time monitoring of the pressure and temperature of the residual working fluid in each area within the system; and determining the opening timing and opening degree of the exhaust valve according to the monitoring results.

[0107] In the embodiment of the present application, the system manages the residual working fluid by means of partition monitoring. Each area is equipped with a high-precision pressure sensor and temperature sensor with a sampling frequency of 100Hz to ensure that the slight changes in the working fluid state can be captured in time. The measurement data of the sensor is processed by digital filtering and input into the control system for analysis and processing.

[0108] In an optional embodiment, the exhaust valve is controlled using a dynamic opening adjustment strategy. The system first evaluates the state of the residual working fluid in each area and calculates the optimal discharge order. For areas with higher pressure, the discharge is carried out by starting with a small opening and gradually increasing the opening to avoid pressure shock caused by instantaneous discharge. When the pressure drops to a certain level, the opening is gradually increased to speed up the discharge. During the entire discharge process, the system will continuously monitor pipeline vibration and temperature changes, and make adjustments immediately if any abnormality is found.

[0109] It should be noted that accurate residual fluid monitoring is crucial to achieve precise control. The system calculates the actual state of the residual fluid based on the measured values ​​of pressure and temperature by establishing a thermodynamic model, providing a basis for the control of the exhaust valve. In addition, the system also implements a fault diagnosis function. When abnormal sensor data is found, it will automatically switch to the backup sensor to ensure the reliability of the monitoring data.

[0110] In summary, by acquiring speed data and monitoring it in real time when the power grid is decoupled, all-round monitoring of the system operation status is achieved, avoiding the one-sided monitoring of the speed at a single moment in the traditional scheme, thereby ensuring the system's rapid response capability in emergencies, and ultimately significantly improving the system's safety and reliability. By dividing the load shedding process into a two-stage control strategy, the step-by-step adjustment of speed control and residual working fluid treatment is achieved, overcoming the limitation of focusing on a single control target in the traditional scheme, and ultimately achieving comprehensive regulation of the system state, effectively preventing the secondary speed surge caused by residual working fluid. By adopting the method of closing the shut-off valve step by step in the first load shedding stage, the impact caused by the simple synchronous closing of all valves in the traditional scheme is avoided, and a smooth transition of the system pressure is achieved, ultimately ensuring the service life of the equipment. By identifying and discharging the residual working fluid in the system in a partitioned manner and discharging it in an orderly manner in the second load shedding stage, the deficiency of the traditional scheme that ignores the influence of residual working fluid is overcome, and the precise control of the internal state of the system is achieved, ultimately improving the reliability of the system's recovery operation. By establishing a load rejection control strategy based on multiple working conditions, the problem of the traditional solution's lack of adaptability to working conditions is solved, and optimal control under different load conditions is achieved, ultimately improving the practicality and scope of application of the control solution. By real-time monitoring and dynamic adjustment of the working fluid parameters in the front-end area of ​​each level of expanders, the limitations of fixed control parameters in the traditional solution are overcome, and adaptive optimization of the control strategy is achieved, ultimately improving the control accuracy and response speed of the system. By establishing a complete system recovery standby strategy, the lack of systematic consideration of the system recovery process in the traditional solution is compensated, and a smooth transition from emergency state to normal operation of the system is achieved, ultimately ensuring the continuity and stability of the system operation.

[0111] Example 2

[0112] Reference Figure 2 - Fig.19 , which is the second embodiment of the present invention, provides a load shedding and overspeed prevention control method when the compressed air energy storage system is decoupled from the power grid.

[0113] Model establishment: This paper studies the load shedding and overspeed prevention actions of the unit itself in response to the adjustment when the CAES system is suddenly disconnected from the power grid and the unit load suddenly drops to 0. Based on this research purpose, a 10MW CAES system energy release process model was established. In order to reduce the complexity of the model, the following assumptions were made during the modeling process: the flow of the working fluid and the working process in the system are both adiabatic processes; the valve action is completed within 0.1s.

[0114] Mathematical model: This article is based on the modular simulation software Apros, and the modules contained in it are the basis for establishing a simulation system. The following is the mathematical model of the main application modules of the model:

[0115] Gas tank: Mass changes in the gas tank:

[0116]

[0117] Where ρ is the air density in the air storage room; m in is the inflow flow; m out is the outflow rate; V is the volume of the gas tank.

[0118] Under constant volume conditions, the energy conservation equation in the gas tank is:

[0119]

[0120] Where, m is the mass of gas; h in and h out is the enthalpy of the inflowing and outflowing gases; h ac is the heat transfer efficiency between gas and gas storage wall; A c is the wall area of ​​the air storage chamber; T and T ac are the air temperature and wall temperature in the air storage chamber respectively.

[0121] The temperature and pressure of the gas in the gas tank change with time:

[0122]

[0123] Where p is the gas pressure in the gas tank; R g is the gas constant of air; V is the volume of the gas tank, m3; c p is the specific heat capacity of air at constant pressure; T ac is the gas temperature in the tank; t is the power generation time; M u is the mass of gas in the tank, kg; k is the air compression index; c v is the specific heat capacity of air at constant volume; h a is the convection heat transfer coefficient in the gas tank; A is the inner surface area of ​​the gas tank; T a is the gas tank wall temperature.

[0124] Expander: The work done by the expander can be calculated by the following formula:

[0125] θ=m(h q -h2)

[0126] Where θ is the power of the expander and m is the mass flow rate of air through the expander.

[0127] The mechanical power generated by the expander can be calculated from the mass flow rate and enthalpy drop of the expander:

[0128] P mek =∑(mΔh)

[0129] Among them, P mekis the mechanical work of the expander.

[0130] Thermal storage tank: During the energy release process, the fluid in the thermal storage tank complies with the law of energy conservation and conforms to the following formula:

[0131]

[0132] Wherein, the subscript HTF is the heat transfer and heat storage medium; i is the number of heat exchanger stages; is the heat transfer medium flow rate of the i-stage heat exchanger; is the inlet temperature of the heat transfer medium of the i-stage heat exchanger; q is the heat loss flow of the heat storage tank wall; T; T hs is the temperature of the thermal storage tank wall

[0133] Synchronous rotor

[0134] The moment of inertia of the rotor has a great influence on the dynamic response and regulation of the system:

[0135]

[0136] Where: J is the moment of inertia; w is the shaft speed, t t ,t c and t1 are expander output torque, compressor input torque and load absorption torque respectively

[0137] The boundary conditions of the model and the rated operating parameters of the expander refer to the actual engineering case: the parameters of the 10MWAACAES system in Bijie, Guizhou, China. The boundary conditions are shown in Table 1:

[0138] Table 1 Boundary conditions

[0139] parameter unit Numeric Energy release power MW 10 Energy release pressure MPa 7 Gas tank pressure MPa 10 Gas tank capacity m3 6000 Backpressure MPa 0.1 Ambient temperature K 298 Energy release time (10MW) s 6550 Thermal storage tank temperature K 393 Thermal storage tank pressure MPa 0.2 Cold storage tank temperature K 298 Cold storage tank pressure MPa 0.1

[0140] Table 2 Rated operation design parameters of each level expander

[0141] <![CDATA[p i ]]> <![CDATA[p o ]]> <![CDATA[T I ]]> <![CDATA[T o ]]> <![CDATA[R e ]]> <![CDATA[e i ]]> <![CDATA[F m ]]> <![CDATA[P o ]]> n unit bar bar ℃ ℃ ％ kg / s MW r / min 1 69.92 25.25 84.64 44.51 2.7691 0.88 32 2.70884 3000 2 24.51 8.75 85.10 43.22 2.8011 0.88 32 2.67396 3000 3 8.57 3.12 85.02 42.86 2.7468 0.88 32 2.42832 3000 4 2.87 0.97 84.96 35.75 2.9588 0.88 32 2.45564 3000

[0142] In the table, p i and p o are inlet pressure and outlet pressure respectively; T I and T o are the inlet temperature and outlet temperature respectively; R e is the expansion ratio; e i is the isentropic efficiency; F m is the mass flow rate; P o is the output power; n is the speed.

[0143] Table 3 Design parameters of heat exchanger under rated working condition

[0144]

[0145]

[0146] In the table, T Hi and T Ho are the inlet and outlet hot water temperatures, respectively; T Ai and T Ao are the inlet air temperature and outlet air temperature respectively; V A is the volume of air in the heat exchanger.

[0147] Model Validation

[0148] This paper simulates the energy release stage model of a 10MW CAES system. Figure 3 As shown, a shutoff valve is installed in front of the air inlet of each stage expander, and an exhaust valve is installed in the front area of ​​the shutoff valve. In addition, the system is equipped with corresponding temperature, speed, power and load rejection adjustment systems, all of which use PID speed regulators as control modules.

[0149] Speed ​​control model

[0150] The speed control system adopts a "slow landing" control strategy: before the actual speed reaches 2900r / min, the real-time target speed is set to 100r / min per minute. After the speed reaches 2900r / min, the real-time target speed is obtained by the following formula:

[0151] v = K2 × (3000-n)

[0152] Where K2 is the acceleration coefficient and n is the actual generator speed, which can be expressed as Figure 4 The speed climbing process is shown in the schematic diagram.

[0153] Grid models, such as Figure 5 As shown, the system outputs electricity through generator G1. One part is used for plant power, and the other part is put into the 220kV grid. The large grid module is supported by generator G2 and connected to load L2. In order to facilitate the measurement of parameters, a measurement point MP is inserted between each module.

[0154] Power Control Model

[0155] like Figure 6 As shown in the figure, as the energy release process proceeds, the air pressure and temperature inside the gas tank gradually decrease, which has a certain impact on the valve opening during the regulation process. Figure 7 As shown in Figure 1, after grid connection, the target output power is set to 10MW. Through regulation and control, the system's output active power gradually increases and eventually reaches the target power. In addition, the inlet pressure and output power of each stage of expanders gradually increase and eventually reach the design value, as shown in Figure 1. Figure 8 , 9 shown.

[0156] Load dynamic adjustment test: simulate load changes from 10MW to 7MW, such as Fig.10 As shown:

[0157] Turbine Inlet Temperature Control Model

[0158] In the CAES system, temperature is an important factor affecting the system output power. The system temperature control is mainly aimed at the turbine inlet temperature. According to the rated operating condition design parameters, the target temperature is set to 85℃. The temperature is adjusted by controlling the heating control valve at the front end of the heat exchanger. The turbine inlet temperature can be stabilized during unit operation. Fig.11 Temperature variation curve under rated operating conditions.

[0159] When the system is connected to the grid, the temperature control is turned on and the temperature gradually rises to the set temperature with a maximum overshoot of 1°C. During the power generation process, the temperature is stabilized at 85°C. Considering the relationship between the annual average ambient temperature under local climatic conditions and the ambient temperature of the model boundary conditions, the inlet temperature of each level of expander is set to 85°C, which is slightly higher than the actual set temperature.

[0160] Load Shedding Control Model

[0161] The control objects of the load shedding test control system include the shut-off valve and exhaust valve at the front end of the expander, which are manually operated according to the test requirements. The control module of the corresponding valve is started. When the module recognizes the disconnection from the grid and detects the increase in speed, it will automatically perform the load shedding action. In addition, the speed control model, power control model and temperature control model are all set with anti-overspeed response control. When it is recognized that the system is decoupled from the grid and the speed exceeds 3000r / min, the control valve opening is directly reduced to zero.

[0162] Mechanism analysis

[0163] After decoupling, the overspeed prevention stage

[0164] Table 4 Experimental results of speed control at different cut-off positions

[0165]

[0166]

[0167] The moment the CAES system is decoupled from the grid, the load suddenly drops to 0. Due to the imbalance between load and output power, the speed will soar. The following experiment will explore the effect of the shut-off valve operating in different positions on speed control.

[0168] like Fig.12As shown in the figure, under 100% rated load, when the speed is controlled by closing the first-stage shut-off valve, the maximum speed and speed recovery time are not much different from those when the final-stage shut-off valve is closed. The speed control effect is better when the second-stage and third-stage shut-off valves are closed. Similarly, under the other two load conditions, the speed control effect of the shut-off valve at different positions is also different, indicating that the shut-off position is not a key factor affecting the speed control effect.

[0169] Table 5 Different load rejection action tests

[0170]

[0171] As shown in Table 5, starting from the fourth-stage shut-off valve, the number of closed valves is gradually increased until all the shut-off valves are closed, and the effect of the number of isolated expanders on the speed control effect is tested.

[0172] like Fig.13 As shown in the figure, the speed control effect is gradually improved by closing and cutting off the expansion machine step by step. Preventing the working fluid from entering the expansion machine at each stage is the key to speed control.

[0173] System recovery standby phase

[0174] The pipelines and heat exchangers with more residual fluid in the system are divided into four areas: the front end of the first-stage expander, the front end of the second-stage expander, the front end of the third-stage expander, and the front end of the fourth-stage expander. After different cut-off valves are installed, the residual fluid parameters in the four areas under four conditions are tested.

[0175] like Fig.14 As shown in the figure, after different shut-off valve actions are performed, the residual working fluid in the pipeline and heat exchanger at the front end of each shut-off valve cannot be released due to the isolation of the pipeline, and the pressure and temperature of these gases are relatively high. In addition, after the shut-off valve is actuated, the air in the low-pressure area will be compressed to generate heat, and the heat will not have time to flow out, causing the temperature in this area to rise. From Figures (a), (b), and (c), it can be seen that the temperature rise is more significant when there is a large amount of residual working fluid.

[0176] like Fig.15 As shown in the figure, under three different working conditions, the speed is controlled by closing all the shut-off valves. When the speed drops to 3000r / min, the speed soars again when the system resumes startup. Therefore, the residual working fluid needs to be exhausted.

[0177] Strategy Analysis

[0178] Fig.16The optimized load shedding operation logic diagram shows that the start and stop of the load shedding control module is determined based on the real-time speed and grid connection status. In addition, after the speed is controlled, in order to avoid the impact of the load shedding action on the speed regulation system, when the speed drops below 3000r / min, the load shedding control system is locked in the closed state through the signal tracking module, and the rotor speed is maintained at 3000r / min through the speed regulating valve. Fig.17 The load shedding regulation system of each valve is shown.

[0179] After the system is decoupled from the grid, the load shedding control module recognizes the off-grid signal and the abnormal speed increase signal, and immediately performs the load shedding action, closes the cut-off valve, and opens the exhaust valve at the same time. Fig.18 The system status when the new strategy is in action is shown (the green valve is open and the red valve is closed). The load rejection action ends when the speed is controlled.

[0180] like Fig.19 The figure shows a comparison of the speed control effects of the traditional strategy and the new strategy under different working conditions. At 100% load conditions, the maximum speed of the traditional strategy is 3312r / min, and the system recovery standby time is 303s. The maximum speed of the new strategy is only 3033r / min, and the system recovery standby time is 104s. The speed control effects are greatly improved. Similarly, the speed control effects of the other two working conditions are greatly improved. It can be seen that the new strategy is superior to the traditional strategy in key indicators (maximum speed, recovery time) to a large extent.

[0181] Example 3

[0182] The present embodiment also provides that the computer device may be a terminal, and the computer device includes a processor, a memory, a communication interface, a display screen and an input device connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be implemented through WIFI, an operator network, NFC (near field communication) or other technologies. The display screen of the computer device may be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device may be a touch layer covered on the display screen, or a button, a trackball or a touchpad provided on the housing of the computer device, or an external keyboard, touchpad or mouse, etc.

[0183] If the function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc. Various media that can store program codes.

[0184] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A load rejection and overspeed prevention control method for a compressed air energy storage system during grid decoupling, characterized in that: Including, obtaining the speed data of the compressed air energy storage system when the power grid is decoupled, and monitoring the speed data; Preset load rejection mode, including control of the cut-off valve and exhaust valve at the front end of each stage of expander; According to the change of the rotational speed data, the load shedding mode is executed to control the rotational speed of the system to fall within a preset range.

2. The load rejection and overspeed prevention control method for the compressed air energy storage system during grid decoupling according to claim 1, characterized in that: The load shedding mode includes: a first load shedding stage, in which the speed is controlled by closing the cut-off valves at the front ends of the expanders at each stage; and a second load shedding stage, in which the residual working fluid is discharged by opening the exhaust valve.

3. The load rejection and overspeed prevention control method for the compressed air energy storage system during grid decoupling according to claim 2, characterized in that: The first load shedding stage includes: detecting whether the system speed exceeds a preset threshold; when the system speed exceeds the preset threshold, closing the shut-off valves at the front end of each stage of the expander step by step in a preset order until the speed drops below 3000r / min.

4. The load rejection and overspeed prevention control method for the compressed air energy storage system during grid decoupling according to claim 3, characterized in that: The second load shedding stage includes: determining whether there is residual working fluid in the pipelines and heat exchangers in the system; when there is residual working fluid, opening the exhaust valve to discharge the high-temperature and high-pressure air remaining in the system.

5. The load rejection and overspeed prevention control method for the compressed air energy storage system during grid decoupling according to claim 4, characterized in that: The execution of the load rejection mode includes: real-time monitoring of the speed change; when the speed drops below 3000r / min, locking the load rejection control system and maintaining the rotor speed through the speed regulating valve.

6. The load rejection and overspeed prevention control method for the compressed air energy storage system during grid decoupling according to claim 5, characterized in that: Also includes: Evaluate the speed control effect of the system under different load conditions; Based on the evaluation results, optimize the execution strategy of the load shedding mode.

7. The load rejection and overspeed prevention control method for the compressed air energy storage system during grid decoupling according to claim 6, characterized in that: The load conditions include a 100% load condition, a 75% load condition and a 50% load condition.

8. The load rejection and overspeed prevention control method for the compressed air energy storage system during grid decoupling according to claim 7, characterized in that: The execution of the load rejection mode also includes: monitoring the working fluid parameters in the front end area of ​​each level of expanders; and adjusting the action sequence of the shut-off valve and the exhaust valve according to the change of the working fluid parameters.

9. The load rejection and overspeed prevention control method for the compressed air energy storage system during grid decoupling according to claim 8, characterized in that: Before executing the load shedding mode, the method also includes: establishing a system recovery standby strategy; and when the system needs to resume operation, performing control according to the recovery standby strategy.

10. The load rejection and overspeed prevention control method for the compressed air energy storage system during grid decoupling according to claim 9, characterized in that: The load shedding mode also includes: real-time monitoring of the pressure and temperature of the residual working fluid in each area inside the system; and determining the opening timing and opening degree of the exhaust valve according to the monitoring results.

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